A meta-analysis of functional outcomes in rat sciatic nerve injury models

Electrical stimulation enhances sciatic nerve regeneration using a silk-based conductive scaffold beyond traditional nerve guide conduits

Despite recent advancements in peripheral nerve regeneration, the creation of nerve conduits with chemical and physical cues to enhance glial cell function and support axonal growth remains challenging. This study aimed to assess the impact of electrical stimulation (ES) using a conductive nerve conduit on sciatic nerve regeneration in a rat model with transection injury. The study involved the fabrication of conductive nerve conduits using silk fibroin and Au nanoparticles (AuNPs). Collagen hydrogel loaded with green fluorescent protein (GFP)-positive adipose-derived mesenchymal stem cells (ADSCs) served as the filling for the conduit. Both conductive and non-conductive conduits were applied with and without ES in rat models. Locomotor recovery was assessed using walking track analysis. Histological evaluations were performed using H&E, luxol fast blue staining and immunohistochemistry. Moreover, TEM analysis was conducted to distinguish various ultrastructural aspects of sciatic tissue. In the ES + conductive conduit group, higher S100 (p < 0.0001) and neurofilament (p < 0.001) expression was seen after 6 weeks. Ultrastructural evaluations showed that conductive scaffolds with ES minimized Wallerian degeneration. Furthermore, the conductive conduit with ES group demonstrated significantly increased myelin sheet thickness and decreased G. ratio compared to the autograft. Immunofluorescent images confirmed the presence of GFP-positive ADSCs by the 6th week. Locomotor recovery assessments revealed improved function in the conductive conduit with ES group compared to the control group and groups without ES. These results show that a Silk/AuNPs conduit filled with ADSC-seeded collagen hydrogel can function as a nerve conduit, aiding in the restoration of substantial gaps in the sciatic nerve with ES. Histological and locomotor evaluations indicated that ES had a greater impact on functional recovery compared to using a conductive conduit alone, although the use of conductive conduits did enhance the effects of ES.

Investigation into effects of tocilizumab and epoetin beta in rats with experimental sciatic nerve injury model

OBJECTIVE

To investigate the effects of tocilizumab (TCZ), epoetin beta (EPO), and their combination on nerve regeneration in a sciatic nerve injury model.

MATERIALS AND METHOD

Male Sprague-Dawley rats were divided into (-) negative control, sham, TCZ, EPO ((+) positive control), and TCZ+EPO groups. The TCZ group received TCZ (8 mg/kg intraperitoneal) immediately after surgery. On day 14th, the EPO group received EPO (5000 IU/kg, intraperitoneal); the TCZ+EPO group received TCZ (8 mg/kg, intraperitoneal), EPO (5000 IU/kg, intraperitoneal), and TCZ (8 mg/kg, intraperitoneal) post-surgery. Motor and sensory functions were assessed pre and post-surgery. Lipid peroxidation and oxidative stress parameters were evaluated biochemically in the serum, and sciatic nerve tissue was evaluated histopathologically using haematoxylin-Eosin and Masson trichrome staining.

CONCLUSIONS

TCZ and EPO decreased nerve injury effects by increasing motor and sensory conduction velocities of the sciatic nerve. Biochemically, TCZ and EPO significantly increased Superoxide Dismutase, Catalase, and Glutathione peroxidase 4 levels while decreasing Lipid Peroxidation levels (p=0.001). Histopathologically, neuronal degeneration following nerve injury was decreased in the groups receiving TCZ and EPO (p=0.001). EPO and TCZ attenuate the adverse effects of nerve injury. However, the TCZ+EPO treatment favoured biochemical activities over tissue and functional activities. This has been confirmed functionally, biochemically, and histopathologically.

Spontaneous regeneration after resection of various lengths of hypoglossal nerve in rats

OBJECTIVES

The objective of this study was to investigate spontaneous neural regeneration and functional recovery after resection of various lengths of the hypoglossal (XII) nerve in adult rats.

