Management of nerve gaps: autografts, allografts, nerve transfers, and end-to-side neurorrhaphy

The effect of a gap concept on peripheral nerve recovery in modified epineurial neurorrhaphy: An experimental study in rats

BACKGROUND

Several factors such as surgical approach that only consider topographic anatomy; inadequate fascicular alignment, extraepineurial sprouting in the repair zone; contact of axons with the suture area are the disadvantages of epineurial neurorrhaphy. Accordingly, axonal mismatch, neuroma, and unfavorable nerve recovery become inevitable. Neurotropism is the theory clarifying appropriate matching of the nerve fibers independently without needing surgical approach. The studies comparing the primary nerve repair with the nerve defects bridged in different ways demonstrated better outcomes of nerve recovery in the groups with a nerve gap. In this study, we aimed to demonstrate the effects of the gap concept in primary nerve repair bridged by own epineurium. We hypothesized that this technique will provide better results in terms of peripheral nerve recovery and will significantly eliminate the occurrence of a neuroma, which is quite possible in epineurial neurorrhaphy.

MATERIALS AND METHODS

A total of 35 Wistar female rats weighing 200 ~ 250 g were randomly divided into five groups each with seven rats. Sham controls constituted Group 1, while the rats with epineural neurorrhaphy were included in Group 2. The remaining three groups were the study groups. In Group 3, after the sciatic nerve transection, epineurium of the distal segment was sleeved and preserved. A 2-mm axonal segment was removed from the epineurium free distal ending and no any procedure was applied to the proximal ending of the transected sciatic nerve. Epineuriums of the both sides were approximated and repaired. In Group 4, a 2-mm axonal segment was removed from the proximal ending of the sciatic nerve after preservation of epineurium and no any procedure was applied to the distal part of sciatic nerve. Epineuriums of the both sides were approximated and repaired. In addition, in Group 5, after epineuriums were sleeved in the both distal and proximal stumps, a 1-mm nerve segment was removed from both endings and epineuriums were repaired in the middle bridging a 2-mm axonal gap again. After a 3 months follow-up period Sciatic Functional Index (SFI) was measured by walking track analysis; the area under the evoked compound muscle action potential (CMAP) and latency periods were calculated via electromyographic (EMG) analysis; and histopathological evaluation were performed to compare the parameters of edema, fibrosis, inflammation, vascularization, axonal degeneration, axonal density, myelination, disorganization, and neuroma occurrence. Vascular structures and nerve fibers were counted at ×200 magnification: +1, +2, and +3 indicated the presence of 0-15, 16-30, and >30 structures, respectively. For uncountable parameters (edema, disorganization, myelination, fibrosis, and inflammation): +1 indicated mild, +2 indicated moderate, and +3 indicated severe.

RESULTS

The differences between the groups with axonal gap repair and epineural neurorrhaphy were not significant regarding to SFI. The areas under CMAP were as follows: 27.9 ± 5.9 (Δ = 12.1%) in Group 1; 16.5 ± 5.5 (Δ = 6.3%) in Group 2; 14.1 ± 6.2 (Δ = 4.8%) in group 3; 13.8 ± 2.3 (Δ = 9.2%) in Group 4, and 22.5 ± 18.3 (Δ = 2.2%) in Group 5. Group 5 (1 mm gap in the distal +1 mm gap in the proximal segments) had a significantly better result in terms of the area under CMAP with the value of 22.5 ± 18.3 m/Mv (p = .031). Axonal density was 0.9 ± 0.6 (Δ = 2.2%) in Group 2, 2.4 ± 0.3 (Δ = 5.1%) in Group 3, 2.8 ± 0.1 (Δ = 7.7%) in Group 4, and 2.8 ± 0.2 (Δ = 4.8%) in Group 5. Myelination was 1.1 ± 0.5 (Δ = 3.4%) in group 2, 2.2 ± 0.2 (Δ = 6.7%) in group 3, 2.4 ± 0.4 (Δ = 6.0%) in Group 4, and 2.7 ± 0.3 (Δ = 4.6%) in Group 5. Disorganization was 2.3 ± 0.4 (Δ = 4.1%) in Group 2, 1.2 ± 0.2 (Δ = 7.7%) in Group 3, 1.3 ± 0.2 (Δ = 6.5%) in Group 4, and 1 ± 0.3 (Δ = 5.9%) in Group 5. And, neuroma occurrence was found 2.2 ± 0.6 (Δ = 2.8%) in Group 2 and 0.3 ± 0.2 (Δ = 0.1%) in Group 4 while neuroma was not encountered in Group 3 and Group 5. Comparison between the epineurial neurorrhaphy group and the groups with axonal defect revealed the statistically significant results in the factors of axonal density (p = .001), myelination (p = .028), disorganization (p = .016) and neuroma (p = .001).

CONCLUSIONS

Creating axonal gap bridged by own epineurium showed favorable results comparing with epineurial neurorrhaphy. Resection of a 1 mm axonal segment from the proximal and distal stumps following the epineurial sleeve procedure and performing the epineurium- only repair can facilitate the nerve regeneration. The feasibility of the described technique has been demonstrated in a small rat model and must be further validated in larger animals before clinical testing.

Graphdiyne-Related Materials in Biomedical Applications and Their Potential in Peripheral Nerve Tissue Engineering

Graphdiyne (GDY) is a new member of the family of carbon-based nanomaterials with hybridized carbon atoms of sp and sp², including α, β, γ, and (6,6,12)-GDY, which differ in their percentage of acetylene bonds. The unique structure of GDY provides many attractive features, such as uniformly distributed pores, highly π-conjugated structure, high thermal stability, low toxicity, biodegradability, large specific surface area, tunable electrical conductivity, and remarkable thermal conductivity. Therefore, GDY is widely used in energy storage, catalysis, and energy fields, in addition to biomedical fields, such as biosensing, cancer therapy, drug delivery, radiation protection, and tissue engineering. In this review, we first discuss the synthesis of GDY with different shapes, including nanotubes, nanowires, nanowalls, and nanosheets. Second, we present the research progress in the biomedical field in recent years, along with the biodegradability and biocompatibility of GDY based on the existing literature. Subsequently, we present recent research results on the use of nanomaterials in peripheral nerve regeneration (PNR). Based on the wide application of nanomaterials in PNR and the remarkable properties of GDY, we predict the prospects and current challenges of GDY-based materials for PNR.

