Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies

Filamented hydrogels as tunable conduits for guiding neurite outgrowth

Anisotropic scaffolds with unidirectionally aligned fibers present an optimal solution for nerve tissue engineering and graft repair. This study investigates the application of filamented light (FLight) biofabrication to create hydrogel matrices featuring highly aligned microfilaments, facilitating neurite guidance and outgrowth from encapsulated chicken dorsal root ganglion (DRG) cells. FLight employs optical modulation instability (OMI) to rapidly and safely (<5 s) fabricate hydrogel constructs with precise microfilament alignment. The tunability of FLight matrices was demonstrated by adjusting four key parameters: stiffness, porosity, growth factor release, and incorporation of biological cues. Matrix stiffness was fine-tuned by varying the projection light dose, yielding matrices with stiffness ranging from 0.6 to 5.7 kPa. Optimal neurite outgrowth occurred at a stiffness of 0.6 kPa, achieving an outgrowth of 2.5 mm over 4 days. Matrix porosity was modified using diffraction gratings in the optical setup. While significant differences in neurite outgrowth and alignment were observed between bulk and FLight gels, further increases in porosity from 40 % to 70 % enhanced cell migration and axon bundling without significantly affecting maximal outgrowth. The incorporation of protein microcrystals containing nerve growth factor (NGF) into the photoresin enabled sustained neurite outgrowth without the need for additional NGF in the media. Finally, laminin was added to the resin to enhance the bioactivity of the biomaterial, resulting in a further increase in maximum neurite outgrowth to 3.5 mm after 4 days of culture in softer matrices. Overall, the varied matrix properties achieved through FLight significantly enhance neurite outgrowth, highlighting the importance of adaptable scaffold characteristics for guiding neurite development. This demonstrates the potential of FLight as a versatile platform for creating ideal matrices for clinical applications in nerve repair and tissue engineering.

Fenugreek seed extract combined with acellular nerve allografts promotes peripheral nerve regeneration and neovascularization in sciatic nerve defects

Background

Acellular nerve allografts (ANAs) have been confirmed to improve the repair and reconstruction of long peripheral nerve defects. However, its efficacy is not comparable to that of autologous nerve grafts, which are used as the gold standard for treating peripheral nerve defects. Our study investigated whether fenugreek seed extract (FSE) exhibits neuroprotective potential and enhances the therapeutic outcomes of ANA repair in peripheral nerve defects.

Methods

Rat Schwann cells were treated with FSE to assess the effects of FSE on cell proliferation and their secretion function of neurotrophic factors in vitro. Sprague-Dawley rats with a unilateral 15-mm sciatic nerve defect were randomized into the ANA group (the 15-mm defect was replaced by an 18-mm ANA), the ANA + FSE group (the 15-mm defect was repaired with an 18-mm ANA with FSE administration for four weeks), and the Auto group (the 15-mm defect was repaired with an autologous graft). After four weeks post-surgery, various behavioral tests and electrophysiological assays were performed to evaluate the motor and sensory behavior as well as nerve conduction of rats. Then, rats were sacrificed, and the nerve grafts were collected for toluidine blue staining, RT-qPCR, immunofluorescence staining, immunohistochemical staining to evaluate nerve regeneration, neovascularization, and neuroinflammation. Their gastrocnemius was harvested for Masson's trichrome staining to examine gastrocnemius muscle recovery.

Results

FSE treatment promoted Schwann cell proliferation and its secretion of neurotrophic factors in vitro. Compared with ANAs alone, FSE treatment combined with ANAs enhanced axonal regeneration, upregulated S100, NF200, P0, MBP, and GAP43 expression, facilitated angiogenesis, and elevated neurotrophic factor expression in regenerating nerves of rats with sciatic nerve defects. In addition, FSE treatment promoted gastrocnemius muscle recovery, stimulated motor and sensory functional recovery and nerve conduction, and mitigated neuroinflammation in rats with sciatic nerve defects after repair with ANAs.

Conclusion

FSE treatment improves the beneficial effects of ANA repair on sciatic nerve defects.

Activation of PAR1 contributes to ferroptosis of Schwann cells and inhibits regeneration of myelin sheath after sciatic nerve crush injury in rats via Hippo-YAP/ACSL4 pathway

OBJECTIVE

Peripheral nerve injury (PNI) is characterized by high incidence and sequela rate. Recently, there was increasing evidence that has shown ferroptosis may impede functional recovery. Our objective is to explore the novel mechanism that regulates ferroptosis after PNI.

METHODS

LC-MS/MS proteomics was used to explore the possible differential signals, while PCR array was performed to investigate the differential factors. Besides, we also tried to activate or inhibit the key factors and then observe the level of ferroptosis. Regeneration of myelin sheath was finally examined in vivo via transmission electron microscopy.

RESULTS

Proteomics analysis suggested coagulation signal was activated after sciatic nerve crush injury, in which high expression of F2 (encoding thrombin) and F2r (encoding PAR1) were observed. Both thrombin and PAR1-targeted activator TRAP6 can induce ferroptosis in RSC96 cells, which can be rescued by Vorapaxar (PAR1 targeted inhibitor) in vitro. Further PCR array revealed that activation of PAR1 induced ferroptosis in RSC96 cells by increasing expression of YAP and ACSL4. Immunofluorescence of sciatic nerve confirmed that the expression of YAP and ACSL4 were simultaneously reduced after PAR1 inhibition, which may contribute to myelin regeneration after injury in SD rats.

CONCLUSION

Inhibition of PAR1 can relieve ferroptosis after sciatic nerve crush injury in SD rats through Hippo-YAP/ACSL4 pathway, thereby regulating myelin regeneration after injury. In summary, PAR1/Hippo-YAP/ACSL4 pathway may be a promising therapeutic target for promoting functional recovery post-sciatic crush injury.

Ex Vivo Human Tissue Functions as a Testing Platform for the Evaluation of a Nerve-Specific Fluorophore

SIGNIFICANCE

Selecting a nerve-specific lead fluorescent agent for translation in fluorescence-guided surgery is time-consuming and expensive. Preclinical fluorescent agent studies rely primarily on animal models, which are a critical component of preclinical testing, but these models may not predict fluorophore performance in human tissues.

AIM

The primary aim of this study was to evaluate and compare two preclinical models to test tissue-specific fluorophores based on discarded human tissues. The secondary aim was to use these models to determine the ability of a molecularly targeted fluorophore, LGW16-03, to label ex vivo human nerve tissues.

APPROACH

Patients undergoing standard-of-care transtibial or transfemoral amputation were consented and randomized to topical or systemic administration of LGW16-03 following amputation. After probe administration, nerves and background tissues were surgically resected and imaged to determine nerve fluorescence signal-to-background tissue ratio (SBR) and signal-to-noise ratio (SNR) metrics. Analysis of variance (ANOVA) determined statistical differences in metric means between administration cohorts and background tissue groups. Receiver operating characteristic (ROC) curve-derived statistics quantified the discriminatory performance of LGW16-03 fluorescence for labeling nerve tissues.

RESULTS

Tissue samples from 18 patients were analyzed. Mean nerve-to-adipose SBR was greater than nerve-to-muscle SBR (p = 0.001), but mean nerve-to-adipose SNR was not statistically different from mean nerve-to-muscle SNR (p = 0.069). Neither SBR nor SNR means were statistically different between fluorophore administration cohorts (p ≥ 0.448). When administration cohorts were combined, nerve-to-adipose SBR was greater than nerve-to-muscle SBR (mean ± standard deviation; 4.2 ± 2.9 vs. 1.8 ± 1.9; p < 0.001), but SNRs for nerve-to-adipose and nerve-to-muscle were not significantly different (5.1 ± 4.0 vs. 3.1 ± 3.4; p = 0.055). ROC curve-derived statistics to quantify LGW16-03 nerve labeling performance varied widely between patients, with sensitivities and specificities ranging from 0.2-99.9% and 0.4-100.0%.

CONCLUSION

Systemic and topical administration of LGW16-03 yielded similar fluorescence labeling of nerve tissues. Both administration approaches provided nerve-specific contrast similar to that observed in preclinical animal models. Fluorescence contrast was generally higher for nerve-to-adipose versus nerve-to-muscle. Ex vivo human tissue models provide safe evaluation of fluorophores in the preclinical phase and can aid in the selection of lead agents prior to first-in-human trials.

