Chapter 8: Current techniques and concepts in peripheral nerve repair

Silicon-induced biofilm improves peripheral nerve defect in rats mediated by VEGF/VEGFR2/ERK

Background: Injury of peripheral nerve capable of regeneration with much poorer prognosis affects people's life quality. The recovery of nerve function after transplantation for peripheral nerve injury remain a worldwide problem. Silicon-induced biofilms as vascularized biological conduits can promote nerve regeneration by encapsulating autologous or allogeneic nerve graft.Objective: We proposed to explore the effect of silicon-induced biofilms on nerves regeneration and whether the VEGF/VEGFR2/ERK pathway was involved in the present study.Methods: Biofilms around the transplanted nerves in peripheral nerve injury rats were induced by silicon. Vascularization and proteins related to VEGF/VEGFR2/ERK were measured. Pathology and morphology of nerves were investigated after encapsulating the transplanted nerves by silicon-induced biofilms.Results: Our results indicated that the biofilms induced by silicon for 6 weeks showed the most intensive vascularization and the optimal effect on nerve regeneration. Moreover, silicon-induced biofilms for 4, 6 and 8 weeks could significantly secrete VEGF with the highest content at week 6 after induction. VEGFR2, VEGF, p-VEGFR2, ERK1, ERK2, p-ERK1 and p-ERK2 were expressed in the biofilms. p-VEGFR2, p-ERK1 and p-ERK2 expression were different at each time point and significantly increased at week 6 compared with that at week 4 or week 8 which was consistent with that 6 week of was the optimum time for biofilms induction to improve the nerve repair after peripheral nerve injury.Conclusion: Our results suggested that combination of silicon-induced autologous vascularized biofilm and autologous transplantation may promote the repair of rat sciatic nerve defect quickly through VEGF/VEGFR2/ERK pathway.

Roles of SMAD and SMAD-Associated Signaling Pathways in Nerve Regeneration Following Peripheral Nerve Injury: A Narrative Literature Review

Although several methods are being applied to treat peripheral nerve injury, a perfect treatment that leads to full functional recovery has not yet been developed. SMAD (Suppressor of Mothers Against Decapentaplegic Homolog) plays a crucial role in nerve regeneration by facilitating the survival and growth of nerve cells following peripheral nerve injury. We conducted a systematic literature review on the role of SMAD in this context. Following peripheral nerve injury, there was an increase in the expression of SMAD1, -2, -4, -5, and -8, while SMAD5, -6, and -7 showed no significant changes; SMAD8 expression was decreased. Specifically, SMAD1 and SMAD4 were found to promote nerve regeneration, whereas SMAD2 and SMAD6 inhibited it. SMAD exerts its effects by promoting neuronal survival and growth through BMP/SMAD1, BMP/SMAD4, and BMP/SMAD7 signaling pathways. Furthermore, it activates nerve regeneration programs via the PI3K/GSK3/SMAD1 pathway, facilitating active regeneration of nerve cells and subsequent functional recovery after peripheral nerve damage. By leveraging these mechanisms of SMAD, novel strategies for treating peripheral nerve damage could potentially be developed. We aim to further elucidate the precise mechanisms of nerve regeneration mediated by SMAD and explore the potential for developing targeted nerve treatments based on these findings.

Biological characteristics of tissue engineered-nerve grafts enhancing peripheral nerve regeneration

BACKGROUND

A favorable regenerative microenvironment is essential for peripheral nerve regeneration. Neural tissue-specific extracellular matrix (ECM) is a natural material that helps direct cell behavior and promote axon regeneration. Both bone marrow-derived mesenchymal stem cells (BMSCs) and adipose-derived mesenchymal stem cells (ADSCs) transplantation are effective in repairing peripheral nerve injury (PNI). However, there is no study that characterizes the in vivo microenvironmental characteristics of these two MSCs for the early repair of PNI when combined with neural tissue-derived ECM materials, i.e., acellular nerve allograft (ANA).

METHODS

In order to investigate biological characteristics, molecular mechanisms of early stage, and effectiveness of ADSCs- or BMSCs-injected into ANA for repairing PNI in vivo, a rat 10 mm long sciatic nerve defect model was used. We isolated primary BMSCs and ADSCs from bone marrow and adipose tissue, respectively. First, to investigate the in vivo response characteristics and underlying molecular mechanisms of ANA combined with BMSCs or ADSCs, eighty-four rats were randomly divided into three groups: ANA group, ANA+BMSC group, and ANA+ADSC group. We performed flow cytometry, RT-PCR, and immunofluorescence staining up to 4 weeks postoperatively. To further elucidate the underlying molecular mechanisms, changes in long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), microRNAs (miRNAs), and messenger RNAs (mRNAs) were systematically investigated using whole transcriptome sequencing. We then constructed protein-protein interaction networks to find 10 top ranked hub genes among differentially expressed mRNAs. Second, in order to explore the effectiveness of BMSCs and ADSCs on neural tissue-derived ECM materials for repairing PNI, sixty-eight rats were randomized into four groups: ANA group, ANA+BMSC group, ANA+ADSC group, and AUTO group. In the ANA+BMSC and ANA+ADSC groups, ADSCs/BMSCs were equally injected along the long axis of the 10-mm ANA. Then, we performed histological and functional assessments up to 12 weeks postoperatively.

RESULTS

The results of flow cytometry and RT-PCR showed that ANA combined with BMSCs exhibited more significant immunomodulatory effects, as evidenced by the up-regulation of interleukin (IL)-10, down-regulation of IL-1β and tumor necrosis factor-alpha (TNF-α) expression, promotion of M1-type macrophage polarization to M2-type, and a significant increase in the number of regulatory T cells (Tregs). ANA combined with ADSCs exhibited more pronounced features of pro-myelination and angiogenesis, as evidenced by the up-regulation of myelin-associated protein gene (MBP and MPZ) and angiogenesis-related factors (TGF-β, VEGF). Moreover, differentially expressed genes from whole transcriptome sequencing results further indicated that ANA loaded with BMSCs exhibited notable immunomodulatory effects and ANA loaded with ADSCs was more associated with angiogenesis, axonal growth, and myelin formation. Notably, ANA infused with BMSCs or ADSCs enhanced peripheral nerve regeneration and motor function recovery with no statistically significant differences.

CONCLUSIONS

This study revealed that both ANA combined with BMSCs and ADSCs enhance peripheral nerve regeneration and motor function recovery, but their biological characteristics (mainly including immunomodulatory effects, pro-vascular regenerative effects, and pro-myelin regenerative effects) and underlying molecular mechanisms in the process of repairing PNI in vivo are different, providing new insights into MSC therapy for peripheral nerve injury and its clinical translation.

Novel artificial nerve transplantation of human iPSC-derived neurite bundles enhanced nerve regeneration after peripheral nerve injury

BACKGROUND

Severe peripheral nerve damage always requires surgical treatment. Autologous nerve transplantation is a standard treatment, but it is not sufficient due to length limitations and extended surgical time. Even with the available artificial nerves, there is still large room for improvement in their therapeutic effects. Novel treatments for peripheral nerve injury are greatly expected.

METHODS

Using a specialized microfluidic device, we generated artificial neurite bundles from human iPSC-derived motor and sensory nerve organoids. We developed a new technology to isolate cell-free neurite bundles from spheroids. Transplantation therapy was carried out for large nerve defects in rat sciatic nerve with novel artificial nerve conduit filled with lineally assembled sets of human neurite bundles. Quantitative comparisons were performed over time to search for the artificial nerve with the therapeutic effect, evaluating the recovery of motor and sensory functions and histological regeneration. In addition, a multidimensional unbiased gene expression profiling was carried out by using next-generation sequencing.

RESULT

After transplantation, the neurite bundle-derived artificial nerves exerted significant therapeutic effects, both functionally and histologically. Remarkably, therapeutic efficacy was achieved without immunosuppression, even in xenotransplantation. Transplanted neurite bundles fully dissolved after several weeks, with no tumor formation or cell proliferation, confirming their biosafety. Posttransplant gene expression analysis highlighted the immune system's role in recovery.

CONCLUSION

The combination of newly developed microfluidic devices and iPSC technology enables the preparation of artificial nerves from organoid-derived neurite bundles in advance for future treatment of peripheral nerve injury patients. A promising, safe, and effective peripheral nerve treatment is now ready for clinical application.

