Magnetically Driven Biofabrication for Tissue Engineering: From Nanoparticle Design to Mag‐ATMP Translation

ABSTRACT

Magnetically driven biofabrication is emerging as a materials‐enabled extension of tissue engineering, integrating advances in magnetic nanoparticle (MNP) design with cells, spheroids, and biomaterial scaffolds to engineer responsive and remotely controllable living systems. Progress in nanoparticle engineering has yielded biocompatible and tunable MNP formulations that can be incorporated into hydrogels, spheroids, organoids, and scaffolds, where they influence cellular behavior, extracellular matrix organization, and mechanotransduction. Externally applied magnetic fields further enable non‐contact control over cell positioning, microtissue assembly, matrix alignment, and dynamic mechanical stimulation, expanding the design space of 3D and 4D biofabrication. This Review critically maps and unifies the multiscale design principles underlying magnetically driven biofabrication, spanning nanoparticle design, magnetic actuation strategies, and biological responses. We compare approaches ranging from single‐cell manipulation and magnetoactive bioinks to spheroid fusion and microfluidic systems with embedded magnetic actuation. We further discuss how physics‐based modeling, data‐informed optimization, and emerging digital twin concepts may help connect material properties, magnetic field design, and biological response. Finally, we examine translational considerations, including Good Manufacturing Practice (GMP)‐compatible nanoparticle formulations, mechanistic clarity, long‐term safety evaluation, and regulatory alignment, converging toward magnetically enabled tissue‐engineered advanced therapy medicinal products (Mag‐TE ATMPs).

Magnetically responsive nanoparticles enable remote control over biomaterials, cells, and engineered tissues. This review summarizes material design, biological safety, fabrication and actuation strategies, computational validation, and translational pathways that support the development of magnetic tissue‐engineering platforms and future magnetically guided advanced therapy medicinal products.

1. Introduction—The Versatility of Magnetic Nanoparticles in Medicine

Magnetic nanoparticles (MNPs) are widely used in biomedical research because their magnetic response can be controlled remotely while their surface chemistry can be adapted for interaction with biological systems. Their properties, including superparamagnetic behavior, nanoscale size, and capacity for surface functionalization, have supported their use across imaging, drug delivery, cell manipulation, and tissue engineering applications. In contrast to bulk ferromagnetic materials, superparamagnetic nanoparticles retain magnetization only in the presence of an external magnetic field, which can reduce remanent magnetization and limit irreversible aggregation after field removal [1]. However, their behavior in biological environments is not defined by magnetic properties alone. Size distribution, surface chemistry, surface and volume composition, crystal structure, colloidal stability, protein corona formation, aggregation state, and field geometry all influence how MNPs interact with cells, extracellular matrices, and implanted tissues.

Initially applied as diagnostic magnetic resonance imaging (MRI) contrast agents, MNPs have since expanded into areas such as magnetically guided drug delivery [2], gene transfection via magnetofection [3, 4], and cell guidance in regenerative medicine [5]. Surface functionalization with targeting ligands can improve local nanoparticle accumulation and support more selective delivery in specific disease models, including tumor‐targeting applications [6]. These examples illustrate the breadth of MNP use, but they also highlight a central challenge: magnetic responsiveness must be coupled to biological compatibility, reproducible formulation, and predictable performance in complex physiological environments.

In tissue engineering and biofabrication, MNPs have been incorporated into scaffolds, hydrogels, cells, spheroids, and organoid‐like systems to introduce magnetic responsiveness into engineered biological constructs. These approaches have been explored for magneto‐responsive scaffold design [7], cell and organoid levitation [8], in vivo stimulation [9], differentiation control [10], and spatial organization of tissues under external magnetic fields [11]. Scaffold‐free assembly and magnetic bioprinting have emerged as a non‐contact technique to spatially organize cells and spheroids into defined architectures with high precision [11, 12]. Figure 1 summarizes the multifaceted roles that magnetic nanoparticles play within the broader context of MNP‐enabled technologies.

FIGURE 1.

Overview of major biomedical and bioengineering applications of MNPs. Schematic representation of the multifunctional roles of MNPs across clinical and research domains. In clinical applications (upper panels), MNPs enable targeted drug delivery through magnetic guidance, localized magnetic hyperthermia for cancer treatment, and serve as contrast agents for magnetic resonance imaging (MRI). In research and tissue engineering contexts (lower panels), MNPs facilitate magneto‐mechanical activation of mechanosensitive ion channels, magnetofection and intracellular delivery of nucleic acids, and spatial tissue patterning within hydrogels, spheroids, and cell assemblies. Collectively, these applications highlight the versatility of MNPs as remotely actuated, multifunctional tools bridging therapeutic intervention, diagnostics, and magnetically driven biofabrication.

Magnetic tools are also relevant to mechanobiology. By applying forces to magnetically labeled cells or subcellular structures, magnetic fields can be used to probe force‐sensitive signaling pathways and study how cells respond to mechanical inputs [13, 14, 15]. These capabilities are particularly relevant for engineering responsive biohybrid systems that can adapt to dynamic physiological conditions, although the extent to which this can be translated into robust therapeutic products remains an open question.

This question is particularly relevant for advanced therapy medicinal products (ATMPs), including gene, cell, and tissue‐engineered therapies. Despite major progress, many ATMPs still face challenges related to manufacturing scalability, process standardization, product consistency, delivery, monitoring, and control after implantation [16]. Tissue‐engineered products are biologically active, but their function is often difficult to guide once they are implanted. MNPs could help address some of these limitations by enabling magnetic positioning, remote actuation, and imaging‐based monitoring. Nevertheless, their translation into future ATMP‐compatible products requires careful consideration of nanoparticle composition, dose, long‐term fate, manufacturing reproducibility, regulatory classification, and safety [17].

In this Review, we examine the role of MNPs as enabling components in magnetically driven biofabrication for tissue engineering. We first discuss MNP composition, magnetic behavior, surface chemistry, colloidal stability, and manufacturing considerations, establishing the materials‐design basis for their use in biological systems. We then review biological interactions, including cellular uptake, intracellular fate, cytotoxicity, immune response, biodistribution, and in vivo persistence. The following sections examine how MNPs are integrated into 3D‐4D biofabrication strategies, including magnetized cells, hydrogels, scaffolds, spheroids, organoids, microfluidic systems, and in situ assembly approaches. We also discuss computational modeling and mechanical measurement strategies used to estimate magnetic forces, construct assembly, and magnetically induced stimulation. Finally, we consider safety, regulatory challenges, and the future development of magnetically responsive tissue‐engineered ATMPs. By organizing the field from nanoparticle design to translational constraints, this Review aims to clarify what has been experimentally demonstrated, where current limitations remain, and which design principles may guide future magnetic biofabrication strategies.

2. Composition and Material Science Perspective of MNPs

A wide range of magnetic materials has been investigated because of their ability to respond to external magnetic fields. These include iron oxides, metallic particles, doped ferrites, gadolinium‐based systems, core–shell composites, Janus particles, and carbon‐based magnetic hybrids. However, magnetic performance alone does not determine suitability for biomedical use. For tissue engineering and magnetic biofabrication, each material must also be evaluated in terms of colloidal stability, surface chemistry, biological compatibility, degradation or clearance, processability, manufacturing reproducibility, eco‐friendliness, and cost‐effectiveness.

This section therefore introduces the broader magnetic nanoparticle landscape and distinguishes between systems that are clinically established or biologically compatible, systems that remain promising but exploratory, and systems whose strong magnetic properties are limited by toxicity or long‐term safety concerns. Detailed biological responses, including cellular uptake, cytotoxicity, biodistribution, and clearance, are discussed separately in Section 3.

2.1. Iron Oxide Nanoparticles (Fe₃O₄, γ‐Fe₂O₃)

Iron oxide nanoparticles, particularly magnetite (Fe₃O₄) and maghemite (γ‐Fe₂O₃), remain the most widely investigated MNPs for biomedical applications [18]. Their use is supported by magnetic responsiveness, chemical stability, surface functionalization capacity, and comparatively favorable biological handling. When prepared below the critical size range for superparamagnetic behavior, iron oxide nanoparticles respond to an external magnetic field while showing limited remanent magnetization after field removal [19, 20]. This is important for applications requiring reversible magnetic control, including imaging, magnetic targeting, magnetic actuation, and particle or cell transport.

At the structural level, Fe₃O₄ exhibits a mixed‐valence inverse spinel configuration (Fe^{2 +}/Fe^{3 +}), providing an attractive magnetic nature (≈92 emu g^{− 1} magnetization for bulk magnetite) and high magnetic susceptibility [21, 22]. Further oxidation of Fe₃O₄ produces γ‐Fe₂O₃, which generally has lower magnetization but improved chemical/compositional stability. In practice, the final magnetic performance of iron oxide nanoparticles depends not only on composition, but also on crystal quality, core size, size distribution, surface coating, and aggregation state [23]. Their degradation products can enter endogenous iron‐handling pathways, although this process depends on dose, coating stability, degradation rate, and tissue context [24].

Surface modification is essential for maintaining colloidal stability and controlling the biological interface. Iron oxide nanoparticles are commonly coated with hydrophilic polymers or small ligands such as polyethylene glycol (PEG) [25], chitosan [26], dextran [27], starch [28], lipids [29], or low‐molecular‐weight ligands like citric acid [30]. These coatings improve dispersion in aqueous or physiological media and provide reactive groups for functionalization with targeting ligands [31], peptides [32], or growth factors [29]. As a result, iron oxide nanoparticles have been used in multimodal systems in cancer research [33], enabling the integration of MRI with targeted drug delivery [34] and localized magnetic hyperthermia within a single nanosystem [35].

For magnetic biofabrication, particle size and shape are particularly important because they influence magnetic responsiveness, surface reactivity, and distribution within cells, hydrogels, spheroids, bioinks, and extracellular matrices. Particle size affects surface area, magnetic relaxation, and saturation magnetization [36], which can influence hyperthermia efficiency [37], MRI contrast [38], and magnetically induced mechanical actuation [39]. Shape can also contribute to magnetic anisotropy and cell‐material interactions. Non‐spherical structures, including nanocubes [40], nanoflowers [41], nanorods [42], and octahedra [43], may show enhanced magnetic response or alignment compared with spherical particles, although their biological performance must be assessed case by case.

2.2. Metallic Nanoparticles (Fe, Co, Ni, Gd)

Metallic magnetic nanoparticles can provide stronger magnetic responses than iron oxides, but their biomedical use is limited by chemical reactivity (i.e., potential chemical instability) and a possible tendency for corrosion, ion release, and toxicity. Elemental iron has a high saturation magnetization, exceeding 200 emu g^{− 1} in bulk form, but bare Fe⁰ rapidly oxidizes in aqueous and physiological environments. This oxidation can release Fe^{2 +}/Fe^{3 +} species and promote Fenton‐type redox reactions, increasing reactive oxygen species formation [44]. As a result, metallic Fe is seldom employed in its bare form and instead stabilized within core‐shell architectures (e.g., Fe@SiO₂, Fe@C, Fe@Au) that preserve high magnetic saturation while suppressing corrosion, ion leaching, and surface oxidation.

Cobalt (Co) and nickel (Ni) nanoparticles, on the other hand, though not as strongly magnetic as pure Fe, demonstrate substantially higher saturation magnetization values (typically 120‐160 emu g^{− 1}) compared to iron oxides (∼70–90 emu g^{− 1}), resulting from their metallic bonding and long‐range ferromagnetic ordering [45]. This enhanced magnetization enables stronger magnetic force generation under external fields, which is advantageous for applications requiring high‐precision actuation, microscale manipulation, or magnetic torque transfer [46]. These properties are useful for microrobotics, microassembly, magnetic torque transfer, and device‐integrated actuation systems [47]. However, their direct use in regenerative medicine is constrained by possible oxidation, ion release, limited physiological clearance pathways, and cytotoxicity [48, 49]. Therefore, Co‐ and Ni‐based systems are better considered as components of external magnetic devices, short‐term actuators, or protected micro/nanosystems rather than as default candidates for long‐term incorporation into regenerative biomaterials.

Gadolinium occupies a different position because its paramagnetic properties are mainly exploited for T₁‐weighted MRI contrast. Gd exhibits seven unpaired 4f electrons, imparting exceptionally high magnetization (200–220 emu g^{− 1}) and efficient spin–lattice relaxation properties that underpin its widespread use as a T₁‐weighted MRI contrast agent in chelated form (e.g., Gd‐DTPA) [50, 51, 52]. Gd‐based chelates are often used clinically, while Gd₂O₃ and Gd‐doped iron oxide nanoparticles have been explored to combine positive and negative MRI contrast mechanisms [51]. However, unchelated or poorly stabilized Gd‐containing systems raise safety concerns related to Gd^{3 +} release and tissue retention.

