Dog sciatic nerve regeneration across a 30-mm defect bridged by a chitosan/PGA artificial nerve graft

Potentially commercializable nerve guidance conduits for peripheral nerve injury: Past, present, and future

Peripheral nerve injuries are a prevalent global issue that has garnered great concern. Although autografts remain the preferred clinical approach to repair, their efficacy is hampered by factors like donor scarcity. The emergence of nerve guidance conduits as novel tissue engineering tools offers a promising alternative strategy. This review aims to interpret nerve guidance conduits and their commercialization from both clinical and laboratory perspectives. To enhance comprehension of clinical situations, this article provides a comprehensive analysis of the clinical efficacy of nerve conduits approved by the United States Food and Drug Administration. It proposes that the initial six months post-transplantation is a critical window period for evaluating their efficacy. Additionally, this study conducts a systematic discussion on the research progress of laboratory conduits, focusing on biomaterials and add-on strategies as pivotal factors for nerve regeneration, as supported by the literature analysis. The clinical conduit materials and prospective optimal materials are thoroughly discussed. The add-on strategies, together with their distinct obstacles and potentials are deeply analyzed. Based on the above evaluations, the development path and manufacturing strategy for the commercialization of nerve guidance conduits are envisioned. The critical conclusion promoting commercialization is summarized as follows: 1) The optimization of biomaterials is the fundamental means; 2) The phased application of additional strategies is the emphasized direction; 3) The additive manufacturing techniques are the necessary tools. As a result, the findings of this research provide academic and clinical practitioners with valuable insights that may facilitate future commercialization endeavors of nerve guidance conduits.

Advances in biomaterial-based tissue engineering for peripheral nerve injury repair

Peripheral nerve injury is a common clinical disease. Effective post-injury nerve repair remains a challenge in neurosurgery, and clinical outcomes are often unsatisfactory, resulting in social and economic burden. Particularly, the repair of long-distance nerve defects remains a challenge. The existing nerve transplantation strategies show limitations, including donor site morbidity and immune rejection issues. The multiple studies have revealed the potential of tissue engineering strategies based on biomaterials in the repair of peripheral nerve injuries. We review the events of regeneration after peripheral nerve injury, evaluates the efficacy of existing nerve grafting strategies, and delves into the progress in the construction and application strategies of different nerve guidance conduits. A spotlight is cast on the materials, technologies, seed cells, and microenvironment within these conduits to facilitate optimal nerve regeneration. Further discussion was conducted on the approve of nerve guidance conduits and potential future research directions. This study anticipates and proposes potential avenues for future research, aiming to refine existing strategies and uncover innovative approaches in biomaterial-based nerve repair. This study endeavors to synthesize the collective insights from the fields of neuroscience, materials science, and regenerative medicine, offering a multifaceted perspective on the role of biomaterials in advancing the frontiers of peripheral nerve injury treatment.

Chitooligosaccharides promote diabetic wound healing by mediating fibroblast proliferation and migration

Diabetic wounds are notoriously difficult to heal due to impaired cell repair mechanisms, reduced angiogenesis, and a heightened risk of infection. Fibroblasts play a vital role in wound healing by producing extracellular matrix (ECM) components and various growth factors, but their function is inhibited in diabetic wounds. Chitooligosaccharides (COS), intermediate products of chitosan degradation, have shown efficacy in promoting tissue repair, yet their role in diabetic wound healing remains underexplored. In a mouse model of diabetic wounds, COS treatment demonstrated substantial bioactivity in accelerating wound healing by enhancing fibroblast proliferation and migration. Additionally, COS increased collagen III deposition and angiogenesis at the wound sites. The COS also mitigated inflammatory responses by controlling leukocyte infiltration and bacterial infection. Mechanistically, COS regulated fibroblast activity via the PI3K/Akt signaling pathway, providing a novel bioactive material for chronic wound healing.

Inhibition of KIF5b-mediated Nav1.8 transport by ropivacaine contributes to axonal regeneration following sciatic nerve injury in rats

Peripheral nerve injury (PNI), typically caused by traumatic accidents or medical events, is currently one of the most common diseases that leads to limb disability. After PNI, tetrodotoxin-resistant voltage-gated sodium channel Nav1.8 is upregulated at the lesion site. Our earlier study suggested that ropivacaine promotes axon regrowth by regulating Nav1.8-mediated macrophage signaling. Nevertheless, the mechanism of ropivacaine in regulation of Nav1.8 expression remains incompletely understood. Kinesin family 5b (KIF5b) was reported to mediate the Nav1.8 axonal transport from dorsal root ganglia (DRGs) to lesion site. Herein, we investigated whether ropivacaine promotes axon regeneration through inhibition of KIF5b-mediated Nav1.8 transport. Reduced levels of KIF5b and Nav1.8 in DRGs coincide with their increase at the lesion site. Nav1.8 mRNA was significantly increased at the lesion site but not in DRGs. Surprisingly, ropivacaine reversed the alterations of Nav1.8 and KIF5b protein expression without affecting Nav1.8 mRNA level. Due to KIF5b overexpression in DRGs, Nav1.8 protein level was significantly decreased in DRGs and increased at the lesion site. We also found KIF5b overexpression significantly impaired behavioral functions, reduced the recovery index of compound muscle action potential (CMAP) amplitude, inhibited axonal regrowth, slowed M1 macrophage infiltration and shift to M2 phenotype, and delayed myelin debris clearance. Notably, all aforementioned results caused by KIF5b overexpression were alleviated by ropivacaine. Furthermore, we demonstrated that inhibition of Nav1.8 transport by A-803467 produced mitigating effects on the impairment of regenerative capacity induced by KIF5b overexpression similar to ropivacaine. These results suggest that ropivacaine promotes axonal regeneration at least partially by inhibiting KIF5b-mediated Nav1.8 forward transport.

Chitosan/PLGA-based tissue engineered nerve grafts with SKP-SC-EVs enhance sciatic nerve regeneration in dogs through miR-30b-5p-mediated regulation of axon growth

Extracellular vesicles from skin-derived precursor Schwann cells (SKP-SC-EVs) promote neurite outgrowth in culture and enhance peripheral nerve regeneration in rats. This study aimed at expanding the application of SKP-SC-EVs in nerve grafting by creating a chitosan/PLGA-based, SKP-SC-EVs-containing tissue engineered nerve graft (TENG) to bridge a 40-mm long sciatic nerve defect in dogs. SKP-SC-EVs contained in TENGs significantly accelerated the recovery of hind limb motor and electrophysiological functions, supported the outgrowth and myelination of regenerated axons, and alleviated the denervation-induced atrophy of target muscles in dogs. To clarify the underlying molecular mechanism, we observed that SKP-SC-EVs were rich in a variety of miRNAs linked to the axon growth of neurons, and miR-30b-5p was the most important among others. We further noted that miR-30b-5p contained within SKP-SC-EVs exerted nerve regeneration-promoting effects by targeting the Sin3a/HDAC complex and activating the phosphorylation of ERK, STAT3 or CREB. Our findings suggested that SKP-SC-EVs-incorporating TENGs represent a novel type of bioactive material with potential application for peripheral nerve repair in the clinic.

Isoflurane conditioning improves functional outcomes after peripheral nerve injury in a sciatic cut repair murine model

Introduction

Anesthetic conditioning has been shown to provide neuroprotection in several neurological disorders. Whether anesthetic conditioning provides protection against peripheral nerve injuries remains unknown. The aim of our current study is to investigate the impact of isoflurane conditioning on the functional outcomes after peripheral nerve injury (PNI) in a rodent sciatic nerve injury model.

Methods

Adult male Lewis rats underwent sciatic nerve cut and repair and exposed to none (Group 1, sham), single isoflurane exposure (Group 2), three-time isoflurane exposure (Group 3), and six-time isoflurane exposure (Group 4). Isoflurane conditioning was established by administration of 2% isoflurane for 1 hour, beginning 1-hour post sciatic nerve cut and repair. Groups 3 and 4 were exposed to isoflurane for 1 hour, 3 and 6 consecutive days respectively. Functional outcomes assessed included compound muscle action potential (CMAP), evoked muscle force (tetanic and specific tetanic force), wet muscle mass, and axonal counting.