METHODS

Twelve weeks after XII nerve resection at lengths ranging from 0.0-15.8 mm, the tongue deviation angle of rats was measured to evaluate the severity of paralysis; thereafter, the XII neurons in the XII nucleus were labeled with Fluoro-Gold (FG), which was injected into the tongue to visualize regenerated XII neurons re-innervating the tongue muscles.

RESULTS

In the XII nerve-resected rats, the regenerative rates, that is, the percentage of the total number of FG-positive neurons on the injured side relative to that on the uninjured side, were divided into two groups; the regenerative rates were more than 77% and less than 6%, respectively. Upon comparing the two groups, the boundary resection length was approximately 10.0 mm. Moreover, the former and latter groups demonstrated tongue deviation angles less than or greater than 15°, respectively.

CONCLUSIONS

The critical nerve gap length for spontaneous neural regeneration was approximately 10.0 mm in XII nerve-resected adult rats, and nerve regeneration occurred in both morphological and functional aspects after resection at less than the critical length.

Delayed repair of the facial nerve and its negative impacts on nerve and muscle regeneration

Background

In this experimental protocol, we evaluated the immediate and delayed repair of the buccal branch of the facial nerve (BBFN) with heterologous fibrin biopolymer (HFB) as a coaptation medium and the use of photobiomodulation (PBM), performing functional and histomorphometric analysis of the BBFN and perioral muscles.

Methods

Twenty-eight rats were divided into eight groups using the BBFN bilaterally (the left nerve was used for PBM), namely: G1 - control group, right BBFN (without injury); G2 - control group, left BBFN (without injury + PBM); G3 - Denervated right BBFN (neurotmesis); G4 - Denervated left BBFN (neurotmesis + PBM); G5 - Immediate repair of right BBFN (neurotmesis + HFB); G6 - Immediate repair of left BBFN (neurotmesis + HFB + PBM); G7 - Delayed repair of right BBFN (neurotmesis + HFB); G8 - Delayed repair of left BBFN (neurotmesis + HFB + PBM). Delayed repair occurred after two weeks of denervation. All animals were sacrificed after six weeks postoperatively.

Results

In the parameters of the BBFN, we observed inferior results in the groups with delayed repair, in relation to the groups with immediate repair, with a significant difference (p < 0.05) in the diameter of the nerve fiber, the axon, and the thickness of the myelin sheath of the group with immediate repair with PBM compared to the other experimental groups. In measuring the muscle fiber area, groups G7 (826.4 ± 69.90) and G8 (836.7 ± 96.44) were similar to G5 (882.8 ± 70.51). In the functional analysis, the G7 (4.10 ± 0.07) and G8 (4.12 ± 0.08) groups presented normal parameters.

Conclusion

We demonstrated that delayed repair of BBFN is possible with HFB, but with worse results compared to immediate repair, and that PBM has a positive influence on nerve regeneration results in immediate repair.

The role of kinases in peripheral nerve regeneration: mechanisms and implications

Peripheral nerve injury disease is a prevalent traumatic condition in current medical practice. Despite the present treatment approaches, encompassing surgical sutures, autologous nerve or allograft nerve transplantation, tissue engineering techniques, and others, an effective clinical treatment method still needs to be discovered. Exploring novel treatment methods to improve peripheral nerve regeneration requires more effort in investigating the cellular and molecular mechanisms involved. Many factors are associated with the regeneration of injured peripheral nerves, including the cross-sectional area of the injured nerve, the length of the nerve gap defect, and various cellular and molecular factors such as Schwann cells, inflammation factors, kinases, and growth factors. As crucial mediators of cellular communication, kinases exert regulatory control over numerous signaling cascades, thereby participating in various vital biological processes, including peripheral nerve regeneration after nerve injury. In this review, we examined diverse kinase classifications, distinct nerve injury types, and the intricate mechanisms involved in peripheral nerve regeneration. Then we stressed the significance of kinases in regulating autophagy, inflammatory response, apoptosis, cell cycle, oxidative processes, and other aspects in establishing conductive microenvironments for nerve tissue regeneration. Finally, we briefly discussed the functional roles of kinases in different types of cells involved in peripheral nerve regeneration.

