Peripheral nerve repair and grafting techniques: a review

Research advancements on nerve guide conduits for nerve injury repair

Peripheral nerve injury (PNI) is one of the most serious causes of disability and loss of work capacity of younger individuals. Although PNS has a certain degree of regeneration, there are still challenges like disordered growth, neuroma formation, and incomplete regeneration. Regarding the management of PNI, conventional methods such as surgery, pharmacotherapy, and rehabilitative therapy. Treatment strategies vary depending on the severity of the injury. While for the long nerve defect, autologous nerve grafting is commonly recognized as the preferred surgical approach. Nevertheless, due to lack of donor sources, neurological deficits and the low regeneration efficiency of grafted nerves, nerve guide conduits (NGCs) are recognized as a future promising technology in recent years. This review provides a comprehensive overview of current treatments for PNI, and discusses NGCs from different perspectives, such as material, design, fabrication process, and composite function.

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.

Peripheral nerve regeneration following scaffold-free conduit transplant of autologous dermal fibroblasts: a non-randomised safety and feasibility trial

BACKGROUND

The use of Bio 3D nerve conduits is a promising approach for peripheral nerve reconstruction. This study aimed to assess their safety in three patients with peripheral nerve defects in their hands.

METHODS

We describe a single institution, non-blinded, non-randomised control trial conducted at Kyoto University Hospital. Eligibility criteria included severed peripheral nerve injuries or a defect in the region distal to the wrist joint not caused by a congenital anomaly; a defect with a length of ≤20 mm in a nerve with a diameter ≤2 mm; failed results of sensory functional tests; ability to register in the protocol within 6 months from the day of injury; refusal of artificial nerve or autologous nerve transplantation; age 20-60 years; and willingness to participate and provide informed written consent. Six weeks before transplantation, skin was harvested, dermal fibroblasts were isolated and expanded, and Bio 3D nerve conduits were created using a Bio 3D printer. Bio 3D nerve conduits were transplanted into the patients' nerve defects. The safety of Bio 3D nerve conduits in patients with a peripheral nerve injury in the distal part of the wrist joint were assessed over a 48-week period after transplantation.

RESULTS

No adverse events related to the use of Bio 3D nerve conduits were observed in any patient, and all three patients completed the trial.

CONCLUSIONS

Bio 3D nerve conduits were successfully used for clinical nerve reconstruction without adverse events and are a possible treatment option for peripheral nerve injuries.

Morphology and morphometry of the ulnar nerve in the forelimb of pigs

The knowledge of the morphology and morphometry of peripheral nerves is essential for developing neural interfaces and understanding nerve regeneration in basic and applied research. Currently, the most adopted animal model is the rat, even though recent studies have suggested that the neuroanatomy of large animal models is more comparable to humans. The present knowledge of the morphological structure of large animal models is limited; therefore, the present study aims to describe the morphological characteristics of the Ulnar Nerve (UN) in pigs. UN cross-sections were taken from seven Danish landrace pigs at three distinct locations: distal UN, proximal UN and at the dorsal cutaneous branch of the UN (DCBUN). The nerve diameter, fascicle diameter and number, number of fibres and fibre size were quantified. The UN diameter was larger in the proximal section compared to the distal segment and the DCBUN. The proximal branch also had a more significant number of fascicles (median: 15) than the distal (median: 10) and the DCBUN (median: 11) segments. Additionally, the mean fascicle diameter was smaller at the DCBUN (mean: 165 μm) than at the distal (mean: 197 μm) and proximal (mean: 199 μm) segments of the UN. Detailed knowledge of the microscopical structure of the UN in pigs is critical for further studies investigating neural interface designs and computational models of the peripheral nervous system.

The effect of conductive aligned fibers in an injectable hydrogel on nerve tissue regeneration

Injectable hydrogels are a promising treatment option for nervous system injuries due to the difficulty to replace lost cells and nervous factors but research on injectable conductive hydrogels is limited and these scaffolds have poor electromechanical properties. This study developed a chitosan/beta-glycerophosphate/salt hydrogel and added conductive aligned nanofibers (polycaprolactone/gelatin/single-wall carbon nanotube (SWCNT)) for the first time and inspired by natural nerve tissue to improve their biochemical and biophysical properties. The results showed that the degradation rate of hydrogels is proportional to the regrowth of axons and these hydrogels' mechanical (hydrogels without nanofibers or SWCNTs and hydrogels containing these additions have the same Young's modulus as the brain and spinal cord or peripheral nerves, respectively) and electrical properties, and the interconnective structure of the scaffolds have the ability to support cells.

Surgical management and final outcomes of chondrosarcoma of the temporomandibular joint: case series and comprehensive literature review

BACKGROUND

Surgical management for chondrosarcoma of the temporomandibular joint (TMJ) is challenging due to the anatomical location involving the facial nerve and the functional joint. The purpose of this case series was to analyze the largest number of TMJ chondrosarcoma cases reported from a single institution and to review the literature about chondrosarcoma involving the TMJ.

METHODS

Ten TMJ chondrosarcoma patients at Seoul National University Dental Hospital were included in this study. Radiographic features, surgical approaches, histopathologic subtypes, and treatment modalities were evaluated. All case reports of TMJ chondrosarcoma published in English from 1954 to 2021 were collected under PRISMA guidelines and comprehensively reviewed.

RESULTS

The lesions were surgically resected in all 10 patients with efforts to preserve facial nerve function. Wide excision including margins of normal tissue was performed to ensure adequate resection margins. All TMJs were reconstructed with a metal condyle except one, which was reconstructed with vascularized costal bone. At last follow-up, all patients were still alive, and there had been no recurrence. Among 47 cases (patients from the literature and our cases), recurrence was specified in 43 and occurred in four (9.5%).

CONCLUSIONS

For surgical management of TMJ chondrosarcoma, wide excision must consider preservation of the facial nerve. Reconstruction using a metal condyle prosthesis and a vascularized free flap is reliable. A more conservative surgical approach correlates with a favorable prognosis for facial nerve recovery. Nevertheless, wide excision is imperative to prevent tumor recurrence. In cases in which the glenoid fossa is unaffected by the tumor, it is deemed unnecessary to reconstruct the glenoid fossa within an oncological setting.

Advances in Facial Reanimation

Facial nerve paralysis is a debilitating clinical entity that presents as a complete or incomplete loss of facial nerve function. The etiology of facial nerve palsy and sequelae varies tremendously. The most common cause of facial paralysis is Bell's palsy, followed by malignant or benign tumors, iatrogenic insults, trauma, virus-associated paralysis, and congenital etiologies.

