Under physiological conditions, as the major cellular ROS producer, the ETC generates free radicals through unavoidable electron escape during adenosine triphosphate (ATP) synthesis. These leaked electrons readily react with molecular oxygen, generating ROS species, such as O^2-. Mitochondrial-derived ROS represent one of the primary pathogenic mediators in OS development due to their continuous production during aerobic respiration [31]. Its initial site of generation is usually considered to be the semiquinone radical (QH^•) or reduced flavin (FMN and FAD). At mitochondrial respiratory Complex I (CI), O^2- may be generated at either the flavin or I_Q site and partitions completely into the mitochondrial matrix. In mitochondrial respiratory Complex III (CIII), O^2- is produced at the Qo site and released into the membrane space and matrix [32]. The vast majority of physiological ROS originates from the electron leakage at CI and CIII, and a small fraction arises from the direct electron leakage from the 3Fe-4S cluster of mitochondrial respiratory Complex II (CII) to oxygen, yielding O^2- [33]. At physiological concentrations, appropriate amounts of ROS are essential factors involved in SCs signaling and metabolic regulation.

Moreover, in pathological niches with intact glia-neuron units, drastic microenvironmental changes trigger significant Ca²⁺ influx through activation of SC surface channels such as TRPA1. This aberrant Ca²⁺ accumulation serves as the priming factor for subsequent mitochondrial dysfunction [34, 35]. Mechanistically, Kievit et al. observed in an in vitro axotomy model that mitochondrial ROS production preceded late-stage Ca²⁺ entry [36]. Owever, this sequence likely reflects a distinctive phenotype of glia-free isolated axon systems. In this highly simplified model, severed axons lack physical ensheathment and metabolic support from SCs. They undergo rapid, autonomous NAD⁺ depletion, which triggers intrinsic mitochondrial collapse and places mitochondrial ROS generation upstream of channel activation. Consequently, in in vivo, ex vivo, or co-culture systems with preserved SC-axon communication, extrinsic glia-derived oxidative stress and localized Ca²⁺ perturbations typically dominate the induction of mitochondrial dysfunction.

The Nox family remains as enzymes that specialize in ROS generation and still play a significant role, with members including NOX1, NOX2 (gp91phox), NOX3, NOX4, NOX5, and DUOX1 and DUOX2 [37]. The distribution of members of this family varies in the peripheral nervous system: dorsal root ganglion neurons express Nox1, Nox2, and Nox4, macrophages express Nox2 and Nox4, and SCs express Nox1 and Nox4 [38]. Due to the structural homology of Nox enzymes, the core mechanism of ROS production is basically the same. This reactive species subsequently undergoes dismutation, either spontaneously or via superoxide dismutase (SOD) catalysis, yielding H₂O₂. The subsequent fate of H₂O₂ is highly dependent on the local microenvironment. H₂O₂ undergoes the Fenton reaction catalyzed by transition metal ions, involving Fe²⁺, generating OH⁻. In the absence of such ions, residual H₂O₂ serves as a substrate for myeloperoxidase (MPO) to generate hypochlorous acid (HOCl), a potent oxidant involved in innate immune responses [39].

Distinct activation modes represent a key factor underlying the functional diversity among enzymes of the Nox family [38]. Regarding Nox1 expressed in SCs, De Logu et al. demonstrated that ROS derived from macrophage Nox2 activate Transient Receptor Potential Ankyrin 1 (TRPA1) channels in SCs, leading to calcium influx and subsequent activation of Nox1. The oxidative product released by activated Nox1 is H₂O₂. Additionally, a high-glucose environment serves as a key activator of Nox4 in Schwann cells. Elevated blood glucose levels inhibit the liver X receptor (LXR) pathway in macrophages, thereby relieving its transcriptional repression on Nox4. This approach leads to upregulated Nox4 expression and subsequently results in massive ROS production [40].

IRI is a biphasic pathological process comprising ischemic and reperfusion phases [37, 41]. At the ischemic stage, blockage of oxidative phosphorylation in mitochondria results in the cessation of ATP synthesis, ionic homeostasis imbalance, calcium overload, intracellular acidosis, and accumulation of succinate [42]. Among these changes, succinate is a mitochondrial metabolite, and evidence suggests that the tissue-specific retention of this molecule serves as a metabolic signature of ischemia, while also functioning as a critical mediator of reperfusion-induced oxidative damage. Under normal physiological conditions, the proton drive (Δp) is less than the redox drive (ΔEH) to maintain the membrane potential (ΔΨm) required for ATP synthesis. However, metabolic alterations during hypoxia invert the relationship (Δp > ΔEH), and this is further exacerbated during reperfusion. Then the abrupt rise in oxygen availability during reperfusion facilitates the rapid oxidation of accumulated succinate by succinate dehydrogenase. This process leads to a burst of electron flow into the mitochondrial respiratory chain, resulting in a marked depletion of the reduced coenzyme Q pool. These changes ultimately initiate Reverse Electron Transport (RET), in which electrons from ubiquinol are reversed and transferred back to CI, and RET triggers a burst of ROS during reperfusion at CI [43, 44]. RET acts as a key amplifier of OS effects during reperfusion, perpetuating a self-reinforcing vicious cycle that exacerbates oxidative damage (Figure 3).

Despite the tissue-specificity of OS mechanisms in different tissues (e.g., neural, cardiac, hepatic, renal), the highly conserved structure of the mitochondrial ETC makes theoretical migration between tissues possible [45]. Moreover, there is evidence that ischemic reperfusion injury secondary to PNI induces an oxidative burst [46, 47]. However, the initiation sites and regulatory mechanisms of ROS generation following RET remain poorly characterized, with limited studies available. In contrast, numerous studies based on myocardial ischemia–reperfusion models have elucidated the mechanism of RET and identified complex I as the primary site of RET-induced ROS production [48]. Thus, these findings in cardiac research may serve as a valuable reference for exploring similar mechanisms in SCs models. Based on this, they can seek clues to formulate hypotheses that are applicable to the PNI model and test them experimentally. This approach could facilitate fundamental exploration at the level of OS mechanisms.

