Engineering Functional Graphenic Materials for Bone Repair

ABSTRACT

Graphene oxide (GO), a chemically versatile and biocompatible derivative of graphene, has emerged as a highly promising material in the field of bone tissue engineering. This review explores the multifaceted role of GO and other functional graphenic materials (FGMs) in supporting bone regeneration by enhancing osteogenesis, angiogenesis, immunomodulation, and biomineralization. We begin by detailing the physiological principles of bone healing, current clinical approaches to bone repair, and the limitations they present. The discussion then progresses through the chemical foundations of GO and its derivatives, emphasizing their unique surface chemistry and tunable reactivity that enable precise functionalization for biomedical applications. Finally, we highlight the potential of FGM‐based composites, with integrated biological molecules, polymers, and small organic compounds, to serve as bioactive, bioresorbable scaffolds that support bone growth and integration. By bridging material science with regenerative medicine, this review underscores the importance of GO as a versatile platform for next‐generation bone regeneration strategies.

Graphene oxide (GO) and its derivatives have many favorable properties for biomedical applications. This is due to the inherent properties of GO including high surface area, functionalizability, mechanical strength, and bioresorbable nature, among other properties outlined above.

1. Physiology of Bones and Injury Treatments

Bone physiology is governed by a balance of cellular processes, extracellular matrix composition, and systemic regulatory mechanisms that collectively govern remodeling and regeneration. Osteoblasts actively produce the organic matrix, primarily composed of type I collagen, while osteoclasts resorb older bone to adapt to mechanical stresses and repair microdamage, ensuring continuous tissue renewal (Clarke 2008; Downey and Siegel 2006). Osteocytes, residing within lacunae, function as critical mechanosensors; these cells detect alterations in mechanical load and subsequently modulate bone turnover in response to external stimuli (Florencio‐Silva et al. 2015). Within bone, vascular networks supply essential nutrients, growth factors, and progenitor cells, facilitating both osteoid mineralization and the establishment of robust bone architecture (Zhu et al. 2021). Consequently, the physiological processes of bone actively maintain structural integrity through continuous metabolic adjustments, demonstrating its exceptional capacity for dynamic remodeling and regeneration across the human lifespan (Zhou et al. 2021).

Despite innate regenerative capacity, the management of bone injuries constitutes a significant clinical challenge due to the complexity of the tissue and underlying healing mechanisms (Bigham‐Sadegh and Oryan 2015; O'Keefe and Mao 2011; Robling et al. 2006). Current strategies for the treatment of bone defects involve the application of autologous or allogenic bone grafts, metallic internal fixation devices, bioresorbable polymers, and engineered synthetic scaffolds designed to modulate the osteogenic microenvironment and accelerate bone regeneration (Figure 1).

FIGURE 1.

The macroscopic and microscopic anatomy of bone, using human femur as an example, the natural healing process of bone after a fracture, and human interventions to treat bone injuries. Figure is created with illustrations from Servier Medical Art under CC BY 4.0 license.

1.1. Nature of Bones: Structure and Mechanical Properties

Anatomy of bone: Bone is the highly mineralized tissue found in humans and other mammals, with a meticulously organized structure that imparts both strength and adaptability. On the macroscopic scale, bone is composed of dense cortical tissue externally, which encloses a core of porous trabecular bone. This architecture simultaneously confers mechanical strength and accommodates marrow and vascular channels (Clarke 2008; Florencio‐Silva et al. 2015). Structurally, cortical bone consists of concentric lamellae organized into osteons, whereas the trabecular region comprises interconnected struts, providing distinct mechanical responses to compressive and tensile forces. At the microscopic level, bone is a composite material consisting predominantly of collagen fibrils interwoven with hydroxyapatite crystals, enabling resilience to variable mechanical loads and efficient energy dissipation (Zhu et al. 2021). Additionally, non‐collagenous proteins such as osteocalcin, fibronectin, and osteopontin mediate cell adhesion and mineral deposition, further shaping the mechanical properties of bone tissue (Florencio‐Silva et al. 2015).

The mechanical support of bone: These structural attributes collectively allow bone to effectively withstand dynamic stresses, yet continuous remodeling remains essential to adapt to changing mechanical demands. The organic matrix is primarily composed of type I collagen and provides tensile strength, while inorganic hydroxyapatite imparts compressive stiffness (Clarke 2008). Together, this mineralized composite achieves a delicate balance between brittleness and flexibility, facilitating rapid repair of microfractures via coordinated osteoclast–osteoblast interactions, thus preserving overall mechanical integrity (Downey and Siegel 2006; Matos et al. 2008). The extensive vascular network within the cancellous region facilitates nutrient delivery and waste removal, and, alongside resident progenitor cells, underpins bone's exceptional regenerative capacity (Zhu et al. 2021). Consequently, therapies aimed at bone regeneration must thoughtfully incorporate these structural and functional considerations to optimize clinical outcomes (X. Zhou et al. 2021).

Influential factors of mechanical properties of bones: The mechanical properties of bone emerge from an interplay among its material composition, hierarchical structure, and biomechanical loading conditions. Bone strength is predominantly influenced by the intrinsic properties of organic type I collagen and inorganic hydroxyapatite crystals (Fonseca et al. 2014; Fratzl et al. 2004; Nyman et al. 2016). Factors such as variations in mineralization levels, collagen cross‐linking density, and hydroxyapatite crystal dimensions significantly affect bone's mechanical performance and its capability to withstand diverse mechanical stresses (Boivin et al. 2000; Unal 2021).

Additionally, bone geometry contributes to bone strength and fracture resistance through size, shape, cortical thickness, and cross‐sectional area (Morgan et al. 2018). Geometric adaptations, such as increases in cortical thickness or perimeter, can substantially enhance resistance to fracture without necessarily requiring increased bone mass (Hart et al. 2017). A comprehensive understanding of these factors is essential for developing targeted strategies to maintain and enhance bone health, especially for populations susceptible to osteoporosis and related skeletal disorders.

1.2. Current Status of Bone Injury Treatments

Bone injuries pose considerable clinical challenges due to the complexity of the underlying healing mechanisms, especially in severe injury (Bigham‐Sadegh and Oryan 2015; O'Keefe and Mao 2011; Robling et al. 2006). These injuries can arise from high‐energy trauma, infections, tumor invasion, and surgical procedures. “Critical‐size” defects are defined as bone defects too extensive to heal spontaneously or with conventional bone grafting methods, often exceeding approximately 2–2.5 times the diameter of the affected bone (Aurégan and Bégué 2014; Schemitsch 2017). Due to their inability to repair independently, these defects need specialized surgical intervention (Nauth et al. 2018; Stevens et al. 2006). Clinical strategies to address bone injuries commonly include bone grafts, metallic implants, bioresorbable materials, or synthetic scaffolds specifically designed to enhance and facilitate bone regeneration.

1.2.1. Metal Implants

Metal implants play a critical role in orthopedic treatments, particularly for addressing extensive bone defects and fractures. Osseointegration, or the effective integration of implants with bone tissue, is essential for achieving long‐term clinical success (Q. Chen and Thouas 2015). Among commonly utilized metallic biomaterials (Table 1), stainless steel, cobalt‐based alloys, titanium alloys, and magnesium alloys are preferred due to their advantageous mechanical properties and established biocompatibility (Okazaki and Gotoh 2008; Staiger et al. 2006).

TABLE 1.

Common metal implants used in orthopedics.

Type	Advantage	Disadvantage	References
Titanium alloys	Excellent strength‐to‐weight ratio Corrosion resistance Strong osteointegration Effective for joint replacements and bone fixation devices	Higher cost	(Q. Chen and Thouas 2015; Long and Rack 1998; Niinomi 2008)
Stainless steel (316l)	Good corrosion resistance Adequate mechanical strength Cost‐effective	Corrosion‐induced metal ion release, risk of systemic toxicity Mechanical fatigue under repetitive loads	(Escalas et al. 1976; Rostoker et al. 1978; Syrett and Davis 1979; Tavares et al. 2010; U. Kamachi Mudali et al. 2003)
Cobalt‐chromium alloys (COCR)	Exceptional wear resistance High mechanical strength Maintains structural integrity under rigorous loading conditions	Potential metal ion release Possible adverse tissue reactions	(Goodship et al. 2009; Kamath et al. 2011; Ramsden et al. 2007)
Shape‐memory alloys (NITI)	Unique super‐elastic properties Shape‐memory effects (returning to original shape after deformation) Suitable for dynamic orthopedic applications	Lower biocompatibility Nickel ion release and associated reactions	(Cragg et al. 1993; Matsumoto et al. 1993; Wever et al. 1998)

While metallic implants exhibit clear advantages regarding mechanical strength and structural stability, clinical hurdles such as corrosion resistance, wear performance, and mechanical property mismatch with native bone persist (Prakasam et al. 2017). Consequently, addressing these challenges through continued advances in materials science and surface modification techniques is essential for enhancing the clinical outcomes and expanding the scope of metal implants within orthopedic medicine.

1.2.2. Bone Grafts

Overview of pros and cons of bone grafts: Bone grafting remains a fundamental technique in orthopedic surgery, particularly for addressing extensive bone defects resulting from traumatic injuries, tumor resection, or congenital anomalies (Chiarello et al. 2013). Autologous bone grafts are bone tissue harvested from one part of the patient's body and transplanted to the area of injury. Autologous bone grafts inherently possess osteoconductive, osteoinductive, and osteogenic properties, making them exceptionally effective in promoting bone regeneration (Bhatt and Rozental 2012; Miron and Zhang 2012). The direct osteogenic capacity of autografts stems from the presence of viable osteoblasts and progenitor cells within graft material typically harvested from donor sites such as the iliac crest, fibula, tibia, or calcaneus (Schmidt 2021). Despite their clinical efficacy, autografts have notable limitations, including donor‐site morbidity, restricted graft availability, and increased complexity and duration of surgical procedures (Einhorn and Gerstenfeld 2015; Giannoudis et al. 2007).

