Superior muscle reinnervation after autologous nerve graft or poly-L-lactide-epsilon-caprolactone (PLC) tube implantation in comparison to silicone tube repair

Beyond the limiting gap length: peripheral nerve regeneration through implantable nerve guidance conduits

Peripheral nerve damage results in the loss of sensorimotor and autonomic functions, which is a significant burden to patients. Furthermore, nerve injuries greater than the limiting gap length require surgical repair. Although autografts are the preferred clinical choice, their usage is impeded by their limited availability, dimensional mismatch, and the sacrifice of another functional donor nerve. Accordingly, nerve guidance conduits, which are tubular scaffolds engineered to provide a biomimetic environment for nerve regeneration, have emerged as alternatives to autografts. Consequently, a few nerve guidance conduits have received clinical approval for the repair of short-mid nerve gaps but failed to regenerate limiting gap damage, which represents the bottleneck of this technology. Thus, it is still necessary to optimize the morphology and constituent materials of conduits. This review summarizes the recent advances in nerve conduit technology. Several manufacturing techniques and conduit designs are discussed, with emphasis on the structural improvement of simple hollow tubes, additive manufacturing techniques, and decellularized grafts. The main objective of this review is to provide a critical overview of nerve guidance conduit technology to support regeneration in long nerve defects, promote future developments, and speed up its clinical translation as a reliable alternative to autografts.

Treadmill training of rats after sciatic nerve graft does not alter accuracy of muscle reinnervation

Background and purpose

After peripheral nerve lesions, surgical reconstruction facilitates axonal regeneration and motor reinnervation. However, functional recovery is impaired by aberrant reinnervation.

Materials and methods

We tested whether training therapy by treadmill exercise (9 × 250 m/week) before (run-idle), after (idle-run), or both before and after (run-run) sciatic nerve graft improves the accuracy of reinnervation in rats. Female Lewis rats (LEW/SsNHsd) were either trained for 12 weeks (run) or not trained (kept under control conditions, idle). The right sciatic nerves were then excised and reconstructed with 5 mm of a congenic allograft. One week later, training started in the run-run and idle-run groups for another 12 weeks. No further training was conducted in the run-idle and idle-idle groups. Reinnervation was measured using the following parameters: counting of retrogradely labeled motoneurons, walking track analysis, and compound muscle action potential (CMAP) recordings.

Results

In intact rats, the common fibular (peroneal) and the soleus nerve received axons from 549 ± 83 motoneurons. In the run-idle group, 94% of these motoneurons had regenerated 13 weeks after the nerve graft. In the idle-run group, 81% of the normal number of motoneurons had regenerated into the denervated musculature and 87% in both run-run and idle-idle groups. Despite reinnervation, functional outcome was poor: walking tracks indicated no functional improvement of motion in any group. However, in the operated hindlimb of run-idle rats, the CMAP of the soleus muscle reached 11.9 mV (normal 16.3 mV), yet only 6.3-8.1 mV in the other groups.

Conclusion

Treadmill training neither altered the accuracy of reinnervation nor the functional recovery, and pre-operative training (run-idle) led to a higher motor unit activation after regeneration.

Engineered neural tissue made using clinical-grade human neural stem cells supports regeneration in a long gap peripheral nerve injury model

A surgical autograft remains the clinical gold-standard therapy for gap repair following peripheral nerve injury, however, challenges remain with achieving full recovery and reducing donor-site morbidity. Engineered Neural Tissue (EngNT) manufactured using differentiated CTX0E03 human stem cells (EngNT-CTX) has been developed as a potential 'off the shelf' allogeneic autograft replacement. Ensheathed within a collagen membrane developed to facilitate biomechanical integration, EngNT-CTX was used to bridge a critical-length (15 mm) sciatic nerve gap injury in athymic nude rats. The effectiveness of EngNT-CTX was compared to an autograft using outcome measures that assessed neuronal regeneration and functional recovery at 8 and 16 weeks. At both time points EngNT-CTX restored electrophysiological nerve conduction and functional reinnervation of downstream muscles to the same extent as the autograft. Histological analysis confirmed that more motor neurons had successfully regenerated through the repair in EngNT-CTX in comparison to the autograft at 8 weeks, which was consistent with the electrophysiology, with the number of motor neurons similar in both groups by 16 weeks. The total number of neurons (motor + sensory) was greater in autografts than EngNT-CTX at 8 weeks, indicating that more sensory fibres may have sprouted in those animals at this time point. In conclusion, this study provides evidence to support the effectiveness of EngNT-CTX as a replacement for the nerve autograft, as the functional regeneration assessed through histological and electrophysiological outcome measures demonstrated equivalent performance. STATEMENT OF SIGNIFICANCE: Following injury a peripheral nerve has the capacity to regenerate naturally, however, in the case of severe damage where there is a gap the current gold-standard microsurgical intervention is an autograft. This is associated with serious limitations including tissue availability and donor-site morbidity. Tissue engineering aims to overcome these limitations by building a construct from therapeutic cells and biomaterials as a means to mimic and replace the autograft. In this study engineered neural tissue (EngNT) was manufactured using human stem cells (CTX) to bridge a critical-length gap injury. When compared to the autograft in an animal model the EngNT-CTX construct restored function to an equivalent or greater extent.

All-Polymer Printed Low-Cost Regenerative Nerve Cuff Electrodes

Neural regeneration after lesions is still limited by several factors and new technologies are developed to address this issue. Here, we present and test in animal models a new regenerative nerve cuff electrode (RnCE). It is based on a novel low-cost fabrication strategy, called "Print and Shrink", which combines the inkjet printing of a conducting polymer with a heat-shrinkable polymer substrate for the development of a bioelectronic interface. This method allows to produce miniaturized regenerative cuff electrodes without the use of cleanroom facilities and vacuum based deposition methods, thus highly reducing the production costs. To fully proof the electrodes performance in vivo we assessed functional recovery and adequacy to support axonal regeneration after section of rat sciatic nerves and repair with RnCE. We investigated the possibility to stimulate the nerve to activate different muscles, both in acute and chronic scenarios. Three months after implantation, RnCEs were able to stimulate regenerated motor axons and induce a muscular response. The capability to produce fully-transparent nerve interfaces provided with polymeric microelectrodes through a cost-effective manufacturing process is an unexplored approach in neuroprosthesis field. Our findings pave the way to the development of new and more usable technologies for nerve regeneration and neuromodulation.