Multimodular Bio-Inspired Organized Structures Guiding Long-Distance Axonal Regeneration

Axonal bundles or axonal tracts have an aligned and unidirectional architecture present in many neural structures with different lengths. When peripheral nerve injury (PNI), spinal cord injury (SCI), traumatic brain injury (TBI), or neurodegenerative disease occur, the intricate architecture undergoes alterations leading to growth inhibition and loss of guidance through large distance. In order to overcome the limitations of long-distance axonal regeneration, here we combine a poly-L-lactide acid (PLA) fiber bundle in the common lumen of a sequence of hyaluronic acid (HA) conduits or modules and pre-cultured Schwann cells (SC) as cells supportive of axon extension. This multimodular preseeded conduit is then used to induce axon growth from a dorsal root ganglion (DRG) explant placed at one of its ends and left for 21 days to follow axon outgrowth. The multimodular conduit proved effective in promoting directed axon growth, and the results may thus be of interest for the regeneration of long tissue defects in the nervous system. Furthermore, the hybrid structure grown within the HA modules consisting in the PLA fibers and the SC can be extracted from the conduit and cultured independently. This “neural cord” proved to be viable outside its scaffold and opens the door to the generation of ex vivo living nerve in vitro for transplantation.

Optimized Decellularization Protocol for Large Peripheral Nerve Segments: Towards Personalized Nerve Bioengineering

Nerve injuries remain clinically challenging, and allografts showed great promise. Decellularized nerve allografts possess excellent biocompatibility and biological activity. However, the vast majority of decellularization protocols were established for small-size rodent nerves and are not suitable for clinical application. We aimed at developing a new method of decellularizing large-diameter nerves suitable for human transplantation. Repeated rounds of optimization to remove immunogenic material and preserve the extracellular structure were applied to the porcine sciatic nerve. Following optimization, extensive in vitro analysis of the acellular grafts via immunocytochemistry, immunohistology, proteomics and cell transplantation studies were performed. Large segments (up to 8 cm) of the porcine sciatic nerve were efficiently decellularized and histology, microscopy and proteomics analysis showed sufficient preservation of the extracellular matrix, with simultaneous consistent removal of immunogenic material such as myelin, DNA and axons, and axonal growth inhibitory molecules. Cell studies also demonstrated the suitability of these acellular grafts for 3D cell culture studies and translation to future large animal studies and clinical trials. By using non-human donors for peripheral nerve transplantation, significant drawbacks associated with the gold standard can be eliminated while simultaneously preserving the beneficial features of the extracellular matrix.

Epineural Neurorrhaphy of a Large Nerve Defect Due to IatroGenic Sciatic Nerve Injury in a Maltese Dog

Simple Summary

Sciatic nerve injury could occur due to mistake of surgery and called as ‘iatrogenic injury’. This type of injury is rare in dogs. Historically, this injury is treated through physiotherapy. However, if the nerve is completely transected, surgery such as nerve repair could be addressed. Unfortunately, if there is a large gap between transected sciatic nerve, it is very difficult to treat. Sometimes amputation is recommended because of permanent problem with dog’s hind leg. By the way, it is not known how long the gap can be treated in dogs before the important decision of whether to amputate the leg or not. Therefore, we would like to described a good result of treating an iatrogenic sciatic nerve injury with a large defect measuring 20 mm in length in a small Maltese dog. The dog suffered nerve injury after hip joint surgery and could not be walking himself for 2 months. So, we decided to treat him by nerve repair despite of large gap. Sensation and walking function of his hind leg was recovered almost completely after 2.5 years. Although sciatic nerve injury with large gap is a concern, it could be treated through surgery, even in small Maltese.

Abstract

Epineural neurorrhaphy is a standard nerve repair method, but it is rarely reported in veterinary literature. Epineural neurorrhaphy in canine sciatic nerve injury are described in this report. An 11-month-old, castrated male Maltese dog, presented with an one-month history of non-weight bearing lameness and knuckling of the right pelvic limb. The dog showed absence of superficial and deep pain perception on the dorsal and lateral surfaces below the stifle joint. The dog had undergone femoral head and neck osteotomy in the right pelvic limb one month prior to referral at a local hospital. Based on physical and neurological examinations, peripheral nerve injury of the right pelvic limb was suspected. Radiography showed irregular bony proliferation around the excised femoral neck. Magnetic resonance imaging revealed sciatic nerve injury with inconspicuous continuity at the greater trochanter level. A sciatic nerve neurotmesis was suspected and surgical repair was decided. During surgery, non-viable tissue of the sciatic nerve was debrided, and epineural neurorrhaphy was performed to bridge a large, 20-mm defect. The superficial and deep pain perception was progressively improved and restored at 3 weeks postoperatively, and the dog exhibited a gradual improvement in motor function. At 10 weeks postoperatively, the dog showed no neurological deficit including knuckling but the tarsal joint hyperextension did not improve due to ankylosis. The dog had undergone tarsal arthrodesis and exhibited almost normal limb function without any neurologic sequela until the last follow-up at 2.5 years postoperatively.

Current Trends in the Reconstruction and Rehabilitation of Jaw following Ablative Surgery

Simple Summary

The Maxilla and mandible provide skeletal support for of the middle and lower third of our faces, allowing for the normal functioning of breathing, chewing, swallowing, and speech. The ablative surgery of jaws in the past often led to serious disfigurement and disruption in form and function. However, with recent strides made in computer-assisted surgery and patient-specific implants, the individual functional reconstruction of the jaw is evolving rapidly and the prompt rehabilitation of both the masticatory function and aesthetics after jaw resection has been made possible. In the present review, the recent advancements in jaw reconstruction technology and future perspectives will be discussed.

Abstract

The reconstruction and rehabilitation of jaws following ablative surgery have been transformed in recent years by the development of computer-assisted surgery and virtual surgical planning. In this narrative literature review, we aim to discuss the current state-of-the-art jaw reconstruction, and to preview the potential future developments. The application of patient-specific implants and the “jaw-in-a-day technique” have made the fast restoration of jaws’ function and aesthetics possible. The improved efficiency of primary reconstructive surgery allows for the rehabilitation of neurosensory function following ablative surgery. Currently, a great deal of research has been conducted on augmented/mixed reality, artificial intelligence, virtual surgical planning for soft tissue reconstruction, and the rehabilitation of the stomatognathic system. This will lead to an even more exciting future for the functional reconstruction and rehabilitation of the jaw following ablative surgery.

Regenerative Role of T Cells in Nerve Repair and Functional Recovery

The immune system is essential in the process of nerve repair after injury. Successful modulation of the immune response is regarded as an effective approach to improving treatment outcomes. T cells play an important role in the immune response of the nervous system, and their beneficial roles in promoting regeneration have been increasingly recognized. However, the diversity of T-cell subsets also delivers both neuroprotective and neurodegenerative functions. Therefore, this review mainly discusses the beneficial impact of T-cell subsets in the repair of both peripheral nervous system and central nervous system injuries and introduces studies on various therapies based on T-cell regulation. Further discoveries in T-cell mechanisms and multifunctional biomaterials will provide novel strategies for nerve regeneration.

