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Many bioartificial nerve guides have been investigated pre-clinically for their nerve regeneration-supporting function, often in comparison to autologous nerve transplantation, which is still regarded as the current clinical gold standard. Enrichment of these scaffolds with cells intended to support axonal regeneration has been explored as a strategy to boost axonal regeneration across these nerve guides Ansselin et al. (1998). In the present study, 20 mm rat sciatic nerve defects were implanted with a cell-seeded microstructured collagen nerve guide (Perimaix) or an autologous nerve graft. Under the influence of seeded, pre-differentiated mesenchymal stromal cells, axons regenerated well into the Perimaix nerve guide. Myelination-related parameters, like myelin sheath thickness, benefitted from an additional seeding with pre-differentiated mesenchymal stromal cells. Furthermore, both the number of retrogradely labelled sensory neurons and the axon density within the implant were elevated in the cell-seeded scaffold group with pre-differentiated mesenchymal stromal cells. However, a pre-differentiation had no influence on functional recovery. An additional cell seeding of the Perimaix nerve guide with mesenchymal stromal cells led to an extent of functional recovery, independent of the differentiation status, similar to autologous nerve transplantation. These findings encourage further investigations on pre-differentiated mesenchymal stromal cells as a cellular support for peripheral nerve regeneration., (© 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.)

A variety of new bioartificial nerve guides have been tested preclinically for their safety and nerve regeneration supporting properties. So far, only a limited number of biomaterials have been tested in humans since the step from preclinical work to a clinical application is challenging. We here present an in vitro model with human Schwann cells (hSCs) as an intermediate step towards clinical application of the nerve guide Perimaix, a collagen-based microstructured 3D scaffold containing numerous longitudinal guidance channels for directed axonal growth. hSCs were seeded onto different prototypes of Perimaix and cultivated for 14 days. hSC adhered to the scaffold, proliferated, and demonstrated healthy Schwann cell morphology (spindle shaped cell bodies, bipolar oriented processes) not only at the surface of the material, but also in the deeper layers of the scaffold. The general well-being of the cells was quantitatively confirmed by low levels of lactate dehydrogenase release into the culture medium. Moreover, conditioned medium of hSCs that were cultivated on Perimaix was able to modify neurite outgrowth from sensory dorsal root ganglion neurons. Overall these data indicate that Perimaix is able to provide a matrix that can promote the attachment and supports process extension, migration, and proliferation of hSC.

Autologous nerve transplantation (ANT) is the clinical gold standard for the reconstruction of peripheral nerve defects. A large number of bioengineered nerve guides have been tested under laboratory conditions as an alternative to the ANT. The step from experimental studies to the implementation of the device in the clinical setting is often substantial and the outcome is unpredictable. This is mainly linked to the heterogeneity of clinical peripheral nerve injuries, which is very different from standardized animal studies. In search of a reproducible human model for the implantation of bioengineered nerve guides, we propose the reconstruction of sural nerve defects after routine nerve biopsy as a first or baseline study. Our concept uses the medial sural nerve of patients undergoing diagnostic nerve biopsy (≥ 2 cm). The biopsy-induced nerve gap was immediately reconstructed by implantation of the novel microstructured nerve guide, Neuromaix, as part of an ongoing first-in-human study. Here we present (i) a detailed list of inclusion and exclusion criteria, (ii) a detailed description of the surgical procedure, and (iii) a follow-up concept with multimodal sensory evaluation techniques. The proximal medial sural nerve biopsy model can serve as a preliminary nature of the injuries or baseline nerve lesion model. In a subsequent step, newly developed nerve guides could be tested in more unpredictable and challenging clinical peripheral nerve lesions (e.g., following trauma) which have reduced comparability due to the different nature of the injuries (e.g., site of injury and length of nerve gap).

The regenerative capacity of the peripheral nervous system is largely related to Schwann cells undergoing proliferation and migration after injury and forming growth-supporting substrates for severed axons. Novel data show that fibroblasts to a certain extent regulate the pro-regenerative behavior of Schwann cells. In the setting of peripheral nerve injury, the fibroblasts that form the epineurium come into close contact with both Schwann cells and peripheral axons, but the potential influence on these latter two cell types has not been studied yet. In the present study we explored whether culture media, conditioned by epineurial fibroblasts can influence Schwann cells and/or neurite outgrowth from dorsal root ganglia neurons in vitro. Our data indicate that epineurial fibroblast-conditioned culture media substantially increase Schwann cell migration and the outgrowth of neurites. Schwann cell proliferation remained largely unaffected. These same read-out parameters were assayed in a condition where epineurial fibroblasts were subjected to stretch-cell-stress, a mechanical stressor that plays an important role in traumatic peripheral nerve injuries. Stretch-cell-stress of epineurial fibroblasts did not further change the positive effects of conditioned media on Schwann cell migration and neurite outgrowth. From these data we conclude that an as yet unknown pro-regenerative role can be attributed to epineurial fibroblasts, implying that such cells may affect the outcome of severe peripheral nerve injury., (Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.)

Evaluation of functional and structural recovery after peripheral nerve injury is crucial to determine the therapeutic effect of a nerve repair strategy. In the present study, we examined the relationship between the structural evaluation of regeneration by means of retrograde tracing and the functional analysis of toe spreading. Two standardized rat sciatic nerve injury models were used to address this relationship. As such, animals received either a 2 cm sciatic nerve defect (neurotmesis) followed by autologous nerve transplantation (ANT animals) or a crush injury with spontaneous recovery (axonotmesis; CI animals). Functional recovery of toe spreading was observed over an observation period of 84 days. In contrast to CI animals, ANT animals did not reach pre-surgical levels of toe spreading. After the observation period, the lipophilic dye DiI was applied to label sensory and motor neurons in dorsal root ganglia (DRG; sensory neurons) and spinal cord (motor neurons), respectively. No statistical difference in motor or sensory neuron counts could be detected between ANT and CI animals.In the present study we could indicate that there was no direct relationship between functional recovery (toe spreading) measured by SSI and the number of labelled (motor and sensory) neurons evaluated by retrograde tracing. The present findings demonstrate that a multimodal approach with a variety of independent evaluation tools is essential to understand and estimate the therapeutic benefit of a nerve repair strategy.