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.

A new protocol for cultivation of predegenerated adult rat Schwann cells

The purpose of this study was to optimize the methodology of cultivation of predegenerated Schwann cells (SCs). SCs were isolated from 7-day-predegenerated sciatic nerves of adult rats. We applied commercially available culture medium for cultivation of endothelial cells endothelial cell culture medium (EBM-2) instead of Dulbecco's Modified Eagle's Medium commonly used to culture adult Schwann cells. Additionally, cell culture medium was supplemented with factors specifically supporting SCs growth as: bovine pituitary extract (5 μg/ml), heregulin (40 ng/ml) and insulin (2.5 ng/ml). Similarly to the reports of others authors, we did not observe any beneficial effects of Forskolin application, so we didn't supplement our medium with it. Cell culture purity was determined by counting the ratio of GFAP, N-Cadherin and NGFR p75-positive cells to total number of cells. About 94-97 % of cells were confirmed as Schwann cells. As a result, we obtained sufficient number and purity of Schwann cells to be applied in different experimental models in rats. EBM-2 medium coated with fibronectin was the best for cultivation of adult rat Schwann cells.

Axonal regeneration after sciatic nerve lesion is delayed but complete in GFAP- and vimentin-deficient mice

Peripheral axotomy of motoneurons triggers Wallerian degeneration of injured axons distal to the lesion, followed by axon regeneration. Centrally, axotomy induces loss of synapses (synaptic stripping) from the surface of lesioned motoneurons in the spinal cord. At the lesion site, reactive Schwann cells provide trophic support and guidance for outgrowing axons. The mechanisms of synaptic stripping remain elusive, but reactive astrocytes and microglia appear to be important in this process. We studied axonal regeneration and synaptic stripping of motoneurons after a sciatic nerve lesion in mice lacking the intermediate filament (nanofilament) proteins glial fibrillary acidic protein (GFAP) and vimentin, which are upregulated in reactive astrocytes and Schwann cells. Seven days after sciatic nerve transection, ultrastructural analysis of synaptic density on the somata of injured motoneurons revealed more remaining boutons covering injured somata in GFAP(-/-)Vim(-/-) mice. After sciatic nerve crush in GFAP(-/-)Vim(-/-) mice, the fraction of reinnervated motor endplates on muscle fibers of the gastrocnemius muscle was reduced 13 days after the injury, and axonal regeneration and functional recovery were delayed but complete. Thus, the absence of GFAP and vimentin in glial cells does not seem to affect the outcome after peripheral motoneuron injury but may have an important effect on the response dynamics.

Immunohistochemical, ultrastructural and functional analysis of axonal regeneration through peripheral nerve grafts containing Schwann cells expressing BDNF, CNTF or NT3

We used morphological, immunohistochemical and functional assessments to determine the impact of genetically-modified peripheral nerve (PN) grafts on axonal regeneration after injury. Grafts were assembled from acellular nerve sheaths repopulated ex vivo with Schwann cells (SCs) modified to express brain-derived neurotrophic factor (BDNF), a secretable form of ciliary neurotrophic factor (CNTF), or neurotrophin-3 (NT3). Grafts were used to repair unilateral 1 cm defects in rat peroneal nerves and 10 weeks later outcomes were compared to normal nerves and various controls: autografts, acellular grafts and grafts with unmodified SCs. The number of regenerated βIII-Tubulin positive axons was similar in all grafts with the exception of CNTF, which contained the fewest immunostained axons. There were significantly lower fiber counts in acellular, untransduced SC and NT3 groups using a PanNF antibody, suggesting a paucity of large caliber axons. In addition, NT3 grafts contained the greatest number of sensory fibres, identified with either IB₄ or CGRP markers. Examination of semi- and ultra-thin sections revealed heterogeneous graft morphologies, particularly in BDNF and NT3 grafts in which the fascicular organization was pronounced. Unmyelinated axons were loosely organized in numerous Remak bundles in NT3 grafts, while the BDNF graft group displayed the lowest ratio of umyelinated to myelinated axons. Gait analysis revealed that stance width was increased in rats with CNTF and NT3 grafts, and step length involving the injured left hindlimb was significantly greater in NT3 grafted rats, suggesting enhanced sensory sensitivity in these animals. In summary, the selective expression of BDNF, CNTF or NT3 by genetically modified SCs had differential effects on PN graft morphology, the number and type of regenerating axons, myelination, and locomotor function.