To address corrosion and improve interface control, metallic or metal‐containing cores are often encapsulated within silica (SiO2) [53], metallic‐organic frameworks (MOFs) based on carbon (C) [54], gold (Au) [55], or combinations thereof with polymeric coatings [56, 57, 58]. (e.g., PEG, PLGA, chitosan). These protective shells can improve colloidal stability, reduce direct exposure of reactive metal surfaces, and provide functional groups for conjugation. Nevertheless, for tissue‐engineering applications, their use remains largely experimental and requires careful evaluation of long‐term stability, degradation, and biological response.

2.3. Composite Magnetic Nanoparticles

Composite MNPs combine a magnetic component with an additional shell, matrix, or functional domain. The purpose of this design is to tune surface chemistry, colloidal stability, degradation, drug loading, optical response, or mechanical coupling without relying only on the magnetic core. These systems are useful when a single material cannot provide the required balance between magnetic performance and biological interface control.

Polymeric and lipid‐based composites, including PEG, PLGA, chitosan, dextran, or lipid hybrids, give rise to soft, biocompatible interfaces that enable drug encapsulation, controlled degradation, and ligand presentation [26, 27, 29, 56, 57]. Zwitterionic or amphiphilic coatings can also reduce nonspecific protein adsorption and prolong circulation, which may be important for injectable formulations [59, 60]. Inorganic shells offer additional functions, silica coatings may provide chemical stability, mesoporosity, and optical transparency [58, 61], whereas gold [55] or silver [62] shells can introduce plasmonic or photothermal properties [55, 62].

Other composite systems are designed to tune magnetic behavior more directly. Hard–soft magnetic nanocomposites, such as FePt/Fe₂O₃, can combine decent magnetization and attractive coercivity values in ways that support magnetothermal conversion [63]. Spinel ferrite composites (CoFe₂O₄, MnFe₂O₄, ZnFe₂O₄) allow adjustment of anisotropy and relaxation behavior, which could be useful for hyperthermia, magnetic sensing, or actuation [64]. Hybrid MOF‐MNP [65]. and MXene‐MNP [66, 67] systems further expand this design space by adding porosity, redox activity, or conductivity.

In biofabrication, composite MNPs are mainly relevant because their interfaces could be adapted to hydrogels, bioinks, scaffolds, or cell‐containing constructs. Parameters such as shell thickness, degradation rate, porosity, and crosslinking chemistry could influence how particles distribute within a material and how efficiently magnetic forces are transferred to the surrounding matrix or cells. These features could support the development of magneto‐responsive hydrogels, magnetic bioinks, and other responsive biomaterial systems. Broader materials aspects of magnetic nanocomposites have been reviewed elsewhere [68]; here, the emphasis is placed on design considerations relevant to magnetic biofabrication and tissue engineering.

2.4. Janus and Carbon‐Based Hybrid Nanostructures

Janus nanoparticles contain two or more spatially distinct domains, allowing magnetic actuation to be combined with optical, chemical, polymeric, or biological functionality. Common examples include Fe₃O₄‐, FePt‐, or CoFe₂O₄‐based domains combined with Au, SiO₂, polymeric, or lipid components [69, 70, 71]. Because of their asymmetric structure, Janus particles can support directional orientation, propulsion, or assembly under external fields. These features have been explored in microscale manipulation, targeted delivery, photothermal systems, and spatially organized tissue‐engineering approaches [72, 73, 74].

Biodegradable Janus systems, such as Fe₃O₄–PLGA or Fe₃O₄–lipid hybrids [75], are of interest because they may combine transient magnetic guidance with degradable interfaces [76]. Carbon‐based magnetic hybrids, including Fe₃O₄@CNT, Fe₃O₄@graphene, and rGO–ferrite composites, combine magnetic responsiveness with electrical conductivity and mechanical reinforcement [75]. When incorporated into hydrogels, fibers, or printed scaffolds, these materials may support electroactive or magneto‐electromechanical environments relevant to neural interfaces, muscle models, or other electrically responsive tissues.

Overall, Janus and carbon‐based systems extend MNP design beyond isotropic particles. However, their use in regenerative medicine remains less mature than that of iron oxide formulations. For translational biofabrication, the main questions are whether these systems can be produced reproducibly, dispersed stably, degraded or cleared safely, and integrated into living constructs without introducing long‐term toxicity. Table 1 compares representative magnetic nanoparticle systems in terms of their principal advantages, limitations, and relevance to magnetic biofabrication and tissue engineering. This comparison distinguishes intrinsic magnetic or multifunctional performance from practical translational readiness: although several material classes provide strong magnetic responses or additional optical, conductive, or catalytic properties, comparatively few currently combine magnetic functionality with biological compatibility, dispersion stability, and scalable manufacturing.

TABLE 1.

Comparative overview of representative magnetic nanoparticle systems and their relevance to biomedical applications, magnetic biofabrication, and tissue engineering.

Material system	Representative examples	Main advantage	Main limitation	Relevance for magnetic biofabrication/Mag‐TE
Iron oxides	Fe3O4, γ‐Fe2O3, Fe3O4@PEG, Fe3O4@dextran, Fe3O4@citric acid	Biocompatible magnetic response; established biomedical use; broad surface chemistry	Performance depends on size, coating, aggregation state, and dose	Most relevant class for magnetic tissue engineering, cell/spheroid loading, hydrogels, scaffolds, MRI, and magnetic actuation
Metallic Fe	Fe0, Fe@SiO2, Fe@C, Fe@Au	Very high magnetic moment and strong magnetic force generation	Rapid oxidation, corrosion, and ROS risk if unprotected	Useful for high‐force actuation or microassembly when encapsulated, but limited for long‐term regenerative use
Co/Ni‐based systems	Co, Ni, Co@Au, Ni@C, CoFe2O4, NiFe2O4	Strong magnetization, coercivity, and torque response	Cytotoxicity, ion release, genotoxicity, and limited clearance	More suitable for magnetic devices, microrobotics, or short‐term actuation than implantable regenerative constructs
Gd‐based systems	Gd chelates, Gd2O3, Gd‐doped iron oxides	Strong T1 MRI contrast and image‐guidance potential	Safety depends on stable chelation/coating; risk of Gd3 + release and retention	Relevant for MRI‐visible constructs, but less established as functional biofabrication additives
Core–shell/polymer/lipid composites	Fe3O4@SiO2, Fe3O4@Au, Fe3O4@PLGA, Fe3O4@lipid	Tunable interface, dispersion, cargo loading, and multifunctionality	Stability, degradation, and reproducibility depend on shell chemistry	Useful for magneto‐responsive bioinks, injectable hydrogels, drug‐loaded scaffolds, and multimodal systems
Doped ferrites and hard–soft composites	CoFe2O4, MnFe2O4, ZnFe2O4, FePt/Fe2O3	Tunable anisotropy, coercivity, relaxation, and magnetothermal behavior	Composition‐dependent safety; less clinically mature than iron oxides	Promising for magnetic stimulation, heating, sensing, and mechanotransduction studies
MOF/MXene magnetic hybrids	Fe3O4@ZIF‐8, Fe3O4@Ti3C2Tx	Porosity, conductivity, redox activity, and catalytic functionality	Early‐stage; unclear long‐term safety and degradation	Exploratory systems for catalytic, electroactive, or sensing biointerfaces
Janus/carbon hybrids	Fe3O4‐PLGA, Fe3O4‐SiO2, Fe3O4@CNT, Fe3O4@graphene	Directional response, anisotropy, conductivity, or mechanical reinforcement	Limited translational maturity; toxicity and reproducibility require validation	Potential for directional actuation, electroactive scaffolds, neural interfaces, and microscale assembly

2.5. Colloidal Stability, Protein Corona, and Formulation Constraints

For biological and biofabrication applications, colloidal stability is as important as magnetic performance. MNPs with strong magnetization may still aggregate in physiological media, sediment during culture, distribute unevenly within hydrogels or bioinks, or show poor reproducibility. Stability is influenced by hydrodynamic size, surface charge, coating chemistry, hydrophilicity, ionic strength, serum proteins, pH, and particle concentration [76, 77, 78]. For this reason, core size and nominal mass concentration should be reported together with hydrodynamic diameter, polydispersity index, zeta potential, and aggregation behavior in the relevant biological or processing medium. Though colloidal stability is often associated with high absolute values of ζ‐potential, steric stabilization may allow colloidal systems to remain stable despite having a low ζ‐potential, even close to 0 mV.

Upon exposure to serum, plasma, or protein‐containing culture media, nanoparticles rapidly acquire a biomolecular corona composed mainly of adsorbed proteins and other biomolecules [79]. Corona can alter the effective biological identity of the particle by altering colloidal stability, surface charge, cellular uptake, immune recognition, biodistribution, and degradation behavior [80]. In iron oxide systems, protein and lipid coronas can also affect colloidal stability, toxicity, and degradation kinetics [81].

These effects are directly relevant to magnetic biofabrication because magnetic actuation depends on reproducible particle dispersion and loading. Aggregation or corona‐driven changes in surface properties can affect MNP integration and distribution within cells, spheroids, hydrogels, bioinks, or extracellular‐matrix‐rich constructs, thereby influencing magnetic force transfer, imaging response, and biological outcome. Standardized characterization under application‐relevant conditions is therefore needed, including assessment in the actual culture medium, serum concentration, hydrogel precursor solution, or bioink formulation used during processing. When protein corona analysis is required, methods such as magnetic separation, size‐exclusion chromatography, field‐flow fractionation, and mass spectrometry‐based proteomics can be used, but incubation and recovery protocols should be reported because they can influence the measured corona composition [82].

2.6. Manufacturing Approaches and Emerging Materials

The synthetic route used to produce MNPs is known to influence crystal structure, size distribution, surface chemistry, magnetic behavior, colloidal stability, and biological performance. Co‐precipitation is widely used because it is simple and scalable, but it can produce particles with quite broad size distributions and heterogeneous surface states. Thermal decomposition of organometallic precursors can generate highly monodisperse nanocrystals with controlled size and high magnetic uniformity, making it useful for mechanistic studies [83]. However, it often requires hydrophobic solvents and post‐synthetic surface exchange, which can complicate biofunctionalization and scale‐up.

Microfluidic‐assisted synthesis offers a route toward more controlled and reproducible MNP production by improving control over mixing, nucleation, and growth [84, 85]. This approach may help reduce batch variability and support continuous production, although translation to clinical‐grade manufacturing still requires validation of scalability, sterility, purification, endotoxin control, and quality assurance. These considerations are particularly relevant for magnetic biofabrication, where small changes in particle properties can affect cell loading, hydrogel distribution, magnetic force generation, and biological response.

Recent material‐development efforts have expanded MNPs beyond conventional iron oxides toward doped ferrites, hard‐soft nanocomposites, MOF‐MNP systems, and MXene‐MNP hybrids [86]. Rather than serving only as heat transducers, these engineered materials could act as magneto‐electromechanical transducers, converting magnetic inputs into localized stresses or electrical potentials that influence cellular mechanosensing and metabolic activity [87]. Emerging MOF‐@MNP and MXene‐@MNP hybrids could extend this concept by integrating ion transport, redox activity, and conductivity within magnetically addressable frameworks. These materials could introduce additional magnetic, conductive, redox‐active, or porous properties, which may support remote stimulation, magnetothermal conversion, electroactive scaffolds, or sensing functions [88, 89, 90]. However, most of these systems remain at an early stage for regenerative medicine, and their long‐term biocompatibility, degradation, and manufacturing reproducibility are not yet established.

The field is therefore moving from exploratory synthesis toward more reproducible and constraint‐aware design. Controlled synthesis, in‐line or in situ/operando characterization, and data‐assisted process optimization may help define relationships between particle design, magnetic response, biological performance, and manufacturing robustness [91]. Within this context, Figure 2 summarizes the design logic that links nanoparticle composition to translational use in magnetic biofabrication. The figure is organized as a stepwise framework, starting from core material selection, moving through nanoparticle architecture and surface engineering, and ending with manufacturing methods and biofabrication applications. The green‐highlighted areas indicate the most translationally favorable choices within each design category, including clinically established or biocompatible core materials, magnetically responsive architectures, surface coatings that support dispersion and biological compatibility, and manufacturing approaches with stronger potential for reproducibility and scale‐up. In contrast, exploratory or higher‐risk material systems, such as Co‐ and Ni‐based particles, are placed outside this favorable (orange box) translational pathway because their magnetic performance is offset by toxicity, clearance, and long‐term safety concerns.

FIGURE 2.

Design space and translational readiness of magnetic nanoparticle systems for magnetic tissue engineering and biofabrication. This schematic outlines the multiscale materials design space of MNP systems, linking material composition, nanoparticle architecture, surface engineering strategies, and manufacturing approaches to magnetic biofabrication and translational readiness. The framework highlights how progressive constraints, arising from biological compatibility, architectural complexity, and manufacturing scalability, shape the transition from exploratory materials design toward application‐oriented magnetic tissue engineering strategies.