Results

We observed an increase in axons, myelin width and a decrease in G-ratio in the isoflurane conditioning groups (3- and 6-days). This correlated with a significant improvement in tetanic and specific tetanic forces, observed in both groups 3 and 4.

Discussion

Isoflurane conditioning (3- and 6-day groups) resulted in improvement in functional outcomes at 12 weeks post peripheral nerve injury and repair in a murine model. Future experiments should be focused on identifying the therapeutic window of isoflurane conditioning and exploring the underlying molecular mechanisms responsible for isoflurane conditioning induced neuroprotection in PNI.

Efficacy of using adipose-derived stem cells and PRP on regeneration of 40 -mm long sciatic nerve defect bridged by polyglycolic-polypropylene mesh in canine model

BACKGROUND

Sciatic nerve repair becomes a focus of research in neurological aspect to restore the normal physical ability of the animal to stand and walk. Tissue engineered nerve grafts (TENGs) provide a promising alternative therapy for regeneration of large gap defects. The present study investigates the regenerative capacity of PRP, ADSCs, and PRP mixed ADSCs on a long sciatic nerve defect (40-mm) bridged by a polyglycolic polypropylene (PGA-PRL) mesh which acts as a neural scaffold.

MATERIALS AND METHODS

The study was conducted on 12 adult male mongrel dogs that were randomly divided into 4 groups: Group I (scaffold group); where the sciatic defect was bridged by a (PGA-PRL) mesh only while the mesh was injected with ADSCs in Group II (ADSCs group), PRP in Group III (PRP group). Mixture of PRP and ADSCs was allocated in Group IV (PRP + ADSCs group). Monthly, all animals were monitored for improvement in their gait and a numerical lameness score was recorded for all groups. 6 months-post surgery, the structural and functional recovery of sciatic nerve was evaluated electrophysiologically, and on the level of gene expression, and both sciatic nerve and the gastrocnemius muscle were evaluated morphometrically, histopathologically.

RESULTS

Numerical lameness score showed improvement in the motor activities of both Group II and Group III followed by Group IV and the scaffold group showed mild improvement even after 6 months. Histopathologically, all treated groups showed axonal sprouting and numerous regenerated fascicles with obvious angiogenesis in proximal cut, and distal portion where Group IV exhibited a significant remyelination with the MCOOL technique. The regenerative ratio of gastrocnemius muscle was 23.81%, 56.68%, 52.06% and 40.69% for Group I, II, III and IV; respectively. The expression of NGF showed significant up regulation in the proximal portion for both Group III and Group IV (P ≤ 0.0001) while Group II showed no significant difference. PDGF-A, and VEGF expressions were up-regulated in Group II, III, and IV whereas Group I showed significant down-regulation for NGF, PDGF-A, and VEGF (P ≤ 0.0001).

CONCLUSION

ADSCs have a great role in restoring the damaged nerve fibers by secreting several types of growth factors like NGF that have a proliferative effect on Schwann cells and their migration. In addition, PRP therapy potentiates the effect of ADSCs by synthesis another growth factors such as PDGF-A, VEGF, NGF for better healing of large sciatic gap defects.

Management of an Early-Onset, Painful Tibial Nerve Neuroma Using an Autologous Nerve Graft

This case report describes the treatment of a postoperative painful neuroma of the tibial nerve using an autologous nerve graft in a dog. The patient presented with sudden non-weight-bearing lameness 10 days after iatrogenic tibial nerve injury during preparation of a reverse saphenous conduit flap. The dog showed severe pain at the surgical site without nerve deficits. A magnetic resonance imaging examination revealed an enlarged tibial nerve at the injury site, consistent with a neuroma. Analgesics were administered over 11 days, but the patient remained in severe pain and non-weight-bearing. Therefore, surgical resection was recommended. The fusiform neuroma was resected microsurgically, and a saphenous nerve graft was transplanted using an epineural nerve repair technique. Histopathological examination was consistent with a neuroma. The dog showed immediate pain relief and weight-bearing the day after surgery with normal motor function. The dog made a full recovery by the last follow-up 6 mo after surgery. If patients develop pain and lameness following surgery or nerve injury, neuroma formation must be considered, even shortly after surgery. Microsurgical resection and autologous nerve transplantation using an epineural nerve repair technique is a viable method to treat painful neuromas and minimize the risk for recurrence in dogs.

Advances of Schwann cells in peripheral nerve regeneration: From mechanism to cell therapy

Peripheral nerve injuries (PNIs) frequently occur due to various factors, including mechanical trauma such as accidents or tool-related incidents, as well as complications arising from diseases like tumor resection. These injuries frequently result in persistent numbness, impaired motor and sensory functions, neuropathic pain, or even paralysis, which can impose a significant financial burden on patients due to outcomes that often fall short of expectations. The most frequently employed clinical treatment for PNIs involves either direct sutures of the severed ends or bridging the proximal and distal stumps using autologous nerve grafts. However, autologous nerve transplantation may result in sensory and motor functional loss at the donor site, as well as neuroma formation and scarring. Transplantation of Schwann cells/Schwann cell-like cells has emerged as a promising cellular therapy to reconstruct the microenvironment and facilitate peripheral nerve regeneration. In this review, we summarize the role of Schwann cells and recent advances in Schwann cell therapy in peripheral nerve regeneration. We summarize current techniques used in cell therapy, including cell injection, 3D-printed scaffolds for cell delivery, cell encapsulation techniques, as well as the cell types employed in experiments, experimental models, and research findings. At the end of the paper, we summarize the challenges and advantages of various cells (including ESCs, iPSCs, and BMSCs) in clinical cell therapy. Our goal is to provide the theoretical and experimental basis for future treatments targeting peripheral nerves, highlighting the potential of cell therapy and tissue engineering as invaluable resources for promoting nerve regeneration.

Beyond the limiting gap length: peripheral nerve regeneration through implantable nerve guidance conduits

Peripheral nerve damage results in the loss of sensorimotor and autonomic functions, which is a significant burden to patients. Furthermore, nerve injuries greater than the limiting gap length require surgical repair. Although autografts are the preferred clinical choice, their usage is impeded by their limited availability, dimensional mismatch, and the sacrifice of another functional donor nerve. Accordingly, nerve guidance conduits, which are tubular scaffolds engineered to provide a biomimetic environment for nerve regeneration, have emerged as alternatives to autografts. Consequently, a few nerve guidance conduits have received clinical approval for the repair of short-mid nerve gaps but failed to regenerate limiting gap damage, which represents the bottleneck of this technology. Thus, it is still necessary to optimize the morphology and constituent materials of conduits. This review summarizes the recent advances in nerve conduit technology. Several manufacturing techniques and conduit designs are discussed, with emphasis on the structural improvement of simple hollow tubes, additive manufacturing techniques, and decellularized grafts. The main objective of this review is to provide a critical overview of nerve guidance conduit technology to support regeneration in long nerve defects, promote future developments, and speed up its clinical translation as a reliable alternative to autografts.

Enhancing regeneration and repair of long-distance peripheral nerve defect injuries with continuous microcurrent electrical nerve stimulation

Introduction

Peripheral nerve injuries, especially those involving long-distance deficits, pose significant challenges in clinical repair. This study explores the potential of continuous microcurrent electrical nerve stimulation (cMENS) as an adjunctive strategy to promote regeneration and repair in such cases.

Methods

The study initially optimized cMENS parameters and assessed its impact on Schwann cell activity, neurotrophic factor secretion, and the nerve regeneration microenvironment. Subsequently, a rat sciatic nerve defect-bridge repair model was employed to evaluate the reparative effects of cMENS as an adjuvant treatment. Functional recovery was assessed through gait analysis, motor function tests, and nerve conduction assessments. Additionally, nerve regeneration and denervated muscle atrophy were observed through histological examination.

Results

The study identified a 10-day regimen of 100uA microcurrent stimulation as optimal. Evaluation focused on Schwann cell activity and the microenvironment, revealing the positive impact of cMENS on maintaining denervated Schwann cell proliferation and enhancing neurotrophic factor secretion. In the rat model of sciatic nerve defect-bridge repair, cMENS demonstrated superior effects compared to control groups, promoting motor function recovery, nerve conduction, and sensory and motor neuron regeneration. Histological examinations revealed enhanced maturation of regenerated nerve fibers and reduced denervated muscle atrophy.

