Regeneration and repair of peripheral nerves with different biomaterials: review

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.

Regenerative strategies for craniofacial disorders

Craniofacial disorders present markedly complicated problems in reconstruction because of the complex interactions of the multiple, simultaneously affected tissues. Regenerative medicine holds promise for new strategies to improve treatment of these disorders. This review addresses current areas of unmet need in craniofacial reconstruction and emphasizes how craniofacial tissues differ from their analogs elsewhere in the body. We present a problem-based approach to illustrate current treatment strategies for various craniofacial disorders, to highlight areas of need, and to suggest regenerative strategies for craniofacial bone, fat, muscle, nerve, and skin. For some tissues, current approaches offer excellent reconstructive solutions using autologous tissue or prosthetic materials. Thus, new “regenerative” approaches would need to offer major advantages in order to be adopted. In other tissues, the unmet need is great, and we suggest the greatest regenerative need is for muscle, skin, and nerve. The advent of composite facial tissue transplantation and the development of regenerative medicine are each likely to add important new paradigms to our treatment of craniofacial disorders.

Repairing nerve gaps by vein conduits filled with lipoaspirate-derived entire adipose tissue hinders nerve regeneration

In spite of great recent advancements, the definition of the optimal strategy for bridging a nerve defect, especially across long gaps, still remains an open issue since the amount of autologous nerve graft material is limited while the outcome after alternative tubulization techniques is often unsatisfactory. The aim of this study was to investigate a new tubulization technique based on the employment of vein conduits filled with whole subcutaneous adipose tissue obtained by lipoaspiration. In adult rats, a 1cm-long defect of the left median nerve was repaired by adipose tissue-vein-combined conduits and compared with fresh skeletal muscle tissue-vein-combined conduits and autologous nerve grafts made by the excised nerve segment rotated by 180°. Throughout the postoperative period, functional recovery was assessed using the grasping test. Regenerated nerve samples were withdrawn at postoperative month-6 and processed for light and electron microscopy and stereology of regenerated nerve fibers. Results showed that functional recovery was significantly slower in the adipose tissue-enriched group in comparison to both control groups. Light and electron microscopy showed that a large amount of adipose tissue was still present inside the vein conduits at postoperative month-6. Stereology showed that all quantitative morphological predictors analyzed performed significantly worse in the adipose tissue-enriched group in comparison to the two control groups. On the basis of this experimental study in the rat, the use of whole adipose tissue for tissue engineering of peripheral nerves should be discouraged. Pre-treatment of adipose tissue aimed at isolating stromal vascular fraction and/or adipose derived stem/precursor cells should be considered a fundamental requisite for nerve repair.

Emerging issues in peripheral nerve repair

It is today widely acknowledged that nerve repair is now more than a matter of perfect microsurgical reconstruction only and that, to further improve clinical outcome, the involvement of different scientific disciplines is required. This evolving reconstructive/regenerative approach is based on the interdisciplinary and integrated pillars of tissue engineering such as reconstructive microsurgery, transplantation and biomaterials. In this paper, some of the most promising innovations for the tissue engineering of nerves, emerging from basic science investigation, are critically overviewed with special focus on those approaches that appear today to be more suitable for clinical translation.

A bio-inspired neural environment to control neurons comprising radial glia, substrate chemistry and topography

Achieving alignment of cells is key to the success of regenerative strategies of neural tissue. We report a high-throughput method to investigate neural cell response to surface chemistry overlaid orthogonally onto a gradient of gradually changing groove widths. Using a bio-inspired approach wherein radial glial cells, which naturally guide neurons in the developing brain, enhance the attachment and directional outgrowth of neurons, we show the differences in the interaction and cellular response of glia, neurons and co-cultured cells. Radial glia were found to preferentially reside in grooves of width 6-35 μm with greater alignment to grooves <10 μm on the hydrophobic and hydrophilic extremes of chemistry. When neurons were sequentially cultured after radial glia, they showed enhanced alignment compared to when they were cultured alone, for all chemistries and groove widths. This is not dependent on co-localisation of the neurons with glia suggesting the radial glial cells pre-condition the substrate giving rise to enhanced attachment and alignment of subsequently cultured neurons. The results indicate a dependence of both primary radial glia and neuron responses on surface chemistry and micro-groove width. Grooved surfaces (width 5-10 μm) of mid-range wettability show the greatest potential to significantly enhance axonal alignment and, therefore, potential regeneration, when pre-conditioned by radial glia, highlighting the importance of surface engineering for neural scaffolds.