3. Biocompatibility and Cytotoxicity

Establishing the biocompatibility of MNPs is essential for their use in tissue engineering and magnetic biofabrication. However, comparisons across studies remain difficult because MNP formulations differ in synthesis route, core composition, surface coating, colloidal stability, dose, exposure time, and biological model [92]. Toxicity values alone are therefore insufficient to define biocompatibility. Instead, safety must be interpreted in relation to nanoparticle design, application context, and the biological environment in which the particles are used.

For regenerative applications, the relevant question is not only whether an MNP formulation is cytocompatible in a short‐term assay but also whether it can support the intended magnetic function without inducing unacceptable oxidative stress, inflammation, impaired differentiation, altered tissue remodeling, or long‐term accumulation [93]. This section therefore focuses on cellular internalization, intracellular fate, systemic distribution, dose‐ and context‐dependent toxicity, and comparative in vitro and in vivo safety profiles.

3.1. Cellular Internalization and Intracellular Fate

MNPs are internalized through endocytic routes that depend on nanoparticle size, surface chemistry, aggregation state, protein corona, and cell type [94, 95]. Major uptake mechanisms include clathrin‐mediated endocytosis, caveolae‐mediated endocytosis, clathrin‐independent pathways, macropinocytosis, and phagocytosis [96, 97, 98]. Particle size strongly influences the pathway: CME, FEME, CLIC/GEEC, and caveolae mechanisms typically internalize particles < 200 nm, whereas larger particles are taken up by macropinocytosis or phagocytosis [94, 99]. Protein corona formation can further modify surface charge, hydrodynamic size, and uptake efficiency [94, 100].

After internalization, MNPs are trafficked through endosomal and lysosomal compartments, where acidic pH and enzymatic activity can promote coating degradation and partial core dissolution [96]. For iron oxide nanoparticles, released iron can be incorporated into endogenous iron‐handling pathways, including ferritin storage and transferrin‐mediated transport [101]. However, excessive intracellular accumulation or rapid dissolution can increase Fe^{2 +}/Fe^{3 +} availability, promote Fenton‐type reactions, and disturb redox homeostasis [102, 103, 104, 105]. This is one mechanism by which high dose, poor coating stability, or prolonged exposure may lead to cytotoxicity.

Reactive oxygen species are among the most reported mediators of MNP‐induced stress, particularly for iron oxide and transition‐metal nanoparticles [106, 107]. At moderate and well‐controlled doses, several iron oxide formulations preserve viability and may support lineage‐specific differentiation, including osteogenic responses in mesenchymal or skeletal progenitor cells [108]. In contrast, higher concentrations, prolonged exposure, or unstable formulations can increase oxidative stress, mitochondrial dysfunction, lipid peroxidation, and cell death [109]. In iron‐rich environments, persistent oxidative stress may also contribute to ferroptotic pathways, although the relevance of this mechanism depends strongly on cell type, intracellular dose, and particle degradation kinetics [106].

3.2. Systemic Fate and Clearance of MNPs

Following systemic administration or release from implanted materials, MNPs interact with plasma proteins and immune components that influence circulation time, biodistribution, and clearance [76, 77, 80]. Opsonin‐enriched coronas promote recognition by the reticuloendothelial system, leading to uptake in liver, spleen, and lymphoid tissues [77, 79, 110]. Protein corona formation, hydrodynamic size, surface charge, coating chemistry, and shape all affect recognition by macrophages and uptake by the mononuclear phagocyte system [107]. In general, larger or aggregated particles are more readily sequestered in the liver and spleen, whereas ultrasmall particles may undergo renal filtration [111].

For tissue‐engineering applications, systemic clearance is only one part of the safety question. Many magnetic biofabrication strategies rely on local MNP retention within cells, spheroids, scaffolds, hydrogels, or extracellular‐matrix‐rich constructs. In these cases, the desired outcome is sufficient local persistence to enable magnetic guidance, imaging, or actuation, while avoiding uncontrolled release, inflammatory activation, or long‐term off‐target accumulation. Safety evaluation should therefore consider both systemic fate and local tissue persistence, especially when MNPs are intended to remain within implanted or maturing constructs.

3.3. Dose, Exposure Time, and Biological Context

Safe integration of MNPs in tissue engineering requires a balance between magnetic functionality and biological compatibility. Biocompatibility is influenced by core composition, particle size, surface charge, coating chemistry, cellular uptake, and exposure duration. However, these physicochemical determinants have already been introduced in Section 2 and in Sections 3.1 and 3.2; here, the emphasis is placed on how these parameters combine to determine biological dose and context‐dependent toxicity.

Iron oxide nanoparticles remain the preferred material class for regenerative applications because they combine magnetic responsiveness with chemical stability, metabolic compatibility, and the strongest biomedical precedent. In contrast, cobalt‐ and nickel‐based systems can provide higher magnetic performance but are more frequently associated with oxidative stress, ion release, and ROS‐mediated toxicity [112]. Particle size and magnetic state also influence biological response; iron oxide cores below the superparamagnetic size range show limited remanent magnetization, reducing the risk of field‐independent aggregation [113]. Surface coatings such as PEG, dextran, or PVP can improve dispersion, reduce protein adsorption and macrophage recognition, and prolong circulation [114], while surface charge [111] influences membrane interaction, uptake, opsonization, and ROS induction.

Toxicity does not scale only with the nominal concentration added to culture medium. Aggregation, sedimentation, uptake efficiency, culture geometry, and exposure time influence the delivered and intracellular dose, which may correlate more closely with toxicity than the initial administered concentration [115]. This is particularly relevant for magnetic biofabrication, where MNPs may be incubated with cells, embedded in hydrogels, loaded into spheroids, or retained within implanted constructs. Several iron oxide formulations show limited toxicity when dose, coating, and exposure time are controlled; for example, 50 nm iron oxide nanoparticles were tolerated up to 100 mg kg^{− 1} in ICR mice over 4 weeks without histopathological changes [116], and polymer‐coated γ‐Fe₂O₃ nanoparticles showed low toxicity in vitro and in vivo [117]. Conversely, chronic or high‐dose exposure can cause systemic effects, including mortality at very high Fe₃O₄ doses (>5 g kg^{− 1} in Kunming mice (LD₅₀ ≈ 5.748 g kg^{− 1})) [118], cardiac injury at elevated Fe₃O₄ exposure (≈160 mg kg^{− 1}) [119], and organ injury or arrhythmia after Ni nanoparticle exposure at 20 mg kg^{− 1} [120].

For regenerative and ATMP‐oriented applications, safety assessment should therefore extend beyond short‐term viability. Relevant endpoints include metabolic activity, membrane damage, ROS production, mitochondrial function, inflammatory markers, differentiation capacity, matrix deposition, and, when appropriate, genotoxicity or ferroptosis‐related markers. These assays should be complemented by in vivo evaluation of local tissue response, biodistribution, organ histology, degradation, and persistence over time.

3.4. Comparative In Vitro and In Vivo Biocompatibility

MNP families show distinct biological and translational profiles. Iron oxide nanoparticles currently provide the strongest precedent for magnetic tissue engineering because they combine magnetic responsiveness with comparatively favorable biological handling and prior proven biomedical use. Gadolinium‐based systems occupy a different translational space, mainly related to imaging and image‐guided applications. In contrast, Co‐ and Ni‐based nanoparticles, despite their stronger magnetic properties, still demonstrate limited use for regenerative applications because of cytotoxicity, ion release, oxidative stress, genotoxicity, and poor long‐term clearance.

Fe₃O₄ and γ‐Fe₂O₃ nanoparticles functionalized with hydrophilic coatings such as carboxymethyldextran, dextran, citric acid, PEG, or related polymeric interfaces have shown good cytocompatibility across several biological models. Reported examples include collagen‐embedded tissue scaffolds [121], embryonic stem cells [122], and magnetized tissue constructs [9]. Clinically used or previously approved iron oxide formulations, including Resovist for MRI contrast and ferumoxytol/Feraheme for iron replacement, provide useful safety precedents. However, these examples should not be interpreted as universal validation of all iron oxide nanoparticles for tissue engineering. Local retention, coating stability, dose, degradation rate, and exposure duration must still be assessed for each magnetic biofabrication strategy [123].

Gd₂O₃ particles serve as T₁ MRI contrast agents with higher r ₁/r ₂ than Gd(III) chelates but require coatings to mitigate Gd^{3 +} toxicity [124]. Reported ligands include poly(acrylic acid) PAA [125], poly(methyl vinyl ether‐alt‐maleic acid) PMVEMA [126], poly(acrylic acid‐co‐maleic acid) PAAMA [127], poly(amido sulfonic acid) PASA [128], citric acid [129], and poly(ethylene glycol) PEG [130]. In vitro, coated Gd₂O₃ nanoparticles have demonstrated acceptable cytocompatibility at concentrations up to 500 µM Gd (Table 2), although their long‐term intracellular behavior and lysosomal dissolution remain areas of active investigation. Importantly, no nanoparticulate Gd formulation has received regulatory approval to date. Instead, only molecular Gd(III) chelates, such as Dotarem and Primovist, are EMA approved for clinical use, while earlier chelates like Magnevist have been withdrawn due to concerns regarding Gd retention and nephrogenic systemic fibrosis (Artirem EN). Their most realistic role in magnetic biofabrication is therefore as MRI‐visible or image‐guidance components rather than as default regenerative additives.

TABLE 2.

Biocompatibility assessment of magnetic nanoparticles across coatings, models, and applications.

Core composition	Nanoparticle composition and surface functionalization	Biological model/application context	Cellular response/in vitro outcome	Animal/clinical findings	Reference/source
🔵 Fe (γ‐Fe2O3)	γ‐Fe2O3 NPs, carboxydextran coating	Clinical use	—	Resovist (ferucarbotran), approved for MRI liver imaging (Bayer Schering Pharma, EU)	EMA Report
🔵 Fe (γ‐Fe2O3)	γ‐Fe2O3 NPs, citric acid coating	Embryonic stem cells	No cytotoxicity at 5 mM [Fe], 30 min incubation	—	[122]
🔵 Fe3O4	Fe3O4 NPs, carboxymethyl‐dextran coating	Clinical use	—	Ferumoxytol, EMA/FDA‐approved for iron‐deficiency anemia	EMA Feraheme (Accessed Nov 2025)
🔵 Fe3O4	Fe3O4 NPs, dextran coating	Clinical use	—	Sinerem MRI contrast (pelvic cancer), discontinued	EMA Sinerem Report (Accessed November 2025)
🔵 Fe3O4	Fe3O4 NPs, citric acid coating	Human periosteum‐derived cells (hPDCs)	No cytotoxicity ≤ 60 µg mL− 1 Fe	Implanted magnetic callus assembloids (4‐week mice): no spleen/liver damage	[11]
🔵 Fe3O4	Fe3O4 NPs, glucuronic acid coating	Neuronal cells	No adverse effects at 20 µg mL− 1 Fe	Extremely low magnetic forces promoted axon growth without reported adverse effects under the tested conditions	[138]
🔵 Fe3O4	Fe3O4 NPs, APTES functionalization	Human adipose‐derived stem cells (hASCs)	No cytotoxicity ≤ 1 mg mL− 1	Subcutaneous implantation + magnetic stimulation → enhanced osteogenesis	[9]
🔵 Fe oxide	Fe oxide NPs, PEG coating	Bone marrow stem cells (BMSCs)	Collagen alignment → upregulated osteogenesis	—	[121]
🔵 Gd	Gd‐DOTA complex (DOTA ligand)	Clinical use	—	Dotarem, IV MRI contrast agent	FDA Label
🔵 Gd2O3	Gd2O3 NPs, citric acid coating	L929 fibroblasts	Bare NPs toxic > 5 µg mL− 1; CA‐coated viable ≤ 100 µg mL− 1	—	[129]
🔵 Gd2O3	Gd2O3 NPs, PEG coating	Glioblastoma cells (F98)	Uptake ≈10%; no viability loss	Tumor growth unaltered (21 days)	[130]
🔵 Gd2O3	Gd2O3 NPs, PAA coating	DU145/NCTC1469/mice	Non‐toxic ≤ 78.6 µg Gd mL− 1	High‐contrast T1 MRI; renal clearance	[125]
🔵 Gd2O3	Gd2O3 NPs, PMVEMA coating	DU145/Balb‐c mice	Low toxicity ≤ 500 µM Gd	0.1 mmol Gd kg− 1; mice survived	[126]
🔵 Gd2O3	Gd2O3 NPs, PAAMA coating	DU145/NCTC1469/mice	Nearly non‐toxic ≤ 500 µM Gd	0.1 mmol Gd kg− 1; mice survived	[127]
🔵 Gd2O3	Gd2O3 NPs, PASA coating	DU145/NCTC1469/mice	100% (DU145), 77% (NCTC1469) viability at 500 µM Gd	Renal excretion; no mortality	[128]
🔴 Ni	NiO NPs, Paeonia emodi leaf extract	Antimicrobial assay (E. coli, S. aureus)	MIC = 7.0 µg mL− 1 (E. coli); 3.5 µg mL− 1 (S. aureus)	10 ppm → survival for 14 days; > 15 ppm → lethality + skin lesions	[137]
🔴 Ni	NiO NPs, mixed plant extracts	Rat skeletal myoblast (L‐6)	IC50 = 1.67 mg mL− 1 (antiproliferative)	—	[139]
🔴 Ni	Nano‐Ni NPs (uncoated)	BEAS‐2B/C57BL/6J mice	≤20 µg mL− 1 non‐toxic; ≥30 µg mL− 1 cytotoxic; DNA damage ≤ 0.5 µg mL− 1	50 µg intratracheal → γH2AX ↑ (DNA damage in lungs)	[132]
🟠 Co	Co3O4 NPs, Rosemary leaf extract	Hep G2/MCF7 cells	No metabolic change ≤ 62.5 (Hep G2)/31.3 (MCF7) µg mL− 1	—	[136]
🟠 Co	Co3O4 NPs (uncoated)	Chinese hamster lung (V79)	20–100 µg mL− 1 → moderate mortality; reduced organelle activity	—	[135]
⚫ Composite	Gd2O3@BSA–Au NPs (BSA functionalized)	HUVEC cells	No toxicity ≤ 80 µg mL− 1	No organ damage (kidney, spleen, liver, heart)	[140]
⚫ Composite	Ni–Co NPs, Sargassum tenerrimum extract	HuH‐7/HCT‐116 cells	IC50 = 65.8 (HuH‐7)/24.7 (HCT‐116) µg mL− 1	—	[133]
⚫ Composite	HAp: CoFe2O4@SiO2 NPs	New Zealand rabbits	—	Biocompatible; no rejection; controlled inflammation; biodegradation > 100 days	[141]