Allografts as a possible alternative: Allografts, or transplanted bone from another human donor, have become increasingly attractive alternatives due to advantages in availability, elimination of donor‐site morbidity, and reduction in operative time (Baldwin et al. 2019; Sakkas et al. 2017). Although lacking viable cells, and thus reduced osteogenic potential, allografts maintain osteoconductive capabilities and can exhibit varying degrees of osteoinductivity depending upon their processing methods. Frequently utilized allografts include fresh‐frozen, freeze‐dried, and demineralized bone matrix, each offering different mechanical properties and rates of biological incorporation. Due to extensive sterilization methods aimed at reducing the risk of disease transmission, these procedures often diminish the osteoinductive properties of the graft material (Laurencin et al. 2006; Stevenson 1999). Consequently, while autografts remain preferred, advancements in allograft processing and synthetic bone substitutes continue to enhance clinical outcomes, making allografts increasingly viable treatments.

Reconstructive strategies for managing significant bone defects, such as post‐traumatic defects of the tibia, have additionally combined metallic implants with biological grafts. For instance, the integration of vascularized fibular grafts with Ilizarov external fixation has demonstrated positive outcomes in healing substantial bone defects, achieving robust mechanical stabilization and promoting early weight‐bearing capabilities (Semaya et al. 2016).

1.2.3. Synthetic and Bioresorbable Scaffolds

Synthetic materials have emerged as crucial alternatives in orthopedic treatments for bone injuries, effectively addressing limitations associated with conventional bone graft techniques. While autografts remain the clinical gold standard due to their intrinsic osteoconductivity, osteoinductivity, and osteogenic potential, they carry significant drawbacks, including donor‐site morbidity, limited graft availability, and increased surgical complexity (Giannoudis et al. 2007). Similarly, allografts raise ongoing concerns about disease transmission, immunogenic responses, and inconsistent healing outcomes despite widespread clinical use (de Grado et al. 2018).

Inorganic scaffolds: Calcium phosphate‐based ceramics, such as hydroxyapatite (HA) and tricalcium phosphate (TCP), have been extensively employed as synthetic bone substitutes due to their natural osteoconductivity and chemical resemblance to native bone minerals. These ceramics effectively guide and support the direct growth of new bone tissue onto their surfaces. Contemporary biomimetic calcium phosphate materials further optimize performance through finely controlled synthesis techniques conducted at low temperatures, thereby accurately replicating bone's nano‐ and micro‐scale structure and composition (Ginebra et al. 2018). Adjustments in porosity, degradation rate, and chemical composition enable precise tuning of scaffold resorption, ensuring synchronization with the bone healing process and thereby enhancing osteointegration and clinical predictability.

Bioactive glasses (BAGs) constitute another promising class of synthetic biomaterials recognized for their active interactions with host tissue (Henri Granel et al. 2019). The osteogenic potential of BAGs arises from an ability to chemically bond with living bone and stimulate osteoblast activity, actively promoting new bone formation. Unfortunately, traditional bioactive glasses suffer from brittleness, limiting their mechanical suitability, particularly in load‐bearing scenarios. Recent innovations have focused on creating organic–inorganic hybrid scaffolds that integrate bioactive glass particles within flexible polymer matrices (Liang et al. 2021). These composite scaffolds leverage the osteogenic advantages of BAGs while addressing mechanical shortcomings through the addition of polymeric components which significantly improved ductility and toughness.

Organic scaffolds: Synthetic biodegradable polymers also offer substantial benefits, particularly in scenarios where permanent implants are undesirable. Polymers such as poly(lactide), poly(glycolide), and poly(propylene fumarate) (PPF) have been widely investigated due to their controlled degradation profiles, eliminating the need for secondary implant‐removal surgeries. Poly(lactide) and poly(glycolide) were among the first biodegradable polymers clinically adopted for orthopedic applications due to their predictable degradation behaviors and excellent biocompatibility (Middleton and Tipton 2000). More recent work has focused on PPF: its tunable mechanical properties and controlled biodegradation make it particularly suitable for advanced manufacturing techniques such as 3D printing (Cai et al. 2019). Specifically, stereolithography‐based PPF scaffolds facilitate highly precise, patient‐specific implants with tailored mechanical and biological characteristics, aligning closely with clinical needs in bone reconstruction procedures.

Chitosan, derived from the deacetylation of chitin, stands out as a bioresorbable material extensively studied for its exceptional biocompatibility, biodegradability, and inherent antimicrobial properties (Nandi et al. 2013). Porous chitosan scaffolds, characterized by high porosity and interconnected macropores, enable efficient nutrient diffusion, cellular attachment, proliferation, and vascularization, essential requirements for successful bone repair. Specifically, when these scaffolds are combined with growth factors such as insulin‐like growth factor‐1 (IGF‐1) and bone morphogenetic protein‐2 (BMP‐2), significant enhancement of bone regeneration has been observed in animal models. IGF‐1 and BMP‐2 facilitate osteoblast proliferation and differentiation, stimulate new bone formation, and accelerate scaffold integration within host tissues (D. Chen et al. 2004; Kirker‐Head 2000; Matsuda et al. 1992). Furthermore, studies highlight that chitosan scaffolds supplemented with these growth factors exhibit improved histological and radiological healing outcomes, demonstrating their potential for rapid and comprehensive bone restoration.

Bioactive composites: Advanced composite biomaterials that integrate structural and biological functionalities represent the forefront of synthetic bone substitutes. These composite scaffolds not only provide mechanical integrity but actively modulate cellular behaviors essential for effective bone repair. For instance, engineered scaffolds containing microchannels and bioinstructive niches can guide cellular infiltration, enhance vascularization, regulate inflammatory responses, and encourage osteogenic differentiation of endogenous stem cells (Li, Cheng, et al. 2024). Incorporation of bioactive molecules such as bone morphogenetic proteins, growth factors, and mesenchymal stem cells into these scaffolds further amplifies their osteoinductive and osteogenic capacities, making them particularly advantageous for managing complex, large‐scale clinical bone defects (de Grado et al. 2018; Roddy et al. 2018).

In summary, continuing advances in synthetic biomaterials are significantly improving orthopedic treatment outcomes. Ongoing research efforts aim to further refine these biomaterials, optimizing their biological interactions and mechanical properties to comprehensively address the multifaceted challenges posed by bone injury management.

2. Graphene Oxide and Derivatives for the Synthesis of Functional Graphenic Materials

Graphene and graphene oxide (GO) have emerged as particularly promising materials for bone regeneration due to their high surface area, mechanical robustness, osteoconductive potential, and ability to interface with cells, proteins, and mineral phases. The remarkable two‐dimensional structure of graphene and unique electronic, mechanical, and thermal properties position it at the forefront of nanomaterials research, while also inspiring the broader “Xenes” classification for related 2D materials (Novoselov et al. 2004; ScienceDirect 2021). Among graphenic materials, graphene oxide (GO) stands out due to its scalable and accessible synthesis, excellent dispersibility in aqueous media, and high‐density of reactive oxygen‐containing groups. These features enable a broad spectrum of chemical modifications, making GO a modular and versatile platform for applications ranging from biomedicine to advanced materials science (Figure 2) (Hummers Jr. and Offeman 1958).

FIGURE 2.

Graphene oxide (GO) and its derivatives have many favorable properties for biomedical applications. This is due to the inherent properties of GO including high surface area, functionalizability, mechanical strength, and bioresorbable nature, among other properties.

2.1. Introduction to Graphene Oxide

Graphene oxide (GO) was first synthesized by Hummers in 1958, predating the isolation of graphene (Dreyer et al. 2010; Hummers Jr. and Offeman 1958; Whitener and Sheehan 2014). In a typical procedure, GO is synthesized from low‐cost graphite under oxidation conditions involving H₂SO₄ and KMnO₄ to promote exfoliation into few‐layer sheets and introduce chemical functionality. The presence of ions and mechanical agitation further aids in the delamination of bulk graphite, reducing the layer count (Nakajima and Matsuo 1994). The GO product offers distinct synthetic and economic advantages over graphene, particularly due to its abundance of oxygen‐containing functional groups (Hofmann and Holst 1939; Lerf et al. 1998).

Therefore, GO serves as a crucial intermediate for diverse functionalization strategies. This versatility is attributed to the presence of oxygen functionalities: predominantly alcohols and epoxides on the basal plane, alongside carboxylic acids at the sheet edges (Hummers Jr. and Offeman 1958; Lerf et al. 1998; Nakajima and Matsuo 1994; Yu et al. 2020). These functionalities provide abundant reactive sites for subsequent chemical modifications. While pristine graphene exhibits remarkable electrical (Castro Neto et al. 2009; García de Abajo 2014; Grigorenko et al. 2012; Li, Yu, et al. 2016; Stoller et al. 2008), optical (Falkovsky 2008; García de Abajo 2013; Li, Yu, et al. 2016), and mechanical properties (Papageorgiou et al. 2017; Sreenivasulu et al. 2018; Zandiatashbar et al. 2014), graphene lacks reactive functional groups which precludes direct participation in chemical transformations. Consequently, the stability of graphene prevents functionalization under mild conditions. Therefore, oxygen‐containing moieties of GO have enabled researchers to synthesize a wide array of functional graphenic materials (FGMs) through reactions at these functional sites, including those involving large molecules such as upcycled plastics (Vickery et al. 2024, 2025) and biopolymers (Aval et al. 2019; Eckhart et al. 2021; Kaur et al. 2017).

2.2. GO‐Derived Precursors for Alternative Functionalization

The oxygen‐containing functionalities of GO facilitate a range of reactions for generating a variety of functional graphenic materials (FGMs). In some cases, these transformations result in derivatives that differ subtly from GO yet confer tailored properties or enable subsequent modification (Figure 3).

FIGURE 3.

Some functionalized graphenic materials (FGMs) are synthesized as intermediates, essential for subsequent functionalization or to impart specific properties retained in final materials. The figure highlights common intermediates and their advantages.

A common example of an FGM intermediate is reduced GO (rGO), synthesized by the partial or selective removal of oxygen functionalities to achieve a more graphene‐like state (i.e., restoration of sp² character) (Emiru and Ayele 2017; Tarcan et al. 2020; Utkan et al. 2023). Reduction is commonly accomplished through thermal, chemical, and electrical methods (Cooper et al. 2012; Imae 2021; Randviir et al. 2014; Z. Su et al. 2023; Tarcan et al. 2020). rGO offers a strategy to tune material properties, leveraging graphene's enhanced electrical and mechanical attributes (Rao et al. 2018; Smith et al. 2019; Valentini et al. 2023), while retaining GO's dispersibility and reactivity (Lerf et al. 1998; Nakajima and Matsuo 1994). rGO can also serve as a synthetic intermediate when oxygen‐containing functionalities may interfere with the reaction or when rGO properties are advantageous in the final material (Dash et al. 2021; Ollik et al. 2021).