Peripheral nerve regeneration using a bioresorbable silk fibroin-based artificial nerve conduit fabricated via a novel freeze-thaw process

While silk fibroin (SF) obtained from silkworm cocoons is expected to become a next-generation natural polymer, a fabrication method for SF-based artificial nerve conduits (SFCs) has not yet been established. Here, we report a bioresorbable SFC, fabricated using a novel freeze-thaw process, which ensures biosafety by avoiding any harmful chemical additives. The SFC demonstrated favorable biocompatibility (high hydrophilicity and porosity with a water content of > 90%), structural stability (stiffness, toughness, and elasticity), and biodegradability, making it an ideal candidate for nerve regeneration. We evaluated the nerve-regenerative effects of the SFC in a rat sciatic-nerve-defect model, including its motor and sensory function recovery as well as histological regeneration. We found that SFC transplantation significantly promoted functional recovery and nerve regeneration compared to silicone tubes and was almost equally effective as autologous nerve transplantation. Histological analyses indicated that vascularization and M2 macrophage recruitment were pronounced inside the SFC. These results suggest that the unique properties of the SFC further enhanced the peripheral nerve regeneration mechanism. As no SFC has been applied in clinical practice, the SFC reported herein may be a promising candidate for repairing extensive peripheral nerve defects.

Treatment of Denervated Muscle Atrophy by Injectable Dual-Responsive Hydrogels Loaded with Extracellular Vesicles

Denervated muscle atrophy, a common outcome of nerve injury, often results in irreversible fibrosis due to the limited effectiveness of current therapeutic interventions. While extracellular vesicles (EVs) offer promise for treating muscle atrophy, their therapeutic potential is hindered by challenges in delivery and bioactivity within the complex microenvironment of the injury site. To address this issue, an injectable hydrogel is developed that is responsive to both ultrasound and pH, with inherent anti-inflammatory and antioxidant properties, designed to improve the targeted delivery of stem cell-derived EVs. This hydrogel system allows for controlled release of EVs from human umbilical cord mesenchymal stem cells (HUC-MSCs), adapting to the specific conditions of the injury environment. In vivo studies using a rat model of nerve injury demonstrated that the EV-loaded hydrogel (EVs@UR-gel) significantly preserved muscle function. Six weeks post-nerve reconstruction, treated rats exhibited muscle strength, circumference, and wet weight reaching 89.53 ± 0.96%, 76.02 ± 7.49%, and 88.0 ± 2.65% of healthy controls, respectively, alongside an improvement in the sciatic nerve index (-0.11±0.09). This platform presents a novel therapeutic approach by maintaining EV bioactivity, enabling tunable release based on the disease state, and facilitating the restoration of muscle structure and function.

Electrically conductive and photocurable MXene-modulated hydrogel conduits for peripheral nerve regeneration: In vitro and in vivo studies

Electroconductive biomaterials, as advanced nerve guidance conduits (NGCs), have shown great promise to accelerate the rate of peripheral nerve repair and regeneration (PNR) but remain among the greatest challenges in regenerative medicine because of frail recovery. Herein, we introduce injectable nanocomposite nerve conduits based on gelatin methacrylate (GelMa) and MXene nanosheets (MX) for PNR. Microstructural studies determine that the addition of MX increases the mean pore size of GelMa NH from 5.8 ± 1.2 μm to 8.4 ± 1.6 μm for the hydrogel containing 0.25 mg/mL MX, for example, leading to higher swelling and degradation rates. The highest electrical conductivity (∼910 μS/cm) is attained for the GelMa-based nanocomposite composed MX with the concentration of 0.125 mg/mL, for the reason that at higher concentrations, agglomeration of the MXs happens. In vitro investigations, including metabolic activity and live-dead assessments by PC12 cells, reveal the biocompatibility of developed nanocomposite hydrogels (NHs) containing different concentrations of MX nanosheets in the range of 0.025-0.25 mg/mL. Implantation of GelMa-MX conduits in a rat model of peripheral nerve injury (PNI) leads to the impressive recovery of the injured sciatic nerve's sensory, motor, and sensory-motor function. Electrophysiological analysis also indicates a significant increase in compound muscle action potential and nerve conduction velocity with a decrease in terminal latency in animals implanted with GelMa-MX conduits compared to control groups (animals implanted with GelMa and animals without implantation). Moreover, histological analysis exhibits a notable absence of fibrous connective tissue in the regenerated nerve fibers with a substantial increase in more organized myelinated axons. Our results demonstrate that GelMa-MX conduits promote regeneration of the injured sciatic nerve and could be promising for peripheral nerve tissue engineering.

E-jet 3D printed aligned nerve guidance conduits incorporated with decellularized extracellular matrix hydrogel encapsulating extracellular vesicles for peripheral nerve repair

Peripheral nerve injury (PNI) as a common clinical issue that presents significant challenges for repair. Factors such as donor site morbidity from autologous transplantation, slow recovery of long-distance nerve damage, and deficiencies in local cytokines and extracellular matrix contribute to the complexity of effective PNI treatment. It is extremely urgent to develop functional nerve guidance conduits (NGCs) as substitutes for nerve autografts. We fabricate an aligned topological scaffold by combining the E-jet 3D printing and electrospinning to exert synergistic topographical cue for peripheral nerve regeneration. To address the limitation of NGCs with hollow lumens in repairing long-distance nerve defects, we modified the internal microenvironment by filling the lumen with umbilical cord-derived decellularized extracellular matrix (dECM) hydrogels and extracellular vesicles (EVs). This approach led to the development of a functional HE-NGC. Herein, the HE-NGCs provided obvious guidance and proliferation to SCs and PC12 in vitro due to the sustained-release effect of dECM hydrogels and the outstanding proliferation-promoting role of EVs. The HE-NGCs was surgically implanted in vivo to bridge 12-mm gap sciatic nerve defect in rats and it had a satisfactory effect in reestablishment of the sciatic nerve, including the recovery of motor functions and the myelination. Further studies revealed that HE-NGCs might promoted axon growth by activating the PI3K/Akt/mTOR and inhibiting the MAPK signaling pathways. These findings indicate that HE-NGCs effectively promote nerve regeneration, offering a promising strategy for applications in peripheral nerve repair. STATEMENT OF SIGNIFICANCE: This study introduces an approach using an E-jet 3D printing system to fabricate three-dimensional aligned scaffolds with varying gap sizes, optimizing the structure for Schwann cells migration. We present, for the first time, a comprehensive investigation into the effects of EVs derived from umbilical cord mesenchymal stem cells on Schwann cells behavior. By leveraging the natural extracellular matrix (ECM), we significantly enhanced the efficacy and longevity of EVs encapsulated within a dECM hydrogel. Our provided strategy involves utilizing EVs to support nerve cell migration and proliferation along aligned NGCs. As the dECM hydrogel degrades, EVs are gradually released, facilitating the deposition of new ECM and enabling the repair of nerve defects up to 12-mm in length.

Correlation Between Relative Value Units and Operative Time for Peripheral Nerve Surgeries

BACKGROUND

The work relative value unit (wRVU) system quantifies surgeons' effort and resources for procedures. Studies have shown its inaccuracy in capturing the complexity of certain plastic and upper extremity surgeries. Analysis for peripheral nerve surgery (PNS), a growing niche within hand and plastic surgery, has not been performed. The authors aim to evaluate the PNS wRVUs by correlation to their operative time.

METHODS

A retrospective analysis with current procedure terminology (CPT) codes for PNS (2005-2021) from the American College of Surgeons National Surgical Quality Improvement Program database was performed. Efficiency was determined by wRVU per operative time. Correlation was performed between operative time with wRVU and wRVU/minute.

RESULTS

A total of 2402 procedures across 21 CPT Codes were included and categorized into neuroplasty, nerve repair, and nerve grafting/transfers with the median operative time being 63.75, 100, and 153.78 minutes respectively. Nerve graft/transfer generated the maximum wRVU (mean 16.35). Neuroplasty generated the minimum wRVU (mean 7.24). Nerve grafts/transfers generated the least wRVUs per minute (0.09). Longer operative times were associated with higher wRVUs. Neuroplasty (R = .86) and nerve repairs (R = .84) had a strong correlation to the operative time. Nerve grafts/transfer had a positive but moderate correlation with the operative time (R = .67). All procedures had a negative correlation between operative time and wRVU/minute.