Schwann cell-seeded scaffold with longitudinally oriented micro-channels for reconstruction of sciatic nerve in rats

To provide a more permissive environment for axonal regeneration, Schwann cells (SCs) were introduced into a collagen-chitosan scaffold with longitudinally oriented micro-channels (L-CCH). The SC-seeded scaffold was then used for reconstruction of a 15-mm-long sciatic nerve defect in rats. The axonal regeneration and functional recovery were examined by a combination of walking track analysis, electrophysiological assessment, Fluoro-Gold retrograde tracing, as well as morphometric analyses to both regenerated axons and target muscles. The findings showed that SCs adhered and migrated into the L-CCH scaffold and displayed a longitudinal arrangement in vitro. Axonal regeneration as well as functional recovery was in the similar range between SCs-seeded scaffold and autograft groups, which were superior to those in L-CCH scaffold alone group. These indicate that the SCs-seeded L-CCH scaffold, which resembles the microstructure as well as the permissive environment of native peripheral nerves, holds great promise in nerve regeneration therapies.

Neuroprotection and axonal regeneration after lumbar ventral root avulsion by re-implantation and mesenchymal stem cells transplant combined therapy

Ventral spinal root avulsion causes complete denervation of muscles in the limb and also progressive death of segmental motoneurons (MN) leading to permanent paralysis. The chances for functional recovery after ventral root avulsion are very poor owing to the loss of avulsed neurons and the long distance that surviving neurons have to re-grow axons from the spinal cord to the corresponding targets. Following unilateral avulsion of L4, L5 and L6 spinal roots in adult rats, we performed an intraspinal transplant of mesenchymal stem cells (MSC) and surgical re-implantation of the avulsed roots. Four weeks after avulsion the survival of MN in the MSC-treated animals was significantly higher than in vehicle-injected rats (45% vs. 28%). Re-implantation of the avulsed roots in the injured spinal cord allowed the regeneration of motor axons. By combining root re-implantation and MSC transplant the number of surviving MN at 28 days post-injury was higher (60%) than in re-implantation alone animals (46%). Electromyographic tests showed evidence of functional re-innervation of anterior tibialis and gastrocnemius muscles by the regenerated motor axons only in rats with the combined treatment. These results indicate that MSC are helpful in enhancing neuronal survival and increased the regenerative growth of injured axons. Surgical re-implantation and MSC grafting combined had a synergic neuroprotective effect on MN and on axonal regeneration and muscle re-innervation after spinal root avulsion.

Use of nerve conduits for peripheral nerve injury repair: A Web of Science-based literature analysis

OBJECTIVE:

To identify global research trends in the use of nerve conduits for peripheral nerve injury repair.

DATA RETRIEVAL:

Numerous basic and clinical studies on nerve conduits for peripheral nerve injury repair were performed between 2002–2011. We performed a bibliometric analysis of the institutions, authors, and hot topics in the field, from the Web of Science, using the key words peripheral nerve and conduit or tube.

SELECTION CRITERIA:

Inclusion criteria: peer-reviewed published articles on nerve conduits for peripheral nerve injury repair, indexed in the Web of Science; original research articles, reviews, meeting abstracts, proceedings papers, book chapters, editorial material, and news items. Exclusion criteria: articles requiring manual searching or telephone access; documents not published in the public domain; and several corrected papers.

MAIN OUTCOME MEASURES:

(a) Annual publication output; (b) publication type; (c) publication by research field; (d) publication by journal; (e) publication by funding agency; (f) publication by author; (g) publication by country and institution; (h) publications by institution in China; (i) most-cited papers.