Interactions of Neuronally Induced Stem Cells from Apical Papilla Spheres, Stems Cells from Apical Papilla, and Human Umbilical Vascular Endothelial Cells on Vasculogenesis and Neurogenesis

INTRODUCTION

Stem cell-based dental pulp regeneration has been extensively studied, mainly focusing on exploiting dental stem cells' osteogenic and angiogenic potentials. Dental stem cells' neurogenic role is often overlooked. Stem cells from apical papilla (SCAPs), originating from the neural crest and capable of sphere formation, display potent neurogenic capacity. This study aimed to investigate the interactions of neuronally induced stem cells from apical papilla (iSCAP) spheres, SCAPs, and human umbilical vascular endothelial cells (HUVECs) on vasculogenesis and neurogenesis.

METHODS

SCAPs were isolated and characterized using flow cytometry and multilineage differentiation assays. SCAP monolayer culture and spheres were neuronally induced by a small molecule neural induction medium, and the neural gene expression and neurite formation at days 0, 3, and 7 were evaluated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and using phase-contrast light and fluorescence microscopy. Direct coculture or pulp-on-chip was used to investigate iSCAP sphere interaction with SCAPs and HUVECs. RT-qPCR, fluorescence microscopy, and immunostaining with β-tubulin III, alpha-smooth muscle actin, and CD31 were used to study neural gene expression, neurite formation, and neurovascular cell interactions.

RESULTS

Neural induction medium with small molecules rapidly induced SCAP differentiation toward neural-like cells. Gene expression of Nestin, β-tubulin III, microtubule-associated protein 2, neuron-specific enolase, and NeuN was higher in iSCAP spheres than in iSCAPs. iSCAP spheres formed more and longer neurites compared with iSCAPs. iSCAP sphere, HUVEC, and SCAP direct coculture significantly enhanced vessel formation along with up-regulated VEGF (P < .001) and multiple neural markers, such as Nestin (P < .01), microtubule-associated protein 2 (P < .001), S100 (P < .001), and NG2 (P < .001). iSCAP spheres, SCAPs, and HUVECs cultured in a pulp-on-chip system promoted endothelial and neural cell migration toward each other and alpha-smooth muscle actin-positive and CD31-positive cells assembling for the vascular constitution.

CONCLUSIONS

iSCAP-formed spheres interact with SCAPs and HUVECs, promoting vasculogenesis and neurogenesis.

Surgery for mononeuropathies

Advancement in microsurgical techniques and innovative approaches including greater use of nerve and tendon transfers have resulted in better peripheral nerve injury (PNI) surgical outcomes. Clinical evaluation of the patient and their injury factors along with a shift toward earlier time frame for intervention remain key. A better understanding of the pathophysiology and biology involved in PNI and specifically mononeuropathies along with advances in ultrasound and magnetic resonance imaging allow us, nowadays, to provide our patients with a logical and sophisticated approach. While functional outcomes are constantly being refined through different surgical techniques, basic scientific concepts are being advanced and translated to clinical practice on a continuous basis. Finally, a combination of nerve transfers and technological advances in nerve/brain and machine interfaces are expanding the scope of nerve surgery to help patients with amputations, spinal cord, and brain lesions.

Strain-induced bands of Büngner formation promotes axon growth in 3D tissue-engineered constructs

Treatment of peripheral nerve lesions remains a major challenge due to poor functional recovery; hence, ongoing research efforts strive to enhance peripheral nerve repair. In this study, we aimed to establish three-dimensional tissue-engineered bands of Büngner constructs by subjecting Schwann cells (SCs) embedded in fibrin hydrogels to mechanical stimulation. We show for the first time that the application of strain induces (i) longitudinal alignment of SCs resembling bands of Büngner, and (ii) the expression of a pronounced repair SC phenotype as evidenced by upregulation of BDNF, NGF, and p75NTR. Furthermore, we show that mechanically aligned SCs provide physical guidance for migrating axons over several millimeters in vitro in a co-culture model with rat dorsal root ganglion explants. Consequently, these constructs hold great therapeutic potential for transplantation into patients and might also provide a physiologically relevant in vitro peripheral nerve model for drug screening or investigation of pathologic or regenerative processes.

Cost-effectiveness analysis of Avance® allograft for the treatment of peripheral nerve injuries in the USA

Aim: Peripheral nerve injury (PNI) is a debilitating condition with significant associated morbidity, and which places a substantial socioeconomic burden on healthcare systems worldwide. Recently, allograft has emerged as a viable surgical alternative to autograft for the treatment of PNI. This study evaluated the cost effectiveness of allograft (Avance® Nerve Graft) compared with autograft for the peripheral nerve repair, from a US payer perspective. Methods: A Markov cohort model was developed to consider the treatment pathways followed by a patient population undergoing a single transected nerve repair with either allograft, or autograft. The marginal difference in meaningful recovery (MR) (effectiveness), and costs, between the two groups were estimated over a lifetime horizon. Deterministic and probabilistic sensitivity analyses (PSA) were performed to consider the uncertainty surrounding the base-case input parameter values and their effect on the overall incremental cost-effectiveness ratio (ICER). Results: The base-case analysis indicates that there is a small difference in the average probability of MR between the two groups (75.15% vs 70.46%; +4.69% with allograft). Allograft also results in cost savings ($12,677 vs $14,023; -$-1346 with allograft) compared with autograft. Deterministic sensitivity analysis shows that the costs of the initial surgical procedures are the main drivers of incremental cost, but that the intervention is likely to be cost saving compared with autograft regardless of the parameter variations made. Conclusion: The use of allograft with the Avance Nerve Graft has the potential to be a cost-effective alternative to autograft for the surgical treatment of PNI in the USA.

Emerging 4D fabrication of next-generation nerve guiding conduits: a critical perspective

The latest advancements in the field of manufacturing for biomedicine, digital health, targeted therapy, and personalized medicine have fuelled the fabrication of smart medical devices. Four-dimensional (4D) fabrication strategies, which combine the manufacturing of three-dimensional (3D) parts with smart materials and/or design, have proved beneficial in creating customized and self-fitting structures that change their properties on demand with time. These frontier techniques that yield dynamic implants can indeed alleviate various drawbacks of current clinical practices, such as the use of sutures and complex microsurgeries and associated inflammation, among others. Among various clinical applications, 4D fabrication has lately made remarkable progress in the development of next-generation nerve-guiding conduits for treating peripheral nerve injuries (PNIs) by improving the end-to-end co-aptation of transected nerve endings. The current perspective highlights the relevance of 4D fabrication in developing state-of-the-art technologies for the treatment of PNIs. Various 4D fabrication/bio-fabrication techniques for PNI treatment are summarized while identifying the challenges and opportunities for the future. Such advancements hold immense promise for improving the quality of life of patients suffering from nerve damage and the potential for extending the treatment of many other disorders. Although the techniques are being described for PNIs, they will lend themselves suitably to certain cases of cranial nerve injuries as well.

Review on electrically conductive smart nerve guide conduit for peripheral nerve regeneration

At present, peripheral nerve injuries (PNIs) are one of the leading causes of substantial impairment around the globe. Complete recovery of nerve function after an injury is challenging. Currently, autologous nerve grafts are being used as a treatment; however, this has several downsides, for example, donor site morbidity, shortage of donor sites, loss of sensation, inflammation, and neuroma development. The most promising alternative is the development of a nerve guide conduit (NGC) to direct the restoration and renewal of neuronal axons from the proximal to the distal end to facilitate nerve regeneration and maximize sensory and functional recovery. Alternatively, the response of nerve cells to electrical stimulation (ES) has a substantial regenerative effect. The incorporation of electrically conductive biomaterials in the fabrication of smart NGCs facilitates the function of ES throughout the active proliferation state. This article overviews the potency of the various categories of electroactive smart biomaterials, including conductive and piezoelectric nanomaterials, piezoelectric polymers, and organic conductive polymers that researchers have employed latterly to fabricate smart NGCs and their potentiality in future clinical application. It also summarizes a comprehensive analysis of the recent research and advancements in the application of ES in the field of NGC.

Google Trends Analysis of Peripheral Nerve Disease and Surgery

BACKGROUND

Despite advances in the surgical management of peripheral nerve pathologies over the past several decades, it is unknown how public awareness of these procedures has changed. We hypothesize that Google searches for peripheral nerve surgery have increased over time.

METHODS

Google Trends was queried for search volumes of a list of 40 keywords related to the following topics in peripheral nerve surgery: spasticity, nerve injury, prosthetics, and nerve pain. Monthly relative search volume over the first 5 years of the study period (2010-2014) was compared with that of the last 5 years (2018-2022) of the study period.

