Bridging larger gaps in peripheral nerves using neural prosthetics and physical therapeutic agents

Histological, immunohistochemical, and morphometric analysis of negative pressure-assisted in-vivo nerve stretch-growth

Axons respond well to mechanical stimuli and can be stretched mechanically to increase their growth rate. Although stretch growth of axons and their transient lengthening ex-vivo has been discussed in literature extensively, however, real applications of this phenomenon are scarcely found. This work presents a technique to translate ex-vivo axonal stretch growth to in-vivo nerve stretch growth. By establishing a rat model of completely transected sciatic nerve injury, the regrowth rate of the proximal nerve stump was examined under the effect of a stretching force developed by negative pressure. In this manuscript, results have been presented based on quantitative and qualitative analysis of the stained nerve tissues. Gross observations have explicitly confirmed that the proximal stump of a whole sectioned sciatic nerve of a Wistar rat stretched in a T-shaped nerve prosthesis using a controlled amount of negative pressure displayed a better outcome in terms of an increase in the total length of proximal nerve stump post-treatment and a higher number of blood vessels with respect to control. The histological and morphometric analyses confirmed that negative pressure-assisted nerve growth provides an alluring control over nerve's regrowth rate. Immunohistochemical staining also supported the existence of a positive correlation between nerve growth and in-vivo application of axial stress on it. This work presents the first holistic evidence on growing nerves in the continuum of in-vivo nerve stretch growth using negative pressure and concludes that systematic and controlled negative pressure applied directly to the resected ends of a sciatic nerve resulted in the enhanced growth rate of regenerating nerve fibres.

Negative Pressure Neurogenesis: A Novel Approach to Accelerate Nerve Regeneration after Complete Peripheral Nerve Transection

Various modalities to facilitate nerve regeneration have been described in the literature with limited success. We hypothesized that negative pressure applied to a sectioned peripheral nerve would enhance nerve regeneration by promoting angiogenesis and axonal lengthening.

METHODS

Wistar rats' sciatic nerves were cut (creating ~7 mm nerve gap) and placed into a silicone T-tube, to which negative pressure was applied. The rats were divided into 4 groups: control (no pressure), group A (low pressure: 10 mm Hg), group B (medium pressure: 20/30 mm Hg) and group C (high pressure: 50/70 mm Hg). The nerve segments were retrieved after 7 days for gross and histological analysis.

RESULTS

In total, 22 rats completed the study. The control group showed insignificant nerve growth, whereas the 3 negative pressure groups showed nerve growth and nerve gap reduction. The true nerve growth was highest in group A (median: 3.54 mm) compared to group B, C, and control (medians: 1.19 mm, 1.3 mm, and 0.35 mm); however, only group A was found to be significantly different to the control group (**P < 0.01). Similarly, angiogenesis was observed to be significantly greater in group A (**P < 0.01) in comparison to the control.

CONCLUSIONS

Negative pressure stimulated nerve lengthening and angiogenesis within an in vivo rat model. Low negative pressure (10 mm Hg) provided superior results over the higher negative pressure groups and the control, favoring axonal growth. Further studies are required with greater number of rats and longer recovery time to assess the functional outcome.

A Systematic Review of the Effectiveness of Cell-Based Therapy in Repairing Peripheral Nerve Gap Defects