RESULTS:

A total of 793 publications on the use of nerve conduits for peripheral nerve injury repair were retrieved from the Web of Science between 2002–2011. The number of publications gradually increased over the 10-year study period. Articles constituted the main type of publication. The most prolific journals were Biomaterials, Microsurgery, and Journal of Biomedical Materials Research Part A. The National Natural Science Foundation of China supported 27 papers, more than any other funding agency. Of the 793 publications, almost half came from American and Chinese authors and institutions.

CONCLUSION:

Nerve conduits have been studied extensively for peripheral nerve regeneration; however, many problems remain in this field, which are difficult for researchers to reach a consensus.

Use of poly(DL-lactide-ε-caprolactone) membranes and mesenchymal stem cells from the Wharton's jelly of the umbilical cord for promoting nerve regeneration in axonotmesis: in vitro and in vivo analysis

Cellular systems implanted into an injured nerve may produce growth factors or extracellular matrix molecules, modulate the inflammatory process and eventually improve nerve regeneration. In the present study, we evaluated the therapeutic value of human umbilical cord matrix MSCs (HMSCs) on rat sciatic nerve after axonotmesis injury associated to Vivosorb® membrane. During HMSCs expansion and differentiation in neuroglial-like cells, the culture medium was collected at 48, 72 and 96 h for nuclear magnetic resonance (NMR) analysis in order to evaluate the metabolic profile. To correlate the HMSCs ability to differentiate and survival capacity in the presence of the Vivosorb® membrane, the [Ca(2+)]i of undifferentiated HMSCs or neuroglial-differentiated HMSCs was determined by the epifluorescence technique using the Fura-2AM probe. The Vivosorb® membrane proved to be adequate and used as scaffold associated with undifferentiated HMSCs or neuroglial-differentiated HMSCs. In vivo testing was carried out in adult rats where a sciatic nerve axonotmesis injury was treated with undifferentiated HMSCs or neuroglial differentiated HMSCs with or without the Vivosorb® membrane. Motor and sensory functional recovery was evaluated throughout a healing period of 12 weeks using sciatic functional index (SFI), extensor postural thrust (EPT), and withdrawal reflex latency (WRL). Stereological analysis was carried out on regenerated nerve fibers. In vitro investigation showed the formation of typical neuroglial cells after differentiation, which were positively stained for the typical specific neuroglial markers such as the GFAP, the GAP-43 and NeuN. NMR showed clear evidence that HMSCs expansion is glycolysis-dependent but their differentiation requires the switch of the metabolic profile to oxidative metabolism. In vivo studies showed enhanced recovery of motor and sensory function in animals treated with transplanted undifferentiated and differentiated HMSCs that was accompanied by an increase in myelin sheath. Taken together, HMSC from the umbilical cord Wharton jelly might be useful for improving the clinical outcome after peripheral nerve lesion.

Optimal time-point for neural stem cell transplantation to delay denervated skeletal muscle atrophy

INTRODUCTION

Transplantation of neural stem cells (NSCs) is a promising treatment to delay denervated skeletal muscle atrophy; however, the optimal time-point between peripheral nerve injury and NSC transplantation needs to be determined.

METHODS

Improvement in rat gastrocnemius muscle function was evaluated after NSCs were transplanted into sectioned distal tibial nerves. We also assessed survival and differentiation. ANOVA was used to compare the mean value of the number of neuron-like cells, cross-sectional area amelioration, the amount of activated fibers, and latency and amplitude of the gastrocnemius compound muscle action potential.

RESULTS

The group in which the NSCs were transplanted 1 week after tibial nerve transection had the largest number of neuron-like cells, maximum cross-sectional area amelioration, and maximum amount of activated gastrocnemius fibers compared with all other groups (P < 0.01).

CONCLUSIONS

The optimal time-point for NSC transplantation for delaying denervated skeletal muscle atrophy is 1 week after severing the nerve.