Discussion

While cMENS shows promise as an adjuvant treatment for long-distance nerve defects, future research should explore extended stimulation durations and potential synergies with tissue engineering grafts to improve outcomes. This study contributes comprehensive evidence supporting the efficacy of cMENS in enhancing peripheral nerve regeneration.

Multifunctional wet-adhesive chitosan/acrylic conduit for sutureless repair of peripheral nerve injuries

The incidence of peripheral nerve injury (PNI) is high worldwide, and a poor prognosis is common. Surgical closure and repair of the affected area are crucial to ensure the effective treatment of peripheral nerve injuries. Despite being the standard treatment approach, reliance on sutures to seal the severed nerve ends introduces several limitations and restrictions. This technique is intricate and time-consuming, and the application of threading and punctate sutures may lead to tissue damage and heightened tension concentrations, thus increasing the risk of fixation failure and local inflammation. This study aimed to develop easily implantable chitosan-based peripheral nerve repair conduits that combine acrylic acid and cleavable N-hydroxysuccinimide to reduce nerve damage during repair. In ex vivo tissue adhesion tests, the conduit achieved maximal interfacial toughness of 705 J m-2 ± 30 J m-2, allowing continuous bridging of the severed nerve ends. Adhesive repair significantly reduces local inflammation caused by conventional sutures, and the positive charge of chitosan disrupts the bacterial cell wall and reduces implant-related infections. This promises to open new avenues for sutureless nerve repair and reliable medical implants.

Ropivacaine Promotes Axon Regeneration by Regulating Nav1.8-mediated Macrophage Signaling after Sciatic Nerve Injury in Rats

BACKGROUND

Continuous nerve block with ropivacaine is commonly performed after repair surgery for traumatic peripheral nerve injuries. After peripheral nerve injury, tetrodotoxin-resistant voltage-gated sodium channel Nav1.8 is upregulated and contributes to macrophage inflammation. This study investigated whether ropivacaine promotes peripheral nerve regeneration through Nav1.8-mediated macrophage signaling.

METHODS

A sciatic nerve transection-repair (SNT) model was established in adult Sprague-Dawley rats of both sexes. The rats received 0.2% ropivacaine or 10 μM Nav1.8-selective inhibitor A-803467 around the injured site or near the sacrum for 3 days. Nerve regeneration was evaluated using behavioral, electrophysiologic, and morphological examinations. Moreover, myelin debris removal, macrophage phenotype, Nav1.8 expression, and neuropeptide expression were assessed using immunostaining, enzyme-linked immunosorbent assay, and Western blotting.

RESULTS

Compared to the SNT-plus-vehicle group, the sensory, motor, and sensory-motor coordination functions of the two ropivacaine groups were significantly improved. Electrophysiologic (mean ± SD: recovery index of amplitude, vehicle 0.43 ± 0.17 vs. ropivacaine 0.83 ± 0.25, n = 11, P < 0.001) and histological analysis collectively indicated that ropivacaine significantly promoted axonal regrowth (percentage of neurofilament 200 [NF-200]-positive area: vehicle 19.88 ± 2.81 vs. ropivacaine 31.07 ± 2.62, n = 6, P < 0.001). The authors also found that, compared to the SNT-plus-vehicle group, the SNT-plus-ropivacaine group showed faster clearance of myelin debris, accompanied by significantly increased macrophage infiltration and transition from the M1 to M2 phenotype. Moreover, ropivacaine significantly attenuated Nav1.8 upregulation at 9 days after sciatic nerve transection (vehicle 4.12 ± 0.30-fold vs. ropivacaine 2.75 ± 0.36-fold, n = 5, P < 0.001), which coincided with the increased expression of chemokine ligand 2 and substance P. Similar changes were observed when using the selective Nav1.8 channel inhibitor A-803467.

CONCLUSIONS

Continuous nerve block with ropivacaine promotes the structural and functional recovery of injured sciatic nerves, possibly by regulating Nav1.8-mediated macrophage signaling.

EDITOR’S PERSPECTIVE

Micro-nanofiber composite biomimetic conduits promote long-gap peripheral nerve regeneration in canine models

Peripheral nerve injuries may result in severe long-gap interruptions that are challenging to repair. Autografting is the gold standard surgical approach for repairing long-gap nerve injuries but can result in prominent donor-site complications. Instead, imitating the native neural microarchitecture using synthetic conduits is expected to offer an alternative strategy for improving nerve regeneration. Here, we designed nerve conduits composed of high-resolution anisotropic microfiber grid-cordes with randomly organized nanofiber sheaths to interrogate the positive effects of these biomimetic structures on peripheral nerve regeneration. Anisotropic microfiber-grids demonstrated the capacity to directionally guide Schwann cells and neurites. Nanofiber sheaths conveyed adequate elasticity and permeability, whilst exhibiting a barrier function against the infiltration of fibroblasts. We then used the composite nerve conduits bridge 30-mm long sciatic nerve defects in canine models. At 12 months post-implant, the morphometric and histological recovery, gait recovery, electrophysiological function, and degree of muscle atrophy were assessed. The newly regenerated nerve tissue that formed within the composite nerve conduits showed restored neurological functions that were superior compared to sheaths-only scaffolds and Neurolac nerve conduit controls. Our findings demonstrate the feasibility of using synthetic biophysical cues to effectively bridge long-gap peripheral nerve injuries and indicates the promising clinical application prospects of biomimetic composite nerve conduits.

Nerve regeneration using decellularized tissues: challenges and opportunities

In tissue engineering, the decellularization of organs and tissues as a biological scaffold plays a critical role in the repair of neurodegenerative diseases. Various protocols for cell removal can distinguish the effects of treatment ability, tissue structure, and extracellular matrix (ECM) ability. Despite considerable progress in nerve regeneration and functional recovery, the slow regeneration and recovery potential of the central nervous system (CNS) remains a challenge. The success of neural tissue engineering is primarily influenced by composition, microstructure, and mechanical properties. The primary objective of restorative techniques is to guide existing axons properly toward the distal end of the damaged nerve and the target organs. However, due to the limitations of nerve autografts, researchers are seeking alternative methods with high therapeutic efficiency and without the limitations of autograft transplantation. Decellularization scaffolds, due to their lack of immunogenicity and the preservation of essential factors in the ECM and high angiogenic ability, provide a suitable three-dimensional (3D) substrate for the adhesion and growth of axons being repaired toward the target organs. This study focuses on mentioning the types of scaffolds used in nerve regeneration, and the methods of tissue decellularization, and specifically explores the use of decellularized nerve tissues (DNT) for nerve transplantation.

Regenerative Strategies in Treatment of Peripheral Nerve Injuries in Different Animal Models

BACKGROUND

Peripheral nerve damage mainly resulted from traumatic or infectious causes; the main signs of a damaged nerve are the loss of sensory and/or motor functions. The injured nerve has limited regenerative capacity and is recovered by the body itself, the recovery process depends on the severity of damage to the nerve, nowadays the use of stem cells is one of the new and advanced methods for treatment of these problems.

METHOD

Following our review, data are collected from different databases "Google scholar, Springer, Elsevier, Egyptian Knowledge Bank, and PubMed" using different keywords such as Peripheral nerve damage, Radial Nerve, Sciatic Nerve, Animals, Nerve regeneration, and Stem cell to investigate the different methods taken in consideration for regeneration of PNI.

RESULT

This review contains tables illustrating all forms and types of regenerative medicine used in treatment of peripheral nerve injuries (PNI) including different types of stem cells " adipose-derived stem cells, bone marrow stem cells, Human umbilical cord stem cells, embryonic stem cells" and their effect on re-constitution and functional recovery of the damaged nerve which evaluated by physical, histological, Immuno-histochemical, biochemical evaluation, and the review illuminated the best regenerative strategies help in rapid peripheral nerve regeneration in different animal models included horse, dog, cat, sheep, monkey, pig, mice and rat.