Modification of tubular chitosan-based peripheral nerve implants: applications for simple or more complex approaches

Surgical treatment of peripheral nerve injuries is still a major challenge in human clinic. Up to now, none of the well-developed microsurgical treatment options is able to guarantee a complete restoration of nerve function. This restriction is also effective for novel clinically approved artificial nerve guides. In this review, we compare surgical repair techniques primarily for digital nerve injuries reported with relatively high prevalence to be valuable attempts in clinical digital nerve repair and point out their advantages and shortcomings. We furthermore discuss the use of artificial nerve grafts with a focus on chitosan-based nerve guides, for which our own studies contributed to their approval for clinical use. In the second part of this review, very recent future perspectives for the enhancement of tubular (commonly hollow) nerve guides are discussed in terms of their clinical translatability and ability to form three-dimensional constructs that biomimick the natural nerve structure. This includes materials that have already shown their beneficial potential in in vivo studies like fibrous intraluminal guidance structures, hydrogels, growth factors, and approaches of cell transplantation. Additionally, we highlight upcoming future perspectives comprising co-application of stem cell secretome. From our overview, we conclude that already simple attempts are highly effective to increase the regeneration supporting properties of nerve guides in experimental studies. But for bringing nerve repair with bioartificial nerve grafts to the next level, e.g. repair of defects > 3 cm in human patients, more complex intraluminal guidance structures such as innovatively manufactured hydrogels and likely supplementation of stem cells or their secretome for therapeutic purposes may represent promising future perspectives.

Efficacy evaluation of personalized coaptation in neurotization for motor deficit after peripheral nerve injury: A systematic review and meta-analysis

INTRODUCTION

Peripheral neurotization, recently as a promising approach, has taken effect in recovering motor function after damage to a peripheral nerve root. Neural anastomosis comprised of nerve conduit and neurorrhaphy participates in the nerve reconstruction. Current literature lacks evidence supporting an individualized coaptation for rescue of locomotor loss in rat subjects with paraplegia secondary to peripheral nerve injury (PNI).

METHODS

This meta-analysis intends to qualify the specificity of gap-specific coaptation in treating a paralyzed limb following PNI. We used a highly sensitive search strategy to identify all published studies in multiple databases up to 1 May 2019. All identified trials were systematically evaluated using specific inclusion and exclusion criteria. Cochrane methodology was also applied to the results of this study.

RESULTS

Twelve studies, including 349 rat subjects, met eligibility criteria. For a medium nerve defect (0.5-3.0 cm), nerve conduit was more likely than neurorrhaphy to precipitate axon regeneration and improve motor outcome of the hemiplegic limb (OR = 3.61, 95% CI = 1.80, 7.26, p < .0003) at 3-month follow-up, whereas neurorrhaphy might take its place in promoting limb motor function in a small nerve gap (<0.5 cm) (OR = 0.48, 95% CI = 0.22, 1.07, p < .007). For a small nerve defect, nerve conduit still demonstrated visible effectiveness in recovery of limb motion albeit poorer than neurorrhaphy (OR = 1.50, 95% CI = 0.92, 2.47, p < .05).

CONCLUSION

Selective neurotization facilitates motor regeneration after nerve transection, and advisable choice of neural coaptation can maximize functional outcome on an individual basis.

Two-Chambered Chitosan Nerve Guides With Increased Bendability Support Recovery of Skilled Forelimb Reaching Similar to Autologous Nerve Grafts in the Rat 10 mm Median Nerve Injury and Repair Model

Tension-free surgical reconstruction of transected digital nerves in humans is regularly performed using autologous nerve grafts (ANGs) or bioartificial nerve grafts. Nerve grafts with increased bendability are needed to protect regenerating nerves in highly mobile extremity parts. We have recently demonstrated increased bendability and regeneration supporting properties of chitosan nerve guides with a corrugated outer wall (corrCNGs) in the common rat sciatic nerve model (model of low mobility). Here, we further modified the hollow corrCNGs into two-chambered nerve guides by inserting a perforated longitudinal chitosan-film (corrCNG[F]s) and comprehensively monitored functional recovery in the advanced rat median nerve model. In 16 adult female Lewis rats, we bilaterally reconstructed 10 mm median nerve gaps with either ANGs, standard chitosan nerve guides (CNGs), CNGs (CNG[F]s), or corrCNG[F]s (n = 8, per group). Over 16 weeks, functional recovery of each forelimb was separately surveyed using the grasping test (reflex-based motor task), the staircase test (skilled forelimb reaching task), and non-invasive electrophysiological recordings from the thenar muscles. Finally, regenerated tissue harvested from the distal part of the nerve grafts was paraffin-embedded and cross-sections were analyzed regarding the number of Neurofilament 200-immunopositive axons and the area of newly formed blood vessels. Nerve tissue harvested distal to the grafts was epon-embedded and semi-thin cross-sections underwent morphometrical analyses (e.g., number of myelinated axons, axon and fiber diameters, and myelin thicknesses). Functional recovery was fastest and most complete in the ANG group (100% recovery rate regarding all parameters), but corrCNG[F]s accelerated the recovery of all functions evaluated in comparison to the other nerve guides investigated. Furthermore, corrCNG[F]s supported recovery of reflex-based grasping (87.5%) and skilled forelimb reaching (100%) to eventually significantly higher rates than the other nerve guides (grasping test: CNGs: 75%, CNG[F]s: 62.5%; staircase test: CNGs: 66.7%, CNG[F]s: 83.3%). Histological and nerve morphometrical evaluations, in accordance to the functional results, demonstrated best outcome in the ANG group and highest myelin thicknesses in the corrCNG[F] group compared to the CNG and CNG[F] groups. We thus clearly demonstrate that corrCNG[F]s represent promising innovative nerve grafts for nerve repair in mobile body parts such as digits.

Synthetic bioresorbable poly-α-hydroxyesters as peripheral nerve guidance conduits; a review of material properties, design strategies and their efficacy to date

Implantable tubular devices known as nerve guidance conduits (NGCs) have drawn considerable interest as an alternative to autografting in the repair of peripheral nerve injuries.

An allogeneic 'off the shelf' therapeutic strategy for peripheral nerve tissue engineering using clinical grade human neural stem cells

Artificial tissues constructed from therapeutic cells offer a promising approach for improving the treatment of severe peripheral nerve injuries. In this study the effectiveness of using CTX0E03, a conditionally immortalised human neural stem cell line, as a source of allogeneic cells for constructing living artificial nerve repair tissue was tested. CTX0E03 cells were differentiated then combined with collagen to form engineered neural tissue (EngNT-CTX), stable aligned sheets of cellular hydrogel. EngNT-CTX sheets were delivered within collagen tubes to repair a 12 mm sciatic nerve injury model in athymic nude rats. Autologous nerve grafts (autografts) and empty tubes were used for comparison. After 8 weeks functional repair was assessed using electrophysiology. Further, detailed histological and electron microscopic analysis of the repaired nerves was performed. Results indicated that EngNT-CTX supported growth of neurites and vasculature through the injury site and facilitated reinnervation of the target muscle. These findings indicate for the first time that a clinically validated allogeneic neural stem cell line can be used to construct EngNT. This provides a potential 'off the shelf' tissue engineering solution for the treatment of nerve injury, overcoming the limitations associated with nerve autografts or the reliance on autologous cells for populating repair constructs.