Magnesium-Encapsulated Injectable Hydrogel and 3D-Engineered Polycaprolactone Conduit Facilitate Peripheral Nerve Regeneration

Peripheral nerve injury is a challenging orthopedic condition that can be treated by autograft transplantation, a gold standard treatment in the current clinical setting. Nevertheless, limited availability of autografts and potential morbidities in donors hampers its widespread application. Bioactive scaffold-based tissue engineering is a promising strategy to promote nerve regeneration. Additionally, magnesium (Mg) ions enhance nerve regeneration; however, an effectively controlled delivery vehicle is necessary to optimize their in vivo therapeutic effects. Herein, a bisphosphonate-based injectable hydrogel exhibiting sustained Mg2+ delivery for peripheral nerve regeneration is developed. It is observed that Mg2+ promoted neurite outgrowth in a concentration-dependent manner by activating the PI3K/Akt signaling pathway and Sema5b. Moreover, implantation of polycaprolactone (PCL) conduits filled with Mg2+ -releasing hydrogel in 10 mm nerve defects in rats significantly enhanced axon regeneration and remyelination at 12 weeks post-operation compared to the controls (blank conduits or conduits filled with Mg2+ -absent hydrogel). Functional recovery analysis reveals enhanced reinnervation in the animals treated with the Mg2+ -releasing hydrogel compared to that in the control groups. In summary, the Mg2+ -releasing hydrogel combined with the 3D-engineered PCL conduit promotes peripheral nerve regeneration and functional recovery. Thus, a new strategy to facilitate the repair of challenging peripheral nerve injuries is proposed.

Incidence of Nerve Injury After Extremity Trauma in the United States

BACKGROUND

Traumatic peripheral nerve injuries cause chronic pain, disability, and long-term reductions in quality of life. However, their incidence after extremity trauma remains poorly understood.

METHODS

The IBM® MarketScan® Commercial Database from 2010 to 2015 was used to identify patients aged 18 to 64 who presented to emergency departments for upper and/or lower extremity traumas. Cumulative incidences were calculated for nerve injuries diagnosed within 2 years of trauma. Cox regression models were developed to evaluate the associations between upper extremity nerve injury and chronic pain, disability, and use of physical therapy or occupational therapy.

RESULTS

The final cohort consisted of 1 230 362 patients with employer-sponsored health plans. Nerve injuries were diagnosed in 2.6% of upper extremity trauma patients and 1.2% of lower extremity trauma patients. Only 9% and 38% of nerve injuries were diagnosed by the time of emergency department and hospital discharge, respectively. Patients with nerve injuries were more likely to be diagnosed with chronic pain (hazard ratio [HR]: 5.9, 95% confidence interval [CI], 4.3-8.2), use physical therapy services (HR: 10.7, 95% CI, 8.8-13.1), and use occupational therapy services (HR: 19.2, 95% CI, 15.4-24.0) more than 90 days after injury.

CONCLUSIONS

The incidence of nerve injury in this national cohort was higher than previously reported. A minority of injuries were diagnosed by emergency department or hospital discharge. These findings may improve practitioner awareness and inform public health interventions for injury prevention.

Chitosan Tubes Inoculated with Dental Pulp Stem Cells and Stem Cell Factor Enhance Facial Nerve-Vascularized Regeneration in Rabbits

Facial nerve injury is a common clinical condition that leads to disfigurement and emotional distress in the affected individuals, and the recovery presents clinical challenges. Tissue engineering is the standard method to repair nerve defects. However, nerve regeneration is still not satisfactory because of poor neovascularization after implantation, especially for the long-segment nerve defects. In the current study, we aimed to investigate the potential of chitosan tubes inoculated with stem cell factor (SCF) and dental pulp stem cells (DPSCs) in facial nerve-vascularized regeneration. In the in vitro experiment, DPSCs were isolated, cultured, and then identified. The optimal concentration of SCF was screened by CCK8. Cytoskeleton and living-cell staining, migration, CCK8 test, and neural differentiation assays were performed, revealing that SCF promoted the biological activity of DPSCs. Surprisingly, SCF increased the neural differentiation of DPSCs. The migration and angiogenesis experiments were carried out to show that SCF promoted the angiogenesis and migration of human umbilical vein endothelial cells (HUVECs). In the facial nerve, 7 mm defects of New Zealand white rabbits, hematoxylin-eosin (HE), immunohistochemistry, toluidine blue staining, and transmission electron microscopy observation were performed at 12 weeks postsurgery to show more nerve fibers and better myelin sheath in the SCF + DPSC group. In addition, the whisker movements, Masson's staining, and western blot assays were performed, demonstrating functional repair and that the expression level of CD31 protein in the group SCF + DPSCs was relatively close to that in the group Autograft. In summary, chitosan tubes inoculated with SCF and DPSCs increased neurovascularization and provided an effective method for repairing facial nerve defects, indicating great promise for clinical application.

Electrospinning porcine decellularized nerve matrix scaffold for peripheral nerve regeneration

The composition and spatial structure of bioscaffold materials are essential for constructing tissue regeneration microenvironments. In this study, by using an electrospinning technique without any other additives, we successfully developed pure porcine decellularized nerve matrix (xDNME) conduits. The developed xDNME was composed of an obvious decellularized matrix fiber structure and effectively retained the natural components in the decellularized matrix of the nerve tissue. The xDNME conduit exhibited superior biocompatibility and the ability to overcome inter-species barriers. In vivo, after 12 weeks of implantation, xDNME significantly promoted the regeneration of rat sciatic nerve. The regenerated nerve fibers completely connected the two ends of the nerve defect, which were about 8 mm apart. The xDNME and xDNME-OPC groups showed myelin structures in the regenerated nerve fibers. In the xDNME group, the average thickness of the regenerated myelin sheath was 0.640 ± 0.013 μm, which was almost comparable to that in the autologous nerve group (0.646 ± 0.017 μm). Electrophysiological experiments revealed that both of the regenerated nerve fibers in the xDNME and xDNME-OPC groups had excellent abilities to transmit electrical signals. Respectively, the average conduction velocities of xDNME and xDNME-OPC were 8.86 ± 3.57 m/s and 6.99 ± 3.43 m/s. In conclusion, the xDNME conduits have a great potential for clinical treatment of peripheral nerve injuries, which may clinically transform peripheral nerve related regenerative medicine.

Application and Prospects of Hydrogel Additive Manufacturing

Hydrogel has become a commonly used material for 3D and 4D printing due to its favorable biocompatibility and low cost. Additive manufacturing, also known as 3D printing, was originally referred to as rapid prototyping manufacturing. Variable-feature rapid prototyping technology, also known as 4D printing, is a combination of materials, mathematics, and additives. This study constitutes a literature review to address hydrogel-based additive manufacturing technologies, introducing the characteristics of commonly used 3D printing hydrogel methods, such as direct ink writing, fused deposition modeling, and stereolithography. With this review, we also investigated the stimulus types, as well as the advantages and disadvantages of various stimulus-responsive hydrogels in smart hydrogels; non-responsive hydrogels; and various applications of additive manufacturing hydrogels, such as neural catheter preparation and drug delivery. The opportunities, challenges, and future prospects of hydrogel additive manufacturing technologies are discussed.