RESULTS

Search volumes for keywords "nerve injury," "nerve laceration," "peripheral nerve injury," "nerve repair," "nerve transfer", "neuroma," "neuroma pain," "nerve pain," "nerve pain surgery," and "neuroma pain surgery" all increased more than 10% points in relative search volume over the study period (P < 0.0001 for each keyword). In contrast, searches for "rhizotomy," "spasticity surgery," "targeted muscle reinnervation," "bionic arm," and "myoelectric prosthesis" either decreased or remained stable. Technical terms such as "selective neurectomy," "hyperselective neurectomy," "regenerative peripheral nerve interface," and "regenerative peripheral nerve interface surgery" did not have adequate search volume to be reported by Google Trends.

CONCLUSIONS

The increase in Google searches related to nerve injury and pain between 2010 and 2022 may reflect increasing public recognition of these clinical entities and surgical techniques addressing them. Technical terms relating to nerve pain are infrequently searched, surgeons should use plain English terms for online discovery. Interest in spasticity and myoelectric prosthetics remains stable, indicating an opportunity for better public outreach.

Outcomes of radiocarpal pinning to facilitate nerve repair in wrist-level ulnar nerve injuries with defect

BACKGROUND

The ideal scenario for ulnar nerve repair is primary end-to-end neurorrhaphy in a tension-free environment. However, this could be complicated by soft tissue loss, scarring, and neuroma formation in a delayed injury, creating a nerve defect. With a wrist-level nerve defect, a flexion position can help shorten the nerve gap; however, maintaining the position can be challenging intraoperatively and postoperatively.

METHODS

Previously, we proposed our method of using a 1.6-mm K wire for radius-lunate-capitate pinning of the wrist in flexion to minimize the nerve gap, thereby facilitating neuroma excision and end-to-end neurorrhaphy in delayed ulnar nerve injury. In this study, we elaborate our method and present our case series.

RESULTS

From October 2018 to July 2020, five patients (mean age: 48.2 years; mean delay from injury to surgery: 84.6 days; mean follow-up: 17.5 months) were retrospectively reviewed. The mean flexion fixation angle was 52°, and the K wire was removed at an average of 5.1 weeks postoperatively. All patients were followed up for a minimum of 12 months. All patients achieved M4 and S3 or S3+ neurologically (according to the criteria of the Nerve Injuries Committee of the British Medical Research Council). The mean disabilities arm, shoulder, and hand score was 14.1. The mean grasp and pinch strengths were, respectively, 76.8% and 63.6% of the contralateral hand. All wrist range of motion returned to normal within 12 weeks. No complications were noted intraoperatively or postoperatively.

CONCLUSION

Our study showed that radiocarpal pinning of the wrist in flexion was safe and convenient to minimize the nerve gap and to facilitate end-to-end neurorrhaphy in limited-sized wrist-level ulnar nerve defects.

Focal Application of Neurotrophic Factors Augments Outcomes of Nerve-Muscle-Endplate Grafting Technique for Limb Muscle Reinnervation

BACKGROUND

 We have developed a novel muscle reinnervation technique called "nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ)." This study aimed to augment the outcomes of the NMEG-NMZ (NN) by focal application of exogenous neurotrophic factors (ENFs) for limb reinnervation.

METHODS

 Adult rats were used to conduct NN plus ENF (NN/ENF) and autologous nerve grafting (ANG, technique control). The nerve innervating the left tibialis anterior (TA) muscle was resected and the denervated TA was immediately treated with NN/ENF or ANG. For NN procedure, an NMEG pedicle was taken from the lateral gastrocnemius muscle and transferred to the NMZ of the denervated TA. For ANG, the nerve gap was bridged with sural nerve. Three months after treatment, the extent of functional and neuromuscular recovery was assessed by measuring static toe spread, maximal muscle force, wet muscle weight, regenerated axons, and innervated motor endplates (MEPs).

RESULTS

 NN/ENF resulted in 90% muscle force recovery of the treated TA, which is far superior to ANG (46%) and NN alone (79%) as reported elsewhere. Toe spread recovered up to 89 and 49% of the control for the NN/ENF and ANG groups, respectively. The average wet muscle weight was 87 and 52% of the control for muscles treated with NN/ENF and ANG, respectively. The mean number of the regenerated axons was 88% of the control for the muscles treated with NN/ENF, which was significantly larger than that for the ANG-repaired muscles (39%). The average percentage of the innervated MEPs in the NN/ENF-treated TA (89%) was higher compared with that in the ANG-repaired TA (48%).

CONCLUSION

 ENF enhances nerve regeneration and MEP reinnervation that further augment outcomes of NN. The NN technique could be an alternative option to treat denervated or paralyzed limb muscles caused by traumatic nerve injuries or lesions.

How Can We Make Hand Surgery Carbon Neutral?

BACKGROUND

Climate change is a major public health threat worldwide. Operating theaters are responsible for extensive waste production due to the resource-intensive nature of surgery, including hand surgery.

METHODS

An online literature search was performed to ascertain the approaches that surgeons may undertake to positively impact the environment.

RESULTS

Surgeons can make hand surgery more carbon neutral through various measures that have been categorized as pre-, intra-, and postoperative interventions. With all changes, the aims are to minimize waste and costs while optimizing patient outcomes.

CONCLUSIONS

Administrative obstacles to implementing pro-climate hospital changes may be overcome by also considering likely cost benefits with many environmentally friendly measures. New measures in hand surgery should consider patient safety, clinical efficacy, cost effectiveness, and the environmental impact.

Thermoelectric Freeze-Casting of Biopolymer Blends: Fabrication and Characterization of Large-Size Scaffolds for Nerve Tissue Engineering Applications

Peripheral nerve injuries (PNIs) are detrimental to the quality of life of affected individuals. Patients are often left with life-long ailments that affect them physically and psychologically. Autologous nerve transplant is still the gold standard treatment for PNIs despite limited donor site and partial recovery of nerve functions. Nerve guidance conduits are used as a nerve graft substitute and are efficient for the repair of small nerve gaps but require further improvement for repairs exceeding 30 mm. Freeze-casting is an interesting fabrication method for the conception of scaffolds meant for nerve tissue engineering since the microstructure obtained comprises highly aligned micro-channels. The present work focuses on the fabrication and characterization of large scaffolds (35 mm length, 5 mm diameter) made of collagen/chitosan blends by freeze-casting via thermoelectric effect instead of traditional freezing solvents. As a freeze-casting microstructure reference, scaffolds made from pure collagen were used for comparison. Scaffolds were covalently crosslinked for better performance under load and laminins were further added to enhance cell interactions. Microstructural features of lamellar pores display an average aspect ratio of 0.67 ± 0.2 for all compositions. Longitudinally aligned micro-channels are reported as well as enhanced mechanical properties in traction under physiological-like conditions (37 °C, pH = 7.4) resulting from crosslinking treatment. Cell viability assays using a rat Schwann cell line derived from sciatic nerve (S16) indicate that scaffold cytocompatibility is similar between scaffolds made from collagen only and scaffolds made from collagen/chitosan blend with high collagen content. These results confirm that freeze-casting via thermoelectric effect is a reliable manufacturing strategy for the fabrication of biopolymer scaffolds for future peripheral nerve repair applications.

4D printed tri-segment nerve conduit using zein gel as the ink for repair of rat sciatic nerve large defect

Zein has enormous potential for application in biomedical field due to biodegradation and biocompatibility, we have recently prepared zein gel as a possible 3D printing ink. Our previous studies found that the pore structure in zein material can reduce early inflammation, promote the polarization of macrophages toward the M2 phenotype, and accelerate nerve regeneration. To further explore the role of zein in nerve repair, we used 4D printing technique to create nerve conduits with zein protein gel, and designed 2 types of tri-segment conduits with different degradation rates. Structural parts printed in support baths with higher water content show faster degradation rates than those printed in support baths with lower water content. The conduits that degraded quickly at both ends and slowly in the middle (CB75-CB40-CB75) and the conduits that degraded slowly at both ends and quickly in the middle (CB40-CB75-CB40) were 4D printed, respectively. Animal experiments suggest that the CB75-CB40-CB75 conduit is better for nerve repair, which may be because its degradation pattern can match to the pattern of nerve regeneration better. Our new strategy through 4D printing indicated that fine modulation in conduit degradation can affect efficacy of nerve repair significantly.