Segregation of motor and sensory axons regenerating through bicompartmental tubes by combining extracellular matrix components with neurotrophic factors

Segregation of regenerating motor and sensory axons may be a good strategy to improve selective functionality of regenerative interfaces to provide closed-loop commands. Provided that extracellular matrix components and neurotrophic factors exert guidance effects on different neuronal populations, we assessed in vivo the potential of separating sensory and motor axons regenerating in a bicompartmental Y-type tube, with each branch prefilled with an adequate combination of extracellular matrix and neurotrophic factors. The severed rat sciatic nerve was repaired using a bicompartmental tube filled with a collagen matrix enriched with fibronectin (FN) and brain-derived neurotrophic factor (BDNF) encapsulated in poly-lactic co-glycolic acid microspheres (FN + MP.BDNF) in one compartment to preferentially attract motor axons and collagen enriched with laminin (LM) and nerve growth factor (NGF) and neurotrophin-3 (NT-3) in microspheres (LM + MP.NGF/NT-3) in the other compartment for promoting sensory axons regeneration. Control animals were implanted with the same Y-tube with a collagen matrix with microspheres (MP) containing PBS (Col + MP.PBS). By using retrotracer labelling, we found that LM + MP.NGF/NT-3 did not attract higher number of regenerated sensory axons compared with controls, and no differences were observed in sensory functional recovery. However, FN + MP.BDNF guided a higher number of regenerating motor axons compared with controls, improving also motor recovery. A small proportion of sensory axons with large soma size, likely proprioceptive neurons, was also attracted to the FN + MP.BDNF compartment. These results demonstrate that muscular axonal guidance can be modulated in vivo by the addition of fibronectin and BDNF.

PEOT/PBT Guides Enhance Nerve Regeneration in Long Gap Defects

Development of new nerve guides is required for replacing autologous nerve grafts for the repair of long gap defects after nerve injury. A nerve guide comprised only of electrospun fibers able to bridge a critical (15 mm) nerve gap in a rat animal model is reported for the first time. The nerve conduits are made of poly(ethylene oxide terephthalate) and poly(butylene terephthalate) (PEOT/PBT), a biocompatible copolymer composed of alternating amorphous, hydrophilic poly(ethylene oxide terephthalate), and crystalline, hydrophobic poly(butylene terephthalate) segments. These guides show suitable mechanical properties, high porosity, and fibers aligned in the longitudinal axis of the guide. In vitro studies show that both neurites and Schwann cells exhibit growth alignment with PA fibers. In vivo studies reveal that, after rat sciatic nerve transection and repair with PEOT/PBT guides, axons grow occupying a larger area compared to silicone tubes. Moreover, after repair of limiting (10 mm) and critical (15 mm) nerve gaps, PEOT/PBT guides significantly increase the percentage of regenerated nerves, the number of regenerated myelinated axons, and improve motor, sensory, and autonomic reinnervation in both gaps. This nerve conduit design combines the properties of PEOT/PBT with electrospun structure, demonstrating that nerve regeneration through long gaps can be achieved through the design of instructive biomaterial constructs.

Preferential Enhancement of Sensory and Motor Axon Regeneration by Combining Extracellular Matrix Components with Neurotrophic Factors

After peripheral nerve injury, motor and sensory axons are able to regenerate but inaccuracy of target reinnervation leads to poor functional recovery. Extracellular matrix (ECM) components and neurotrophic factors (NTFs) exert their effect on different neuronal populations creating a suitable environment to promote axonal growth. Here, we assessed in vitro and in vivo the selective effects of combining different ECM components with NTFs on motor and sensory axons regeneration and target reinnervation. Organotypic cultures with collagen, laminin and nerve growth factor (NGF)/neurotrophin-3 (NT3) or collagen, fibronectin and brain-derived neurotrophic factor (BDNF) selectively enhanced sensory neurite outgrowth of DRG neurons and motor neurite outgrowth from spinal cord slices respectively. For in vivo studies, the rat sciatic nerve was transected and repaired with a silicone tube filled with a collagen and laminin matrix with NGF/NT3 encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres (MP) (LM + MP.NGF/NT3), or a collagen and fibronectin matrix with BDNF in PLGA MPs (FN + MP.BDNF). Retrograde labeling and functional tests showed that LM + MP.NGF/NT3 increased the number of regenerated sensory neurons and improved sensory functional recovery, whereas FN + MP.BDNF preferentially increased regenerated motoneurons and enhanced motor functional recovery. Therefore, combination of ECM molecules with NTFs may be a good approach to selectively enhance motor and sensory axons regeneration and promote appropriate target reinnervation.

Experimental immunological demyelination enhances regeneration in autograft-repaired long peripheral nerve gaps

Peripheral nerve long gap defects are a clinical challenge in the regeneration field. Despite the wide variety of surgical techniques and therapies, autografting is the "gold standard" for peripheral nerve gap reconstruction. The pathological process of Wallerian degeneration from the time of acute injury to efficient regeneration requires several weeks. Regeneration time is critical for nerve reconstruction. Immunological demyelination induced by anti-galactocerebroside antibodies plus guinea pig complement was used to shorten the treatment time. Based on an antigen-antibody complex reaction, the demyelinating agent induced an acute and severe demyelination, leading to the pathological process of Wallerian degeneration during the demyelinating period. This method was used to treat a 12 mm-long sciatic nerve defect in rats. The control groups were injected with one of the demyelinating agent components. The results indicated that anti-galactocerebroside antibodies plus guinea pig complement can significantly shorten treatment time and promote nerve regeneration and functional recovery. In addition, the demyelinating agent can increase the mRNA levels of nerve growth factors and can regulate inflammation. In conclusion, treatment with anti-galactocerebroside antibodies plus guinea pig complement can promote axonal regeneration. This therapy provides a novel method to improve functional recovery in the treatment of long nerve defects.

Functional evaluation of peripheral nerve regeneration and target reinnervation in animal models: a critical overview

Peripheral nerve injuries usually lead to severe loss of motor, sensory and autonomic functions in the patients. Due to the complex requirements for adequate axonal regeneration, functional recovery is often poorly achieved. Experimental models are useful to investigate the mechanisms related to axonal regeneration and tissue reinnervation, and to test new therapeutic strategies to improve functional recovery. Therefore, objective and reliable evaluation methods should be applied for the assessment of regeneration and function restitution after nerve injury in animal models. This review gives an overview of the most useful methods to assess nerve regeneration, target reinnervation and recovery of complex sensory and motor functions, their values and limitations. The selection of methods has to be adequate to the main objective of the research study, either enhancement of axonal regeneration, improving regeneration and reinnervation of target organs by different types of nerve fibres, or increasing recovery of complex sensory and motor functions. It is generally recommended to use more than one functional method for each purpose, and also to perform morphological studies of the injured nerve and the reinnervated targets.