Ultrasonographic Contrast and Therapeutic Effects of Hydrogen Peroxide-Responsive Nanoparticles in a Rat Model with Sciatic Neuritis

Purpose

Peripheral nerve damage lacks an appropriate diagnosis consistent with the patient's symptoms, despite expensive magnetic resonance imaging or electrodiagnostic assessments, which cause discomfort. Ultrasonography is valuable for diagnosing and treating nerve lesions; however, it is unsuitable for detecting small lesions. Poly(vanillin-oxalate) (PVO) nanoparticles are prepared from vanillin, a phytochemical with antioxidant and anti-inflammatory properties. Previously, PVO nanoparticles were cleaved by H2O2 to release vanillin, exert therapeutic efficacy, and generate CO2 to increase ultrasound contrast. However, the role of PVO nanoparticles in peripheral nerve lesion models is still unknown. Herein, we aimed to determine whether PVO nanoparticles can function as contrast and therapeutic agents for nerve lesions.

Methods

To induce sciatic neuritis, rats were administered a perineural injection of carrageenan using a nerve stimulator under ultrasonographic guidance, and PVO nanoparticles were injected perineurally to evaluate ultrasonographic contrast and therapeutic effects. Reverse transcription-quantitative PCR was performed to detect mRNA levels of pro-inflammatory cytokines, ie, tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2.

Results

In the rat model of sciatic neuritis, PVO nanoparticles generated CO2 bubbles to increase ultrasonographic contrast, and a single perineural injection of PVO nanoparticles suppressed the expression of tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2, reduced the expression of F4/80, and increased the expression of GAP43.

Conclusion

The results of the current study suggest that PVO nanoparticles could be developed as ultrasonographic contrast agents and therapeutic agents for nerve lesions.

Functional outcomes of nerve allografts augmented with mesenchymal stem cells and surgical angiogenesis in a rat sciatic nerve defect model

BACKGROUND

Motor function recovery following acellular nerve allograft (ANA) repair remains inferior to autologous nerve reconstruction. We investigated the functional recovery of ANAs after combined mesenchymal stem cell (MSC) delivery and surgical angiogenesis in a rat sciatic nerve defect model.

METHODS

In 100 Lewis rats, unilateral sciatic nerve defects were reconstructed with (I) autografts, (II) ANAs, (III) ANAs wrapped with a superficial inferior epigastric artery fascial (SIEF) flap, combined with either (IV) undifferentiated MSCs or (V) Schwann cell-like differentiated MSCs. The tibialis anterior muscle area was evaluated during the survival period using ultrasonography. Functional recovery, histomorphometry, and immunofluorescence were assessed at 12 and 16 weeks.

RESULTS

At 12 weeks, the addition of surgical angiogenesis and MSCs improved ankle contractures. The SIEF flap also significantly improved compound muscle action potential (CMAP) outcomes compared with ANAs. Autografts outperformed all groups in muscle force and weight. At 16 weeks, ankle contractures of ANAs remained inferior to autografts and SIEF, whereas the CMAP amplitude was comparable between groups. The muscle force of autografts remained superior to all other groups, and the muscle weight of ANAs remained inferior to autografts. No differences were found in histomorphometry outcomes between SIEF groups and ANAs. Vascularity, determined by CD34 staining, was significantly higher in SIEF groups compared with ANAs.

CONCLUSIONS

The combination of surgical angiogenesis and MSCs did not result in a synergistic improvement in functional outcomes. In a short nerve gap model, the adipofascial flap may provide sufficient MSCs to ANAs without additional ex vivo MSC seeding.