Mechanism of Danggui Sini underlying the treatment of peripheral nerve injury based on network pharmacology and molecular docking: A review

Danggui Sini is a traditional Chinese medicine prescription for treating peripheral nerve injury (PNI). We studied the mechanisms of this decoction through network pharmacology analysis and molecular docking. Using R language and Perl software, the active components and predicted targets of Danggui Sini, as well as the related gene targets of PNI, were mined through TCMSP, GeneCards, OMIM, TTD, and DrugBank. The network diagram of active components and intersection targets was constructed using Cytoscape software and the STRING database. The CytoNCA plug-in was used to screen out the core compounds and key targets. The genes were analyzed for Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment. AutoDock was used to analyze the molecular docking of key targets and core compounds of diseases. The drug component disease target regulatory network showed that the key components included quercetin, kaempferol, naringenin, and licochalcone A, which play key roles in the whole network and may be the primary compounds associated with the action of Danggui Sini against PNI. PPI network topology analysis showed high degree values for RELA, JUN, MAPK1, RB1, and FOS. Enrichment analysis showed that the core targets of Danggui Sini participated in pathways associated with neurogenesis-multiple diseases. Molecular docking showed that the active ingredients in Danggui Sini had a good binding ability with key targets. We conclude that many active components of Danggui Sini play therapeutic roles in PNI treatment by regulating RELA, JUN, MAPK1, RB1, and FOS, and multiple other targets in inflammation, immunity, and lipid metabolism.

Molecular Basis of Surgical Coaptation Techniques in Peripheral Nerve Injuries

Peripheral nerve injuries requiring surgical repair affect over 100,000 individuals in the US annually. Three accepted methods of peripheral repair include end-to-end, end-to-side, and side-to-side neurorrhaphy, each with its own set of indications. While it remains important to understand the specific circumstances in which each method is employed, a deeper understanding of the molecular mechanisms underlying the repair can add to the surgeon's decision-making algorithm when considering each technique, as well as help decide nuances in technique such as the need for making epineurial versus perineurial windows, length and dept of the nerve window, and distance from target muscle. In addition, a thorough knowledge of individual factors that are active in a particular repair can help guide research into adjunct therapies. This paper serves to summarize the similarities and divergences of the three commonly used nerve repair strategies and the scope of molecular mechanisms and signal transduction pathways in nerve regeneration as well as to identify the gaps in knowledge that should be addressed if we are to improve clinical outcomes in our patients.

Conditioning electrical stimulation fails to enhance sympathetic axon regeneration

Peripheral nerve injuries are common, and there is a critical need for the development of novel therapeutics to complement surgical repair. Conditioning electrical stimulation (CES) is a novel variation to the well-studied perioperative electrical stimulation, both of which have displayed success in enhancing the regeneration of motor and sensory axons in an injured peripheral nerve. CES is a clinically attractive alternative not only because of its ability to be performed at the bedside prior to a scheduled nerve repair surgery, but it has also been shown to be superior to perioperative electrical stimulation in the enhancement of motor and sensory regeneration. However, the effects of CES on sympathetic regeneration are unknown. Therefore, we tested the effects of two clinically relevant CES paradigms on sympathetic axon regeneration and distal target reinnervation. Because of the long history of evidence for the enhancement of motor and sensory axons in response to electrical stimulation, we hypothesize that CES will also enhance sympathetic axon regeneration. Our results indicate that the growth of sympathetic axons is acutely inhibited by CES; however, at a longer survival time point post-injury, there is no difference between sham CES and the CES groups. There has been evidence to suggest that the growth of sympathetic axons is inhibited by a conditioning lesion, and that sympathetic axons may respond to electrical stimulation by sprouting rather than elongation. Our data indicate that sympathetic axons may retain some regenerative ability after CES, but no enhancement is exhibited, which may be accounted for by the inability of the current clinically relevant electrical stimulation paradigm to recruit the small-caliber sympathetic axons into activity. Further studies will be needed to optimize electrical stimulation parameters in order to enhance the regeneration of all neuron types.

Effect of necrostatin-1 on sciatic nerve crush injury in rat models

BACKGROUND

Necrostatin-1 (Nec-1) is an inhibitor of the receptor interacting protein (RIP)1 kinase, which acts as an inhibitor of necroptosis, a special form of necrosis. In the present study, the effect of Nec-1 on peripheral nerve injury (PNI) was investigated.

METHODS

The PNI model was established by inducing sciatic nerve injury. Hematoxylin-eosin and immunofluorescence staining techniques were used to assess the extent of injury to nerve fibers and necrosis of Schwann cells (SCs). Western blotting was performed to detect the expression of necroptosis-related factors (RIP1 and RIP3). The concentrations of tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and the oxidative stress-related enzyme malondialdehyde (MDA) were determined to indicate the degree of inflammation and oxidative stress.

RESULTS

Nec-1 could decrease the degree of peripheral nerve lesions after PNI and protect SCs and axons by inhibiting necroptosis. Furthermore, Nec-1 could reduce necroptosis by inhibiting RIP1 and effectively reduce inflammation and reactive oxygen species production at the early stage of PNI.

CONCLUSIONS

Alleviation of necroptosis by Nec-1 may provide new insights into therapies for the early stages of peripheral nerve repair after PNI.

Repair of Long Peripheral Nerve Defects in Sheep: A Translational Model for Nerve Regeneration

Despite advances in microsurgery, full functional recovery of severe peripheral nerve injuries is not commonly attained. The sheep appears as a good preclinical model since it presents nerves with similar characteristics to humans. In this study, we induced 5 or 7 cm resection in the peroneal nerve and repaired with an autograft. Functional evaluation was performed monthly. Electromyographic and ultrasound tests were performed at 6.5 and 9 months postoperation (mpo). No significant differences were found between groups with respect to functional tests, although slow improvements were seen from 5 mpo. Electrophysiological tests showed compound muscle action potentials (CMAP) of small amplitude at 6.5 mpo that increased at 9 mpo, although they were significantly lower than the contralateral side. Ultrasound tests showed significantly reduced size of tibialis anterior (TA) muscle at 6.5 mpo and partially recovered size at 9 mpo. Histological evaluation of the grafts showed good axonal regeneration in all except one sheep from autograft 7 cm (AG7) group, while distal to the graft there was a higher number of axons than in control nerves. The results indicate that sheep nerve repair is a useful model for investigating long-gap peripheral nerve injuries.

Reinnervation of Paralyzed Limb Muscle by Nerve-Muscle-Endplate Grafting Technique

BACKGROUND

We have developed a novel reinnervation technique called nerve-muscle-endplate grafting in the native motor zone (NMEG-NMZ). However, it remains unknown whether the NMEG-NMZ is effective for limb reinnervation.

OBJECTIVE

To evaluate the efficacy of the NMEG-NMZ in limb muscle reinnervation.

METHODS

Forty-five adult rats were divided into 3 groups: NMEG, end-to-end anastomosis (EEA, technique control), and denervation control (DC). The left tibialis anterior muscle was denervated by resecting its nerve. For NMEG-NMZ, the denervated tibialis anterior was reinnervated by transferring a NMEG pedicle from the lateral gastrocnemius muscle. Three months after surgery, static toe spread analysis was performed for all rats and muscle force was measured for the rats treated with NMEG and EEA. Muscle weight, myofiber morphology, regenerated axons, and reinnervated motor endplates in the treated muscles were also quantified and compared with those in the DC group.

RESULTS

NMEG-NMZ technique resulted in better muscle force recovery (79% of the control) compared with EEA (51% of the control, P = .048). Toe spread analysis in NMEG-NMZ reinnervated muscles showed static sciatic index = -16.8, whereas -41.4 in EEA, P < .0001). The average weight of the NMEG-NMZ reinnervated muscles (86%) was greater than those of the EEA treated (71%) and DC (26%) muscles (all P < .0001). The mean count of the regenerated axons in the muscles with NMEG-NMZ was 76% of the control, which was larger than that in the muscles with EEA (46%), P < .0001.

CONCLUSION

NMEG-NMZ technique has unique advantages and is superior to EEA for muscle reinnervation and functional recovery.