Peripheral nerve repair: a hot spot analysis on treatment methods from 2010 to 2014

Therapeutic strategies for neurological deficits and for promoting nerve regeneration after peripheral nerve injuries have received much focus in clinical research. Advances in basic research in recent years have increased our understanding of the anatomy of peripheral nerves and the importance of the microenvironment. Various new intervention methods have been developed, but with varying effectiveness. In the present study, we selected 911 papers on different repair methods for peripheral nerve injury from the Web of Science and indexed in the Science Citation Index from 2010 to 2014. We quantitatively examine new repair methods and strategies using bibliometrics, and we discuss the present state of knowledge and the problems and prospects of various repair methods, including nerve transfer, neural transplantation, tissue engineering and genetic engineering. Our findings should help in the study and development of repair methods for peripheral nerve injury.

A consistent, quantifiable, and graded rat lumbosacral spinal cord injury model

The purpose of this study is to develop a rat lumbosacral spinal cord injury (SCI) model that causes consistent motoneuronal loss and behavior deficits. Most SCI models focus on the thoracic or cervical spinal cord. Lumbosacral SCI accounts for about one third of human SCI but no standardized lumbosacral model is available for evaluating therapies. Twenty-six adult female Sprague-Dawley rats were randomized to three groups: sham (n=9), 25 mm (n=8), and 50 mm (n=9). Sham rats had laminectomy only, while 25 mm and 50 mm rats were injured by dropping a 10 g rod from a height of 25 mm or 50 mm, respectively, onto the L4-5 spinal cord at the T13/L1 vertebral junction. We measured footprint length (FL), toe spreading (TS), intermediate toe spreading (ITS), and sciatic function index (SFI) from walking footprints, and static toe spreading (STS), static intermediate toe spreading (SITS), and static sciatic index (SSI) from standing footprints. At six weeks, we assessed neuronal and white matter loss, quantified axons, diameter, and myelin thickness in the peroneal and tibial nerves, and measured cross-sectional areas of tibialis anterior and gastrocnemius muscle fibers. The result shows that peroneal and tibial motoneurons were respectively distributed in 4.71 mm and 5.01 mm columns in the spinal cord. Dropping a 10-g weight from 25 mm or 50 mm caused 1.5 mm or 3.75 mm gaps in peroneal and tibial motoneuronal columns, respectively, and increased spinal cord white matter loss. Fifty millimeter contusions significantly increased FL and reduced TS, ITS, STS, SITS, SFI, and SSI more than 25 mm contusions, and resulted in smaller axon and myelinated axon diameters in tibial and peroneal nerves and greater atrophy of gastrocnemius and anterior tibialis muscles, than 25 mm contusions. This model of lumbosacral SCI produces consistent and graded loss of white matter, motoneuronal loss, peripheral nerve axonal changes, and anterior tibialis and gastrocnemius muscles atrophy in rats.

The development of a normalization method for comparing nerve regeneration effectiveness among different graft types

The inability to compare directly different nerve grafts has been a significant factor hindering the advance of nerve graft development. Due to the abundance of variables that exist in nerve graft construction and multiple assessment types, there has been limited success in comparing nerve graft effectiveness among experiments. Using mathematical techniques on nerve conduction velocity (NCV) autograft data, a normalization function was empirically derived that normalizes differences in gap lengths. Further analysis allowed for the development of the relative regeneration ratio (RRR). The RRR function allows researchers to directly compare nerve graft results based on the NCV data from their respective studies as long as the data was collected at the same post-operation time. This function also allows for comparisons between grafts tested at different gap lengths. Initial testing of this RRR function provided confidence that the function is accurate for a continuum of gap lengths and different nerve graft types.

Biofabrication and testing of a fully cellular nerve graft

Rupture of a nerve is a debilitating injury with devastating consequences for the individual's quality of life. The gold standard of repair is the use of an autologous graft to bridge the severed nerve ends. Such repair however involves risks due to secondary surgery at the donor site and may result in morbidity and infection. Thus the clinical approach to repair often involves non-cellular solutions, grafts composed of synthetic or natural materials. Here we report on a novel approach to biofabricate fully biological grafts composed exclusively of cells and cell secreted material. To reproducibly and reliably build such grafts of composite geometry we use bioprinting. We test our grafts in a rat sciatic nerve injury model for both motor and sensory function. In particular we compare the regenerative capacity of the biofabricated grafts with that of autologous grafts and grafts made of hollow collagen tubes by measuring the compound action potential (for motor function) and the change in mean arterial blood pressure as consequence of electrically eliciting the somatic pressor reflex. Our results provide evidence that bioprinting is a promising approach to nerve graft fabrication and as a consequence to nerve regeneration.

In vitro and in vivo degradation of non-woven materials made of poly(ε-caprolactone) nanofibers prepared by electrospinning under different conditions

The aim of this study was to prepare non-woven materials from a biodegradable polymer, poly(epsilon-caprolactone) (PCL) by electrospinning. PCL was synthesized by ring-opening polymerization of epsilon-caprolactone in bulk using stannous octoate as the catalyst under nitrogen atmosphere. PCL was then processed into non-woven matrices composed of nanofibers by electrospinning of the polymer from its solution using a high voltage power supply. The effects of PCL concentration, composition of the solvent (a mixture of chloroform and DMF with different DMF content), applied voltage and tip-collector distance on fiber diameter and morphology were investigated. The diameter of fibers increased with the increase in the polymer concentration and decrease in the DMF content significantly. Applied voltage and tip-collector distance were found critical to control 'bead' formation. Elongation-at-break, ultimate strength and Young's modulus were obtained from the mechanical tests, which were all increased by increasing fiber diameter. The fiber diameter significantly influenced both in vitro degradation (performed in Ringer solution) and in vivo biodegradation (conducted in rats) rates. In vivo degradation was found to be faster than in vitro. Electrospun membranes were more hydrophobic than PCL solvent-casted ones; therefore, their degradation was a much slower process.

Joint use of a chitosan/PLGA scaffold and MSCs to bridge an extra large gap in dog sciatic nerve

BACKGROUND

Tissue-engineered nerve grafts (TENGs) constitute a promising alternative to nerve autografts that are recognized as the gold standard for surgical repair of peripheral nerve gaps.

OBJECTIVE

To investigate the feasibility of using TENGs for bridging extra large peripheral nerve gaps in large animals.

METHODS

TENGs were constructed by incorporating autologous bone marrow mesenchymal stem cells (MSCs) into a neural scaffold that consisted of a chitosan conduit inserted with poly(lactic-co-glycolic acid) (PLGA) fibers. A 60-mm-long sciatic nerve gap in dogs was bridged by TENGs, chitosan/PLGA scaffolds, or nerve autografts. At 12 months postsurgery, behavioral analysis, electrophysiology, retrograde fluorogold tracing, and histological examination were performed.