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.

Failed Targeted Muscle Reinnervation: Findings at Revision Surgery and Concepts for Success

Although it was initially described for improved myoelectric control, targeted muscle reinnervation (TMR) has quickly gained popularity as a technique for neuroma control. With this rapid increase in utilization has come broadening indications and variability in the described technique. As a result, it becomes difficult to interpret published outcomes. Furthermore, there is no literature discussing the management of failed cases which are undoubtedly occurring.

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

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

Surgical Treatment of Foot Drop: Patient Evaluation and Peripheral Nerve Treatment Options

Foot drop is a common clinical condition which may substantially impact physical function and health-related quality of life. The etiologies of foot drop are diverse and a detailed history and physical examination are essential in understanding the underlying pathophysiology and capacity for spontaneous recovery. Patients presenting with acute foot drop or those without significant spontaneous recovery of motor deficits may be candidates for surgical intervention. The timing, mechanism, and severity of neural injury resulting in foot drop influence the selection of the most appropriate peripheral nerve surgery, which may include direct nerve repair, neurolysis, nerve grafting, or nerve transfer.

Minimally Invasive Surgical Approach for Open Common Peroneal Nerve Neurolysis in the Setting of Previous Posterior Schwannoma Removal

The common peroneal nerve (CPN) runs laterally around the fibular neck and enters the peroneal tunnel, where it divides into the deep, superficial, and recurrent peroneal nerves. CPN entrapment is the most common neuropathy of the lower extremity and is vulnerable at the fibular neck because of its superficial location. Schwannomas are benign, encapsulated tumors of the nerve sheath that can occur sporadically or in cases of neurocutaneous conditions, such neurofibromatosis type 2. In cases with compressive neuropathy resulting in significant or progressive motor loss, decompression and neurolysis should be attempted. We present a technical note for the treatment of CPN compressive neuropathy in the setting of a previous ipsilateral schwannoma removal with a minimally invasive surgical approach and neurolysis of the CPN at the fibular neck.

Revision of Carpal Tunnel Surgery

Carpal tunnel release is one of the most commonly performed upper extremity procedures. The majority of patients experience significant improvement or resolution of their symptoms. However, a small but important subset of patients will experience the failure of their initial surgery. These patients can be grouped into persistent, recurrent, and new symptom categories. The approach to these patients starts with a thorough clinical examination and is supplemented with electrodiagnostic studies. The step-wise surgical management of revision carpal tunnel surgery consists of the proximal exploration of the median nerve, Guyon’s release with neurolysis, the rerelease of the transverse retinaculum, evaluation of the nerve injury, treatment of secondary sites of compression, and potential ancillary procedures. The approach and management of failed carpal tunnel release are reviewed in this article.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Towards the translation of electroconductive organic materials for regeneration of neural tissues

Carbon-based conductive and electroactive materials (e.g., derivatives of graphene, fullerenes, polypyrrole, polythiophene, polyaniline) have been studied since the 1970s for use in a broad range of applications. These materials have electrical properties comparable to those of commonly used metals, while providing other benefits such as flexibility in processing and modification with biologics (e.g., cells, biomolecules), to yield electroactive materials with biomimetic mechanical and chemical properties. In this review, we focus on the uses of these electroconductive materials in the context of the central and peripheral nervous system, specifically recent studies in the peripheral nerve, spinal cord, brain, eye, and ear. We also highlight in vivo studies and clinical trials, as well as a snapshot of emerging classes of electroconductive materials (e.g., biodegradable materials). We believe such specialized electrically conductive biomaterials will clinically impact the field of tissue regeneration in the foreseeable future. STATEMENT OF SIGNIFICANCE: This review addresses the use of conductive and electroactive materials for neural tissue regeneration, which is of significant interest to a broad readership, and of particular relevance to the growing community of scientists, engineers and clinicians in academia and industry who develop novel medical devices for tissue engineering and regenerative medicine. The review covers the materials that may be employed (primarily focusing on derivatives of fullerenes, graphene and conjugated polymers) and techniques used to analyze materials composed thereof, followed by sections on the application of these materials to nervous tissues (i.e., peripheral nerve, spinal cord, brain, optical, and auditory tissues) throughout the body.

Waste-derived biomaterials as building blocks in the biomedical field

Recent developments in the biomedical arena have led to the fabrication of innovative biomaterials by utilizing bioactive molecules obtained from biological wastes released from fruit and beverage processing industries, and fish, meat, and poultry industries. These biological wastes that end up in water bodies as well as in landfills are an affluent source of animal- and plant-derived proteins, bio ceramics and polysaccharides such as collagens, gelatins, chitins, chitosans, eggshell membrane proteins, hydroxyapatites, celluloses, and pectins. These bioactive molecules have been intricately designed into scaffolds and dressing materials by utilizing advanced technologies for drug delivery, tissue engineering, and wound healing relevance. These biomaterials are environment-friendly, biodegradable, and biocompatible, and show excellent tissue regeneration attributes. Additionally, being cost-effective they can reduce the burden on the healthcare system as well as provide a sustainable solution to waste management. In this review, the current trends in the utilization of plant and animal waste-derived biomaterials in various biomedical fields are considered along with a separate section on their applications as xenografts.

How Fiber Surface Topography Affects Interactions between Cells and Electrospun Scaffolds: A Systematic Review

Electrospun scaffolds have a 3D fibrous structure that attempts to imitate the extracellular matrix in order to be able to host cells. It has been reported in the literature that controlling fiber surface topography produces varying results regarding cell–scaffold interactions. This review analyzes the relevant literature concerning in vitro studies to provide a better understanding of the effect that controlling fiber surface topography has on cell–scaffold interactions. A systematic approach following PRISMA, GRADE, PICO, and other standard methodological frameworks for systematic reviews was used. Different topographic interventions and their effects on cell–scaffold interactions were analyzed. Results indicate that nanopores and roughness on fiber surfaces seem to improve proliferation and adhesion of cells. The quality of the evidence is different for each studied cell–scaffold interaction, and for each studied morphological attribute. The evidence points to improvements in cell–scaffold interactions on most morphologically complex fiber surfaces. The discussion includes an in-depth evaluation of the indirectness of the evidence, as well as the potentially involved publication bias. Insights and suggestions about dose-dependency relationship, as well as the effect on particular cell and polymer types, are presented. It is concluded that topographical alterations to the fiber surface should be further studied, since results so far are promising.