Functional recovery and muscle atrophy in pre-clinical models of peripheral nerve transection and gap-grafting in mice: effects of 4-aminopyridine

We recently demonstrated a repurposing beneficial effect of 4-aminopyridine (4-AP), a potassium channel blocker, on functional recovery and muscle atrophy after sciatic nerve crush injury in rodents. However, this effect of 4-AP is unknown in nerve transection, gap, and grafting models. To evaluate and compare the functional recovery, nerve morphology, and muscle atrophy, we used a novel stepwise nerve transection with gluing (STG), as well as 7-mm irreparable nerve gap (G-7/0) and 7-mm isografting in 5-mm gap (G-5/7) models in the absence and presence of 4-AP treatment. Following surgery, sciatic functional index was determined weekly to evaluate the direct in vivo global motor functional recovery. After 12 weeks, nerves were processed for whole-mount immunofluorescence imaging, and tibialis anterior muscles were harvested for wet weight and quantitative histomorphological analyses for muscle fiber cross-sectional area and minimal Feret’s diameter. Average post-injury sciatic functional index values in STG and G-5/7 models were significantly greater than those in the G-7/0 model. 4-AP did not affect the sciatic functional index recovery in any model. Compared to STG, nerve imaging revealed more misdirected axons and distorted nerve architecture with isografting. While muscle weight, cross-sectional area, and minimal Feret’s diameter were significantly smaller in G-7/0 model compared with STG and G-5/7, 4-AP treatment significantly increased right TA muscle mass, cross-sectional area, and minimal Feret’s diameter in G-7/0 model. These findings demonstrate that functional recovery and muscle atrophy after peripheral nerve injury are directly related to the intervening nerve gap, and 4-AP exerts differential effects on functional recovery and muscle atrophy.

Engineered neuronal microtissue provides exogenous axons for delayed nerve fusion and rapid neuromuscular recovery in rats

Nerve injury requiring surgical repair often results in poor functional recovery due to the inability of host axons to re-grow long distances and reform meaningful connections with the target muscle. While surgeons can re-route local axon fascicles to the target muscle, there are no technologies to provide an exogenous source of axons without sacrificing healthy nerves. Accordingly, we have developed tissue engineered neuromuscular interfaces (TE-NMIs) as the first injectable microtissue containing motor and sensory neurons in an anatomically-inspired architecture. TE-NMIs provide axon tracts that are intended to integrate with denervated distal structures and preserve regenerative capacity during prolonged periods without host innervation. Following implant, we found that TE-NMI axons promoted Schwann cell maintenance, integrated with distal muscle, and preserved an evoked muscle response out to 20-weeks post nerve transection in absence of innervation from host axons. By repopulating the distal sheath with exogenous axons, TE-NMIs also enabled putative delayed fusion with proximal host axons, a phenomenon previously not achievable in delayed repair scenarios due to distal axon degeneration. Here, we found immediate electrophysiological recovery after fusion with proximal host axons and improved axon maturation and muscle reinnervation at 24-weeks post-transection (4-weeks following delayed nerve fusion). These findings show that TE-NMIs provide the potential to improve functional recovery following delayed nerve repair.

Nerve regeneration conduit from inverted human umbilical cord vessel in the treatment of proper palmar digital nerve sections

Treatment of digital nerve injuries, particularly in case of a gap, is challenging. Recovery of finger sensitivity is often incomplete and can impair personal and occupational activity. The need for better nerve regeneration has given rise to alternative treatments such as nerve conduits. This study aimed to evaluate the safety and efficacy of a conduit of freeze-dried inverted human umbilical cord vessel for regeneration in digital nerve section. Twenty-three patients with a mean nerve gap of 6.11 mm (range 2-30 mm and static 2-point discrimination (s2PD) > 15 mm underwent surgical repair of digital nerve section using a nerve regeneration conduit. The primary endpoint was recovery of sensitivity after conduit implantation. Secondary endpoints comprised progression of pain, functional symptoms, pressure threshold, hand-specific symptoms and disabilities, and restored innervation. Mean follow-up was 10.1 ± 4.1 months (range 1-14 months). Sensitivity recovered progressively in the months following implantation. There was a mean decrease of 8.54 mm in s2PD between baseline and last follow-up (p < 0.001). Complete innervation recovered in 83.3% of cases at last follow-up. Pressure threshold and hand-related quality of life improved significantly and symptoms due to nerve sectioning (pain, cold intolerance, hypoesthesia, hyperesthesia) resolved almost completely. There were no safety issues related to the nerve conduit. These results indicate that freeze-dried inverted human umbilical vessels can be a safe and effective option as conduit for digital nerve regeneration.

Inverted human umbilical artery as a 3D scaffold for sciatic nerve regeneration in rats

Treatment of peripheral nerve injuries (PNIs) remains a challenge. Interposing a graft delivers better regenerative outcomes. Autografts present major drawbacks which have given rise to the development of alternatives such as artificial scaffolds, some of which are very promising. This study was designed to investigate the potential use of an inverted human umbilical cord artery (iHUA) as a 3D scaffold nerve chamber, for nerve regeneration after transection of the sciatic nerve (SN) in rats. Rats underwent surgical SN transection in their right hindlimb, followed by suture of the device at the resected stumps. Local tolerance, insert biodegradability and nerve reconstruction over time were thoroughly studied by histopathological and morphometric analysis, completed by functional test assessment of sensitivity and motricity recovery. We have demonstrated that nerve reconstruction in the presence of an iHUA insert is effective. The device is well tolerated and highly biodegraded. Although the regenerated nerve is still immature at the end of our study, signs of sensitivity and partial functional recovery were witnessed, confirming our histological findings. Our results support the potential clinical use of iHUA as a 3D scaffold to bridge nerve discontinuity and guide axonal regrowth in selected cases of PNIs.

Exercise facilitates regeneration after severe nerve transection and further modulates neural plasticity

Patients with severe traumatic peripheral nerve injury (PNI) always suffer from incomplete recovery and poor functional outcome. Physical exercise-based rehabilitation, as a non-invasive interventional strategy, has been widely acknowledged to improve PNI recovery by promoting nerve regeneration and relieving pain. However, effects of exercise on chronic plastic changes following severe traumatic PNIs have been limitedly discussed. In this study, we created a long-gap sciatic nerve transection followed by autograft bridging in rats and tested the therapeutic functions of treadmill running with low intensity and late initiation. We demonstrated that treadmill running effectively facilitated nerve regeneration and prevented muscle atrophy and thus improved sensorimotor functions and walking performance. Furthermore, exercise could reduce inflammation at the injured nerve as well as prevent the overexpression of TRPV1, a pain sensor, in primary afferent sensory neurons. In the central nervous system, we found that PNI induced transcriptive changes at the ipsilateral lumber spinal dorsal horn, and exercise could reverse the differential expression for genes involved in the Notch signaling pathway. In addition, through neural imaging techniques, we found volumetric, microstructural, metabolite, and neuronal activity changes in supraspinal regions of interest (i.e., somatosensory cortex, motor cortex, hippocampus, etc.) after the PNI, some of which could be reversed through treadmill running. In summary, treadmill running with late initiation could promote recovery from long-gap nerve transection, and while it could reverse maladaptive plasticity after the PNI, exercise may also ameliorate comorbidities, such as chronic pain, mental depression, and anxiety in the long term.

Promoting Nerve Regeneration: Electrical Stimulation, Gene Therapy, and Beyond

Peripheral nerve injuries often result in life-altering functional deficits even with optimal management. Unlike the central nervous system, peripheral nerves have the ability to regenerate lost axons after injury; however, axonal regeneration does not equate to full restoration of function. To overcome this physiological shortcoming, advances in nerve regeneration and repair are paramount, including electrical stimulation, gene therapy, and surgical technique advancements.

Translational bioengineering strategies for peripheral nerve regeneration: opportunities, challenges, and novel concepts

Peripheral nerve injuries remain a challenging problem in need of better treatment strategies. Despite best efforts at surgical reconstruction and postoperative rehabilitation, patients are often left with persistent, debilitating motor and sensory deficits. There are currently no therapeutic strategies proven to enhance the regenerative process in humans. A clinical need exists for the development of technologies to promote nerve regeneration and improve functional outcomes. Recent advances in the fields of tissue engineering and nanotechnology have enabled biomaterial scaffolds to modulate the host response to tissue repair through tailored mechanical, chemical, and conductive cues. New bioengineered approaches have enabled targeted, sustained delivery of protein therapeutics with the capacity to unlock the clinical potential of a myriad of neurotrophic growth factors that have demonstrated promise in enhancing regenerative outcomes. As such, further exploration of combinatory strategies leveraging these technological advances may offer a pathway towards clinically translatable solutions to advance the care of patients with peripheral nerve injuries. This review first presents the various emerging bioengineering strategies that can be applied for the management of nerve gap injuries. We cover the rationale and limitations for their use as an alternative to autografts, focusing on the approaches to increase the number of regenerating axons crossing the repair site, and facilitating their growth towards the distal stump. We also discuss the emerging growth factor-based therapeutic strategies designed to improve functional outcomes in a multimodal fashion, by accelerating axonal growth, improving the distal regenerative environment, and preventing end-organs atrophy.