Enhancing Functional Recovery after Segmental Nerve Defect Using Nerve Allograft Treated with Plasma-Derived Exosome

BACKGROUND

Nerve injuries can result in detrimental functional outcomes. Currently, autologous nerve graft offers the best outcome for segmental peripheral nerve injury. Allografts are alternatives, but do not have comparable results. This study evaluated whether plasma-derived exosome can improve nerve regeneration and functional recovery when combined with decellularized nerve allografts.

METHODS

The effect of exosomes on Schwann cell proliferation and migration were evaluated. A rat model of sciatic nerve repair was used to evaluate the effect on nerve regeneration and functional recovery. A fibrin sealant was used as the scaffold for exosome. Eighty-four Lewis rats were divided into autograft, allograft, and allograft with exosome groups. Gene expression of nerve regeneration factors was analyzed on postoperative day 7. At 12 and 16 weeks, rats were subjected to maximum isometric tetanic force and compound muscle action potential. Nerve specimens were then analyzed by means of histology and immunohistochemistry.

RESULTS

Exosomes were readily taken up by Schwann cells that resulted in improved Schwann cell viability and migration. The treated allograft group had functional recovery (compound muscle action potential, isometric tetanic force) comparable to that of the autograft group. Similar results were observed in gene expression analysis of nerve regenerating factors. Histologic analysis showed no statistically significant differences between treated allograft and autograft groups in terms of axonal density, fascicular area, and myelin sheath thickness.

CONCLUSIONS

Plasma-derived exosome treatment of decellularized nerve allograft may provide comparable clinical outcomes to that of an autograft. This can be a promising strategy in the future as an alternative for segmental peripheral nerve repair.

CLINICAL RELEVANCE STATEMENT

Off-the-shelf exosomes may improve recovery in nerve allografts.

Development and preclinical evaluation of bioactive nerve conduits for peripheral nerve regeneration: A comparative study

In severe peripheral nerve injuries, nerve conduits (NCs) are good alternatives to autografts/allografts; however, the results the available devices guarantee for are still not fully satisfactory. Herein, differently bioactivated NCs based on the new polymer oxidized polyvinyl alcohol (OxPVA) are compared in a rat model of sciatic nerve neurotmesis (gap: 5 mm; end point: 6 weeks). Thirty Sprague Dawley rats are randomized to 6 groups: Reverse Autograft (RA); Reaxon®; OxPVA; OxPVA + EAK (self-assembling peptide, mechanical incorporation); OxPVA + EAK-YIGSR (mechanical incorporation); OxPVA + Nerve Growth Factor (NGF) (adsorption). Preliminarily, all OxPVA-based devices are comparable with Reaxon® in Sciatic Functional Index score and gait analysis; moreover, all conduits sustain nerve regeneration (S100, β-tubulin) without showing substantial inflammation (CD3, F4/80) evidences. Following morphometric analyses, OxPVA confirms its potential in PNI repair (comparable with Reaxon®) whereas OxPVA + EAK-YIGSR stands out for its myelinated axons total number and density, revealing promising in injury recovery and for future application in clinical practice.

Ultrasound therapy for a week promotes regeneration and reduces pro-inflammatory macrophages in a rat sciatic nerve autograft model