By contrast, Ni‐ and Co‐based nanoparticles have limited suitability for long‐term tissue‐engineering applications. Ni exposure has been associated with inflammatory, genotoxic, and carcinogenic outcomes [48]. For example, inhalation of ∼1 g nano‐Ni caused fulminant pulmonary toxicity and death in experimental mammals, emphasizing their extreme hazard potential [131]. Regulatory bodies reflect this high‐risk profile: the International Agency for Research on Cancer (IARC) classifies Ni compounds as Group 1 carcinogens, whereas metallic and alloy nickel fall under Group 2B, meaning “possibly carcinogenic to humans” [132]. Mechanistically, Ni NPs generate persistent ROS, disrupt mitochondrial function, promote DNA–protein crosslinks, and activate NF‐κB–mediated inflammatory pathways.

On the other hand, Co‐based nanoparticles, including cobalt metal, cobalt oxide (Co₃O₄), and cobalt ferrite (CoFe₂O₄) can induce oxidative stress, lysosomal destabilization, mitochondrial dysfunction, and apoptosis [133, 134]. For example, 20–100 µg mL^{− 1} Co₃O₄ caused measurable cytotoxicity and organelle dysfunction in V79 fibroblasts, including impaired mitochondrial respiration and increased lipid peroxidation [135]. These properties may be useful in antimicrobial or anticancer settings, where cytotoxicity is part of the intended mechanism [136, 137], but they are poorly aligned with regenerative strategies that require cell survival, extracellular matrix formation, and controlled tissue remodeling. Accordingly, Co‐ and Ni‐based systems are more realistic as components of external magnetic devices, microrobotics systems, or short‐term cytotoxic platforms than as constitutive components of implantable living constructs.

Taken together, these comparisons show that magnetic performance alone is insufficient for selecting MNPs for regenerative medicine. The most suitable material systems must balance magnetic responsiveness with colloidal stability, biological tolerance, metabolic handling, and translational precedent. Table 2 summarizes representative biocompatibility findings across MNP classes, coatings, biological models, and application contexts. To make the qualitative comparison in Figure 3 transparent, the radar plot is accompanied by an author‐defined scoring matrix based on five criteria: clinical validation, in vitro/in vivo biocompatibility, magnetic responsiveness, low toxicity/ROS risk, and cytotoxic/antimicrobial potency. This scoring highlights why iron oxide‐based systems currently occupy the most favorable translational space for magnetic tissue engineering, whereas Gd‐based systems are more closely linked to imaging, and Co/Ni‐based systems remain constrained by safety concerns despite strong magnetic or cytotoxic performance.

FIGURE 3.

Comparative biological and translational profiles of representative magnetic nanoparticle material classes. (A) Integrated radar plot comparing iron oxide, Gd‐based, Co‐based, and Ni‐based nanoparticle systems across five literature‐informed criteria. (B) Individual radar plots showing the dominant attribute profile of each material class. Iron oxide nanoparticles display the most balanced regenerative profile, whereas Gd‐based systems are mainly positioned by their clinical imaging relevance. Co‐ and Ni‐based systems show stronger cytotoxic or antimicrobial activity but reduced suitability for long‐term regenerative applications. (C) Author‐defined 0–4 scoring matrix used to generate the radar plots. Scores are based on representative literature summarized in Table 3 and are intended for qualitative comparison, not absolute ranking. For toxicity/ROS generation, higher scores indicate greater biological concern.

4. Integration With Advanced Biofabrication Techniques

The integration of MNPs into biofabrication frameworks enables engineered tissues to respond to externally applied magnetic fields. Beyond their established roles in hyperthermia, imaging, and drug delivery, MNPs are increasingly being explored as tools for magnetic assembly, spatial patterning, and mechanical stimulation in tissue engineering. These approaches form the basis of magnetic tissue engineering (Mag‐TE), where magnetic fields are used to guide biological organization across different lengths of scale.

Magnetic biofabrication strategies can be broadly grouped into three modalities: (i) scaffold‐free approaches involving magnetized cells, spheroids, or organoids; (ii) scaffold‐based systems where magnetic materials are embedded within hydrogels, fibers, or composite bioinks; and (iii) medium‐based strategies, such as magneto‐Archimedes levitation, which exploit differences in magnetic susceptibility within paramagnetic culture media.

This section traces the hierarchical integration of magnetic cues beginning at the single‐cell level, where mechanical forces originate and progressively advancing toward multicellular assembly, hydrogel embedding, mesoscale organization, and automated systems for 4D biofabrication.

4.1. Single‐Cell Magneto‐Mechanobiology

At the single‐cell level, magnetic tools can be used to apply defined forces to cells or subcellular structures. When MNPs are internalized, attached to the plasma membrane, or targeted to intracellular domains, externally applied magnetic fields can generate pico‐ to nano‐newton forces. These forces can affect cytoskeletal organization, nuclear deformation, and mechanosensitive pathways such as YAP/TAZ, RhoA/ROCK, mTOR, and mechanosensitive ion channels [142]. Compared with direct mechanical loading, magnetic stimulation offers a non‐contact approach with temporal control over force application. Recent reviews, including Wang et al. [143]. Garcia‐Gonzalez et al. [144] and the broader mechanotransduction review by Abdel Fattah and Ranga [145] summarize how magnetic probes and nanoparticles have been used to study and modulate force‐sensitive cellular behavior.

Experimental studies have further demonstrated how magnetic actuation can probe mechanobiology at the single‐cell level inside living systems. Asgeirsson et al. used magnetically actuated probes embedded in collagen to quantify how individual cells sense and remodel 3D matrices, revealing dynamic feedback between magnetically applied forces and ECM reorganization [146]. Lee et al. showed that remote magnetic torques can activate mechanosensitive ion channels in freely moving animals, establishing long‐range, non‐invasive control over neuronal and mechanosensory pathways [147]. Advances in magnetogenetics, recently reviewed by Latypova et al. [148], further illustrate how magnetic fields can selectively switch intracellular signaling cascades. Complementing these biological approaches, Gomez‐Cruz et al. [149] demonstrated how magneto‐active substrates applying oscillatory or multiaxial deformation drive distinct cytoskeletal and functional responses in astrocytes.

4.2. Patterning Magnetized Cells Within Hydrogels

By exploiting differences in magnetic responsiveness, magnetized cells or cell‐laden microgels can be selectively aligned, patterned, or spatially compartmentalized within hydrogels through the application of external magnetic fields. This strategy can generate gradients, anisotropic structures, and layered constructs that resemble selected structural features of native tissues. In practice, patterning depends on the magnetic loading of the cells or microgels, the stiffness and gelation kinetics of the hydrogel, the geometry of the magnetic field, and the time window during which cells remain mobile before matrix stabilization. Recent reviews, including Chansoria et al. and Santos et al., highlight how magnetic fields offer a uniquely contactless, programmable means of guiding spatial organization in 3D engineered tissues [150, 151].

Several studies demonstrate the use of magnetic patterning across tissue types. Richard et al. achieved 3D magnetic alignment of cardiac cells within hydrogels, generating anisotropic architectures that resemble native myocardium [152]. Zwi‐Dantsis et al. demonstrated remote magnetic manipulation to dynamically pattern cardiac tissues in situ [153]. For musculoskeletal applications, Wright et al. used magnetic fields to orient collagen fibers and embedded cells, producing tendon‐mimetic constructs with aligned organization [154]. Beyond single‐cell orientation, Jewett et al. showed rapid magnetic assembly of pre‐patterned microvessels, illustrating how field‐guided organization can support the formation of perfusable microvascular structures [155]. Collectively, these strategies show that static gradients or rotating fields can be engineered to program cell positioning and orientation with sub‐millimeter precision. These examples show that static gradients or rotating fields can guide cell positioning and orientation with sub‐millimeter resolution, although precision depends strongly on construct geometry, field design, magnetic loading, and material properties.

In these systems, spatial organization is determined by the balance between magnetic force, hydrogel resistance, and the timing of matrix crosslinking. Before gelation, magnetized cells or microgels can be displaced along field gradients, concentrated into defined regions, or aligned along field lines. As the hydrogel crosslinks, these patterns become mechanically stabilized, allowing the magnetic field to define tissue architecture without direct physical contact. The resulting structures can include aligned cell bands, cell‐density gradients, compartmentalized regions, or anisotropic extracellular‐matrix organization, depending on field geometry and material formulation.

4.3. MNPs Embedded in Hydrogels and Bioinks

MNPs can also be incorporated directly into polymer networks such as alginate, GelMA, collagen, silk‐gelatin blends, or PEG‐based materials. This approach produces magnetoactive hydrogels that can respond to external magnetic fields through deformation, alignment, stiffening, heating, or local force transfer. Wychowaniec and Brougham reviewed how magnetic fabrication technologies can be used to introduce anisotropy, actuation, and stimulus‐responsive behavior into soft materials [156]. Early work in this area focused largely on acellular systems for magnetorheological stiffening, shape change, and soft robotic actuation. For example, Tang et al. engineered hybrid hydrogels with programmable magnetization and rapid deformation kinetics [157], while Maiz‐Fernández et al. developed alginate‐based actuators with both electrical and magnetic responsiveness [158]. A relevant example is the stimuli‐responsive nanocomposite hydrogel developed by Tognato et al., in which low‐intensity magnetic fields organized iron oxide nanoparticles into anisotropic filamentous structures within a GelMA matrix, guiding cell alignment and enabling the fabrication of magnetically responsive 3D‐printed constructs for soft robotics and bioactuation [159].

The field has since moved toward cell‐laden magnetoactive hydrogels and printable bioinks. Incorporating MNPs into GelMA or alginate matrices can improve shape fidelity, filament stability, and anisotropy during printing. Pardo et al. demonstrated magnetically assisted 3D bioprinting of anisotropic constructs using MNP‐containing bioinks [160]. Abtahi et al. used magnetic reinforcement to produce interpenetrating polymer network nanocomposites with mechanical properties relevant to cartilage regeneration [161]. In another example, Chakraborty et al. developed silk‐gelatin‐based magnetic bioinks capable of time‐dependent shape changes under magnetic fields for cartilage‐oriented applications [162].

Some non‐magnetic scaffold‐design strategies can still provide useful principles for spatial patterning. For example, Kalogeropoulou et al. used computational design based on L‐systems and Archimedean tessellations to introduce controlled void architectures into printed scaffolds, which may be relevant for future biomaterial–MNP hybrid systems [163]. Although this study did not involve magnetic actuation, it illustrates how scaffold geometry can be computationally controlled to influence tissue organization. In magnetic biofabrication, similar design principles may be useful when combined with field‐guided particle alignment or magnetoactive bioinks; however, this connection remains conceptual and requires experimental validation.

Computational approaches are also being developed for magnetoactive soft materials. Perez‐Garcia et al. introduced a topology‐optimization strategy for ultra‐soft magneto‐active structures that combines numerical modeling with machine‐learning‐guided parameter exploration [164]. This work shows how magnetization profiles and material layouts can be designed to improve deformation efficiency and directional actuation. For biofabrication, such approaches may eventually help define magnetoactive material architectures, but their use in cell‐laden regenerative systems remains at an early stage.

