Reactive Oxygen Species-Regulating Nanoengineered Hydrogels for Bone Regeneration: A Mechanism-Based Framework of Responsive Delivery, Intrinsic Scavenging, Nanozyme Catalysis, and Osteoimmunomodulation

Abstract

Bone regeneration is frequently impaired by excessive reactive oxygen species (ROS). Persistent oxidative stress disrupts mitochondrial function, sustains inflammation, and suppresses osteogenic differentiation. Nanoengineered hydrogels provide versatile platforms for local microenvironment remodeling. This review summarizes recent advances in ROS-regulating nanoengineered hydrogels for bone regeneration, with emphasis on redox microenvironment remodeling and osteoimmunomodulation. ROS-responsive hydrogels exploit pathological oxidants as endogenous triggers for on-demand release of small molecules, proteins, neuropeptides, ions, and nanocomposites. Intrinsic ROS-scavenging hydrogels directly attenuate oxidative injury through redox-active polymers, polyphenols, nanomaterials, metal-ion chelation, and oxygen-regulating components. Nanozyme-integrated hydrogels provide catalytic functions that regulate superoxide, hydrogen peroxide, glucose metabolism, oxygen availability, and mitochondrial oxidative stress. ROS-regulated osteoimmunomodulatory hydrogels reshape immune–bone crosstalk by promoting pro-regenerative macrophage functions, suppressing excessive osteoclastogenesis, controlling infection-associated inflammation, and enhancing angiogenic and osteogenic signaling. Remaining challenges include defining disease-specific therapeutic redox windows, establishing standardized mechanistic and safety assessments, and improving long-term nanoengineered-component biocompatibility. Future development of personalized hydrogel systems may accelerate translation toward precision bone-regenerative therapy.

Graphical Abstract

Introduction

Bone regeneration is frequently compromised in critical-sized defects caused by trauma, tumor resection, infection, congenital malformation, osteoporosis, aging, and metabolic disorders.^1,2 Autologous bone grafting remains a commonly used clinical strategy, but its application is limited by donor-site morbidity, restricted graft availability, unpredictable resorption, and incomplete integration.³ Allografts and synthetic substitutes can partly overcome supply limitations, yet they may lack sufficient osteoinductivity, vascularization capacity, or immunological compatibility. Therefore, successful bone regeneration requires more than the implantation of an osteoconductive scaffold. It requires reconstruction of a dynamic local microenvironment, and reactive oxygen species (ROS) are central regulators of this microenvironment.^4,5 ROS, including superoxide anion, hydrogen peroxide, hydroxyl radicals, and related oxidants, are generated by inflammatory cells, mitochondria, NADPH oxidases, endothelial cells, and bone-related cells after injury.^6,7 ROS exert concentration-, species-, compartment-, and time-dependent biological effects. H₂O₂, the most extensively characterized ROS in redox signaling, provides a useful quantitative reference. Intracellular H₂O₂ concentrations of approximately 1–10 nM have been associated with physiological oxidative eustress and second-messenger signaling. However, sustained concentrations above approximately 100 nM are generally associated with oxidative distress and biomolecular damage. These values should not be regarded as universal thresholds for all ROS species, because ROS levels vary substantially among cell types, subcellular compartments, injury stages, and measurement approaches. At physiological concentrations, ROS act as intracellular second messengers that participate in host defense, cellular migration, angiogenesis, osteogenic differentiation, and normal bone remodeling.^8,9 However, excessive or persistent ROS accumulation overwhelms endogenous antioxidant systems and induces oxidative stress.^10,11 This pathological state can impair mitochondrial respiration, damage DNA and proteins, promote lipid peroxidation, accelerate cellular senescence, and disturb osteoblast–osteoclast coupling.^12,13 Consequently, excessive ROS suppresses osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), impairs endothelial-cell function, promotes osteoclastogenesis, and delays mineralized-tissue formation.^14,15 Glutathione (GSH) represents a major non-enzymatic component of this endogenous redox-buffering system. GSH peroxidases use GSH as an electron donor to reduce H₂O₂ and lipid peroxides, generating oxidized glutathione (GSSG). Reduced GSH is present at millimolar concentrations in most mammalian cells, with cytosolic concentrations commonly reported in the range of approximately 1–11 mM and GSH/GSSG ratios of approximately 30:1–100:1 under reducing physiological conditions. In bone, GSH homeostasis is particularly relevant to osteoblast function. GSH biosynthesis increases during osteoblast differentiation, whereas GSH depletion promotes ROS accumulation, RUNX2 oxidation and destabilization, and impaired matrix mineralization. Successful bone regeneration requires controlled redox homeostasis rather than indiscriminate ROS elimination.

The pathological relevance of oxidative stress is particularly evident in aged, osteoporotic, diabetic, infected, and inflammatory bone defects.¹⁶ In aged bone, elevated ROS contributes to stem-cell senescence and reduced regenerative competence.^17,18 In osteoporosis, oxidative stress and chronic inflammation promote osteoclast activity while impairing osteoblast function. In diabetes, sustained hyperglycemia enhances advanced glycation end-product formation, mitochondrial dysfunction, and glucose-associated ROS production, resulting in defective angiogenesis, persistent inflammation, and impaired bone turnover. Similarly, periodontitis and infected bone defects are characterized by a self-amplifying cycle in which bacterial stimulation, inflammatory-cell infiltration, ROS generation, and tissue damage continuously reinforce one another.¹⁹ These observations indicate that redox dysregulation is not a secondary event in bone repair failure.²⁰ Instead, it is a major determinant of whether a defect progresses from early inflammation to regenerative healing. Redox imbalance is also closely linked to osteoimmunomodulation. Bone healing is initiated by an inflammatory phase in which neutrophils, macrophages, monocytes, lymphocytes, and other immune cells clear debris, control pathogens, and recruit reparative cells.^21,22 Although macrophage phenotypes are often simplified as pro-inflammatory M1-like and pro-regenerative M2-like states, macrophage behavior is dynamic and changes throughout the healing process.²³ Excessive ROS can prolong pro-inflammatory macrophage activation, activate inflammasome-associated pathways, and sustain secretion of cytokines that favor bone resorption.^24,25 Conversely, restoration of local redox homeostasis can facilitate inflammation resolution, promote pro-regenerative macrophage functions, reduce osteoclast overactivation, and improve crosstalk among immune cells, BMSCs, endothelial cells, and osteoblast-lineage cells.²⁶

Hydrogels are promising materials for redox-microenvironment remodeling because they provide hydrated, extracellular-matrix-like three-dimensional networks with tunable mechanical properties, degradability, injectability, adhesiveness, and cargo-loading capacity.^27,28 Conventional hydrogels can serve as local depots for cells, proteins, drugs, ions, and nanoparticles.²⁹ However, passive diffusion-based release may result in premature cargo loss, insufficient retention, or a mismatch between therapeutic release and the evolving biological state of the defect.³⁰ Nanoengineering expands hydrogel functionality by incorporating redox-active nanomaterials, ROS-cleavable linkers, catalytic nanozymes, bioactive ions, oxygen-generating components, and stimuli-responsive carriers. These nanoengineered hydrogels can recognize pathological redox cues, scavenge harmful oxidants, convert metabolic substrates, release therapeutic cargo on demand, and regulate immune–bone crosstalk. Recent studies have demonstrated several distinct design strategies. ROS-responsive hydrogels use excessive oxidants as endogenous triggers for network degradation or controlled cargo release, enabling localized delivery of anti-inflammatory molecules, proteins, neuropeptides, and catalytic nanocomposites.³¹ Intrinsic ROS-scavenging hydrogels rely on redox-active matrix components, polyphenols, MXene nanosheets, metal-ion chelation, or oxygen-regulating systems to directly restore local redox balance.³² Nanozyme-integrated hydrogels further introduce catalytic functions, including superoxide dismutase-, catalase-, and glucose oxidase-like activity, to regulate glucose metabolism, hydrogen peroxide conversion, oxygen availability, and mitochondrial oxidative stress. Moreover, ROS-regulated osteoimmunomodulatory hydrogels aim to reshape the immune microenvironment by controlling macrophage phenotypes, suppressing infection-associated inflammation, inhibiting excessive osteoclastogenesis, and strengthening macrophage-mediated support for angiogenesis and osteogenesis.³³

Several recent reviews have summarized ROS-responsive hydrogels from the perspectives of crosslinking and fabrication strategies, drug delivery, or biomedical applications of the broader field of bone-regenerative hydrogels.^31–33 In contrast, the present review adopts a bone-regeneration-centered, mechanism-oriented framework for ROS-regulating nanoengineered hydrogels. Rather than categorizing these systems solely according to polymer composition, cargo type, or disease, this review distinguishes ROS-triggered therapeutic delivery, intrinsic ROS scavenging, nanozyme-mediated catalytic ROS and metabolic regulation, and ROS-regulated osteoimmunomodulation. This framework further emphasizes that ROS responsiveness, direct ROS elimination, and catalytic redox regulation represent mechanistically distinct strategies. This review summarizes recent advances in ROS-regulating nanoengineered hydrogels for bone regeneration, with an emphasis on redox microenvironment remodeling and osteoimmunomodulation. Rather than categorizing materials solely by polymer composition or cargo type, this review classifies them according to their dominant therapeutic mechanism: (i) ROS-responsive hydrogel platforms for on-demand therapeutic delivery; (ii) intrinsic ROS-scavenging hydrogels for redox microenvironment remodeling; (iii) nanozyme-integrated hydrogels for catalytic ROS regulation and metabolic microenvironment remodeling; and (iv) ROS-regulated osteoimmunomodulatory hydrogels (Figure 1). Remaining challenges include defining disease-specific therapeutic redox windows, establishing standardized mechanistic and safety assessments, and improving long-term nanoengineered-component biocompatibility. Future development of personalized hydrogel systems may accelerate translation toward precision bone-regenerative therapy.