Another example of GO modification is the creation of Claisen graphene (CG). Synthesized via the Johnson‐Claisen rearrangement, CG enables the alteration of specific basal plane oxygen groups, transforming allylic alcohols into reduction‐proof esters (Sydlik and Swager 2013), which can be further modified by subsequent reactions. Hydrolysis following the Johnson‐Claisen rearrangement enables basal plane functionalization with carboxylic acids, which are typically confined to flake edges (Hummers Jr. and Offeman 1958; Lerf et al. 1998; Nakajima and Matsuo 1994; Sydlik and Swager 2013). This functionalization improves the edge‐limited reactivity of native GO.

Halogenation of graphene presents another method for FGM synthesis, introducing reactive sites onto the graphenic backbone. This strategy underscores the chemical versatility offered by tailored functionalities for specific applications. Similar to GO and rGO synthesis, halogenated graphene has gained interest due to its intrinsic properties. Varying degrees and types of halogenation allow for precise tuning of graphene's electronic, optical, and chemical characteristics, achievable through methods such as direct halogenation, solution‐based approaches, and plasma treatments (Karlický et al. 2013; Robinson et al. 2010; Zbořil et al. 2010).

2.3. Synthetic Versatility of the Graphene Oxide Framework

The synthesis of FGMs, including GO, rGO, and halogenated graphene, transforms graphene from a chemically inert material into a versatile platform for further functionalization. Researchers leverage the presence of halogens, epoxides, alcohols, and carboxylic acids to enable subsequent reactions. This capability makes these GO derivatives a highly tailorable class of materials, possessing the potential to address diverse application requirements. This section will focus on strategies that enhance biocompatibility and osteoinductive potential for bone tissue engineering.

2.3.1. Carboxylic Acid Functionalization of GO for Bone Regeneration

GO is rich in carboxylic acid groups, predominantly located at the sheet edges and defect sites, making them an ideal reactive platform for biomedical modifications (Cheng et al. 2021; Gao 2015; Rodríguez‐Pastor et al. 2022). In bone tissue engineering, these functional groups have been used to enhance biocompatibility and osteoinductive potential through various nucleophilic substitution reactions, including ester, thioester, and amide formations (Govindarajan et al. 2023). Among the oxygenated functionalities present on GO, carboxylic acids are the most widely used and easily accessible for further chemical modification (Gao 2015; Yu et al. 2020) due to their high reactivity and straightforward conjugation chemistry (Figure 4) (Yu et al. 2020).

FIGURE 4.

Graphene oxide (GO) possesses diverse oxygen‐containing functional groups, each with unique reactivity and steric characteristics. Carboxylic acids (red) are located primarily at sheet edges and function predominantly as electrophiles. Epoxides (blue) and alcohols (green) are found on the basal plane, acting as electrophiles and nucleophiles, respectively. The GO flake schematic shows solid lines to indicate visible sheet edges, while dashed lines represent the continuation of the extended graphene lattice beyond the visualized area. The accompanying plot compares the relative chemical reactivity and steric accessibility of each functional group. A summary table categorizes each group by role and location. Carboxylic acids and alcohols typically act as an electrophile and a nucleophile, respectively, though in some cases they can also function as a nucleophile and an electrophile.

Enhancing carboxyl content during graphene oxide synthesis: GO typically exhibits carboxylic acid functionalities largely confined to the sheet edges (Dimiev and Eigler 2016; Gao 2015; Yu et al. 2020) and defect sites (Dimiev and Eigler 2016), limiting the number of available sites for bioactive molecule attachment. The carboxylic acid content can be selectively increased during GO synthesis by adjusting the potassium permanganate‐to‐graphite ratio. XPS analysis revealed that raising the KMnO₄/graphite ratio led to an increase in carboxyl group density, which eventually plateaued, indicating a threshold beyond which further oxidation does not yield additional carboxylic functionalities (Arnold, Crytzer, et al. 2019; Holt et al. 2021).

Building on these findings, another effective strategy employs a modified Hummers–Offemann reaction using single‐layer, thermally reduced graphene oxide as the precursor (Rodríguez‐Pastor et al. 2022). In this approach, the absence of interlayer stacking prevents the formation of graphite intercalated compounds, thereby allowing potassium permanganate to selectively attack structural defects and sheet edges. This method results in a substantial enhancement of carboxyl groups. The resulting GO derivative contains more than 55% of the oxygen functionalities as carboxylic moieties, with improved hydrophilicity and more negative zeta potentials, making this GO particularly beneficial for subsequent covalent bioconjugation and osteoinductive performance.

These diverse chemical routes, encompassing both pre‐synthetic and post‐synthetic modifications, underscore the significant potential to enhance the reactivity and functional density of graphene oxide by increasing its carboxylic acid content. By tailoring the surface chemistry to provide more active sites for covalent modification, these strategies not only facilitate robust biofunctionalization but also improve the overall biocompatibility of graphene oxide, particularly for applications in bone tissue engineering.

Covalent modification of graphene oxide carboxylic acids: Utilizing carboxylic acids on graphene oxide (GO) as electrophiles for covalent modification with nucleophiles is, the most common chemical synthesis route to create functional graphenic materials (Dimiev and Eigler 2016). This process involves reacting GO's carboxylic acid groups with nucleophiles, such as amines, alcohols, or related compounds, to form amide, ester, or ester‐derivative bonds (Yu et al. 2020). Amide and ester bonds can be formed by reacting carboxylic acids directly with amines or alcohols through thermal amidation (Allen et al. 2011; Lanigan and Sheppard 2013) and Fischer esterification (Khan et al. 2021), respectively. Alternatively, carboxylic acids can be activated to enhance electrophilicity, often through conversion to acid chlorides or by using carbodiimide coupling agents (e.g., EDC/NHS). These activated carbonyls can then react with amines or alcohols to form amide or ester bonds, respectively.

Challenges of thermal amidation and Fischer esterification for bioactive GO: Carboxylic acids are relatively unreactive functional groups, so forming amide or ester bonds directly typically requires elevated temperatures to drive the reaction forward. Although advances in catalysis have improved the efficiency of these transformations, both amidation and transesterification reactions still generally demand high thermal input (Khan et al. 2021; Lanigan and Sheppard 2013). These elevated temperatures can lead to partial thermal reduction of graphene oxide, altering its structure and properties, and may also degrade or denature labile biological molecules, making such conditions less suitable for functionalizing GO with sensitive biomolecules.

Drawbacks of acid chloride activation for bioactive GO: A common strategy to enhance the reactivity of carboxylic acids is activation via acid chlorides, which generates a more reactive electrophile that can be readily coupled with amines or alcohols to form amides and esters, respectively. Acid chloride activation is an effective strategy for covalently modifying graphene oxide (GO) (Gao 2015) to create functional graphenic materials. This method involves converting the carboxylic acid groups on GO into highly reactive acyl chlorides using reagents such as thionyl chloride (SOCl₂) or oxalyl chloride (COCl)₂. The resulting acyl chloride groups readily react with nucleophiles, such as amines, alcohols, and hydroxyl‐containing biomolecules, to form amide or ester linkages (Gao 2015). This process allows for the stable attachment of bioactive molecules to the GO surface, providing greater control over the functionalization process and producing highly reactive intermediates that efficiently conjugate with a variety of molecules. However, this synthetic approach is best suited for molecules that are not delicate, as the reaction conditions involving acyl chlorides can be harsh (Wirth 2001) and may lead to the degradation or denaturation of sensitive biomolecules.

Advantages of carbodiimide chemistry for creating bioactive functional graphenic materials: Carbodiimide activation of carboxylic acids is a widely used strategy to enhance their electrophilicity, enabling their reaction with nucleophiles such as amines and alcohols to form amide and ester bonds, respectively. This approach has become particularly popular for functionalizing graphene oxide (GO) with bioactive molecules, as it offers greater compatibility with sensitive biomolecular cargo. Carbodiimide chemistry, particularly using 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide (EDC) in combination with N‐hydroxysuccinimide (NHS), is well‐established for facilitating these transformations under mild, aqueous conditions. These reaction conditions minimize the risk of thermal degradation or denaturation of labile biological molecules (Shahriari et al. 2021), making EDC/NHS coupling a preferred method for covalently attaching polymers (Song et al. 2022; Y. Zhang et al. 2020), proteins (J. Shen et al. 2010; Srivastava et al. 2014), peptides (Joshi et al. 2024; Li, Zheng, et al. 2016), and small bioactive molecules to GO (Durán and Fávaro 2018).

Numerous studies have demonstrated the effectiveness of EDC/NHS chemistry in covalently modifying GO to develop advanced materials for bone regeneration (Du et al. 2020; Fang et al. 2020; D. Li et al. 2025; Q. Xie et al. 2024). Collagen, a major structural protein in bone extracellular matrix, is frequently used in these composites to provide a biologically relevant and biocompatible scaffold. One notable example is the development of a GO–collagen composite scaffold, where GO was covalently crosslinked to type I collagen using EDC/NHS chemistry to form stable amide bonds between carboxyl groups on GO and amine groups in collagen. After biomimetic mineralization in simulated body fluid, the resulting GO–Col scaffolds significantly enhanced bone regeneration in a rat cranial defect model by promoting apatite formation and improving mechanical strength (C. Zhou et al. 2018). In another study, GO was first loaded with curcumin via π–π stacking and hydrogen bonding, then covalently crosslinked with type I collagen using EDC/NHS chemistry, yielding a composite scaffold with improved structural integrity and osteogenic potential (Q. Xie et al. 2024).