Vasopressin-induced intracellular Ca²⁺ concentration responses in non-neuronal cells of the rat dorsal root ganglion

Arginine-vasopressin (AVP) is a nonapeptide of hypothalamic origin that has been shown to exert many important cognitive and physiological functions in neurons and terminals of both the central and peripheral nervous system (CNS and PNS). Here we report for the first time that AVP induced an increase in intracellular Ca²⁺ concentration ([Ca²⁺](i)) in non-neuronal cells isolated from the rat dorsal root ganglion (DRG) and cultured in vitro. The ratiometric [Ca²⁺](i) measurements showed that AVP evoked [Ca²⁺](i) responses in the non-neuronal cells and these concentration-dependent (100 pM to 1 μM) responses increased with days in vitro in culture, reaching a maximum amplitude after 4-5 day. Immunostaining by anti-S-100 antibody revealed that more than 70% of S-100 positive cells were AVP-responsive, indicating that glial cells responded to AVP and increased their [Ca²⁺](i). The responses were inhibited by depletion of the intracellular Ca²⁺ stores or in the presence of inhibitors of phospholipase C, indicating a metabotropic response involving inositol trisphosphate, and were mediated by the V₁ subclass of AVP receptors, as evidenced by the use of the specific blockers for V₁ and OT receptors, (d(CH₂)₅¹,Tyr(Me)²,Arg⁸)-Vasopressin and (d(CH₂)₅¹,Tyr(Me)²,Thr⁴,Orn⁸,des-Gly-NH₂⁹)-Vasotocin, respectively. V(1a) but not V(1b) receptor mRNA was expressed sustainably through the culture period in cultured DRG cells. These results suggest that AVP modulates the activity of DRG glial cells via activation of V(1a) receptor.

A simple technique for augmentation of axonal ingrowth into chondroitinase-treated acellular nerve grafts using nerve growth factor

BACKGROUND AND PURPOSE

Improvement in axonal regeneration may lead to the development of longer nerve grafts and improved outcomes for patients with peripheral nerve injury. Although the use of acellular nerve grafts has been well documented (Groves et al, Exp Neurol. 2005;195:278-292; Krekoski et al, J Neurosci. 2001;21:6206-6213; Massey et al, Exp Neurol. 2008;209:426-445; Neubauer et al, Exp Neurol. 2007;207:163-170; Zuo et al, Exp Neurol. 2002;176:221-228), less is known about the ability of neurotrophic factors to enhance axonal regeneration. This study evaluates axonal ingrowth augmentation using acellular, chondroitinase-treated nerve grafts doped with nerve growth factor (NGF).

METHODS

Acellular chondroitinase-treated murine nerve grafts were placed in experimental (NGF-treated grafts) and control (carrier-only grafts) rats. Five days after implantation, axonal regeneration was assessed by immunocytochemistry along with digital image analysis.

RESULTS

Higher axon count was observed throughout the length of the nerve in the NGF group (P < 0.0001), peaking at 3 mm from proximal repair (P = 0.02). Although the NGF group displayed a higher axon count per slice, the mean diameter of individual NGF axons was smaller (P < 0.0001), potentially consistent with induction of sensory axons (Rich et al, J Neurocytol. 1987;16:261-268; Sofroniew et al, Annu Rev Neurosci. 2001;24:1217-1128; Yip et al, J Neurosci. 1984;4:2986-2992).

CONCLUSION

The simple technique of doping acellular, chondroitinase-treated nerve grafts with NGF can augment axonal ingrowth and possibly preferentially induce sensory axons.

A novel nanoparticle delivery system for in vivo targeting of the sciatic nerve: impact on regeneration

Aim: Innovative solutions in the development of drug delivery systems targeting the nerve tissue are awaited. In this regard, a novel system for the delivery of drugs to the sciatic nerve was created using nanomedical principles. Materials & methods: Chitosan was the vehicle material used in the experiment. Heparin bound to growth factors has been administered to enhance peripheral nerve regeneration, and since heparin possesses the appropriate charge to be able to form nanoparticles with chitosan, it appears to be a good candidate to base this new delivery system on. Results: Maximal absorption took place throughout the extracellular matrix at day 15. No major inflammatory response was observed, indicating that this is a safe and biocompatible system for drug delivery to nerves. Sensorimotor performance and nerve regeneration of mice receiving these nanoparticles were superior as compared with controls. Conclusion: Our work demonstrates a versatile nanoparticle delivery system that successfully targets drugs ‘in vivo’ to the sciatic nerve, opening novel avenues in the field of nanomedicine to the design of therapeutic strategies that enhance axonal regeneration.