A Review on the Technological Advances and Future Perspectives of Axon Guidance and Regeneration in Peripheral Nerve Repair

Despite a significant advance in the pathophysiological understanding of peripheral nerve damage, the successful treatment of large nerve defects remains an unmet medical need. In this article, axon growth guidance for peripheral nerve regeneration was systematically reviewed and discussed mainly from the engineering perspective. In addition, the common approaches to surgery, bioengineering approaches to emerging technologies such as optogenetic stimulation and magnetic stimulation for functional recovery were discussed, along with their pros and cons. Additionally, clear future perspectives of axon guidance and nerve regeneration were addressed.

Muscle-in-Vein Conduits for the Treatment of Symptomatic Neuroma of Sensory Digital Nerves

Background: Considering the debilitating burden of neuroma resulting in a significant loss of function and excruciating pain, the use of muscle-in-vein conduits (MVCs) for the reconstruction of painful neuroma of sensory nerves of the fingers was assessed. Methods: We retrospectively analyzed 10 patients who underwent secondary digital nerve repair by MVCs. The recovery of sensibility was evaluated by static and moving two-point discrimination (2PDs, 2PDm) and Semmes-Weinstein monofilament testing (SWM). The minimum follow-up was set 12 months after the operation. Results: The median period between trauma and nerve repair was 13.4 weeks (IQR 53.5). After neuroma resection, defects ranged from 10–35 mm (mean 17.7 mm, SD 0.75). The successful recovery of sensibility was achieved in 90% of patients after a median follow-up of 27.0 months (IQR 31.00). The mean 2PDs and 2PDm was 8.1 mm (SD 3.52) and 5.2 mm (SD 2.27), respectively. Assessment by SWM resulted in a mean value of 3.54 (SD 0.69). Reduction in pain was achieved among all patients; eight patients reported the complete relief of neuropathic pain. There was no recurrence of neuroma in any patient. Conclusions: Muscle-in-vein conduits provide an effective treatment for painful neuroma of digital nerves, resulting in satisfactory restoration of sensory function and relief of pain.

Occurrence of Lymphangiogenesis in Peripheral Nerve Autografts Contrasts Schwann Cell-Induced Apoptosis of Lymphatic Endothelial Cells In Vitro

Peripheral nerve injuries pose a major clinical concern world-wide, and functional recovery after segmental peripheral nerve injury is often unsatisfactory, even in cases of autografting. Although it is well established that angiogenesis plays a pivotal role during nerve regeneration, the influence of lymphangiogenesis is strongly under-investigated. In this study, we analyzed the presence of lymphatic vasculature in healthy and regenerated murine peripheral nerves, revealing that nerve autografts contained increased numbers of lymphatic vessels after segmental damage. This led us to elucidate the interaction between lymphatic endothelial cells (LECs) and Schwann cells (SCs) in vitro. We show that SC and LEC secretomes did not influence the respective other cell types’ migration and proliferation in 2D scratch assay experiments. Furthermore, we successfully created lymphatic microvascular structures in SC-embedded 3D fibrin hydrogels, in the presence of supporting cells; whereas SCs seemed to exert anti-lymphangiogenic effects when cultured with LECs alone. Here, we describe, for the first time, increased lymphangiogenesis after peripheral nerve injury and repair. Furthermore, our findings indicate a potential lymph-repellent property of SCs, thereby providing a possible explanation for the lack of lymphatic vessels in the healthy endoneurium. Our results highlight the importance of elucidating the molecular mechanisms of SC–LEC interaction.

Biological Approach in the Treatment of External Popliteal Sciatic Nerve (Epsn) Neurological Injury: Review

The external popliteal sciatic nerve (EPSN) is the nerve of the lower extremity most frequently affected by compressive etiology. Its superficial and sinuous anatomical course is closely related to other rigid anatomical structures and has an important dynamic neural component. Therefore, this circumstance means that this nerve is exposed to multiple causes of compressive etiology. Despite this fact, there are few publications with extensive case studies dealing with treatment. In this review, we propose to carry out a narrative review of the neuropathy of the EPSN, including an anatomical reminder, its clinical presentation and diagnosis, as well as its surgical and biological approach. The most novel aspect we propose is the review of the possible role of biological factors in the reversal of this situation.

Novel Tissue-Engineered Multimodular Hyaluronic Acid-Polylactic Acid Conduits for the Regeneration of Sciatic Nerve Defect

The gold standard for the treatment of peripheral nerve injuries, the autograft, presents several drawbacks, and engineered constructs are currently suitable only for short gaps or small diameter nerves. Here, we study a novel tissue-engineered multimodular nerve guidance conduit for the treatment of large nerve damages based in a polylactic acid (PLA) microfibrillar structure inserted inside several co-linear hyaluronic acid (HA) conduits. The highly aligned PLA microfibers provide a topographical cue that guides axonal growth, and the HA conduits play the role of an epineurium and retain the pre-seeded auxiliary cells. The multimodular design increases the flexibility of the device. Its performance for the regeneration of a critical-size (15 mm) rabbit sciatic nerve defect was studied and, after six months, very good nerve regeneration was observed. The multimodular approach contributed to a better vascularization through the micrometrical gaps between HA conduits, and the pre-seeded Schwann cells increased axonal growth. Six months after surgery, a cross-sectional available area occupied by myelinated nerve fibers above 65% at the central and distal portions was obtained when the multimodular device with pre-seeded Schwann cells was employed. The results validate the multi-module approach for the regeneration of large nerve defects and open new possibilities for surgical solutions in this field.

Nerve Injuries in Total Knee Arthroplasty

Nerve injury is one of the potential complications of total knee arthroplasty. The extent of the injury includes motor and sensory dysfunction, either temporary or permanent. Although the consequences of nerve injury may be dramatic, the probability of occurrence during the course of primary knee arthroplasty is low, around 0.12% to 0.4%. Local dressing removal and knee flexion are imperative, and the initial investigations include ultrasound or MRI and nerve conduction studies. The extent of recovery depends on the type and severity of the initial nerve palsy; however, most patients are expected to have at least a partial recovery.

Electrospun Polycaprolactone (PCL)-Amnion Nanofibrous Membrane Promotes Nerve Regeneration and Prevents Fibrosis in a Rat Sciatic Nerve Transection Model

Functional recovery after peripheral nerve injury repair is typically unsatisfactory. An anastomotically poor microenvironment and scarring at the repair site are important factors impeding nerve regeneration. In this study, an electrospun poly-e-caprolactone (PCL)-amnion nanofibrous membrane comprising an amnion membrane and nonwoven electrospun PCL was used to wrap the sciatic nerve repair site in the rat model of a sciatic nerve transection. The effect of the PCL-amnion nanofibrous membrane on improving nerve regeneration and preventing scarring at the repair site was evaluated by expression of the inflammatory cytokine, sciatic functional index (SFI), electrophysiology, and histological analyses. Four weeks after repair, the degree of nerve adhesion, collagen deposition, and intraneural macrophage invasion of the PCL-amnion nanofibrous membrane group were significantly decreased compared with those of the Control group. Moreover, the PCL-amnion nanofibrous membrane decreased the expression of pro-inflammatory cytokines such as interleukin(IL)-6, Tumor Necrosis Factor(TNF)-a and the number of pro-inflammatory M1 macrophages, and increased the expression of anti-inflammatory cytokine such as IL-10, IL-13 and anti-inflammatory M2 macrophages. At 16 weeks, the PCL-amnion nanofibrous membrane improved functional recovery, including promoting nerve Schwann cell proliferation, axon regeneration, and reducing the time of muscle denervation. In summary, the PCL-amnion nanofibrous membrane effectively improved nerve regeneration and prevent fibrosis after nerve repair, which has good clinical application prospect for tissue repair.

Neurorrhaphy in Presence of Polyethylene Glycol Enables Immediate Electrophysiological Conduction in Porcine Model of Facial Nerve Injury

Facial nerve trauma often leads to disfiguring facial muscle paralysis. Despite several promising advancements, facial nerve repair procedures often do not lead to complete functional recovery. Development of novel repair strategies requires testing in relevant preclinical models that replicate key clinical features. Several studies have reported that fusogens, such as polyethylene glycol (PEG), can improve functional recovery by enabling immediate reconnection of injured axons; however, these findings have yet to be demonstrated in a large animal model. We first describe a porcine model of facial nerve injury and repair, including the relevant anatomy, surgical approach, and naive nerve morphometry. Next, we report positive findings from a proof-of-concept experiment testing whether a neurorrhaphy performed in conjunction with a PEG solution maintained electrophysiological nerve conduction at an acute time point in a large animal model. The buccal branch of the facial nerve was transected and then immediately repaired by direct anastomosis and PEG application. Immediate electrical conduction was recorded in the PEG-fused nerves (n = 9/9), whereas no signal was obtained in a control cohort lacking calcium chelating agent in one step (n = 0/3) and in the no PEG control group (n = 0/5). Nerve histology revealed putative-fused axons across the repair site, whereas no positive signal was observed in the controls. Rapid electrophysiological recovery following nerve fusion in a highly translatable porcine model of nerve injury supports previous studies suggesting neurorrhaphy supplemented with PEG may be a promising strategy for severe nerve injury. While acute PEG-mediated axon conduction is promising, additional work is necessary to determine if physical axon fusion occurs and the longer-term fate of distal axon segments as related to functional recovery.