2.3.2. Basal Plane Functionalization of GO for Enhanced Bone Regeneration

To fully harness the potential of GO in biomedical applications, expanding functionalization beyond the sheet edges to include the basal plane is essential. Carboxylic acids located at edge and defect sites are highly accessible and amenable to amide bond formation with proteins, peptides, and other signaling molecules. However, their limited abundance restricts the overall functionalization density. These edge‐focused strategies also risk promoting GO aggregation and reducing material dispersibility. In contrast, the basal plane contains a greater number of oxygen‐containing groups, including epoxides and alcohols, offering more surface area for modification. However, basal plane functionality is sterically hindered and less chemically reactive, making it more difficult to functionalize. Despite these challenges, developing robust and selective methods to target basal plane functionalities remains a critical goal for increasing functional loading and enhancing the performance of GO‐based biomaterials.

Epoxide functionalization of GO for enhanced bone regeneration: Utilizing epoxide groups on graphene oxide (GO) as electrophilic sites for covalent modification is another chemical synthesis strategy to develop functional graphenic materials. This method involves nucleophilic ring‐opening reactions, wherein nucleophiles attack and open the epoxide rings on GO's basal plane, forming stable covalent linkages. However, due to their location primarily on the basal plane, epoxides on GO may exhibit reduced accessibility and reactivity because of steric hindrance, influencing the efficiency and extent of these modifications (Piñeiro‐García and Semetey 2023).

Although nucleophilic epoxide ring‐opening reactions have been used to functionalize graphene oxide (GO) (Gonçalves et al. 2024; Piñeiro‐García et al. 2021), few studies have applied this strategy to develop graphenic materials specifically for bone regeneration. One specific method involves using a Lewis acid‐catalyzed Arbuzov reaction to functionalize GO epoxide groups with trialkyl phosphite, forming phosphate graphene (PG). This reaction introduces phosphate functionalities onto the GO surface, yielding a material with intrinsic osteoinductive properties. PG promotes bone regeneration by releasing calcium (Ca²⁺) and phosphate (PO₄ ³⁻) ions in aqueous environments, key components for bone mineralization (Arnold, Holt, Daneshmandi, et al. 2019; Arnold, Holt, Tang, and Sydlik 2019; Daneshmandi et al. 2022; Orlando et al. 2024).

Limited use of basal plane alcohols in GO functionalization for bone regeneration: Similar to epoxides, alcohol groups on graphene oxide (GO) are primarily located on the basal plane (Gao 2015), where steric hindrance limits their accessibility and reactivity. These alcohols are typically tertiary, further reducing their nucleophilicity and making them less reactive toward common electrophiles (S. Guo et al. 2022). While tertiary alcohols can, in principle, act as weak nucleophiles, there is limited research exploring their use in nucleophilic substitution reactions for covalent modification of GO. As a result, functionalization strategies employing alcohol nucleophiles to create bioactive graphenic materials, particularly for bone regeneration, remain underexplored.

While few studies have employed the alcohol groups on graphene oxide (GO) directly as nucleophiles to synthesize functional graphenic materials for bone regeneration, there are reports of modifying these alcohols to introduce more reactive functionalities. This strategy leverages the presence of alcohols as chemical handles rather than as reactive centers themselves. For example, a Claisen rearrangement can be used to convert GO's allylic alcohols into esters, which offer improved reactivity for downstream functionalization (Collins et al. 2011; Sydlik and Swager 2013). Such transformations expand the synthetic versatility of GO and open new pathways for the incorporation of bioactive moieties relevant to regenerative medicine (Holt, Arnold, and Sydlik 2017; J. Schmidt et al. 2020).

Mitsunobu reaction enables mild functionalization of GO with bioactive molecules: Recently, a novel approach for utilizing alcohols on graphene oxide by employing the Mitsunobu reaction, in which carboxylic acids act as nucleophiles rather than electrophiles. This reaction enhanced the reactivity of the basal plane alcohols and enabled the covalent attachment of bioactive molecules under mild conditions, preserving the structure and function of delicate compounds. This strategy was successfully used to conjugate amino acids, small bioactive molecules, and even proteins to GO, highlighting the potential of this method for generating bioactive graphenic materials without compromising molecular integrity or bioactivity (Wolf et al. 2025).

2.3.3. Impurities, Dispersion, and Chemical Compatibility

Synthesizing functional graphenic materials (FGMs) requires careful control over impurities, solvent interactions, and reaction conditions to ensure optimal functionalization. One of the primary concerns is the presence of sulfate impurities from the graphene oxide (GO) synthetic process, particularly when using the Hummers method (Dimiev and Eigler 2016). Sulfates can strongly associate with oxygen‐containing functional groups on the basal plane of GO, effectively blocking key reactive sites and hindering subsequent functionalization efforts (de Mendonça et al. 2018). This issue extends beyond sulfates to other common impurities such as residual metal ions and adsorbed water, which can associate with both the basal plane and sheet‐edge oxygen functionalities (Ambrosi et al. 2012; Liu, Gong, et al. 2017; Schmuck et al. 2024; Toh and Pumera 2013; Wong et al. 2014). Therefore, rigorous purification methods such as dialysis, repeated washing, freeze drying, or thermal treatment are often necessary to remove these contaminants and create a more chemically accessible GO surface (Ambrosi et al. 2012; de Mendonça et al. 2018; Liu, Gong, et al. 2017; Schmuck et al. 2024).

Beyond impurity management, solvent selection plays a crucial role in determining the success of FGM synthesis. The polarity of the solvent must be carefully matched to the graphenic material to ensure proper dispersion and prevent aggregation due to π–π stacking between graphene sheets, which can otherwise limit the availability of functional groups for reaction (Dimiev and Eigler 2016; Qamar et al. 2024). Most importantly, the hydrophilicity of graphenic materials or functional groups will dictate which solvent it is best dispersed in. For example, GO usually disperse better than reduced GO in water. On the other hand, DMF and DMSO are usually preferred to disperse non‐oxidized graphene. In addition to solvent polarity, the solvent‐to‐graphene ratio must be optimized, as inadequate dispersion can lead to flocculation and uneven functionalization due to shielded graphenic surface (Qamar et al. 2024). Various dispersion techniques, including mechanical stirring, sonication (Gao 2015; Qamar et al. 2024), and controlled heating, are often employed to maintain a stable and homogeneous suspension (Qamar et al. 2024).

Another key consideration is the choice of chemical functionalization strategy. For example, radical‐based chemistries are often incompatible with GO, as its extended conjugated structure can act as an electron sink, effectively quenching radical reactions and reducing functionalization efficiency. Selecting alternative functionalization strategies, such as nucleophilic addition or covalent coupling under controlled conditions, ensures a more effective modification of GO while maintaining its structural integrity.

3. Graphene Oxide and Derivatives in Bone Regeneration

The incorporation of these materials into various matrices improves key cellular processes, including cell proliferation, differentiation, and mineralization, all of which are critical for effective bone regeneration and subsequent bone tissue formation (Figure 5) (Holt, Wright, et al. 2017; M. Wu et al. 2021). The unique physicochemical properties of graphene derivatives, such as their mechanical strength, tunable biocompatibility, and capacity for interaction with biological molecules, render them attractive for the development of materials designed to support both osteogenesis and angiogenesis, thereby promoting bone regeneration (Dubey et al. 2015; Jodati et al. 2021).

FIGURE 5.

Bone regeneration in progressive multi‐steps. Angiogenesis and immune microenvironment modulation (early stage), osteogenic differentiation (mid stage), and extracellular mineralization (late stage). Figure is created with illustrations from Servier Medical Art under CC BY 4.0 license.

For instance, graphene oxide (GO) nanosheets with varying degrees of oxidation demonstrate the capacity to promote bone tissue formation while eliciting only a moderate immune response, thus establishing a beneficial osteo‐immunomodulatory environment (J. Su et al. 2020; Xue et al. 2018). This includes the upregulation of vascular‐related receptors, enhancing angiogenesis, and the stimulation of osteogenic differentiation of mesenchymal stem cells (MSCs) through mechanisms such as the modulation of cell microenvironments (Mohammadrezaei et al. 2018; Newby et al. 2020; S. Park et al. 2023) and the enhancement of mineralization processes (Liu, Shen, et al. 2017; Mohammadrezaei et al. 2018), suggesting that graphenic materials can facilitate bone healing, ultimately aiding in the restoration of bone tissue.

3.1. Vascularization and Immunomodulation Mediated by Graphene Derivatives

Graphene‐mediated modulation of immune responses: Incorporating graphenic materials modulates immune response, establishing an environment conducive to both osteogenesis and angiogenesis. This modulation is achieved through the activation of signaling pathways, including Erk1/2, and the upregulation of Hif‐1α, factors involved in the secretion of vascular endothelial growth factors (VEGF), platelet‐derived growth factor (PDGF), and other growth factors crucial for bone regeneration processes (Zhang, Chang, et al. 2016). Furthermore, GO has been shown to promote angiogenesis by inhibiting the maturation of RANKL‐induced osteoclasts and enhancing the secretion of PDGF, resulting in an osteoclast‐endothelial crosstalk that improves bone regeneration (W. Liu et al. 2024).

Immunomodulation supporting osteogenesis: Furthermore, a favorable anti‐inflammatory response is crucial for enhancing bone regeneration. Macrophages, key responders to implanted biomaterials, secrete OSM, PGE2, and BMP‐2, stimulating osteogenesis and osseointegration (H. Wang et al. 2022). In this context, GO's ability to significantly promote the polarization of M0 macrophages to the M2 (healing) phenotype is noteworthy. This polarization shift establishes an anti‐inflammatory microenvironment, promoting implant‐bone integration and osteogenic differentiation (X. Qi et al. 2023; H. Wang et al. 2022). Moreover, GO can activate monocytes which can communicate pro‐osteogenic signals to MCSs. This monocyte activation enhances osteogenesis by upregulating the Wnt and BMP signaling pathways, leading to increased OSM (Oncostatin M) production (Bordoni et al. 2019).

Osteoinductive properties of graphene: The incorporation of graphenic materials into implants has been shown to foster a favorable environment for bone regeneration. For instance, GO‐enriched collagen membranes have been observed to induce the secretion of PGE2, a key mediator in osteoblastic differentiation and inflammation, thereby providing an early trigger for the osteogenic differentiation process (Radunovic et al. 2017). Furthermore, reduced graphene oxide (rGO) coatings on titanium implants can optimize the adsorption of growth factors by enhancing electrostatic and physical interactions at the material's surface. This enhancement can significantly promote the expression of ALP, BMP‐2, RUNX‐2, OCN, and OPN of stem cells post‐differentiation (Lu et al. 2021).