Figure 1.

Scheme for ROS-regulating nanoengineered hydrogels for bone regeneration: redox microenvironment remodeling and osteoimmunomodulation. The downward arrow indicates decreased ROS levels.

ROS-Responsive Hydrogel Platforms for On-Demand Therapeutic Delivery

ROS are rapidly elevated after bone injury as a consequence of inflammatory-cell infiltration, ischemia–reperfusion, mitochondrial dysfunction, and bacterial infection.³⁴ While transient ROS signaling participates in host defense and repair initiation, sustained oxidative stress impairs osteogenic differentiation and disrupts bone remodeling.³⁵ ROS-rich lesions provide a disease-associated biochemical signal to achieve localized and on-demand therapeutic delivery. Compared with conventional hydrogels that release payloads primarily through passive diffusion or bulk degradation, ROS-responsive hydrogels remain relatively stable under physiological conditions.³⁶ When exposed to excessive oxidants, they undergo linker cleavage, network disassembly, altered swelling, or accelerated degradation. The recent development of ROS-responsive hydrogel systems for bone regeneration has expanded the therapeutic repertoire from small-molecule antioxidants to proteins, neuropeptides, bioactive ions, and catalytic nanocomposites (Table 1). Importantly, rather than necessarily direct ROS elimination, ROS acts as an endogenous trigger. This distinction is critical for separating ROS-responsive delivery systems from intrinsically antioxidant hydrogels and nanozyme-integrated catalytic platforms, which are discussed in subsequent sections.

Table 1.

Comparison of ROS-Responsive Hydrogel Platforms for On-Demand Therapeutic Delivery in Bone Regeneration

Hydrogel Platform	ROS-Responsive Mechanism	Therapeutic Cargo	Target Pathological Setting/Model	Therapeutic Mechanism	Reference
DHAC-DMF hydrogel: dopamine-modified hyaluronic acid/carboxymethyl chitosan network	ROS-labile boronate ester bonds undergo cleavage under oxidative stress, accelerating hydrogel degradation and DMF release	Dimethyl fumarate (DMF)	Rat calvarial bone defect	Suppresses inflammatory cytokines, alleviates oxidative injury, promotes a favorable immune microenvironment, and enhances osteogenic differentiation and calvarial bone regeneration	[37]
RRG-MRL: ROS-responsive scavenging GelMA hydrogel crosslinked with NHS-TK-NHS	Thioketal-containing NHS-TK-NHS linkers are cleaved by elevated ROS, causing network degradation and METRNL release	Meteorin-like protein (METRNL)	Rat cranial bone-defect model	Reduces oxidative stress and inflammation, promotes BMSC homing through SDF-1/CXCL12 upregulation, and enhances endothelial angiogenesis through c-Kit/PI3K/Akt signaling	[38]
PTHC hydrogel: poly(vinyl alcohol)/TSPBA network containing nano-hydroxyapatite and curculigoside	Dynamic borate ester bonds respond to both acidic pH and high ROS, enabling sustained and on-demand release of HA and curculigoside	Nano-hydroxyapatite (HA) and curculigoside (CCG)	Rat critical-sized calvarial defect	Scavenges excess ROS and releases HA/CCG to promote osteogenesis, angiogenesis, and neurogenesis	[39]
AAT-ZCG hydrogel: poly(acrylamide-co-acryloylphenylboronic acid)/tannic acid hydrogel incorporating ZCG cascade nanozymes	Glucose/ROS-responsive dynamic boronate ester network disintegrates in diabetic microenvironments, releasing tannic acid and ZCG	Tannic acid; cerium–zoledronic acid–glucose oxidase nanozyme complex (ZCG)	Diabetic rat cranial bone defect	Catalytically scavenges ROS. Inhibit osteoclast overactivation. Promotes M2-like macrophage polarization, angiogenesis, osteogenesis, and restoration of bone-remodeling balance.	[40]
CGRP@PVA/tsPBA hydrogel: injectable poly(vinyl alcohol)/tsPBA hydrogel	ROS-mediated disruption of the PVA/tsPBA network enables sustained CGRP release in oxidative periodontal lesions	Calcitonin gene-related peptide (CGRP)	db/db mouse model of diabetes-associated periodontitis and alveolar bone loss	Restores neuro-angiogenic signaling, promotes type H vessel formation and osteoprogenitor recruitment, reduces osteoclast-associated bone loss, and enhances alveolar bone regeneration.	[41]

Abbreviations: AAT, acrylamide–acryloylphenylboronic acid–tannic acid; BMSC, bone marrow mesenchymal stem cell; CCG, curculigoside; CGRP, calcitonin gene-related peptide; DMF, dimethyl fumarate; GelMA, gelatin methacryloyl; GOx, glucose oxidase; HA, hydroxyapatite; METRNL, meteorin-like protein; PTHC, PVA/TSPBA/HA/CCG hydrogel; ROS, reactive oxygen species; TSPBA/tsPBA, tetra-substituted phenylboronic-acid-derived crosslinker; ZCG, cerium–zoledronic acid–glucose oxidase nanozyme complex.

ROS-Triggered Delivery of Anti-Inflammatory and Osteoprotective Small Molecules

A representative small-molecule delivery strategy was reported by Huang et al, who developed a ROS-responsive hydrogel for controlled dimethyl fumarate (DMF) release in bone regeneration.³⁷ DMF is a clinically used anti-inflammatory and antioxidant-response-modulating molecule with potential to reduce oxidative injury and inflammatory signaling in bone defects.^42,43 Encapsulation within a ROS-responsive hydrogel provides two advantages over direct administration, including limiting premature payload loss under relatively normal redox conditions, and enabling enhanced DMF release in regions of excessive oxidative stress, where anti-inflammatory intervention is most needed. The biomaterial uses pathological ROS as a signal of local demand. In an oxidative defect niche, accelerated network degradation or cleavage of ROS-sensitive motifs releases DMF, thereby attenuating inflammation and creating conditions more favorable for osteogenic differentiation.³⁷ Such systems are particularly relevant to inflammatory bone defects, where early excessive ROS can suppress the transition from inflammatory clearance to tissue formation. However, the therapeutic objective should not be complete ROS depletion. Instead, responsive delivery should reduce persistent pathological ROS while preserving the low-level redox signaling required for cellular migration, angiogenesis, and osteogenesis.

ROS-Responsive Delivery of Pro-Regenerative Proteins

Protein therapeutics are attractive for bone repair but are frequently limited by rapid proteolysis, short local retention, and poor temporal control. Xu et al addressed these issues through a ROS-responsive scavenging GelMA hydrogel loaded with meteorin-like protein (METRNL) (Figure 2).³⁸ In this system, ROS-cleavable NHS-TK-NHS linkers are disrupted in oxidative defect sites, leading to hydrogel degradation and METRNL release.³⁸ The platform therefore converts high local ROS concentrations into a trigger for protein liberation. The biological effects of METRNL delivery extended beyond direct osteogenesis. Released METRNL promoted endothelial-cell angiogenic activity through c-Kit/PI3K/Akt signaling and enhanced stromal cell-derived factor-1 expression.³⁸ This study highlights that ROS-responsive delivery can be used to coordinate multiple regenerative processes rather than merely protect osteoblasts from oxidative damage. By coupling local protein release with stem-cell homing and vascularization, the hydrogel functioned as a microenvironment-modulating system capable of linking the inflammatory stage of repair to subsequent osteogenic progression.⁴⁴ The study also underscores the importance of cargo-sensitive design. Protein-loaded ROS-responsive hydrogels must preserve bioactivity during synthesis, sterilization, storage, and release. In addition, cleavage kinetics should be matched to the concentration range and duration of ROS elevation in the target defect. Overly sensitive materials may release cargo prematurely, whereas insufficiently responsive networks may fail to provide therapeutic concentrations during the early inflammatory phase.

Figure 2.

Chemical illustration of a smart ROS-responsive scavenging GelMA hydrogel loaded with meteorin-like protein (METRNL) to facilitate sequential bone regeneration steps (adapted from Advanced Healthcare Materials. 2025;14:e2500060).³⁸ (A) Preparation of Hydrogels. (B) Therapeutic effect of hydrogel on cranial bone defects.

Dual pH/ROS-Responsive Systems for Neurovascularized Bone Regeneration

Bone repair depends on the coordinated recovery of vascular, neural, and osteogenic compartments. Wang et al developed a pH/ROS dual-responsive injectable hydrogel incorporating nano-hydroxyapatite and curculigoside for neurovascularized bone regeneration (Figure 3).³⁹ The hydrogel was constructed through dynamic borate ester chemistry, enabling responsiveness to the acidic and oxidative conditions of the injury microenvironment. Under these pathological stimuli, the system released its bioactive components while simultaneously improving local redox homeostasis. This dual-responsive strategy is valuable because bone defects rarely exhibit isolated oxidative stress. Instead, inflammation-associated ROS elevation is often accompanied by local acidosis, altered metabolism, and hypoxia. Integrating pH and ROS responsiveness may therefore enhance specificity relative to a single-stimulus design. In the reported system, stimulus-triggered delivery supported angiogenesis, neurogenesis, and osteogenesis, ultimately promoting reconstruction of the microvascular network and sensory nerve repair.³⁹ ROS-responsive hydrogels are not limited to delivering osteoinductive factors, but can include re-establishing neurovascular regulation. Nevertheless, multistimulus systems require careful optimization. The relationship between pH, ROS concentration, and release behavior may differ substantially among acute traumatic defects, diabetic bone lesions, infected defects, and periodontal bone loss.