Peripheral nerve defects repaired with autogenous vein grafts filled with platelet-rich plasma and active nerve microtissues and evaluated by novel multimodal ultrasound techniques

BACKGROUND

Developing biocompatible nerve conduits that accelerate peripheral nerve regeneration, lengthening and functional recovery remains a challenge. The combined application of nerve microtissues and platelet-rich plasma (PRP) provides abundant Schwann cells (SCs) and various natural growth factors and can compensate for the deficiency of SCs in the nerve bridge, as well as the limitations of applying a single type of growth factor. Multimodal ultrasound evaluation can provide additional information on the stiffness and microvascular flow perfusion of the tissue. This study was designed to investigate the effectiveness of a novel tissue-engineered nerve graft composed of an autogenous vein, nerve microtissues and PRP in reconstructing a 12-mm tibial nerve defect and to explore the value of multimodal ultrasound techniques in evaluating the prognosis of nerve repair.

METHODS

In vitro, nerve microtissue activity was first investigated, and the effects on SC proliferation, migration, factor secretion, and axonal regeneration of dorsal root ganglia (DRG) were evaluated by coculture with nerve microtissues and PRP. In vivo, seventy-five rabbits were equally and randomly divided into Hollow, PRP, Micro-T (Microtissues), Micro-T + PRP and Autograft groups. By analysing the neurological function, electrophysiological recovery, and the comparative results of multimodal ultrasound and histological evaluation, we investigated the effect of these new nerve grafts in repairing tibial nerve defects.

RESULTS

Our results showed that the combined application of nerve microtissues and PRP could significantly promote the proliferation, secretion and migration of SCs and the regeneration of axons in the early stage. The Micro-T + PRP group and Autograft groups exhibited the best nerve repair 12 weeks postoperatively. In addition, the changes in target tissue stiffness and microvascular perfusion on multimodal ultrasound (shear wave elastography; contrast-enhanced ultrasonography; Angio PlaneWave UltrasenSitive, AngioPLUS) were significantly correlated with the histological results, such as collagen area percentage and VEGF expression, respectively.

CONCLUSION

Our novel tissue-engineered nerve graft shows excellent efficacy in repairing 12-mm defects of the tibial nerve in rabbits. Moreover, multimodal ultrasound may provide a clinical reference for prognosis by quantitatively evaluating the stiffness and microvescular flow of nerve grafts and targeted muscles.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Dielectric Elastomer Actuators, Neuromuscular Interfaces, and Foreign Body Response in Artificial Neuromuscular Prostheses: A Review of the Literature for an In Vivo Application

The inability to replace human muscle in surgical practice is a significant challenge. An artificial muscle controlled by the nervous system is considered a potential solution for this. Here, this is defined as a neuromuscular prosthesis. Muscle loss and dysfunction related to musculoskeletal oncological impairments, neuromuscular diseases, trauma or spinal cord injuries can be treated through artificial muscle implantation. At present, the use of dielectric elastomer actuators working as capacitors appears a promising option. Acrylic or silicone elastomers with carbon nanotubes functioning as the electrode achieve mechanical performances similar to human muscle in vitro. However, mechanical, electrical, and biological issues have prevented clinical application to date. Here materials and mechatronic solutions are presented which can tackle current clinical problems associated with implanting an artificial muscle controlled by the nervous system. Progress depends on the improvement of the actuation properties of the elastomer, seamless or wireless integration between the nervous system and the artificial muscle, and on reducing the foreign body response. It is believed that by combining the mechanical, electrical, and biological solutions proposed here, an artificial neuromuscular prosthesis may be a reality in surgical practice in the near future.

Ultrasound-guided platelet-rich plasma injection and multimodality ultrasound examination of peripheral nerve crush injury

Ultrasound-guided platelet-rich plasma (PRP) injection is able to make up for the limitations of applying a single growth factor. The goal of this study was to investigate the effects of serial ultrasound-guided PRP injections of the appropriate concentration on the treatment of sciatic nerve crush injury, and explore the value of multimodality ultrasound techniques in evaluating the prognosis of crushed peripheral nerve. In vitro, optimal concentration of PRP (from 150%, 250%, 450%, and 650%) was screened due for its maximal effect on proliferation and neurotrophic function of Schwann cells (SCs). In vivo, ninety rabbits were equally and randomly divided into normal control, model, PRP-2.5×, PRP-4.5×, and PRP-6.5× groups. The neurological function and electrophysiological recovery evaluation, and the comparison of the multimodality ultrasound evaluation with the histological results of sciatic nerve crush injury were performed to investigate the regenerative effects of PRP at different concentrations on the sciatic nerve crush injury. Our results showed that the PRP with a 4.5-fold concentration of whole blood platelets could significantly stimulate the proliferation and secretion of SCs and nerve repair. The changes in stiffness and blood perfusion were positively correlated with the collagen area percentage and VEGF expression in the injured nerve, respectively. Thus, serial ultrasound-guided PRP injections at an appropriate concentration accelerates the recovery of axonal function. Multimodality ultrasound techniques provide a clinical reference for prognosis by allowing the stiffness and microcirculation perfusion of crush-injured peripheral nerves to be quantitatively evaluated.

Effect of Intraoperative Electrical Stimulation on Recovery after Rat Sciatic Nerve Isograft Repair

Peripheral nerve injuries, associated with significant morbidity, can benefit from electrical stimulation (ES), as demonstrated in animal studies through improved axonal growth. This study combined the clinical gold standard of isograft repair in a rat model of sciatic nerve injury to evaluate the effects of intraoperative ES on functional tests and histology. Forty rats underwent a surgically induced gap injury to the right sciatic nerve and subsequent repair with an isograft. Half of these rats were randomly selected to receive 10 min of intraoperative ES. Functional testing, including response time to a heat stimulus and motor functional tests, were conducted. Histology of the sciatic nerves and gastrocnemius muscles were analyzed after 6 and 12 weeks of recovery. Rats that underwent ES treatment showed incremental improvements in motor function between weeks 2 and 12, with a significantly higher push-off response than the no-ES controls after 6 weeks. Although no differences were detected between groups in the sensory testing, significant improvements over time were noted in the ES group. Histology parameters, sciatic nerve measures, and gastrocnemius muscle weights demonstrated nerve recovery over time for both the ES and no-ES control groups. Although ES promoted improvements in motor function comparable to that in previous studies, the benefits of intraoperative ES were not detectable in other metrics of this rat model of peripheral nerve injury. Future work is needed to optimize sensory testing in the rodent injury model and compare electrical activity of collagen scaffolds to native tissue to detect differences.

Neurotrophic effects of dental pulp stem cells in repair of peripheral nerve after crush injury

BACKGROUND

Nerve diseases and injuries, which are usually accompanied by motor or sensory dysfunction and disorder, impose a heavy burden upon patients and greatly reduce their quality of life. Dental pulp stem cells (DPSCs), derived from the neural crest, have many characteristics that are similar to those of neural cells, indicating that they can be an ideal source for neural repair.

AIM

To explore the potential roles and molecular mechanisms of DPSCs in crushed nerve recovery.

METHODS

DPSCs were isolated, cultured, and identified by multilineage differentiation and flow cytometry. Western blot and immunofluorescent staining were applied to analyze the expression levels of neurotrophic proteins in DPSCs after neural induction. Then, we collected the secretions of DPSCs. We analyzed their effects on RSC96 cell proliferation and migration by CCK8 and transwell assays. Finally, we generated a sciatic nerve crush injury model in vivo and used the sciatic function index, walking track analysis, muscle weight, and hematoxylin & eosin (H&E) staining to further evaluate the nerve repair ability of DPSCs.