Original submitted 22 July 2011; Revised submitted 8 December 2011; Published online 4 April 2012

Transfer of vesicles from schwann cells to axons: a novel mechanism of communication in the peripheral nervous system

Schwann cells (SCs) are the glial component of the peripheral nervous system, with essential roles during development and maintenance of axons, as well as during regenerative processes after nerve injury. SCs increase conduction velocities by myelinating axons, regulate synaptic activity at presynaptic nerve terminals and are a source of trophic factors to neurons. Thus, development and maintenance of peripheral nerves are crucially dependent on local signaling between SCs and axons. In addition to the classic mechanisms of intercellular signaling, the possibility of communication through secreted vesicles has been poorly explored to date. Interesting recent findings suggest the occurrence of lateral transfer mediated by vesicles from glial cells to axons that could have important roles in axonal growth and axonal regeneration. Here, we review the role of vesicular transfer from SCs to axons and propose the advantages of this means in supporting neuronal and axonal maintenance and regeneration after nerve damage.

Mesenchymal progenitor cells derived from traumatized muscle enhance neurite growth

The success of peripheral nerve regeneration is governed by the rate and quality of axon bridging and myelination that occurs across the damaged region. Neurite growth and the migration of Schwann cells is regulated by neurotrophic factors produced as the nerve regenerates, and these processes can be enhanced by mesenchymal stem cells (MSCs), which also produce neurotrophic factors and other factors that improve functional tissue regeneration. Our laboratory has recently identified a population of mesenchymal progenitor cells (MPCs) that can be harvested from traumatized muscle tissue debrided and collected during orthopaedic reconstructive surgery. The objective of this study was to determine whether the traumatized muscle-derived MPCs exhibit neurotrophic function equivalent to that of bone marrow-derived MSCs. Similar gene- and protein-level expression of specific neurotrophic factors was observed for both cell types, and we localized neurogenic intracellular cell markers (brain-derived neurotrophic factor and nestin) to a subpopulation of both MPCs and MSCs. Furthermore, we demonstrated that the MPC-secreted factors were sufficient to enhance in vitro axon growth and cell migration in a chick embryonic dorsal root ganglia (DRG) model. Finally, DRGs in co-culture with the MPCs appeared to increase their neurotrophic function via soluble factor communication. Our findings suggest that the neurotrophic function of traumatized muscle-derived MPCs is substantially equivalent to that of the well-characterized population of bone marrow-derived MPCs, and suggest that the MPCs may be further developed as a cellular therapy to promote peripheral nerve regeneration.

Fibrin conduit supplemented with human mesenchymal stem cells and immunosuppressive treatment enhances regeneration after peripheral nerve injury

To address the need for the development of bioengineered replacement of a nerve graft, a novel two component fibrin glue conduit was combined with human mesenchymal stem cells (MSC) and immunosupressive treatment with cyclosporine A. The effects of MSC on axonal regeneration in the conduit and reaction of activated macrophages were investigated using sciatic nerve injury model. A 10mm gap in the sciatic nerve of a rat was created and repaired either with fibrin glue conduit containing diluted fibrin matrix or fibrin glue conduit containing fibrin matrix with MSC at concentration of 80×10(6) cells/ml. Cells were labeled with PKH26 prior to transplantation. The animals received daily injections of cyclosporine A. After 3 weeks the distance of regeneration and area occupied by regenerating axons and ED1 positives macrophages was measured. MSC survived in the conduit and enhanced axonal regeneration only when transplantation was combined with cyclosporine A treatment. Moreover, addition of cyclosporine A to the conduits with transplanted MSC significantly reduced the ED1 macrophage reaction.