CONCLUSIONS

Nerve grafts/transfers had reduced compensation compared to neuroplasty or nerve repairs. Compensation did not reflect the procedure efficiency. This disparity in wRVU allocation for complex PNS underscores the need for remuneration reform.

Granulocyte colony-stimulating factor promotes regeneration of severed facial nerve in rats

Background and aim

The administration of growth and neurotrophic factors has been attempted experimentally as a new therapeutic strategy for severe facial paralysis. Granulocyte colony-stimulating factor (G-CSF) has an effect on the treatment of central nervous system injuries, such as cerebral infarction and spinal cord injury. This study aimed at examining the effects of G-CSF on facial nerve regeneration in rats.

Methods

The left facial nerve of rats was either partially resected (resection group) or severed and sutured (suture group) at the main trunk outside the temporal bone. In each surgical group, saline or G-CSF was administered via the gelatin hydrogel drug delivery system. The suture group was further divided into two subgroups for the late administration of G-CSF (2 weeks after surgical treatment) or immediate administration of G-CSF after surgical treatment. Recovery of the facial nerve was assessed by the evaluation of facial movements (after 12 weeks), complex muscle action potential amplitude measurements (after 2, 4, 8, and 12 weeks), electroneurography values (after 12 weeks), and histological evaluation (comparison of myelinated axon diameters among the groups).

Results

Recovery of the function and morphology of damaged nerves was faster in the suture groups than in the resection group. In the suture groups, recovery was faster for G-CSF-treated rats than for saline-treated rats. Furthermore, recovery was faster in the group that received G-CSF immediately after surgical treatment than in the group that received G-CSF 2 weeks later. However, the group that received G-CSF 2 weeks later also showed faster recovery than did the control group.

Conclusion

G-CSF effectively promoted nerve regeneration during facial nerve paralysis. Thus, G-CSF may be a potential treatment strategy for injured facial nerves as it has been safely administered in clinical treatments for hematological diseases.

Polyethylene Glycol-Mediated Axonal Fusion Promotes Early Sensory Recovery after Digital Nerve Injury: A Randomized Clinical Trial

BACKGROUND

Peripheral nerve repair is limited by Wallerian degeneration coupled with the slow and inconsistent rates of nerve regrowth. In more proximal injuries, delayed nerve regeneration can cause debilitating muscle atrophy. Topical application of polyethylene glycol (PEG) during neurorrhaphy facilitates the fusion of severed axonal membranes, immediately restoring action potentials across the coaptation site. In preclinical animal models, PEG fusion resulted in remarkable early functional recovery.

METHODS

This is the first randomized clinical trial comparing functional outcomes between PEG fusion and standard neurorrhaphy. Participants with digital nerve transections were followed up at 2 weeks, 1 month, and 3 months postoperatively. The primary outcome was assessed using the Medical Research Council Classification (MRCC) rating for sensory recovery at each time point. Semmes-Weinstein monofilaments and static 2-point discrimination determined MRCC ratings. Postoperative quality of life was measured using the Michigan Hand Outcomes Questionnaire.

RESULTS

Forty-eight transected digital nerves (25 control and 23 PEG) across 22 patients were analyzed. PEG-fused nerves demonstrated significantly higher MRCC scores at 2 weeks (OR, 16.95; 95% CI, 1.79 to 160.38; P = 0.008) and 1 month (OR, 13.40; 95% CI, 1.64 to 109.77; P = 0.009). Participants in the PEG cohort also had significantly higher average Michigan Hand Outcomes Questionnaire scores at 2 weeks (Hodge g , 1.28; 95% CI, 0.23 to 2.30; P = 0.0163) and 1 month (Hodge g , 1.02; 95% CI, 0.04 to 1.99; P = 0.049). No participants had adverse events related to the study drug.

CONCLUSION

PEG fusion promotes early sensory recovery and improved patient well-being following peripheral nerve repair of digital nerves.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

The limelight of adipose-derived stem cells in the landscape of neural tissue engineering for peripheral nerve injury

BACKGROUND AND AIMS

Challenges in treating peripheral nerve injury include prolonged repair time and insufficient functional recovery. Stem cell therapy coupled with neural tissue engineering has been shown to induce nerve regeneration following peripheral nerve injury. Among these stem cells, adipose-derived stem cells (ADSCs) are preferred due to their accessibility, expansion, multidirectional differentiation, and production of essential nutrient factors for nerve growth. In recent years, ADSC-laden nerve guide conduit has been utilized to enhance the therapeutic effects of tissue-engineered nerve grafts. This review explores existing research that recognizes the roles played by ADSCs in inducing peripheral nerve regeneration following injury and summarizes the different methods of application of ADSC-laden nerve conduit in neural tissue engineering.

Decellularized Biohybrid Nerve Promotes Motor Axon Projections

Developing nerve grafts with intact mesostructures, superior conductivity, minimal immunogenicity, and improved tissue integration is essential for the treatment and restoration of neurological dysfunctions. A key factor is promoting directed axon growth into the grafts. To achieve this, biohybrid nerves are developed using decellularized rat sciatic nerve modified by in situ polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). Nine biohybrid nerves are compared with varying polymerization conditions and cycles, selecting the best candidate through material characterization. These results show that a 1:1 ratio of FeCl3 oxidant to ethylenedioxythiophene (EDOT) monomer, cycled twice, provides superior conductivity (>0.2 mS cm-1), mechanical alignment, intact mesostructures, and high compatibility with cells and blood. To test the biohybrid nerve's effectiveness in promoting motor axon growth, human Spinal Cord Spheroids (hSCSs) derived from HUES 3 Hb9:GFP cells are used, with motor axons labeled with green fluorescent protein (GFP). Seeding hSCS onto one end of the conduit allows motor axon outgrowth into the biohybrid nerve. The construct effectively promotes directed motor axon growth, which improves significantly after seeding the grafts with Schwann cells. This study presents a promising approach for reconstructing axonal tracts in humans.

Decoding the regulatory role of ATP synthase inhibitory factor 1 (ATPIF1) in Wallerian degeneration and peripheral nerve regeneration

ATP synthase inhibitory factor 1 (ATPIF1), a key modulator of ATP synthase complex activity, has been implicated in various physiological and pathological processes. While its role is established in conditions such as hypoxia, ischemia-reperfusion injury, apoptosis, and cancer, its involvement remains elusive in peripheral nerve regeneration. Leveraging ATPIF1 knockout transgenic mice, this study reveals that the absence of ATPIF1 impedes neural structural reconstruction, leading to delayed sensory and functional recovery. RNA-sequencing unveils a significant attenuation in immune responses following peripheral nerve injury, which attributes to the CCR2/CCL2 signaling axis and results in decreased macrophage infiltration and activation. Importantly, macrophages, not Schwann cells, are identified as key contributors to the delayed Wallerian degeneration in ATPIF1 knockout mice, and affect the overall outcome of peripheral nerve regeneration. These results shed light on the translational potential of ATPIF1 for improving peripheral nerve regeneration.

In Vitro Models for Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) resulting in lesions is highly prevalent clinically, but current therapeutic approaches fail to provide satisfactory outcomes in many patients. While peripheral nerves have intrinsic regenerative capacity, the regenerative capabilities of peripheral nerves are often insufficient to restore full functionality. This highlights an unmet need for developing more effective strategies to repair damaged peripheral nerves and improve regenerative success. Consequently, researchers are actively exploring a variety of therapeutic strategies, encompassing the local delivery of trophic factors or bioactive molecules, the design of advanced biomaterials that interact with regenerating axons, and augmentation with nerve guidance conduits or complex prostheses. However, clinical translation of these technologies remains limited, emphasizing the need for continued research on peripheral nerve regeneration modalities that can enhance functional restoration. Experimental models that accurately recapitulate key aspects of peripheral nerve injury and repair biology can accelerate therapeutic development by enabling systematic testing of new techniques. Advancing regenerative therapies for PNI requires bridging the gap between basic science discoveries and clinical application. This review discusses different in vitro models of peripheral nerve injury and repair, including their advantages, limitations, and potential applications.