Macrophage polarization induced by GO‐coated implants: GO coatings on titanium implants downregulate M1 (inflammatory) macrophage‐associated cytokines, such as IL‐1β, IL‐6, TNF‐α, and IFN‐γ, and upregulate the expression of M2 macrophage‐associated cytokines, such as IL‐10 and TGF‐β, supporting the growth and differentiation of MSCs (Freytes et al. 2013; Q. Li et al. 2020). Similar results have been observed with the addition of GO to processed pyritum composite hydrogels (Shi et al. 2023).

The capacity of graphenic materials to modulate the immune response, promote angiogenesis, and enhance osteogenic differentiation underscores their efficacy in directing bone regeneration. By establishing a microenvironment conducive to bone healing, these materials present a powerful strategy for advancing next‐generation bone implants and regenerative therapies. Further refinement of graphenic material design will be essential to optimize their translational potential.

3.2. Graphenic Materials Induce Osteogenic Differentiation

Graphenic materials can direct stem cell fate through their distinctive physical properties, fostering favorable cellular interactions. The physical cues presented by a material, including matrix stiffness and cell‐recognized tension, are known to influence stem cell lineage specification (Harris et al. 2014; Huang et al. 2015). Therefore, the physical properties of graphenic materials can play a crucial role in regulating osteogenic cellular responses through various signaling pathways (Figure 6).

FIGURE 6.

Main pathways for osteogenic differentiation are activated by FGMs. Wingless‐related integration site (Wnt), focal adhesion kinase (FAK), p38 mitogen‐activated protein kinase (p38, MAPK), Ras homolog gene family—Member A (RhoA), Rho‐associated protein kinase (ROCK), extracellular signal‐regulated kinase ½ (ERK ½), phosphatidylinositol 3‐kinase (PI3K), protein kinase B (Akt), glycogen synthase kinase‐3β (GSK‐3β). Figure is created with illustrations from Servier Medical Art under CC BY 4.0 license.

Effect of graphene derivatives on signaling pathways: Graphene‐based materials can initiate a cascade of reactions through mechanical stimuli, promoting osteogenic differentiation without the need for chemical triggers. This process induces changes in the extracellular matrix (ECM) and macrophage polarization, and regulates several signaling pathways involved in bone regeneration (J. Guo et al. 2023; M. Wu et al. 2021). For example, controlling the size of GO flakes can enhance the expression of focal adhesion and the development of subordinate signals via the extracellular signal‐regulated kinase ERK–MAPK pathway, promoting osteogenesis from MSCs (Y. Chen et al. 2019; S. Park et al. 2023). Furthermore, graphenic materials can also mediate cytoskeletal deformation through the RhoA/ROCK1/ERK1/2 signaling pathway to accelerate the osteogenic differentiation of MSCs (Lu et al. 2021).

Incorporation of graphene derivatives into biomaterials can also enhance the osteogenic differentiation of MSCs through the activation of signaling pathways related to β‐catenin protein stimulation, such as the PI3K/Akt/GSK‐3β/β‐catenin and Wnt/β‐catenin signaling pathways (X. Chen et al. 2024; He et al. 2020; C. Wu et al. 2015; X. Wu et al. 2018; D. Xu et al. 2022). These pathways play a key role in bone regeneration by regulating the activity of osteoblasts and osteoclasts. Additionally, GO can induce osteogenic differentiation by activating the FAK/P38 signaling pathway, coupled with the upregulation of focal adhesion expression on the material's surface (Li and Wang 2020).

Graphene derivatives affect differentiation: Graphene derivatives can actively influence mesenchymal stem cell differentiation, making GO and related functional graphenic materials increasingly attractive for bone tissue regeneration. Low‐oxygen‐content graphene sheets have been shown to induce osteogenic differentiation in mesenchymal stem cells even without chemical induction, likely through sheet structure and topography that regulate specific integrin heterodimers and corresponding extracellular matrix proteins (MacDonald et al. 2021; Newby et al. 2020). Comparisons among GO‐based platforms further suggest that reduced oxygen content can improve osteogenic efficiency, while remaining oxygen‐containing groups provide sites for functionalization that may further support mesenchymal stem cell proliferation and differentiation (J.‐W. Yang et al. 2018). This osteoactivity has motivated the incorporation of GO into bone‐regenerative composites. For example, GO‐modified poly(methyl methacrylate) bone cements promote early osteogenesis by increasing anabolic gene expression, including COL1A1, BMP4, BMP2, RUNX2, and ALP, while suppressing catabolic genes such as MMP2 and MMP9 (Mirza et al. 2019). Similarly, GO incorporated into carbon fiber–polyether ether ketone composites accelerates osteogenic differentiation and promotes osseointegration (Qin et al. 2023).

Similarly, coating titanium implants with reduced GO increases early osteogenic differentiation markers and upregulates osteogenic gene expression (Jang et al. 2024; Kang, Jeong, et al. 2021), showing improved bone matrix formation and osteo‐integration in rabbit calvarial bone defects (Jang et al. 2024). Moreover, titanium‐based implants coated with rGO have demonstrated improved cell attachment and proliferation, ALP activity, biomineralization, osteogenic gene expression, and osteointegration than implants treated with rhBMP2 (Shin et al. 2022).

The capacity of graphenic materials to direct stem cell fate and enhance osteogenic differentiation positions them as a promising platform for bone regeneration strategies. Their influence on the bone‐implant interface, coupled with the potential for biomimetic design, suggests that continued development of graphenic materials will yield more effective and biologically integrated solutions for bone repair.

3.3. Biomineralization Upregulation Induced by Graphene Derivatives

Osteoblasts secrete proteins crucial for bone matrix deposition and mineralization. These processes yield calcium and phosphate ions, whose deposition marks late‐stage bone regeneration (Kang, Jeong, et al. 2021). GO and related FGMs possess structural and functional attributes that can enhance the mechanical strength, biocompatibility, and multifunctionality of resulting scaffolds, key factors for bone regeneration (Ren et al. 2017; Rosa et al. 2019).

Graphenic control of osteogenesis: The expression of osteogenic genes during MSC differentiation, including BSP and RUNX2, can be upregulated by rGO in a concentration‐dependent manner. The RUNX2 gene further promotes the expression of OSX, BSP, and OCN, key proteins in new bone matrix formation and mineralization (Li, Cao, et al. 2024). Moreover, the incorporation of GO into natural polymer‐based scaffolds can enhance functional moieties within the polymer structure, aiding in mimicking bone tissue features and ion organization to facilitate osteogenesis and matrix mineralization (Holt, Wright, et al. 2017; Norahan et al. 2019).

Promotion of biomineralization by graphene derivatives: The covalent conjugation of GO within collagen scaffolds has been shown to enhance biomimetic mineralization, increasing calcium content and promoting a homogeneous distribution of bone‐like apatite deposition across the porous structure (S. Kang et al. 2015; C. Zhou et al. 2018). Similarly, the incorporation of single‐layer GO into alginate microgels not only promotes osteogenic differentiation but also upregulates mineralization, potentially through the attraction of calcium ions to the negatively charged surface of the GO sheets during the osteogenic process (Soleymani et al. 2024). This facilitation of calcium deposition has also been observed with the addition of rGO to polycaprolactone nanofibrous meshes (Marrella et al. 2018).

Further, coating scaffolds with graphene derivatives can influence the mechanical and physical properties of these structures, enhancing osteogenic differentiation and bone matrix mineralization. This surface modification increases the surface area and charge density, which can enhance cell attachment and proliferation, as well as improve osteo‐metabolism to promote mineral deposition. This process can induce hydroxyapatite nucleation and growth, even without the addition of osteogenic inducing agents, potentially accelerating bone regeneration, as observed for titanium‐ and polyurethane‐based scaffolds (Kang, Jeong, et al. 2021; K. Li et al. 2018; Sanati et al. 2022; Zancanela et al. 2016). GO‐coated scaffolds have demonstrated improved bone matrix formation and osseointegration in vivo, providing evidence for their efficacy in treating irregular bone defects (Jang et al. 2024; Kwak et al. 2022; Sanati et al. 2022).

The capacity of these materials to enhance bone regeneration, by influencing osteogenic gene expression, mimicking bone tissue features, and promoting hydroxyapatite deposition, highlights their promise in the development of advanced bone scaffolds. These materials, with their tunable surface chemistry and mechanical properties, offer a unique platform for creating biomimetic environments that support bone repair. Further research into the precise control of graphene‐based material properties will be critical for optimizing their clinical translation in bone tissue engineering.

3.4. Limitations in the Use of Graphene Derivatives for Bone Regeneration

Graphene and its derivatives have garnered substantial interest in bone regeneration due to their attractive attributes, discussed above. However, while graphene‐based materials present promising avenues for bone regeneration, careful consideration of the limitations is crucial when developing research in this area.

For instance, some research shows potential cytotoxicity, particularly at elevated concentrations or with specific derivatives of GO (Meng et al. 2024; Seonwoo et al. 2022). These cytotoxic effects can be influenced by factors such as size, shape, and surface functionalization, necessitating meticulous control and optimization of these parameters during the synthesis of graphene‐based materials intended for bone regeneration (M. S. Kang et al. 2022). Additionally, while graphene can enhance the mechanical properties of scaffolds, its integration with other materials, such as hydrogels or ceramics, frequently leads to compromised mechanical strength, which can hinder its utility in load‐bearing applications (Ding et al. 2022; Hosseini and Laurencin 2022). Furthermore, the therapeutic benefits of immunomodulatory agents can be negated by disturbances in the balance of pro‐ and anti‐inflammatory responses, impeding effective bone repair. In this context, excessive GO content may exert detrimental effects on the pro‐ and anti‐inflammatory balance, thereby adversely affecting bone regeneration (X. Qi et al. 2023; Zheng et al. 2021).