A multifunctional ATP-generating system by reduced graphene oxide-based scaffold repairs neuronal injury by improving mitochondrial function and restoring bioelectricity conduction

Peripheral nerve injury usually impairs neurological functions. The excessive oxidative stress and disrupted bioelectrical conduction gives rise to a hostile microenvironment and impedes nerve regeneration. Therefore, it is of urgent need to develop tissue engineering products which help alleviate the oxidative insults and restore bioelectrical signals. Melatonin (MLT) is an important endogenous hormone that diminishes the accumulation of reactive oxygen species. Reduced graphene oxide (RGO) possesses the excellent electrical conductivity and biocompatibility. In this study, a multilayered MLT/RGO/Polycaprolactone (PCL) composite scaffold was fabricated with beaded nanostructures to improve cell attachment and proliferation. It also exhibited stable mechanical properties by high elastic modulus and guaranteed structural integrity for nerve regeneration. The live/dead cell staining and cell counting kit assay were performed to evaluate the toxicity of the scaffold. JC-1 staining was carried out to assess the mitochondrial potential. The composite scaffold provided a biocompatible interface for cell viability and improved ATP production for energy supply. The scaffold improved the sensory and locomotor function recovery by walking track analysis and electrophysiological evaluation, reduced Schwann cell apoptosis and increased its proliferation. It further stimulated myelination and axonal outgrowth by enhancing S100β, myelin basic protein, β3-tubulin, and GAP43 levels. The findings demonstrated functional and morphological recovery by this biomimetic scaffold and indicated its potential for translational application.

A Technique to Reconstruct a Nerve Injured at Its Bifurcation Site Using Autograft and End-to-Side Neurorrhaphy

Peripheral nerves injuries are relatively frequent after high-energy trauma in both upper and lower limb. This case report describes the reconstruction of a 5-cm nerve defect involving the superficial peroneal nerve (SPN) where it divides into its two terminal branches. A 5-cm nerve graft was harvested from the proximal part of the medial dorsal cutaneous nerve (MDN) and interposed to fill the gap between the distal stump of the SPN and the intermediate dorsal cutaneous nerve (IDN). The stump of the MDN was then sutured with an end-to-side (ETS) technique to the IDN, distally to the nerve graft, by opening a window in the epineurium of IDN. The sensory restoration of the dorsal area of the foot after 8 months was evaluated satisfactory from the authors. Tenderness and Tinel’s sign at the lesion site were not present. The patient’s satisfaction was excellent. The results of this case may suggest that a nerve defect involving a bifurcation point can be treated with satisfactory results using one distal stump as donor nerve for a nerve autograft to bridge the nerve gap followed by an ETS neurorrhaphy of donor one on the other stump. In this way, it is possible to reconstruct a bifurcation point by creating a new division point with the same Y-shape in a more distal position, without adding morbidity due to the harvesting of a nerve graft from another area of the body.

Micropatterned Poly(D,L-Lactide-Co-Caprolactone) Conduits With KHI-Peptide and NGF Promote Peripheral Nerve Repair After Severe Traction Injury

Severe traction injuries after stretch to peripheral nerves are common and challenging to repair. The nerve guidance conduits (NGCs) are promising in the regeneration and functional recovery after nerve injuries. To enhance the repair of severe nerve traction injuries, in this study KHIFSDDSSE (KHI) peptides were grafted on a porous and micropatterned poly(D,L-lactide-co-caprolactone) (PLCL) film (MPLCL), which was further loaded with a nerve growth factor (NGF). The adhesion number of Schwann cells (SCs), ratio of length/width (L/W), and percentage of elongated SCs were significantly higher in the MPLCL-peptide group and MPLCL-peptide-NGF group compared with those in the PLCL group in vitro. The electromyography (EMG) and morphological changes of the nerve after severe traction injury were improved significantly in the MPLCL-peptide group and MPLCL-peptide-NGF group compared with those in the PLCL group in vivo. Hence, the NGCs featured with both bioactive factors (KHI peptides and NGF) and physical topography (parallelly linear micropatterns) have synergistic effect on nerve reinnervation after severe traction injuries.

Two-Dimensional Nanomaterials for Peripheral Nerve Engineering: Recent Advances and Potential Mechanisms

Peripheral nerve tissues possess the ability to regenerate within artificial nerve scaffolds, however, despite the advance of biomaterials that support nerve regeneration, the functional nerve recovery remains unsatisfactory. Importantly, the incorporation of two-dimensional nanomaterials has shown to significantly improve the therapeutic effect of conventional nerve scaffolds. In this review, we examine whether two-dimensional nanomaterials facilitate angiogenesis and thereby promote peripheral nerve regeneration. First, we summarize the major events occurring after peripheral nerve injury. Second, we discuss that the application of two-dimensional nanomaterials for peripheral nerve regeneration strategies by facilitating the formation of new vessels. Then, we analyze the mechanism that the newly-formed capillaries directionally and metabolically support neuronal regeneration. Finally, we prospect that the two-dimensional nanomaterials should be a potential solution to long range peripheral nerve defect. To further enhance the therapeutic effects of two-dimensional nanomaterial, strategies which help remedy the energy deficiency after peripheral nerve injury could be a viable solution.

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.

Outcomes of Tibial Nerve Repair and Transfer: A Structured Evidence-Based Systematic Review and Meta-Analysis

Although nerve transfer and repair are well-established for treatment of nerve injury in the upper extremity, there are no established parameters for when or which treatment modalities to utilize for tibial nerve injuries. The objective of our study is to conduct a systematic review of the effectiveness of end-to-end repair, neurolysis, nerve grafting, and nerve transfer in improving motor function after tibial nerve injury. PubMed, Cochrane, Medline, and Embase libraries were queried according to the PRISMA guidelines for articles that present functional outcomes after tibial nerve injury in humans treated with nerve transfer or repair. The final selection included Nineteen studies with 677 patients treated with neurolysis (373), grafting (178), end-to-end repair (90), and nerve transfer (30), from 1985 to 2018. The mean age of all patients was 27.0 ± 10.8 years, with a mean preoperative interval of 7.4 ± 10.5 months, and follow-up period of 82.9 ± 25.4 months. The mean graft repair length for nerve transfer and grafting patients was 10.0 ± 5.8 cm, and the most common donor nerve was the sural nerve. The most common mechanism of injury was gunshot wound, and the mean MRC of all patients was 3.7 ± 0.6. Good outcomes were defined as MRC ≥ 3. End-to-end repair treatment had the greatest number of good outcomes, followed by neurolysis. Patients with preoperative intervals less than 7 months were more likely to have good outcomes than those greater than 7 months. Patients with sport injuries had the highest percentage of good outcomes in contrast to patients with transections and who were in MVAs. We found no statistically significant difference in good outcomes between the use of sural and peroneal donor nerve grafts, nor between age, graft length, and MRC score.