RESULTS

The outcomes of TENGs were similar to those of autografts and better than those of scaffolds alone.

CONCLUSION

Introduction of autologous MSCs to a chitosan/PLGA scaffold improved the repair and rehabilitation of a large gap after peripheral nerve injury in dogs. Autologous MSCs may be a source of support cells for neural tissue engineering.

Repair of rat sciatic nerve gap by a silk fibroin-based scaffold added with bone marrow mesenchymal stem cells

Tissue-engineered nerve grafts (TENGs), typically consisting of a neural scaffold included with support cells and/or growth factors, represent a promising alternative to autologous nerve grafts for surgical repair of large peripheral nerve gaps. Here, we developed a new design of TENGs by introducing bone marrow mesenchymal stem cells (MSCs) of rats, as support cells, into a silk fibroin (SF)-based scaffold, which was composed of an SF nerve guidance conduit and oriented SF filaments as the conduit lumen filler. The biomaterial SF had been tested to possess good biocompatibility and noncytoxicity with MSCs before the TENG was implanted to bridge a 10-mm-long gap in rat sciatic nerve. Functional and histological assessments showed that at 12 weeks after nerve grafting, TENGs yielded an improved outcome of nerve regeneration and functional recovery, which was better than that achieved by SF scaffolds and close to that by autologous nerve grafts. During 1-4 weeks after nerve grafting, MSCs contained in the TENG significantly accelerated axonal growth, displaying a positive reaction to S-100 (a Schwann cell marker). During 1-3 weeks after nerve grafting, MSCs contained in the TENG led to gene expression upregulation of S100 and several growth factors (brain-derived neurotrophic factor, ciliary neurotrophic factor, and basic fibroblast growth factor). These results suggest that the cell behaviors and neurotrophic functions of MSCs might be responsible for their promoting effects on peripheral nerve regeneration.

Passive and active exercise improve regeneration and muscle reinnervation after peripheral nerve injury in the rat

INTRODUCTION

Lesions of peripheral nerves cause loss of motor and sensory function and also lead to hyperreflexia and hyperalgesia. Activity-dependent therapies promote axonal regeneration and functional recovery and may improve sensory-motor coordination and restoration of adequate circuitry at the spinal level.

METHODS

We compared the effects of passive (bicycle) and active (treadmill) exercise on nerve regeneration and modulation of the spinal H reflex after transection and repair of the rat sciatic nerve. Animals were evaluated during 2 months using electrophysiological, functional, and histological methods.

RESULTS

Moderate exercise for 1 hour/day, either active treadmill walking or passive cycling, improved muscle reinnervation, increased the number of regenerated axons in the distal nerve, and reduced the increased excitability of spinal reflexes after nerve lesion.

DISCUSSION

Maintenance of denervated muscle activity and afferent input, by active or passive exercise, may increase trophic factor release to act on regenerating axons and to modulate central neuronal plasticity.

Sustained growth factor delivery promotes axonal regeneration in long gap peripheral nerve repair

The aim of this study was to evaluate the long-term effect of localized growth factor delivery on sciatic nerve regeneration in a critical-size (> 1 cm) peripheral nerve defect. Previous work has demonstrated that bioactive proteins can be encapsulated within double-walled, poly(lactic-co-glycolic acid)/poly(lactide) microspheres and embedded within walls of biodegradable polymer nerve guides composed of poly(caprolactone). Within this study, nerve guides containing glial cell line-derived neurotrophic factor (GDNF) were used to bridge a 1.5-cm defect in the male Lewis rat for a 16-week period. Nerve repair was evaluated through functional assessment of joint angle range of motion using video gait kinematics, gastrocnemius twitch force, and gastrocnemius wet weight. Histological evaluation of nerve repair included assessment of Schwann cell and neurofilament location with immunohistochemistry, evaluation of tissue integration and organization throughout the lumen of the regenerated nerve with Masson's trichrome stain, and quantification of axon fiber density and g-ratio. Results from this study showed that the measured gastrocnemius twitch force in animals treated with GDNF was significantly higher than negative controls and was not significantly different from the isograft-positive control group. Histological assessment of explanted conduits after 16 weeks showed improved tissue integration within GDNF releasing nerve guides compared to negative controls. Nerve fibers were present across the entire length of GDNF releasing guides, whereas nerve fibers were not detectable beyond the middle region of negative control guides. Therefore, our results support the use of GDNF for improved functional recovery above negative controls following large axonal defects in the peripheral nervous system.

3D ingrowth of bovine articular chondrocytes in biodegradable cryogel scaffolds for cartilage tissue engineering

A feasibility study was undertaken to examine the potential of biodegradable HEMA-lactate-dextran (HEMA-LLA-D)-based cryogels as scaffolds for cartilage tissue engineering. This was a preliminary in vitro study giving essential information on the biocompatibility of cryogels with cartilage cells. HEMA-lactate (HEMA-LLA) and HEMA-LLA-D were synthesized and characterized by different techniques. Cryogel scaffolds with supermacroporous structures were produced by cryogenic treatment of these macromers. Chondrocytes obtained from bovine articular cartilage were seeded onto cylindrical cryogels and cultured. The samples were examined by several microcopical techniques for cell viability and morphological analyses were performed at two culture points. Histological study of the constructs revealed the cells' growth on the surface and within the scaffolds. Confocal microscopical images demonstrated that the majority of live vs. dead cells had been attached to and integrated with the pores of the scaffold. SEM analysis showed round to oval-shaped chondrocytic cells interconnected with each other by communicating junctions. The chondrocytes rapidly proliferated in the cryogels, manifesting that they fully covered the scaffold surface after 9 days and almost filled the spaces in the pores of the scaffold after 15 days of culture. Chondrocytes secreted significant amount of extracellular matrix in the scaffolds and exhibited highly interconnective morphology. Light and transmission electron microscopy revealed groups of active cartilage cells closely apposed to the cryogel. We concluded that cryogel scaffolds could be excellent candidates for cartilage tissue regeneration with their extraordinary properties, including soft, elastic nature, highly open interconnected pore structure and very rapid, controllable swellability.

Polysialic acid immobilized on silanized glass surfaces: a test case for its use as a biomaterial for nerve regeneration

The immobilization of polysialic acid (polySia) on glass substrates has been investigated with regard to the applicability of this polysaccharide as a novel, biocompatible and bioresorbable material for tissue engineering, especially with regard to its use in nerve regeneration. PolySia, a homopolymer of alpha-2,8-linked sialic acid, is involved in post-translational modification of the neural cell adhesion molecule (NCAM). The degradation of polySia can be controlled which makes it an interesting material for coating and for scaffold construction in tissue engineering. Here, we describe the immobilization of polySia on glass surfaces via an epoxysilane linker. Whereas glass surfaces will not actually be used in nerve regeneration scaffolds, they provide a simple and efficient means for testing various methods for the investigation of immobilized polySia. The modified surfaces were investigated with contact angle measurements and the quantity of immobilized polySia was examined by the thiobarbituric acid assay and a specific polySia-ELISA. The interactions between the polySia-modified surface and immortalized Schwann cells were evaluated via cell adhesion and cell viability assays. The results show that polySia can be immobilized on glass surfaces via the epoxysilane linker and that surface-bound polySia has no toxic effects on Schwann cells. Therefore, as a key substance in the development of vertebrates and as a favourable substrate for the cultivation of Schwann cells, it offers interesting features for the use in nerve guidance tubes for treatment of peripheral nerve injuries.