CONCLUSION

Old surgical attempts such as neurorrhaphy, autogenic nerve transplantation, and Schwann cell implantation have a limited power of recovery in cases of large nerve defects. Stem cell therapy including mesenchymal stromal cells has a high potential differentiation capacity to renew and form a new nerve and also restore its function.

Properties of Resorbable Conduits Based on Poly(L-Lactide) Nanofibers and Chitosan Fibers for Peripheral Nerve Regeneration

New tubular conduits have been developed for the regeneration of peripheral nerves and the repair of defects that are larger than 3 cm. The conduits consist of a combination of poly(L-lactide) nanofibers and chitosan composite fibers with chitin nanofibrils. In vitro studies were conducted to assess the biocompatibility of the conduits using human embryonic bone marrow stromal cells (FetMSCs). The studies revealed good adhesion and differentiation of the cells on the conduits just one day after cultivation. Furthermore, an in vivo study was carried out to evaluate motor-coordination disorders using the sciatic nerve functional index (SFI) assessment. The presence of chitosan monofibers and chitosan composite fibers with chitin nanofibrils in the conduit design increased the regeneration rate of the sciatic nerve, with an SFI value ranging from 76 to 83. The degree of recovery of nerve conduction was measured by the amplitude of M-response, which showed a 46% improvement. The conduit design imitates the oriented architecture of the nerve, facilitates electrical communication between the damaged nerve's ends, and promotes the direction of nerve growth, thereby increasing the regeneration rate.

Neural tissue-engineered prevascularization in vivo enhances peripheral neuroregeneration via rapid vascular inosculation

Neural tissue engineering techniques typically face a significant challenge, simulating complex natural vascular systems that hinder the clinical application of tissue-engineered nerve grafts (TENGs). Here, we report a subcutaneously pre-vascularized TENG consisting of a vascular endothelial growth factor-induced host vascular network, chitosan nerve conduit, and inserted silk fibroin fibers. Contrast agent perfusion, tissue clearing, microCT scan, and blood vessel 3D reconstruction were carried out continuously to prove whether the regenerated blood vessels were functional. Moreover, histological and electrophysiological evaluations were also applied to investigate the efficacy of repairing peripheral nerve defects with pre-vascularized TENG. Rapid vascular inosculation of TENG pre-vascularized blood vessels with the host vascular system was observed at 4 ​d bridging the 10 ​mm sciatic nerve defect in rats. Transplantation of pre-vascularized TENG in vivo suppressed proliferation of vascular endothelial cells (VECs) while promoting their migration within 14 ​d post bridging surgery. More importantly, the early vascularization of TENG drives axonal regrowth by facilitating bidirectional migration of Schwann cells (SCs) and the bands of Büngner formation. This pre-vascularized TENG increased remyelination, promoted recovery of electrophysiological function, and prevented atrophy of the target muscles when observed 12 weeks post neural transplantation. The neural tissue-engineered pre-vascularization technique provides a potential approach to discover an individualized TENG and explore the innovative neural regenerative process.

Schwann cell-encapsulated chitosan-collagen hydrogel nerve conduit promotes peripheral nerve regeneration in rodent sciatic nerve defect models

Chitosan has various tissue regeneration effects. This study was designed to investigate the nerve regeneration effect of Schwann cell (SC)-encapsulated chitosan-collagen hydrogel nerve conduit (CCN) transplanted into a rat model of sciatic nerve defect. We prepared a CCN consisting of an outer layer of chitosan hydrogel and an inner layer of collagen hydrogel to encapsulate the intended cells. Rats with a 10-mm sciatic nerve defect were treated with SCs encapsulated in CCN (CCN+), CCN without SCs (CCN-), SC-encapsulated silicone tube (silicone+), and autologous nerve transplanting (auto). Behavioral and histological analyses indicated that motor functional recovery, axonal regrowth, and myelination of the CCN+ group were superior to those of the CCN- and silicone+ groups. Meanwhile, the CCN- and silicone+ groups showed no significant differences in the recovery of motor function and nerve histological restoration. In conclusion, SC-encapsulated CCN has a synergistic effect on peripheral nerve regeneration, especially axonal regrowth and remyelination of host SCs. In the early phase after transplantation, SC-encapsulated CCNs have a positive effect on recovery. Therefore, using SC-encapsulated CCNs may be a promising approach for massive peripheral nerve defects.

Experimental Study on Repairing Peripheral Nerve Defects with Novel Bionic Tissue Engineering

Peripheral nerve defects are a worldwide problem, and autologous nerve transplantation is currently the gold-standard treatment for them. Tissue-engineered nerve (TEN) grafts are widely considered promising methods for the same, and have attracted much attention. To improve repair, the incorporation of bionics into TEN grafts has become a focus of research. In this study, a novel bionic TEN graft with a biomimetic structure and composition is designed. For this purpose, a chitin helical scaffold is fabricated by means of mold casting and acetylation using chitosan as the raw material, following which a fibrous membrane is electrospun on the outer layer of the chitin scaffold. The lumen of the structure is filled with human bone mesenchymal stem cell-derived extracellular matrix and fibers to provide nutrition and topographic guidance, respectively. The prepared TEN graft is then transplanted to bridge 10 mm sciatic nerve defects in rats. Morphological and functional examination shows that the repair effects of the TEN grafts and autografts are similar. The bionic TEN graft described in this study shows great potential for application and offers a new way to repair clinical peripheral nerve defects.

Artificial PGA/Collagen-based Bilayer Conduit in Short Gap Interposition Setting Provides Comparable Regenerative Potential to Direct Suture

The aim of this study was to evaluate whether the Nerbridge, an artificial polyglycolic acid conduit with collagen matrix, is comparable to direct nerve suture in a rat sciatic nerve injury model in a short-gap interposition (SGI) setting.

Methods

Sixty-six female Lewis rats were randomly divided into the sham group (n = 13); no reconstruction (no-recon) group (n = 13; rat model with 10 mm sciatic nerve defect); direct group (n = 20; rat sciatic nerve injury directly connected by 10-0 Nylon); and SGI group (n = 20; sciatic nerve injury repaired using 5-mm Nerbridge). Motor function and histological recovery were evaluated. The sciatic nerve and gastrocnemius muscle were harvested for quantification of the degree of nerve regeneration and muscle atrophy.

Results

The SGI and direct groups achieved equal recovery in both functional and histological outcomes. At weeks 3 and 8 postsurgery, there was a significant improvement in the sciatic functional index of the SGI group when compared with that of the no-recon group (P < 0.05). Furthermore, the direct and SGI groups had less muscle atrophy at 4 and 8 weeks postsurgery compared with the no-recon group (P < 0.05). The axon density and diameter at the distal site in the SGI group were significantly higher than that in the no-recon group and comparable to that in the direct and sham groups.

Conclusion

An artificial nerve conduit has equal potential as direct suture in motor nerve reconstruction when used in the SGI setting.

Enhanced sciatic nerve regeneration with fibrin scaffold containing human endometrial stem cells and insulin encapsulated chitosan particles: An in vivo study

BACKGROUND

Based on recent advances in tissue engineering and stem cell therapy in nervous system diseases treatments, this study aimed to investigate sciatic nerve regeneration using human endometrial stem cells (hEnSCs) encapsulated fibrin gel containing chitosan nanoparticle loaded by insulin (Ins-CPs). Stem cells and also Insulin (Ins), which is a strong signaling molecule in peripheral nerve regeneration, play an important role in neural tissue engineering.

METHODS

The fibrin hydrogel scaffold containing insulin loaded chitosan particles was synthesized and characterized. Release profiles of insulin from hydrogel was determined through UV-visible spectroscopy. Also, human endometrial stem cells encapsulated in hydrogel and its cell biocompatibility were assigned. Furthermore, the sciatic nerve crush injury was carried out and prepared fibrin gel was injected at the crush injury site by an 18-gage needle. Eight and twelve weeks later, the recovery of motor and sensory function and histopathological evaluation were assessed.