In the OS state, polyunsaturated fatty acids (PUFAs) on the SC membrane are the primary targets of ROS damage. Among these, the essential fatty acids n-6 and n-3 are required for standard membrane structure and fluidity as well as for arachidonic acid-like production. Not only do ROS directly attack PUFAs, leading to disruption of cell membrane integrity, but lipid peroxides generated by this process also cause neurological changes such as axonopathy and demyelination when accumulated over time [49]. Moreover, as PUFAs are ubiquitously present in the phospholipid bilayer of organelle membranes, ROS can also damage the subcellular structures of SCs, such as altered mitochondrial membrane permeability and endoplasmic reticulum stress.

Crucially, the progression from general oxidative damage to ferroptosis in SCs is tightly linked to the collapse of the endogenous antioxidant defense system under sustained OS [50]. Excessive ROS generation rapidly depletes intracellular glutathione (GSH), which subsequently inactivates Glutathione Peroxidase 4 (GPX4). As GPX4 is the primary enzyme responsible for reducing toxic lipid hydroperoxides to non-toxic lipid alcohols, its OS-induced inactivation removes the critical brake on lipid peroxidation [51]. Furthermore, severe OS can impair System Xc- (SLC7A11), restricting cystine uptake and exacerbating GSH depletion, thereby forming a vicious cycle that sensitizes SCs to ferroptosis [52].

In addition, the Fenton reaction triggered by excessive H₂O₂ and ferrous ions (Fe²⁺), in SCs would induce ferroptosis [53]. Iron death is an iron-dependent form of non-apoptotic cell death, and the response is mediated by increased intracellular iron content and Acyl-CoA Synthetase Long-Chain Family Member 4 (ACSL4) expression. Divalent iron catalyzes the Fenton reaction, initiating lipid peroxidation that disrupts and ruptures the SC membrane, ultimately resulting in cell death. ACSL4 exacerbates the damage to the cell membrane by increasing the content of polyunsaturated fatty acids in the cell membrane, making the lipid peroxidation reaction more prone to occur. In contrast, knockdown of the ACSL4 gene significantly suppresses lipid peroxidation and iron-mediated cytotoxicity, while the morphology and function of the cell membrane are better maintained [54] (Figure 4). These results underscore the critical role of ROS in mediating ferroptosis in SCs and highlight the targeted inhibition of ferroptosis as a highly promising therapeutic strategy for mitigating OS-induced damage and enhancing SC survival.

In the context of peripheral neuropathy and nerve regeneration, OS-induced SC ferroptosis has profound pathological consequences. It not only directly leads to demyelination [55], but also disrupts local iron homeostasis and releases lipid peroxides into the microenvironment [56]. This toxic milieu exacerbates neuroinflammation and impedes macrophage-mediated myelin debris clearance, ultimately creating a hostile environment that severely hinders axonal regrowth and subsequent remyelination [56]. These results underscore the critical role of ROS in mediating SC ferroptosis. They also highlight targeted ferroptosis inhibition as a highly promising therapeutic strategy. This approach could mitigate OS-induced damage while enhancing SC survival and overall nerve regeneration [57].

SCs can remove myelin sheaths, guide axonal regeneration, and provide the physical structural and trophic support that will, in turn, promote Neural repair of peripheral nerves [58]. However, OS directly or indirectly impairs the repair capacity of Schwann cells through a multidimensional mechanism that impairs the following: (1) Proliferation limitation: OS significantly inhibits the proliferation and survival of SCs, and its effects are dose-dependent but do not lead to a complete arrest of SCs’ proliferation in the concentration range studied [54, 59]. (2) Inhibition of neurotrophic factor secretion: Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) can promote the migration of SC [60]. In Ma et al.'s experiments, H2O2-induced OS significantly decreased the levels of BDNF and NGF secreted by SCs [61]. (3) Extracellular matrix alterations: the extracellular matrix (ECM) regulates SCs’ proliferation, migration, and myelin formation [62]. It has been demonstrated in spinal cord injury studies that excess ROS can cause degradation of key scaffolding components, such as laminin and fibronectin, in the extracellular matrix ECM, destroying the physical support structures necessary for axonal regeneration [63]. Peripheral nerve tissue is also rich in similar ECM components, such as laminin and fibronectin [62]. Therefore, OS may similarly damage this ECM and impair nerve regeneration. In addition, the OS conditions in peripheral nerve tissues contributed to the dysfunction of mitochondrial metabolism, immunomodulation, and other functions in SCs [64, 65]. If SCs are in a high-glycemic environment, OS will synergistically exacerbate the metabolic disturbances of the cells [66]. The above interactions between the pathologic microenvironment and SCs will be further developed in subsequent sections (Figure 5).

ROS function as pivotal signaling mediators in the context of cellular injury, orchestrating adaptive responses, damage resolution, autophagic homeostasis, and intracellular signal transduction [67]. Such regulatory roles of ROS are particularly prominent in the repair process following PNI. Upon activation of the repair program, SCs undergo a series of coordinated stages, including dedifferentiation, microenvironmental remodeling, the secretion of neurotrophic factors, and axonal regeneration. Each stage critically depends on the dynamic balance between ROS generation and elimination.

It is worth noting that ROS are not merely harmful metabolic byproducts. Recent studies have demonstrated that injury-induced H₂O₂ acts as a pro-regenerative signal. Negro et al. showed that H₂O₂ activates ERK1/2 and c-Jun to drive Schwann cell phenotype conversion. Simultaneously, it upregulates Ctgf via YAP/TEAD to remodel the ECM, which guides Schwann cell migration and oriented axonal growth [68, 69]. Moreover, ROS exhibit stage-specific regulatory effects during nerve repair, driven by a concentration window phenomenon. At certain phases, maintaining an appropriate level of ROS can positively influence SC behavior. This underscores the dose-dependent and temporally specific nature of ROS signaling in the SC-mediated repair process. For instance, during the dedifferentiation phase, SCs may increase ROS production to activate pro-proliferative signaling pathways, thereby facilitating adaptive cellular responses and promoting proliferation [70]. While moderate levels of ROS facilitate intracellular signaling and cytoskeletal remodeling during the axon guidance stage, they also contribute to growth cone navigation. Furthermore, ROS participates in bidirectional interactions with the autophagy system via the mTOR pathway. This interplay helps sustain the metabolic homeostasis of SCs [71].

In summary, the generation and elimination of intracellular ROS is a tightly regulated process, and the maintenance of redox equilibrium is essential for preserving normal cellular physiology. Consequently, dynamic and accurate regulation of intracellular ROS levels across different stages of nerve injury and repair is a crucial determinant of SCs’ repair capacity and successful peripheral nerve regeneration [72–74].