Mesenchymal stem cells and local tacrolimus delivery synergistically enhance neurite extension

BACKGROUND

The aim of this study was to investigate the combined effect of mesenchymal stem cells (MSC) and local delivery of tacrolimus (FK506) on nerve regeneration when applied to nerve autografts and decellularized allografts.

METHODS

A three-dimensional in vitro compartmented cell culture system consisting of a neonatal dorsal root ganglion adjacent to a nerve graft was used to evaluate the regenerating neurites into the peripheral nerve scaffold. Nerve autografts and allografts were treated with (i) undifferentiated MSCs, (ii) FK506 (100 ng/mL) or (iii) both (N = 9/group). After 48 hours, neurite extension was measured to quantify nerve regeneration and stem cell viability was evaluated.

RESULTS

Stem cell viability was confirmed in all MSC-treated grafts. Neurite extension was superior in autografts treated with FK506, and MSCs and FK506 combined (p < 0.001 and p = 0.0001, respectively), and autografts treated with MSCs (p = 0.12) were comparable to untreated autografts. In allografts, FK506 treatment and combined treatment were superior to controls (p < 0.001 and p = 0.0001, respectively), and treatment with MSCs (p = 0.09) was comparable to controls. All autograft groups were superior compared to their respective allograft treatment group (p < 0.05) in neurite extension.

CONCLUSIONS

Alone, either MSC or FK506 treatment improved neurite outgrowth, and combined they further enhanced neurite extension in both autografts and allografts.

Preparation and characterization of conductive nerve guide conduit filled with dual drug-loaded nanofibers

Peripheral nerve injury (PNI) has become one of the common clinical diseases. How to promote the regeneration and function recovery of the damaged peripheral nerve has been the focus of attention in the medical field. Evidence suggests that the longitudinal filling of oriented fibers in nerve guide conduit (NGC) is especially beneficial to the repair of long gap PNI. In this study, polypyrrole (PPy) nanospheres (PNSs) were prepared by the soft-templating method, and mixed with poly (lactic acid) (PLA) to prepare conductive PNSs/PLA NGC, and the optimal ratio of PNSs was 4.5%. PLA and vascular endothelial growth factor (VEGF) as shell, chitosan (CS) and paeoniflorin (PF) as core, oriented coaxial nanofibers were obtained and then filled into PNSs/PLA NGC. The composite NGC has excellent mechanical properties, electrical conductivity, hydrophilic properties, and degradation properties. Besides, the successive release of VEGF and PF can play a synergistic role in promoting nerve regeneration. In vitro experiments showed that the composite NGC was nontoxic and suitable for the adhesion and proliferation of nerve cells. In addition, PNSs combined with electrical stimulation (ES) can significantly promote the differentiation and proliferation of nerve cells, which is conducive to nerve regeneration. These positive results indicate that the composite NGC is a promising candidate in the repair of long gap PNI.

Carbon-nanotube yarns induce axonal regeneration in peripheral nerve defect

Carbon nanotubes (CNTs) are cylindrical nanostructures and have unique properties, including flexibility, electrical conductivity, and biocompatibility. We focused on CNTs fabricated with the carbon nanotube yarns (cYarn) as a possible substrate promoting peripheral nerve regeneration with these properties. We bridged a 15 mm rat sciatic nerve defect with five different densities of cYarn. Eight weeks after the surgery, the regenerated axons crossing the CNTs, electromyographical findings, and muscle weight ratio of the lower leg showed recovery of the nerve function by interfacing with cYarn. Furthermore, the sciatic nerve functional index (SFI) at 16 weeks showed improvement in gait function. A 2% CNT density tended to be the most effective for nerve regeneration as measured by both histological axonal regeneration and motor function. We confirmed that CNT yarn promotes peripheral nerve regeneration by using it as a scaffold for repairing nerve defects. Our results support the future clinical application of CNTs for bridging nerve defects as an off-the-shelf material.

Chitin scaffold combined with autologous small nerve repairs sciatic nerve defects

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

Reverse engineering of an anatomically equivalent nerve conduit

Reconstruction of peripheral nervous tissue remains challenging in critical-sized defects due to the lack of Büngner bands from the proximal to the distal nerve ends. Conventional nerve guides fail to bridge the large-sized defect owing to the formation of a thin fibrin cable. Hence, in the present study, an attempt was made to reverse engineer the intricate epi-, peri- and endo-neurial tissues using Fused Deposition Modeling based 3D printing. Bovine serum albumin protein nanoflowers (NF) exhibiting Viburnum opulus 'Roseum' morphology were ingrained into 3D printed constructs without affecting its secondary structure to enhance the axonal guidance from proximal to distal ends of denuded nerve ends. Scanning electron micrographs confirmed the uniform distribution of protein NF in 3D printed constructs. The PC-12 cells cultured on protein ingrained 3D printed scaffolds demonstrated cytocompatibility, improved cell adhesion and extended neuronal projections with significantly higher intensities of NF-200 and tubulin expressions. Further suture-free fixation designed in the current 3D printed construct aids facile implantation of printed conduits to the transected nerve ends. Hence the protein ingrained 3D printed construct would be a promising substitute to treat longer peripheral nerve defects as its structural equivalence of endo- and perineurial organization along with the ingrained protein NF promote the neuronal extension towards the distal ends by minimizing axonal dispersion.

Elastin-like Proteins to Support Peripheral Nerve Regeneration in Guidance Conduits

Synthetic nerve guidance conduits (NGCs) offer an alternative to harvested nerve grafts for treating peripheral nerve injury (PNI). NGCs have been made from both naturally derived and synthesized materials. While naturally derived materials typically have an increased capacity for bioactivity, synthesized materials have better material control, including tunability and reproducibility. Protein engineering is an alternative strategy that can bridge the benefits of these two classes of materials by designing cell-responsive materials that are also systematically tunable and consistent. Here, we tested a recombinantly derived elastin-like protein (ELP) hydrogel as an intraluminal filler in a rat sciatic nerve injury model. We demonstrated that ELPs enhance the probability of forming a tissue bridge between the proximal and distal nerve stumps compared to an empty silicone conduit across the length of a 10 mm nerve gap. These tissue bridges have evidence of myelinated axons, and electrophysiology demonstrated that regenerated axons innervated distal muscle groups. Animals implanted with an ELP-filled conduit had statistically higher functional control at 6 weeks than those that had received an empty silicone conduit, as evaluated by the sciatic functional index. Taken together, our data support the conclusion that ELPs support peripheral nerve regeneration in acute complete transection injuries when used as an intraluminal filler. These results support the further study of protein engineered recombinant ELP hydrogels as a reproducible, off-the-shelf alternative for regeneration of peripheral nerves.