Figure 3.

Schematic illustration of the fabrication of pH and ROS dual-response multi-bioactive PTHC hydrogel for neuro-vascularized bone regeneration (adapted from Mater Today Bio. 2024;29:101369).³⁹ The upward arrows indicates increased expression or levels of the indicated regenerative factors, whereas the downward arrow indicates decreased pH.

Glucose/ROS-Responsive Multifunctional Hydrogel for Diabetic Bone Defects

Diabetic bone defects pose a distinct challenge because persistent hyperglycemia, excessive ROS production, chronic inflammation, vascular dysfunction, and imbalanced osteoblast–osteoclast activity coexist within the same lesion.^45,46 Fu et al developed a glucose/ROS-responsive multifunctional hydrogel to address these interconnected pathological features.⁴⁰ The system incorporated tannic-acid-mediated dynamic borate ester bonds and a cascade nanocomposite composed of cerium, zoledronic acid, and glucose oxidase. Under the glucose-rich and ROS-rich diabetic microenvironment, the hydrogel released tannic acid and the nanocomposite in a stimulus-dependent manner. This platform is particularly notable because release control was integrated with sequential therapeutic reactions. Glucose oxidase consumed local glucose but generated hydrogen peroxide and gluconic acid. Cerium-based catalytic activity subsequently reduced peroxide-associated oxidative stress, while acidic reaction products promoted degradation of the nanocomposite and release of zoledronic acid to suppress excessive osteoclast activation.⁴⁰ Thus, the hydrogel did not simply release a single therapeutic molecule. It implemented a staged response, in which diabetic microenvironmental cues initiated a cascade of metabolic, anti-inflammatory, angiogenic, osteogenic, and anti-resorptive effects. Future systems may further exploit this concept by programming sequential release profiles, such as early anti-inflammatory intervention followed by delayed osteogenic or pro-angiogenic stimulation.

ROS-Responsive Neuropeptide Delivery in Diabetic Periodontal Bone Loss

ROS-responsive hydrogels may also be used to restore disrupted neurovascular signaling.⁴⁷ Zhan et al reported an injectable poly(vinyl alcohol)/tsPBA hydrogel for ROS-responsive delivery of calcitonin gene-related peptide (CGRP) in diabetes-associated periodontitis.⁴¹ This work identified impaired sensory-nerve signaling as a contributor to deficient alveolar bone regeneration under diabetic conditions. Because free CGRP is susceptible to rapid degradation, hydrogel encapsulation enabled local protection and stimulus-dependent release in the oxidative periodontal environment. The released CGRP promoted type H vessel formation and enhanced the recruitment of osteogenic progenitors, thereby restoring a neuro-angiogenic axis that supports alveolar bone regeneration.⁴¹ Importantly, the authors described the hydrogel primarily as a ROS-responsive delivery carrier rather than a potent ROS-scavenging material. ROS-responsive hydrogel platforms do not need to directly neutralize oxidants to improve redox-related pathology. Instead, they can exploit ROS accumulation to deliver biological signals that restore cellular communication networks disrupted by oxidative stress.

Intrinsic ROS-Scavenging Hydrogels for Redox Microenvironment Remodeling

In contrast to the ROS-responsive delivery systems, intrinsic ROS-scavenging hydrogels contain redox-active chemical groups, antioxidant components, or immobilized nanomaterials that directly regulate excessive oxidants within the defect site.^48,49 Their therapeutic activity does not depend primarily on stimulus-triggered payload release.⁵⁰ Instead, these systems remodel the local redox microenvironment through direct radical neutralization, electron or hydrogen donation, metal-ion chelation, suppression of Fenton-type reactions, or restoration of endogenous antioxidant defenses.⁵¹ Such functions are particularly relevant in aged, osteoporotic, diabetic, hypoxic, and inflammatory bone defects.⁵² In these conditions, persistent oxidative stress disrupts mitochondrial homeostasis, accelerates stem-cell senescence, impairs angiogenesis, and uncouples bone formation from resorption.^53,54 Recent studies have integrated antioxidant functions with osteoconductive matrices, oxygen-generating components, bioactive polyphenols, and metabolic regulation, enabling hydrogels to act as local redox microenvironment remodelers rather than passive structural fillers (Table 2).

Table 2.

Comparison of Intrinsic ROS-Scavenging Hydrogels for Redox Microenvironment Remodeling in Bone Regeneration

Hydrogel Platform and Principal Components	Intrinsic Redox-Regulating Mechanism	Additional Microenvironmental Function	Target Pathological Setting/Model	Therapeutic Mechanism	Reference
PSeR hydrogel: PEGylated poly(glycerol sebacate) (PEGS-NH2)/poly(γ-glutamic acid) (γ-PGA) hydrogel incorporating rapamycin-loaded poly(diselenide-carbonate) nanomicelles	γ-PGA-associated carboxyl groups chelate Fe2⁺ and suppress extracellular Fenton-type ROS generation; ROS-responsive diselenide nanomicelles reduce intracellular oxidative stress in senescent BMSCs	Rapamycin-mediated restoration of antioxidant capacity and delay of stem-cell senescence	Aged bone-defect repair model	Protects DNA replication, improves BMSC self-renewal and osteogenic differentiation, and rejuvenates aged bone repair.	[55]
GM hydrogel: transglutaminase-crosslinked gallic-acid-embedded gelatin hydrogel containing Ti3C2 MXene nanosheets	MXene nanosheets directly scavenge hydroxyl radicals and DPPH radicals; gallic acid provides supplementary antioxidant activity	Improved compressive strength and osteogenic matrix support	Rat critical-sized calvarial defect	Reduces oxidative injury to MC3T3-E1 cells, increases ALP activity, calcium-nodule formation, and osteogenic-gene expression	[56]
Tannic-acid-based MeSF nanocomposite hydrogel: methacrylated silk fibroin matrix incorporating tannic-acid-derived redox-active nanocomponents	Phenolic hydroxyl groups in tannic acid neutralize ROS through electron-transfer and hydrogen-donation reactions	Anti-inflammatory regulation, tissue adhesion, and mechanically supportive silk-fibroin matrix	Preclinical bone-defect repair model	Create a pro-regenerative niche that supports osteogenesis and bone repair.	[57]
CSP-GM micro-oxygen reservoir: CaO2@SiO2@polydopamine nanoparticles incorporated into GelMA microspheres	Polydopamine scavenges ROS, while the SiO2@polydopamine shell moderates CaO2 hydrolysis and prevents abrupt oxidative stress during oxygen release	Sustained oxygen supply, recovery of mitochondrial function, and activation of Nrf2/HO-1 antioxidant signaling	Hypoxic bone-defect microenvironment and in vivo bone-regeneration model	Coordinates oxygen delivery with ROS scavenging, restores BMSC mitochondrial homeostasis and antioxidant defenses, and promotes angiogenesis and osteogenesis under hypoxia.	[58]
Glucose-responsive antioxidant hydrogel: glucose-sensitive hydrogel designed for diabetic bone regeneration; exact formulation should follow the corrected publication	Glucose-responsive activation is coupled with ROS scavenging to restore local redox homeostasis under hyperglycemic conditions	Regulation of diabetic metabolic microenvironment and protection of reparative cells from hyperglycemia-associated oxidative injury	Diabetic bone-defect model	Reduces glucose-associated oxidative stress, improves local homeostasis and osteogenic cell function, and supports bone regeneration in the diabetic microenvironment.	[59]

Abbreviations: BMSC, bone marrow mesenchymal stem cell; CaO₂, calcium peroxide; CSP-GM, CaO₂@SiO₂@polydopamine nanoparticle-loaded GelMA microspheres; DPPH, 2,2-diphenyl-1-picrylhydrazyl; GelMA, gelatin methacryloyl; GM, gallic-acid-embedded gelatin/MXene hydrogel; MeSF, methacrylated silk fibroin; PEGS-NH₂, amine-functionalized PEGylated poly(glycerol sebacate); PSeR, PEGS-NH₂/γ-PGA hydrogel containing rapamycin-loaded poly(diselenide-carbonate) nanomicelles; ROS, reactive oxygen species.

Multihierarchical ROS Regulation for Rejuvenating Aged Bone Repair

A representative multilevel antioxidant strategy was developed by He et al for aged bone repair. Their injectable system combined a PEGylated poly(glycerol sebacate)/poly(γ-glutamic acid) hydrogel with rapamycin-loaded poly(diselenide-carbonate) nanomicelles (Figure 4).⁵⁵ This architecture was designed to regulate ROS at extracellular, intracellular, and cellular homeostasis levels simultaneously. At the extracellular level, carboxyl-rich hydrogel components reduced oxidative injury by chelating ferrous ions, thereby limiting Fenton-type reactions and hydroxyl-radical generation. At the intracellular level, the diselenide-containing nanomicelles interacted with elevated ROS in senescent bone marrow mesenchymal stem cells, contributing to the removal of excessive intracellular oxidants. In parallel, rapamycin supported sustained restoration of cellular antioxidant capacity through autophagy-associated regulation. The combined effect was not merely an acute reduction in ROS concentration, but functional rejuvenation of senescent stem cells, including preservation of DNA replication, improved self-renewal, and enhanced osteogenic differentiation. Since redox dysregulation is distributed across extracellular matrix, cytoplasm, mitochondria, and cellular stress-response pathways, a single antioxidant mechanism may be insufficient in aged bone defects.⁶⁰ Multihierarchical systems that integrate extracellular radical suppression with intracellular ROS regulation and long-term cellular homeostasis may be more effective for reversing age-associated regenerative dysfunction.

