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Peripheral nerve injury is a serious disease and its repair is challenging. A cable-style autologous graft is the gold standard for repairing long peripheral nerve defects; however, ensuring that the minimum number of transplanted nerve attains maximum therapeutic effect remains poorly understood. In this study, a rat model of common peroneal nerve defect was established by resecting a 10-mm long right common peroneal nerve. Rats receiving transplantation of the common peroneal nerve in situ were designated as the in situ graft group. Ipsilateral sural nerves（10–30 mm long） were resected to establish the one sural nerve graft group, two sural nerves cable-style nerve graft group and three sural nerves cable-style nerve graft group. Each bundle of the peroneal nerve was 10 mm long. To reduce the barrier effect due to invasion by surrounding tissue and connective-tissue overgrowth between neural stumps, small gap sleeve suture was used in both proximal and distal terminals to allow repair of the injured common peroneal nerve. At three months postoperatively, recovery of nerve function and morphology was observed using osmium tetroxide staining and functional detection. The results showed that the number of regenerated nerve fibers, common peroneal nerve function index, motor nerve conduction velocity, recovery of myodynamia, and wet weight ratios of tibialis anterior muscle were not significantly different among the one sural nerve graft group, two sural nerves cable-style nerve graft group, and three sural nerves cable-style nerve graft group. These data suggest that the repair effect achieved using one sural nerve graft with a lower number of nerve fibers is the same as that achieved using the two sural nerves cable-style nerve graft and three sural nerves cable-style nerve graft. This indicates that according to the ‘multiple amplification＇ phenomenon, one small nerve graft can provide a good therapeutic effect for a large peripheral nerve defect.

Background Repairing large nerve defects remains challenging, and no definitive method has been established. We developed a nerve lengthening device for humans and achieved nerve defect repair through nerve lengthening in three cases. The purpose of this report is to describe the clinical course of three cases treated by nerve lengthening and to discuss its effectiveness in the treatment of nerve defects. Methods The target population included males and females aged 20–65 years with peripheral nerve injuries that cannot undergo primary suturing in the limbs were recruited. Three patients were included in this study. The nerve gaps were 13 mm, 15 mm and 100 mm, respectively. We developed a special nerve lengthening device. Starting from postoperative day 1, nerve lengthening was initiated on the proximal and distal ends at a rate of 0.5–1 mm daily (0.25 mm x 2–4 times) using the device. Monthly evaluations post-nerve suturing assessed nerve regeneration, pain, and adverse events. We observed postoperative courses for over 2 years. Results There were two radial nerve injury cases and one median nerve injury case. Functional recovery was observed in cases of shorter nerve defects repaired through nerve lengthening. However, significant functional restoration was not attainable for cases of longer nerve defects or those with prolonged post-injury intervals. Furthermore, in chronic cases, it was confirmed that this method could be used to gradually lengthened and repair severed nerves. There were no reports of pain or lengthening-related troubles during nerve lengthening. Conclusion It was found that good nerve regeneration can be achieved with short nerve defects. Compared to free nerve grafting, this new treatment is promising as it does not require the sacrifice of healthy nerves from the donor site or leave surgical scars. We demonstrated the potential of nerve lengthening as a new treatment option for nerve defects. This study is registered and published in the Japan Registry of Clinical Trials (Project No. jRCTs032180098, https://jrct.niph.go.jp/re/reports/detail/17847 ). Registration date: 28/01/2019.