Biodegradable fibrin conduit promotes long-term regeneration after peripheral nerve injury in adult rats

Peripheral nerve injuries are often associated with loss of nerve tissue and require autologous nerve grafts to provide a physical substrate for axonal growth. Biosynthetic neural conduits could be an alternative treatment strategy in such injuries. The present study investigates the long-term effects of a tubular fibrin conduit on neuronal regeneration, axonal sprouting and recovery of muscle weight following peripheral nerve injury and repair in adult rats. Sciatic axotomy was performed proximally in the thigh to create a 10-mm gap between the nerve stumps. The injury gap was bridged by using a 14-mm-long fibrin glue conduit, entubulating 2 mm of the nerve stump at each end. A reversed autologous nerve graft was used as a control. The regenerative response from sensory and motor neurones was evaluated following retrograde labelling with Fast Blue fluorescent tracer. In control experiments, at 16 weeks following peripheral nerve grafting, 5184 (±574 standard error of mean (SEM)) sensory dorsal root ganglion neurones and 1001 (±37 SEM) spinal motor neurones regenerated across the distal nerve-graft interface. The fibrin conduit promoted regeneration of 60% of sensory neurones and 52% of motor neurones when compared to the control group. The total number of myelinated axons in the distal nerve stump in the fibrin-conduit group reached 86% of the control and the weight of gastrocnemius and soleus muscles recovered to 82% and 89% of the controls, respectively. The present results suggest that a tubular fibrin conduit can be used to promote neuronal regeneration following peripheral nerve injury.

Treatment of a segmental nerve defect in the rat with use of bioabsorbable synthetic nerve conduits: a comparison of commercially available conduits

BACKGROUND

The use of biodegradable synthetic nerve conduits for the reconstruction of segmental nerve defects has been extensively reported in both animal and human studies, with a majority of studies evaluating sensory nerve recovery. However, few studies have compared these nerve conduits for functional motor recovery. The purpose of this study was to compare three commercially available, synthetic, bioabsorbable nerve conduits and autograft with respect to compound muscle action potentials, maximum isometric tetanic force, wet muscle weight, and nerve histomorphometry.

METHODS

Eighty Lewis rats were divided into four groups according to the type of repair of a 10-mm excision of the sciatic nerve: group I had a reversed autograft; group II, a poly-DL-lactide-epsilon-caprolactone conduit; group III, a type-I collagen conduit; and group IV, a polyglycolic acid conduit. All results were compared with the contralateral side. At twelve weeks, the rats underwent bilateral measurements of the compound muscle action potentials of the tibialis anterior and flexor digiti quinti brevis muscles, isometric tetanic force and muscle weight of the tibialis anterior, and peroneal nerve histomorphometry.

RESULTS

At twelve weeks, no difference in the percentage of recovery between the autograft and the poly-DL-lactide-epsilon-caprolactone conduit was observed with respect to compound muscle action potentials, isometric muscle force, muscle weight, and axon count measurements. The poly-DL-lactide-epsilon-caprolactone and collagen conduits remained structurally stable at twelve weeks, while the polyglycolic acid conduits had completely collapsed. The polyglycolic acid conduit had the poorest results, with a recovery rate of 15% for compound muscle action potentials and 29% for muscle force.

CONCLUSIONS

The functional outcome in this rat model was similar for the autograft and the poly-DL-lactide-epsilon-caprolactone conduits when they were used to reconstruct a 10-mm sciatic nerve defect. Functional recovery following the use of the polyglycolic acid conduit was the poorest.

Conductive Core-Sheath Nanofibers and Their Potential Application in Neural Tissue Engineering

We have prepared conductive core-sheath nanofibers via a combination of electrospinning and aqueous polymerization. Specifically, nanofibers electrospun from poly(ε-caprolactone) (PCL) and poly((L)-lactide) (PLA) were employed as templates to generate uniform sheaths of polypyrrole (PPy) via in situ polymerization. These conductive core-sheath nanofibers offer a unique system for studying the synergistic effect of different cues on neurite outgrowth in vitro. We found that explanted dorsal root ganglia (DRG) adhered well to the conductive core-sheath nanofibers and generated neurites across the surface when there was a nerve growth factor in the medium. Furthermore, the neurites could be oriented along one direction and enhanced by 82% in terms of maximum length when uniaxially aligned conductive core-sheath nanofibers are compared with their random counterparts. Electrical stimulation, when applied through the mats of conductive core-sheath nanofibers, was found to further increase the maximum length of neurite for random and aligned samples by 83% and 47%, respectively, relative to the controls without electrical stimulation. Combined together, these results suggest the potential use of the conductive core-sheath nanofibers as scaffolds in applications such as neural tissue engineering.

Nerve tubes for peripheral nerve repair

The concept of the nerve tube has been a major topic of research in the field of peripheral nerve regeneration for more than 25 years. The first nerve tubes are currently available for clinical use. This article gives an overview of the experimental and clinical data on nerve tubes for peripheral nerve repair and critically analyzes the data on which the step from laboratory to clinical use is based. In addition, it briefly discusses the different modifications to the common single lumen nerve tubes that may improve the results of generation.

Accuracy of motor axon regeneration across autograft, single-lumen, and multichannel poly(lactic-co-glycolic acid) nerve tubes

OBJECTIVE

The accuracy of motor axon regeneration becomes an important issue in the development of a nerve tube for motor nerve repair. Dispersion of regeneration across the nerve tube may lead to misdirection and polyinnervation. In this study, we present a series of methods to investigate the accuracy of regeneration, which we used to compare regeneration across autografts and single-lumen poly(lactic-co-glycolic acid) (PLGA) nerve tubes. We also present the concept of the multichannel nerve tube that may limit dispersion by separately guiding groups of regenerating axons.

METHODS

The simultaneous tracing of the tibial and peroneal nerves with fast blue and diamidino yellow was performed 8 weeks after the repair of a 1-cm nerve gap in the rat sciatic nerve to determine the percentage of double-projecting motoneurons. Sequential tracing of the peroneal nerve with diamidino yellow 1 week before repair and fast blue 8 weeks after repair was performed to determine the percentage of correctly directed peroneal motoneurons.