At the molecular level, this precise regulation relies heavily on the dynamic equilibrium between two core signaling networks: pro-survival and pro-apoptotic pathways [57]. Excessive in vivo ROS can directly or indirectly activate multiple intracellular signaling pathways, influencing cell fate by regulating gene expression. In pro-survival signaling, ROS promote cell survival by triggering pathways such as Nrf2/ARE, MAPK/ERK, PI3K/Akt, and NF-κB [29, 75–77], which upregulate the expression of molecular chaperones. Conversely, in pro-apoptotic signaling, elevated ROS activate the JAK/STAT, ATM/p53, and MAPK/JNK/p38 pathways [46], enhancing the expression of pro-apoptotic proteins such as Bax and Caspase-3, ultimately leading to cell apoptosis. Therefore, achieving a dynamic balance between these opposing pathways through the precise regulation of key signaling nodes represents a central mechanism for governing SC survival.

This molecular foundation enables the manipulation of ROS kinetics through engineering strategies. For example, mung bean-derived carbon dots (MB-CDs) activate Nrf2 and downstream Heme Oxygenase-1 (HO-1) and GPX4, converting hemoglobin into CO, Fe²⁺, and bilirubin to halt SC ferroptosis via lipid peroxidation inhibition [30]. Similarly, porous nanocomposites effectively activate the PI3K/Akt signaling pathway through the sustained release of selenium, reducing ROS generation while suppressing apoptosis, and endowing cells with enhanced migration and nerve regeneration capabilities [75].

These mechanisms construct a systematic framework for ROS regulation: applying active substances restores intracellular anti-oxidation and anti-apoptosis homeostasis, while biocompatible slow-release materials, such as nanoplatforms or hydrogels, enhance spatiotemporal targeting during nerve regeneration. Integrating fragmented pathway research into a synergistic oxidative stress network deepens the understanding of ROS dynamics and provides a solid theoretical foundation [76, 77] for coupling molecular mechanisms with physical stimuli, such as biomimetic matrix topographies, to strategically tailor therapeutic intracellular responses.

Understanding and precise monitoring of this dynamic balance is a prerequisite for intervening in the ROS-SC interaction. Nevertheless, molecular characteristics such as millisecond half-life and complex diffusion kinetics pose a significant challenge for its accurate detection. Currently, commonly employed methods for ROS detection include electron paramagnetic resonance (EPR), fluorescent staining, chemiluminescence, chromatographic techniques, spectrophotometry, electrochemical biosensors, and fluorescent protein-based approaches. However, these mainstream detection techniques still exhibit various limitations [78]. To facilitate a critical assessment of these methods, we have synthesized their key advantages and limitations in Table 1, providing a comprehensive perspective on their utility for monitoring ROS dynamics in nerve regeneration research.

In conclusion, excessive OS disrupts SC function via ferroptosis and signaling impairments. However, SCs counteract this redox imbalance through intrinsic antioxidant defenses, a self-rescue mechanism that forms the biological basis for the biomaterial designs discussed in the next section.

Following recognition by autophagy receptors, damaged mitochondria are sequestered into autophagosomes characterized by a double-membrane structure. These autophagosomes then fuse with lysosomes, where lysosomal hydrolases ultimately degrade the enclosed mitochondria [89]. This process helps alleviate oxidative damage by clearing dysfunctional organelles and degrading protein aggregates, thus limiting further ROS production. It is involved in preserving cellular homeostasis while actively facilitating tissue repair processes within the injury microenvironment [90].

The specific mechanisms are as follows: (1) PTEN-induced putative kinase 1/Parkin (PINK1/Parkin)pathway: OS-induced mitochondrial dysfunction or structural damage reduces ΔΨ_m, thereby preventing PINK1 translocation into the inner mitochondrial membrane for degradation. Instead, PINK1 accumulates on the outer mitochondrial membrane, where it recruits and activates the E3 ubiquitin ligase Parkin. Parkin, in turn, tags damaged mitochondria by ubiquitinating their outer membrane proteins. Autophagy receptors, such as p62/SQSTM1, subsequently recognize these ubiquitinated proteins and interact with autophagy-related proteins, like LC3, to initiate autophagosome formation. This process ultimately delivers the sequestered mitochondria to lysosomes for degradation [91]. (2) NIX/BCL2 Interacting Protein 3 (BNIP3) pathway: Under OS, the expression levels of BNIP3 and NIX are markedly upregulated. These proteins directly interact with LC3 via their LC3-interacting region (LIR), thereby initiating mitophagy [92]. (3) FUN14 Domain-Containing Protein 1(FUNDC1) pathway: FUNDC1 is an outer mitochondrial membrane protein that primarily initiates mitophagy by interacting with LC3 [93]. These pathways act synergistically to preserve mitochondrial functional homeostasis by eliminating damaged mitochondria and reducing ROS accumulation, thereby playing a pivotal role in maintaining cellular equilibrium and promoting repair following PNI.

The AMPK and Mechanistic Target of Rapamycin (mTOR) signaling pathways play key roles in regulating macroautophagy in SCs. The occurrence of OS is accompanied by enhanced SC activity and increased energy consumption. The resulting low-glucose environment enables AMPK to directly activate Unc-51-Like Kinase 1(ULK1) through phosphorylation at Serine 317 and Serine 777. As the key initiator kinase of autophagy, ULK1 promotes autophagy in SCs upon activation to counteract energy stress. Concurrently, ROS elevates the AMP/ATP ratio, which activates AMPK and induces autophagosome formation. This process clears damaged cellular components, thereby reducing further ROS production and exerting an indirect antioxidant effect. However, under nutrient-sufficient conditions (a high-glucose environment), mTOR signaling phosphorylates ULK1 at Ser757 and disrupts the interaction between ULK1 and AMPK, blocking ULK1 activation and preventing excessive autophagy in SCs [94, 95]. Taken together, this mechanism is bidirectionally and precisely regulated by nutrient availability, leading to the activation or inhibition of ULK1 through the AMPK and mTOR signaling pathways, respectively. Although ULK1 regulation produces divergent effects on SCs, the net outcome is the same: maintaining cellular survival and function. Elucidating the interplay between autophagy and antioxidant mechanisms in SCs will aid the development and validation of targeted therapies.