During peripheral nerve transposition repair, if the diameter difference between transposed nerves is large or multiple distal nerves must be repaired at the same time, traditional epineurial neurorrhaphy has the problem of high tension at the suture site, which may even lead to the failure of nerve suture. We investigated whether a small gap bio-sleeve suture with different inner diameters at both ends can be used to repair a 2-mm tibial nerve defect by proximal transposition of the common peroneal nerve in rats and compared the results with the repair seen after epineurial neurorrhaphy. Three months after surgery, neurological function, nerve regeneration, and recovery of nerve innervation muscle were assessed using the tibial nerve function index, neuroelectrophysiological testing, muscle biomechanics and wet weight measurement, osmic acid staining, and hematoxylin-eosin staining. There was no obvious inflammatory reaction and neuroma formation in the tibial nerve after repair by the small gap bio-sleeve suture with different inner diameters at both ends. The conduction velocity, muscle strength, wet muscle weight, cross-sectional area of muscle fibers, and the number of new myelinated nerve fibers in the bio-sleeve suture group were similar to those in the epineurial neurorrhaphy group. Our findings indicate that small gap bio-sleeve suture with different inner diameters at both ends can achieve surgical suture between nerves of different diameters and promote regeneration and functional recovery of injured peripheral nerves.

The injuries of the peripheral nerves are relatively frequent. Some of them may lead to defects which cannot be repaired with direct end-to-end repair without tension. These injuries may cause function loss to the patient, and they consist a challenge for the treating microsurgeon. Autologous nerve grafts remain the gold standard for bridging the peripheral nerve defects. Nevertheless, there are selected cases where alternative types of nerve reconstruction can be performed in order to cover the peripheral nerve defects. In all these types of reconstruction, the basic principles of microsurgery are necessary and the surgeon should be aware of them in order to achieve a successful reconstruction. The purpose of the present review was to present the most current data concerning the surgical options available for bridging such defects.

Aims Peripheral nerve defects are often difficult to recover from, and there is no optimal repair method. Therefore, it is important to explore new methods of repairing peripheral nerve defects. This study explored the efficacy of nerve grafts constructed from chitin biological conduits combined with small autogenous nerves (SANs) and platelet‐rich plasma (PRP) for repairing 10‐mm sciatic nerve defects in rats. Methods To prepare 10‐mm sciatic nerve defects, SANs were first harvested and PRP was extracted. The nerve grafts consisted of chitin biological conduits combined with SAN and PRP, and were used to repair rat sciatic nerve defects. These examinations, including measurements of axon growth efficiency, a gait analysis, electrophysiological tests, counts of regenerated myelinated fibers and observations of their morphology, histological evaluation of the gastrocnemius muscle, retrograde tracing with Fluor‐Gold (FG), and motor endplates (MEPs) distribution analysis, were conducted to evaluate the repair status. Results Two weeks after nerve transplantation, the rate and number of regenerated axons in the PRP‐SAN group improved compared with those in the PRP, SAN, and Hollow groups. The PRP‐SAN group exhibited better recovery in terms of the sciatic functional index value, composite action potential intensity, myelinated nerve fiber density, myelin sheath thickness, and gastrectomy tissue at 12 weeks after transplantation, compared with the PRP and SAN groups. The results of FG retrograde tracing and MEPs analyses showed that numbers of FG‐positive sensory neurons and motor neurons as well as MEPs distribution density were higher in the PRP‐SAN group than in the PRP or SAN group. Conclusions Nerve grafts comprising chitin biological conduits combined with SANs and PRP significantly improved the repair of 10‐mm sciatic nerve defects in rats and may have therapeutic potential for repairing peripheral nerve defects in future applications. Schematic shows a novel method on treating peripheral nerve defect. The nerve grafts comprising chitin biological conduits combined with SANs and PRP can enhance the repair of 10‐mm sciatic nerve defects in rats. PRP and SANs in the graft are completely self‐derived and obtained quickly and safely.