RESULTS

The in vitro experiments showed that the insulin can promote hEnSCs proliferation within a certain concentration range. Animals' treatment confirmed that developed fibrin gel containing Ins-CPs and hEnSCs significantly improves motor function and sensory recovery. Hematoxylin and Eosin (H&E) images provided from cross-sectional and, longitudinal-sections of the harvested regenerative nerve showed that regenerative nerve fibers had been formed and accompanied with new blood vessels in the fibrin/insulin/hEnSCs group.

CONCLUSION

Our results demonstrated that the prepared hydrogel scaffolds containing insulin nanoparticles and hEnSCs could be considered as a potential biomaterial aimed at regeneration of sciatic nerves.

Nerve Regeneration Effect of a Composite Bioactive Carboxymethyl Chitosan-Based Nerve Conduit with a Radial Texture

Chitosan (CTS) has been used as a nerve guidance conduit (NGC) material for bridging peripheral nerve defects due to its biocompatible, biodegradable, and non-toxic properties. However, the nerve regeneration effect of chitosan alone is restricted due to its inadequate biological activity. Herein, a composite, bioactive chitosan based nerve conduit, consisting of outer warp-knitted tube scaffold made from medical-grade chitosan fiber, and inner porous cross linked carboxymethyl chitosan (C-CM-CTS) sponge with radial texture was developed. The inner wall of the scaffold was coated with C-CM-CTS solution. CM-CTS provided favorable bioactivities in the composite chitosan-based nerve conduit. An in vitro study of CM-CTS revealed its satisfying biocompatibility with fibroblast and its inhibition of oxidative damage to Schwann cells. As the internal filler of the NGC, the lyophilized sponge of C-CM-CTS showed a longitudinal guidance effect for nerve reconstruction. After 10 mm defect in rat sciatic nerve was bridged with the composite bioactive chitosan-based nerve conduit, the nerve conduit was able to effectively promote axonal regeneration and played a positive role in inducing nerve regeneration and functional recovery. In addition to the functional advantages, which are equal to those of an autograft; the technology for the preparation of this conduit can be put into mass production.

Chitosan degradation products promote healing of burn wounds of rat skin

Burns can impair the barrier function of the skin, and small burns can also cause high mortality. The WHO has described that over 180,000 people die of burns worldwide each year. Thus, the treatment of burn wounds is a major clinical challenge. Chitooligosaccharides (COS) are alkaline amino oligosaccharides with small molecular weights obtained by enzyme or chemical degradation of chitosan. With the characteristics of biocompatibility, water solubility and degradability, it has attracted increasing attention in the fields of biomedicine. In the present study, we used COS to treat deep second-degree burn wounds of rat skin and found that COS was able to promote wound healing. We also revealed that COS could promote fibroblast proliferation. Transcriptome sequencing analysis was performed on COS-treated fibroblasts to identify the underlying mechanisms. The results showed that COS was able to promote wound healing through regulation of the mitogen-activated protein kinase (MAPK) pathway and growth factor Hepatocyte Growth Factor (HGF). Our results provide a potential drug for burn wound therapy and the related molecular mechanism.

Sustainable applications of polyhydroxyalkanoates in various fields: A critical review

PHA is one of the most promising candidates in bio-polymer family which is biodegradable and environment-friendly in nature. In recent years, it has been applied as a biodegradable alternative for petroleum-based plastic across different domains. In literature, several research groups have scrutinised the biocompatibility and biodegradability of PHA in both in vivo settings as well as in in vitro conditions. Microbial yield polyhydroxyalkanoates (PHAs) are promoted at present as biodegradable plastics. On the other hand, only a limited number of products is being commercially manufactured out of PHAs (e.g., bottles). A succession of microbes (prokaryotes in addition to eukaryotes) has been identified as potential candidates that can disintegrate PHAs. These materials have been successfully employed in packaging industry, medical devices and implants, moulded goods, paper coatings, adhesives, performance additives, mulch films, non-woven fabrics, etc. The present paper reviews and focuses on the potential applications of PHA and its derivatives in different industries.

Blood vessel remodeling in late stage of vascular network reconstruction is essential for peripheral nerve regeneration

One of the bottlenecks of advanced study on tissue engineering in regenerative medicine is rapid and functional vascularization. For a deeper comprehension of vascularization, the exhaustive, dynamic, and three-dimensional depiction of perfused vascular network reconstruction during peripheral nerve regeneration was performed using Micro-CT scanning. The 10 mm defect of sciatic nerve in rat was bridged by the autologous or tissue engineered nerve. The blood vessel anastomosis between nerve stumps and autologous nerve accomplished at 4 days to 1 week after surgery, which was a sufficient basis for the mature vascular network re-establishment. The stronger ability for sprouting angiogenesis and vascular remodeling of autologous nerve compared with tissue engineered nerve was revealed. However, common phases of vascularization in peripheral nerve regeneration were painted: hypoxic initiation, sprouting angiogenesis, and remodeling and maturation. The effect of less-concerned vascular remodeling on nerve regeneration was further analyzed after nerve crush injury. The blockage of vascular remodeling in late stage by VEGF injection significantly inhibited axons and myelin sheaths regeneration, which attenuated the impulse conduction toward reinnervated muscles. It was illustrated that a large amount of immature blood vessels rather than necessary vascular remodeling elevated local inflammation level in nerve regeneration microenvironment. The figures inspired us to understand the close connections between vascularization and peripheral nerve regeneration from a broader dimension to achieve better constructions, regulations and repair effects of tissue engineered nerves in clinic.

Implantable nerve guidance conduits: Material combinations, multi-functional strategies and advanced engineering innovations

Nerve guidance conduits (NGCs) have attracted much attention due to their great necessity and applicability in clinical use for the peripheral nerve repair. Great efforts in recent years have been devoted to the development of high-performance NGCs using various materials and strategies. The present review provides a comprehensive overview of progress in the material innovation, structural design, advanced engineering technologies and multi functionalization of state-of-the-art nerve guidance conduits NGCs. Abundant advanced engineering technologies including extrusion-based system, laser-based system, and novel textile forming techniques in terms of weaving, knitting, braiding, and electrospinning techniques were also analyzed in detail. Findings arising from this review indicate that the structural mimetic NGCs combined with natural and synthetic materials using advanced manufacturing technologies can make full use of their complementary advantages, acquiring better biomechanical properties, chemical stability and biocompatibility. Finally, the existing challenges and future opportunities of NGCs were put forward aiming for further research and applications of NGCs.

Implantable Biomaterials for Peripheral Nerve Regeneration-Technology Trends and Translational Tribulations

The use of autografted nerve in surgical repair of peripheral nerve injuries (PNI) is severely limited due to donor site morbidity and restricted tissue availability. As an alternative, synthetic nerve guidance channels (NGCs) are available on the market for surgical nerve repair, but they fail to promote nerve regeneration across larger critical gap nerve injuries. Therefore, such injuries remain unaddressed, result in poor healing outcomes and are a limiting factor in limb reconstruction and transplantation. On the other hand, a myriad of advanced biomaterial strategies to address critical nerve injuries are proposed in preclinical literature but only few of those have found their way into clinical practice. The design of synthetic nerve grafts should follow rational criteria and make use of a combination of bioinstructive cues to actively promote nerve regeneration. To identify the most promising NGC designs for translation into applicable products, thorough mode of action studies, standardized readouts and validation in large animals are needed. We identify design criteria for NGC fabrication according to the current state of research, give a broad overview of bioactive and functionalized biomaterials and highlight emerging composite implant strategies using therapeutic cells, soluble factors, structural features and intrinsically conductive substrates. Finally, we discuss translational progress in bioartificial conduits for nerve repair from the surgeon's perspective and give an outlook toward future challenges in the field.

Combined use of chitosan-PGLA nerve grafts and bone marrow mononuclear cells to repair a 50-mm-long median nerve defect combined with an 80-mm-long ulnar nerve defect in the human upper arm

BACKGROUND

Severe peripheral nerve injury, especially the long-distance peripheral nerve defect caused severe functional disability to patients. And there is always a lack of effective and less side effects of repair methods for clinics. A case study was performed to observe the regenerative outcomes of the surgical repair of long-distance peripheral nerve defects in the upper arm with chitosan-poly(glycolide-co-lactide) (PGLA) nerve grafts combined with bone marrow mononuclear cells (BMMCs).