Enhancement of nerve regeneration along a chitosan conduit combined with bone marrow mesenchymal stem cells

Many studies have been dedicated to the development of scaffolds for improving post-traumatic nerve regeneration with different biomaterials. Nerve autografting is the most common surgical procedure currently used to repair nerve defects as a gold standard. To address the disadvantages of limited availability of donor nerves and donor site morbidity, we have fabricated chitosan conduits and seeded them combined with bone marrow mesenchymal stem cells (BMSCs) as an alternative. The conduits were tested for efficacy in bridging the critical gap (8 mm) in sciatic nerves of adult rats, which including sciatic nerve function index (SFI), ethology observation, histologic detection, immunohistochemistry detection. The BMSCs were tested for survival rate and differentiation by fluorescence labeling. Six weeks after operation, the SFI, average regenerated fiber density, and fiber diameter in nerves bridged with BMSCs were similar to those treated with autograft, but significantly higher than those bridged with chitosan conduits only (P < 0.05) because of the differentiation of BMSCs. Evidence is thus provided to support the effect of using multi-channel chitosan conduits seeded with BMSCs to treat critical defects in peripheral nerves. This provides the basis to pursue chitosan and BMSCs combination is an effective method to improve the nerve healing, which may be used as an alternative to the conventional nerve autografts.

Vascular endothelial growth factor-loaded poly(lactic-co-glycolic acid) microspheres-induced lateral axonal sprouting into the vein graft bridging two healthy nerves: nerve graft prefabrication using controlled release system

The most commonly used surgical technique for repairing segmental nerve defects is autogenous nerve grafting; however, this method causes donor site morbidity. In this study, we sought to produce prefabricated nerve grafts that can serve as a conduit instead of autologous nerve using a controlled release system created with vascular endothelial growth factor (VEGF)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres. The study was performed in vitro and in vivo. For the in vitro studies, VEGF-loaded PLGA microspheres were prepared. Thirty rats were used for the in vivo studies. Vein grafts were sutured between the tibial and peroneal nerves in all animals. Three groups were created, and an epineural window, partial incision, and microsphere application were performed, respectively. Walking track analysis, morphologic, and electron microscopic assessment were performed at the end of the eight weeks. Microspheres were produced in spherical shapes as required. Controlled release of VEGF was achieved during a 30-days period. Although signs of nerve injury occurred initially in the partial incision groups according to the indexes of peroneal and tibial function, it improved gradually. The index values were not affected in the other groups. There were many myelinated fibers with large diameters in the partial incision and controlled release groups, while a few myelinated fibers that passed through vein graft in the epineural window group. Thereby, prefabrication was carried out for the second and third groups. It was demonstrated that nerve graft can be prefabricated by the controlled delivery of VEGF.

Axonal regeneration and motor neuron survival after microsurgical nerve reconstruction

Rodent models are used extensively for studying nerve regeneration, but little is known about how sprouting and pruning influence peripheral nerve fiber counts and motor neuron pools. The purpose of this study was to identify fluctuations in nerve regeneration and neuronal survival over time. One hundred and forty-four Lewis rats were randomized to end-to-end repair or nerve grafting (1.5 cm graft) after sciatic nerve transection. Quantitative histomorphometry and retrograde labeling of motor neurons were performed at 1, 3, 6, 9, 12, and 24 months and supplemented by electron microscopy. Fiber counts and motor neuron counts increased between 1 and 3 months, followed by plateau. End-to-end repair resulted in persistently higher fiber counts compared to the grafting for all time points (P < 0.05). Percent neural tissue and myelin width increased with time while fibrin debris dissipated. In conclusion, these data detail the natural history of regeneration and demonstrate that overall fiber counts may remain stable despite pruning.

The effect of intraluminal contact mediated guidance signals on axonal mismatch during peripheral nerve repair

The current microsurgical gold standard for repairing long gap nerve injuries is the autograft. Autograft provides a protective environment for repair and a natural internal architecture, which is essential for regeneration. Current clinically approved hollow nerve guidance conduits allow provision of this protective environment; however they fail to provide an essential internal architecture to the regenerating nerve. In the present study both structured and unstructured intraluminal collagen fibres are investigated to assess their ability to enhance conduit mediated nerve repair. This study presents a direct comparison of both structured and unstructured fibres in vivo. The addition of intraluminal guidance structures was shown to significantly decrease axonal dispersion within the conduit and reduced axonal mismatch of distal nerve targets (p < 0.05). The intraluminal fibres were shown to be successfully incorporated into the host regenerative process, acting as a platform for Schwann cell migration and axonal regeneration. Ultimately the fibres were able to provide a platform for nerve regeneration in a long term regeneration study (16 weeks) and facilitated increased guidance of regenerating axons towards their distal nerve targets.

The long-term functional recovery of repair of sciatic nerve transection with biogenic conduits

INTRODUCTION

The aim of this study was to evaluate long-term regenerative capacity over a 15-mm nerve gap of an autologous nerve conduit, the biogenic conduit (BC), 16 weeks after sciatic nerve transection in the rat.

METHODS

A 19-mm long polyvinyl chloride (PVC) tube was implanted parallely to the sciatic nerve. After implantation, a connective tissue cover developed around the PVC-tube, the so-called BC. After removal of the PVC-tube the BCs filled with fibrin (n = 8) were compared to autologous nerve grafts (n = 8). Sciatic functional index (SFI) was evaluated every 4 weeks, histological evaluation was performed at 16 weeks postimplantation. Regenerating axons were visualized by retrograde labelling.

RESULTS

SFI revealed no significant differences. Nerve area and axon number in the BC group were significantly lower than in the autologous nerve group (P < 0.05; P < 0.01). Analysis of myelin formation showed no significant difference in both groups. Analysis of N-ratio revealed lower values in the BC group (P < 0.001).