RESULTS

DPSCs highly expressed several specific neural markers, including GFAP, S100, Nestin, P75, and NF200, and were inclined toward neural differentiation. Furthermore, neural-induced DPSCs (N-DPSCs) could express neurotrophic factors, including NGF, BDNF, and GDNF. The secretions of N-DPSCs could enhance the proliferation and migration of Schwann cells. In vivo, both DPSC and N-DPSC implants alleviated gastrocnemius muscle atrophy. However, in terms of anatomy and motor function, as shown by H&E staining, immunofluorescent staining, and walking track analyses, the repair effects of N-DPSCs were more sustained, potent, and effective than those of DPSCs and the controls.

CONCLUSION

In summary, this study demonstrated that DPSCs are inclined to differentiate into neural cells. N-DPSCs express neurotrophic proteins that could enhance the proliferation and migration of SCs. Furthermore, our results suggested that N-DPSCs could help crushed nerves with functional recovery and anatomical repair in vivo. Thus, DPSCs or N-DPSCs could be a promising therapeutic cell source for peripheral nerve repair and regeneration.

Cutaneous nerve-conscious surgical repair of vascular access-related aneurysm assisted by anatomical ultrasonography in hemodialysis patients

BACKGROUND

The superficial runoff veins anatomically run alongside the cutaneous nerves in the volar forearm. Consequently, the surgical repair of vascular access (VA)-associated venous aneurysms attached to the cutaneous nerves could cause intraoperative nerve injury. Therefore, we proposed a cutaneous nerve-conscious VA-related aneurysmal repair assisted by nerve ultrasonography. This ultrasonography aids in the preoperative examination of the courses of the nerves neighboring the aneurysm.

METHODS

Sixteen consecutive patients who underwent surgical revisions of VA-related aneurysms (14 venous aneurysms and two arterial pseudoaneurysms) were enrolled. The locations of aneurysms derived from preexisting arteriovenous fistulas included 11 radiocephalic arteriovenous fistulas in the wrist or distally, three radiocephalic arteriovenous fistulas at the antecubital fossa, and two brachiocephalic arteriovenous fistulas at the antecubital fossa or in the distal upper arm. A preoperative ultrasonographic scan of the cutaneous nerve trunks that ran peripherally toward and along the aneurysms was attempted to avoid nerve injuries during operations. Basically, the aneurysms were resected from the proximal to the distal ends after being separated from the preserved adjacent nerves.

RESULTS

The cutaneous nerve trunks that coursed toward and along the aneurysm could be identified by preoperative ultrasonography and could be preserved intraoperatively based on ultrasonographic findings in all patients. In four patients, the cutaneous nerve branch was unexpectedly or intentionally severed for a seamless surgical process because the nerve branch that divided from the cutaneous nerve trunk was strongly attached to the aneurysm. They subsequently suffered from hypoesthesia, but did not experience neuropathic pain.

CONCLUSION

Preoperative ultrasonographic examination of the cutaneous nerve facilitated the intraoperative prevention of cutaneous nerve injury in VA-related aneurysmectomy. Nerve-sparing VA surgery assisted by preoperative nerve ultrasonography based on the understanding of topological anatomy might contribute to the reduction in postoperative neuropathy and enhance comfort in the daily life of hemodialysis patients.

Recovery of sensory function after the implantation of oriented-collagen tube into the resected rat sciatic nerve

Introduction

In the present study, we examined the effect of oriented collagen tube (OCT) implantation on the recovery of sensory function of the resected rat sciatic nerve.

Materials and methods

After a 10-mm long portion of the sciatic nerve of a rat was resected, an OCT was placed in the site of nerve defect. Recovery of the sensory function was evaluated using Von Frey test every 3 days after surgery. The regenerated tissue were histologically and ultrastructurally analyzed 2 and 4 weeks after the surgery.

Results

The sensory reflexes of the OCT group were restored to the level of that of the intact group after 15 days. Hematoxylin and eosin staining revealed the cross-linking between the proximal and distal stumps after 2 weeks. After 4 weeks, Luxol Fast Blue and immunohistochemical staining revealed the presence of myelin sheath from the proximal to distal region of the regenerated tissue and S100B staining confirmed the presence of Schwann cells. Interestingly, no myelin sheath was ultrastructurally observed around the regenerated axons at the central region after 2 weeks.

Conclusions

These results suggest that OCTs facilitate the recovery of sensory function. Additionally, the non-myelinated axons contributed to the recovery of the sensory function.

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Von Frey test results in the OCT group on POD 15 were comparable at the sham group.

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OCT group showed regeneration of unmyelinated axons in 2 weeks.

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Myelination was observed from proximal to distal after 4 weeks OCT implantation.

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In the OCT group, a large number of blood vessels were observed in nerve in 2 weeks.

Therapeutic effects of nerve leachate-treated adipose-derived mesenchymal stem cells on rat sciatic nerve injury

Peripheral nerve injury (PNI) is a common condition, often resulting from physical nerve injury and trauma. Successful repair of the peripheral nerve is dependent on the regenerative activity of Schwann cells (SCs). Application of SC-like adipose-derived mesenchymal stem cells (ADSCs) may be a suitable cell-based therapy for PNI. In the present study, nerve leachate derived from the rat sciatic nerve was used to induce the differentiation of ADSCs. These cells were placed in an acellular biological scaffold, which was then grafted to a rat sciatic nerve to bridge a 1-cm gap. Sprague-Dawley rats were divided into four groups: Scaffold only, untreated ADSCs + scaffold, nerve leachate-treated ADSCs + scaffold and autograft. Two-months post-transplant, the structure and function of the regenerated nerves and the recovery of the innervated muscles was analyzed. After transplant, there was a significant increase in the average area (15.86%; P<0.05), density (23.13%; P<0.05) and thickness (43.24%; P<0.05) of regenerated nerve fibers in the nerve leachate-treated ADSCs + scaffold group compared with the untreated ADSCs + scaffold group. The nerve conduction velocity in the nerve leachate-treated ADSCs + scaffold and autograft groups was superior to that in the other groups. In the nerve leachate-treated ADSCs + scaffold group, the cross-sectional area of the gastrocnemius increased by 39.28% (P<0.05) and the cross-sectional area of collagen fibers decreased by 29.87% (P<0.05) compared with the ADSCs + scaffold group. Moreover, the therapeutic effect of nerve leachate-treated ADSCs + scaffold on PNI was similar to that of an autograft. These results suggest that nerve leachate-treated ADSCs may promote the repair of PNI.

A new treatment for lingual nerve injury: an anatomical feasibility study for using a buccal nerve pedicle graft

PURPOSE

Lingual nerve (LN) palsy is a serious complication in dentistry and repaired by direct suture or a free graft technique. To our knowledge, there has been no study using a (long) buccal nerve (BN) graft as a donor for LN repair. Therefore, we aimed to clarify the location of the BN and investigate if it is feasible to reroute the BN to the LN.