RESULTS

In the cases in which there was successful regeneration across single-lumen nerve tubes, more motoneurons had double projections to both the tibial and peroneal nerve branches after single-lumen nerve tube repair (21.4%) than after autograft repair (5.9%). After multichannel nerve tube repair, this percentage was slightly reduced (16.9%), although not significantly. The direction of regeneration was nonspecific after all types of repair.

CONCLUSION

Retrograde tracing techniques provide new insights into the process of regeneration across nerve tubes. The methods and data presented in this study can be used as a basis for the development of a nerve tube for motor nerve repair.

Chapter 27: Neural plasticity after nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory, and autonomic functions in the denervated segments of the body due to the interruption of axons, degeneration of distal nerve fibers, and eventual death of axotomized neurons. Functional deficits caused by nerve injuries can be compensated by reinnervation of denervated targets by regenerating injured axons or by collateral branching of undamaged axons, and remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of adequate target reinnervation; however, plasticity has limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain and hyperreflexia. After axotomy, neurons shift from a transmitter to a regenerative phenotype, activating molecular pathways that promote neuronal survival and axonal regeneration. Peripheral nerve injuries also induce a cascade of events, at the molecular, cellular, and system levels, initiated by the injury and progressing throughout plastic changes at the spinal cord, brainstem nuclei, thalamus, and brain cortex. Mechanisms involved in these changes include neurochemical changes, functional alterations of excitatory and inhibitory synaptic connections, sprouting of new connections, and reorganization of sensory and motor central maps. An important direction for research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, and are also able to modulate central nervous system reorganization, amplifying positive adaptive changes that improve functional recovery and also reducing undesirable effects.

Impact of different types of facial nerve reconstruction on the recovery of motor function: an experimental study in adult rats

OBJECTIVE

Poor functional recovery after facial nerve reconstruction is characterized by mass movements and synkinesis. Major reasons are axonal sprouting from the regenerating axons leading to misdirected reinnervation and hyperinnervation as well as polyinnervation of the mimic muscle end plates. We analyzed whether or not the type of nerve reconstruction influenced these pathological phenomena.

METHODS

The experiments were performed on 48 adult rats divided into four groups. One group served as an intact control and the experimental groups were subjected to facial-facial nerve repair (FFN), facial nerve interpositional grafting, and hypoglossal-facial nerve repair (HFN), with 12 subjects in each group. Two months later, functional recovery was measured by biometrical motion analysis of whisking. Retrograde fluorescence labeling of the brainstem motoneurons was used to quantify the degree of collateral axonal branching at the lesion site. Fluorescence histochemistry of sections through the levator labii superioris muscle was performed to quantify the degree of polyinnervation after surgery.

RESULTS

The type of nerve reconstruction significantly influenced the regeneration. The whisking amplitude did not recover completely regardless of the type of reconstruction. The angular velocity and angular acceleration of the vibrissal hairs showed a full recovery after facial nerve interpositional grafting and HFN, whereas these parameters remained decreased after FFN. Significantly less collateral branching and polyinnervation of the end plates were determined after grafting and HFN than after FFN.

CONCLUSION

No type of immediate facial nerve reconstruction results in a full recovery in the rat. However, the morphological and functional recovery was significantly better after grafting and HFN than after FFN.

Re-activation of atrophic motor Schwann cells after hypoglossal-facial nerve anastomosis

Facial nerve lesions are common in humans and often require surgical intervention. If repair is delayed, reinnervation can be facilitated by transposing the freshly cut hypoglossal nerve end-to-end directly to the distal facial nerve, allowing for uncompromised hypoglossal axons to reinnervate the denervated facial musculature (hypoglossal-facial anastomosis, HFA). Schwann cells (SCs) in the distal nerve stump have an important function in promoting axonal regeneration by expressing multiple regeneration-associated proteins. Chronically denervated SCs cease to express those factors, but it is unknown whether they can be reactivated by fresh axonal sprouts and regain part of their function. We evaluated SC function and viability in distal facial nerve stump of rats at various time points after chronic denervation as well as following immediate or delayed HFA by assessing their expression of growth-associated protein 43 kDa (GAP-43) and the neuregulin receptors erbB2 and erbB4. Our results show that maximal upregulation of those factors in denervated SCs occurred a few weeks after nerve transection, indicating that a short period of denervation might even be beneficial before nerve repair. Motor SCs denervated for 32 weeks had downregulated their activity and ceased to express the regeneration-associated factors. SCs immediately re-expressed GAP-43, erbB2, and erbB4 following contact with fresh hypoglossal motor axons, demonstrating they are competent to promote regeneration even after long-term denervation.

Misdirection of regenerating motor axons after nerve injury and repair in the rat sciatic nerve model

Misdirection of regenerating axons is one of the factors that can explain the poor results often found after nerve injury and repair. In this study, we quantified the degree of misdirection and the effect on recovery of function after different types of nerve injury and repair in the rat sciatic nerve model; crush injury, direct coaptation, and autograft repair. Sequential tracing with retrograde labeling of the peroneal nerve before and 8 weeks after nerve injury and repair was performed to quantify the accuracy of motor axon regeneration. Digital video analysis of ankle motion was used to investigate the recovery of function. In addition, serial compound action potential recordings and nerve and muscle morphometry were performed. In our study, accuracy of motor axon regeneration was found to be limited; only 71% (+/-4.9%) of the peroneal motoneurons were correctly directed 2 months after sciatic crush injury, 42% (+/-4.2%) after direct coaptation, and 25% (+/-6.6%) after autograft repair. Recovery of ankle motion was incomplete after all types of nerve injury and repair and demonstrated a disturbed balance of ankle plantar and dorsiflexion. The number of motoneurons from which axons had regenerated was not significantly different from normal. The number of myelinated axons was significantly increased distal to the site of injury. Misdirection of regenerating motor axons is a major factor in the poor recovery of nerves that innervate different muscles. The results of this study can be used as basis for developing new nerve repair techniques that may improve the accuracy of regeneration.

The role of evaluation methods in the assessment of peripheral nerve regeneration through synthetic conduits: a systematic review

Object

A number of evaluation methods that are currently used to compare peripheral nerve regeneration with alternative repair methods and to judge the outcome of a new paradigm were hypothesized to lack resolving power. This would too often lead to the conclusion that the outcome of a new paradigm could not be discerned from the outcome of the current gold standard, the autograft. As a consequence, the new paradigm would incorrectly be judged as successful.

Methods

An overview of the methods that were used to evaluate peripheral nerve regeneration after grafting of the rat sciatic nerve was prepared. All articles that were published between January 1975 and December 2004 and concerned grafting of the rat sciatic nerve (minimum graft length 5 mm) and in which the experimental method was compared with an untreated or another grafted nerve were included. The author scored the presence of statistically significant differences between paradigms.

Results

Evaluation of nerve fiber count, nerve fiber density, N-ratio, nerve histological success ratio, compound muscle action potential, muscle weight, and muscle tetanic force are methods that were demonstrated to have resolving power.