Insights Into the Epidemiology of Peripheral Nerve Injuries in the United States: Systematic Review

BACKGROUND

Peripheral nerve injuries (PNI) range from mild neurapraxia to severe transection, leading to significant morbidity. Despite their impact, the societal implications of PNI in the United States are not well understood. This study aims to systematically review the literature on PNI epidemiology in the United States. We hypothesize that this review will reveal significant gaps in the understanding of PNI incidence, demographics, and economic impact.

METHODS

Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we queried the literature for studies on PNI that reported at least one of the following: incidence rates, demographics, affected nerve distribution, injury mechanisms, surgical intervention rates, and associated direct costs. Exclusion criteria included non-English publications, abstracts, conference proceedings, reviews, or editorials, studies published before 2000, non-US studies, or studies focusing solely on digital nerves or plexus injuries.

RESULTS

Fifteen studies met the inclusion criteria. Data indicate a higher incidence of upper extremity nerve injuries compared with lower extremity injuries. The literature lacks comprehensive reporting on surgical intervention rates, with no recent data since 2013. There is a notable absence of nationwide epidemiological data on PNI mechanisms and recent cost data, with most information over a decade old and primarily focused on inpatient costs, neglecting outpatient visits, physical therapy, and medication expenses.

CONCLUSION

The epidemiological data on PNI are limited and outdated, highlighting the need for further research. Future studies should focus on recent trends in PNI incidence, injury mechanisms, and financial burden, including comprehensive reporting on surgical interventions, to inform strategies aimed at improving patient outcomes and health care resource allocation.

Potential of Stem-Cell-Induced Peripheral Nerve Regeneration: From Animal Models to Clinical Trials

Peripheral nerve injury has become an increasingly prevalent clinical concern, causing great morbidity in the community. Although there have been significant advancements in the treatment of peripheral nerve damage in recent years, the issue of long-term nerve regeneration remains. Furthermore, Wallerian degeneration has created an obstacle to long-term nerve regeneration. For this reason, there has been extensive research on the use of exogenous and endogenous stem cells as an adjunct or even primary treatment option for peripheral nerve injury. The plasticity and inducibility of stem cells make them an enticing option for initiating neuronal cell regrowth and optimal sensory and functional nerve regeneration. Peripheral nerve injury has a broad range of causative factors and etiologies. As such, unique stem cell-induced peripheral nerve treatments are being investigated to ameliorate the damage incited by all causes, including trauma, neuropathy, and systemic neurodegenerative diseases. This review is oriented to outline the potential role of stem cell therapies in peripheral nerve injury versus the current standards of care, compare the benefits and drawbacks of specific stem cell lines under investigation, and highlight the current models of stem cell therapy in the peripheral nervous system, with the ultimate goal of narrowing down and optimizing the role and scope of stem cell therapy in peripheral nerve injury.

Automated production of nerve repair constructs containing endothelial cell tube-like structures

Engineered neural tissue (EngNT) is a stabilised aligned cellular hydrogel that offers a potential alternative to the nerve autograft for the treatment of severe peripheral nerve injury. This work aimed to automate the production of EngNT, to improve the feasibility of scalable manufacture for clinical translation. Endothelial cells were used as the cellular component of the EngNT, with the formation of endothelial cell tube-like structures mimicking the polarised vascular structures formed early on in the natural regenerative process. Gel aspiration-ejection for the production of EngNT was automated by integrating a syringe pump with a robotic positioning system, using software coded in Python to control both devices. Having established the production method and tested mechanical properties, the EngNT containing human umbilical vein endothelial cells (EngNT-HUVEC) was characterised in terms of viability and alignment, compatibility with neurite outgrowth from rat dorsal root ganglion neurons and formation of endothelial cell networksin vitro. EngNT-HUVEC manufactured using the automated system contained viable and aligned endothelial cells, which developed into a network of multinucleated endothelial cell tube-like structures inside the constructs and an outer layer of endothelialisation. The EngNT-HUVEC constructs were made in various sizes within minutes. Constructs provided support and guidance to regenerating neuritesin vitro. This work automated the formation of EngNT, facilitating high throughput manufacture at scale. The formation of endothelial cell tube-like structures within stabilised hydrogels provides an engineered tissue with potential for use in nerve repair.

Design and Applications of Supramolecular Peptide Hydrogel as Artificial Extracellular Matrix

Supramolecular peptide hydrogels (SPHs) consist of peptides containing hydrogelators and functional epitopes, which can first self-assemble into nanofibers and then physically entangle together to form dynamic three-dimensional networks. Their porous structures, excellent bioactivity, and high dynamicity, similar to an extracellular matrix (ECM), have great potential in artificial ECM. The properties of the hydrogel are largely dependent on peptides. The noncovalent interactions among hydrogelators drive the formation of assemblies and further transition into hydrogels, while bioactive epitopes modulate cell-cell and cell-ECM interactions. Therefore, SPHs can support cell growth, making them ideal biomaterials for ECM mimics. This Review outlines the classical molecular design of SPHs from hydrogelators to functional epitopes and summarizes the recent advancements of SPHs as artificial ECMs in nervous system repair, wound healing, bone and cartilage regeneration, and organoid culture. This emerging SPH platform could provide an alternative strategy for developing more effective biomaterials for tissue engineering.

Case Series of Traumatic Peripheral Nerve Injuries in Pediatric Patients Treated with Allograft Repair

Purpose

In the adult literature, allograft reconstruction of gapped peripheral nerve injuries has gained popularity over autologous nerve grafting. Allografts have demonstrated similar recovery while eliminating donor site morbidity. There is no well-defined incidence or treatment of such injuries in children. Our study explores the epidemiology and outcomes of traumatic pediatric peripheral nerve injuries treated with allograft.

Methods

This is a retrospective case series of a prospectively maintained database of all pediatric patients who underwent nerve allograft reconstruction at a Level I trauma center between September 2011 and July 2021.

Results

We identified 24 allograft nerve reconstructions in 18 patients, average age 12.9 years (range 1.5-17.0) and 78% male. Five patients (28%) were injured in a motor vehicle accident, and four were injured by sharp laceration, machinery, and blast injury (22%). The most injured nerve was digital (n = 10, 42%) followed by 8 (33%) ulnar, and 4 (17%) median. The average gap length was 30.3 ± 23.8 mm (range 4-87 mm). Fifteen nerves were repaired within 24 hours (63%). Average follow-up was 13.7 ± 14.5 months (range 1.6-46.8 months). At final follow-up, 9 (38%) had full sensory recovery, 6 (25%) protective sensation, 2 (8%) deep pressure, and 1 (4%) no sensation but a positive Tinel's sign.

Conclusions

Allograft reconstruction is a viable option for the treatment of traumatic pediatric peripheral nerve injuries with gaps not amenable to direct repair.

Type of study/level of evidence

Therapeutic IV.

Skeletal muscle reprogramming enhances reinnervation after peripheral nerve injury

Peripheral Nerve Injuries (PNI) affect more than 20 million Americans and severely impact quality of life by causing long-term disability. PNI is characterized by nerve degeneration distal to the site of nerve injury resulting in long periods of skeletal muscle denervation. During this period, muscle fibers atrophy and frequently become incapable of "accepting" innervation because of the slow speed of axon regeneration post injury. We hypothesize that reprogramming the skeletal muscle to an embryonic-like state may preserve its reinnervation capability following PNI. To this end, we generate a mouse model in which NANOG, a pluripotency-associated transcription factor is expressed locally upon delivery of doxycycline (Dox) in a polymeric vehicle. NANOG expression in the muscle upregulates the percentage of Pax7+ nuclei and expression of eMYHC along with other genes that are involved in muscle development. In a sciatic nerve transection model, NANOG expression leads to upregulation of key genes associated with myogenesis, neurogenesis and neuromuscular junction (NMJ) formation. Further, NANOG mice demonstrate extensive overlap between synaptic vesicles and NMJ acetylcholine receptors (AChRs) indicating restored innervation. Indeed, NANOG mice show greater improvement in motor function as compared to wild-type (WT) animals, as evidenced by improved toe-spread reflex, EMG responses and isometric force production. In conclusion, we demonstrate that reprogramming muscle can be an effective strategy to improve reinnervation and functional outcomes after PNI.