While GO and related FGMs have demonstrated tremendous promise in bone regeneration, their clinical translation is still limited by several challenges, including cytotoxicity at high concentrations, poor dispersion, reduced mechanical integrity when combined with certain biomaterials, and the potential for dysregulated immune responses. However, many of these drawbacks stem from the use of unmodified or partially characterized graphene derivatives. By leveraging the rich surface chemistry of graphene oxide (GO), researchers can introduce controlled, covalent functionalization to create functional graphenic materials (FGMs) with improved biocompatibility, targeted bioactivity, and tunable degradation. These chemical modifications not only enhance the therapeutic properties of GO but also mitigate potential toxicity and improve integration with polymers, biological molecules, and inorganic components. The following section explores the synthetic strategies that enable precise tuning of GO's chemical structure, establishing a foundation for the rational design of FGMs that overcome the limitations of pristine graphene and unlock its full potential in bone tissue engineering.

4. FGM Based Composites for Bone Regeneration

The ability to precisely tune the chemistry, surface functionality, and architecture of FGMs makes them well‐suited for use in synthetic bone scaffolds. This versatility also enables FGMs to be readily integrated into composite materials. Composites are materials engineered from two or more distinct constituent components, retaining their individual identities rather than forming a homogeneous alloy. This allows for strategic component arrangement to suit specific applications (Hu 2012; S.‐J. Park and Seo 2011, 7).

Composite materials are designed to improve material performance by combining complementary properties from distinct components. Consequently, composite engineering has enabled the development of a vast array of materials to address diverse challenges (De et al. 2024; Hu 2012; Kaptan and Kartal 2024). Classified by matrix type (organic, metal, polymer, ceramic) and filler orientation (shape and arrangement), composites offer a wide range of engineering possibilities to address various challenges (Altenbach et al. 2004; Aznaw 2025; Nagavally 2016).

FGMs are well‐suited as filler components. The extensive range of potential fillers and FGM types enables the creation of numerous FGM‐based composites, expanding their applicability (Figure 7).

FIGURE 7.

FGMs can be integrated with diverse materials to form synthetic scaffolds tailored for bone grafts. These composites can be tailored for site‐specific and injury‐specific bone regeneration. The above figure demonstrates the variable methods of incorporation, including coatings, bulk material, and nanostructured composites.

4.1. Organic FGM Composites

In bone and cartilage tissue engineering, FGMs have demonstrated the ability to deliver growth factors and enhance stem cell differentiation. The unique structural features of FGMs and their various chemical modifications enhance their utility in composite materials (Adeel et al. 2018). The ability to attach bioactive molecules to graphene‐based materials also enables improved tissue regeneration and repair by enhancing mechanical properties, biocompatibility, and controlled release. Together, these features make FGMs a viable component in composites designed for regenerative applications (H. Shen et al. 2020).

4.2. FGM Composites With Biological Macromolecules

The integration of biological macromolecules, such as RNA and proteins, with FGMs offers a promising strategy for developing advanced synthetic bone grafts. FGM composites leverage the mechanical strength and biocompatibility of FGMs with the biological activity of macromolecules to promote cellular adhesion, proliferation, and differentiation. This approach aims to fabricate bone grafts that provide structural support while actively directing bone regeneration.

RNA‐based FGM composites: FGMs can also enhance bone tissue regeneration through the targeted delivery of biological macromolecules. One promising strategy involves utilizing GO as a platform for small interfering RNA (siRNA) delivery. For example, a study demonstrated that nanosized GO, functionalized with polyethylene glycol and polyethylenimine, effectively delivered siRNA targeting Ckip‐1 to titania nanotubes. This resulted in improved in vitro osteogenic differentiation and enhanced in vivo osseointegration. This composite system represents a viable approach for implant functionalization, offering clinical potential in dental and orthopedic applications (L. Zhang et al. 2017).

In addition to siRNA, messenger RNA (mRNA) delivery via FGMs is being investigated. A polypyrrole‐graphene oxide hybrid film, electropolymerized on indium tin oxide substrates, was developed for electrically controlled mRNA delivery. This system offers optimal electrical conductivity and mRNA‐loading capacity, enabling precise control over pre‐osteogenic mRNA absorption and release. Human adipose‐derived mesenchymal stem cells cultured on this film exhibited significantly enhanced osteogenic differentiation upon electrical stimulation, demonstrating the potential of electrically responsive FGMs in directing cell behavior (H. Kim et al. 2022).

In another example, a GO‐based hybrid platform (GOHP), comprised of GO‐coated indium tin oxide modified with gold nanostructures and arginine‐glycine‐aspartic acid (RGD) peptides, effectively guided human adipose‐derived mesenchymal stem cell differentiation into osteoblasts. This platform, particularly with high‐density functionalization, displayed comparable osteogenic efficiency to chemical vapor deposition graphene, inducing osteogenesis through upregulation of Wnt signaling and extracellular matrix deposition. The facile production and cost‐effectiveness of GOHP further underscore the potential of GO‐based platforms for bone‐regenerative therapies (Kang, Kim, et al. 2021).

FGM coupled with proteins: Protein and peptide interactions with FGMs represent an additional strategy for bone tissue engineering. GO supports multiple modes of enzyme immobilization, including noncovalent adsorption and covalent binding, which can improve thermostability and reusability. These protein‐GO conjugates can then be assembled to create multifunctional and biomimetic nanocomposites (Y. Zhang et al. 2013). Covalent binding of BMP‐2‐derived peptides to graphene scaffolds can also enhance protein adsorption and osteogenic differentiation, underscoring the critical role of binding modes in bioactivity (Z. Xu et al. 2023).

FGM‐based composites have demonstrated promise in fabricating biomimetic scaffolds and films for bone repair. A photo‐crosslinked sericin methacryloyl/GO hydrogel effectively promoted bone growth and repair in rat skull defects by stimulating bone marrow stem cell differentiation, exhibiting favorable cell compatibility and activation of specific signaling pathways (C. Qi et al. 2020). Ultrathin GO/lysine films, fabricated via layer‐by‐layer assembly, exhibited controlled growth, antibacterial activity, and promoted osteogenic differentiation of human dental pulp stem cells, showcasing their potential as dual‐functional bone‐implant coatings (M. Li et al. 2019). Additionally, the interaction between Bombyx mori silk fibroin (SF) and GO in aqueous solutions yielded SF/GO films with unique nanotopographies, improved modulus, and enhanced osteogenic differentiation of human mesenchymal stem cells, even in the absence of additional inducers (Y. Shuai et al. 2018).

Beyond structural support, GO also enables controlled delivery. Studies have demonstrated that GO flakes within self‐assembling peptide hydrogels effectively bind and slowly release transforming growth factor beta‐3, maintaining its bioactivity and promoting intervertebral disc regeneration (Ligorio et al. 2021). Peptide signals have also been delivered from a graphenic substrate. Incorporating GO functionalized with a BMP‐2 peptide into SF electrospun scaffolds improves biocompatibility and osteogenic differentiation of bone marrow stromal cells, highlighting cooperative effects between GO and the peptide (J. Wu et al. 2019).

4.3. Small Organic Compounds

In addition to macromolecules, small molecules possessing specific biological activities can be integrated with GO to further enhance bone regeneration and repair. A biomimetic GO‐DMB (demineralized bone) hybrid scaffold, incorporating baicalin, was developed to enhance bone regeneration by modulating repair‐immune system interactions. This scaffold, utilizing GO as a drug delivery carrier, effectively transitioned inflammatory M1 macrophages into pro‐healing M2 macrophages, promoting angiogenesis and osteogenesis. In vivo, it mitigated inflammatory responses and enhanced calvarial bone regeneration, demonstrating a bifunctional approach to effective bone repair (B. Guo et al. 2021). Similarly, methyl vanillate (MV) was investigated for its synergistic osteogenesis with biocompatible reduced graphene oxide in bone marrow stromal cells. Delivery of MV through gelatin‐reduced graphene oxide enhanced osteoinduction, highlighting the potential of small organic molecules to promote bone repair via specific signaling pathways, such as Wnt/β‐catenin (Jiao et al. 2019).

Beyond drug delivery, small organic molecules contribute to the creation of biomimetic environments that guide mineralization and cell behavior. For example, GO‐based nanohybrids can act as templates for hydroxyapatite formation, promoting crystal nucleation and growth while supporting cell adhesion and proliferation. This ability to direct mineral formation is complemented by GO–collagen scaffolds, where covalent incorporation of GO increases mechanical stiffness without compromising cytocompatibility. The resulting stiffness, which approaches that of osteoid tissue, enhances hMSC osteogenic differentiation through mechanosensitive pathways, including focal adhesion formation, cytoskeletal organization, and ERK signaling. Together, these systems highlight how GO can be used to engineer both the chemical and mechanical features of the microenvironment to drive bone tissue regeneration (S. Kang et al. 2015).

A biomimetic bone environment requires more than the presence of a “bone‐like” component; it must integrate structural, mechanical, and mineral‐forming cues that cells can interpret. For example, peptide nanofibers can be used on GO as a template for hydroxyapatite formation, driving mineralization (Wang, Ouyang, et al. 2015). Here, the designed nanofibers mimic key functions of collagen fibrils: they self‐assemble into nanoscale fibrous structures, provide functional groups for hydroxyapatite nucleation, and guide early apatite formation along the fiber axis. GO serves as a two‐dimensional support that organizes the peptide nanofibers and later mediates HA microsphere formation during longer mineralization. Type I collagen, the major non‐mineral component of bone, has been used similarly, but collagen alone provides a relatively soft microenvironment that may be insufficient for osteogenic commitment (S. Kang et al. 2015). By covalently conjugating mechanically stiff GO flakes into the 3D collagen scaffold, the material retains a collagen‐based architecture while increasing scaffold stiffness about three‐fold, thereby shifting the matrix toward a more osteoinductive mechanical environment. This mechanical remodeling is biologically meaningful: hMSCs on GO–collagen scaffolds showed enhanced osteogenic differentiation, increased calcium deposition, stronger RUNX2 expression, and activation of focal adhesion/mechanotransduction‐associated signals including vinculin, FAK phosphorylation, ERK phosphorylation, F‐actin organization, and ROCK‐dependent osteogenic gene expression. Together, these studies suggest that GO‐based composites can create biomimetic bone environments through complementary mechanisms: in collagen scaffolds, GO reinforces the matrix so that cells experience a stiffer, osteogenic 3D niche; in GO‐peptide nanofiber systems, GO supports a fibrous organic template that directs HA nucleation and growth. Thus, the biomimicry in these materials is not merely compositional, but environmental, arising from the coordinated presentation of extracellular matrix‐like architecture, mechanical stiffness, and mineralization‐guiding interfaces.