Functional and immunological peculiarities of peripheral nerve allografts

This review addresses the accumulating evidence that live (not decellularized) allogeneic peripheral nerves are functionally and immunologically peculiar in comparison with many other transplanted allogeneic tissues. This is relevant because live peripheral nerve allografts are very effective at promoting recovery after segmental peripheral nerve injury via axonal regeneration and axon fusion. Understanding the immunological peculiarities of peripheral nerve allografts may also be of interest to the field of transplantation in general. Three topics are addressed: The first discusses peripheral nerve injury and the potential utility of peripheral nerve allografts for bridging segmental peripheral nerve defects via axon fusion and axon regeneration. The second reviews evidence that peripheral nerve allografts elicit a more gradual and less severe host immune response allowing for prolonged survival and function of allogeneic peripheral nerve cells and structures. Lastly, potential mechanisms that may account for the immunological differences of peripheral nerve allografts are discussed.

Clinical Outcomes After Neurolysis for the Treatment of Peroneal Nerve Palsy: A Systematic Review and Meta-Analysis

BACKGROUND

Neurolysis techniques have been adapted for decompression of peripheral nerves in multiple locations, including the common peroneal nerve (CPN) at the fibular neck. The aim of this study was to conduct a systematic review and meta-analysis to summarize the clinical outcomes of neurolysis for the management of peroneal nerve palsy (PNP).

METHODS

Preferred Reporting Systems for Systematic Reviews and Meta-Analyses guidelines were followed for this meta-analysis. Four databases were queried, and randomized clinical trials, cohort studies, case-control studies, and case series with n > 10 published in English that evaluated clinical outcomes of neurolysis for the treatment of PNP and foot drop were included. Two reviewers completed screening and data extraction. Methodological quality was evaluated using the Newcastle-Ottawa Scale.

RESULTS

A total of 493 articles were identified through literature search. Title and abstract screening identified 39 studies for full-text screening. Ten articles met the inclusion criteria for qualitative analysis, and 8 had complete data for meta-analysis.Overall, there were 368 patients (370 nerves) who had neurolysis of the CPN for PNP, of which 59.2% (n = 218) were men and 40.8% (n = 150) were women. The mean age of the patients was 47.1 years (SD, 10.0 years), mean time to surgery was 9.65 months (SD, 6.3 months), and mean follow-up time was 28 months (SD, 14.0 months). The median preoperative Medical Research Council (MRC) score was 1 (IQR 0, 3), with 42.2% (n = 156) having MRC score of 0. The median postoperative MRC score was 5 (IQR 4, 5), with 53.9% (n = 199) having MRC score of 5. Complications of neurolysis of the peroneal nerve for treatment of PNP included postoperative infection (0.54%, n = 2), wound dehiscence (0.27%, n = 1), hematoma (0.54%, n = 2), bleeding (0.27%, n = 1), relapse of PNP (0.27%, n = 1), and 1 case of mortality due to sepsis.

CONCLUSIONS

Our meta-analysis shows that neurolysis of the CPN is safe and improves ankle dorsiflexion strength in patients with PNP. Future studies should use a standardized method of measuring sensory outcomes, and studies of higher levels of evidence are needed to better assess the clinical outcomes of neurolysis for treatment of PNP.

PDLLA/β-TCP/HA/CHS/NGF Sustained-release Conduits for Peripheral Nerve Regeneration

Using nerve guide conduits (NGCs) to promote the regeneration of PNI is a feasible alternative to autograft. Compared with NGCs made of single material, composite NGCs have a greater development prospect. Our previous research has confirmed that poly(D, L-lactic acid)/β-tricalcium phosphate/hyaluronic acid/chitosan/nerve growth factor (PDLLA/β-TCP/HA/CHS/NGF) NGCs have excellent physical and chemical properties, which can slowly release NGF and support cell adhesion and proliferation. In this study, PDLLA/β-TCP/HA/CHS/NGF NGCs were prepared and used to bridge a 10 mm sciatic nerve defect in 200-250 g Sprague-Dawley (SD) rat to verify the performance of the NGCs in vivo. Substantial improvements in nerve regeneration were observed after using the PDLLA/β-TCP/HA/CHS/NGF NGCs based on gross post-operation observation, triceps wet weight analysis and nerve histological assessment. In vivo studies illustrate that the PDLLA/β-TCP/HA/CHS/NGF sustained-release NGCs can effectively promote peripheral nerve regeneration, and the effect is similar to that of autograft.

End-to-side neurorrhaphy in peripheral nerves: Does it work?

Acute peripheral nerve injuries are common and can cause physical disabilities with sensory and functional sequelae; they therefore require surgery. The aim of this study was to conduct a systematic review to assess the clinical applicability of end-to-side neurorrhaphy in peripheral nerve reconstruction, based on available evidence. We carried out a systematic review of the literature using MEDLINE/PubMed, EMBASE, Cochrane Library, Web of Science, Scielo and Scopus through March 16, 2021. Most of the selected studies were qualitative and employed nonrandomized groups of patients, without standardized scales for assessing outcomes, which made statistical analysis difficult. Efficacy varied from 24% to 81%. Factors for better outcome included the type of injury, type of injured nerve (sensory, motor or mixed), presence of an epineural window, topography, injury extension <1.3 cm, and intervention within 2 weeks of injury. Clinical studies so far lack scientific evidence on end-to-side neurorrhaphy in peripheral nerve lesions.

Therapeutic Potential of Complementary and Alternative Medicines in Peripheral Nerve Regeneration: A Systematic Review

Despite the progressive advances, current standards of treatments for peripheral nerve injury do not guarantee complete recovery. Thus, alternative therapeutic interventions should be considered. Complementary and alternative medicines (CAMs) are widely explored for their therapeutic value, but their potential use in peripheral nerve regeneration is underappreciated. The present systematic review, designed according to guidelines of Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols, aims to present and discuss the current literature on the neuroregenerative potential of CAMs, focusing on plants or herbs, mushrooms, decoctions, and their respective natural products. The available literature on CAMs associated with peripheral nerve regeneration published up to 2020 were retrieved from PubMed, Scopus, and Web of Science. According to current literature, the neuroregenerative potential of Achyranthes&nbsp;bidentata, Astragalus&nbsp;membranaceus, Curcuma&nbsp;longa, Panax&nbsp;ginseng, and Hericium&nbsp;erinaceus are the most widely studied. Various CAMs enhanced proliferation and migration of Schwann cells in vitro, primarily through activation of MAPK pathway and FGF-2 signaling, respectively. Animal studies demonstrated the ability of CAMs to promote peripheral nerve regeneration and functional recovery, which are partially associated with modulations of neurotrophic factors, pro-inflammatory cytokines, and anti-apoptotic signaling. This systematic review provides evidence for the potential use of CAMs in the management of peripheral nerve injury.