Aligned Fibroporous Matrix Generated from a Silver Ion and Graphene Oxide-Incorporated Ethylene Vinyl Alcohol Copolymer as a Potential Biomaterial for Peripheral Nerve Repair

Developing an ideal nerve conduit for proper nerve regeneration still faces several challenges. The attempts to fabricate aligned substrates for neuronal growth have enhanced the hope of successful nerve regeneration. In this wok, we have attempted to generate an electrospun matrix with aligned fibers from a silver and graphene oxide-incorporated ethylene vinyl alcohol copolymer (EVAL). The presence of silver was analyzed using UV-visible spectra, XPS spectra, and ICP. Raman spectra and FTIR spectra confirmed the presence of GO. The complexation of Ag+ with - OH of EVAL enabled the generation of aligned fibers. The fiber diameter (>1 μm) provided sufficient space for forming focal adhesion by the neurites and filopodia of N2a and C6 cells, respectively. The fiber diameter enabled the neurites and filopodia of the cells to align on the fibers. The incorporation of GO has contributed to the cell-material interactions. The morphological and mechanical properties of fibers obtained in the study ensure that the EVAL-Ag-GO-0.01 matrix is a potential substrate for developing a nerve guidance conduit/nerve wrap (NGC/W).

Increased efficiency of peripheral nerve regeneration using supercritical carbon dioxide-based decellularization in acellular nerve graft

Acellular nerve grafts (ANGs) are a promising therapeutic for patients with nerve defects caused by injuries. Conventional decellularization methods utilize a variety of detergents and enzymes. However, these methods have disadvantages, such as long processing times and the presence of detergents that remain on the graft. In this study, we aimed to reduce process time and minimize the risks associated with residual detergents by replacing them with supercritical carbon dioxide (scCO2) and compared the effectiveness to Hudson's decellularization method, which uses several detergents. The dsDNA and the expression of MHC1 and 2 were significantly reduced in both decellularized groups, which confirmed the effective removal of cellular debris. The extracellular matrix proteins and various factors were found to be better preserved in the scCO2 ANGs compared to the detergent-ANGs. We conducted behavioral tests and histological analyses to assess the impact of scCO2 ANGs on peripheral nerve regeneration in animal models. Compared with Hudson's method, the scCO2 method effectively improved the efficacy of peripheral nerve regeneration. Therefore, the decellularization method using scCO2 is not only beneficial for ANG synthesis, but it may also be helpful for therapeutics by enhancing the efficacy of peripheral nerve regeneration.

The neuroma map: A systematic review of the anatomic distribution, etiologies, and surgical treatment of painful traumatic neuromas

BACKGROUND

This study analyzed all reported cases of painful traumatic neuromas to better understand their anatomic distribution, etiologies, and surgical treatment.

METHODS

PubMed, Embase, Cochrane, and Web of Science were searched in October 2023 for articles describing painful traumatic neuromas.

RESULTS

In total, 414 articles reporting 5,562 neuromas were included and categorized into head/neck, trunk, upper extremity, lower extremity, and autonomic nerves. Distribution was as follows: Head/neck: 83 articles reported on 393 neuromas (93.2% iatrogenic) most frequently involving the lingual (44.4%), cervical plexus (15.0%), great auricular (8.6%), inferior/superior alveolar (8.3%), and occipital (7.2%) nerves. Trunk: 47 articles reported on 552 neuromas (92.9% iatrogenic) most commonly involving the intercostal (40.0%), ilioinguinal (18.2%) and genitofemoral (16.2%) nerves. Upper extremity: 160 articles reported on 2082 neuromas (42.2% after amputation) most frequently involving the digital (47.0%), superficial radial (18.3%), and median (7.0%) nerves. Lower extremity: 128 articles reported on 2,531 neuromas (53.0% after amputation) most commonly involving the sural (17.9%), superficial peroneal (17.3%), and saphenous (16.0%) nerves. Autonomic nerves: 17 articles reported on 53 neuromas (100% iatrogenic) most frequently involving the biliary tract (64.2%) and vagus nerve (18.9%). Compared with the extremities, neuromas in the head/neck and trunk had significantly longer symptom duration before surgical treatment and the nerve end was significantly less frequently reconstructed after neuroma excision.

CONCLUSION

Painful neuromas are predominantly reported in the extremities yet may occur throughout the body primarily after iatrogenic injury. Knowledge of their anatomic distribution from head to toe will encourage awareness to avoid injury and expedite diagnosis to prevent treatment delay.

Sciatic Nerve Entrapment from Cerclage Wiring in Intramedullary Nail Fixation

Cerclage wiring may be used to optimize the stability of intramedullary nail or plate fixations in comminuted proximal femoral fractures, periprosthetic fractures, and other selected cases. In this article, we presented a novel case of iatrogenic sciatic nerve entrapment from cerclage wiring used to supplement intramedullary nail fixation. We also illustrate and highlight the role of ultrasound in assessing the sciatic nerve to make a timely diagnosis.

Shape-Persistent Conductive Nerve Guidance Conduits for Peripheral Nerve Regeneration

To solve the problems of slow regeneration and mismatch of axon regeneration after peripheral nerve injury, nerve guidance conduits (NGCs) have been widely used to promote nerve regeneration. Multichannel NGCs have been widely studied to mimic the structure of natural nerve bundles. However, multichannel conduits are prone to structural instability. Thermo-responsive shape memory polymers (SMPs) can maintain a persistent initial structure over the body temperature range. Electrical stimulation (ES), utilized within nerve NGCs, serves as a biological signal to expedite damaged nerve regeneration. Here, an electrospun shape-persistent conductive NGC is designed to maintain the persistent tubular structure in the physiological temperature range and improve the conductivity. The physicochemical and biocompatibility of these P, P/G, P/G-GO, and P/G-RGO NGCs are conducted in vitro. Meanwhile, to evaluate biocompatibility and peripheral nerve regeneration, NGCs are implanted in subcutaneous parts of the back of rats and sciatic nerves assessed by histology and immunofluorescence analyses. The conductive NGC displays a stable structure, good biocompatibility, and promoted nerve regeneration. Collectively, the shape-persistent conductive NGC (P/G-RGO) is expected to promote peripheral nerve recovery, especially for long-gap and large-diameter nerves.

Optimizing Outcomes in Revision Peripheral Nerve Surgery of the Upper Extremity

Peripheral nerve surgeries for compressive neuropathy in the upper extremity are generally successful. However, cases that either fail or have complications requiring revision surgery are challenging. During revision consideration, surgeons should perform a comprehensive preoperative workup to understand the etiology of the patient's symptoms and categorize symptoms as persistent, recurrent, or new in relation to the index procedure. Revision surgery often requires an open, extensile approach with additional procedures to optimize outcomes. Even with proper workup and treatment, clinical outcomes of revision surgeries are inferior compared to primary surgeries and patients should be well informed prior to undergoing such procedures.

Muscle-resident mesenchymal progenitors sense and repair peripheral nerve injury via the GDNF-BDNF axis

Fibro-adipogenic progenitors (FAPs) are muscle-resident mesenchymal progenitors that can contribute to muscle tissue homeostasis and regeneration, as well as postnatal maturation and lifelong maintenance of the neuromuscular system. Recently, traumatic injury to the peripheral nerve was shown to activate FAPs, suggesting that FAPs can respond to nerve injury. However, questions of how FAPs can sense the anatomically distant peripheral nerve injury and whether FAPs can directly contribute to nerve regeneration remained unanswered. Here, utilizing single-cell transcriptomics and mouse models, we discovered that a subset of FAPs expressing GDNF receptors Ret and Gfra1 can respond to peripheral nerve injury by sensing GDNF secreted by Schwann cells. Upon GDNF sensing, this subset becomes activated and expresses Bdnf. FAP-specific inactivation of Bdnf (Prrx1Cre; Bdnffl/fl) resulted in delayed nerve regeneration owing to defective remyelination, indicating that GDNF-sensing FAPs play an important role in the remyelination process during peripheral nerve regeneration. In aged mice, significantly reduced Bdnf expression in FAPs was observed upon nerve injury, suggesting the clinical relevance of FAP-derived BDNF in the age-related delays in nerve regeneration. Collectively, our study revealed the previously unidentified role of FAPs in peripheral nerve regeneration, and the molecular mechanism behind FAPs' response to peripheral nerve injury.