METHODS

Twenty-four sides from 12 fresh-frozen Caucasian cadaveric heads were used in this study. The mean age at death was 73.9 ± 13.4 years. The LN was dissected on the floor of the oral cavity medial to the third molar tooth. Next, the mucosa with the buccinator muscle, pterygomandibular raphe, and superior pharyngeal constrictor muscle on the retromolar area was retracted anteriorly to widen the pathway of the LN. Finally, the BN was cut and transposed to the LN through this widened pathway to its feasibility.

RESULTS

The mean diameter of the BN and vertical distance from the horizontal part of the retromolar trigone to the BN was 1.47 ± 0.32 mm and 18.53 ± 6.21 mm, respectively. On all sides, the BN was able to be transposed to the LN without tension.

CONCLUSION

Such a technique might be used for the patients with LN injury and who have lost sensation of the tongue.

Platelet-Rich Plasma Combined with Low-Dose Ultrashort Wave Therapy Accelerates Peripheral Nerve Regeneration

Finding treatments that accelerate peripheral nerve regeneration, prolongation, and functional recovery remains a challenging task. Platelet-rich plasma (PRP) contains numerous growth factors and active proteins, and low-dose ultrashort waves (USWs) stimulate the formation of nerve-nourishing vessels, which are powerful for nerve regeneration. The goal of this study was to evaluate the synergistic effects of serial ultrasound-guided PRP injections combined with low-dose USWs radiation on peripheral nerve regeneration in a crush injury model. Fifty rabbits were equally and randomly divided into normal control, model, USW, PRP, and PRP+USW groups. The neurological function, electrophysiological recovery, and histological and morphological evaluation of regenerated nerves, as well as a targeted muscle recovery assessment, were performed to investigate the regenerative effect of PRP combined with USW therapy. Our results showed that the PRP+USW group had the better early axonal regeneration and displayed the earliest positive compound muscle action potential among the treatment groups. At postintervention week 12, a histological evaluation showed similar expression of the S-100 protein in the PRP+USW and normal control groups. Moreover, the morphological assessment revealed a significant increase in the myelinated nerve fiber density and diameter and myelin sheath thickness compared with the USW and PRP groups. The morphometry of the target muscles indicated the lowest reduction in the percent volume in the PRP+USW group, and an ultrasound examination of the targeted muscle showed the best improvement in stiffness and perfusion parameters at 12 weeks after crush injury. Thus, serial ultrasound-guided PRP injections combined with low-dose USW radiation exert a synergistic effect on accelerating functional axon recovery and decreasing atrophy of the target muscles in a crush injury model. Impact Statement This research describes that the application of platelet-rich plasma combined with low-dose ultrashort waves treatment exert a synergistic effect on accelerating peripheral nerve regeneration. With the extensive use of platelet-rich plasma and physical factors in regenerative medicine or clinical rehabilitation medicine, our findings may help establish effective strategies for repairing peripheral nerve injury.

The Surgical Management of Nerve Gaps: Present and Future

Peripheral nerve injuries can result in significant morbidity, including motor and/or sensory loss, which can affect significantly the life of the patient. Nowadays, the gold standard for the treatment of nerve section is end-to-end neurorrhaphy. Unfortunately, in some cases, there is segmental loss of the nerve trunk. Nerve mobilization allows primary repair of the sectioned nerve by end-to-end neurorrhaphy if the gap is less than 1 cm. When the nerve gap exceeds 1 cm, autologous nerve grafting is the gold standard of treatment. To overcome the limited availability and the donor site morbidity, other techniques have been used: vascularized nerve grafts, cellular and acellular allografts, nerve conduits, nerve transfers, and end-to-side neurorrhaphy. The purpose of this review is to present an overview of the literature on the applications of these techniques in peripheral nerve repair. Furthermore, preoperative evaluation, timing of repair, and future perspectives are also discussed.

Advances of tooth-derived stem cells in neural diseases treatments and nerve tissue regeneration

Nerous system diseases, both central and peripheral, bring an incredible burden onto patients and enormously reduce their quality of life. Currently, there are still no effective treatments to repair nerve lesions that do not have side effects. Stem cell-based therapies, especially those using dental stem cells, bring new hope to neural diseases. Dental stem cells, derived from the neural crest, have many characteristics that are similar to neural cells, indicating that they can be an ideal source of cells for neural regeneration and repair. This review summarizes the neural traits of all the dental cell types, including DPSCs, PDLCs, DFCs, APSCs and their potential applications in nervous system diseases. We have summed up the advantages of dental stem cells in neural repair, such as their neurotrophic and neuroprotective traits, easy harvest and low rejective reaction rate, among others. Taken together, dental stem cells are an ideal cell source for neural tissue regeneration and repair.

Chitin/Chitosan: Versatile Ecological, Industrial, and Biomedical Applications

Chitin is a linear polysaccharide of N-acetylglucosamine, which is highly abundant in nature and mainly produced by marine crustaceans. Chitosan is obtained by hydrolytic deacetylation. Both polysaccharides are renewable resources, simply and cost-effectively extracted from waste material of fish industry, mainly crab and shrimp shells. Research over the past five decades has revealed that chitosan, in particular, possesses unique and useful characteristics such as chemical versatility, polyelectrolyte properties, gel- and film-forming ability, high adsorption capacity, antimicrobial and antioxidative properties, low toxicity, and biocompatibility and biodegradability features. A plethora of chemical chitosan derivatives have been synthesized yielding improved materials with suggested or effective applications in water treatment, biosensor engineering, agriculture, food processing and storage, textile additives, cosmetics fabrication, and in veterinary and human medicine. The number of studies in this research field has exploded particularly during the last two decades. Here, we review recent advances in utilizing chitosan and chitosan derivatives in different technical, agricultural, and biomedical fields.

Redistribution of nerve strain enables end-to-end repair under tension without inhibiting nerve regeneration

End-to-end repair under no or low tension leads to improved outcomes for transected nerves with short gaps, compared to repairs with a graft. However, grafts are typically used to enable a tension-free repair for moderate to large gaps, as excessive tension can cause repairs to fail and catastrophically impede recovery. In this study, we tested the hypothesis that unloading the repair interface by redistributing tension away from the site of repair is a safe and feasible strategy for end-to-end repair of larger nerve gaps. Further, we tested the hypothesis that such an approach does not adversely affect structural and functional regeneration. In this study, we used a rat sciatic nerve injury model to compare the integrity of repair and several regenerative outcomes following end-to-end repairs of nerve gaps of increasing size. In addition, we proposed the use of a novel implantable device to safely repair end-to-end repair of larger nerve gaps by redistributing tension away from the repair interface. Our data suggest that redistriubution of tension away from the site of repair enables safe end-to-end repair of larger gap sizes. In addition, structural and functional measures of regeneration were equal or enhanced in nerves repaired under tension – with or without a tension redistribution device – compared to tension-free repairs. Provided that repair integrity is maintained, end-to-end repairs under tension should be considered as a reasonable surgical strategy. All animal experiments were performed under the approval of the Institutional Animal Care and Use Committee of University of California, San Diego (Protocol S11274).