VEGF-induced growth cone enhancement is diminished by inhibiting tyrosine-residue 1214 of VEGFR-2

Axonal outgrowth is of paramount significance for establishing the intricate neuronal network both during embryogenesis and nerve regeneration. Vascular endothelial growth factor (VEGF), which is known for its essential role in vascular sprouting and its involvement in cancer, has recently been found to exert a trophic activity on neurons leading to an increased axonal outgrowth. Although two receptors, VEGFR-2 and neuropilin-1, were identified on neurons, the signaling pathways associated with them are not well understood. The aim of this study was to analyze the influence of VEGF on the growth cone morphology and motility of dorsal root ganglia (DRG) neurons. Moreover, we aimed for a deeper understanding of VEGFR-2 on growth cones that potentially mediates the stimulating and attractive effects. We cultivated chicken DRG in medium containing mouse VEGF and analyzed growth cone size. The data presented here show a positive effect of VEGF on growth cone size. Furthermore, we interrupted the activity of VEGFR-2 by either blocking the tyrosine residue 1214 (tyr1214) or by inhibiting the receptor phosphorylation with axitinib, a novel small molecule, which has recently entered phase III trials for cancer treatment. Disruption of the VEGFR-2 leads to a significantly diminished growth cone size. Based on these findings, we propose a positive effect of VEGF on peripheral nervous system growth cone size and show for the first time quantitative data to underline this hypothesis. Additionally, we propose that VEGFR-2 and especially the tyr1214-dependent pathway of VEGFR-2 are of importance in VEGF signaling in the growth cone of DRG neurons.

UTP affects the Schwannoma cell line proteome through P2Y receptors leading to cytoskeletal reorganisation

Glial cells in the peripheral nervous system, such as Schwann cells, respond to nucleotides, which play an important role in axonal regeneration and myelination. Metabotropic P2Y receptor agonists are promising therapeutic molecules for peripheral neuropathies. Nevertheless, the proteomic mechanisms involved in nucleotide action on Schwann cells remain unknown. Here, we studied intracellular protein changes in RT4-D6P2T Schwann cells after treatment with nucleotides and Nucleo CMP Forte (CMPF), a nucleotide-based drug. After treatment with CMPF, 2-D DIGE revealed 11 differential gel spots, which were all upregulated. Among these, six different proteins were identified by MS. Some of these proteins are involved in actin remodelling (actin-related protein, Arp3), membrane vesicle transport (Rab GDP dissociation inhibitor β, Rab GDI), and the endoplasmic reticulum stress response (protein disulfide isomerase A3, PDI), which are hallmarks of a possible P2Y receptor signalling pathway. Expression of P2Y receptors in RT4-D6P2T cells was demonstrated by RT-PCR and a transient elevation of intracellular calcium measured in response to UTP. Actin reorganisation was visualized after UTP treatment using phalloidin-FITC staining and was blocked by the P2Y antagonist suramin, which also inhibited Arp3, Rab GDI, and PDI protein upregulation. Our data indicate that extracellular UTP interacts with Schwann P2Y receptors and activates molecular machinery that induces changes in the glial cell cytoskeleton.

Growth factor delivery systems and repair strategies for damaged peripheral nerves

Artificial nerve conduits (NCs) are, in certain cases, instrumental for repairing damaged peripheral nerves, although therapeutic efficacy remains often suboptimal. Considerable efforts have been made to improve the therapeutic performance of NCs. This article reviews recent developments in NC-technology for peripheral nerve regeneration with a main focus on growth factors delivery systems and repair strategies. Commonly used materials for NC fabrication include collagen, silk fibroin, and biodegradable aliphatic polyesters. The basic NC structure, i.e., a hollow tube, can be manufactured by diverse methods: spinning mandrel technology, sheet rolling, injection-molding, freeze-drying, and electro-spinning. Polymeric and cellular delivery systems for growth factors can be integrated in the NC wall or within luminal structures such as gels, fibers, or biological materials providing binding affinity for the bioactive compounds. NCs with sustained growth factor delivery generally improve significantly the axonal outgrowth in nerve defect models, although restoration of sensory and motor functions remains inferior to that achieved with autologous nerve grafts. To improve therapeutic outcomes, further biofunctionalization of NCs will be needed, i.e., adjusting degradation kinetics of NC scaffolding to be compatible with axonal regeneration; delivering multiple growth factors at individually optimized kinetics; incorporating modality specific glial cells and furnishing NCs with guiding nanostructures.