Figure 4.

Schematics of multi-hierarchy ROS scavenging system for aged bone regeneration (adapted from Adv Mater. 2024;36(9):e2306552).⁵⁵ The downward arrow indicates reduced hydroxyl radical (•OH) levels.

MXene-Based Nanocomposite Hydrogels with Direct ROS-Scavenging Activity

Two-dimensional nanomaterials provide another route for constructing intrinsically antioxidant hydrogels. Zhao et al incorporated MXene nanosheets into a gelatin-based nanocomposite hydrogel to improve both osteogenic performance and ROS-scavenging capacity in critical-sized calvarial defects.⁵⁶ The MXene-containing hydrogel acted as a multifunctional matrix, in which the nanomaterial phase contributed direct redox regulation. Meanwhile, the gelatin network provided a cell-supportive and biodegradable three-dimensional environment. The incorporation of MXene nanosheets enabled the hydrogel to reduce oxidative stress while supporting osteogenic cellular activity.⁵⁶ Importantly, optimization of MXene concentration was necessary because antioxidant efficacy, mechanical behavior, cell compatibility, and nanosheet dispersion are interdependent. The optimized formulation promoted new bone formation in a rat critical-sized calvarial-defect model, demonstrating that intrinsic ROS-scavenging capacity can be incorporated into a hydrogel matrix without relying on diffusible antioxidant drugs. MXene-based hydrogels are attractive because their two-dimensional morphology offers a high interfacial area for interactions with reactive species and cells. However, their translational development requires careful assessment of nanosheet degradation, long-term tissue retention, potential oxidative transformation, and dose-dependent cytocompatibility.

Polyphenol-Based Antioxidant Hydrogels for Simultaneous Redox and Inflammatory Regulation

Polyphenol-containing hydrogels provide a biomimetic strategy for direct radical scavenging because phenolic hydroxyl groups can participate in electron-transfer and hydrogen-donation reactions. Wang et al developed a tannic-acid-based nanocomposite methacrylated silk fibroin hydrogel with the capacity to scavenge ROS, reduce inflammation, and support bone regeneration.⁵⁷ The system integrated methacrylated silk fibroin as a mechanically supportive and biocompatible matrix with tannic acid as a redox-active polyphenolic component. The inclusion of tannic acid endowed the hydrogel with intrinsic antioxidant functionality and helped suppress oxidative-stress-associated inflammation.⁵⁷ This is important because sustained ROS accumulation and inflammatory signaling reinforce each other in bone defects. ROS activate inflammatory pathways, whereas inflammatory cells further generate ROS, generating a self-amplifying pathological cycle. A hydrogel capable of simultaneously attenuating oxidative stress and inflammatory activity can therefore facilitate the transition from early inflammatory clearance toward a pro-regenerative microenvironment. Silk fibroin is advantageous in this setting because it provides a versatile matrix with favorable biocompatibility, structural stability, and processability. Combined with tannic acid and inorganic nanocomponents, the resulting hydrogel can provide mechanical support, local adhesion, and redox regulation. Nevertheless, polyphenol-based designs require careful control of loading concentration and crosslinking chemistry. Excessive polyphenol incorporation may alter gelation behavior, affect degradation kinetics, or influence cell adhesion, whereas insufficient loading may produce only transient antioxidant activity.

Coupling ROS Scavenging with Local Oxygen Restoration

Persistent hypoxia and oxidative stress frequently coexist in large bone defects. Hypoxia can impair mitochondrial respiration and angiogenesis, while mitochondrial dysfunction can further increase ROS production. Rui et al addressed this coupled pathological state by constructing an implantable micro-oxygen reservoir system based on CaO2@SiO2@polydopamine nanoparticles incorporated into GelMA microspheres.⁵⁸ The system provided sustained local oxygen release while maintaining broad-spectrum ROS-scavenging capacity. The CaO2 core served as an oxygen-generating component, whereas the SiO2 and polydopamine layers regulated oxygen release and contributed antioxidant functionality. After incorporation into GelMA microspheres, the composite system recreated an extracellular-matrix-like microenvironment that supported bone marrow stromal-cell adhesion and proliferation. Under hypoxic conditions, it reduced intracellular and mitochondrial ROS, preserved mitochondrial membrane potential, and enhanced antioxidant defense responses. The reported regenerative effects were associated with modulation of the Nrf2/HO-1 pathway, leading to improved angiogenesis and osteogenesis. This study demonstrates that redox remodeling should not be considered independently of oxygen regulation. In hypoxic bone lesions, simply scavenging ROS may be insufficient if cellular metabolism remains compromised because of inadequate oxygen availability. Conversely, uncontrolled oxygen delivery may exacerbate oxidative injury. Therefore, oxygen-generating antioxidant hydrogels require balanced kinetics, in which oxygen release and ROS-scavenging activity are coordinated to avoid creating secondary oxidative stress.

Redox Homeostasis Regulation in Diabetic Bone Regeneration

Diabetic bone defects are characterized by sustained hyperglycemia, excessive oxidative stress, mitochondrial dysfunction, chronic inflammation, impaired angiogenesis, and reduced osteogenic activity.⁶¹ Liu et al developed a smart glucose-responsive hydrogel with ROS-scavenging and homeostasis-regulating functions for diabetic bone regeneration.⁵⁹ The central therapeutic objective was restoration of the redox and metabolic homeostasis disrupted by the diabetic microenvironment. This strategy recognizes that hyperglycemia is not only a systemic metabolic abnormality but also a local pathological signal that sustains ROS production in bone defects. By coupling glucose responsiveness with intrinsic ROS-scavenging activity, the hydrogel was designed to preferentially exert its therapeutic effects in a high-glucose microenvironment. Such a design may reduce oxidative damage to reparative cells, and improve the survival and osteogenic function of mesenchymal stem cells. Collectively, intrinsic ROS-scavenging hydrogels demonstrate that bone regeneration can be enhanced by actively reconstructing the redox microenvironment. Their mechanisms include multilevel extracellular and intracellular ROS regulation, polyphenol-mediated radical neutralization, nanomaterial-assisted antioxidant activity, and coordinated oxygen–ROS homeostasis.

Catalytic ROS Regulation and Metabolic Microenvironment Remodeling by Nanozyme-Integrated Hydrogels

Although intrinsic antioxidant hydrogels can directly neutralize excessive ROS through redox-active matrix components, nanozyme-integrated hydrogels introduce catalytic functions. They can continuously convert pathological substrates within the bone-defect microenvironment. Nanozymes are nanomaterials with enzyme-mimetic activities, including superoxide dismutase (SOD)-, catalase (CAT)-, glutathione peroxidase-, peroxidase-, and glucose oxidase (GOx)-like activities. Their incorporation into hydrogels enables local retention of catalytic nanomaterials, minimizes nanoparticle aggregation and leakage, and prolongs their interactions with ROS-rich tissue environments. More importantly, catalytic regulation can extend beyond ROS removal. This catalytic paradigm differs from the ROS-responsive delivery platforms. In nanozyme-integrated hydrogels, ROS and related metabolites are themselves catalytic substrates. The therapeutic objective is therefore to reconstruct a pathological metabolic-redox network rather than merely release an antioxidant payload. Recent studies have increasingly combined nanozymes with injectable or microsphere-based hydrogels to achieve sustained catalytic regulation in diabetic, hypoxic, inflammatory, and periodontal bone defects (Table 3).

Table 3.

Comparison of Nanozyme-Integrated Hydrogels for Catalytic ROS Regulation and Metabolic Microenvironment Remodeling in Bone Regeneration