Based on pore size, NGCs can be categorized into large-pore, small-pore, and multi-channel scaffold types. These structural features directly influence cellular behavior, mass exchange, and ultimately the efficacy of nerve regeneration [116–118]. Therefore, designing the ideal pore size of NGCs requires in-depth consideration of its decisive role in determining the fate of Schwann cells within the OS microenvironment. Studies have shown that sufficiently large channels and highly interconnected porous structures can effectively promote the ingrowth of new blood vessels and the exchange of nutrients. [119, 120]. This is critical for reversing the energy depletion of Schwann cells caused by mitochondrial dysfunction under oxidative stress. Furthermore, the open three-dimensional structure provides space for early infiltration of immune cells, particularly macrophages, facilitating their polarization toward the alternatively activated macrophage(M2) pro-regenerative phenotype. This, in turn, accelerates the clearance of myelin debris exacerbated by oxidative stress and fundamentally breaks the vicious cycle of inflammation and oxidative stress [119].

In contrast, scaffolds with excessively small pores, while physically blocking fibroblast invasion and reducing fibrotic scar formation, may simultaneously act as a physical barrier, limiting Schwann cells from obtaining sufficient oxygen and nutrients [119].Under oxidative stress, this nutrient-restricted environment renders Schwann cells more susceptible to ferroptosis, ultimately leading to regeneration failure [121].Thus, an ideal NGC should not be a single homogeneous structure, but rather should possess graded pore sizes or composite pore architectures, so as to ensure the metabolic demands and viability of Schwann cells under stressful conditions while providing topographical guidance.

Based on the above biological requirements, researchers have developed various multilevel channel structures. For example, Maeng et al. constructed a GelMA/PECDA multichannel nerve conduit with good biocompatibility. The 200-μm main channel, combined with micro/nanoporous structures on the inner wall, acted synergistically to significantly enhance nerve regeneration efficiency in animal experiments [122]. Another approach exerts its effects by regulating the cell growth environment. Wang et al. utilized radial and longitudinal foaming techniques to flexibly adjust the pore size distribution of PCL/PVP fiber scaffolds, such that the dimensional variations of the nanoscale grooves effectively guided the directional migration of Schwann cells from the periphery to the center and from the bottom to the top of the scaffold, significantly improving cell infiltration efficiency [123].

In summary, while multichannel conduits excel at providing macroscopic guidance to enhance nerve regeneration efficiency, gradient foaming scaffolds utilize nanoscale groove variations to precisely direct the migration and infiltration of SCs from the periphery to the center. Both strategies demonstrate that over-reliance on uniform pore sizes is problematic, as excessively large channels may lack topographical precision, whereas excessively small pores act as a physical barrier that induces nutrient restriction and SC ferroptosis under oxidative stress. Therefore, the ideal NGC must adopt graded or composite pore architectures to balance vascular nutrient exchange with topographical guidance.

The nature of the material is one of the core elements determining the function of NGCs and is a key research direction in neural tissue engineering [124, 125]. The material system has evolved from natural to synthetic and composite materials, with progressive optimization of their respective performance merits enabling structurally and functionally synergistic integration. Natural materials have garnered significant attention due to their excellent biocompatibility. These materials can be broadly categorized into two types. One type consists of biological tissue-derived materials such asECM. The other type includes natural polymers such as chitosan (CS), collagen, hyaluronic acid (HA), and fibrin [126, 127]. A representative example is CS, whose reactive amino groups along the molecular chain enable diverse chemical modifications, endowing it with excellent biological properties. As a result, CS is considered a highly promising biomaterial for nerve repair. Other natural polymers such as collagen, alginate, and glycosaminoglycans have also shown great potential in this field [128–130]. Li et al. [131] fabricated a nerve conduit by combining biocompatible CS with biodegradable HA. This conduit effectively promoted the proliferation of SCs while inhibiting excessive fibroblast growth, thereby reducing scar formation and tissue adhesion, and ultimately facilitating peripheral nerve repair and regeneration. By comparison, synthetic materials such as polylactic acid (PLA), polyglycolic acid (PGA), and polycaprolactone (PCL) exhibit superior mechanical strength and elasticity [132, 133]. To overcome the limitations of single-material properties, composite materials are designed to integrate the advantages of multiple components, aiming to construct NGCs with enhanced functional performance and improved adaptability to the native tissue environment. Beyond their intrinsic physicochemical properties, the selection of these materials must consider their ability to modulate SC redox homeostasis—a criterion that increasingly guides the development of next-generation NGCs.

In light of the increasingly diverse range of available biomaterials, researchers must establish a comprehensive evaluation framework that explicitly links each material property to SC fate under oxidative stress: (1) Biohistocompatibility: Traditionally, the concept of biohistocompatibility referred primarily to the absence of harmful responses within the host.

Contemporary definitions, however, require more than just compliance with basic safety parameters such as non-toxicity and non-carcinogenicity. Increasingly, emphasis is being placed on the material’s ability to engage in dynamic, bidirectional interactions with host tissues and to adapt to the local biological environment [134, 135]. Jin’s team [136] embedded a urolithin A (UA) hydrogel, which is known for its anti-inflammatory and antioxidant properties, into the lumen of a PCL-based UA NGC. This strategy effectively reduced ROS production and inflammation by leveraging the material’s adaptive response to the microenvironment. (2) Biodegradation rate: The biodegradation rate plays a critical role in determining the pace and effectiveness of nerve regeneration. Fast-degrading materials such as CS, gelatin, and PLGA typically degrade within weeks to months, making them well-suited for acute nerve repair. While slow-degrading materials like PCL may take several months or even years to degrade, they offer prolonged and stable microenvironmental support for the regeneration of long-segmental nerve defects [137–140]. (3) Mechanical properties: Mechanical properties, as fundamental attributes of material performance, play a critical role in ensuring the functional integrity of nerve conduits under complex physiological conditions [141]. Insufficient compressive strength compromises the material’s ability to withstand dynamic pressure and tensile forces during peripheral nerve regeneration, whereas excessive rigidity may inflict mechanical damage on nerve stumps and regenerating microvessels [142]. Type I collagen, for instance, is widely employed as a base material for NGCs due to its excellent biocompatibility, biodegradability, and low immunogenicity. However, its inherently poor mechanical strength poses a risk of structural collapse [143, 144]. To overcome this limitation, Duan et al. [145] developed a mineralized collagen composite conduit by integrating mineralized collagen with type I collagen. This strategy significantly improves the compressive strength of the conduit while maintaining its bioactivity, thereby enhancing its potential for clinical application [146]. This multidimensional evaluation framework calls for researchers to move beyond the limitations of single-performance metrics and achieve synergistic improvements in bio-responsiveness and functional durability through strategies such as biomimetic design and composite modification (Table 3). Each material category inherently presents a distinct trade-off between bioactivity and physical robustness, prompting the field to increasingly favor composite and biomimetic designs that reconcile these competing demands while introducing new challenges in fabrication reproducibility and long-term in vivo stability.