Next generation nerve guides: materials, fabrication, growth factors, and cell delivery

Nerve guides are increasingly being used surgically to repair acute peripheral nerve injuries. This is not only due to an increase in the number of commercially available devices, but also clinical acceptance. However, regeneration distance is typically limited to 20-25 mm, in part due to the basic tubular design. A number of experimental studies have shown improvements in nerve regeneration distance when conduits incorporate coatings, internal scaffolds, topographical cues, or the delivery of support cells. Current studies on designing nerve guides for maximizing nerve regeneration focus both on cell-containing and cell-free devices, the latter being clinically attractive as "off the shelf" products. Arguably better results are obtained when conduits are used in conjunction with support cells (e.g., Schwann cells or stem cells) that can improve regeneration distance and speed of repair, and provide informative experimental data on how Schwann and neuronal cells respond in regenerating injured nerves. In this review we discuss the range of current nerve guides commercially available and appraise experimental studies in the context of the future design of nerve guides for clinical use.

Effects of low level laser therapy on proliferation and neurotrophic factor gene expression of human schwann cells in vitro

Previous studies have been proposed that proliferation and release of certain growth factors by different types of cells can be modulated by low level laser therapy. We aimed to demonstrate the effect of laser irradiation on human schwann cell proliferation and neurotrophic factor gene expression in vitro. Human schwann cells (SCs) were harvested from sural nerve that was obtained from organ donor followed by treatment with an 810 nm, 50 mW diode laser (two different energies: 1 J/cm(2) and 4 J/cm(2)) in three consecutive days. SC proliferation was measured, after first irradiation on days 1, 4 and 7 by the MTT assay. Real time PCR analysis was utilized on days 5 and 20 to evaluate the expression of key genes involved in nerve regeneration consist of NGF, BDNF and GDNF. Evaluation of cellular proliferation following one day after laser treatment revealed significant decrease in cell proliferation compared to control group. However on day 7, significant increase in proliferation was found in both the irradiated groups in comparison with the control group. No significant difference was found between the laser treated groups. Treatment of SCs with laser resulted in significant increase in NGF gene expression on day 20. Difference between two treated groups and control group was not significant for BDNF and GDNF gene expression. Our results demonstrate that low level laser therapy stimulate human schwann cell proliferation and NGF gene expression in vitro.

A biomaterials approach to peripheral nerve regeneration: bridging the peripheral nerve gap and enhancing functional recovery

Microsurgical techniques for the treatment of large peripheral nerve injuries (such as the gold standard autograft) and its main clinically approved alternative--hollow nerve guidance conduits (NGCs)--have a number of limitations that need to be addressed. NGCs, in particular, are limited to treating a relatively short nerve gap (4 cm in length) and are often associated with poor functional recovery. Recent advances in biomaterials and tissue engineering approaches are seeking to overcome the limitations associated with these treatment methods. This review critically discusses the advances in biomaterial-based NGCs, their limitations and where future improvements may be required. Recent developments include the incorporation of topographical guidance features and/or intraluminal structures, which attempt to guide Schwann cell (SC) migration and axonal regrowth towards their distal targets. The use of such strategies requires consideration of the size and distribution of these topographical features, as well as a suitable surface for cell-material interactions. Likewise, cellular and molecular-based therapies are being considered for the creation of a more conductive nerve microenvironment. For example, hurdles associated with the short half-lives and low stability of molecular therapies are being surmounted through the use of controlled delivery systems. Similarly, cells (SCs, stem cells and genetically modified cells) are being delivered with biomaterial matrices in attempts to control their dispersion and to facilitate their incorporation within the host regeneration process. Despite recent advances in peripheral nerve repair, there are a number of key factors that need to be considered in order for these new technologies to reach the clinic.