Hybrid material mimics a hypoxic environment to promote regeneration of peripheral nerves

Between nerve defects, a bridge formed by multiple cells is the fundamental structure for guiding axons across this damaged region. Here, we developed a functional material that mimics hypoxia during the early stages of nerve regeneration by deferoxamine. We used this material and single-cell sequencing to analyze the "bridge" structure between peripheral nerve defects. We found that hypoxia in damaged tissues might play a key role in stimulating macrophages, promoting endothelial-to-mesenchymal transition, and driving the migration of endothelial cells to the injured region to form regenerative bridge tissue and guide the subsequent regeneration of Schwann cells and axons. The results showed that the final nerve defect repair outcomes were similar with autografts after intervention by this material. This study challenges the view that hypoxia is exclusively involved in peripheral nerve regeneration and provides a potentially valuable candidate material for clinical use.

Biomimetic nerve guidance conduit containing engineered exosomes of adipose-derived stem cells promotes peripheral nerve regeneration

BACKGROUND

Efficient and stable delivery of neurotrophic factors (NTFs) is crucial to provide suitable microenvironment for peripheral nerve regeneration. Neurotrophin-3 (NT-3) is an important NTF during peripheral nerve regeneration which is scarce in the first few weeks of nerve defect. Exosomes are nanovesicles and have been served as promising candidate for biocarrier. In this work, NT-3 mRNA was encapsulated in adipose-derived stem cell (ADSC)-derived exosomes (Exo^NT-3). These engineered exosomes were applied as NT-3 mRNA carrier and then were loaded in nerve guidance conduit (Exo^NT-3-NGC) to bridge rat sciatic nerve defect.

METHOD

NT-3 mRNA was encapsulated in exosomes by forcedly expression of NT-3 mRNA in the donor ADSCs. Exo^NT-3 were co-cultured with SCs in vitro; after 24 h of culture, the efficiency of NT-3 mRNA delivery was evaluated by qPCR, western blotting and ELISA. Then, Exo^NT-3 were loaded in alginate hydrogel to construct the nerve guidance conduits (Exo^NT-3-NGC). Exo^NT-3-NGC were implanted in vivo to reconstruct 10 mm rat sciatic nerve defect. The expression of NT-3 was measured 2 weeks after the implantation operation. The sciatic nerve functional index (SFI) was examined at 2 and 8 weeks after the operation. Moreover, the therapeutic effect of Exo^NT-3-NGC was also evaluated by morphology assay, immunofluorescence staining of regenerated nerves, function evaluation of gastrocnemius muscles after 8 weeks of implantation.

RESULTS

The engineered exosomes could deliver NT-3 mRNA to the recipient cells efficiently and translated into functional protein. The constructed NGC could realize stable release of exosomes at least for 2 weeks. After NGC implantation in vivo, Exo^NT-3-NGC group significantly promote nerve regeneration and improve the function recovery of gastrocnemius muscles compared with control exosomes (Exo^empty-NGC) group.

CONCLUSION

In this work, NGC was constructed to allow exosome-mediated NT-3 mRNA delivery. After Exo^NT-3-NGC implantation in vivo, the level of NT-3 could restore which enhance the nerve regeneration. Our study provide a potential approach to improve nerve regeneration.

Adhesive Tissue Engineered Scaffolds: Mechanisms and Applications

A variety of suture and bioglue techniques are conventionally used to secure engineered scaffold systems onto the target tissues. These techniques, however, confront several obstacles including secondary damages, cytotoxicity, insufficient adhesion strength, improper degradation rate, and possible allergic reactions. Adhesive tissue engineering scaffolds (ATESs) can circumvent these limitations by introducing their intrinsic tissue adhesion ability. This article highlights the significance of ATESs, reviews their key characteristics and requirements, and explores various mechanisms of action to secure the scaffold onto the tissue. We discuss the current applications of advanced ATES products in various fields of tissue engineering, together with some of the key challenges for each specific field. Strategies for qualitative and quantitative assessment of adhesive properties of scaffolds are presented. Furthermore, we highlight the future prospective in the development of advanced ATES systems for regenerative medicine therapies.

Electroactive nanomaterials in the peripheral nerve regeneration

Severe peripheral nerve injuries are threatening the life quality of human beings. Current clinical treatments contain some limitations and therefore extensive research and efforts are geared towards tissue engineering approaches and development. The biophysical and biochemical characteristics of nanomaterials are highly focused on as critical elements in the design and fabrication of regenerative scaffolds. Recent studies indicate that the electrical properties and nanostructure of biomaterials can significantly affect the progress of nerve repair. More importantly, these studies also demonstrate the fact that electroactive nanomaterials have substantial implications for regulating the viability and fate of primary supporting cells in nerve regeneration. In this review, we summarize the current knowledge of electroconductive and piezoelectric nanomaterials. We exemplify typical cellular responses through cell-material interfaces, and the nanomaterial-induced microenvironment rebalance in terms of several key factors, immune responses, angiogenesis and oxidative stress. This work highlights the mechanism and application of electroactive nanomaterials to the development of regenerative scaffolds for peripheral nerve tissue engineering.

Human motor endplate remodeling after traumatic nerve injury

OBJECTIVE

Current management of traumatic peripheral nerve injuries is variable with operative decisions based on assumptions that irreversible degeneration of the human motor endplate (MEP) follows prolonged denervation and precludes reinnervation. However, the mechanism and time course of MEP changes after human peripheral nerve injury have not been investigated. Consequently, there are no objective measures by which to determine the probability of spontaneous recovery and the optimal timing of surgical intervention. To improve guidance for such decisions, the aim of this study was to characterize morphological changes at the human MEP following traumatic nerve injury.

METHODS

A prospective cohort (here analyzed retrospectively) of 18 patients with traumatic brachial plexus and axillary nerve injuries underwent biopsy of denervated muscles from the upper extremity from 3 days to 6 years after injury. Muscle specimens were processed for H & E staining and immunohistochemistry, with visualization via confocal and two-photon excitation microscopy.

RESULTS

Immunohistochemical analysis demonstrated varying degrees of fragmentation and acetylcholine receptor dispersion in denervated muscles. Comparison of denervated muscles at different times postinjury revealed progressively increasing degeneration. Linear regression analysis of 3D reconstructions revealed significant linear decreases in MEP volume (R = -0.92, R2 = 0.85, p = 0.001) and surface area (R = -0.75, R2 = 0.56, p = 0.032) as deltoid muscle denervation time increased. Surprisingly, innervated and structurally intact MEPs persisted in denervated muscle specimens from multiple patients 6 or more months after nerve injury, including 2 patients who had presented > 3 years after nerve injury.

CONCLUSIONS

This study details novel and critically important data about the morphology and temporal sequence of events involved in human MEP degradation after traumatic nerve injuries. Surprisingly, human MEPs not only persisted, but also retained their structures beyond the assumed 6-month window for therapeutic surgical intervention based on previous clinical studies. Preoperative muscle biopsy in patients being considered for nerve transfer may be a useful prognostic tool to determine MEP viability in denervated muscle, with surviving MEPs also being targets for adjuvant therapy.