CONCLUSION

This study reveals the suitability of BC for nerve gap bridging over a period of 16 weeks with functional recovery to comparable extent as the autologous nerve graft despite impaired histomorphometric parameters.

Spatiotemporal expression profiling of proteins in rat sciatic nerve regeneration using reverse phase protein arrays

Background

Protein expression profiles throughout 28 days of peripheral nerve regeneration were characterized using an established rat sciatic nerve transection injury model. Reverse phase protein microarrays were used to identify the spatial and temporal expression profile of multiple proteins implicated in peripheral nerve regeneration including growth factors, extracellular matrix proteins, and proteins involved in adhesion and migration. This high-throughput approach enabled the simultaneous analysis of 3,360 samples on a nitrocellulose-coated slide.

Results

The extracellular matrix proteins collagen I and III, laminin gamma-1, fibronectin, nidogen and versican displayed an early increase in protein levels in the guide and proximal sections of the regenerating nerve with levels at or above the baseline expression of intact nerve by the end of the 28 day experimental course. The 28 day protein levels were also at or above baseline in the distal segment however an early increase was only noted for laminin, nidogen, and fibronectin. While the level of epidermal growth factor, ciliary neurotrophic factor and fibroblast growth factor-1 and -2 increased throughout the experimental course in the proximal and distal segments, nerve growth factor only increased in the distal segment and fibroblast growth factor-1 and -2 and nerve growth factor were the only proteins in that group to show an early increase in the guide contents. As expected, several proteins involved in cell adhesion and motility; namely focal adhesion kinase, N-cadherin and β-catenin increased earlier in the proximal and distal segments than in the guide contents reflecting the relatively acellular matrix of the early regenerate.

Conclusions

In this study we identified changes in expression of multiple proteins over time linked to regeneration of the rat sciatic nerve both demonstrating the utility of reverse phase protein arrays in nerve regeneration research and revealing a detailed, composite spatiotemporal expression profile of peripheral nerve regeneration.

Growth-Promoting Effects of Quercetin on Peripheral Nerves in Rats

Objectives

The present study evaluated in vitro and in vivo the effects of quercetin (QC), a major ingredient in various flavonoids, on peripheral nerve regeneration.

Methods

In the in vitro study, we found that QC at concentrations of 0.1, 1, and 10 μg/mL could significantly promote the survival and outgrowth of cultured Schwann cells as compared with the controls treated with culture medium only. In the in vivo study, we evaluated peripheral nerve regeneration across a 15-mm gap in the sciatic nerve of the rat, using a silicone rubber nerve chamber filled with the QC solution. In the control group, the chambers were filled with normal saline only.

Results

At the end of 8 weeks, morphometric data revealed that all 3 QC groups significantly increased the count and density of myelinated axons as compared with the controls. Electro-physiological measurements showed that the QC-treated group at 1 μg/mL had a significantly larger area of evoked muscle action potential (MAP) compared with the controls. In addition, the amplitude of the MAP in the QC-treated groups at 0.1 and 1 μg/mL was significantly larger than that in the controls.

Conclusions

All of these results indicate that QC treatment has nerve growth–promoting effects which may lead to a promising herbal medicine for the recovery of regenerating peripheral nerves.

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.

Surgical management of facial nerve paralysis in the pediatric population

BACKGROUND

In the pediatric patient population, both the pathology and the surgical managements of seventh cranial nerve palsy are complicated by the small size of the patients. Adding to the technical difficulty is the relative infrequency of the diagnosis, thus making it harder to become proficient in the management of the condition. The magnitude of the functional and aesthetic deficits these children manifest is significantly troubling to both the patient and the parents, which makes immediate attention, treatment, and functional restoration essential.

METHODS

A literature search using PubMed (http://www.pubmed.org) was undertaken to identify the current state of surgical management of pediatric facial paralysis.

RESULTS

Although a multitude of techniques have been used, the ideal reconstructive procedure that addresses all of the functional and cosmetic needs of these children has yet to be described. Certainly, future research and innovative thinking will yield progressively better techniques that may, one day, emulate the native facial musculature with remarkable precision.

CONCLUSION

The necessity for surgical intervention in children with facial nerve paralysis differs depending on many factors including the acute/chronic nature of the defect as well as the extent of functional and cosmetic damage. In this article, we review the surgical procedures that have been used to treat pediatric facial nerve paralysis and provide therapeutic facial reanimation.

Bioartificial reconstruction of peripheral nerves using the rat median nerve model

Different bioartificial tubes were recommended for peripheral nerve reconstruction in the past. In order to replace autologous nerve grafts this materials are still under review in different animal studies. Most of them are dealing with the rodent peripheral nerves. One very popular animal model to study different materials is the rat median nerve model. With its easy excess, simple behavioral tests and reliable long term results it is attractive to many scientists in this field. This review gives an overview about the past, current and future options in this model for bioartificial nerve tubes. It summarizes the evolution of successful implantation of different materials across short nerve gaps and demonstrates the obstacles arising from long nerve gaps and the problems associated to them.