Nanozyme-Integrated Hydrogel Platform	Enzyme-Like Activity and Catalytic Cascade	Primary Microenvironmental Target	Additional Therapeutic Functions	Bone-Regeneration Outcome	Reference
GMAP microspheres: GelMA hydrogel microspheres encapsulating Au@Pt bimetallic nanoparticles	Au@Pt exhibits glucose oxidase-like and catalase-like activities, enabling glucose consumption and H2O2 decomposition with concurrent ROS elimination	Hyperglycemia and oxidative stress in diabetic bone defects	Protects BMSC proliferation under high-glucose conditions; enhances osteogenic differentiation and paracrine activity; suppresses inflammation and promotes angiogenesis	Significantly improves bone formation in diabetic bone-defect models through coordinated metabolic and redox correction	[62]
MCPtA/PAM hydrogel: Mn@Co3O4@Pt nanozyme loaded with alendronate and Mg2⁺, incorporated into a glucose-responsive borate-ester-crosslinked hydrogel	Pt-mediated GOx-like glucose depletion; Mn-modulated Co3O4-mediated SOD- and CAT-like conversion of superoxide and H2O2	Hyperglycemia, glycation-associated oxidative stress, and redox imbalance in diabetic bone defects	Alendronate suppresses excessive osteoclast activity; Mg2⁺ supports osteogenesis; promotes M2-like macrophage polarization and vascularized bone repair	Restores osteoblast–osteoclast balance and accelerates bone regeneration through integrated glucose depletion, ROS scavenging, anti-resorption, and osteogenic stimulation	[63]
Ch_MnP/risedronate hydrogel: thiolated chitosan crosslinked with MnP-conjugated PEG-maleimide and containing catalase and risedronate	Mn-porphyrin acts as a biomimetic SOD, converting O2•− to H2O2; catalase decomposes H2O2 and generates O2	Combined oxidative stress and hypoxia in large bone defects	Sustained risedronate release suppresses osteoclast-associated bone resorption; oxygen generation supports a less hypoxic regenerative niche	Enhances osteogenic-cell proliferation and differentiation, suppresses osteoclast precursor activity, and promotes calvarial bone regeneration	[64]
Metal-free antioxidant nanozyme/bioactive hydrogel: metal-free antioxidant nanozyme integrated into a bioactive hydrogel scaffold	Reported antioxidant nanozyme activity enables catalytic attenuation of excessive ROS; the precise enzyme-mimetic spectrum should be verified from the full article before final manuscript submission	Oxidative stress during bone reconstruction	Avoids the potential concerns of long-term metal-ion release associated with transition-metal nanozymes	Functions as an antioxidant scaffold that supports bone reconstruction under oxidative stress	[65]
MZT@S/PPP hydrogel: Mn–Zn–tannic acid nanozyme modified with the mitochondria-targeting peptide SS31 and encapsulated in thermosensitive PLGA–PEG–PLGA hydrogel	SOD-like and CAT-like catalytic activities remove ROS; SS31 promotes mitochondrial localization and clearance of mitochondria-derived ROS	Mitochondrial dysfunction, oxidative stress, and impaired oxidative phosphorylation in diabetes-associated periodontitis	Restores mitochondrial oxidative phosphorylation; promotes M2 macrophage polarization, angiogenesis, and osteogenesis	Reduces alveolar bone loss and promotes new alveolar bone formation by restoring metabolic, immune, and redox homeostasis	[66]

Abbreviations: BMSC, bone marrow mesenchymal stem cell; CAT, catalase; Ch_MnP, chitosan/Mn-porphyrin hydrogel; GOx, glucose oxidase; GMAP, GelMA microspheres containing Au@Pt nanoparticles; H₂O₂, hydrogen peroxide; MCPtA, Mn@Co₃O₄@Pt nanozyme loaded with alendronate and Mg²⁺; MZT@S, Mn–Zn–tannic acid@SS31 nanozyme; PAM, borate-ester-crosslinked glucose-responsive hydrogel; PPP, PLGA–PEG–PLGA; ROS, reactive oxygen species; SOD, superoxide dismutase.

Bimetallic Nanozyme Microspheres for Coordinated Glucose Depletion and ROS Elimination

Hui et al developed GelMA-based composite microspheres encapsulating Au@Pt bimetallic nanozymes for diabetic bone regeneration.⁶² The bimetallic nanozyme exhibited glucose oxidase-like and catalase-like activities, allowing glucose consumption and hydrogen peroxide decomposition to occur in a coordinated manner. This cascade catalytic mechanism is particularly relevant to diabetic bone defects. Persistent hyperglycemia drives the accumulation of advanced glycation end products and enhances mitochondrial ROS production. They impaire the proliferation, osteogenic differentiation, and paracrine activity of bone marrow mesenchymal stem cells. In the Au@Pt nanozyme system, glucose consumption reduced the metabolic source of hyperglycemia-associated oxidative injury, whereas catalase-like activity converted excessive hydrogen peroxide into less harmful products and oxygen. By concurrently regulating glucose and ROS, the microspheres protected stem cells under high-glucose conditions and improved their osteogenic potential.⁶² The study highlights the value of microsphere-based hydrogel architectures for nanozyme delivery. Compared with freely dispersed nanoparticles, hydrogel microspheres can improve local retention, reduce rapid diffusion from irregular defects, and provide a three-dimensional matrix that supports cell–material interactions. However, cascade designs also require careful balancing of glucose oxidase-like and catalase-like activities.

Multifaceted Catalytic Regulation of Diabetic Bone Metabolism

Liu et al further expanded the cascade nanozyme concept by engineering a Mn@Co₃O₄@Pt nanozyme loaded with alendronate and Mg²⁺ ions, termed MCPtA, for diabetic bone regeneration.⁶³ The nanozyme was derived from a bimetallic metal–organic framework and incorporated into a composite hydrogel. Its multifunctional design integrated GOx-, SOD-, and CAT-like catalytic activities with anti-resorptive and osteogenic ionic cues (Figure 5).⁶³ The Pt component provided glucose oxidase-like activity, thereby reducing local glucose concentrations. In parallel, Mn-modulated Co₃O₄ enhanced SOD- and CAT-like catalytic functions, enabling conversion of superoxide and hydrogen peroxide into less harmful species. This multistep catalytic process reduced oxidative stress and glycation-associated injury within the diabetic defect microenvironment. In addition, the incorporation of alendronate restrained excessive osteoclast activity, whereas Mg²⁺ contributed to osteogenic regulation. Thus, the system addressed the diabetic bone lesion through simultaneous metabolic correction, redox regulation, and restoration of the osteogenesis–osteoclastogenesis balance.⁶³ This study is important because it illustrates that catalytic ROS regulation should be considered within the broader context of metabolic remodeling. In diabetes, ROS accumulation is not an isolated pathological event but is closely linked to glucose excess, mitochondrial dysfunction, chronic inflammation, and imbalanced bone turnover.⁶⁷ A multifunctional catalytic hydrogel can interrupt this interconnected pathological network at several points.

Figure 5.

Enzyme-like activities of GelMA-based composite microspheres encapsulating Au@Pt bimetallic nanozymes (adapted from ACS Nano. 2025;19(2):2677–2694).⁶³ (A) Catalytic reaction diagram of MCPtA. (B) SOD-like catalytic mechanism diagram (top) and the ultraviolet absorption spectrum at the end point of NBT reaction (bottom). (C) DPPH• scavenging mechanism diagram (top) and the absorbance variation at 517 nm within 180 min (bottom). (D) H2O2 scavenging ratio every hour until 6 h. (E) GOx-like catalytic mechanism diagram (top) and the ultraviolet absorption spectrum at the end point of TMB oxidation reaction (bottom). (F) SOD-like reaction paths (top) and the corresponding free-energy variations with the reaction coordinate (bottom). (G) CAT-like reaction paths (top) and the corresponding free-energy variations with the reaction coordinate (bottom).

Mn-Porphyrin/Catalase Hydrogels for Coupling ROS Conversion, Oxygen Generation, and Anti-Resorptive Therapy

Hypoxia and oxidative stress frequently coexist in large bone defects.^68,69 Local oxygen deprivation impairs oxidative phosphorylation and angiogenesis, while the resulting mitochondrial dysfunction can further increase ROS production. Kim et al designed an in situ-forming hydrogel containing manganese porphyrin (MnP), catalase, and risedronate to simultaneously regulate ROS, hypoxia, and osteoclast-associated bone resorption.⁶⁴ The system was based on thiolated chitosan and MnP-conjugated polyethylene glycol-maleimide, which formed a hydrogel through a click reaction. MnP served as a biomimetic SOD, converting superoxide into hydrogen peroxide, while catalase decomposed hydrogen peroxide and generated oxygen. This sequential catalytic process avoids the accumulation of hydrogen peroxide that can occur when superoxide dismutation is not coupled with downstream peroxide removal. The resulting oxygen generation also addressed local hypoxia, which is particularly relevant in poorly vascularized large bone defects.⁶⁴ In vitro, the hydrogel enhanced the proliferation and osteogenic differentiation of MG-63 cells under ROS-rich conditions. In a calvarial defect model, these combined effects promoted bone regeneration. This work emphasizes that nanozyme-integrated hydrogels may be designed as sequential reaction systems. Superoxide conversion, peroxide decomposition, oxygen generation, and sustained drug release can be integrated into a single material platform.⁷⁰ Nevertheless, oxygen-producing catalytic systems require careful calibration because excessive oxygen tension may itself disturb cellular redox balance. The rate of oxygen production should therefore be matched to local diffusion, consumption, and vascularization dynamics.

Metal-Free Antioxidant Nanozymes as Catalytic Scaffolds for Bone Reconstruction

Most catalytic nanozymes used for bone regeneration contain transition metals or metal oxides, such as cerium, manganese, platinum, cobalt, and iron. Although these materials can provide strong catalytic activity, their long-term degradation, biodistribution, and metal-ion release require rigorous evaluation. Yang et al reported a metal-free antioxidant nanozyme incorporated into a bioactive hydrogel as an antioxidant scaffold for bone reconstruction.⁶⁵ This study provides an important alternative direction for catalytic redox regulation. The metal-free nanozyme platform was designed to provide broad-spectrum antioxidant activity while avoiding reliance on metal-based catalytic centers. Its integration into a bioactive hydrogel created a local scaffold capable of reducing oxidative stress and supporting bone reconstruction.⁶⁵ Conceptually, this strategy is significant because it separates nanozyme catalytic behavior from conventional metal-dependent enzyme mimetics. Metal-free systems may reduce concerns related to metal accumulation and ion-associated toxicity, while retaining the potential for durable catalytic ROS regulation.