Scaffolds for peripheral nerve repair and reconstruction

Trauma-associated peripheral nerve defect is a widespread clinical problem. Autologous nerve grafting, the current gold standard technique for the treatment of peripheral nerve injury, has many internal disadvantages. Emerging studies showed that tissue engineered nerve graft is an effective substitute to autologous nerves. Tissue engineered nerve graft is generally composed of neural scaffolds and incorporating cells and molecules. A variety of biomaterials have been used to construct neural scaffolds, the main component of tissue engineered nerve graft. Synthetic polymers (e.g. silicone, polyglycolic acid, and poly(lactic-co-glycolic acid)) and natural materials (e.g. chitosan, silk fibroin, and extracellular matrix components) are commonly used along or together to build neural scaffolds. Many other materials, including the extracellular matrix, glass fabrics, ceramics, and metallic materials, have also been used to construct neural scaffolds. These biomaterials are fabricated to create specific structures and surface features. Seeding supporting cells and/or incorporating neurotrophic factors to neural scaffolds further improve restoration effects. Preliminary studies demonstrate that clinical applications of these neural scaffolds achieve satisfactory functional recovery. Therefore, tissue engineered nerve graft provides a good alternative to autologous nerve graft and represents a promising frontier in neural tissue engineering.

Potential Roles of Dental Pulp Stem Cells in Neural Regeneration and Repair

This review summarizes current advances in dental pulp stem cells (DPSCs) and their potential applications in the nervous diseases. Injured adult mammalian nervous system has a limited regenerative capacity due to an insufficient pool of precursor cells in both central and peripheral nervous systems. Nerve growth is also constrained by inhibitory factors (associated with central myelin) and barrier tissues (glial scarring). Stem cells, possessing the capacity of self-renewal and multicellular differentiation, promise new therapeutic strategies for overcoming these impediments to neural regeneration. Dental pulp stem cells (DPSCs) derive from a cranial neural crest lineage, retain a remarkable potential for neuronal differentiation, and additionally express multiple factors that are suitable for neuronal and axonal regeneration. DPSCs can also express immunomodulatory factors that stimulate formation of blood vessels and enhance regeneration and repair of injured nerve. These unique properties together with their ready accessibility make DPSCs an attractive cell source for tissue engineering in injured and diseased nervous systems. In this review, we interrogate the neuronal differentiation potential as well as the neuroprotective, neurotrophic, angiogenic, and immunomodulatory properties of DPSCs and its application in the injured nervous system. Taken together, DPSCs are an ideal stem cell resource for therapeutic approaches to neural repair and regeneration in nerve diseases.

Quantification of human upper extremity nerves and fascicular anatomy

INTRODUCTION

In this study we provide detailed quantification of upper extremity nerve and fascicular anatomy. The purpose is to provide values and trends in neural features useful for clinical applications and neural interface device design.

METHODS

Nerve cross-sections were taken from 4 ulnar, 4 median, and 3 radial nerves from 5 arms of 3 human cadavers. Quantified nerve features included cross-sectional area, minor diameter, and major diameter. Fascicular features analyzed included count, perimeter, area, and position.

RESULTS

Mean fascicular diameters were 0.57 ± 0.39, 0.6 ± 0.3, 0.5 ± 0.26 mm in the upper arm and 0.38 ± 0.18, 0.47 ± 0.18, 0.4 ± 0.27 mm in the forearm of ulnar, median, and radial nerves, respectively. Mean fascicular diameters were inversely proportional to fascicle count.

CONCLUSION

Detailed quantitative anatomy of upper extremity nerves is a resource for design of neural electrodes, guidance in extraneural procedures, and improved neurosurgical planning. Muscle Nerve 56: 463-471, 2017.

Comparison of repair of peripheral nerve transection in predegenerated muscle with and without a vein graft

BACKGROUND

Despite substantial research into the topic and valiant surgical efforts, reconstruction of peripheral nerve injury remains a challenging surgery. This study was conducted to evaluate the effectiveness of axonal regeneration of a transected sciatic nerve through a vein conduit containing degenerated skeletal muscle compared with axonal regeneration in a transected sciatic nerve through degenerated skeletal muscle alone.

METHODS

In two of the three experimental rat groups, 10 mm of the left sciatic nerve was transected and removed. The proximal and distal ends of the transected sciatic nerve were then approximated and surrounded with either (a) a degenerated skeletal muscle graft; or (b) a graft containing both degenerated skeletal muscle and vein. In the group receiving the combined vein and skeletal muscle graft, the vein walls were subsequently sutured to the proximal and distal nerve stump epineurium. Sciatic functional index (SFI) was used for assessment of functional recovery. Tracing study and histological procedures were used to assess axonal regeneration.

RESULTS

At 60 days, the gait functional recovery as well as the mean number of myelinated axons in the middle and distal parts of the sciatic nerve significantly increased in the group with the vein graft compared to rats with only the muscular graft (P < 0.05). Mean diameter of myelinated nerve fiber of the distal sciatic nerve was also improved with the vein graft compared to the muscle graft alone (P < 0.05). The mean number of DiI-labeled motor neurons in the L4-L5 spinal segment increased in the vein with muscle group but was not significantly different between the two groups.

CONCLUSIONS

These findings demonstrated that a graft consisting of not only predegenerated muscle, but also predegenerated muscle with vein more effectively supported nerve regeneration, thus promoting functional recovery after sciatic nerve injury in rats.

Neuroprotective effects of ultrasound-guided nerve growth factor injections after sciatic nerve injury

Nerve growth factor (NGF) plays an important role in promoting neuroregeneration after peripheral nerve injury. However, its effects are limited by its short half-life; it is therefore important to identify an effective mode of administration. High-frequency ultrasound (HFU) is increasingly used in the clinic for high-resolution visualization of tissues, and has been proposed as a method for identifying and evaluating peripheral nerve damage after injury. In addition, HFU is widely used for guiding needle placement when administering drugs to a specific site. We hypothesized that HFU guiding would optimize the neuroprotective effects of NGF on sciatic nerve injury in the rabbit. We performed behavioral, ultrasound, electrophysiological, histological, and immunohistochemical evaluation of HFU-guided NGF injections administered immediately after injury, or 14 days later, and compared this mode of administration with intramuscular NGF injections. Across all assessments, HFU-guided NGF injections gave consistently better outcomes than intramuscular NGF injections administered immediately or 14 days after injury, with immediate treatment also yielding better structural and functional results than when the treatment was delayed by 14 days. Our findings indicate that NGF should be administered as early as possible after peripheral nerve injury, and highlight the striking neuroprotective effects of HFU-guided NGF injections on peripheral nerve injury compared with intramuscular administration.