A Novel Standardized Peripheral Nerve Transection Method and a Novel Digital Pressure Sensor Device Construction for Peripheral Nerve Crush Injury

Peripheral nerve injury (PNI) is common in all walks of life, and the most common PNIs are nerve crush and nerve transection. While optimal functional recovery after crush injury occurs over weeks, functional recovery after nerve transection with microsurgical repair and grafting is poor, and associated with permanent disability. The gold-standard treatment for nerve transection injury is microsurgical tensionless end-to-end suture repair. Since it is unethical to do experimental PNI studies in humans, it is therefore indispensable to have a simple, reliable, and reproducible pre-clinical animal model for successful evaluation of the efficacy of a novel treatment strategy. The objective of this article is two-fold: (A) To present a novel standardized peripheral nerve transection method in mice, using fibrin glue for modeling peripheral nerve transection injury, with reproducible gap distance between the severed nerve ends, and (B) to document the step-wise description of constructing a pressure sensor device for crush injury pressure measurements. We have successfully established a novel nerve transection model in mice using fibrin glue, and demonstrated that this transection method decreases surgical difficulties and variability by avoiding microsurgical manipulations on the nerve, ensuring the reproducibility and reliability of this animal model. Although it is quite impossible to exactly mimic the pathophysiological changes seen in nerve transection with sutures, we hope that the close resemblance of our novel pre-clinical model with gold-standard suturing can be easily reproduced by any lab, and that the data generated by this method significantly contributes to better understanding of nerve pathophysiology, molecular mechanisms of nerve regeneration, and the development of novel strategies for optimal functional recovery. In case of peripheral nerve crush injury, current methods rely on inter-device and operator precision to limit the variation with applied pressure. While the inability to accurately quantify the crush pressure may result in reduced reproducibility between animals and studies, there is no documentation of a pressure monitoring device that can be readily used for real-time pressure measurements. To address this deficit, we constructed a novel portable device comprised of an Arduino UNO microcontroller board and force sensitive resistor (FSR) capable of reporting the real-time pressure applied to a nerve. This novel digital pressure sensor device is cheap, easy to construct and assemble, and we believe that this device will be useful for any lab performing nerve crush injury in rodents.

Immunomodulatory effects of mesenchymal stem cells in peripheral nerve injury

Various immune cells and cytokines are present in the aftermath of peripheral nerve injuries (PNI), and coordination of the local inflammatory response is of great significance for the recovery of PNI. Mesenchymal stem cells (MSCs) exhibit immunosuppressive and anti-inflammatory abilities which can accelerate tissue regeneration and attenuate inflammation, but the role of MSCs in the regulation of the local inflammatory microenvironment after PNI has not been widely studied. Here, we summarize the known interactions between MSCs, immune cells, and inflammatory cytokines following PNI with a focus on the immunosuppressive role of MSCs. We also discuss the immunomodulatory potential of MSC-derived extracellular vesicles as a new cell-free treatment for PNI.

Potential of Fibrin Glue and Mesenchymal Stem Cells (MSCs) to Regenerate Nerve Injuries: A Systematic Review

Cell-based therapy is a promising treatment to favor tissue healing through less invasive strategies. Mesenchymal stem cells (MSCs) highlighted as potential candidates due to their angiogenic, anti-apoptotic and immunomodulatory properties, in addition to their ability to differentiate into several specialized cell lines. Cells can be carried through a biological delivery system, such as fibrin glue, which acts as a temporary matrix that favors cell-matrix interactions and allows local and paracrine functions of MSCs. Thus, the aim of this systematic review was to evaluate the potential of fibrin glue combined with MSCs in nerve regeneration. The bibliographic search was performed in the PubMed/MEDLINE, Web of Science and Embase databases, using the descriptors ("fibrin sealant" OR "fibrin glue") AND "stem cells" AND "nerve regeneration", considering articles published until 2021. To compose this review, 13 in vivo studies were selected, according to the eligibility criteria. MSCs favored axonal regeneration, remyelination of nerve fibers, as well as promoted an increase in the number of myelinated fibers, myelin sheath thickness, number of axons and expression of growth factors, with significant improvement in motor function recovery. This systematic review showed clear evidence that fibrin glue combined with MSCs has the potential to regenerate nervous system lesions.

Progress on the Experimental Research of Sciatic Nerve Injury with Acupuncture

Objective

To collect and summarize relevant literatures on the experimental researches of sciatic nerve injury (SNI) with acupuncture during the last decade providing a guideline for effectively treating SNI with acupuncture in the future.

Methods

The Chinese and English databases including China National Knowledge Infrastructure (CNKI), Wanfang Data Knowledge Service Platform (WanFang Data), VIP Information Chinese Journal Service Platform (VIP Date), and PubMed were searched from 2009 to 2020 with keywords of “acupuncture and moxibustion OR acupuncture OR electroacupuncture OR scalp acupuncture OR wrist-ankle acupuncture OR acupoint injection OR ear acupuncture” AND “sciatic nerve OR sciatic nerve injury OR sciatic injury OR SNI.” The collected data were mainly evaluated in the items of animal model of SNI, type of interventions, selection of acupuncture points (acupoints), course of treatment and its frequency, and approaches of assessment.

Results

A total of 89 studies were included in this analysis. Among them, the most commonly used animal models of SNI were produced by the clamp or transverse injury in the rats; the most frequently used intervention was electroacupuncture with dilatational wave of 2/100 Hz; the frequency of acupuncture was mainly performed once per day lasting for more than 2 weeks; the mainly selected acupoints were Huantiao (GB30), Zusanli (ST36), and Yanglingquan (GB34); and the approaches of assessment were contained with behavioral, functional, morphological, histological, cellular, and molecular measurements.

Conclusion

The results indicated that the experimental researches of SNI with acupuncture has made marked progress in recent years, which may provide important clues for further investigating the underlying mechanisms of acupuncture for the treatment of SNI in the future.

A Rabbit Model for Peripheral Nerve Reconstruction Studies Avoiding Automutilation Behavior

Background  The rabbit sciatic nerve injury model may represent a valuable alternative for critical gap distance seen in humans but often leads to automutilation. In this study, we modified the complete sciatic nerve injury model for avoiding autophagy.

Materials and Methods  In 20 adult female New Zealand White rabbits, instead of transecting the complete sciatic nerve, we unilaterally transected the tibial portion and preserved the peroneal portion. Thereby loss of sensation in the dorsal aspect of the paw was avoided. The tibial portion was repaired in a reversed autograft approach in a length of 2.6 cm. In an alternative repair approach, a gap of 2.6 cm in length was repaired with a chitosan-based nerve guide.

Results  During the 6-month follow-up period, there were no incidents of autotomy. Nerve regeneration of the tibial portion of the sciatic nerve was evaluated histologically and morphometrically. A clear difference between the distal segments of the healthy contralateral and the repaired tibial portion of the sciatic nerve was detectable, validating the model.

Conclusion  By transecting the isolated tibial portion of the rabbit sciatic nerve and leaving the peroneal portion intact, it was possible to eliminate automutilation behavior.

Nerve gaps repaired with acellular nerve allografts recellularized with Schwann-like cells: Preclinical trial

BACKGROUND

Acellular nerve allografts (ANA) recellularized with mesenchymal stem cells (MSC) or Schwann cells (SC) are, at present, a therapeutic option for peripheral nerve injuries (PNI). This study aimed to evaluate the regenerative and functional capacity of a recellularized allograft (RA) compared with autograft nerve reconstruction in PNI.

METHODS

Fourteen ovines were randomly included in two groups (n=7). A peroneal nerve gap 30 mm in length was excised, and nerve repair was performed by the transplantation of either an autograft or a recellularized allograft with SC-like cells. Evaluations included a histomorphological analysis of the ANA, MSC pre differentiated into SC-like cells, at one year follow-up functional limb recovery (support and gait), and nerve regeneration using neurophysiological tests and histomorphometric analysis. All evaluations were compared with the contralateral hindlimb as the control.