Conclusions

A number of evaluation methods are not suitable to demonstrate a significant difference between experimental paradigms in peripheral nerve regeneration. It is preferable to apply a combination of evaluation methods with resolving power to evaluate nerve regeneration properly.

Neural plasticity after peripheral nerve injury and regeneration

Injuries to the peripheral nerves result in partial or total loss of motor, sensory and autonomic functions conveyed by the lesioned nerves to the denervated segments of the body, due to the interruption of axons continuity, degeneration of nerve fibers distal to the lesion and eventual death of axotomized neurons. Injuries to the peripheral nervous system may thus result in considerable disability. After axotomy, neuronal phenotype switches from a transmitter to a regenerative state, inducing the down- and up-regulation of numerous cellular components as well as the synthesis de novo of some molecules normally not expressed in adult neurons. These changes in gene expression activate and regulate the pathways responsible for neuronal survival and axonal regeneration. Functional deficits caused by nerve injuries can be compensated by three neural mechanisms: the reinnervation of denervated targets by regeneration of injured axons, the reinnervation by collateral branching of undamaged axons, and the remodeling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of specificity in target reinnervation; plasticity in human has, however, limited effects on disturbed sensory localization or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain, hyperreflexia and dystonia. Recent research has uncovered that peripheral nerve injuries induce a concurrent cascade of events, at the systemic, cellular and molecular levels, initiated by the nerve injury and progressing throughout plastic changes at the spinal cord, brainstem relay nuclei, thalamus and brain cortex. Mechanisms for these changes are ubiquitous in central substrates and include neurochemical changes, functional alterations of excitatory and inhibitory connections, atrophy and degeneration of normal substrates, sprouting of new connections, and reorganization of somatosensory and motor maps. An important direction for ongoing research is the development of therapeutic strategies that enhance axonal regeneration, promote selective target reinnervation, but are also able to modulate central nervous system reorganization, amplifying those positive adaptive changes that help to improve functional recovery but also diminishing undesirable consequences.

Characterization of tests of functional recovery after median and ulnar nerve injury and repair in the rat forelimb

The majority of human peripheral nerve injuries occur in the upper limb but the majority of studies in the rat are performed in the hindlimb. The upper and lower limbs differ in dexterity and control by supraspinal systems, so an upper limb model is a better representation of the common form of human injury. The purpose of this study was to further develop a rat model involving lesions of the median and ulnar nerves. To produce different degrees of misdirection of axons following nerve repair, we studied nerve crush, cut and repair of the two nerves, and cut and repair with crossover. Assessment of functional recovery was performed using a battery of motor and sensory tests: the staircase test, which assesses skilled forepaw reaching; grip strength meter, which assesses grip strength; pawprint analysis, which assesses toe spread and print length; horizontal ladder, which assesses forepaw placement during skilled locomotion; modified Randall-Selitto device and electronic von Frey probes, which assess fine touch; and cold probes, which assess temperature sensation. All tests revealed deficits in forepaw function after nerve injury except the print length and modified Randall-Selitto device. The time course of functional recovery was observed over 15 weeks. The final degree of functional recovery achieved was related to the misdirection of axon regeneration. The tests that most clearly revealed the effects of axon misdirection on function were the skilled paw reaching and grip strength tests. The lesion model and functional tests that we have developed will be useful in testing therapeutic strategies for treating the consequences of inaccurate axon regeneration following peripheral nerve injury in humans.

Culturing of glial and neuronal cells on polysialic acid

Although peripheral nerves exhibit regeneration capacities after transection injuries, the success of nerve repair depends crucially on the length of the gap. In addition to autologous nerve grafting as the conventional neurosurgical treatment to overcome long gaps, alternative strategies are needed. Numerous experimental studies have been undertaken to find the optimal material for production of artificial prostheses, which can be introduced as conduits between the nerve stumps. The current study follows the aim to establish polysialic acid (polySia), a homopolymer of alpha2,8-linked sialic acid residues, as a novel, biocompatible, and bioresorbable material for nerve tissue engineering. As a first step towards this goal, protocols for efficient coating of cell culture dishes with soluble polySia were established. In addition, primary nerve cells which are candidates for reconstructive therapies, including neonatal and adult Schwann cells, neural progenitor cells, spinal ganglionic neurons and motoneurons were cultured on polySia substrates. Cultures were evaluated with regard to cell survival and cell proliferation capacities. polySia turned out to be stable under cell culture conditions, and induced degradable and degradation products had no negative effects on cell cultures. Furthermore, polySia revealed its compatibility for several cell types derived from rat embryonic, postnatal and adult nervous tissue when used as a substrate.

Synergistic terminal motor end-to-side nerve graft repair: investigation in a non-human primate model

End-to-side nerve repair has re-emerged in the literature in recent years but clinical applications for this technique are not yet fully defined and clinical reports are rare and controversial. Hypothetically, there might be useful functional results performing peripheral end-to-side nerve graft repair using synergistic terminal branches with defined motor function. An end-to-side nerve graft repair bridging from the terminal motor branch of deep branch of the ulnar nerve to the thenar motor branch of the median nerve was performed in non-human primates. The results in this non-human primate model demonstrate the efficacy of end-to-side nerve graft repair at the level of peripheral terminal motor branches. End-to-side neurorrhaphy may present a viable alternative in conditions of unsuitable end-to-end coaptation and inappropriate nerve grafting procedures.

Effect of conduit repair on aberrant motor axon growth within the nerve graft in rats

After peripheral nerve injury, minimizing axonal misdirection has been a matter of importance to obtain good functional outcomes. In general, it becomes more challenging as the nerve defect length is longer. As previous works suggested that a conduit repair leaving a short gap could induce some target-specific reinnervation, we expected that a distally placed conduit combined with nerve graft would enhance the specificity of reinnervation, especially in dealing with a long gap. To test this, a 14-mm-long gap was created in the rat sciatic nerves and repaired with either 1) whole nerve graft (WG), 2) interfascicular nerve grafts (FG), or 3) whole nerve graft combined with distally placed silicone tube leaving a 5-mm gap (TUBG). At the end of follow up, the extent of target specific reinnervation (measurement of the compound muscle action potentials evoked by stimulation of the sciatic nerve and its tibial and common peroneal fascicles) and the accuracy of motoneuronal projection (sequential retrograde labeling of the common peroneal motor pool) were assessed. Both assessments revealed that groups FG and TUBG had a similar selectivity, which was significantly higher than in group WG. Consistent with these results, the functional recovery as assessed by walking track analysis showed no significant difference between groups FG and TUBG, whereas those were significantly superior to group WG. In contrast, histomorphometric assessment of the regenerating axons and wet muscle weight showed no significant difference among the three groups. In conclusion, conduit repair would have some effects on reducing motor axonal misdirection, and it might be more effective when used in the management of a large defect in combination with nerve graft.