METHODS

The right upper arm of a 29-year-old woman was injured, leaving a 50-mm-long median nerve defect, an 80-mm-long ulnar nerve defect, and muscle and blood vessel disruptions. The nerve defects were repaired by implanting BMMC-containing chitosan-PGA nerve grafts on the 40th day after injury. A series of functional assessments were carried out from 2 weeks to 66 months after surgical repair. Sensory function was assessed by the pinprick test, two-point discrimination test and Semmes-Weinstein monofilament test. Motor function was evaluated by the range of motion of the wrist joint and muscle power. Autonomic function was monitored by laser-Doppler perfusion imaging (LDPI). Tissue morphology was observed through ultrasonic investigations.

RESULTS

No adverse events, such as infection, allergy, or rejection, caused by the treatment were detected during the follow-up period. Sensory and pinprick nociception in the affected thumb, index, and middle fingers were restored gradually from the 6th month after surgery. The monofilament tactile sensation was 0.4 g in the terminal finger pulp of the thumb and index finger, 2.0 g in the middle finger, and greater than 300 g in the ring finger and little finger at the 66th month. Motor function recovery was detected at the 5th month after surgery, when the muscle strength of the affected forearm flexors began to recover. At the 66th month after surgery, the patient's forearm flexor strength was grade 4, with 80° of palmar flexion, 85° of dorsal extension, 8° of radial deviation, 40° of ulnar deviation, 40° of anterior rotation, and 85° of posterior rotation of the affected wrist. The patient could perform holding, picking up, and some other daily activities with the affected hand. The patient's sweating function of the affected hand was close to the level of the healthy hand. LDPI showed that the skin blood flow perfusion was significantly increased, with perfusion similar to on the normal side in some areas. Neuromusculoskeletal ultrasonography showed the presence of nerve structures.

CONCLUSIONS

These results suggest that chitosan-PGLA nerve grafts combined with BMMCs could effectively repair long-distance nerve defects and achieve good clinical results.

3D Printed Personalized Nerve Guide Conduits for Precision Repair of Peripheral Nerve Defects

The treatment of peripheral nerve defects has always been one of the most challenging clinical practices in neurosurgery. Currently, nerve autograft is the preferred treatment modality for peripheral nerve defects, while the therapy is constantly plagued by the limited donor, loss of donor function, formation of neuroma, nerve distortion or dislocation, and nerve diameter mismatch. To address these clinical issues, the emerged nerve guide conduits (NGCs) are expected to offer effective platforms to repair peripheral nerve defects, especially those with large or complex topological structures. Up to now, numerous technologies are developed for preparing diverse NGCs, such as solvent casting, gas foaming, phase separation, freeze-drying, melt molding, electrospinning, and three-dimensional (3D) printing. 3D printing shows great potential and advantages because it can quickly and accurately manufacture the required NGCs from various natural and synthetic materials. This review introduces the application of personalized 3D printed NGCs for the precision repair of peripheral nerve defects and predicts their future directions.

Repair of ovine peripheral nerve injuries with xenogeneic human acellular sciatic nerves prerecellularized with allogeneic Schwann-like cells-an innovative and promising approach

INTRODUCTION

The iatrogenic effects of repairing peripheral nerve injuries (PNIs) with autografts (AGTs) encouraged the present study to involve a new approach consisting of grafting xenogeneic prerecellularized allogeneic cells instead of AGTs.

METHODS

We compared sheep's AGT regenerative and functional capacity with decellularized human nerves prerecellularized with allogeneic Schwann-like cell xenografts (onwards called xenografts). Mesenchymal stem cells were isolated from ovine adipose tissue and induced in vitro to differentiate into Schwann-like cells (SLCs). Xenografts were grafted in ovine sciatic nerves. Left sciatic nerves (20 mm) were excised from 10 sheep. Then, five sheep were grafted with 20 mm xenografts, and five were reimplanted with their nerve segment rotated 180° (AGT).

RESULTS

All sheep treated with xenografts or AGT progressively recovered the strength, movement, and coordination of their intervened limb, which was still partial when the study was finished at sixth month postsurgery. At this time, numerous intrafascicular axons were observed in the distal and proximal graft extremes of both xenografts or AGTs, and submaximal nerve electrical conduction was observed. The xenografts and AGT-affected muscles appeared partially stunted.

CONCLUSIONS

Xenografts and AGT were equally efficacious in starting PNI repair and justified further studies using longer observation times. The hallmarks from this study are that human xenogeneic acellular scaffolds were recellularized with allogenic SCL and were not rejected by the nonhuman receptors but were also as functional as AGT within a relatively short time postsurgery. Thus, this innovative approach promises to be more practical and accessible than AGT or allogenic allografts and safer than AGT for PNI repair.

Proteomic Analysis of Silk Fibroin Reveals Diverse Biological Function of Different Degumming Processing From Different Origin

Silk, as a kind of natural fibrin, has been prepared into various biomaterials due to its excellent biocompatibility and mechanicalness. However, there are some controversies on the biocompatibility of silk fibroin (SF), especially when it coexists with sericin. In this study, two kinds of silk from Jiangsu and Zhejiang were degummed with two concentrations of Na₂CO₃ solution, respectively, to obtain four kinds of silk fibroin. The effects of different degumming treatments on silk fibroin properties were analyzed by means of color reaction, apparent viscosity measurement, and transmission electron microscope and isobaric tags for relative and absolute quantification analyses, and the effects of different silk fibroin membranes on the growth of Schwann cells were evaluated. The results showed that the natural silk from Zhejiang treated with 0.05% Na₂CO₃ solution had a fuller structure, higher apparent viscosity, and better protein composition. While SF obtained by degumming with 0.5% Na₂CO₃ solution was more beneficial to cell adhesion and proliferation due to the thorough removal of sericin. This study may provide important theoretical and experimental bases for the selection of biomaterials for fabricating artificial nerve grafts.

Delivery of nitric oxide-releasing silica nanoparticles for in vivo revascularization and functional recovery after acute peripheral nerve crush injury

Nitric oxide (NO) has been shown to promote revascularization and nerve regeneration after peripheral nerve injury. However, in vivo application of NO remains challenging due to the lack of stable carrier materials capable of storing large amounts of NO molecules and releasing them on a clinically meaningful time scale. Recently, a silica nanoparticle system capable of reversible NO storage and release at a controlled and sustained rate was introduced. In this study, NO-releasing silica nanoparticles (NO-SNs) were delivered to the peripheral nerves in rats after acute crush injury, mixed with natural hydrogel, to ensure the effective application of NO to the lesion. Microangiography using a polymer dye and immunohistochemical staining for the detection of CD34 (a marker for revascularization) results showed that NO-releasing silica nanoparticles increased revascularization at the crush site of the sciatic nerve. The sciatic functional index revealed that there was a significant improvement in sciatic nerve function in NO-treated animals. Histological and anatomical analyses showed that the number of myelinated axons in the crushed sciatic nerve and wet muscle weight excised from NO-treated rats were increased. Moreover, muscle function recovery was improved in rats treated with NO-SNs. Taken together, our results suggest that NO delivered to the injured sciatic nerve triggers enhanced revascularization at the lesion in the early phase after crushing injury, thereby promoting axonal regeneration and improving functional recovery.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

The balanced microenvironment regulated by the degradants of appropriate PLGA scaffolds and chitosan conduit promotes peripheral nerve regeneration

Tissue-engineered nerve grafts (TENGs) are the most promising way for repairing long-distance peripheral nerve defects. Chitosan and poly (lactic-co-glycolic acid) (PLGA) scaffolds are considered as the promising materials in the pharmaceutical and biomedical fields especially in the field of tissue engineering. To further clarify the effects of a chitosan conduit inserted with various quantity of poly (lactic-co-glycolic acid) (PLGA) scaffolds, and their degrades on the peripheral nerve regeneration, the chitosan nerve conduit inserted with different amounts of PLGA scaffolds were used to repair rat sciatic nerve defects. The peripheral nerve regeneration at the different time points was dynamically and comprehensively evaluated. Moreover, the influence of different amounts of PLGA scaffolds on the regeneration microenvironment including inflammatory response and cell state were also revealed. The modest abundance of PLGA is more instrumental to the success of nerve regeneration, which is demonstrated in terms of the structure of the regenerated nerve, reinnervation of the target muscle, nerve impulse conduction, and overall function. The PLGA scaffolds aid the migration and maturation of Schwann cells. Furthermore, the PLGA and chitosan degradation products in a correct ratio neutralize, reducing the inflammatory response and enhancing the regeneration microenvironment. The balanced microenvironment regulated by the degradants of appropriate PLGA scaffolds and chitosan conduit promotes peripheral nerve regeneration. The findings represent a further step towards programming TENGs construction, applying polyester materials in regenerative medicine, and understanding the neural regeneration microenvironment.