In musculoskeletal and soft‐tissue engineering, MNP‐containing bioinks and hydrogels can support remote actuation of embedded cells and controlled anisotropy. Magnetically oriented collagen and MNP‐reinforced hydrogels have been used to generate tendon‐like aligned constructs [154], while magnetorheological bioinks have facilitated in situ magnetic‐field‐assisted printing of aligned muscle tissues [165]. Moreover, magnetic assembly of microstructures has also been used to form pre‐patterned capillary‐scale microvessels through guided deposition [155].

Magnetic responsiveness can further be used for mechanobiological stimulation within scaffolds. Kalogeropoulou et al. developed an in vitro magnetomechanical stimulation device that delivered tunable magnetic cues to hMSC‐laden osteochondral scaffolds, enhancing chondrogenic and osteogenic differentiation [166]. This example shows how magnetoactive hydrogels and magnetic actuation platforms can be combined to deliver dynamic mechanical cues during tissue maturation. Overall, embedding MNPs in hydrogels or bioinks provides a route to remotely deform, align, stimulate, or reshape engineered constructs, but performance depends on particle distribution, matrix mechanics, field geometry, and cell compatibility.

4.4. Organoid and Spheroid Magneto‐Assembloids

At the mesoscale, magnetically functionalized spheroids (MNP‐loaded spheroids) and organoids act as programmable tissue units that can be dynamically bottom‐up positioned, fused, or mechanically stimulated in the presence of external magnetic fields. This allows their integration into higher‐order assembloids with precisely controlled geometry and composition.

Several studies have demonstrated deterministic assembly of multicellular units. Byun et al. used magnetically controlled stem‐cell spheroids to construct 3D tissues with tunable contractility, showing that magnetic positioning can influence collective force generation [167, 168]. Demri et al. demonstrated remote magnetic microengineering of spheroids into continuous cellular fibers, showing how field‐guided assembly yields structurally coherent, elongated structures [169]. Similarly, Koudan et al. patterned tissue spheroids using polymer microcapsules containing Fe₃O₄ nanoparticles, enabling positional control without exposing cells directly to high nanoparticle doses [170].

Magnetic levitation offers another route for contact‐free assembly. These methods rely on negative magnetophoresis, where diamagnetic cells are levitated within a paramagnetic medium whose susceptibility is increased using additives such as Gd^{3 +}. This magneto‐Archimedes effect allows 3D aggregation without incorporating MNPs directly into cells. Anil‐Inevi et al. maintained high‐viability levitated cultures using ring‐magnet configurations [171], while Moncal et al. used levitation platforms to template spheroid organization based on density and magnetization [172]. Similarly, Parfenov et al. using Gd³⁺ paramagnetic medium extended magnetic levitation to orbital microgravity, utilizing space‐based platforms to assemble cm‐scale cartilage constructs in high magnetic fields [8, 173]. These studies show that levitation can support scaffold‐free assembly, including in reduced‐gravity environments, but the approach remains constrained by magnet dimensions, paramagnetic media requirements, and levitation depth.

Magnetic assembly has also been applied to organoid and tissue‐building systems. Kim et al. used magnetized gold nanoparticles to standardize brain organoid formation, reducing heterogeneity while limiting direct exposure to cytotoxic magnetic materials in delicate cells [174]. Abdel Fattah et al. used targeted magnetic stimulation within developing tissues to activate mechanosensitive pathways and guide tissue patterning [175]. For vascular applications, Seok et al. magnetically assembled endothelial‐cell‐coated spheroids to promote vascularized tissue constructs [176], while Parfenov et al. generated tubular tissues through magnetoacoustic levitational assembly, illustrating how magnetic cues coordinate spheroid fusion within confined geometries [177].

Computational modeling has also been used to investigate magnetic mesoscale assembly. Rodríguez et al. developed a phase‐field framework showing how superparamagnetic nanoparticles can accelerate spheroid fusion under magnetic guidance by adding magnetic body forces that reduce the energetic barrier for early neck formation [178]. This supports the use of models to interpret fusion kinetics and optimize assembly conditions in advance.

Magnetic mesoscale assembly has also been used to create regenerative assembloids from human periosteal‐derived cells/microtissues loaded with MNPs. Ioannidis et al. demonstrated that magnetically augmented cartilaginous hPDC microtissues can be fused into callus assembloids, with dynamic magnetic stimulation during in vitro maturation accelerating in vivo regeneration and bone formation [11].

The strategies discussed in Sections 4.2–4.4 can be organized into scaffold‐based and scaffold‐free magnetic biofabrication approaches. Scaffold‐based systems use hydrogels, fibers, or composite matrices as magnetic‐responsive environments for cell patterning, deformation, anisotropic guidance, or contraction. In contrast, scaffold‐free systems exploit magnetic forces to assemble, shape, or stimulate cells, spheroids, organoids, or tissue units without relying on a permanent supporting matrix. Representative examples of these two strategy classes are summarized in Figure 4.

FIGURE 4.

Representative scaffold‐based and scaffold‐free magnetic biofabrication strategies. Magnetic biofabrication strategies can be broadly organized according to whether magnetic functionality is incorporated into an exogenous scaffold or used to guide cells, aggregates, or developing tissues without a permanent supporting matrix. Scaffold‐based approaches include magnetic patterning within hydrogels, magnetized hydrogel systems, and magnetized fibers, enabling spatial cell patterning, compartmentalization, field‐responsive deformation, actuation, anisotropic guidance, and controlled contraction. Scaffold‐free approaches include shape‐specific biofabrication, label‐free biofabrication, and magnetic mechanical stimulation, enabling field‐defined construct geometry, tissue formation without exogenous magnetic labeling, and remote regulation of maturation and extracellular matrix remodeling. Representative panels are adapted from previously published studies as indicated in each panel, with permission where required.

4.5. Toward In Situ Magnetic Biofabrication

In situ magnetic biofabrication aims to guide, assemble, or stimulate magnetically responsive cells, spheroids, microtissues, capsules, or bioinks directly within a defect site. The concept is attractive because magnetic fields can act at a distance and may help organize materials in geometries that are difficult to access using conventional printing or surgical placement. However, most current examples remain proof‐of‐concept demonstrations, and true in situ assembly will require improved field localization, device design, and validation in clinically relevant defect models.

Recent bioprinting‐based assembloid strategies provide useful precedents for contactless manipulation of delicate tissue units. Roth et al. compared aspiration‐assisted spheroid manipulation with magnetic spheroid lifting using an electromagnet integrated into a bioprinting nozzle [179]. Magnetic pick‐and‐place control enabled reproducible positioning of neural spheroids and supported the fabrication of centimeter‐scale neural assembloids. Although this study was performed in a bioprinting context, it illustrates how magnetic forces can manipulate delicate spheroids without direct mechanical gripping. Similar principles could be useful in defect environments where nozzle access is limited, or surface geometry is irregular.

Magnetic fields can also guide continuous bioink streams or cell‐laden materials. Hwangbo et al. developed a magnetic‐field‐assisted in situ bioprinting process using a magnetorheological bioink to form aligned muscle constructs at the defect site [165]. This work shows that magnetic cues can pattern not only discrete spheroids but also printed bioink structures within complex geometries.

A more direct step toward clinical translation was recently demonstrated by Go et al., who engineered human adipose‐derived MSC‐based magnetic microrobots capable of navigating joint spaces and promoting cartilage regeneration in vivo [180]. This system shows how magnetic guidance can support not only structural assembly but also the in situ delivery of therapeutic cell populations within mechanically dynamic, clinically relevant environments such as the knee joint. This system shows how magnetic guidance can support delivery and retention of therapeutic cell populations within mechanically dynamic environments such as the knee joint. It also links magnetic tissue assembly to magnetic cell therapy, although additional work is needed to establish broader applicability for regenerative biofabrication.

Recent advances in miniaturized magnet arrays and adaptive field‐localization strategies are rapidly moving this concept toward translational feasibility. A key experimental step in that direction was recently demonstrated by Santos et al., who used remote magnetic stimulation to enhance mechanosensitive responses and bone‐forming potential in vivo [9]. This represents an important step toward post‐implantation magnetic conditioning, although the approach still relied on pre‐formed constructs and limited field localization. Achieving fully programmable in situ assembly will require the co‐development of magnetic devices, field‐generating setups, imaging or feedback methods, and computational models that can predict field gradients and force distributions and construct behavior in irregular defects.

Magnetic microrobotics systems further illustrate possible future directions. Du et al. showed that magnetic microrobot swarms can navigate confined biological spaces, reconfigure collective patterns, and perform spatially programmable tasks such as movement through vascular channels [181]. Although not focused on tissue formation, such work indicates how field‐guided microscale systems could eventually support navigation, mapping, or local manipulation of MNP‐loaded single cells or spheroids during future in situ biofabrication procedures.

For surgical and translational implementation, magnetic biofabrication also requires dedicated field‐generating platforms capable of controlling where, when, and how magnetic forces are applied. These platforms can support pre‐surgical fabrication, in vitro stimulation, intraoperative targeting or fixation, and post‐fabrication stimulation. Figure 5 summarizes representative magnetic fabrication, stimulation, and fixation platforms that illustrate how magnetic strategies can be translated from material‐ or cell‐level manipulation toward device‐assisted tissue engineering workflows.

FIGURE 5.

Magnetic biofabrication and stimulation platforms. Magnetic biofabrication can be implemented through dedicated field‐generating devices and magnetic actuation platforms that control construct fabrication, targeting, fixation, or stimulation. Fabrication‐oriented platforms include spatially patterned organoid transfer, in situ magnetic‐field‐assisted assembly, targeted in situ magnetic biofabrication, and miniaturized skeletal tissue fabrication. Stimulation and fixation platforms include magnetomechanical scaffolds for in vitro stimulation, magnetic band‐assisted in situ fixation, and dynamic magnetic stimulation systems that modulate angiogenic or regenerative responses. These examples illustrate how field configuration, device architecture, and actuation mode determine whether magnetic systems are used primarily for tissue assembly, spatial targeting, fixation, or post‐fabrication stimulation. Representative panels are adapted from previously published studies as indicated in each panel, with permission where required.

4.6. Magnetic Integration With Microfluidic and Organ‐on‐Chip Platforms

Microfluidic and organ‐on‐chip platforms provide controlled environments for integrating magnetic actuation with perfusion, oxygenation, biochemical gradients, and real‐time observation. In these systems, magnetically labeled cells, spheroids, or microtissues can be guided, patterned, aggregated, or mechanically stimulated under defined culture conditions. Kheiri et al. demonstrated 4D force‐patterning approaches that achieve spatial control of angiogenesis, showing how controlled magnetic forces can reconfigure cellular architectures, modulate endothelial sprouting, and provide contactless stimulation within confined microenvironments [182].

Magnetic actuation has also been incorporated into muscle‐on‐chip platforms. Demri et al. demonstrated magnetic bioprinting and cyclic actuation of stretchable muscle tissues, enabling magnetically induced contractile behavior and anisotropic alignment during maturation [183]. Earlier systems, such as the skeletal muscle‐on‐chip platform by Yoshioka et al., used magnetic elements to support actuator‐guided muscle fiber formation and quantify contractile forces [184]. Together, these studies show how magnetic cues can be integrated into engineered microenvironments to guide tissue assembly, maturation, and functional readouts.

By programming magnetic fields in space and time, microfluidic platforms may support more standardized positioning, fusion, and maturation of spheroids or organoids. When combined with robotic handling, imaging feedback, and computational field optimization, these systems could contribute to automated culture workflows for organoid or microtissue production. In this context, MNPs can act as micromechanical actuators, while device‐level magnetic sensing technologies can provide functional readouts of engineered tissues [185].

Building on these examples, Figure 6 provides a conceptual synthesis of the chapter. Rather than treating magnetic biofabrication as a single method, the scheme frames it as a multiscale framework. This overview connects single‐cell magnetomechanobiology, scaffold‐based and scaffold‐free assembly, in situ biofabrication, and magnetic stimulation into a unified roadmap for advanced biofabrication. Together, the studies discussed in this chapter show that magnetic biofabrication is not a single methodology, but a multiscale framework for remotely regulating cells, materials, and developing tissues. Figure 4 summarized representative scaffold‐based and scaffold‐free strategies, Figure 5 highlighted device‐assisted fabrication, fixation, and stimulation platforms, and Figure 6 integrated these concepts into a broader roadmap for advanced magnetic biofabrication. Finally, Table 3 complements these figures by comparing the principal magnetic actuation setups discussed throughout the present section, including their additive value, limitations, optimal applications, and representative references.

FIGURE 6.

Conceptual roadmap of magnetic integration with advanced biofabrication techniques. Magnetic integration in biofabrication can operate across multiple biological and technological scales, ranging from single‐cell magnetomechanobiology to scaffold‐based patterning, scaffold‐free assembly, device‐assisted fabrication, and post‐fabrication stimulation. Magnetic nanoparticles, magnetic materials, and magnetic field configurations can be used to guide cell positioning, control hydrogel or fiber organization, assemble spheroids or organoids, support in situ targeting, and deliver remote mechanical cues during tissue maturation. This schematic summarizes the present section conceptually by linking magnetic inputs, biological building blocks, fabrication platforms, and stimulation strategies into a multiscale framework for spatial organization, dynamic conditioning, and translational deployment of engineered tissues.