The treatment of long-gap peripheral nerve injury (PNI) is still a substantial clinical problem. Graphene-based scaffolds possess extracellular matrix (ECM) characteristic and can conduct electrical signals, therefore have been investigated for repairing PNI. Combined with electrical stimulation (ES), a well performance should be expected. We aimed to determine the effects of reduced graphene oxide fibers (rGOFs) combined with ES on PNI repair in vivo. rGOFs were prepared by one-step dimensionally confined hydrothermal strategy (DCH). Surface characteristics, chemical compositions, electrical and mechanical properties of the samples were characterized. The biocompatibility of the rGOFs were systematically explored both in vitro and in vivo. Total of 54 Sprague-Dawley (SD) rats were randomized into 6 experimental groups: a silicone conduit (S), S+ES, S+rGOFs-filled conduit (SGC), SGC+ES, nerve autograft, and sham groups for a 10-mm sciatic defect. Functional and histological recovery of the regenerated sciatic nerve at 12 weeks after surgery in each group of SD rats were evaluated. rGOFs exhibited aligned micro- and nano-channels with excellent mechanical and electrical properties. They are biocompatible in vitro and in vivo. All 6 groups exhibited PNI repair outcomes in view of neurological and morphological recovery. The SGC+ES group achieved similar therapeutic effects as nerve autograft group ( > 0.05), significantly outperformed other treatment groups. Immunohistochemical analysis showed that the expression of proteins related to axonal regeneration and angiogenesis were relatively higher in the SGC+ES. The rGOFs had good biocompatibility combined with excellent electrical and mechanical properties. Combined with ES, the rGOFs provided superior motor nerve recovery for a 10-mm nerve gap in a murine acute transection injury model, indicating its excellent repairing ability. That the similar therapeutic effects as autologous nerve transplantation make us believe this method is a promising way to treat peripheral nerve defects, which is expected to guide clinical practice in the future.

In this study, a biological conduit, consisting of an adipocyte-derived mesenchymal stem cell (AdMSCs) sheet and amniotic membrane (AM), was designed for the reconstruction of peripheral nerve defects. To evaluate the effect of the produced conduit on neural regeneration, a 10-mm sciatic nerve defect was created in rats, and experiments were carried out on six groups, i.e., sham control group (SC), negative control group (NC), nerve autograft group (NG), the biological conduit (AdMSCs + AM) group, the commercial PGA tube conduit (PGA) group, and the conduit only consisting of AM (AM) group. The effects of different nerve repair methods on the peripheral nerve and gastrocnemius muscle were evaluated by functional, histological, and immunohistochemical tests. When the number of myelinated axons was compared between the groups of AdMSCs + AM and PGA, it was higher in the AdMSCs + AM group ( p < 0.05). The percentage of gastrocnemius collagen bundle area of AdMSCs + AM group was found to be statistically lower than the PGA group ( p < 0.05). The muscle fiber diameter of AdMSCs + AM group was lower than that of the NG group, but significantly higher than that of the PGA group and the AM group ( p < 0.001). Muscle weight index was significantly higher in the AdMSCs + AM group compared to the PGA group (p < 0.05 ). It was observed that nerve regeneration was faster in the AdMSCs + AM group, and there was an earlier improvement in pin-prick score and sciatic functional index compared to the PGA group and the AM group. In conclusion, the biological conduit prepared from the AdMSCs sheet and AM is regarded as a new biological conduit that can be used as an alternative treatment method to nerve autograft in clinical applications. Graphical Abstract

Nerve regeneration after peripheral nerve injury (PNI) depends on exogenous and endogenous pro-healing signals in the microenvironment. Maintaining immune system homeostasis and remodeling the regenerative microenvironment are crucial prerequisites for promoting nerve regeneration. Here, a double-layer PSM/Gel-SC(IL-4) nerve guide conduit was fabricated by photocrosslinking poly (ethylene glycol) diacrylate (PEGDA) and methacrylic acid-sodium alginate (SAMA) hydrogel as the outer layer, with GelMA encapsulating IL-4 overexpressing Schwann cells as the inner layer. PSM/Gel-SC(IL-4) conduit enabled the sustained release of IL-4, inducing pro-healing macrophages polarization through JAK1/STAT6 pathway in vitro. The polarized macrophages further triggered the cellular cascade reactions, enhancing the pro-healing characteristics of endothelial cells and Schwann cells. In addition, PSM/Gel-SC(IL-4) conduit significantly promoted functional recovery and nerve regeneration in 12-mm rat sciatic nerve defect model, induced pro-healing macrophage polarization at the early stage and accelerated angiogenesis and myelination at the nerve regeneration stage. This study developed a novel immunomodulatory strategy to remodel the regenerative microenvironment, and explored the underlying cellular and molecular mechanism, demonstrating considerable therapeutic potential for long-distance nerve defect. [Display omitted] •PSM/Gel-SC(IL-4) nerve guiding conduit achieves the sustained release of IL-4.•PSM/Gel-SC(IL-4) NGC promote nerve regeneration and functional recovery in 12 mm defect model.•PSM/Gel-SC(IL-4) NGC modulate the immune microenvironment during PNI repair.•PSM/Gel-SC(IL-4) NGC trigger the Mφ-EC/SC cellular cascade reactions.