4.4. Polymer FGM Composites

Polymer composites offer another promising avenue for the fabrication of FGM‐based biomaterials. These composites leverage the mechanical strength, biocompatibility, and surface functionality of graphene, while polymers contribute flexibility, processability, and tailored degradation profiles. This synergistic combination enables the design of scaffolds and implants exhibiting enhanced structural integrity, controlled drug release, and improved cellular interactions, facilitating effective bone regeneration.

Implantable composites for bone‐related applications must solve two connected problems: they need sufficient mechanical and structural reliability, but they also need to provide biological or therapeutic functions that conventional single‐phase materials cannot easily deliver. Carbon fiber reinforced polymers can be used for structural support, where the carbon fibers provide low density, stiffness, and high mechanical performance, while the polymer matrix binds the fibers into a defined geometry, transfers load between them, and protects them from chemical and mechanical damage (Chua et al. 2021). This division of labor allows the composite to combine strength, durability, lightness, and radiolucency, while manufacturing methods such as sheet molding and 3D printing provide additional control over device shape and customization. In another composite system, reduced GO‐loaded chitosan hydrogel, chitosan forms the hydrogel network that can carry Teriparatide, whereas reduced GO contributes high drug‐loading capacity and photothermal responsiveness, enabling near‐infrared light to trigger pulsatile drug release (X. Wang et al. 2021). Together, these studies suggest that carbon–polymer composites are most useful when each component performs a distinct but cooperative function: the polymer phase gives the material processability, cohesion, and form, while the carbon‐based phase provides reinforcement, interfacial activity, or external stimulus responsiveness. Therefore, the composite is not simply a mixture of carbon and polymer; it is an engineered interface in which mechanical support, manufacturability, and biological function are integrated into one material platform.

Chemically functionalized graphene was investigated for its capacity to enhance stem cell osteogenesis and inhibit biofilm formation in polymer composites for orthopedic applications. Poly(ε‐caprolactone) (PCL) composites incorporating graphene, particularly amine‐functionalized GO (AGO) and GO particles, significantly improved human mesenchymal stem cell proliferation. AGO proved particularly effective in augmenting stem cell osteogenesis and mineralization, while functionalized GO, especially AGO, effectively inhibited biofilm formation by inducing bacterial cell death through membrane damage (Kumar et al. 2015).

4.4.1. Biopolymers

Biopolymers provide a compelling foundation for graphene‐based composites in bone tissue engineering, owing to their inherent biocompatibility and biodegradability. The integration of graphene with biopolymers, such as collagen, chitosan, and silk fibroin, yields a versatile platform for enhancing mechanical properties, promoting cellular activity, and facilitating bone regeneration.

FGMs‐collagen complexes: Collagen is a key constituent of bone tissue and has been extensively investigated in combination with graphene. Incorporation of GO into collagen matrices enhances mechanical strength and promotes osteogenic differentiation (S. Liu et al. 2019). Fish scale‐derived type I collagen, crosslinked with graphene via electrostatic self‐assembly, has also yielded promising results. Varying graphene content significantly improved mechanical strength, electrical conductivity, and porous structure, with 10% graphene‐collagen scaffolds exhibiting a threefold increase in Young's modulus and successful osteogenesis (Rebecca et al. 2023). Furthermore, rGO‐coated collagen scaffolds can also display enhanced mechanical strength and improved human bone marrow‐derived mesenchymal stem cell viability, proliferation, and increased bone formation in rabbit cranial bone defects, underscoring the benefits of rGO coating (Bahrami et al. 2021).

Chitosan based FGM composites: Natural polymer scaffolds can mimic parts of the bone extracellular matrix, but they often lack the mechanical stability, degradation control, and interfacial strength needed for reliable bone regeneration. Across these studies, GO repeatedly addresses this weakness by acting as a chemically interactive reinforcing phase rather than as a passive filler: GO carboxyl groups have been covalently linked with chitosan amine groups, producing porous chitosan–GO scaffolds whose hydrophilicity, water retention, pore interconnectivity, and enzymatic stability supported osteoblast attachment, proliferation, and pore infiltration (Depan et al. 2011). This principle has been further extended in carboxymethyl chitosan, where GO cross‐linking improved water retention and increased modulus and hardness while also supporting osteogenic gene expression and bone repair when combined with bone morphogenetic protein‐2 (Ruan et al. 2016). Sulfonated GO has also been used to improve chitosan scaffolds, producing a more hydrophilic, mechanically stronger, interconnected porous scaffold that also sustained tetracycline release and accelerated in vivo bone healing (Mahanta et al. 2019). The material has been further enhanced in electrospun polyhydroxybutyrate–chitosan scaffolds, where GO reduced fiber diameter, improved hydrophilicity and mechanical properties, slowed degradation, and increased surface biomineralization and alkaline phosphatase activity in MG‐63 cells (Motiee et al. 2023). Together, these findings suggest that GO improves polymer scaffolds through a coupled structural mechanism: its oxygen‐containing groups promote hydrogen bonding, electrostatic interactions, or covalent coupling with polymer chains, while its stiff two‐dimensional geometry improves load transfer and helps stabilize the scaffold architecture. The implication is that graphenic materials are valuable in bone scaffolds not simply because they “reinforce” polymers, but because they convert soft, degradable, weakly osteoinductive matrices into hydrated, interconnected, mechanically competent environments that cells can colonize and remodel.

The second challenge is that a bone‐regenerative scaffold must do more than maintain shape; it must organize biological signals, support mineral formation, and bias cells toward an osteogenic phenotype. In GO/poly‐L‐lysine films, GO improves interactions with biomacromolecules and concentrates osteogenic inducers at the surface, promoting mesenchymal stem cell proliferation and osteogenic differentiation (W. Qi et al. 2014). This idea was moved toward biomimetic mineralization by using poly‐dopamine‐functionalized reduced GO, where the poly‐dopamine coating improved cell adhesion and proliferation and provided catechol‐rich nucleation sites for hydroxyapatite formation by MC3T3‐E1 preosteoblasts (Cheng et al. 2015). GO can also cooperate with an inorganic osteoconductive phase: when GO and β‐tricalcium phosphate were incorporated into silk fibroin/soy protein isolate scaffolds, the composite showed improved physicochemical properties and synergistically enhanced alkaline phosphatase activity and osteogenesis‐related gene expression in bone marrow mesenchymal stem cells (F. Liu et al. 2020) for a case for intrinsic GO bioactivity was further strengthened by showing that 0.5 wt.% GO in fish gelatin/chitosan scaffolds enhanced in vitro osteogenic differentiation and promoted ectopic osteogenesis in vivo, including collagen formation, calcium deposition, and bone‐cell recruitment even without conventional osteoinductive additives (Șelaru et al. 2022).

These results indicate that graphenic materials provide an interfacial biological function: their charged, aromatic, and oxygenated surfaces can adsorb osteogenic molecules, bind proteins, assist mineral nucleation, and modulate cell adhesion and differentiation. Therefore, the broader implication is that future GO‐based bone scaffolds should be designed around controlled interfacial chemistry: GO content, dispersion, functionalization, and polymer coupling, because these parameters determine whether the composite behaves merely as a stronger material or as a genuinely osteoactive microenvironment.

4.4.2. Synthetic Polymers for FGM Composites

PLGA based applications: Synthetic polymers provide another crucial class of materials for graphene‐based composites in bone tissue engineering. When combined with graphene, synthetic polymers offer enhanced mechanical strength, controlled degradation, and improved biological activity, facilitating the development of advanced scaffolds and implants. Poly(lactic‐co‐glycolic acid) (PLGA) has been extensively investigated in combination with graphene. PLGA composites have been widely studied and exhibit significant enhancements in hydrophilicity, swelling ratio, degradation, bioactivity, and tensile strength. This combination of properties makes PLGA‐GO an exceptionally promising material for accelerating bone tissue regeneration (Kaur et al. 2017).

PLGA scaffolds are biodegradable, but their hydrophobicity and limited bioactivity reduce their ability to guide tissue regeneration. GO can be incorporated into electrospun PLGA nanofibers to improve hydrophilicity and adsorption of proteins and osteogenic inducers (Luo et al. 2015) which enhanced mesenchymal stem cell adhesion, proliferation, and osteogenic differentiation. Another example, uses GO‐PLGA/hydroxyapatite microcarriers, where GO enabled efficient BMP‐2 immobilization and hydroxyapatite provided osteoconductive mineral cues, together promoting pre‐osteoblast proliferation, alkaline phosphatase activity, osteogenic gene expression, and mineralization (Fu et al. 2017). Similar interfacial design principles appear beyond bone: graphene nanosheets in aligned PLGA microribbons improved hydrophilicity, conductivity, mechanics, and groove‐like topography to support neural differentiation, while GO and RGD peptide co‐functionalization improved nanofiber hydrophilicity and vascular smooth muscle cell attachment and proliferation (Shin et al. 2017). Together, these studies suggest that graphenic materials convert otherwise passive polymer scaffolds into tissue‐instructive interfaces, with their function determined by scaffold design: osteogenic signal retention for bone, conductivity and topographic guidance for neural tissue, and adhesive biofunctionality for vascular tissue.

Composites using PCL: Poly(ε‐caprolactone) (PCL) is another synthetic polymer widely used in biomedicine. PCL composites incorporating poly(ethylenimine) conjugated GO significantly enhanced hMSC proliferation, osteogenesis, and bacterial inhibition, demonstrating potential as bioactive resorbable biomaterials for orthopedic applications (Holmes et al. 2016; Kumar et al. 2016). PCL/graphene scaffolds, fabricated through solvent casting, showed improved mechanical properties and biocompatibility with increasing graphene content, suggesting suitability for bone tissue engineering (Anitasari et al. 2023). 3D‐printed PCL bone scaffolds enhanced with zinc‐doped HA and zinc‐doped HA reduced GO nanoparticles exhibited increased stiffness and improved cell osteogenesis, highlighting their potential for effective bone tissue regeneration (Maleki‐Ghaleh et al. 2021).