Electrically conductive coatings in tissue engineering

Recent interest in tissue engineering (TE) has focused on electrically conductive biomaterials. This has been inspired by the characteristics of the cells' microenvironment where signalling is supported by electrical stimulation. Numerous studies have demonstrated the positive influence of electrical stimulation on cell excitation to proliferate, differentiate, and deposit extracellular matrix. Even without external electrical stimulation, research shows that electrically active scaffolds can improve tissue regeneration capacity. Tissues like bone, muscle, and neural contain electrically excitable cells that respond to electrical cues provided by implanted biomaterials. To introduce an electrical pathway, TE scaffolds can incorporate conductive polymers, metallic nanoparticles, and ceramic nanostructures. However, these materials often do not meet implantation criteria, such as maintaining mechanical durability and degradation characteristics, making them unsuitable as scaffold matrices. Instead, depositing conductive layers on TE scaffolds has shown promise as an efficient alternative to creating electrically conductive structures. A stratified scaffold with an electroactive surface synergistically excites the cells through active top-pathway, with/without electrical stimulation, providing an ideal matrix for cell growth, proliferation, and tissue deposition. Additionally, these conductive coatings can be enriched with bioactive or pharmaceutical components to enhance the scaffold's biomedical performance. This review covers recent developments in electrically active biomedical coatings for TE. The physicochemical and biological properties of conductive coating materials, including polymers (polypyrrole, polyaniline and PEDOT:PSS), metallic nanoparticles (gold, silver) and inorganic (ceramic) particles (carbon nanotubes, graphene-based materials and Mxenes) are examined. Each section explores the conductive coatings' deposition techniques, deposition parameters, conductivity ranges, deposit morphology, cell responses, and toxicity levels in detail. Furthermore, the applications of these conductive layers, primarily in bone, muscle, and neural TE are considered, and findings from in vitro and in vivo investigations are presented. STATEMENT OF SIGNIFICANCE: Tissue engineering (TE) scaffolds are crucial for human tissue replacement and acceleration of healing. Neural, muscle, bone, and skin tissues have electrically excitable cells, and their regeneration can be enhanced by electrically conductive scaffolds. However, standalone conductive materials often fall short for TE applications. An effective approach involves coating scaffolds with a conductive layer, finely tuning surface properties while leveraging the scaffold's innate biological and physical support. Further enhancement is achieved by modifying the conductive layer with pharmaceutical components. This review explores the under-reviewed topic of conductive coatings in tissue engineering, introducing conductive biomaterial coatings and analyzing their biological interactions. It provides insights into enhancing scaffold functionality for tissue regeneration, bridging a critical gap in current literature.

Comparison of Neural Recovery Effects of Botulinum Toxin Based on Administration Timing in Sciatic Nerve-Injured Rats

This study aimed to assess the effects of the timing of administering botulinum neurotoxin A (BoNT/A) on nerve regeneration in rats. Sixty 6-week-old rats with a sciatic nerve injury were randomly divided into four groups: the immediately treated (IT) group (BoNT/A injection administered immediately post-injury), the delay-treated (DT) group (BoNT/A injection administered one week post-injury), the control group (saline administered one week post-injury), and the sham group (only skin and muscle incisions made). Nerve regeneration was assessed 3, 6, and 9 weeks post-injury using various techniques. The levels of glial fibrillary acid protein (GFAP), astroglial calcium-binding protein S100β (S100β), growth-associated protein 43 (GAP43), neurofilament 200 (NF200), and brain-derived neurotrophic factor (BDNF) in the IT and DT groups were higher. ELISA revealed the highest levels of these proteins in the IT group, followed by the DT and control groups. Toluidine blue staining revealed that the average area and myelin thickness were higher in the IT group. Electrophysiological studies revealed that the CMAP in the IT group was significantly higher than that in the control group, with the DT group exhibiting significant differences starting from week 8. The findings of the sciatic functional index analysis mirrored these results. Thus, administering BoNT/A injections immediately after a nerve injury is most effective for neural recovery. However, injections administered one week post-injury also significantly enhanced recovery. BoNT/A should be administered promptly after nerve damage; however, its administration during the non-acute phase is also beneficial.

The outcomes of peripheral nerve surgeries in Africa: Narrative synthesis from existing literature

BACKGROUND

In Africa, peripheral nerve pathologies are a major source of disability, and the results of surgical therapies differ greatly among countries. The goal of this narrative review is to compile the most recent data on peripheral nerve surgery results in Africa, pinpoint critical variables that affect surgical outcomes, and offer suggestions for enhancing patient care.

METHODS

A comprehensive literature review was conducted, focusing on studies published over the past four decades. The sources included peer-reviewed journals, hospital records, and reports from healthcare organizations. The review examined outcomes related to functional recovery, quality of life, and postoperative complications.

RESULTS

The outcomes of peripheral nerve surgeries in Africa are influenced by the availability of medical infrastructure, the level of surgeon expertise, and the timeliness of the intervention. Urban centers with better resources tend to report more favorable outcomes, whereas rural areas face significant challenges. Common barriers include limited access to advanced surgical tools, a shortage of specialized surgeons, and inadequate postoperative care and rehabilitation services. Despite these challenges, successful interventions have been reported, particularly in settings where targeted training programs and international collaborations are in place.

CONCLUSION

Enhancing surgeon training programs, building comprehensive postoperative care and rehabilitation facilities, and investing in healthcare infrastructure are critical to improving peripheral nerve surgery results in Africa. International and regional collaborations can be extremely helpful in advancing these initiatives by enabling the sharing of knowledge and granting access to cutting-edge methods. Patients with peripheral nerve injuries across the continent may experience improved functional recovery and overall quality of life if these criteria are met.

A stretchable, electroconductive tissue adhesive for the treatment of neural injury

Successful nerve repair using bioadhesive hydrogels demands minimizing tissue-material interfacial mechanical mismatch to reduce immune responses and scar tissue formation. Furthermore, it is crucial to maintain the bioelectrical stimulation-mediated cell-signaling mechanism to overcome communication barriers within injured nerve tissues. Therefore, engineering bioadhesives for neural tissue regeneration necessitates the integration of electroconductive properties with tissue-like biomechanics. In this study, we propose a stretchable bioadhesive based on a custom-designed chemically modified elastin-like polypeptides (ELPs) and a choline-based bioionic liquid (Bio-IL), providing an electroconductive microenvironment to reconnect damaged nerve tissue. The stretchability akin to native neural tissue was achieved by incorporating hydrophobic ELP pockets, and a robust tissue adhesion was obtained due to multi-mode tissue-material interactions through covalent and noncovalent bonding at the tissue interface. Adhesion tests revealed adhesive strength ~10 times higher than commercially available tissue adhesive, Evicel®. Furthermore, the engineered hydrogel supported in vitro viability and proliferation of human glial cells. We also evaluated the biodegradability and biocompatibility of the engineered bioadhesive in vivo using a rat subcutaneous implantation model, which demonstrated facile tissue infiltration and minimal immune response. The outlined functionalities empower the engineered elastic and electroconductive adhesive hydrogel to effectively enable sutureless surgical sealing of neural injuries and promote tissue regeneration.

Research advancements on nerve guide conduits for nerve injury repair

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

Surgical Repair of Obstetric Brachial Plexus Injuries: A Case Series and Discussion of the Current Literature

OBJECTIVE

To assess factors which may influence surgical success following brachial plexus reconstruction for obstetric brachial plexus injury (OBPI).

METHODS

We retrospectively reviewed the charts of 27 consecutive patients who underwent brachial plexus reconstruction following OBPI by a single pediatric neurosurgeon, 22 of which had adequate follow-up be included in analysis. Data on preoperative function, intraoperative findings, and postoperative outcomes were collected. Mallet grades for abduction, external rotation, and hand-to-mouth were used as a measure of upper trunk function.

RESULTS

All patients undergoing brachial plexus reconstruction (n = 27) were found to have some degree of upper-trunk injury intra-operatively. Of the 22 patients with adequate follow-up to be included in the analysis, 17 had some degree of improvement in Mallet grade postoperatively. Prior to surgery, 95% (21/22) of patients had an abduction Mallet grade of 1, compared to 23% (5/22) at the time of maximum improvement (P < 0.001). These values were 100% (20/20) to 35% (5/14) (P < 0.001), and 95% (21/22) to 27% (6/22) (P < 0.001) for external rotation and hand-to-mouth, respectively. The average time to maximum Mallet grade was 583 days (standard deviation 356 days). Age at time of surgery and time to maximum recovery were not found to be correlated.