Peripheral nerve injury causes long-term motor dysfunction. Ultrasound (US) therapy is expected to accelerate peripheral nerve regeneration. However, its optimal usage and effects on macrophage phenotypes during peripheral nerve regeneration remain unknown. In this study, we investigated the optimal duration of US therapy and its effects on macrophage phenotype. Twenty-seven rats with autologous sciatic nerve grafting were divided into three groups: two received US therapy (1 MHz frequency, intensity of 140 mW/cm², 20% duty cycle, 5 min/day) for one (US1) or 4 weeks (US4), and one group received sham stimulation. Immunohistochemistry was performed 3 and 7 days after injury in another set of 12 rats. Eight weeks after the injury, the compound muscle action potential amplitude of the gastrocnemius in the US1 and US4 groups was significantly higher than that in the sham group. The toe-spreading test showed functional recovery, whereas the gait pattern during treadmill walking did not recover. There were no significant differences in motor function, histomorphometry, or muscle weight between groups. Immunohistochemistry showed that US therapy decreased the number of pro-inflammatory macrophages seven days after injury. Therefore, US therapy for both one or 4 weeks can similarly promote reinnervation and reduce proinflammatory macrophages in autograft model rats.

Time course of functional recovery after 1 cm sciatic nerve resection in rats with or without surgical intervention - measured by grip strength and locomotor activity

The rat sciatic nerve (SN) is the most frequently used model in experimental research on peripheral nerve injuries. Within the broad range of evaluation methods to determine the experimental outcome, recovery of behavior represents the major criterion to assess functional regeneration. The grasping test indicates when recovery begins and its improvement with time. However, lesions of the SN have yet remained unstudied with this method. Therefore, rats received a SN resection and were divided into experimental groups: 1) control with lesion only, 2) nerve bridge, and 3) autograft. During weekly sessions, the grasping test measured the grip strength, and the locomotor behavior was assessed in the open field. Finally, the nerves were prepared for electrophysiology and histomorphometry. Autograft recovered grasping after 7 weeks with the strongest improvement afterwards. Nerve tube allowed grasping by week 12. Control animals did not recover. In the open field, no differences were observed between the groups. Recordings were possible only in the autograft group, which could be explained by higher number of regenerated fibers. This study indicates that grasping data correspond with physiological and anatomical findings. We conclude that the grasping test is a valid method to evaluate functional recovery after SN resection in rats.

Morphofunctional Improvement of the Facial Nerve and Muscles with Repair Using Heterologous Fibrin Biopolymer and Photobiomodulation

Peripheral nerve injuries impair the patient's functional capacity, including those occurring in the facial nerve, which require effective medical treatment. Thus, we investigated the use of heterologous fibrin biopolymer (HFB) in the repair of the buccal branch of the facial nerve (BBFN) associated with photobiomodulation (PBM), using a low-level laser (LLLT), analyzing the effects on axons, muscles facials, and functional recovery. This experimental study used twenty-one rats randomly divided into three groups of seven animals, using the BBFN bilaterally (the left nerve was used for LLLT): Control group-normal and laser (CGn and CGl); Denervated group-normal and laser (DGn and DGl); Experimental Repair Group-normal and laser (ERGn and ERGl). The photobiomodulation protocol began in the immediate postoperative period and continued for 5 weeks with a weekly application. After 6 weeks of the experiment, the BBFN and the perioral muscles were collected. A significant difference (p < 0.05) was observed in nerve fiber diameter (7.10 ± 0.25 µm and 8.00 ± 0.36 µm, respectively) and axon diameter (3.31 ± 0.19 µm and 4.07 ± 0.27 µm, respectively) between ERGn and ERGl. In the area of muscle fibers, ERGl was similar to GC. In the functional analysis, the ERGn and the ERGI (4.38 ± 0.10) and the ERGI (4.56 ± 0.11) showed parameters of normality. We show that HFB and PBM had positive effects on the morphological and functional stimulation of the buccal branch of the facial nerve, being an alternative and favorable for the regeneration of severe injuries.

Evaluation of peripheral nerve regeneration in Murphy Roths Large mouse strain following transection injury

Aim: Murphy Roths Large (MRL/MpJ) mice have demonstrated the ability to heal with minimal or no scar formation in several tissue types. In order to identify a novel animal model, this study sought to evaluate whether this attribute applies to peripheral nerve regeneration. Materials & methods: This was a two-phase study. 6-week-old male mice were divided into two interventional groups: nerve repair and nerve graft. The MRL/MpJ was compared with the C57BL/6J strain for evaluation of both functional and histological outcomes. Results: MRL/MpJ strain demonstrated superior axon myelination and less scar formation, however functional outcomes did not show significant difference between strains. Conclusion: Superior histological outcomes did not translate into superior peripheral nerve regeneration in MRL/MpJ strain.