TABLE 3.

Magnetic actuation setups presented across Section 4, with advantages, limitations, optimal applications, and corresponding references.

Actuation setup	Additive value	Limitations	Best use case	Key references
Magnetic tweezers and microprobes	Precise pico–nanoNewton actuation; subcellular control; ideal for mechanotransduction studies	Low throughput; single‐cell only; microscopy‐dependent	Single‐cell force probing; mechanotransduction	[146]
Torque‐generating rotational MNP systems	Remote activation of mechanosensitive ion channels; works in vivo; pathway‐specific	Requires specialized MNP functionalization; limited spatial selectivity	Magnetogenetics; neuronal/mechanosensory control	[147]
Magneto‐active substrates	Programmable strain profiles; oscillatory and multiaxial loading; compatible with soft tissues	Fabrication complexity; force transmission dependent on adhesion	Dynamic mechanobiology; astrocyte and soft‐tissue models	[149, 167, 168]
Static permanent magnet Arrays for hydrogel or cell alignment	Simple, stable, no heating; generates anisotropy in hydrogels; robust for bioinks	Fixed gradients; depth penetration limited	Tendon/muscle alignment; anisotropic patterning	[154]
Rotating magnetic fields/dynamic reorientation systems	Enables reconfiguration, patterning, active shaping; supports cardiac tissue assembly	Requires motorized systems; precision depends on geometry	Cardiac tissue patterning; dynamic reorientation	[153]
Magnetoactive bioink and field‐assisted printing systems	Improved filament fidelity; anisotropy during printing; shape‐morphing constructs	Printer–magnet integration needed; field heterogeneity	3D bioprinting; cartilage/tendon/muscle patterning	[160, 165]
Interpenetrating polymer networks (IPN) with MNPs	Mechanical reinforcement; cartilage‐relevant stiffness; enhanced structural fidelity	Complex formulation; MNP distribution affects behavior	Cartilage regeneration constructs	[161]
Magnetic levitation (negative magnetophoresis)	Contact‐free assembly; avoids direct MNP exposure; scalable; works in microgravity	Requires paramagnetic media (Gd3 +); shallow levitation depth; magnet size constraints	Scaffold‐free 3D assembly; microgravity biofabrication	[8, 171, 172, 173]
Ring‐Magnet / Gradient‐Based Spheroid Fusion Platforms	Precise positioning; fiber‐like and tubular assembly; good mesoscale control	Limited complexity; sensitive to geometry and spacing	Tubular constructs; aligned spheroid fibers	[169, 170]
External/wearable magnetic stimulation devices	Non‐invasive; enables in situ mechanostimulation; clinically realistic	Limited depth targeting; coarse field localization	Post‐implantation stimulation; bone regeneration	[9]
Electromagnetic coil systems (Helmholtz/solenoid)	Tunable dynamic stimulation; programmable fields; imaging compatible	Heat generation; power demands; high cost	Mechanobiology; long‐term dynamic stimulation	[156]
Computationally optimized field architectures	Predictive control of fusion kinetics; supports rational device design	Requires accurate biophysical parameters; validation needed	Optimizing spheroid assembly and gradients	[178]
Magnetic Assembly for engineered assembloids	Patient‐derived hPDC assembloids; dynamic stimulation accelerates ossification; magnetic memory preserved in vivo	Requires high‐fidelity MNP loading; field localization still external	Skeletal assembloids; regenerative implants	[11]

5. Predictive Computational Modeling and Mechanical Stimulus Measurements

Magnetic biofabrication requires control over both magnetic fields and the mechanical cues generated within cells, spheroids, hydrogels, or tissue constructs. As discussed in Section 4, magnetic fields can be used to assemble tissues, guide cellular organization, and stimulate mechanosensitive pathways. However, the biological outcome depends not only on the applied field, but also on MNP loading, particle distribution, material mechanics, construct geometry, and the duration of stimulation. Computational modeling and mechanical measurements are therefore important for linking magnetic field parameters to biological responses and for reducing empirical trial‐and‐error during platform development.

In this section, we first summarize measurement approaches used to quantify mechanical forces across length scales. We then discuss computational models that predict MNP movement, followed by models of spheroid and microtissue assembly. Finally, we outline how these components could support predictive, data‐informed biofabrication workflows, while emphasizing current limitations and validation needs.

5.1. Mechanical Stimulus Measurements

Mechanical forces are central regulators of development, homeostasis, and regeneration across diverse tissues [186, 187, 188]. In magnetic tissue engineering, MNPs incorporated into cells, spheroids, or scaffolds can convert externally applied magnetic fields into local mechanical cues. Magnetic stimulation has been reported to influence progenitor cell differentiation [189], proliferation, alignment, and collagen I deposition [190]. Targeted magnetic actuation can deliver piconewton‐level forces to mechanosensitive receptors [191], while MNP‐containing hydrogels provide magneto‐responsive anisotropy for remote tissue engineering [192]. Additional studies have shown that cyclic magnetic stimulation can guide cardiomyogenic differentiation in embryonic stem cells [193] and that tendon‐mimetic magnetic scaffolds can activate YAP/TAZ signaling and pro‐healing gene programs in hASCs [194].

To interpret such effects, magnetic actuation must be connected to measurable mechanical outputs. The relevant measurement method depends on the scale of interest. At the molecular and subcellular level, optical tweezers, magnetic tweezers, and atomic force microscopy can quantify local force application and receptor‐ or cytoskeleton‐associated responses [195, 196, 197, 198]. At the cellular level, AFM, optical tweezers, and magnetic tweezers can probe cell stiffness, adhesion, and force transmission [199, 200, 201, 202, 203, 204]. At the microtissue level, AFM, microtweezers, micropipette aspiration, compression testing, ultrasoft hydrogels, and oil‐droplet mechanosensors can be used to estimate spheroid mechanics, interfacial tension, and internal stress [188, 205, 206, 207]. At the tissue scale, tensile and compressive testing, indentation, elastography, and pressure myography provide information on bulk mechanical properties and functional maturation [208, 209, 210].

These measurements provide the experimental basis for validating computational models. For example, field‐generated forces can be compared with measured deformation, fusion kinetics, cell alignment, or tissue stiffness. Such validation is essential because the same applied magnetic field could produce different mechanical outputs depending on particle concentration, particle localization, matrix stiffness, construct geometry, and biological remodeling.

5.2. Computational Models of MNP Movement

Numerous computational models have been developed to describe MNP behavior in external magnetic fields within biological fluids or tissue‐like environments. Most models include two main components: first, a description of the magnetic field, often obtained analytically or by solving magnetostatic equations using the finite element method (FEM); and second, a mechanical or transport model that predicts MNP movement based on a force balance between magnetic forces and interactions with the surrounding medium.

Many of these models originate from magnetic drug targeting and related biomedical transport applications. Simulated MNP trajectories have been used to study transport in cylindrical vessels [211], in pulsating, blood‐mimicking laminar flows [212, 213], and in static ferrofluids under gradient fields [214]. Computational Fluid Dynamics (CFD) simulations coupled with magnetostatic forces have been employed to model MNP delivery in tumorous and healthy microvasculature [207], their transport in blood vessels and human arteries [213, 215, 216], and their capture on stents for restenosis treatment [217]. More recently, Wirthl et al. applied a multiphase porous media model to investigate capture of MNPs in tumor spheroids in magnet‐equipped flow chambers [218].

These models provide a useful foundation, but they do not fully represent magnetic biofabrication environments. Most focus on particle motion in fluids, where the main forces are magnetic attraction, hydrodynamic drag, diffusion, and sometimes particle‐particle interactions. In contrast, biofabrication often involves viscoelastic hydrogels, dense cell aggregates, spheroids, extracellular matrix, and time‐dependent tissue remodeling. In these settings, MNP movement or force transfer may be constrained by matrix stiffness, pore size, particle binding, cell‐generated forces, gelation kinetics, and degradation.

Therefore, MNP transport models need to be adapted before they can accurately predict magnetic biofabrication outcomes. FEM can be used to calculate field distributions and gradients of different magnetic setups, while CFD or particle‐tracking approaches can predict movement in fluidic systems. For hydrogels and tissues, these models must be extended with viscoelastic material descriptions, particle‐matrix interactions, and experimentally measured mechanical properties. This distinction is important because a model that accurately predicts MNP transport in a vessel or microfluidic channel may not predict MNP‐induced force transfer inside a cell‐laden hydrogel or fusing spheroid assembly.

5.3. Computational Models of Magnetized Cell and Spheroid Assembly

In magnetic biofabrication, computational modeling must go beyond MNP trajectory prediction and account for the behavior of cells, spheroids, or microtissues as deformable biological units. In spheroid‐based systems, magnetic forces acting on MNPs are transmitted to multicellular aggregates that also exhibit adhesion, interfacial tension, viscosity, active contractility, and extracellular matrix remodeling. As a result, magnetically guided assembly depends on both external field‐generated forces and endogenous tissue mechanics.

Several computational frameworks have been used to model tissue fusion and multicellular organization. These include Lattice Boltzmann methods [219], individual cell‐based models [220, 221], Metropolis Monte Carlo approaches [222, 223], Cellular Particle Dynamics [224, 225], Cellular Potts and Kinetic Monte Carlo models [226], agent‐based models [227], phase‐field formulations [228], and center‐based models [227]. These approaches can capture different aspects of tissue self‐assembly, including cell sorting, compaction, fusion, shape evolution, and interface dynamics. However, most were originally developed for spontaneous morphogenesis or tissue fusion and do not include external magnetic forces. Recent work has begun to couple magnetic and mechanical effects more directly. A phase‐field model reproduced spheroid fusion with embedded superparamagnetic nanoparticles under external magnetic fields [178].

In a microgravity study, FEM was used to compute magnetic fields and predict MNP trajectories, followed by Surface Evolver simulations to model the fusion dynamics of magnetically assembled chondrospheres [8]. Similarly, finite element models have been used to explore the assembly of stem cell spheroids directed by multiple magnetic sources [168]. In addition, agent‐based models have been validated for periosteum‐derived spheroids incubated with MNPs [11].

These examples show that magnetic assembly can be modeled, but current approaches remain limited. Most models simulate a small number of spheroids or simplified geometries, use static field configurations, and focus mainly on early assembly or fusion. They often neglect active cellular responses, changes in tissue mechanics over time, heterogeneous MNP loading, extracellular matrix deposition, proliferation, vascularization, and degradation. Experimental validation is also often restricted to small‐scale in vitro systems. These limitations matter because magnetic biofabrication is intended to control living materials whose properties change during culture and maturation.

Future models should therefore define clearly what is included and what is neglected. At minimum, predictive models for magnetic spheroid assembly should include magnetic field distribution, MNP loading, aggregate size, drag or matrix resistance, contact mechanics, and fusion kinetics. More advanced models should incorporate time‐dependent material properties, active cell‐generated stresses, ECM deposition, and heterogeneous cell populations. Hybrid approaches that combine FEM‐based magnetic field modeling with phase‐field, agent‐based, or continuum tissue models may provide a practical route toward more realistic simulations. However, such models require systematic validation using measured assembly trajectories, fusion times, deformation fields, tissue stiffness, and biological readouts.

Table 4 summarizes computational approaches used to simulate MNP movement, spheroid assembly, and magnetically guided spheroid assembly. The table also highlights the importance of distinguishing between models that predict particle transport, models that predict tissue fusion, and models that attempt to couple magnetic forces with multicellular behavior.

TABLE 4.

Computational methods and tools used to simulate MNP movement, non‐magnetic spheroid assembly, and magnetically driven spheroid assembly.