Nerve prostheses are widely utilized to reconstruct segmental (gap) defects in peripheral nerves as an alternative to nerve grafting. However, with increasing gap length, the effectiveness of a nerve prosthesis becomes sub-optimal, which subsequently has made repairing larger gaps in peripheral nerves a significant challenge in the field of regenerative medicine. Recently, the structure of nerve prostheses has been significantly revised, which interestingly, has provided a promising avenue for the housing and proliferation of supportive cells. In this systematic review, cell implantation in synthetic nerve prostheses to enhance the regenerative capability of an injured nerve with a focus on identifying the cell type and mode of cell delivery is discussed. Of interest are the studies employing supportive cells to bridge gaps greater than 10 mm without the aid of nerve growth factors. The results have shown that cell therapy in conjunction with nerve prostheses becomes inevitable and has dramatically boosted the ability of these prostheses to maintain sustainable nerve regeneration across larger gaps and helped to attain functional recovery, which is the ultimate goal. The statistical analysis supports the use of differentiated bone-marrow-derived mesenchymal stem cells suspended in oxygen-carrying hydrogels in chitosan prostheses for bridging gaps of up to 40 mm; however, based on the imperfect repair outcomes, nerve grafting should not yet be replaced altogether.

Design and fabrication of a nerve-stretching device for in vivo mechanotransduction of peripheral nerve fibers

The potential of peripheral nerves to regenerate under the effect of axial tensile forces was not previously extensively explored due to the lack of capabilities of translating ex vivo axonal stretch-growth to in vivo studies, until the development of a nerve stretcher. The nerve stretcher, which we have designed and manufactured recently, is a device that uses a controlled amount of axial tensile force (vacuum/negative gauge pressure) applied directly to a sectioned peripheral nerve in vivo to expedite nerve regrowth rate. Using this platform, a series of experiments was carried out to observe the effect of in vivo axial stretch on axonal lengthening. During these experiments, a few challenges necessitated redesigning the device like a sudden loss of stretching force due to vacuum leakage, erroneous feedback from vacuum sensor due to sensor drift, and inability to control and operate the device remotely. Here we present an improved design of the nerve stretcher along with its integration with a state-of-the-art online vacuum monitoring facility to control, collect, process, and visualize negative gauge pressure data in real-time.

Temporal changes in the spinal cord transcriptome after peripheral nerve injury

Peripheral nerve injury may trigger changes in mRNA levels in the spinal cord. Finding key mRNAs is important for improving repair after nerve injury. This study aimed to investigate changes in mRNAs in the spinal cord following sciatic nerve injury by transcriptomic analysis. The left sciatic nerve denervation model was established in C57BL/6 mice. The left L4-6 spinal cord segment was obtained at 0, 1, 2, 4 and 8 weeks after severing the sciatic nerve. mRNA expression profiles were generated by RNA sequencing. The sequencing results of spinal cord mRNA at 1, 2, 4, and 8 weeks after severing the sciatic nerve were compared with those at 0 weeks by bioinformatic analysis. We identified 1915 differentially expressed mRNAs in the spinal cord, of which 4, 1909, and 2 were differentially expressed at 1, 4, and 8 weeks after sciatic nerve injury, respectively. Sequencing results indicated that the number of differentially expressed mRNAs in the spinal cord was highest at 4 weeks after sciatic nerve injury. These mRNAs were associated with the cellular response to lipid, ATP metabolism, energy coupled proton transmembrane transport, nuclear transcription factor complex, vacuolar proton-transporting V-type ATPase complex, inner mitochondrial membrane protein complex, tau protein binding, NADH dehydrogenase activity and hydrogen ion transmembrane transporter activity. Of these mRNAs, Sgk1, Neurturin and Gpnmb took part in cell growth and development. Pathway analysis showed that these mRNAs were mainly involved in aldosterone-regulated sodium reabsorption, oxidative phosphorylation and collecting duct acid secretion. Functional assessment indicated that these mRNAs were associated with inflammation and cell morphology development. Our findings show that the number and type of spinal cord mRNAs involved in changes at different time points after peripheral nerve injury were different. The number of differentially expressed mRNAs in the spinal cord was highest at 4 weeks after sciatic nerve injury. These results provide reference data for finding new targets for the treatment of peripheral nerve injury, and for further gene therapy studies of peripheral nerve injury and repair. The study procedures were approved by the Ethics Committee of the Peking University People's Hospital (approval No. 2017PHC004) on March 5, 2017.