Neuromuscular Regeneration: Perspective on the Application of Mesenchymal Stem Cells and Their Secretion Products

Mesenchymal stem cells are posing as a promising character in the most recent therapeutic strategies and, since their discovery, extensive knowledge on their features and functions has been gained. In recent years, innovative sources have been disclosed in alternative to the bone marrow, conveying their associated ethical concerns and ease of harvest, such as the umbilical cord tissue and the dental pulp. These are also amenable of cryopreservation and thawing for desired purposes, in benefit of the donor itself or other patients in pressing need. These sources present promising possibilities in becoming useful cell sources for therapeutic applications in the forthcoming years. Effective and potential applications of these cellular-based strategies for the regeneration of peripheral nerve are overviewed, documenting recent advances and identified issues for this research area in the near future. Finally, besides the differentiation capacities attributed to mesenchymal stem cells, advances in the recognition of their effective mode of action in the regenerative theatre have led to a new area of interest: the mesenchymal stem cells' secretome. The paracrine modulatory pathway appears to be a major mechanism by which these are beneficial to nerve regeneration and comprehension on the specific growth factors, cytokine, and extracellular molecules secretion profiles is therefore of great interest.

Influence of Tacrolimus (FK506) on Nerve Regeneration Using Allografts: A Rat Sciatic Nerve Model

PURPOSE

FK506 is an immunosuppressant agent used to prevent rejection after organ transplantation. The aim of the present study was to assess effects of tacrolimus (FK506) on peripheral nerve regeneration using allografts in a rat sciatic nerve model.

MATERIALS AND METHODS

Thirty male white Wistar rats were divided randomly into a normal control (NC) group (n = 10), an allograft (ALLO) group (n = 10), and an FK506-treated (ALLO/FK506) group (n = 10). In the NC group, the left sciatic nerve was exposed through a gluteal muscle incision and, after homeostasis, the muscle was sutured. In the ALLO group, the left sciatic nerve was exposed through a gluteal muscle incision and transected proximal to the tibioperoneal bifurcation, where a 10-mm segment was excised. The same procedure was performed in the ALLO/FK506 group. The harvested nerves of the ALLO group served as allografts for the ALLO/FK506 group and vice versa. The NC and ALLO groups received sterile olive oil 300 μL intraperitoneally once a day for 1 week and the ALLO/FK506 group received FK506 300 μL (1 mg/kg) intraperitoneally once a day for 1 week.

RESULTS

Behavioral, functional, and biomechanical recovery and gastrocnemius muscle mass showed earlier regeneration of axons in the ALLO/FK506 than in the ALLO group (P < .05). Histomorphometric and immunohistochemical studies also showed earlier regeneration of axons in the ALLO/FK506 than in the ALLO group (P < .05).

CONCLUSIONS

Administration of FK506 could accelerate functional recovery of the sciatic nerve after nerve allografting. It could have clinical implications for the surgical management of patients after facial nerve transection.

Wharton's jelly derived mesenchymal stromal cells: Biological properties, induction of neuronal phenotype and current applications in neurodegeneration research

Multipotent mesenchymal stromal cells, also known as mesenchymal stem cells (MSC), can be isolated from bone marrow or other tissues, including fat, muscle and umbilical cord. It has been shown that MSC behave in vitro as stem cells: they self-renew and are able to differentiate into mature cells typical of several mesenchymal tissues. Moreover, the differentiation toward non-mesenchymal cell lineages (e.g. neurons) has been reported as well. The clinical relevance of these cells is mainly related to their ability to spontaneously migrate to the site of inflammation/damage, to their safety profile thanks to their low immunogenicity and to their immunomodulation capacities. To date, MSCs isolated from the post-natal bone marrow have represented the most extensively studied population of adult MSCs, in view of their possible use in various therapeutical applications. However, the bone marrow-derived MSCs exhibit a series of limitations, mainly related to their problematic isolation, culturing and use. In recent years, umbilical cord (UC) matrix (i.e. Wharton's jelly, WJ) stromal cells have therefore emerged as a more suitable alternative source of MSCs, thanks to their primitive nature and the easy isolation without relevant ethical concerns. This review seeks to provide an overview of the main biological properties of WJ-derived MSCs. Moreover, the potential application of these cells for the treatment of some known dysfunctions in the central and peripheral nervous system will also be discussed.

Regenerative medicine applications in combat casualty care

The purpose of this report is to describe regenerative medicine applications in the management of complex injuries sustained by service members injured in support of the wars in Afghanistan and Iraq. Improvements in body armor, resuscitative techniques and faster transport have translated into increased patient survivability and more complex wounds. Combat-related blast injuries have resulted in multiple extremity injuries, significant tissue loss and amputations. Due to the limited availability and morbidity associated with autologous tissue donor sites, the introduction of regenerative medicine has been critical in managing war extremity injuries with composite massive tissue loss. Through case reports and clinical images, this report reviews the application of regenerative medicine modalities employed to manage combat-related injuries. It illustrates that the novel use of hybrid reconstructions combining traditional and regenerative medicine approaches are an effective tool in managing wounds. Lessons learned can be adapted to civilian care.

Application of topical pharmacological agents at the site of peripheral nerve injury and methods used for evaluating the success of the regenerative process

Traumatic injuries of the peripheral nerves are very common. Surgical repair of the damaged nerve is often complicated by scar tissue formation around the damaged nerve itself. The main objective of this study is to present the recent data from animal experimental studies where pharmacological topical agents are used at the site of peripheral nerve repair. Some of the most commonly topical agents used are tacrolimus (FK506), hyaluronic acid and its derivatives, and melatonin, whereas methylprednisolone and vitamin B12 have been used less. These studies have shown that the abovementioned substances have neuroprotective and neuroregenerative properties though different mechanisms. The successes of the regenerative process of the nerve repair in experimental research, using topical agents, can be evaluated using variety of methods such as morphological, electrophysiologic, and functional evaluation. However, most authors agree that despite good microsurgical repair and topical application of these substances, full regeneration and functional recovery of the nerve injured are almost never achieved.

Epineurial repair of an iatrogenic facial nerve neurotmesis after total ear canal ablation and lateral bulla osteotomy in a dog with concurrent cranio-mandibular osteopathy

A 7-year-old male entire West Highland white terrier was referred to the Small Animal Hospital at the University of Glasgow for bilateral, chronic, medically unresponsive otitis media and externa. A history of cranio-mandibular osteopathy was also reported. Bilateral total ear canal ablation and lateral bulla osteotomy was performed with the aid of a pneumatic burr. Extensive bone proliferation was present bilaterally originating from the caudal mandibular ramus and tympanic bulla which incorporated the horizontal canal on each side. The right facial nerve was identified leaving the stylomastoid foramen and running in a cranial direction through a 1.5 cm diameter cuff of bone surrounding the horizontal canal and external acoustic meatus. Despite careful dissection, a facial nerve neurotmesis ensued which required microsurgical epineurial repair. Neurologic examination performed 12 h post-operatively revealed abnormalities consistent with right facial nerve paralysis. At 3 months, the facial nerve function was found to have improved significantly and was assessed to be normal four months after surgery. To the authors' knowledge, this clinical communication described the first reported clinical case where unilateral facial nerve paralysis resulting from iatrogenic facial nerve neurotmesis was successfully treated by microsurgical epineurial repair.