Goal	Models	Approach	References
MNP movement	Mapped/externally solved magnetics (analytical or FEM) + particle tracking	Analytically or FEM‑computed magnetic forces; flow given as prescribed or simple laminar profiles; particle motion advanced via force‑balance ODEs combining magnetic and hydrodynamic drag.	[211, 212, 214, 217]
	FEM‐coupled magnetics with CFD + particle tracking	Solve magnetic field with FEM and flow with CFD; integrate particle motion via equations of motion with magnetic and hydrodynamic forces;	[213, 215, 216, 229]
	Continuum transport in porous media	Advection‐diffusion with magnetic body force terms in a porous medium; FEM solution for concentrations and fluxes	[218]
Spheroid assembly	Hydrodynamic models	Lattice Boltzmann simulates fluid‑like behavior during early fusion; Smoothed Particle Hydrodynamics (SPH) models elastic–plastic solid and fluid continuum behavior of spheroids during fusion	[219, 220]
	Non‐magnetic agent‐based fusion/sorting models	Agents represent cells or spheroids whose interactions are governed by adhesion forces, active contractility, and viscous resistance, enabling the simulation of sorting, compaction, and spheroid fusion dynamics	[221]
	Energy‐based models	MMC (Metropolis Monte Carlo) and Cellular Potts/KMC minimize global energy functions to simulate sorting, fusion, and interface evolution	[222, 223, 226]
	Cellular Particle Dynamics (CPD)	Particle–spring mechanical representation of cells; captures viscoelastic fusion and tension‑driven shape changes	[224, 225]
	Phase‐field models	Continuum interface description predicts coalescence, shape evolution, and fusion kinetics	[228]
Magnetic spheroid assembly	Phase‐field	Magnetic fields from FEM, coupled with phase‐field fusion of MNP‐loaded spheroids	[178]
	Surface Evolver + FEM	FEM computes magnetic fields and MNP motion with standard equations of motion; Surface Evolver models surface‐energy‐driven fusion dynamics	[8]
	Magnetic‐field‐coupled agent‐based assembly models	Each spheroid acts as an agent in the simulation. Their magnetically guided assembly is driven by a grid‐based magnetic field, which is interpolated at each spheroid's location.	[11]

5.4. Toward Predictive and Data‐Informed Magnetic Biofabrication Workflows

The combination of mechanical measurements, magnetic field modeling, and biological readouts could support more predictive magnetic biofabrication workflows. In such workflows, experimentally measured inputs could be used to parameterize simulations, and model predictions could guide the design of magnetic field configurations, material formulations, and stimulation protocols. This approach does not yet constitute a fully realized clinical digital twin for magnetic tissue engineering, but it provides a practical framework to decrease ‘wasting’ of time for trial‐and‐error working mode and improve reproducibility.

A predictive magnetic biofabrication model would require several classes of input. These include magnetic field maps, field gradients, magnet geometry, MNP size and magnetization, MNP loading per cell or spheroid, construct geometry, medium or hydrogel viscosity, matrix stiffness, spheroid size, and experimentally measured fusion or deformation behavior. Depending on the application, additional biological inputs may include cell type, viability, differentiation status, matrix deposition, and changes in mechanical properties during maturation. The outputs of such models should also be defined explicitly. For MNP transport, useful predictions include particle trajectories, capture efficiency, and spatial distribution. For spheroid or microtissue assembly, relevant outputs include assembly time, positional accuracy, fusion kinetics, aggregate deformation, local stress distribution, and final construct geometry. For magnetoactive hydrogels or implanted constructs, models may predict field penetration, strain distribution, magnetic force density, and the spatial pattern of mechanical stimulation. These predictions can then be compared with experimental measurements such as imaging‐based tracking, rheology, compression testing, histology, gene expression, or matrix deposition.

At present, several important biological processes remain difficult to model. These include active cell remodeling, proliferation, apoptosis, heterogeneous differentiation, immune response, vascularization, tissue degradation, and patient‐specific variability. Therefore, digital twin terminology should be used cautiously in this field. A useful near‐term goal is not a fully autonomous clinical digital twin, but a validated modeling pipeline that links magnetic field design to measurable mechanical and biological outcomes. Machine learning and optimization methods may support this process when sufficient experimental data are available. For example, they could be used to relate field parameters, MNP loading, spheroid size, or hydrogel mechanics to outputs such as assembly accuracy, fusion time, tissue stiffness, or ECM deposition. However, these models should remain constrained by physical principles and validated experimentally to avoid purely correlative predictions. In this context, AI‐assisted methods are best viewed as tools for parameter exploration and optimization rather than replacements for mechanistic modeling.

Figure 7 summarizes a proposed physics‐guided framework for predictive magnetic biofabrication. In this framework, mechanical characterization, magnetic field mapping, particle or tissue‐scale simulations, and experimental validation are iteratively combined. At the same time, Table 5 summarizes the main modeling approaches, input parameters, and validation strategies that could support predictive magnetic biofabrication workflows. The table is organized from field‐level and particle‐level models toward construct‐ and tissue‐level simulations. Magnetic field modeling defines the spatial distribution of magnetic flux density and field gradients generated by a given magnet or coil configuration. MNP trajectory and transport models then use these field maps together with particle size, magnetization, fluid viscosity, Brownian diffusion, and drag to predict particle motion or capture. At the construct scale, spheroid fusion, Cellular Potts, agent‐based, phase‐field, and tissue‐scale FEM models can be used to describe aggregate compaction, interface evolution, deformation, and stress distribution. Finally, machine‐learning or hybrid models may help connect experimentally measured inputs with outputs such as fusion time, morphology, stiffness, or matrix deposition, if predictions remain physically constrained and experimentally validated. Together, these approaches highlight that no single model is sufficient for magnetic biofabrication; instead, predictive workflows will likely require coupled magnetic, mechanical, transport, and biological validation layers.

FIGURE 7.

Proposed physics‐guided framework for predictive magnetic biofabrication. The schematic illustrates an integrated predictive biofabrication pipeline linking multiscale mechanical characterization, physics‐guided modeling, and AI‐assisted optimization. Experimentally derived material and tissue‐level mechanical descriptors provide input to simulations of nanoparticle dynamics, magnetic field distributions, and magnetized microtissue behavior, enabling application‐specific magnetic actuation design. Iterative digital twin feedback loops integrate quantitative stimulation outputs with experimental validation to refine biofabrication strategies, supporting scalable, standardized, and application‐oriented magnetic tissue engineering workflows.

TABLE 5.

Computational approaches, parameters, and validation methods in magnetically driven biofabrication.

Computational approach	Key parameters	Validation methods
Analytical formulas for magnetic field modeling (FEM)	Magnetic flux density B; field gradient ∇B; remanence Br; magnet geometry; mesh density	3D Hall probe field mapping; predicted map—experiment correlation
MNP trajectory modeling (CFD + particle dynamics)	Particle radius r; magnetization M; drag coefficient ζ; viscosity µ; Brownian diffusion D; magnetic force Fmag = V(M·∇B)	µPIV tracking; fluorescent MNP motion tracking; microfluidic assays
Transport in vessels/hydrogels	Flow velocity v; shear stress τ; shear rate γ̇; vessel radius R; hydrogel viscoelasticity G′, G″	Microfluidic chips; rheometry; MNP capture assays
Spheroid fusion modeling (phase‐field)	Interfacial tension σ; tissue viscosity η; magnetic body force density fmag; free‐energy functional F(φ)	Fusion kinetics; shape evolution; ECM deposition imaging
Cellular potts/Monte Carlo	Adhesion energy J; contractility κ; volume constraint λV; MNP density ρMNP	Compaction; contact angles; histology
Agent‐based models	Cell motility µcell; active tension T; heterogeneity in MNP loading; applied ∇B	Cell tracking; high‐content imaging; MNP uptake quantification
Tissue‐scale FEM biomechanics	Elastic modulus E; Poisson ratio ν; nonlinear stress–strain σ(ε); magnetic susceptibility χ	Compression/tension tests; indentation; elastography
Continuum viscoelastic/magnetorheological models	Storage modulus G′; loss modulus G″; polymer density ρgel; relaxation time τR; magnetic torque τmag	Dynamic rheology; strain–stress mapping; alignment imaging
In situ magnetic assembly modeling	Magnet configuration; field superposition B = Σ Bi; gradient shaping ∇B; defect geometry	Assembly precision; µCT/MRI tracking; spatial error analysis
Machine learning/hybrid models	Training variables: fusion time tfuse, ECM density ρECM, field parameters (B, ∇B, M); predictions: morphology, stiffness E	Cross‐validation; prediction accuracy; experimental matching

6. Safety and Regulatory Considerations

As MNPs move from exploratory biofabrication tools toward functional components of tissue‐engineered implants, their translation will depend on rigorous safety assessment, reproducible manufacturing, and appropriate regulatory classification. MNPs have already been evaluated in diagnostic and therapeutic contexts, including MRI contrast agents and iron‐replacement therapies. However, their incorporation into living constructs introduces additional questions that are not fully addressed by these earlier use cases. These include local degradation, long‐term retention, remodeling‐dependent release, interaction with immune cells, compatibility with repeated magnetic stimulation, and potential interference with diagnostic imaging.

Magnetically engineered tissues also occupy a complex regulatory space because they may combine nanoparticles, viable cells, scaffolds, bioactive matrices, and external actuation devices. Depending on their composition and intended use, such products may fall within advanced therapy medicinal product (ATMP), medical device, medicinal product, or combination‐product frameworks. This section summarizes the main safety considerations for MNP‐enabled tissue‐engineered constructs and outlines the regulatory challenges associated with their manufacturing, classification, and clinical deployment.

6.1. Safety Concerns

Metallic and metal‐oxide MNPs have been extensively investigated for biomedical applications, as discussed in earlier sections. Ni‐ and Co‐based systems have mainly been explored in antimicrobial, catalytic, or anticancer settings, where cytotoxicity can be part of the intended function. By contrast, Fe‐ and Gd‐based systems are more closely associated with diagnostic imaging, iron replacement, and imaging‐oriented biomedical applications. Iron oxide nanoparticles are particularly relevant for magnetic tissue engineering because they combine magnetic responsiveness with comparatively favorable biological handling and stronger precedent in clinical or preclinical biomedical use.

Although some MNP formulations have been administered clinically as intravenous agents, their use in tissue‐engineered implants raises different safety questions. Injected contrast agents or iron‐replacement products are generally evaluated for systemic administration, circulation, metabolism, and clearance. In contrast, magnetized tissue constructs may retain MNPs locally for extended periods while the extracellular matrix remodels and the implant matures. Even when the total Fe dose is lower than that used in diagnostic or therapeutic administration, the local release kinetics, degradation profile, and spatial distribution of iron can differ substantially. This may influence macrophage uptake, lysosomal dissolution, ferritin buffering, local oxidative stress, and the risk of tissue‐level iron accumulation.

Existing in vivo studies provide encouraging short‐term evidence for MNP‐containing regenerative constructs, including osteogenic and chondrogenic responses without major organ toxicity in selected models [11, 123]. However, long‐term longitudinal studies extending beyond 6–12 months remain limited. This represents an important gap for evaluating chronic accumulation, remodeling‐dependent release, local immune responses, and delayed tissue effects. Macrophage‐driven degradation may also interact with magnetic actuation, potentially influencing cytokine secretion, oxidative stress, and the local immune microenvironment. These processes require comparative evaluation under static, cyclic, and non‐stimulated conditions.

A second safety layer concerns remote post‐operative magnetic stimulation. Preliminary in vivo studies suggest that static or cyclic magnetic field exposure can enhance mechanosensitive responses and bone‐forming potential in specific models [9]. However, the long‐term local and systemic effects of repeated magnetic stimulation of MNP‐containing living constructs remain insufficiently characterized. Existing exposure and MRI safety frameworks provide useful context, but they are not designed specifically for repeated, localized stimulation of implanted magnetoactive tissues. At present, there are no harmonized thresholds defining safe field strength, gradient, frequency, duration, or duty cycle for MNP‐containing regenerative implants. In addition, implanted magnetized constructs may create MRI susceptibility artifacts, local field distortions, displacement forces, torque effects, or signal changes over time. Systematic MRI‐compatibility testing will therefore be needed for future clinical translation.

6.2. Regulatory Pathways and Challenges

For clinical use, MNP‐containing products must demonstrate safety, quality, and efficacy under Good Manufacturing Practice (GMP) conditions. This is a major translational bottleneck because only a limited number of MNP formulations are manufactured at clinical grade, and most experimental formulations used in magnetic biofabrication are not produced under GMP‐compliant processes. Regulators increasingly expect Quality‐by‐Design (QbD)‐aligned manufacturing strategies, where critical material attributes and critical process parameters are defined, controlled, and validated. For magnetic tissue‐engineering products, relevant release criteria may include nanoparticle identity, size distribution, coating stability, sterility, endotoxin levels, MNP loading per cell or construct, magnetization uniformity, magnetic responsiveness, degradation rate, potency, and batch comparability. Importantly, chemical modification or surface functionalization of an approved nanoparticle formulation may require a new safety assessment, because coating chemistry can alter biodistribution, degradation, immune recognition, and biological response [230].

Regulatory classification will depend on product composition, intended use, and primary mechanism of action (MoA). In the European Union, under Directive 2001/83/EC Article 1(2) (https://eur‐lex.europa.eu/eli/dir/2001/83/oj/eng), diagnostic MNP formulations used as MRI contrast agents are generally assessed as medicinal products when their intended purpose is diagnostic. However, when MNPs are combined with viable human cells, hydrogels, scaffolds, or biologically active matrices, classification becomes more complex. If the cellular component is substantially manipulated or intended to regenerate, repair, or replace tissue, the product may fall within the advanced therapy medicinal product (ATMP) framework. If a device component or scaffold provides a structural or physical function, the Medical Device Regulation (MDR 2017/745; https://eur‐lex.europa.eu/eli/reg/2017/745/oj/eng) may also become relevant, particularly for combined or borderline products. In practice, classification is likely to be assessed case by case according to the claimed intended use, the role of the cellular component, the contribution of the MNPs, and the primary MoA.