Reduction of post-traumatic neuroma and epineural scar formation in rat sciatic nerve by application of microcrystallic chitosan

Injury of peripheral nerve is associated with the development of post-traumatic neuroma at the end of the proximal stump, often being the origin of neuropathic pain. This type of pain is therapy-resistant and therefore extremely nagging for patients. We examined the influence of the microcrystallic chitosan gel applied to the proximal stump of totally transected sciatic nerve on the neuroma formation and neuropathic pain development in rats. In 14 rats, right sciatic nerve was transected and the distal stump was removed to avoid spontaneous rejoining. In the chitosan (experimental) group (n = 7), the proximal stump was covered with a thin layer of the microcrystallic chitosan gel. In control animals (n = 7), the cut nerve was left unsecured. Autotomy, an animal model of neuropathic pain, was monitored daily for 20 weeks following surgery. Then, the animals were perfused transcardially and the proximal stumps of sciatic nerves were dissected and subjected to histologic evaluation. The presence, size, and characteristics of neuromas as well as extraneural fibrosis were examined. In chitosan group, the incidence and the size of the neuroma were markedly reduced, as compared with the control group; however, there was no difference in autotomy behavior between groups. In addition, extraneural fibrosis was significantly reduced in chitosan group when compared to the control group. The results demonstrate beneficial influence of microcrystallic chitosan applied to the site of nerve transection on the development of post-traumatic neuroma and reduction of extraneural fibrosis, however without reduction of neuropathic pain.

Neural tissue engineering using embryonic and induced pluripotent stem cells

With the recent start of the first clinical trial evaluating a human embryonic stem cell-derived therapy for the treatment of acute spinal cord injury, it is important to review the current literature examining the use of embryonic stem cells for neural tissue engineering applications with a focus on diseases and disorders that affect the central nervous system. Embryonic stem cells exhibit pluripotency and thus can differentiate into any cell type found in the body, including those found in the nervous system. A range of studies have investigated how to direct the differentiation of embryonic cells into specific neural phenotypes using a variety of cues to achieve the goal of replacing diseased or damaged neural tissue. Additionally, the recent development of induced pluripotent stem cells provides an intriguing alternative to the use of human embryonic stem cell lines for these applications. This review will discuss relevant studies that have used embryonic stem cells to replicate the tissue found in the central nervous system as well as evaluate the potential of induced pluripotent stem cells for the aforementioned applications.

Hyaluronan tetrasaccharide promotes regeneration of peripheral nerve: in vivo analysis by film model method

Hyaluronan (HA) is known to inhibit neurons from regenerating in the central nervous system. However, hyaluronan tetrasaccharide (HA4) was found in in vitro experiments to promote outgrowth of neurons. To investigate the promotion by HA4 of nerve regeneration in vivo, we analyzed outgrowth of regenerating axons treated with HA4, using a film model method. After the common peroneal nerve in mice was transected, the proximal end of cut nerve was placed on a sheet of thin plastic film, immersed in several drops of HA4 solution, covered with another sheet of film, and then kept in vivo. Six hours after the procedure, terminal sprouts had grown out from ending bulbs formed at the cut end of parent nerve administered with HA4 solution 100 or 1000 μg/mL, while no sprouts were observed in groups treated with 10 μg/mL of HA4 or in controls. On the 2nd day after axotomy (day 2), many regenerating axons in the group treated with 100 μg/mL of HA4 extended onto the flat film for a longer distance than those treated with 1000 μg/mL of HA4 and controls. With the optimal dose of HA4 (100 μg/mL), axonal outgrowth was significantly (p<0.01) greater than that in controls at each time point. Schwann cells appeared migrating from parent nerve onto the film from day 3 as well as in controls. Thus, enhanced outgrowth of regenerating axons and normal behavior of migratory Schwann cells suggested that HA4 promoted regeneration of neurons without the mediation of Schwann cells.