Background Traditionally known for bone regeneration, the Ilizarov technique's effectiveness in nerve reconstruction, particularly for extensive nerve damage, has yet to be widely recognized. Case presentation This report presents a case study and proposes the innovative use of the Ilizarov technique for reconstructing extended nerve defects. In this study, we reviewed a 43‐year‐old male diagnosed with an open fracture of the right tibia combined with soft tissue injury resulting in a mangled injury in which a large part of his right tibial bone and nerve were lost. The patient was cured and the sensorimotor function was recovered after distraction osteogenesis by the Ilizarov technique, which is a unique application of this technique to repair a substantial long nerve defect, a rare occurrence in medical literature. It highlights the method of nerve lengthening, which is achieved by attaching the nerve stump to the bone stump. This approach allows for significant nerve regeneration and ensures a stable progression of the nerve, as the bone stump acts as a carrier, overcoming the challenges of direct nerve lengthening. Conclusions The adaptability and effectiveness of the Ilizarov technique in a new area suggests the need to reconsider traditional approaches to complex nerve reconstruction. Placing this case within the context of current medical knowledge underscores the potential of this technique to revolutionize the treatment of extended nerve defects, offering hope for improved outcomes in challenging scenarios. This study demonstrates successful tissue regeneration through distraction osteogenesis via the Ilizarov technique. Particularly noteworthy is our innovative approach to nerve lengthening, where we attach the nerve stump to the bone stump, thus promoting substantial nerve regeneration and ensuring steady progress. This technique effectively addresses common challenges associated with direct nerve lengthening.

Despite the regenerative capabilities of peripheral nerves, severe injuries or neuronal trauma of critical size impose immense hurdles for proper restoration of neuro-muscular circuitry. Autologous nerve grafts improve re-establishment of connectivity, but also comprise substantial donor site morbidity. We developed a rat model which allows the testing of different cell applications, i.e., mesenchymal stem cells, to improve nerve regeneration in vivo. To mimic inaccurate alignment of autologous nerve grafts with the injured nerve, a 20 mm portion of the sciatic nerve was excised, and sutured back in place in reversed direction. To validate the feasibility of our novel model, a fibrin gel conduit containing autologous undifferentiated adipose-derived stem cells was applied around the coaptation sites and compared to autologous nerve grafts. After evaluating sciatic nerve function for 16 weeks postoperatively, animals were sacrificed, and gastrocnemius muscle weight was determined along with morphological parameters (g-ratio, axon density & diameter) of regenerating axons. Interestingly, the addition of undifferentiated adipose-derived stem cells resulted in a significantly improved re-myelination, axon ingrowth and functional outcome, when compared to animals without a cell seeded conduit. The presented model thus displays several intriguing features: it imitates a certain mismatch in size, distribution and orientation of axons within the nerve coaptation site. The fibrin conduit itself allows for an easy application of cells and, as a true critical-size defect model, any observed improvement relates directly to the performed intervention. Since fibrin and adipose-derived stem cells have been approved for human applications, the technique can theoretically be performed on humans. Thus, we suggest that the model is a powerful tool to investigate cell mediated assistance of peripheral nerve regeneration.