The United States follows a related but distinct logic through the Food and Drug Administration (FDA) Office of Combination Products (OCP). Magnetically engineered constructs may be evaluated as biologic, device, drug, or combination products depending on the primary MoA. Products combining viable cells with magnetic particles and external actuation devices may require input from different FDA centers, including the Center for Biologics Evaluation and Research (CBER) and the Center for Devices and Radiological Health (CDRH). However, no standardized release assays currently exist for magnetic ATMP‐like products or magnetically actuated tissue constructs. Assays for magnetic force output, torque, anisotropy, field responsiveness, magnetization decay, degradation kinetics, and imaging compatibility remain insufficiently harmonized [231, 232]. The European regulatory landscape is also evolving with the introduction of the Substances of Human Origin (SoHO) framework. Depending on the extent of manipulation and the intended clinical function, human cell‐ or tissue‐derived products may fall under SoHO oversight, ATMP regulation, medical device regulation, or a combination of these frameworks [233]. Acellular or scaffold‐only products may avoid ATMP classification in some cases, but human‐derived extracellular matrix materials can still require regulatory oversight related to procurement, processing, safety, and traceability. For MNP‐enabled regenerative products, this creates a complex classification space because the final product may include a cellular component, a scaffold or matrix, a nanoparticle component, and an external magnetic actuation system.

At present, this complex intersection of frameworks results in very few registered clinical trials involving MNPs combined with ATMPs or regenerative therapies (ClinicalTrials.gov, https://clinicaltrials.gov/, accessed October 9, 2025). Indeed, the Committee for Advanced Therapies (CAT) lists only one combined‐ATMP recommendation involving magnetic nanoparticles with manipulated lymphocytes for melanoma treatment (EMA Scientific Recommendations for ATMP Classification). Current clinical translation of MNP‐containing regenerative therapies therefore remains limited. This limited clinical penetration reflects not only scientific immaturity, but also the absence of harmonized guidance for hybrid nanomaterial‐cellular constructs. Existing regulatory frameworks do not yet fully address the diversity of nanoparticle functionalization strategies, local retention of MNPs within living tissues, magnetic actuation after implantation, MRI compatibility, or long‐term monitoring requirements.

Consequently, neither current ATMP regulations nor MDR provisions fully capture the diversity of nanoparticle functionalizations or their hybrid interactions with living systems, as also reflected in the EMA horizon‐scanning report on nanotechnology‐based medicinal products for human use (https://www.ema.europa.eu/en/documents/report/nanotechnology‐based‐medicinal‐products‐human‐use‐eu‐horizon‐scanning‐report_en.pdf). The translation of magnetic biofabrication will require coordinated development of safety testing, manufacturing standards, and regulatory guidance. Key needs include long‐term biodistribution and degradation studies, standardized magnetic characterization, validated potency assays, field‐exposure safety thresholds, MRI‐compatibility testing, and post‐implantation monitoring strategies. Table 6 summarizes the main safety, regulatory, and translational considerations that should be addressed during the development of MNP‐enabled tissue‐engineered constructs and magnetic biofabrication platforms.

TABLE 6.

Safety and regulatory considerations for magnetic nanoparticle–Enabled tissue‐engineered constructs.

Domain	Key considerations	Current status	Identified gaps/needs
Material composition	Fe‐oxide, Gd‐oxide versus Co/Ni systems	Fe/Gd clinically validated (diagnostic use); Co/Ni limited to cytotoxic contexts	Long‐term implant safety data for Fe/Gd in regenerative settings
Mode of administration	Injection versus local implantation	Injection well characterized; implantation emerging	Remodeling‐dependent degradation and local accumulation kinetics
Degradation & metabolism	Macrophage uptake, ferritin buffering, lysosomal dissolution	Short‐term in vivo safety demonstrated	Chronic (> 6–12 month) biodistribution and clearance studies
Magnetic exposure	Static versus cyclic fields; amplitude, frequency, duration	MRI safety guidelines exist	No implant‐specific stimulation thresholds or harmonized standards
Immunological effects	Oxidative stress, cytokine release, immune modulation	Limited mechanistic data	Comparative studies under static versus cyclic actuation
Manufacturing (GMP)	QbD, batch comparability, sterility	Few GMP‐grade MNPs available	Magnetic‐specific release assays (force, torque, anisotropy)
EU regulatory classification	ATMP, MDR, SoHo	Case‐by‐case assessment	No harmonized pathway for hybrid MNP–cell constructs
US regulatory classification	Combination products (FDA OCP)	Joint CBER/CDRH review possible	Lack of magnetic‐specific guidance documents
Clinical translation	Trials, registries, long‐term monitoring	Very limited clinical experience	International regulatory harmonization and safety registries

7. Outlook of Magnetic Biofabrication: From Smart Materials to Mag‐ATMPs

The future development of magnetic biofabrication will depend on the coordinated integration of nanoparticle engineering, mechanobiology, magnetic actuation technologies, computational modeling, manufacturing control, and regulatory preparedness. Progress in magnetic materials has clarified how particle composition, surface chemistry, colloidal stability, magnetic responsiveness, and degradation behavior influence biological performance. In parallel, biofabrication studies increasingly show that magnetic fields can guide cell organization, spheroid assembly, hydrogel patterning, and mechanobiological stimulation. However, the translation of these approaches into clinically relevant products will require predictable manufacturing, standardized characterization, long‐term safety assessment, and regulatory alignment.

These interconnected requirements are summarized in Figure 8, which presents a Magnetically Driven Biofabrication Toolbox. The figure highlights the main components required for Mag‐TE development, including material formulation, magnetic actuation, computational modeling, experimental validation, manufacturing control, and translational assessment. Rather than representing independent modules, these components should be considered as interdependent design constraints. For example, nanoparticle formulation affects magnetic force generation, cell compatibility, degradation, imaging contrast, and regulatory classification. Similarly, magnetic field design influences assembly precision, mechanical stimulation, device complexity, and safety evaluation.

FIGURE 8.

Magnetically driven biofabrication toolbox. Conceptual overview of the key domains defining magnetically driven biofabrication, including materials design, magnetic actuation strategies, computational modeling, experimental validation, and translational considerations. The framework highlights how these elements integrate to support the design, validation, and clinical translation of magnetic nanoparticle–enabled tissue engineering and Mag‐ATMP platforms.

A central priority would be the continued development of safe‐by‐design MNP formulations. Future particles should combine reproducible magnetic responsiveness with stable colloidal behavior, defined surface chemistry, and predictable degradation or clearance. When incorporated into hydrogels, spheroids, organoids, or microtissues, these formulations must provide sufficient magnetic functionality without compromising viability, differentiation, matrix deposition, or long‐term tissue integration. This will require systematic comparison of particle dose, coating chemistry, loading efficiency, magnetic response, and biological outcome under application‐relevant conditions.

Magnetoactive biomaterials will also need to move beyond proof‐of‐concept demonstrations. MNP‐containing hydrogels, bioinks, and cellular building blocks should be evaluated not only for their ability to deform, align, or respond to magnetic fields, but also for their manufacturability, batch reproducibility, sterilization compatibility, and stability during culture or implantation. High‐throughput encapsulation, microfluidic assembly, and magnetically enabled bioreactor systems may support more reproducible production of magnetically responsive microtissues. However, these workflows will need to remain compatible with GMP principles, including control of raw materials, process parameters, potency assays, and release criteria.

Predictive modeling could support this transition by linking magnetic field design, particle loading, material properties, and biological response. Near‐term models are most likely to be useful for specific tasks such as predicting MNP trajectories, field gradients, spheroid assembly, fusion kinetics, construct deformation, or local mechanical stimulation. More advanced data‐informed models may eventually incorporate imaging, mechanical testing, and biological readouts to iteratively refine actuation protocols. In this context, digital twin concepts should be viewed as a future‐oriented framework rather than an established standard for Mag‐TE. Their value will depend on the availability of validated experimental datasets, well‐defined model inputs, transparent assumptions, and measurable biological outputs.

Regulatory alignment will remain a critical prerequisite for clinical translation. Magnetically engineered constructs that combine MNPs with viable cells, hydrogels, scaffolds, or external actuation devices occupy a complex classification space. Their development will require clear definition of the intended use, primary mechanism of action, magnetic exposure conditions, nanoparticle degradation profile, and long‐term safety strategy. Standardized assays will be needed to quantify MNP loading, magnetic responsiveness, force or torque output, degradation kinetics, imaging compatibility, and biological potency. Early interaction with regulatory authorities, together with long‐term safety registries, could help clarify development pathways for magnetic cellular therapies and MNP‐enabled regenerative constructs.

Among the most promising translational directions are injectable magnetic tissue‐engineered advanced therapy medicinal products (Mag‐TE ATMPs). The most suitable early targets are likely to be defects where conventional implantation or bioprinting is limited by geometry, access, mechanical loading, or the need for spatial organization after delivery. Examples include irregular bone defects, non‐union fractures, osteochondral lesions, focal cartilage defects, tendon‐to‐bone interfaces, volumetric muscle loss, and poorly accessible soft‐tissue defects. In these settings, magnetically responsive spheroids, microtissues, or cell‐laden biomaterials could be delivered minimally invasively and then guided, retained, aligned, or mechanically conditioned within the defect volume. Magnetic control may be particularly valuable when the therapeutic goal is not only cell delivery, but also spatial assembly, anisotropic organization, local mechanostimulation, or post‐implantation maturation. These systems could combine minimally invasive delivery with remote positioning, magnetic stimulation, and non‐invasive imaging. In skeletal repair, for example, magnetically responsive spheroids, microtissues, or cell‐laden biomaterials could be guided or conditioned within defect sites to support local assembly, maturation, and regeneration. Similar principles may also be relevant to vascular, muscular, neural, and soft‐tissue applications, where spatial organization and mechanical cues are important for function. Nevertheless, these applications would require improved field localization, device design, imaging feedback, long‐term safety evaluation, and clinically realistic delivery strategies.

Overall, magnetic biofabrication is moving from isolated demonstrations of magnetic manipulation toward more integrated platforms that combine material design, biological response, computational prediction, and translational planning. Its clinical potential will depend on whether magnetic responsiveness can be converted into reproducible, safe, and biologically meaningful control over tissue formation. The most realistic near‐term advances will likely arise from well‐defined applications where magnetic fields provide a clear advantage over conventional fabrication or stimulation methods, such as contactless spheroid assembly, post‐implantation mechanostimulation, image‐guided delivery, or spatial organization within difficult‐to‐access defects. This trajectory defines a practical path toward Mag‐TE platforms and, ultimately, toward minimally invasive and patient‐adapted regenerative strategies.

8. Conclusion

Magnetic nanoparticles provide more than a passive additive for tissue engineering; they introduce a remotely controllable physical interface between engineered materials, living cells, and external magnetic fields. In this Review, we have discussed how MNP composition, surface chemistry, colloidal stability, biological response, magnetic actuation, computational modeling, and regulatory considerations collectively define the emerging field of magnetic biofabrication.

Current evidence supports the use of iron oxide‐based systems as the most translationally relevant MNP class for regenerative applications, while Gd‐based systems remain more closely linked to imaging, and Co/Ni‐based materials are constrained by safety concerns. At the biofabrication level, magnetic fields can support cell and spheroid assembly, hydrogel and bioink patterning, mechanobiological stimulation, and potentially in situ organization of regenerative constructs. However, clinical translation will require stronger links between magnetic field parameters, mechanical stimulus measurements, biological outcomes, manufacturing reproducibility, and long‐term safety.

The development of Mag‐TE ATMPs will therefore depend on safe‐by‐design nanoparticle formulations, validated actuation platforms, predictive computational tools, standardized release assays, and regulatory pathways adapted to hybrid nanomaterial‐cellular products. If these challenges are addressed, magnetic biofabrication could become a useful strategy for creating responsive, image‐compatible, and minimally invasive regenerative systems. Its strongest contribution will likely be in applications where contactless spatial control, remote mechanical stimulation, or post‐implantation guidance provides a clear biological or clinical advantage.

Author Contributions

Konstantinos Ioannidis: conceptualization, methodology, funding acquisition, writing – original draft, writing – review and editing, project administration, data curation, supervision, software, investigation, formal analysis, visualization. Dimitrios Lefas: data curation, visualization, writing – review and editing, software. Maya Guilliams: writing – review and editing. Jackie Van Grootenbril: visualization, software, data curation, writing – review and editing. Isaak Decoene: writing – original draft. Dimitrios Sakellariou: writing – review and editing, formal analysis. Bart Smeets: writing – review and editing, writing – original draft, funding acquisition. Stefanos Mourdikoudis: writing – review and editing, writing – original draft. Ioannis Papantoniou: supervision, conceptualization, writing – original draft, writing – review and editing, funding acquisition.

Funding

This research was supported by the Research Foundation – Flanders (Fonds Wetenschappelijk Onderzoek; FWO) under grant numbers G042425N, 1SD7225N, and 1SA4426N, and by the KU Leuven Research Council (Onderzoeksraad KU Leuven) under grant numbers C24M/22/058 and ID‐N/3M230283.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.