CONCLUSIONS

Brachial plexus reconstruction is an effective treatment modality for patients without spontaneous recovery of upper extremity function following OBPI, although identifying the optimal age-range for surgery remains elusive. Patients with intraoperative findings consistent with a more severe injury may be less likely to benefit from surgery.

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

Introduction

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

Methods

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

Results

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

Discussion

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

A tacrolimus-eluting nerve guidance conduit enhances regeneration in a critical-sized peripheral nerve injury rat model

Critical-sized peripheral nerve injuries pose a significant clinical challenge and lead to functional loss and disability. Current regeneration strategies, including autografts, synthetic nerve conduits, and biologic treatments, encounter challenges such as limited availability, donor site morbidity, suboptimal recovery, potential immune responses, and sustained stability and bioactivity. An obstacle in peripheral nerve regeneration is the immune response that can lead to inflammation and scarring that impede the regenerative process. Addressing both the immunological and regenerative needs is crucial for successful nerve recovery. Here, we introduce a novel biodegradable tacrolimus-eluting nerve guidance conduit engineered from a blend of poly (L-lactide-co-caprolactone) to facilitate peripheral nerve regeneration and report the testing of this conduit in 15-mm critical-sized gaps in the sciatic nerve of rats. The conduit's diffusion holes enable the local release of tacrolimus, a potent immunosuppressant with neuro-regenerative properties, directly into the injury site. A series of in vitro experiments were conducted to assess the ability of the conduit to maintain a controlled tacrolimus release profile that could promote neurite outgrowth. Subsequent in vivo assessments in rat models of sciatic nerve injury revealed significant enhancements in nerve regeneration, as evidenced by improved axonal growth and functional recovery compared to controls using placebo conduits. These findings indicate the synergistic effects of combining a biodegradable conduit with localized, sustained delivery of tacrolimus, suggesting a promising approach for treating peripheral nerve injuries. Further optimization of the design and long-term efficacy studies and clinical trials are needed before the potential for clinical translation in humans can be considered.

Innervated breast reconstruction: a narrative review of neurotization techniques and outcomes

Background and Objective

While significant sensation recovery improvements in neurotized breasts following reconstruction have been reported, sensation testing methods and surgical techniques have been widely variable. This narrative review aims to summarize available literature on current neurotization practices and sensory recovery outcomes in patients undergoing innervated breast reconstruction.

Methods

A comprehensive literature search of PubMed Medline, Web of Science, and Embase was conducted to identify all studies reporting outcomes of neurotization in breast reconstruction surgeries. Data analyzed included operative times, neurotization techniques, sensory outcomes, and methods as well as patient reported outcomes.

Key Content and Findings

Despite the heterogeneity of various studies reviewed, all forms of neurotization achieved earlier and superior sensory recovery throughout the reconstructed breast skin compared to non-innervated breasts. In absence of randomized controlled trials or high-quality comparative studies, further evidence is required to objectively confirm this technique offers better sensory recovery.

Conclusions

Neurotization at the time of breast reconstruction may lead to improved sensation and patient reported outcomes delineating improved quality of life compared to non-innervated breasts. Future studies need to standardize the way that breast sensation is measured and determine pre-operative variables leading to expected changes in final sensation recovery to help manage surgical outcome expectations of both the surgeon and the patient.

Rethinking Oncologic Facial Nerve Reconstruction in the Acute Phase Through Classification of the Level of Injury

Early facial nerve reconstruction should be offered in every patient with oncological resections of the facial nerve due to the debilitating functional and psychosocial consequences of facial nerve palsy. Oncologic pathology or oncologic resection accounts for the second most common cause of facial nerve palsy. In the case of these acute injuries, selecting an adequate method for reconstruction to optimize functional and psychosocial well-being is paramount. Authors advocate consideration of the level of injury as a framework for approaching the viable options of reconstruction systematically. Authors breakdown oncologic injuries to the facial nerve in three levels in relation to their nerve reconstruction methods and strategies: Level I (intracranial to intratemporal), Level II (intratemporal to extratemporal and intraparotid), and Level III (extratemporal and extraparotid). Clinical features, common clinical scenarios, donor nerves available, recipient nerve, and reconstruction priorities will be present at each level. Additionally, examples of clinical cases will be shared to illustrate the utility of framing acute facial nerve injuries within injury levels. Selecting donor nerves is critical in successful facial nerve reconstruction in oncological patients. Usually, a combination of facial and nonfacial donor nerves (hybrid) is necessary to achieve maximal reinnervation of the mimetic muscles. Our proposed classification of three levels of facial nerve injuries provides a selection guide, which prioritizes methods for function nerve reconstruction in relation of the injury level in oncologic patients while prioritizing functional outcomes.

Paralysis of the trapezius muscle: evaluation and surgical management

Background

Paralysis of the trapezius muscle most commonly results from iatrogenic injury to the spinal accessory nerve.

Methods

The clinical presentation and physical examination findings of trapezius palsy have been well characterized, but unfortunately the diagnosis of this condition is oftentimes missed or delayed, sometimes leading to unnecessary surgery on the rotator cuff or tendon of the long head of the biceps.

Results

The diagnosis can be confirmed using electromyography with nerve conduction studies. Although nonoperative treatment may help some patients with temporary neurapraxia of the spinal accessory nerve, nerve repair with or without nerve grafting should be performed soon for patients suspected of a nerve transection. Nerve transfers can be considered within the first year after the injury when nerve repair and grafting cannot be completed. For chronic trapezius palsy, transfer of the levator scapulae and rhomboids has been refined and represents a very successful surgical procedure. Rarely, scapulothoracic arthrodesis is considered for individuals with failed tendon transfers or multiple nerve involvement.

Conclusion

Trapezius palsy is oftentimes missed. An accurate diagnosis allows consideration of various treatment modalities that have been reported to provide good outcomes for properly selected patients.

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.

The phenotypic changes of Schwann cells promote the functional repair of nerve injury

Functional recovery after nerve injury is a significant challenge due to the complex nature of nerve injury repair and the non-regeneration of neurons. Schwann cells (SCs), play a crucial role in the nerve injury repair process because of their high plasticity, secretion, and migration abilities. Upon nerve injury, SCs undergo a phenotypic change and redifferentiate into a repair phenotype, which helps in healing by recruiting phagocytes, removing myelin fragments, promoting axon regeneration, and facilitating myelin formation. However, the repair phenotype can be unstable, limiting the effectiveness of the repair. Recent research has found that transplantation of SCs can be an effective treatment option, therefore, it is essential to comprehend the phenotypic changes of SCs and clarify the related mechanisms to develop the transplantation therapy further.

Growth Factors to Enhance Nerve Regeneration: Approaching Clinical Translation

Following nerve injury, growth factors (GFs) are transiently upregulated in injured neurons, proliferating Schwann cells, and denervated muscle and skin. They act on these same cells and tissues to promote nerve regeneration and end-organ reinnervation. Consequently, much attention has been focused on developing GF-based therapeutics. A major barrier to clinical translation of GFs is their short half-life. To provide sustained GF treatment to the affected nerve, muscle, and skin in a safe and practical manner, engineered drug delivery systems are needed. This review highlights recent advancements in GF-based therapeutics and discusses the remaining hurdles for clinical translation.

Novel Technologies to Address the Lower Motor Neuron Injury and Augment Reconstruction in Spinal Cord Injury

Lower motor neuron (LMN) damage results in denervation of the associated muscle targets and is a significant yet under-appreciated component of spinal cord injury (SCI). Denervated muscle undergoes a progressive degeneration and fibro-fatty infiltration that eventually renders the muscle non-viable unless reinnervated within a limited time window. The distal nerve deprived of axons also undergoes degeneration and fibrosis making it less receptive to axons. In this review, we describe the LMN injury associated with SCI and its clinical consequences. The process of degeneration of the muscle and nerve is broken down into the primary components of the neuromuscular circuit and reviewed, including the nerve and Schwann cells, the neuromuscular junction, and the muscle. Finally, we discuss three promising strategies to reverse denervation atrophy. These include providing surrogate axons from local sources; introducing stem cell-derived spinal motor neurons into the nerve to provide the missing axons; and finally, instituting a training program of high-energy electrical stimulation to directly rehabilitate these muscles. Successful interventions for denervation atrophy would significantly expand reconstructive options for cervical SCI and could be transformative for the predominantly LMN injuries of the conus medullaris and cauda equina.