Excessive rigidity disrupts the delicate mechanical microenvironment, which renders SCs increasingly vulnerable to OS [147]. Emerging evidence suggests that the ideal matrix stiffness should mimic the native neural ECM, modulating cell behavior through integrin-mediated mechanotransduction [148, 149]. Furthermore, material mechanical properties function as active regulators rather than passive supports [150]. SCs transduce physical stimuli, such as matrix stiffness or mechanical stretching, into biochemical signals through integrin-mediated mechanotransduction and mechanosensitive channels [141, 150]. This mechanochemical coupling facilitates the homeostasis of pro-survival signaling pathways and metabolic fitness, creating a synergistic framework where material engineering actively participates in biological regeneration.

Electrophysiologic homeostasis of nerve cells is the basis for maintaining the physiologic function of the nervous system [13]. Neuroinjury-induced oxidative stress not only exacerbates microenvironmental deterioration by triggering a surge of proinflammatory cytokines and aberrant protease secretion but also critically disrupts the functional integrity of voltage-gated ion channels, such as Na⁺/K⁺-ATPase [151–153]. Specifically, ROS can induce thiol-oxidizing modifications that alter the conformation of ion or protein channels on the neuronal membrane, resulting in a marked prolongation of the action potential refractory period and consequently disrupting neuronal electrical signaling [154, 155]. This dual disruption of the electrochemical microenvironment initiates a vicious cycle: oxidative stress aggravates environmental deterioration and impairs the myelin regenerative capacity of SCs, and impaired action potential conduction suppresses the secretion of neurotrophic factors. Together, these effects culminate in the failure of axonal regeneration.

Based on this, the design of the new generation of conductive bioscaffolds has evolved from the traditional concept of electrical conductivity to the “electroactivity-modulated” smart materials [156, 157]. Fundamentally, the material must integrate efficient charge transport across the cell-substrate interface with the capacity to modulate both cell-substrate and cell-cell interactions [158–162]. These materials contribute to the optimization of the nerve regeneration microenvironment through several mechanisms. They promote the adhesion of SCs and growth factors, facilitating initial cellular integration. They also modulate cell–matrix interactions to fine-tune the scaffold’s molecular architecture and surface charge distribution. Moreover, they enable functional electrical coupling between the scaffold and host tissues, which is essential for neuromodulation and signal conduction [163]. For example, graphene-based composite scaffolds, owing to their unique sp²-hybridized orbital structure, can establish a three-dimensional conductive network that promotes electrical coupling among SCs. Additionally, the abundant π-electron cloud on their surface enables efficient scavenging of oxidative species such as OH⁻, thereby achieving a synergistic enhancement of both electrical conductivity and antioxidant capacity [162, 164, 165].

Biologically, this graphene-mediated microenvironment optimization facilitates the dual activation of Schwann cells in the peripheral nervous system and astroglia in the central nervous system. In vivo evidence confirms that this translates to robust remyelination by upregulated MBP and restored functional electrical coupling, significantly increasing nerve conducting velocity and compound motor action potentials compared to pure PCL controls [165].

Moreover, conductive scaffolds are not merely physical conductors of electrical current; more importantly, the weak electrical signals they induce can act as exogenous biophysical signals that activate endogenous calcium signalling in Schwann cells [166] and downstream FAK/AKT pro-survival pathways [167]. This, in turn, counteracts the OS microenvironment [74] and ultimately reverses the OS-induced suppression of neurotrophic factor (e.g., BDNF and NGF) secretion by Schwann cells [166, 167]. Notably, graphene-based scaffolds distinguish themselves from most conductive polymers by offering concurrent charge transfer and intrinsic ROS scavenging, whereas other conductive materials predominantly rely on exogenous biophysical stimulation to indirectly alleviate oxidative stress. This distinction underscores the growing importance of multifunctionality in scaffold design for the OS-compromised microenvironment.

Compared with conventional scaffolds, biomimetic ECM scaffolds mimic physiological structures, not only restoring anatomical integrity but also enabling targeted functional reconstruction [168]. Bionic ECM scaffolds reconstruct nanofiber networks mimicking basement membrane pore size and mechanical gradients via electrospinning, 3D printing, and other techniques, thereby accelerating guided axon regeneration and reducing ROS exposure time [169–171]. Such scaffolds provide not only physical support for regenerating tissues but also act as dynamic signaling platforms. Through the multimodal integration of bioactive molecules, anti-inflammatory agents, antioxidants, and conductive components, they enable precise regulation of the regenerative microenvironment [127, 172, 173].

As discussed in earlier sections, the OS environment induces mitochondrial metabolic dysfunction and homeostatic imbalance in SCs. Jiang et al. fabricated a multilayered conduit combining PCL nanofiber topology with blend-loaded melatonin (MLT) and reduced graphene oxide (RGO). Biologically, while RGO restores bioelectrical conduction, MLT maintains a stable ΔΨ_m as confirmed by JC-1 assay, which bioenergetically prevents the proton motive force reversal to abort the RET-induced ROS burst at Complex I and III. This metabolic rescue amplifies ATP supply for energy-demanding myelin regeneration, achieving functional and morphological recovery close to autologous nerve grafts in a 10-mm rat sciatic nerve defect model. Beyond chemical ROS-scavenging designs, the anisotropic physical topology of biomimetic ECMs (e.g., aligned nanofibers and microgrooves) independently drives directional SC migration and upregulates crucial myelination-associated genes, including Mbp and Sox10. Mechanistically, this topographic guidance running via cytoskeleton-mediated mechanotransduction specifically targets and activates three major intracellular cascades: the Wnt/β-catenin, ERK/MAPK, and TGF-β signaling pathways [174]. This biophysical regulation runs parallel and complementary to biochemical antioxidant signaling, cooperatively rescuing SC functions and accelerating re-myelination within the hostile oxidative niche.