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Guide scaffolds are necessary for construction of TENGs to benefeat Schwann cell migration and maturation.

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A large number of acid degradation products of PLGA scaffolds adversely affect cell proliferation, migration and apoptosis.

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Appropriate amount of PLGA scaffolds balance positive cell guidance and negative degradation inflammation.

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Dosage of PLGA and its combination with complementary biomaterials are key factors that affect regeneration effects.

Dysregulated miR-29a-3p/PMP22 Modulates Schwann Cell Proliferation and Migration During Peripheral Nerve Regeneration

Schwann cells switch to a repair phenotype following peripheral nerve injury and create a favorable microenvironment to drive nerve repair. Many microRNAs (miRNAs) are differentially expressed in the injured peripheral nerves and play essential roles in regulating Schwann cell behaviors. Here, we examine the temporal expression patterns of miR-29a-3p after peripheral nerve injury and demonstrate significant up-regulation of miR-29a-3p in injured sciatic nerves. Elevated miR-29a-3p inhibits Schwann cell proliferation and migration, while suppressed miR-29a-3p executes reverse effects. In vivo injection of miR-29a-3p agomir to rat sciatic nerves hinders the proliferation and migration of Schwann cells, delays the elongation and myelination of axons, and retards the functional recovery of injured nerves. Mechanistically, miR-29a-3p modulates Schwann cell activities via negatively regulating peripheral myelin protein 22 (PMP22), and PMP22 extensively affects Schwann cell metabolism. Our results disclose the vital role of miR-29a-3p/PMP22 in regulating Schwann cell phenotype following sciatic nerve injury and shed light on the mechanistic basis of peripheral nerve regeneration.

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Nerve-specific extracellular matrix hydrogel promotes functional regeneration following nerve gap injury

Nerve transection requires surgical intervention to restore function. The standard of care involves coaptation when a tension-free repair is achievable, or interposition of a graft or conduit when a gap remains. Despite advances, nerve gap injury is associated with unsatisfactory recovery. This study investigates the use of a decellularized, porcine nerve-derived hydrogel filler (peripheral nerve matrix, PNM) for conduits in an 8 mm rat sciatic nerve gap model. The decellularized tissue maintained multiple nerve-specific matrix components and nerve growth factors. This decellularized tissue was used to formulate hydrogels, which were deployed into conduits for nerve gap repair. Nerve recovery was assessed up to 24 weeks post injury by gait analysis, electrophysiology, and axon counting. Deployment of PNM within conduits was shown to improve electrophysiologic response and axon counts compared with those of empty conduit controls. These results indicate that PNM has potential benefits when used as a filler for conduits in nerve gap injuries.

Chitin scaffold combined with autologous small nerve repairs sciatic nerve defects

Although autologous nerve transplantation is the gold standard for treating peripheral nerve defects, it has many clinical limitations. As an alternative, various tissue-engineered nerve grafts have been developed to substitute for autologous nerves. In this study, a novel nerve graft composed of chitin scaffolds and a small autologous nerve was used to repair sciatic nerve defects in rats. The novel nerve graft greatly facilitated regeneration of the sciatic nerve and myelin sheath, reduced atrophy of the target muscle, and effectively restored neurological function. When the epineurium of the small autogenous nerve was removed, the degree of nerve regeneration was similar to that which occurs after autogenous nerve transplantation. These findings suggest that our novel nerve graft might eventually be a new option for the construction of tissue-engineered nerve scaffolds. The study was approved by the Research Ethics Committee of Peking University People's Hospital (approval No. 2019PHE27) on October 18, 2019.

Natural Flammulina velutipes-Based Nerve Guidance Conduit as a Potential Biomaterial for Peripheral Nerve Regeneration: In Vitro and In Vivo Studies

The treatment and repair of serious peripheral nerve injuries remain challenging in the clinical practice, while the application of multifunctional nerve guidance conduits (NGCs) based on naturally derived polymers has attracted much attention in recent years because of their excellent physicochemical properties and biological characteristics. Flammulina velutipes (Curt. ex FV) is a popular edible mushroom characterized by hollow tubular structures, antibacterial activities, and high nutritional properties. In this study, FV is utilized to construct NGCs (labeled FVC) via a freeze-drying technique without chemical modifications. The morphology, physical properties, cellular biocompatibility, antibacterial properties, and nerve regeneration capacity of FVC were assessed both in vitro and in vivo. FVC is composed of hollow tubes and evenly irregular interconnected micropores with 73.8 ± 5.5% porosity and 476.1 ± 12.9 μm hollow tube diameter. The inner surface of the FVC presents multiple microgrooves elongated parallel to the long axis. Moreover, FVC possessed strong antibacterial activity and could inhibit Gram-positive Staphylococcus aureus growth by up to 96.0% and Gram-negative Escherichia coli growth by up to 94.8% in vitro. FVC exhibited excellent biocompatibility and effectively promoted PC-12 cell proliferation and elongation in vitro. When applied to repair critical-sized sciatic nerve defects, FVC could effectively stimulate nerve functional recovery and axonal outgrowth in a rat model. Interestingly, Western blot analysis indicated that growth-associated protein 43 (GAP-43) had increased expression levels in the FVC group compared with the autograft group. This result suggested that by activating the Janus activated kinase2 (JAK2)/Phosphorylation ofsignal transducer and activator of transcription-3 (STAT3) signaling pathway, FVC upregulated Phosphorylation of signal transducer and activator of transcription-3 (P-STAT3) in vivo, resulting in the secretion of GAP-43. Collectively, a natural NGC FVC was fabricated based on FV without chemical modifications. The morphology, physical properties, cellular biocompatibility, antibacterial properties, and nerve regeneration capacity of FVC provide new insights for its further optimization and application in the field of nerve tissue engineering.

[In vivo degradation and histocompatibility of modified chitosan based on conductive composite nerve conduit]

Objective

To investigate the in vivo degradation and histocompatibility of modified chitosan based on conductive composite nerve conduit, so as to provide a new scaffold material for the construction of tissue engineered nerve.

Methods

The nano polypyrrole (PPy) was synthesized by microemulsion polymerization, blended with chitosan, and then formed conduit by injecting the mixed solution into a customized conduit formation model. After freeze-drying and deacidification, the nano PPy/chitosan composite conduit (CP conduit) was prepared. Then the CP conduits with different acetyl degree were resulted undergoing varying acetylation for 30, 60, and 90 minutes (CAP1, CAP2, CAP3 conduits). Fourier infrared absorption spectrum and scanning electron microscopy (SEM) were used to identify the conduits. And the conductivity was measured by four-probe conductometer. The above conduits were implanted after the subcutaneous fascial tunnels were made symmetrically on both sides of the back of 30 female Sprague Dawley rats. At 2, 4, 6, 8, 10, and 12 weeks after operation, the morphology, the microstructure, and the degradation rate were observed and measured to assess the in vivo degradation of conduits. HE staining and anti-macrophage immunofluorescence staining were performed to observe the histocompatibility in vivo.

Results

The characteristic peaks of the amide Ⅱ band around 1 562 cm ^-1 appeared after being acetylated, indicating that the acetylation modification of chitosan was successful. There was no significant difference in conductivity between conduits ( P>0.05). SEM observation showed that the surfaces of the conduits in all groups were similar with relatively smooth surface and compact structure. After the conduits were implanted into the rats, with the extension of time, all conduits were collapsed, especially on the CAP3 conduit. All conduits had different degrees of mass loss, and the higher the degree of acetylation, the greater the mass change ( P<0.05). SEM observation showed that there were more pores at 12 weeks after implantation, and the pores showed an increasing trend as the degree of acetylation increased. Histological observation showed that there were more macrophages and lymphocytes infiltration in each group at the early stage. With the extension of implantation time, lymphocytes decreased, fibroblasts increased, and collagen fibers proliferated significantly.