Mitochondria-Targeted Nanozyme Hydrogels for Metabolic and Immune Microenvironment Remodeling

Because mitochondria are a major intracellular source of ROS, local extracellular antioxidant activity may be insufficient to correct persistent oxidative stress in diabetic and inflammatory bone defects.^71,72 Yan et al developed a mitochondria-targeted nanozyme hydrogel for diabetes-associated periodontitis by incorporating Mn–Zn–tannic acid nanozymes modified with the mitochondria-targeting peptide SS31 into a PLGA–PEG–PLGA thermosensitive hydrogel.⁶⁶ The nanozyme exhibited SOD-like and CAT-like activities, while SS31 enhanced mitochondrial localization and promoted the removal of mitochondria-derived ROS. This intracellular targeting strategy enabled the hydrogel to restore mitochondrial oxidative phosphorylation, rather than simply reduce total ROS levels. Improved mitochondrial function was associated with enhanced osteogenesis and angiogenesis. In vivo, the system reduced alveolar bone loss and promoted new bone formation in diabetes-associated periodontitis.⁶⁶ Mitochondria-targeted nanozyme hydrogels represent a potentially important advance because they address the subcellular origin of oxidative stress. Nevertheless, mitochondrial targeting efficiency may vary among immune cells, osteoblast-lineage cells, endothelial cells, and periodontal cells. In addition, excessive intracellular antioxidant activity could interfere with physiological mitochondrial redox signaling. Future platforms should seek to achieve cell-selective, dose-controlled, and temporally regulated mitochondrial ROS modulation. Collectively, nanozyme-integrated hydrogels provide a versatile catalytic strategy for remodeling pathological bone microenvironments.

ROS-Regulated Osteoimmunomodulation by Nanoengineered Hydrogels

Bone regeneration is closely coupled with the local immune response.^73,74 After injury, immune cells infiltrate the defect site and initiate inflammatory clearance, angiogenesis, extracellular-matrix remodeling, and osteogenic repair.^75,76 However, persistent oxidative stress can disrupt this sequence by sustaining inflammatory signaling, promoting osteoclastogenesis, impairing osteogenic progenitor-cell function, and preventing the establishment of a pro-regenerative immune microenvironment. Therefore, ROS regulation and osteoimmunomodulation are interdependent processes. Nanoengineered hydrogels can reduce excessive ROS while simultaneously directing immune-cell activity, suppressing inflammation-associated bone resorption, and enhancing communication between macrophages, endothelial cells, and osteogenic progenitors. Recent nanoengineered hydrogels have therefore integrated ROS regulation with macrophage modulation, osteoclast inhibition, and angiogenesis to reconstruct an osteoimmune microenvironment favorable for bone repair (Table 4).

Table 4.

Comparison of ROS-Regulated Osteoimmunomodulatory Nanoengineered Hydrogels for Bone Regeneration

Hydrogel Platform and Principal Components	Redox/Antimicrobial Function	Major Osteoimmunomodulatory Mechanism	Target Pathological Setting	Regenerative Outcome	Reference
Mg@PEG-PLGA hydrogel: PEG-coated Mg microspheres embedded in a phase-transforming PEG-PLGA hydrogel	Mg reacts with water to release H2 and Mg2⁺; H2 scavenges excessive ROS	Reduces intracellular ROS and inhibits IκBα/NF-κB signaling; promotes M2-like macrophage polarization; suppresses osteoclastogenesis	Osteoporotic femoral bone defects	Restores the osteogenesis–osteoclastogenesis balance and promotes repair of osteoporotic bone defects.	[77]
GOE1 hydrogel: self-assembled chlorhexidine acetate/epigallocatechin-3-gallate nanoparticles in a GelMA/oxidized hyaluronic acid matrix	Chlorhexidine provides antibacterial activity; EGCG confers antioxidant and anti-inflammatory effects	Modulates macrophage phenotype transition, including IL-17-producing macrophage-associated immune regulation, to establish a pro-regenerative periodontal immune niche	Diabetes-associated periodontitis	Reduces infection-associated inflammation and oxidative stress, alleviating periodontal tissue destruction and alveolar bone loss.	[78]
CDFBCS@SA hydrogel: dynamically crosslinked modified carboxymethyl cellulose and carboxymethyl chitosan loaded with sinapic acid	pH/ROS dual-responsive release of sinapic acid; antibacterial and antioxidant activity	Downregulates inflammatory mediators, reduces oxidative stress, and regulates macrophage polarization to maintain periodontal immune homeostasis	Inflammatory periodontal bone defects	Establishes a favorable local immune microenvironment and enhances periodontal bone regeneration.	[79]
BPPP/GP hydrogel: polydopamine-modified black-phosphorus nanosheets with immobilized Pd nanoparticles (BP@PDA-Pd) in a GelMA/methacrylated poly(γ-glutamic acid) hydrogel	Mild NIR photothermal stimulation enhances antioxidant enzyme-like ROS-scavenging activity	Enables spatiotemporal M2-like macrophage polarization and promotes secretion of pro-osteogenic and pro-angiogenic factors	Osteoporotic bone defects	Reduces local inflammation, supports endogenous cell recruitment and revascularization, and enhances osteogenic repair.	[80]
Nar-CuCDs/Gel hydrogel: naringin–copper carbon dots incorporated into a dual-crosslinked hydrogel scaffold	ROS scavenging and antibacterial activity mediated by Nar-CuCDs	Promotes M2-like macrophage polarization and improves macrophage–BMSC osteogenic crosstalk	Preclinical bone-defect repair model	Optimizes the bone immune microenvironment, enhances BMSC osteogenic differentiation, and promotes bone-defect repair.	[81]

Abbreviations: BMSC, bone marrow mesenchymal stem cell; BP, black phosphorus; CuCDs, copper carbon dots; EGCG, epigallocatechin-3-gallate; GelMA, gelatin methacryloyl; H₂, hydrogen; NIR, near-infrared; PEG-PLGA, polyethylene glycol-poly(lactic-co-glycolic acid); ROS, reactive oxygen species; SA, sinapic acid.

Hydrogen- and Magnesium-Mediated Regulation of Macrophage Polarization and Osteoclastogenesis

Zhou et al developed an injectable Mg@PEG-PLGA hydrogel that generated molecular hydrogen and released Mg²⁺ ions for the repair of osteoporotic bone defects (Figure 6).⁷⁷ The hydrogel contained PEG-coated magnesium microparticles dispersed in a phase-transforming PEG-PLGA matrix. After implantation, magnesium reacted with water to generate hydrogen, while the porous hydrogel structure provided local mechanical support and enabled tissue infiltration. The system exerted osteoimmunomodulatory effects through coordinated ROS scavenging and macrophage regulation. Molecular hydrogen reduced intracellular oxidative stress, whereas Mg²⁺ ions further contributed to the regulation of inflammatory signaling. The hydrogel decreased the expression of the pro-inflammatory macrophage marker iNOS and increased the expression of Arg-1, indicating a shift toward an anti-inflammatory and pro-regenerative macrophage phenotype. It also reduced the secretion of TNF-α and IL-1β while increasing the levels of TGF-β and IL-10. Mechanistically, these effects were associated with inhibition of the IκBα/NF-κB signaling pathway.⁷⁷ Importantly, the immune effects were coupled with regulation of bone turnover. The Mg@PEG-PLGA hydrogel inhibited osteoclastogenesis while promoting osteogenic differentiation, thereby addressing the imbalance between bone formation and bone resorption characteristic of osteoporosis. This study demonstrates that ROS-regulated osteoimmunomodulation can be achieved through a combination of hydrogen therapy, therapeutic-ion release, and hydrogel-mediated local retention. Such strategies are particularly relevant to osteoporotic bone defects, in which oxidative stress, chronic inflammation, and osteoclast overactivation coexist.

Figure 6.

Schematic illustration of the mechanism by which the injectable Mg@PEG-PLGA hydrogel effectively promoted osteoporotic bone regeneration (adapted from Theranostics. 2024;14(9):3739–3759).⁷⁷

Antibacterial and Antioxidant Immune Regulation in Periodontal Bone Regeneration

Diabetes-associated periodontitis is characterized by bacterial infection, excessive oxidative stress, impaired host defense, and persistent inflammation-mediated alveolar bone loss. Ge et al developed a multifunctional hydrogel system for this complex microenvironment by incorporating self-assembled nanoparticles composed of chlorhexidine acetate and epigallocatechin-3-gallate into a GelMA/oxidized hyaluronic acid hydrogel matrix (Figure 7).⁷⁸ The resulting platform combined antibacterial, antioxidant, and immunomodulatory functions. The antibacterial component reduced the microbial burden that continuously drives inflammatory-cell activation and ROS production. Meanwhile, the antioxidant component reduced excessive oxidative stress within the periodontal lesion. This combination is important because infection and ROS accumulation reinforce each other. Bacterial virulence factors stimulate inflammatory ROS production, whereas oxidative injury further weakens periodontal tissue homeostasis and promotes inflammatory bone destruction. By targeting both processes, the hydrogel improved the local inflammatory microenvironment under diabetic conditions.⁷⁸ This study illustrates that osteoimmunomodulation in periodontal bone regeneration must extend beyond macrophage polarization alone. Effective immune regulation may require simultaneous control of bacterial infection, redox imbalance, inflammatory mediators, and impaired tissue repair. The integration of antimicrobial and antioxidant functions within a hydrogel matrix may therefore be particularly advantageous for diabetic periodontal lesions, where systemic metabolic dysregulation further complicates local immune resolution.

Figure 7.