The effects of graft source and orientation on outcomes after ablation of a branched peripheral nerve

Segmental peripheral nerve injuries (PNI) are the most common cause of enduring nervous system dysfunction. The peripheral nervous system (PNS) has an extensive and highly branching organization. While much is known about the factors that affect regeneration through sharp bisections and linear ablations of peripheral nerves, very little has been investigated or documented about PNIs that ablate branch points. Such injuries present additional complexity compared to linear segmental defects. This study compared outcomes following ablation of a branch point with branched grafts, specifically examining how graft source and orientation of the branched graft contributed to regeneration. The model system was Lewis rats that underwent a 2.5 cm ablation that started in the sciatic nerve trunk and included the peroneal/tibial branch point. Rats received grafts that were rat sciatic autograft, inbred sciatic allograft, and inbred femoral allograft, each of which was a branched graft of 2.5 cm. Allografts were obtained from Lewis rats, which is an inbred strain. Both branches of the sciatic grafts were mixed motor and sensory while the femoral grafts were smaller in diameter than sciatic grafts and one branch of the femoral graft is sensory and the other motor. All branched grafts were sutured into the defect in two orientations dictated by which branch in the graft was sutured to the tibial vs peroneal stumps in recipients. Outcome measures include compound muscle action potentials (CMAPs) and CatWalk gait analysis throughout the recovery period, with toluidine blue for intrinsic nerve morphometry and retrograde labeling conducted at the 36-week experimental end point. Results indicate that graft source and orientation does play a significant role earlier in the regenerative process but by 36 weeks all groups showed very similar indications of regeneration across multiple outcomes.

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.

The Grasping Test Revisited: A Systematic Review of Functional Recovery in Rat Models of Median Nerve Injury

The rat median nerve model is a well-established and frequently used model for peripheral nerve injury and repair. The grasping test is the gold-standard to evaluate functional recovery in this model. However, no comprehensive review exists to summarize the course of functional recovery in regard to the lesion type. According to PRISMA-guidelines, research was performed, including the databases PubMed and Web of Science. Groups were: (1) crush injury, (2) transection with end-to-end or with (3) end-to-side coaptation and (4) isogenic or acellular allogenic grafting. Total and respective number, as well as rat strain, type of nerve defect, length of isogenic or acellular allogenic allografts, time at first signs of motor recovery (FSR) and maximal recovery grasping strength (MRGS), were evaluated. In total, 47 articles met the inclusion criteria. Group I showed earliest signs of motor recovery. Slow recovery was observable in group III and in graft length above 25 mm. Isografts recovered faster compared to other grafts. The onset and course of recovery is heavily dependent from the type of nerve injury. The grasping test should be used complementary in addition to other volitional and non-volitional tests. Repetitive examinations should be planned carefully to optimize assessment of valid and reliable data.

Implantable Biomaterials for Peripheral Nerve Regeneration–Technology Trends and Translational Tribulations