The bionic ECM scaffold, with its multidimensional bionic advantages in structure, signal, and function, is promoting the upgrade of peripheral nerve repair from “passive support” to “intelligent guidance.” Chen et al.'s composite conduit actively scavenges ROS via disulfide bonds. This suppresses NF-κB/IL-1β and restores PI3K/AKT/mTOR signaling, which promotes Schwann cell proliferation and angiogenesis. Consequently, the repair strategy shifts from passive guidance to active microenvironmental reprogramming. [175]. Through the biomimicry of the native microenvironment and the integration of multimodal regulatory strategies, this approach improves both the spatial and temporal precision of axonal regeneration. It thereby establishes a robust foundation for the construction of personalized nerve grafts capable of achieving tissue integration and functional restoration [176].

These biomimetic ECM strategies promote regeneration through distinct yet complementary mechanisms: physical anisotropic topologies directly drive SC migration and myelination gene expression via mechanotransduction signaling, whereas biochemical modifications actively scavenge ROS, prevent RET-induced oxidative bursts, and restore bioelectrical conduction. Although combining these physical and biochemical cues successfully shifts nerve repair from passive guidance to active microenvironmental reprogramming, realizing a clinically feasible solution still requires further optimization of the dynamic coupling between material degradation and factor release, as well as maintaining the long-term stability of the scaffold-cell interface.

The significant increase in ROS levels at the site of nerve injury provides a theoretical basis for the construction of a ROS-responsive drug-controlled release system. Such systems are typically engineered with ROS-sensitive linkers to create stable ROS-responsive materials. They may also incorporate hydrogels or nanoparticle-based carriers loaded with functional cells, neurotrophic factors, antioxidants, and anti-inflammatory agents to enable intelligent stimulus-responsive release and precise therapeutic modulation [180, 181]. ROS-responsive drug piggyback systems vary in the drugs that researchers choose to piggyback. According to the different purposes, they can be broadly categorized into the following four types: (1) Antioxidants can effectively scavenge free radicals and reduce ROS levels, thereby reducing oxidative stress and cell damage [182, 183]. (2) NGF plays a critical role in the nervous system. It facilitates the elongation of neuronal axons and also contributes to the formation of myelin sheaths, both of which are essential for nerve repair and signal conduction [8, 171]. (3) Anti-inflammatory drugs reduce the local inflammatory response by down-regulating pro-inflammatory factors such as TNF-α, IL-6, and IL1-β. Moreover, since OS and inflammation are mutually reinforcing, controlling inflammation can in turn alleviate oxidative stress, thereby further breaking the vicious cycle [60, 133, 184]. [4] Gene therapy drugs can act directly on key pathological links after nerve injury, for example, PINK1 mRNA enters the cell and directs the synthesis of PINK1 protein, which is closely related to mitochondrial autophagy [185].

The above strategies facilitate the diverse development of ROS-responsive systems. o precisely modulate the oxidative and senescent microenvironment, Zhao et al. developed a ROS/Ca²⁺-responsive dynamic hydrogel composed of HA-PBA, TPA, and CS-EDTA. [185]. This hydrogel delivers engineered extracellular vesicles (EVs) loaded with PINK1 mRNA. Through dual modifications, these EVs specifically target DPP4 receptors on senescent SCs. Crucially, once internalized, the PINK1 mRNA directly activates the PINK1/Parkin-mediated mitophagy pathway, which clears damaged mitochondria and halts ROS accumulation. This targeted intervention reverses SC senescence and restores pro-regenerative capacity, thereby accelerating nerve repair. In a complementary approach, Dong et al. engineered a ROS-responsive and thermosensitive hydrogel system (PTCM@PMet nanoparticles embedded within mPEG-PA-PP) to selectively deliver the H₂S donor, peroxyTCM. Triggered by the high-ROS injury microenvironment, peroxyTCM releases H₂S. Of note, beyond acting as a direct chemical ROS scavenger, H₂S serves as a gaseous signaling molecule that is known to activate the Nrf2/HO-1 antioxidant axis and suppress NF-κB-mediated inflammation. This dual-pathway modulation is expected to protect Schwann cells from lipid peroxidation-induced injury, decisively reshaping the hostile oxidative niche into a pro-regenerative milieu [115]. Moreover, this experiment employed the fluorescent probe 7-nitro-4-methylcoumarin (AzMC) to monitor and visualize the accumulation of H₂O₂ and H₂S in the cellular environment, thereby providing a more intuitive reflection of the actual ROS response.

Overall, the ROS-responsive controlled release system offers a novel approach to precisely regulate oxidative stress and inflammation following nerve injury through the synergistic integration of material design and drug loading. Nevertheless, it is worth noting that uncertainties remain regarding the specificity of the response and the persistence of efficacy under multiple pathological stimuli. Consequently, related research needs to further focus on assessing stability and practicality under complex in vivo environments [186].

Exosomes are nanoscale vesicles originating from endosomal compartments that carry various biologically active molecules, including RNA and proteins. Through non-cell-autonomous mechanisms, they regulate key cellular processes such as migration, differentiation, and responses to tissue injury, thereby promoting neurite outgrowth and axonal regeneration in the peripheral nervous system [187–189]. Recent studies have shown that exosomes derived from SCs can deliver miR-21 to specifically suppress PTEN expression, thereby relieving the inhibition of the PI3K/Akt signaling pathway. This activation subsequently upregulates anti-apoptotic proteins, promoting neuronal survival and axonal regeneration [190].

In recent years, engineering exosomes to enhance their own functions or improve their targeting has gradually become a new development trend. The engineering approaches that can be employed include direct modification of exosomes, induction of cell differentiation, and pretreatment of parent cells, among others [191]. Applying this direct modification strategy, Liu et al. loaded polyphenol-engineered Saccharina japonica exosomes (CA@Exos) onto electroconductive microneedles to achieve deep-tissue delivery [192]. Concurrently, the application of exogenous electrical stimulation via this bioelectric scaffold significantly amplifies the cellular uptake of these exosomes. Mechanistically, the released caffeic acid (CA) specifically inhibits the formation of AGEs and blocks AGE-RAGE interactions, while mitigating ROS accumulation through the upregulation of antioxidant enzymes such as Sod2 and Hmox1. Furthermore, the combined bio-electroceutical intervention facilitates Ca²⁺ influx, activating Camk2a/Camk2b-mediated Erk1/2 and cGMP-PKG signaling cascades. This targeted multi-pathway modulation fosters robust crosstalk between Schwann cells and vascular endothelial cells. Ultimately, this seamless coupling of redox homeostasis with neuroangiogenesis establishes a self-amplifying loop that significantly accelerates chronic tissue repair [192]. These examples underscore the versatility of exosome engineering: by coupling innate targeting with tailored cargo and surface modifications, exosome platforms can be precisely configured to counteract specific oxidative and inflammatory pathologies in the injured nerve microenvironment.