Schematic depiction of (A) the fabrication of the GOE1 hydrogel, and (B) illustration detailing the role of GOE1 by reducing inflammation through the IL-17 pathway (adapted from Adv Mater. 2025;37(3):e2412240).⁷⁸ The upward arrows indicate increased expression or levels of the indicated cytokines or cellular markers.

Besides, Yao et al developed a pH/ROS dual-responsive hydrogel for inflammatory periodontal bone defects by dynamically crosslinking modified carboxymethyl cellulose and carboxymethyl chitosan to load sinapic acid.⁷⁹ It maintains periodontal immune homeostasis through long-term modulation of inflammation, oxidative stress, and macrophage behavior. Sinapic acid is a natural phenolic compound with antibacterial, antioxidant, and immunomodulatory properties. The dynamic hydrogel network enabled its sustained and microenvironment-responsive release under the acidic and oxidative conditions associated with periodontitis. In vitro and in vivo, the system reduced inflammatory-factor expression, decreased oxidative stress, and regulated macrophage polarization, thereby establishing a more favorable periodontal microenvironment for bone regeneration.⁷⁹ This work demonstrates that the immune-regulatory function of ROS-responsive hydrogels can be strengthened by integrating naturally derived anti-inflammatory compounds. It also highlights the value of dynamic networks, where bacterial activity, pH fluctuation, ROS accumulation, and inflammatory-cell infiltration vary over time. By coupling stimuli-responsive release with macrophage-directed immune regulation, the hydrogel supported regeneration of inflammatory periodontal bone defects rather than merely suppressing local inflammation.

Mild Photothermal Enhancement of ROS Scavenging and Osteoimmune Regulation

Song et al developed a photocurable GelMA/methacrylated poly(γ-glutamic acid) hydrogel containing polydopamine-modified black phosphorus nanosheets decorated with palladium nanoparticles (BP@PDA-Pd).⁸⁰ The composite hydrogel exhibited near-infrared responsiveness, enabling mild photothermal stimulation to enhance its antioxidant enzyme-like activity. Rather than relying solely on passive ROS scavenging, the platform allowed external photothermal stimulation to regulate the magnitude and timing of redox modulation. Under mild near-infrared irradiation, the hydrogel reduced local ROS levels and alleviated inflammation. More importantly, it promoted macrophage polarization toward an anti-inflammatory M2-like phenotype. The polarized macrophages secreted pro-osteogenic and pro-angiogenic growth factors, including BMP-2 and VEGF, thereby linking immune regulation to enhanced osteogenesis, vascularization, and endogenous stem-cell recruitment.⁸⁰ In an osteoporotic bone-defect model, the system improved bone regeneration through early immune modulation followed by promotion of angiogenesis and bone formation. This study provides a useful example of spatiotemporal osteoimmunomodulation. Mild photothermal treatment can be applied after implantation to enhance nanozyme-like antioxidant activity at selected time points, potentially allowing the material response to be adapted to the changing phases of bone healing. However, the thermal dose must be precisely controlled. Excessive heat exposure could aggravate inflammation, compromise surrounding cells, or alter the degradation behavior of the hydrogel.

Macrophage–BMSC Crosstalk for Osteoimmune Reconstruction

Wei et al designed a naringin carbon-dot complex hydrogel with ROS-scavenging, antibacterial, osteogenic, and osteoimmunomodulatory properties.⁸¹ The carbon-dot-based nanocomponents were incorporated into a hydrogel scaffold to create a local microenvironment capable of simultaneously reducing oxidative stress and regulating macrophage behavior. This multifunctionality is particularly useful for bone defects in which microbial contamination, ROS accumulation, and inadequate osteogenic signaling occur concurrently. The hydrogel promoted anti-inflammatory M2-like macrophage polarization and enhanced macrophage–bone marrow mesenchymal stem cell (BMSC) crosstalk.⁸¹ This interaction improved BMSC adhesion, proliferation, spreading, and osteogenic differentiation. Thus, the material did not promote bone formation only through direct effects on stem cells. It also established an immune-mediated paracrine environment that favored osteogenesis. This study emphasizes the importance of evaluating osteoimmunomodulatory hydrogels using multicellular models. Measurements limited to macrophage markers or osteogenic genes alone cannot fully capture the immune–bone interaction. Future studies should assess how hydrogel-regulated macrophages influence osteoblast-lineage cells, osteoclast precursors, endothelial cells, and sensory neurons. Collectively, these studies show that ROS-regulated osteoimmunomodulation is a central mechanism by which nanoengineered hydrogels improve bone regeneration. By reducing excessive ROS, these materials can limit prolonged inflammatory signaling, guide macrophages toward pro-regenerative states, suppress osteoclastogenesis, control infection, and enhance macrophage-mediated support of angiogenesis and osteogenesis.

Despite the promising regenerative outcomes reported for these systems, direct comparison reveals important differences in their therapeutic strengths and limitations. Since elevated ROS can trigger network cleavage, degradation, or cargo release, ROS-responsive delivery hydrogels provide a relatively high degree of pathological cue-dependent control. This feature can improve spatial and temporal matching between therapeutic delivery and oxidative injury, which may reduce unnecessary exposure under relatively physiological conditions. However, their performance depends strongly on the concentration, duration, and spatial distribution of ROS within the defect. Intrinsic ROS-scavenging hydrogels offer a more direct approach to redox-microenvironment remodeling without requiring a separate drug-release process. Their relative simplicity may be advantageous when persistent oxidative stress is a dominant pathological feature. Nevertheless, direct antioxidant activity is not inherently selective for pathological ROS. Excessive or prolonged scavenging may interfere with the physiological redox signaling. Compared with these two strategies, nanozyme-integrated hydrogels provide sustained catalytic regulation and can act on multiple components of the pathological metabolic–redox network. SOD-, CAT-, and GOx-like activities can be combined to make such systems particularly attractive for diabetic and hypoxic bone defects. However, cascade catalytic systems are also more difficult to control. The activities of sequential enzymes or enzyme mimetics must be carefully balanced to prevent excessive oxygen generation. ROS-regulated osteoimmunomodulatory hydrogels provide another level of biological control by linking redox remodeling with macrophage activity, osteoclastogenesis, antibacterial responses, angiogenesis, and osteogenesis. However, this broader biological activity also makes mechanistic evaluation more challenging. To complement this mechanistic comparison, we summarizes representative hydrogel systems for which explicit quantitative data are available, including ROS-regulating performance, mechanical properties, degradation behavior, osteogenic or immunomodulatory effects, and in vivo regenerative outcomes (Table 5).

Table 5.

Quantitative Comparison of Representative ROS-Regulating Hydrogels for Bone Regeneration

Hydrogel System	ROS-Scavenging/Catalytic Efficiency	Mechanical Properties	Degradation Behavior	Osteogenic/Immunomodulatory Performance	Quantitative in vivo Outcomes	Reference
PTHC hydrogel (PVA/TSPBA/nHA/curculigoside)	ROS-scavenging activity confirmed under oxidative conditions; no directly comparable percentage reported	Compressive modulus: 227.10 ± 95.69 kPa; gelation time <80 s	ROS-responsive degradation evaluated in 100 μM H2O2 over 30 d; degradation accelerated under oxidative conditions	ALP activity approximately 2-fold higher than the PTH group; enhanced BMP2, RUNX2, OPN, and OCN expression	Rat critical-sized calvarial defect, 8 weeks: BV/TV 33.46 ± 6.81%; BMD 0.30 ± 0.03 g/cm3; vascular volume 7.82 ± 1.16 mm3; CD31-positive area 12.66 ± 3.25%; VEGFA-positive area 9.02 ± 2.81%	[39]
AAT-ZCG hydrogel	At 2 mM Ce, ZCG inhibited 46.32% of superoxide generation within 1 min; CAT-like reaction increased oxygen concentration from 6.5 to 9.0 mg/mL	Storage modulus >700 Pa; tolerated strain up to 480%; self-healed hydrogel sustained approximately 800% deformation	Under ROS, rapid disintegration within 1 h and complete disintegration by 48 h. In vivo remaining hydrogel: 24.2% at 7 d, 12.3% at 14 d, 7.7% at 21 d; nearly complete at 28 d and completely degraded by 42 d	Promoted osteogenesis and M2 macrophage polarization; quantitative cellular-marker values were mainly presented graphically	Diabetic rat cranial defect: BV/TV 0.49 ± 0.01 at 4 weeks and 0.67 ± 0.01 at 8 weeks; BS/BV 7.72 ± 0.18 at 4 weeks and 10.21 ± 0.39 at 8 weeks	[40]
GM/GM400 hydrogel (gallic-acid gelatin/Ti3C2 MXene)	Scavenged •OH and DPPH radicals; exact percentage not explicitly reported in accessible text	Compressive strength 44–75.6 kPa; compressive modulus 24–44.5 kPa	Quantitative degradation value not explicitly reported	Increased ALP secretion, calcium-nodule formation, and expression of ALP, OCN, and RUNX2; numerical fold changes not explicitly reported	Rat critical-sized calvarial defect; significant new bone formation reported, but explicit BV/TV/BMD values were not provided in accessible text	[56]
2Mg@PEG-PLGA hydrogel	Reduced intracellular and in vivo ROS through sustained H2 generation; exact ROS-reduction percentage not explicitly reported	Injectable phase-transforming hydrogel; quantitative modulus not reported in accessible text	Maintained pH at 7.02–7.85 during 28 d immersion; osteogenesis-supportive Mg2⁺ concentration of approximately 50–200 μg/mL was maintained; hydrogel was completely degraded by 8 weeks in vivo	Promoted M2 macrophage polarization, inhibited IκB/NF-κB signaling and osteoclastogenesis, and enhanced osteogenesis; quantitative marker ratios were mainly graphical	Osteoporotic rat femoral defect: approximately half of the defect was filled with new bone at 4 weeks, and the defect was almost filled at 8 weeks	[77]