Conclusion

The modified chitosan basedon conductive composite nerve conduit made of nano-PPy/chitosan composite with different acetylation degrees has good biocompatibility, conductivity, and biodegradability correlated with acetylation degree in vivo, which provide a new scaffold material for the construction of tissue engineered nerve.

Chitosan grafted/cross-linked with biodegradable polymers: A review

Public perception of polymers has been drastically changed with the improved plastic management at the end of their life. However, it is widely recognised the need of developing biodegradable polymers, as an alternative to traditional petrochemical polymers. Chitosan (CH), a biodegradable biopolymer with excellent physiological and structural properties, together with its immunostimulatory and antibacterial activity, is a good candidate to replace other polymers, mainly in biomedical applications. However, CH has also several drawbacks, which can be solved by chemical modifications to improve some of its characteristics such as solubility, biological activity, and mechanical properties. Many chemical modifications have been studied in the last decade to improve the properties of CH. This review focussed on a critical analysis of the state of the art of chemical modifications by cross-linking and graft polymerization, between CH or CH derivatives and other biodegradable polymers (polysaccharides or proteins, obtained from microorganisms, synthetized from biomonomers, or from petrochemical products). Both techniques offer the option of including a wide variety of functional groups into the CH chain. Thus, enhanced and new properties can be obtained in accordance with the requirements for different applications, such as the release of drugs, the improvement of antimicrobial properties of fabrics, the removal of dyes, or as scaffolds to develop bone tissues.

Biocompatibility and biosafety of butterfly wings for the clinical use of tissue-engineered nerve grafts

In a previous study, we used natural butterfly wings as a cell growth matrix for tissue engineering materials and found that the surface of different butterfly wings had different ultramicrostructures, which can affect the qualitative growth of cells and regulate cell growth, metabolism, and gene expression. However, the biocompatibility and biosafety of butterfly wings must be studied. In this study, we found that Sprague-Dawley rat dorsal root ganglion neurons could grow along the structural stripes of butterfly wings, and Schwann cells could normally attach to and proliferate on different species of butterfly wings. The biocompatibility and biosafety of butterfly wings were further examined through subcutaneous implantation in Sprague-Dawley rats, intraperitoneal injection in Institute of Cancer Research mice, intradermal injection in rabbits, and external application to guinea pigs. Our results showed that butterfly wings did not induce toxicity, and all examined animals exhibited normal behaviors and no symptoms, such as erythema or edema. These findings suggested that butterfly wings possess excellent biocompatibility and biosafety and can be used as a type of tissue engineering material. This study was approved by the Experimental Animal Ethics Committee of Jiangsu Province of China (approval No. 20190303-18) on March 3, 2019.

Biomimetic and hierarchical nerve conduits from multifunctional nanofibers for guided peripheral nerve regeneration

Development of a functional nerve conduit to replace autografts remains a significant challenge particularly considering the compositional complexity and structural hierarchy of native peripheral nerves. In the present study, a multiscale strategy was adopted to fabricate 3D biomimetic nerve conduit from Antheraea pernyi silk fibroin (ApF)/(Poly(L-lactic acid-co-caprolactone)) (PLCL)/graphene oxide (GO) (ApF/PLCL/GO) nanofibers via nanofiber dispersion, template-molding, freeze-drying and crosslinking. The resultant conduits exhibit parallel multichannels (ϕ = 125 µm) surrounded by biomimetic fibrous fragments with tailored degradation rate and improved mechanical properties in comparison with the scaffold without GO. In vitro studies showed that such 3D biomimetic nerve scaffolds had the ability to offer an effective guiding interface for neuronal cell growth. Furthermore, these conduits showed a similarity to autografts in vivo repairing sciatic nerve defects based on a series of analysis (walking track, triceps weight, morphogenesis, vascularization, axonal regrowth and myelination). The conduits almost completely degraded within 12 weeks. These findings demonstrate that the 3D hierarchical nerve guidance conduit (NGC) with fascicle-like structure have great potential for peripheral nerve repair.

Functionalized nerve conduits for peripheral nerve regeneration: A literature review

Functionalized neurotube are a third-generation of conduits with chemical or architectural bioactivity developed for axonal proliferation. The goal of this review is to provide a synopsis of the functionalized nerve conduits described in the literature according to their chemical and architectural properties and answer two questions: what are their mechanisms of action? Has their efficacy been proven compared to the autologous nerve graft? Our literature review relates all kind of conduits corresponding to functionalized neurotubes in peripheral nerve regeneration found in Medline and PubMed Central. Studies developing nerve gaps, chemotactic or structural features promoting each conduit, results, efficiency were selected. Fifty-five studies were selected and classified in: (a) intraluminal neurotrophic factors; (b) cell-based therapy (combined-in-vein muscles, amniotic membrane, Schwann cells, stem cells); (c) extracellular matrix proteins; (d) tissue engineering; (e) bioimplants. Functionalized neurotubes showed significantly better functional results than after end-to-end nerve suture. No studies can be able to show that neurotube results were better than autologous nerve graft results. We included all studies regardless of effectives to evaluate quality of reinnervation with modern tubulization. Functionalized neurotubes promote basic conduits for peripheral nerve regeneration. Thanks to bioengineering and microsurgery improvement, further neurotubes could promote best level of regeneration and functional recovery to successfully bridge a critical nerve gap.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates

Severe injuries to peripheral nerves are challenging to repair. Standard-of-care treatment for nerve gaps >2 to 3 centimeters is autografting; however, autografting can result in neuroma formation, loss of sensory function at the donor site, and increased operative time. To address the need for a synthetic nerve conduit to treat large nerve gaps, we investigated a biodegradable poly(caprolactone) (PCL) conduit with embedded double-walled polymeric microspheres encapsulating glial cell line–derived neurotrophic factor (GDNF) capable of providing a sustained release of GDNF for >50 days in a 5-centimeter nerve defect in a rhesus macaque model. The GDNF-eluting conduit (PCL/GDNF) was compared to a median nerve autograft and a PCL conduit containing empty microspheres (PCL/Empty). Functional testing demonstrated similar functional recovery between the PCL/GDNF-treated group (75.64 ± 10.28%) and the autograft-treated group (77.49 ± 19.28%); both groups were statistically improved compared to PCL/Empty-treated group (44.95 ± 26.94%). Nerve conduction velocity 1 year after surgery was increased in the PCL/GDNF-treated macaques (31.41 ± 15.34 meters/second) compared to autograft (25.45 ± 3.96 meters/second) and PCL/Empty (12.60 ± 3.89 meters/second) treatment. Histological analyses included assessment of Schwann cell presence, myelination of axons, nerve fiber density, and g-ratio. PCL/GDNF group exhibited a statistically greater average area occupied by individual Schwann cells at the distal nerve (11.60 ± 33.01 μm2) compared to autograft (4.62 ± 3.99 μm2) and PCL/Empty (4.52 ± 5.16 μm2) treatment groups. This study demonstrates the efficacious bridging of a long peripheral nerve gap in a nonhuman primate model using an acellular, biodegradable nerve conduit.

The progress of biomaterials in peripheral nerve repair and regeneration

Repair and regeneration of the injured peripheral nerve (PN) is a challenging issue in clinics. Although the regeneration outcome of large PN defects is currently unsatisfactory, recently, the study of PN repair has considerably progressed. In particular, biomaterials for repairing PNs, such as nerve guidance conduits and nerve repair membranes, have been well developed. Herein, we summarize the anatomy of the PN, the pathophysiological features of the nerve injury, and the repair process post injury. Then, we highlight the progress in the development of natural and synthetic biomaterials and summarize the applications, advantages, and disadvantages of these materials. These materials can be used as nerve repair membranes and nerve conduits in the field of PN repair. Finally, we discuss the challenges encountered and development strategies for PN repair in the future.