Nerve repair: toward a sutureless approach

Peripheral nerve repair for complete section injuries employ reconstructive techniques that invariably require sutures in their application. Sutures are unable to seal the nerve, thus incapable of preventing leakage of important intraneural fluids from the regenerating nerve. Furthermore, sutures are technically demanding to apply for direct repairs and often induce detrimental scarring that impedes healing and functional recovery. To overcome these limitations, biocompatible and biodegradable glues have been used to seal and repair peripheral nerves. Although creating a sufficient seal, they can lack flexibility and present infection risks or cytotoxicity. Other adhesive biomaterials have recently emerged into practice that are usually based on proteins such as albumin and collagen or polysaccharides like chitosan. These adhesives form their union to nerve tissue by either photothermal (tissue welding) or photochemical (tissue bonding) activation with laser light. These biomaterial adhesives offer significant advantages over sutures, such as their capacity to unite and seal the epineurium, ease of application, reduced invasiveness and add the potential for drug delivery in situ to facilitate regeneration. This paper reviews a number of different peripheral nerve repair (or reconstructive) techniques currently used clinically and in experimental procedures for nerve injuries with or without tissue deficit.

Promoting nerve regeneration in a neurotmesis rat model using poly(DL-lactide-ε-caprolactone) membranes and mesenchymal stem cells from the Wharton's jelly: in vitro and in vivo analysis

In peripheral nerves MSCs can modulate Wallerian degeneration and the overall regenerative response by acting through paracrine mechanisms directly on regenerating axons or upon the nerve-supporting Schwann cells. In the present study, the effect of human MSCs from Wharton's jelly (HMSCs), differentiated into neuroglial-like cells associated to poly (DL-lactide-ε-caprolactone) membrane, on nerve regeneration, was evaluated in the neurotmesis injury rat sciatic nerve model. Results in vitro showed successful differentiation of HMSCs into neuroglial-like cells, characterized by expression of specific neuroglial markers confirmed by immunocytochemistry and by RT-PCR and qPCR targeting specific genes expressed. In vivo testing evaluated during the healing period of 20 weeks, showed no evident positive effect of HMSCs or neuroglial-like cell enrichment at the sciatic nerve repair site on most of the functional and nerve morphometric predictors of nerve regeneration although the nociception function was almost normal. EPT on the other hand, recovered significantly better after HMSCs enriched membrane employment, to values of residual functional impairment compared to other treated groups. When the neurotmesis injury can be surgically reconstructed with an end-to-end suture or by grafting, the addition of a PLC membrane associated with HMSCs seems to bring significant advantage, especially concerning the motor function recovery.

Challenges for nerve repair using chitosan-siloxane hybrid porous scaffolds

The treatment of peripheral nerve injuries remains one of the greatest challenges of neurosurgery, as functional recover is rarely satisfactory in these patients. Recently, biodegradable nerve guides have shown great potential for enhancing nerve regeneration. A major advantage of these nerve guides is that no foreign material remains after the device has fulfilled its task, which spares a second surgical intervention. Recently, we studied peripheral nerve regeneration using chitosan-γ-glycidoxypropyltrimethoxysilane (chitosan-GPTMS) porous hybrid membranes. In our studies, these porous membranes significantly improved nerve fiber regeneration and functional recovery in rat models of axonotmetic and neurotmetic sciatic nerve injuries. In particular, the number of regenerated myelinated nerve fibers and myelin thickness were significantly higher in rat treated with chitosan porous hybrid membranes, whether or not they were used in combination with mesenchymal stem cells isolated from the Wharton's jelly of the umbilical cord. In this review, we describe our findings on the use of chitosan-GPTMS hybrids for nerve regeneration.

Perspectives of employing mesenchymal stem cells from the Wharton's jelly of the umbilical cord for peripheral nerve repair

Mesenchymal stem cells (MSCs) from Wharton's jelly present high plasticity and low immunogenicity, turning them into a desirable form of cell therapy for the injured nervous system. Their isolation, expansion, and characterization have been performed from cryopreserved umbilical cord tissue. Great concern has been dedicated to the collection, preservation, and transport protocols of the umbilical cord after the parturition to the laboratory in order to obtain samples with higher number of viable MSCs without microbiological contamination. Different biomaterials like chitosan-silicate hybrid, collagen, PLGA90:10, poly(DL-lactide-ɛ-caprolactone), and poly(vinyl alcohol) loaded with electrical conductive materials, associated to MSCs have also been tested in the rat sciatic nerve in axonotmesis and neurotmesis lesions. The in vitro studies of the scaffolds included citocompatibility evaluation of the biomaterials used and cell characterization by imunocytochemistry, karyotype analysis, differentiation capacity into neuroglial-like cells, and flow cytometry. The regeneration process follow-up has been performed by functional analysis and the repaired nerves processed for stereological studies permitted the morphologic regeneration evaluation. The MSCs from Wharton's jelly delivered through tested biomaterials should be regarded a potentially valuable tool to improve clinical outcome especially after trauma to sensory nerves. In addition, these cells represent a noncontroversial source of primitive mesenchymal progenitor cells, which can be harvested after birth, cryogenically stored, thawed, and expanded for therapeutic uses. The importance of a longitudinal study concerning tissue engineering of the peripheral nerve, which includes a multidisciplinary team able to develop biomaterials associated to cell therapies, to perform preclinical trials concerning animal welfare and the appropriate animal model is here enhanced.

A human hair keratin hydrogel scaffold enhances median nerve regeneration in nonhuman primates: an electrophysiological and histological study

A human hair keratin biomaterial hydrogel scaffold was evaluated as a nerve conduit luminal filler following median nerve transection injury in 10 Macaca fascicularis nonhuman primates (NHP). A 1 cm nerve gap was grafted with a NeuraGen® collagen conduit filled with either saline or keratin hydrogel and nerve regeneration was evaluated by electrophysiology for a period of 12 months. The keratin hydrogel-grafted nerves showed significant improvement in return of compound motor action potential (CMAP) latency and recovery of baseline nerve conduction velocity (NCV) compared with the saline-treated nerves. Histological evaluation was performed on retrieved median nerves and abductor pollicis brevis (APB) muscles at 12 months. Nerve histomorphometry showed a significantly larger nerve area in the keratin group compared with the saline group and the keratin APB muscles had a significantly higher myofiber density than the saline group. This is the first published study to show that an acellular biomaterial hydrogel conduit filler can be used to enhance peripheral nerve regeneration and motor recovery in an NHP model.