The magnetothermal controlled-release system, leveraging localized heating of magnetic nanomaterials under an alternating magnetic field, enables precise delivery of neurogenerative factors and coordinated regulation of the OS microenvironment [193–195]. This feature is conducive to loading magnetic nanoparticles, exosomes, neurotrophic factors, or antioxidants together in a thermosensitive hydrogel. By using the magnetic field-triggered thermal energy, the swelling-shrinking behavior of the hydrogel can be dynamically regulated to achieve the on-demand release of active substances [196–198]. Additionally, magnetothermal stimulation activates TRPV1 channels, leading to a calcium ion influx that promotes Schwann cell migration and axonal growth. Beyond triggering drug release, magnetothermal cues directly activate specific intracellular pathways. For instance, magnetic composite scaffolds can activate the Heat Shock Protein 70 pathway to enhance synergistic tissue regeneration [199]. Furthermore, Kuznetsova et al. engineered a magnetic fibrin hydrogel that generates localized heating upon alternating magnetic field (AMF) exposure. This remote thermal cue specifically targets thermosensitive TRPV1 ion channels, triggering a Ca²⁺ influx that promotes 3D neurite outgrowth and axonal extension [200].

Although systematic application of TRPV1-targeted magnetothermal effects to NGC design remains in its early stages, the recent demonstration of magnetic fibrin hydrogels as implantable neural interfaces [200] provides a strong proof-of-concept that this modality can be integrated into next-generation nerve scaffolds, warranting further mechanistic investigation.

3D bioprinting can be used to fabricate biocompatible and functionally active neural scaffolds and offers innovative solutions to meet complex neural tissue repair needs by precisely modulating the spatial distribution of cells and biomaterials. Leveraging computer-aided design, 3D printing enables the personalized fabrication of structures with physiological shapes and microstructural features, better meeting the needs of individual patients [201, 202]. Despite its considerable potential, current 3D printing technology still faces significant limitations. One key issue lies in its inability to fully replicate and integrate the complex multimodal signals present in the physiological microenvironment of implantable nerve conduits. Moreover, effectively coordinating stem cell differentiation within these constructs remains a major challenge.

4D bioprinting builds upon 3D printing by introducing a time-dependent dynamic response. This technology enables printed structures to adapt to physiological environments in real time. It achieves this adaptability by combining smart-responsive materials such as temperature-sensitive hydrogels, light-responsive hydrogels, and shape memory polymers with preprogrammed structural designs. Examples of such designs include anisotropic shrinkage, gradient degradation, and predesigned deformation patterns. The core breakthroughs are reflected in three key aspects: (1) By studying and mimicking the dynamic changes of key structures such as the extracellular matrix during the nerve regeneration process, researchers can reconstruct a functional microenvironment at the injury site. This reconstructed microenvironment is not fixed in form. Instead, it can continuously adapt and remodel itself in coordination with the distinct stages of nerve regeneration. Such adaptability ensures sustained support for cellular activity and promotes progressive tissue repair. (2) Employ computational programming to precisely regulate the spatiotemporal release of neurotrophic factors and antioxidants. This enables the deliberate setting of parameters such as dosage, timing, and release location, facilitating alignment with the evolving demands of nerve regeneration. (3) Integrate electrically active scaffolds with conventional biological scaffolds that provide structural support and directional guidance, thereby synergistically enhancing the conduction of electrical signals between neurons [203–206].

Currently, the application of 4D bioprinting specifically targeting OS in nerve repair remains largely unexplored. However, recent dynamic designs provide a strong foundational framework. For example, Wang et al. developed a 4D-printed shape-memory conduit (PLATMC/Ti₃C₂T_x MXene) that autonomously self-rolls at 37 °C within 20 s to rapidly wrap injured nerves [206]. Mechanistically, its pre-programmed microchannels offer topographical guidance for directional SC migration via cytoskeleton-mediated mechanotransduction, while the conductive Ti₃C₂T_x matrix promotes SC maturation and robust angiogenesis. Although their study focused on biophysical cues, Ti₃C₂T_x intrinsically possesses potent ROS-scavenging properties, attributed to its inherently reducing Ti-C skeleton and antioxidant enzyme-mimicking properties (e.g., SOD-like and CAT-like activities) [207, 208]. This reveals a promising, untapped strategy: integrating such nanomaterials into 4D-printed scaffolds can synergistically couple morphological self-adaptation with active OS neutralization to comprehensively remodel the hostile regenerative microenvironment.

To systematically summarize these cutting-edge strategies, the representative applications of smart biomaterial systems (including external physical field stimulation, magneto-thermal controlled release, and 4D bioprinting) for ROS scavenging and nerve regeneration are summarized in Table 4.

In summary, tissue engineering has evolved from passive conduits to active, intelligent delivery systems capable of precise ROS regulation. These advanced engineering milestones establish a robust foundation for the targeted translational applications discussed next.

Following mechanical injury to peripheral nerves, SCs are one of the earliest cell types to respond to injury [13]. By inducing mitochondrial dysfunction and DNA damage, oxidative stress not only directly impairs the repair phenotype of SCs, but more crucially, drives their transition from pro-regenerative “repair SCs” to inhibitory “senescent SCs,” thereby deteriorating the regenerative microenvironment [4, 27]. This process is regulated by the Nrf2 antioxidant pathway; insufficient Nrf2 activity accelerates the senescent transition of SCs, whereas Nrf2 activation helps sustain the repair phenotype and resist senescence [30, 105].