Challenges and Future Directions

Despite substantial progress, ROS-regulating nanoengineered hydrogels remain at an early translational stage. However, the clinical development of such systems is complicated by the dynamic and heterogeneous nature of bone-defect microenvironments, the multifunctionality of nanoengineered platforms, and the limited standardization of preclinical evaluation. Future progress will require a shift from proof-of-concept demonstrations of reduced ROS levels toward rigorous evidence that materials restore stage-specific redox homeostasis, immune resolution, vascularization, and long-term bone function.⁸²

The Challenge of Defining Therapeutic Redox Windows and Stage-Specific Therapeutic Regulation

ROS is not uniformly detrimental during bone repair. Low and transient ROS levels participate in antimicrobial defense, cellular migration, angiogenesis, osteogenic differentiation, and bone remodeling. In contrast, persistent or excessive ROS can induce mitochondrial dysfunction, cellular senescence, inflammatory activation, and osteoclast overactivation.⁸³ Therefore, the major challenge is not simply to eliminate ROS, but to define the appropriate redox range for each stage of bone healing. This challenge is particularly relevant because ROS concentrations vary spatially and temporally within a defect.⁸⁴ The early inflammatory phase may require partial preservation of ROS-dependent host defense, whereas the subsequent reparative phase may benefit from attenuation of chronic oxidative stress. In addition, different pathological conditions exhibit distinct redox features. Aged bone defects are frequently associated with stem-cell senescence and mitochondrial dysfunction, diabetic defects are characterized by hyperglycemia-associated oxidative stress and impaired metabolic regulation, whereas infected periodontal defects involve bacterial stimulation, inflammatory ROS production, and local acidosis.^85–87 Future studies should evaluate multiple ROS species, including superoxide, hydrogen peroxide, hydroxyl radicals, and peroxynitrite, while considering local pH, glucose concentration, oxygen tension, inflammatory cytokines, and bacterial products. Real-time or longitudinal assessment of local redox status in vivo will be particularly important for determining whether hydrogels restore physiological redox homeostasis rather than causing excessive antioxidant suppression. Future hydrogels should also incorporate stage-specific therapeutic functions. For example, early-stage systems may prioritize infection control, moderation of excessive inflammation, and partial ROS reduction. At later stages, therapeutic activity should gradually decline to permit physiological bone remodeling and matrix maturation. Such temporal regulation may be achieved through sequential crosslink cleavage, layered or compartmentalized hydrogel structures, controlled nanoparticle degradation, or multiple carriers with different release kinetics. Importantly, the optimal therapeutic redox window is unlikely to be universal because aged, diabetic, osteoporotic, and infected bone defects exhibit different ROS sources, concentrations, and temporal profiles. Future ROS-regulating hydrogels should therefore incorporate disease-specific response thresholds and temporally adaptive regulation to suppress pathological ROS while preserving physiological redox signaling.

Safety and Degradation of Nanoengineered Components

The incorporation of nanomaterials provides powerful redox-regulating functions but introduces additional biosafety concerns. Transition-metal nanozymes, including cerium-, manganese-, cobalt-, platinum-, and iron-containing materials, may exhibit long-term retention, ion release, altered catalytic activity, or off-target biodistribution during degradation.⁸⁸ Similarly, MXene nanosheets, carbon dots, black phosphorus, and other nanomaterials require careful evaluation of degradation products, oxidative transformation, cellular uptake, and clearance pathways.⁸⁹ Hydrogel degradation should also be matched to the time course of tissue repair.⁹⁰ Hydrogels that degrade too rapidly may lose mechanical support and therapeutic function before sufficient bone formation occurs. Conversely, excessively persistent hydrogels or nanoparticles may interfere with remodeling, induce chronic foreign-body responses, or complicate clinical imaging and revision surgery. In all cases, safety assessment should include dose-dependent studies and evaluation in clinically representative large-animal models. Most ROS-regulating hydrogels have been evaluated in small-animal calvarial, femoral, or periodontal-defect models.⁹¹ Although these models are useful for initial validation, they often do not reproduce the scale, load-bearing environment, vascularity, immune complexity, and mechanical demands of human bone defects. Small-animal models may also underestimate the effects of chronic comorbidities. Large-animal studies will be particularly important for evaluating hydrogel injectability, defect filling, local retention, degradation, mechanical stability, surgical handling, and long-term bone integration. Future studies should also employ disease-relevant models that better reflect clinical applications. Establishing common evaluation frameworks would improve comparison across platforms and facilitate identification of materials with genuine translational potential.

Manufacturing, Sterilization, Regulatory, and Commercialization Considerations

The clinical translation of nanoengineered hydrogels will depend on reproducible and scalable manufacturing. Many current systems involve multistep nanoparticle synthesis, complex surface modification, dynamic crosslinking, or encapsulation of biologically sensitive proteins and enzymes. These processes may introduce batch-to-batch variability in nanoparticle size, catalytic activity, drug loading, crosslinking density, degradation behavior, and release kinetics. Sterilization represents another major challenge. Gamma irradiation, ethylene oxide, filtration, and heat treatment may alter polymer networks, degrade bioactive proteins, change nanozyme activity, or induce premature oxidation of ROS-responsive linkers. Therefore, sterilization procedures must be optimized specifically for each formulation.⁹² Long-term storage stability, lyophilization compatibility, transport requirements, and point-of-care preparation should also be considered during early material design. Regulatory evaluation will be especially complex for combination products containing hydrogels, nanomaterials, drugs, proteins, therapeutic ions, or catalytic enzymes. To facilitate translation, future studies should define critical quality attributes, including mechanical properties, degradation rate, nanoparticle distribution, catalytic activity, endotoxin level, sterility, payload stability, and in vitro release behavior. Beyond regulatory evaluation, commercialization will require translation from laboratory-scale synthesis to reproducible, scalable, and quality-controlled production. Complex multicomponent systems may require multiple nanoparticle-synthesis, surface-modification, crosslinking, loading, and purification steps. Consequently, early-stage material development should consider not only biological performance but also raw-material availability, process robustness, sterilization compatibility, shelf stability, packaging, transportation, and ease of clinical preparation. Establishing well-defined critical quality attributes and acceptable manufacturing ranges will be essential for ensuring consistent mechanical properties, degradation behavior, catalytic activity, payload release, and biological performance during scale-up.

Future Opportunities for Personalized and Multimodal Bone Regeneration

Future ROS-regulating hydrogels are likely to evolve from general antioxidant materials toward personalized, disease-specific regenerative platforms. Different clinical contexts require distinct therapeutic priorities. Multimodal strategies may further improve therapeutic efficacy by integrating redox regulation with gene delivery, extracellular vesicles, immunoregulatory peptides, oxygen modulation, bioactive ions, photothermal stimulation, or mechanical reinforcement.⁹³ However, the design principle should be rational integration rather than indiscriminate addition of functions. Each component should address a clearly defined pathological mechanism, and the overall system should retain controllable degradation, safety, manufacturability, and clinical usability. Designing simpler systems with clearly defined components and reproducible manufacturing processes may ultimately be more clinically realistic.

Key Unresolved Research Questions and Priorities

Despite rapid progress in ROS-regulating nanoengineered hydrogels, several fundamental questions remain unresolved and should be prioritized in future investigations. What constitutes an optimal therapeutic redox window for different bone-defect conditions and healing stages? Future studies should longitudinally characterize multiple ROS species, including superoxide, hydrogen peroxide, hydroxyl radicals, and peroxynitrite, together with local pH, oxygen tension, glucose concentration, inflammatory mediators, and other disease-specific parameters. Which ROS species, cellular sources, and subcellular compartments should be targeted? Future investigations should distinguish extracellular from intracellular ROS regulation and determine whether targeting specific ROS sources or subcellular compartments provides advantages over broad antioxidant suppression. How can causal interactions among redox regulation, immune modulation, angiogenesis, osteogenesis, and osteoclastogenesis be established? Future studies should employ temporally resolved multicellular models and determine how hydrogel-regulated macrophages influence osteogenic progenitors, osteoclast precursors, endothelial cells, and other components of the regenerative niche.

Conclusion

ROS-regulating nanoengineered hydrogels are evolving from passive antioxidant materials toward active regulators of the bone-regenerative microenvironment. Across ROS-responsive delivery, intrinsic scavenging, nanozyme-mediated catalysis, and osteoimmunomodulation, the central design principle is not to eliminate ROS as completely as possible, but to restore an appropriate redox state while preserving physiological ROS-dependent signaling. Therefore, the therapeutic value of these systems depends on matching the magnitude, location, and duration of redox regulation to the dominant pathological mechanism and stage of bone healing. From this perspective, increasing material complexity or multifunctionality is not inherently advantageous unless it produces more precise control of the redox–immune–bone network. In the future, the most effective strategy may achieve sufficient and temporally appropriate correction of pathological oxidative stress to permit inflammation resolution, vascularization, osteogenesis, and balanced bone remodeling.

Funding Statement

There is no funding to report.

Disclosure

The author(s) report no conflicts of interest in this work.