Polymer‐enriched 3D graphene foams (GFs) using PCL showed enhanced flexibility, handleability, and biomineralization, demonstrating promise for bone‐related applications (Wang, Xiong, et al. 2015). Calcium silicate PCL scaffolds with graphene, fabricated via 3D printing, promoted proliferation and osteogenesis of Wharton's Jelly‐derived mesenchymal stem cells through the fibroblast growth factor receptor pathway, showcasing dual bioactivities in promoting osteogenesis and vascularization (Lin et al. 2019).

Other polymers: Other synthetic polymers, including poly(vinyl alcohol) (PVA), poly(propylene fumarate) (PPF), poly(N‐isopropylacrylamide) (PNIPAAm), and zwitterionic hydrogels, have also been successfully integrated with graphene. GO‐incorporated zwitterionic hydrogels synergistically improved physicochemical properties and promoted osteogenic differentiation in rat calvarial defects (Q. Wang et al. 2023). PVA nanocomposite scaffolds with GO showed significant improvements in mechanical properties, making them potential candidates for bone tissue engineering (C. Shuai et al. 2015). PPF nanocomposites reinforced with various nanomaterials, including GO, exhibited favorable cytocompatibility, suggesting potential for in vivo safety and efficacy studies (Farshid et al. 2015). PNIPAAm‐based copolymer/GO composites with chitosan formed thermosensitive, injectable hydrogels that enhanced osteogenic differentiation of human dental pulp stem cells (Amiryaghoubi et al. 2020).

Furthermore, self‐supporting graphene hydrogel films exhibited excellent biocompatibility and osteoinductivity, demonstrating potential as osteoinductive membranes in guided bone regeneration techniques (Lu et al. 2013). Additionally, 3D bioprinted artificial periosteum, formulated with gelatin‐dopamine, methacrylated gelatin, methacrylated silk fibroin, GO nanosheets, and bone marrow mesenchymal stem cells, effectively enhanced osteogenesis in vitro and in vivo, presenting a promising strategy for bone defect repair (Sun et al. 2023). Carbon nanomaterials, including carbon nanotubes (CNTs) and graphene, incorporated into nanofibrous poly(l‐lactic acid) scaffolds, promoted bone mesenchymal stem cell adhesion, proliferation, and osteogenic differentiation, with graphene demonstrating a stronger osteoinductive effect than CNTs (Duan et al. 2015).

4.5. Inorganic FGM Composites

Inorganic FGM composites present a promising avenue for enhancing bone tissue regeneration by integrating the mechanical strength and bioactivity of inorganic materials with the unique properties of graphene. These composites are designed to improve osteogenesis, biocompatibility, and mechanical performance for diverse applications in bone tissue engineering.

Across distinct scaffold systems, graphene modifications consistently enhance osteogenic activity by promoting both early and downstream differentiation. Mineralized three‐dimensional graphene scaffolds promoted accelerated osteogenic commitment and robust osteogenic differentiation of hMSCs, showcasing their promise as a platform for hMSC culture and osteoconductive tissue‐engineered constructs (Zhang, Li, et al. 2016). GO‐modified β‐tricalcium phosphate bioceramics enhanced proliferation, alkaline phosphatase activity, and osteogenic gene expression of human bone marrow stromal cells, attributed to the activation of the Wnt/β‐catenin signaling pathway (C. Wu et al. 2015).

Incorporating GO and FGMs into hydroxyapative (HAp) composites enhance minteral formation, osteoblast viability, and osteogenic differentiation across myltiple material architecutres (de Vasconcellos et al. 2019; S. Medeiros et al. 2018). rGO has been found to be particularly useful in this context. Hydroxyapatite‐rGO nanocomposites exhibited enhanced fracture toughness and improved osteoblast cell proliferation and alkaline phosphatase activity (Y. Liu et al. 2013). rGO‐coated biphasic calcium phosphate effectively promoted osteogenesis in calvarial defects, with composite concentration being a critical factor (J.‐W. Kim et al. 2017).

Furthermore, the integration of graphene with other inorganic materials has yielded promising results. Titania‐graphene nanocomposites enhanced human cell attachment and prevented nanoparticle migration and agglomeration, demonstrating favorable biomimetic bone activity (Kandiah et al. 2014). Calcium silicate ceramic coatings, reinforced with graphene plates, exhibited significantly improved wear resistance and comparable biocompatibility to pure calcium silicate coatings (Y. Xie et al. 2015). Graphene oxide/copper nanoderivatives demonstrated antimicrobial mechanisms, synergistic osteogenic activity, and in vivo anti‐infective behavior, rendering them suitable for implantable biomaterials in infected bone defect repair (Y. Yang et al. 2022).

4.6. Coatings

FGM‐based coatings present a versatile strategy for enhancing the biocompatibility, osteogenesis, and antibacterial properties of biomedical implants. Through the application of FGMs to diverse substrates, researchers seek to improve implant integration and functionality.

Graphene oxide (GO)‐based coatings can enhance osseointegration andprovide antibacterial properties in certain applications. Studies have demonstrated that GO coatings on various substrates like quartz (Zhao et al. 2015) and titanium (Baheti et al. 2023; Park et al. 2016; Subbiah et al. 2014) promote hydroxyapatite formation, cell adhesion, proliferation, and osteogenic differentiation. Surface modifications incorporating GO, such as graphene/hydroxyapatite nanocomposites (Depan et al. 2011) and GO‐fibronectin matrices (Mahanta et al. 2019), have shown significant improvements in these cellular responses, suggesting their potential for orthopedic and dental applications, as well as bone tissue engineering. Furthermore, graphene‐coated titanium can facilitate the sustained release of growth factors, accelerating bone regeneration (Lu et al. 2021).

Beyond promoting bone growth, GO‐based coatings can also exhibit antibacterial effects. Functionalizing GO with gelatin (Zhao et al. 2016) or combining it with gallium nanoparticles (Y. Yang et al. 2023) has shown promise in inhibiting bacterial growth while maintaining or enhancing biocompatibility and osteogenic potential. GO/copper nanocomposites on scaffolds have further demonstrated the ability to enhance both bone formation and blood vessel development (Zhang, Chang, et al. 2016).

Research into the direct impact of GO on osteoblasts reveals nuanced effects depending on the substrate material, with potential to enhance mineralized matrix formation on titanium (Zancanela et al. 2016). Likewise, GO‐modified surface topographies, such as microgrooves on titanium, can guide cell behavior and improve implant integration (H. Wang et al. 2022). The fabrication of GO/hydroxyapatite composite coatings via electrochemical deposition further enhances crystallinity, bonding strength, and overall biocompatibility (Zeng et al. 2016). These collective findings highlight the versatile potential of GO‐based coatings for improving the performance and longevity of biomedical implants.

5. Conclusion and Future Perspectives

This review has examined the broad potential of graphene oxide (GO) and functional graphenic materials (FGMs) in advancing synthetic bone grafts. Owing to their exceptional mechanical strength, high surface area, biocompatibility, and tunable surface chemistry, FGMs offer an attractive platform for engineering materials that closely mimic the complexity of native bone. These properties allow for precise functionalization with bioactive molecules, enabling scaffolds that actively participate in bone regeneration processes such as osteogenesis, angiogenesis, immunomodulation, and biomineralization.

The integration of FGMs with biological macromolecules, small organic compounds, and a wide range of polymers has yielded promising results across diverse regenerative strategies. From targeted RNA and protein delivery systems to the fabrication of biomimetic hydrogels, films, and coatings, FGM‐based composites are demonstrating multifunctional capabilities that extend well beyond traditional graft materials. Biopolymers such as collagen, chitosan, and silk fibroin, as well as synthetic polymers like PLGA, PCL, and PVA, have been successfully paired with GO to enhance scaffold strength, cellular compatibility, and osteoinductive potential.

In addition to organic composites, inorganic FGM hybrids incorporating calcium phosphate or hydroxyapatite have exhibited impressive osteogenesis and bone integration both in vitro and in vivo. These materials not only emulate the mineral content of bone but also improve mechanical properties, drug delivery, and antibacterial performance when used as coatings or structural additives. Together, these advances present FGMs as powerful tools in the development of next‐generation, patient‐specific bone regeneration therapies capable of overcoming the limitations of autografts, allografts, and metal implants.

Despite this rapid progress, several critical challenges must be addressed to ensure the clinical translation of FGM‐based materials. Long‐term in vivo studies are necessary to clarify the degradation behavior, systemic distribution, and immunological responses to graphenic composites. Standardized protocols and large animal models will be essential for rigorously validating their safety and efficacy across orthopedic and dental indications.

Looking ahead, combining multiple functionalization strategies may unlock synergistic effects that enhance regenerative outcomes. For example, integrating growth factors with biodegradable polymers or leveraging controlled drug delivery with topographical cues represents a promising strategy for refining bone repair. Advances in fabrication technologies, including 3D printing, bioprinting, and electrospinning, will further enable patient‐specific scaffold design with precisely tailored mechanical and biological properties.

Finally, interdisciplinary collaboration across materials science, tissue engineering, immunology, and clinical practice will be crucial for overcoming regulatory hurdles and establishing guidelines for reproducible, scalable production. With continued innovation and systematic validation, FGMs are poised to redefine the future of bone tissue engineering and improve clinical outcomes for patients with complex skeletal injuries.

Author Contributions

Anne M. Arnold: writing – original draft, writing – review and editing, visualization. Sebastian Guajardo: writing – original draft, writing – review and editing, visualization. Chenyun Deng: writing – original draft, writing – review and editing, visualization. Stefanie A. Sydlik: writing – review and editing, funding acquisition, conceptualization, project administration. Jason D. Orlando: writing – original draft, writing – review and editing.

Funding

The authors would like to thank the NSF Division of Materials Research veteran supplement (award ID: 1905665) and the Scott Institute Seed Fund for financial support.

Disclosure

Declaration of generative AI and AI‐assisted technologies in the writing process: During the preparation of this work the author(s) used ChatGPT and Google Gemini to homogenize the writing style of the authors, editing the text, and checking references. After using these tools, the authors reviewed and edited the content as needed and take full responsibility for the content of the publication.

Conflicts of Interest

The authors declare no conflicts of interest.

Guajardo, S. , Orlando J. D., Deng C., Arnold A. M., and Sydlik S. A.. 2026. “Engineering Functional Graphenic Materials for Bone Repair.” Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology 18, no. 4: e70070. 10.1002/wnan.70070.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.