Specifically, SCs upregulate the expression of pro-inflammatory factors such as tumor necrosis factor-α (TNFα) and interleukin-6 (IL-6), along with chemokines such as CCL2, through perceived destructive signals in the microenvironment [212, 213]. Subsequently, the above factors recruit monocytes/macrophages to the site of injury, and the polarization of classically activated macrophage (M1) promotes the development of inflammation [214]. At the same time, Nox in SCs, M1, and neutrophils is activated and releases large amounts of ROS. For repair Schwann cells, moderate ROS levels serve as essential second messengers that sustain c-Jun expression and maintain their dedifferentiated state, as evidenced by studies showing that H₂O₂ directly modulates c-Jun and ERK activation in injured nerves [69], and that c-Jun is the master transcriptional regulator of the Schwann cell repair program [215]. However, excessive ROS triggers axonal growth cone collapse and retraction, a positive feedback between inflammation and OS formation that is a key component of Wallerian degeneration [9, 38]. The large amount of ROS generated during this process damages the myelin debris produced by SCs, which will impede nerve regeneration. SCs, macrophages, and neutrophils are all capable of phagocytosing and removing myelin debris [216, 217]. As inflammation progresses into the chronic phase, SCs induce polarization of M1 toward M2, which secretes vascular endothelial growth factor (VEGF) with pro-angiogenic effects [210, 214]. Demyelinated SCs form “Büngner bands” along the trajectory of neovascularization, providing structural guidance for axonal regeneration [218, 219].

Studies have shown that after PNI occurs, the expression of the key antioxidant defense pathway Nrf2 in SCs is downregulated, resulting in a decrease in their antioxidant capacity [64]. This change, to some extent, helps to establish the Wallerian degeneration microenvironment, thereby supporting the process of peripheral nerve repair. In addition, SCs secrete various neurotrophic factors, which regulate the survival, migration, adhesion, and chemotaxis of cells, thereby further promoting axonal regeneration [220] (as shown in Figure 7). The above-mentioned cascade reaction composed of inflammation and OS is not only a classic pathological change after PNI, but also one of the core theoretical foundations for guiding antioxidant treatment.

Although the inflammation-OS cascade is a ubiquitous pathological mechanism following PNI [10], it must be emphasized that different experimental PNI models exhibit divergent characteristics. In the nerve crush model, the basal lamina surrounding the axons remains intact, allowing axons to regrow within their original basal lamina tubes. In contrast, in the cut injury model, the connective tissue and basal lamina tubes are disrupted, compelling regenerating axons to cross the tissue bridge formed between the severed stumps [221]. Therefore, PNI should not be treated as a homogeneous pathological condition. Clearly distinguishing the microenvironmental disparities among these injury models holds significant clinical translational value, suggesting that treatment strategies for peripheral nerve injury must shift toward precision and customized therapy [222].

DPN is a typical metabolic peripheral neuropathy, and one of the core pathologic bases of its pathologic basis lies in the metabolic disorders and OS triggered by chronic hyperglycemia [223]. Redundant glucose is shifted to the polyol pathway for metabolism due to increased hexokinase activity in the high glucose environment. At this point, SCs metabolize glucose to fructose with the vascular endothelium-expressed aldose reductase AR, which depletes nicotinamide adenine dinucleotide phosphate (NADPH). Decreased levels of NADPH impede GSH synthesis, and cellular antioxidant capacity decreases [66]. Additionally, the Maillard reaction, polyol pathway, ketone body metabolism, and Wolff pathway produce AGEs. Hyperglycemic Glucose (HG) leads to an abnormal accumulation of AGEs [224]. Then, an abnormal accumulation of AGEs results in binding to RAGE on SCs and activating pathways such as NF-κB, JNK, and NLRP3, generating ROS and inflammatory factors that lead to SC damage and dysfunction [225, 226]. Not only that, the HG environment also activates signaling pathways such as PKC [227]. Together, the above pathways promote OS onset and further elicit an inflammatory infiltrate.

A study showed that the infiltration of M1 and resting CD4⁺ memory T cells was increased under DPN conditions. Meanwhile, the infiltration of M2, resting mast cells, monocytes, and T follicular helper cells was decreased, which may be related to the development of DPN [132]. Moreover, in vitro studies have shown that high glucose conditions promote sustained M1 polarization of macrophages by downregulating IRG1 expression, suggesting a potential mechanism by which M1 macrophages may persist in diabetic complications such as DPN [228]. However, direct evidence for increased M1 infiltration and decreased M2 in DPN development remains to be established. Also, HG-induced mitochondrial dysfunction and inhibition of the Nrf2 pathway resulted in a decrease in the antioxidant capacity of SCs and a weakening of the ability to withstand stress [229, 230]. As for mast cells, HG-stimulated secretion of factors inhibits myelin formation in SCs [231]. In summary, OS-inflammation co-propels DPN progression. The major cells involved in the process are similar to those of PNI, but the pathologic changes differ in different microenvironments. In general, cells can mitigate greater damage from stressful environments through autophagy. However, HG inhibits the autophagy function of SCs, which is detrimental to the remodeling of the microenvironment [94]. Therefore, modulating the relevant signaling pathways and restoring autophagy in SCs is a promising therapeutic strategy.

SCs are the origin of NF1, and their tumorigenesis is due to mutations in the NF1 gene within SCs [232]. The mutation results in the deletion of the protein encoding the NF1 gene that inhibits Ras activity, and sustained activation of the Ras signaling pathway. Downstream signaling pathways (e.g., Raf-MEK-ERK, PI3K-Akt-mTOR, etc.) are subsequently activated, promoting the proliferation, migration, and survival of SCs [233]. At the same time, SCs secrete large amounts of Kit ligand to recruit both NF1 mast cells and CSF1 to recruit macrophages. Both NF1 mast cells and macrophages promote the migration and proliferation of SCs by inducing angiogenesis, providing nutrient support, and secreting large amounts of TGFβ to stimulate collagen production by fibroblasts and the formation of tumor strom [234–236]. In conclusion, the pathological microenvironmental regulation of NF1 by SCs-immune cells influences tumor formation to a certain extent, and the study of the mechanisms of cell-cell interactions contributes to the understanding of disease onset and progression. Additionally, activation of signaling pathways such as mTOR has been observed to upregulate ROS production in several studies [16, 237]. Moreover, ROS plays a dual role in cancer. On the one hand, ROS are carcinogenic risk factors in their own right and may also cause damage to the DNA of cells. On the other hand, the cytotoxicity of excess ROS can also act on tumor cells [16]. Therefore, modulation of OS-related signaling pathways in NF1 to intervene in NF1 may serve as a new therapeutic tool.