Enhanced Peripheral Nerve Regeneration by a High Surface Area to Volume Ratio of Nerve Conduits Fabricated from Hydroxyethyl Cellulose/Soy Protein Composite Sponges

Abstract

Multichannel nerve guide conduits (MCNGCs) have been widely studied and exhibited outstanding nerve repair function. However, the effect of the geometric structure of MCNGCs on the nerve repair function was still not clear. Herein, we postulated that MCNGCs with different inner surface area-to-volume ratios (ISA/V) of the channels inside the nerve guide conduits (NGCs) would show different nerve repair functions. Therefore, in current work, we constructed a series of hydroxyethyl cellulose/soy protein sponge-based nerve conduit (HSSN) with low, medium, and high ISA/V from hydroxyethyl cellulose (HEC)/soy protein isolate (SPI) composite sponges, which were abbreviated as HSSN-L, HSSN-M and HSSN-H, respectively. These NGCs were applied to bridge and repair a 10 mm long sciatic nerve defect in a rat model. Finally, the influence of ISA/V on nerve repair function was evaluated by electrophysiological assessment, histological investigation, and in vivo biodegradability testing. The results of electrophysiological assessment and histological investigation showed that the regenerative nerve tissues bridged with HSSN-H and HSSN-M had higher compound muscle action potential amplitude ratio, higher percentage of positive NF200 and S100 staining, larger axon diameter, lower G-ratio, and greater myelination thickness. Furthermore, the regenerative nerve tissues bridged with HSSN-H also showed higher density of regenerated myelinated nerve fibers and more number of myelin sheath layers. On the whole, the repair efficiency of the peripheral nerve in HSSN-H and HSSN-M groups might be better than that in HSSN-L. These results indicated that higher ISA/V based on HEC/SPI composite sponge may result in greater nerve repair functions. The conclusion provided a probable guiding principle for the structural designs of NGCs in the future.

The advances in nerve tissue engineering: From fabrication of nerve conduit toin vivonerve regeneration assays

“…Some methods can be used for histological assessment of implanted nerve including hematoxylin and eosin (H&E) staining (Zhuang et al, ). Not only can H&E staining clearly show the formation of new neural bundles throughout the conduit (longitudinal sections) and their accumulation as a fasciculate structure, but it can also be used to visualize the presence of blood vessels and connective tissue in longitudinal and cross sections (Zhao et al, ; Zhuang et al, ).…”

“…For evaluation of the myelin sheath status of nerve fibers, toluidine blue and luxol fast blue (LFB) staining are commonly performed (Carriel, Garzon, Alaminos, & Campos, ; Zhao et al, ).…”

“…In addition to histological evaluation of nerve regeneration by conduit therapy, target muscle should be also evaluated in terms of structural analysis. Histological evaluation of the target muscles is often performed by H&E (the muscle fiber is stained in red; Zhuang et al, ) and Masson's trichrome staining (in cross sections, the muscle fibers are stained in red, and the collagen fibers are stained in green; Zhao et al, ).…”

“…The electron microscopic images can be used to assess the diameter of axons, density of myelinated axons, and thickness of myelin sheath. G‐ratio, a very reliable ratio for evaluation of axonal myelination in the repaired nerve, is calculated by the axon diameter to the myelinated fiber diameter (Zhao et al, ). Other less commonly used ratios include the N‐ratio and success ratio.…”

“…Success ratio is another ratio that evaluates the presence of myelinated nerve fibers distal to the entire implanted nerve, and it shows the success or failure of nerve repair (Vleggeert‐Lankamp, ). A transmission electron microscope is also used for ultrastructural analysis of target muscles (Zhao et al, ).…”