Assessment of in vivo behavior of polymer tube nerve grafts simultaneously with the peripheral nerve regeneration process using scanning electron microscopy technique

In this study, scanning electron microscopy (SEM) has been applied for instantaneous assessment of processes occurring at the site of regenerating nerve. The technique proved to be especially useful when an artificial implant should have been observed but have not yet been extensively investigated before for assessment of nerve tissue. For in vivo studies, evaluation of implant's morphology and its neuroregenerative properties is of great importance when new prototype is developed. However, the usually applied histological techniques require separate and differently prepared samples, and therefore, the results are never a 100% comparable. In our research, we found SEM as a technique providing detailed data both on an implant behavior and the nerve regeneration process inside the implant. Observations were carried out during 12-week period on rat sciatic nerve injury model reconstructed with nerve autografts and different tube nerve grafts. Samples were analyzed with haematoxylin-eosin (HE), immunocytochemical staining for neurofillament and S-100 protein, SEM, TEM, and the results were compared. SEM studies enabled to obtain characteristic pictures of the regeneration process similarly to TEM and histological studies. Schwann cell transformation and communication as well as axonal outgrowth were identified, newly created and matured axons could be recognized. Concurrent analysis of biomaterial changes in the implant (degradation, collapsing of the tube wall, migration of alginate gel) was possible. This study provides the groundwork for further use of the described technique in the nerve regeneration studies.

Hybrid conducting polymer-hydrogel conduits for axonal growth and neural tissue engineering

Successfully and efficiently bridging peripheral nerve gaps without the use of autografts is a substantial clinical advance for peripheral nerve reconstructions. Novel templating methods for the fabrication of conductive hydrogel guidance channels for axonal regeneration are designed and developed. PEDOT is electrodeposited inside the lumen to create fully coated-PEDOT agarose conduits and partially coated-PEDOT agarose conduits.

Natural conduits for bridging a 15-mm nerve defect: comparison of the vein supported by muscle and bone marrow stromal cells with a nerve autograft

OBJECT

The gold standard for reconstructing large nerve defects, the nerve autograft, results in donor-site morbidity. This detrimental consequence drives the search for alternatives. We used a vein filled with a small piece of fresh muscle to prevent the vein from collapsing and with bone marrow stromal cells (BMSCs) to enhance regeneration.

METHODS

In 60 rats, a 15-mm sciatic nerve defect was bridged with a nerve autograft, a vein filled with muscle or a vein filled with muscle and BMSCs. Toe spread and pinprick were used to evaluate motor and sensory function. Compound muscle action potentials (CMAPs) and the gastrocnemius muscle index (GMI) were recorded to assess conduction properties and denervation atrophy. Extensive histology was performed to confirm presence of BMSCs and to evaluate regeneration by staining neural tissue for Schwann cells and neural growth factor.

RESULTS

After 12 weeks, all animals responded with toe spread and pinprick reaction; significant differences were found between groups. Six weeks post grafting no difference was found comparing the GMI between the groups. Group I had a significant increase in GMI at 12 weeks compared to group II and group III. The CMAP measurements showed comparable results at 6 weeks post grafting. Twelve weeks after reconstruction, group I had significantly better results compared to group II and group III. Group III showed a tendency to outperform group II at 12 weeks postoperatively. Immunofluorescence analysis showed an increased number of Schwann cells in group III compared to group II. The BMSCs were visible 6 and 12 weeks postoperatively.

CONCLUSIONS

This study is a step forward in the search for an alternative to the nerve autograft because it demonstrates the beneficial effect of BMSCs to a conduit. However, our data do not demonstrate sufficient benefit to warrant clinical implementation at this stage.

FDA approved guidance conduits and wraps for peripheral nerve injury: a review of materials and efficacy

Several nerve guidance conduits (NGCs) and nerve protectant wraps are approved by the US Food and Drug Administration (FDA) for clinical use in peripheral nerve repair. These devices cover a wide range of natural and synthetic materials, which may or may not be resorbable. This review consolidates the data pertaining to all FDA approved materials into a single reference, which emphasizes material composition alongside pre-clinical and clinical safety and efficacy (where possible). This article also summarizes the key advantages and limitations for each material as noted in the literature (with respect to the indication considered). In this context, this review provides a comprehensive reference for clinicians which may facilitate optimal material/device selection for peripheral nerve repair. For materials scientists, this review highlights predicate devices and evaluation methodologies, offering an insight into current deficiencies associated with state-of-the-art materials and may help direct new technology developments and evaluation methodologies thereof.

Spatiotemporal expression profiling of proteins in rat sciatic nerve regeneration using reverse phase protein arrays

Background

Protein expression profiles throughout 28 days of peripheral nerve regeneration were characterized using an established rat sciatic nerve transection injury model. Reverse phase protein microarrays were used to identify the spatial and temporal expression profile of multiple proteins implicated in peripheral nerve regeneration including growth factors, extracellular matrix proteins, and proteins involved in adhesion and migration. This high-throughput approach enabled the simultaneous analysis of 3,360 samples on a nitrocellulose-coated slide.

Results

The extracellular matrix proteins collagen I and III, laminin gamma-1, fibronectin, nidogen and versican displayed an early increase in protein levels in the guide and proximal sections of the regenerating nerve with levels at or above the baseline expression of intact nerve by the end of the 28 day experimental course. The 28 day protein levels were also at or above baseline in the distal segment however an early increase was only noted for laminin, nidogen, and fibronectin. While the level of epidermal growth factor, ciliary neurotrophic factor and fibroblast growth factor-1 and -2 increased throughout the experimental course in the proximal and distal segments, nerve growth factor only increased in the distal segment and fibroblast growth factor-1 and -2 and nerve growth factor were the only proteins in that group to show an early increase in the guide contents. As expected, several proteins involved in cell adhesion and motility; namely focal adhesion kinase, N-cadherin and β-catenin increased earlier in the proximal and distal segments than in the guide contents reflecting the relatively acellular matrix of the early regenerate.

Conclusions

In this study we identified changes in expression of multiple proteins over time linked to regeneration of the rat sciatic nerve both demonstrating the utility of reverse phase protein arrays in nerve regeneration research and revealing a detailed, composite spatiotemporal expression profile of peripheral nerve regeneration.

The role of neuregulin-1 in the response to nerve injury

Axons and Schwann cells exist in a highly interdependent relationship: damage to one cell type invariably leads to pathophysiological changes in the other. Greater understanding of communication between these cell types will not only give insight into peripheral nerve development, but also the reaction to and recovery from peripheral nerve injury. The type III isoform of neuregulin-1 (NRG1) has emerged as a key signaling factor that is expressed on axons and, through binding to erbB2/3 receptors on Schwann cells, regulates multiple phases of their development. In adulthood, NRG1 is dispensable for the maintenance of the myelin sheath; however, this factor is required for both axon regeneration and remyelination following nerve injury. The outcome of NRG1 signaling depends on interactions with other pathways within Schwann cells such as Notch, integrin and cAMP signaling. In certain circumstances, this signaling pathway may be maladaptive; for instance, direct binding of Mycobacterium leprae onto erbB2 receptors produces excessive activation and can actually promote demyelination. Attempts to modulate this pathway in order to promote nerve repair will therefore need to give consideration to the exact isoform used, as well as how it is processed and the context in which it is presented to the Schwann cell.