The use of autografted nerve in surgical repair of peripheral nerve injuries (PNI) is severely limited due to donor site morbidity and restricted tissue availability. As an alternative, synthetic nerve guidance channels (NGCs) are available on the market for surgical nerve repair, but they fail to promote nerve regeneration across larger critical gap nerve injuries. Therefore, such injuries remain unaddressed, result in poor healing outcomes and are a limiting factor in limb reconstruction and transplantation. On the other hand, a myriad of advanced biomaterial strategies to address critical nerve injuries are proposed in preclinical literature but only few of those have found their way into clinical practice. The design of synthetic nerve grafts should follow rational criteria and make use of a combination of bioinstructive cues to actively promote nerve regeneration. To identify the most promising NGC designs for translation into applicable products, thorough mode of action studies, standardized readouts and validation in large animals are needed. We identify design criteria for NGC fabrication according to the current state of research, give a broad overview of bioactive and functionalized biomaterials and highlight emerging composite implant strategies using therapeutic cells, soluble factors, structural features and intrinsically conductive substrates. Finally, we discuss translational progress in bioartificial conduits for nerve repair from the surgeon’s perspective and give an outlook toward future challenges in the field.

A Combined Conduit-Bioactive Hydrogel Approach for Regeneration of Transected Sciatic Nerves

Transected peripheral nerve injury (PNI) affects the quality of life of patients, which leads to socioeconomic burden. Despite the existence of autografts and commercially available nerve guidance conduits (NGCs), the complexity of peripheral nerve regeneration requires further research in bioengineered NGCs to improve surgical outcomes. In this work, we introduce multidomain peptide (MDP) hydrogels, as intraluminal fillers, into electrospun poly(ε-caprolactone) (PCL) conduits to bridge 10 mm rat sciatic nerve defects. The efficacy of treatment groups was evaluated by electromyography and gait analysis to determine their electrical and motor recovery. We then studied the samples' histomorphometry with immunofluorescence staining and automatic axon counting/measurement software. Comparison with negative control group shows that PCL conduits filled with an anionic MDP may improve functional recovery 16 weeks postoperation, displaying higher amplitude of compound muscle action potential, greater gastrocnemius muscle weight retention, and earlier occurrence of flexion contracture. In contrast, PCL conduits filled with a cationic MDP showed the least degree of myelination and poor functional recovery. This phenomenon may be attributed to MDPs' difference in degradation time. Electrospun PCL conduits filled with an anionic MDP may become an attractive tissue engineering strategy for treating transected PNI when supplemented with other bioactive modifications.

Histomorphometry in Peripheral Nerve Regeneration: Comparison of Different Axon Counting Methods

BACKGROUND

Histomorphometry quantitatively evaluates nerve regeneration. Total myelinated fiber count (TMFC) is most accurately obtained manually across full nerve cross-sections, but most researchers opt for automated, sampled analysis. Few of the numerous techniques available have been validated. The goal of this study was to compare common histomorphometric methods (full manual [FM], sampled manual [SM], and sampled automatic [SA]) to determine their reliability and consistency.

MATERIAL AND METHODS

Twenty-four rats underwent sciatic nerve (SN) repair with 20mm isografts; SNs distal to the graft were analyzed. TMFC was manually determined in each full cross-section. Counts were also extrapolated from sampled fields, both manually and automatically with ImageJ software. Myelinated fiber diameter, axon diameter, and myelin sheath thickness were measured manually in full and sampled fields; G-ratio was calculated. Repeated-measures MANOVA, Spearman correlation, and Wilcoxon signed-rank tests were performed. A systematic review of histomorphometry in rat SN repair was performed to analyze the variability of techniques in the literature.

RESULTS

FM TMFC was 13,506 ± 4,217. Both sampled methods yielded significantly different TMFCs (SM:14.4 ± 13.4%, P< 0.001; SA:21.8 ± 44.7%, P = 0.037). All three methods strongly correlated with each other, especially FM and SM (r_s = 0.912, P< 0.001). FM fiber diameter, axon diameter, and myelin sheath thickness did not differ from SM (P = 0.493, 0.209, and 0.331, respectively). 65% of papers used sampling; 78% utilized automated or semi-automated analysis. Software, sampling, and histomorphometric parameters varied widely.

CONCLUSION

SM and SA analysis are reliable with standardized, systematic sampling. Transparency is essential to allow comparison of data; meanwhile, researchers must be cognizant of the wide variety of methodologies in the literature.