Comparison of nylon, vicryl, and fibrin glue for nerve grafting in rats

OBJECTIVES

For nerve injuries, not amendable to tensionless epineural coaptation of the nerve, autografts are the preferred treatment. Although absorbable sutures are not recommended for nerve repair, there is no evidence that non-absorbable sutures are superior to absorbable sutures. This study aims to assess the effectiveness of non-absorbable monofilament nylon sutures, absorbable monofilament vicryl sutures, and fibrin glue when used for nerve grafting.

METHODS

Lewis rats (N = 32) were subjected to a sciatic nerve transection and randomly assigned to a group: graft with Nylon, graft with Vicryl, graft with Fibrin Glue, or no graft. Motor function, sensory function, and thermal pain were assessed during a 12-week recovery period, and immunohistochemistry was used to assess macrophage response.

RESULTS

At 12 weeks, the Vicryl and Nylon groups had significantly larger ankle angles at to lift off, which is a measure of motor function, compared to injured controls (p < 0.05). Grafted rats displayed no difference in thermal response but hypersensitivity to mechanical stimuli compared to the uninjured hindlimb. The Nylon, Vicryl, and Fibrin Glue groups all had significantly less atrophy of the gastrocnemius muscle compared to injured controls (p < 0.0001). In the Fibrin Glue group, 3/9 grafts did not incorporate. The Nylon group had significantly less (p = 0.0004) axon growth surrounding the suture holes compared to the Vicryl group. There were no differences in the axon counts, motor neurons, or sensory neurons between all grafted rats.

CONCLUSIONS

These results demonstrate that vicryl sutures work just as well as nylon for nerve recovery after injury and grafting.

Pleiotropic effects of nitric oxide sustained-release system for peripheral nerve repair

The regenerative microenvironment after peripheral nerve injury is imbalanced and difficult to rebalance, which is mainly affected by inflammation, oxidative stress, and inadequate blood supply. The difficulty in remodeling the nerve regeneration microenvironment is the main reason for slow nerve regeneration. Traditional drug treatments have certain limitations, such as difficulty in penetrating the blood-nerve barrier and lack of pleiotropic effects. Therefore, there is an urgent need to build multifunctional nerve grafts that can effectively regulate the regenerative microenvironment and promote nerve regeneration. Nitric oxide (NO), a highly effective gas transmitter with diatomic radicals, is an important regulator of axonal growth and migration, synaptic plasticity, proliferation of neural precursor cells, and neuronal survival. Moreover, NO provides potential anti-inflammation, anti-oxidation, and blood vessel promotion applications. However, excess NO may cause cell death and neuroinflammatory cell damage. The prerequisite for NO treatment of peripheral nerve injury is that it is gradually released over time. In this study, we constructed an injectable NO slow-release system with two main components, including macromolecular NO donor nanoparticles (mPEG-P(MSNO-EG) nanoparticles, NO-NPs) and a carrier for the nanoparticles, mPEG-PA-PP injectable temperature-sensitive hydrogel. Due to the multiple physiological regulation of NO and better physiological barrier penetration, the conduit effectively regulates the inflammatory response and oxidative stress of damaged peripheral nerves, promotes nerve vascularization, and nerve regeneration and docking, accelerating the nerve regeneration process. STATEMENT OF SIGNIFICANCE: The slow regeneration speed of peripheral nerves is mainly due to the destruction of the regeneration microenvironment. Neural conduits with drug delivery capabilities have the potential to improve the microenvironment of nerve regeneration. However, traditional drugs are hindered by the blood nerve barrier and cannot effectively target the injured area. NO, an endogenous gas signaling molecule, can freely cross the blood nerve barrier and act on target cells. However, excessive NO can lead to cell apoptosis. In this study, a NO sustained-release system was constructed to regulate the microenvironment of nerve regeneration through various pathways and promote nerve regeneration.

BDNF-loaded chitosan-based mimetic mussel polymer conduits for repair of peripheral nerve injury

Care for patients with peripheral nerve injury is multifaceted, as traditional methods are not devoid of limitations. Although the utilization of neural conduits shows promise as a therapeutic modality for peripheral nerve injury, its efficacy as a standalone intervention is limited. Hence, there is a pressing need to investigate a composite multifunctional neural conduit as an alternative treatment for peripheral nerve injury. In this study, a BDNF-loaded chitosan-based mimetic mussel polymer conduit was prepared. Its unique adhesion characteristics allow it to be suture-free, improve the microenvironment of the injury site, and have good antibacterial properties. Researchers utilized a rat sciatic nerve injury model to evaluate the progression of nerve regeneration at the 12-week postoperative stage. The findings of this study indicate that the chitosan-based mimetic mussel polymer conduit loaded with BDNF had a substantial positive effect on myelination and axon outgrowth. The observed impact demonstrated a favorable outcome in terms of sciatic nerve regeneration and subsequent functional restoration in rats with a 15-mm gap. Hence, this approach is promising for nerve tissue regeneration during peripheral nerve injury.

Cnicin promotes functional nerve regeneration

BACKGROUND

The limited regenerative capacity of injured axons hinders functional recovery after nerve injury. Although no drugs are currently available in the clinic to accelerate axon regeneration, recent studies show the potential of vasohibin inhibition by parthenolide, produced in Tanacetum parthenium, to accelerate axon regeneration. However, due to its poor oral bioavailability, parthenolide is limited to parenteral administration.

PURPOSE

This study investigates another sesquiterpene lactone, cnicin, produced in Cnicus benedictus for promoting axon regeneration.

RESULTS

Cnicin is equally potent and effective in facilitating nerve regeneration as parthenolide. In culture, cnicin promotes axon growth of sensory and CNS neurons from various species, including humans. Neuronal overexpression of vasohibin increases the effective concentrations comparable to parthenolide, suggesting an interaction between cnicin and vasohibin. Remarkably, intravenous administration of cnicin significantly accelerates functional recovery after severe nerve injury in various species, including the anastomosis of severed nerves. Pharmacokinetic analysis of intravenously applied cnicin shows a blood half-life of 12.7 min and an oral bioavailability of 84.7 % in rats. Oral drug administration promotes axon regeneration and recovery after nerve injury in mice.

CONCLUSION

These results highlight the potential of cnicin as a promising drug to treat axonal insults and improve recovery.

Redesigned Electrodes for Improved Intraoperative Nerve Conduction Studies during the Treatment of Peripheral Nerve Injuries

Traumatic peripheral nerve injuries (PNI), present with symptoms ranging from pain to loss of motor and sensory function. Difficulties in intraoperative visual assessment of nerve functional status necessitate intraoperative nerve conduction studies (INCSs) by neurosurgeons and neurologists to determine the presence of functioning axons in the zone of a PNI. This process, also referred to as nerve "inching", uses a set of stimulating and recording electrode hooks to lift the injured nerve from the surrounding surgical field and to determine whether an electrical stimulus can travel through the zone of injury. However, confounding electrical signal artifacts can arise from the current workflow and electrode design, particularly from the mandatory lifting of the nerve, complicating the definitive assessment of nerve function and neurosurgical treatment decision-making. The objective of this study is to describe the design process and verification testing of our group's newly designed stimulating and recording electrodes that do not require the lifting or displacement of the injured nerve during INCSs. Ergonomic in vivo analysis of the device within a porcine model demonstrated successful intraoperative manipulation of the device, while quantitative nerve action potential (NAP) signal analysis with an ex vivo simulated "inching" procedure on healthy non-human primate nerve tissue demonstrated excellent reproducible recorded NAP fidelity and the absence of NAP signal artifacts at all points of recording. Lastly, electrode pullout force testing determined maximum forces of 0.43 N, 1.57 N, and 3.61 N required to remove the device from 2 mm, 5 mm, and 1 cm nerve models, respectively, which are well within established thresholds for nerve safety. These results suggest that these new electrodes can safely and successfully perform accurate PNI assessment without the presence of artifacts, with the potential to improve the INCS standard of care while remaining compatible with currently used neurosurgical technology, infrastructure, and clinical workflows.