RESULTS

The nerve allograft was successfully decellularized and more than 70% of MSC were pre differentiated into SC-like cells. Functional assessment in both treated groups improved similarly over time (p <0.05). Neurophysiological results (latency, amplitude, and conduction velocity) also improved in both treated groups at twelve months. Histological results demonstrated a less organized arrangement of nerve fibers (p <0.05) with an active remyelination process (p <0.05) in both treated groups compared with controls at twelve months.

CONCLUSIONS

ANA recellularized with SC-like cells proved to be a successful treatment for nerve gaps. Motor recovery and nerve regeneration were satisfactorily achieved in both graft groups compared with their contralateral nontreated nerves. This approach could be useful for the clinical therapy of PNI.

Limb Muscle Reinnervation with the Nerve-Muscle-Endplate Grafting Technique: An Anatomical Feasibility Study

BACKGROUND

Peroneal nerve injuries results in tibialis anterior (TA) muscle paralysis. TA paralysis could cause "foot drop," a disabling condition that can make walking difficult. As current treatment methods result in poor functional recovery, novel treatment approaches need to be studied. The aim of this study was to explore anatomical feasibility of limb reinnervation with our recently developed nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ).

METHODS

As the NMEG-NMZ technique involves in nerves and motor endplates (MEPs), the nerve supply patterns and locations of the MEP bands within the gastrocnemius (GM) and TA muscles of rats were investigated using Sihler's stain and whole-mount acetylcholinesterase (AChE) staining, respectively. Five adult rats underwent TA nerve transaction. The denervated TA was reinnervated by transferring an NMEG pedicle from the ipsilateral lateral GM. At the end of a 3-month recovery period, maximal muscle force was measured to document functional recovery.

RESULTS

The results showed that the TA was innervated by the deep peroneal nerve. A single MEP band was located obliquely in the middle of the TA. The GM was composed of two neuromuscular compartments, lateral (GM-l) and medial (GM-m), each of which was innervated by a separate nerve branch derived from the tibial nerve and had a vertically positioned MEP band. The locations of MEP bands in the GM and TA muscles and nerve supply patterns demonstrated that an NMEG pedicle can be harvested from the GM-l and implanted into the NMZ within the TA muscle. The NMEG-NMZ pilot study showed that this technique resulted in optimal muscle force recovery.

CONCLUSION

NMEG-NMZ surgery is feasible for limb reinnervation. Specifically, the denervated TA caused by peroneal nerve injuries can be reinnervated with a NMEG from the GM-l.

Repair of peripheral nerve injuries using a prevascularized cell-based tissue-engineered nerve conduit

One of the major challenges in the development of a larger and longer nerve conduit for peripheral nerve repair is the limitation in oxygen and nutrient diffusion within the tissue after transplantation preventing Schwann cell and axonal migration. This restriction is due to the slow neovascularization process of the graft starting from both nerve endings. To overcome this limitation, we propose the design of a living tissue-engineered nerve conduit made of an internal tube with a three-dimensional structure supporting axonal migration, which is inserted inside a hollow external tube that plays the role of an epineurium and is strong enough to be stitched to the severed nerve stumps. The internal tube is made of a rolled living fibroblast sheet and can be seeded with endothelial cells to promote the formation of a network containing capillary-like structures which allow rapid inosculation with the host nerve microvasculature after grafting. Human nerve conduits were grafted in immunodeficient rats to bridge a 15 mm sciatic nerve gap. Human capillaries within the pre-vascularized nerve conduit successfully connected to the host circulation 2 weeks after grafting. Twenty-two weeks after surgery, rats transplanted with the nerve conduits had a similar motor function recovery compared to the autograft group. By promoting rapid vascularization of the internal nerve tube from both ends of the nerve stumps, this endothelialized nerve conduit model displays a favorable environment to enhance axonal migration in both larger caliber and longer nerve grafts.

Application of Human Epineural Conduit Supported with Human Mesenchymal Stem Cells as a Novel Therapy for Enhancement of Nerve Gap Regeneration

Various therapeutic methods have been suggested to enhance nerve regeneration. In this study, we propose a novel approach for enhancement of nerve gap regeneration by applying human epineural conduit (hEC) supported with human mesenchymal stem cells (hMSC), as an alternative to autograft repair. Restoration of 20 mm sciatic nerve defect with hEC created from human sciatic nerve supported with hMSC was tested in 4 experimental groups (n = 6 each) in the athymic nude rat model (Crl:NIH-Foxn1^rnu): 1 - No repair control, 2 - Autograft control, 3 - Matched diameter hEC filled with 1 mL saline, 4 - Matched diameter hEC supported with 3 × 10⁶ hMSC. Assessments included: functional tests: toe-spread and pinprick, regeneration assessment by immunofluorescence staining: HLA-1, HLA-DR, NGF, GFAP, Laminin B, S-100, VEGF, vWF and PKH26 labeling; histomorphometric analysis of myelin thickness, axonal density, fiber diameter and myelinated nerve fibers percentage; Gastrocnemius Muscle Index (GMI) and muscle fiber area ratio. Best sensory and motor function recovery, as well as GMI and muscle fiber area ratio, were observed in the autograft group, and were comparable to the hEC with hMSC group (p = 0.038). Significant improvements of myelin thickness (p = 0.003), fiber diameter (p = 0.0296), and percentage of myelinated fibers (p < 0.0001) were detected in hEC group supported with hMSC compared to hEC with saline controls. At 12-weeks after nerve gap repair, hEC combined with hMSC revealed increased expression of neurotrophic and proangiogenic factors, which corresponded with improvement of function comparable with the autograft control. Application of our novel hEC supported with hMSC provides a potential alternative to the autograft nerve repair.

Protease Activated Receptor 1 and Its Ligands as Main Regulators of the Regeneration of Peripheral Nerves

In contrast with the brain and spinal cord, peripheral nerves possess a striking ability to regenerate after damage. This characteristic of the peripheral nervous system is mainly due to a specific population of glial cells, the Schwann cells. Schwann cells promptly activate after nerve injury, dedifferentiate assuming a repair phenotype, and assist axon regrowth. In general, tissue injury determines the release of a variety of proteases which, in parallel with the degradation of their specific targets, also activate plasma membrane receptors known as protease-activated receptors (PARs). PAR1, the prototypical member of the PAR family, is also known as thrombin receptor and is present at the Schwann cell plasma membrane. This receptor is emerging as a possible regulator of the pro-regenerative capacity of Schwann cells. Here, we summarize the most recent literature data describing the possible contribution of PAR1 and PAR1-activating proteases in regulating the regeneration of peripheral nerves.

Development of a conduit of PLGA-gelatin aligned nanofibers produced by electrospinning for peripheral nerve regeneration

A promising alternative to conventional nerve grafting is the use of artificial grafts made from biodegradable and biocompatible materials and support cells. The aim of this study has been to produce a biodegradable nerve conduit and investigate the cytocompatibility with stem cells and its regeneration promoting properties in a rat animal model. A poly (lactic-co-glycolic acid) (PLGA) conduit of aligned nanofibers was produced by the electrospinning method, functionalized with gelatin and seeded either with mouse embryonic stem cells (mESCs) or with human mesenchymal stem cells (SHED). The cell proliferation and viability were analyzed in vitro. The conduits were implanted in a rat model of sciatic nerve lesion by transection. The functional recovery was monitored for 8 weeks using the Sciatic Functional Index (SFI) and histological analyses were used to assess the nerve regeneration. Scaffolds of aligned PLGA fibers with an average diameter of 0.90 ± 0.36 μm and an alignment coefficient of 0.817 ± 0.07 were produced. The treatment with gelatin increased the fiber diameter to 1.05 ± 0.32 μm, reduced the alignment coefficient to 0.655 ± 0.045 and made the scaffold very hydrophilic. The cell viability and Live/dead assay showed that the stem cells remained viable and proliferated after 7 days in culture. Confocal images of phalloidin/DAPI staining showed that the cells adhered and proliferated widely, in fully adaptation with the biomaterial. The SFI values of the group that received the conduit were similar to the values of the control lesioned group. In conclusion, conduits composed of PLGA-gelatin nanofibers were produced and promoted a very good interaction with the stem cells. Although in vitro studies have shown this biomaterial to be a promising biomaterial for the regeneration of nerve tissue, in vivo studies of this graft have not shown significant improvements in nerve regeneration.