Several nerve guidance conduits (NGCs) and nerve protectant wraps are approved by the US Food and Drug Administration (FDA) for clinical use in peripheral nerve repair. These devices cover a wide range of natural and synthetic materials, which may or may not be resorbable. This review consolidates the data pertaining to all FDA approved materials into a single reference, which emphasizes material composition alongside pre-clinical and clinical safety and efficacy (where possible). This article also summarizes the key advantages and limitations for each material as noted in the literature (with respect to the indication considered). In this context, this review provides a comprehensive reference for clinicians which may facilitate optimal material/device selection for peripheral nerve repair. For materials scientists, this review highlights predicate devices and evaluation methodologies, offering an insight into current deficiencies associated with state-of-the-art materials and may help direct new technology developments and evaluation methodologies thereof.

FDA approved guidance conduits and wraps for peripheral nerve injury: A review of materials and efficacy

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

This study was performed to determine whether vein grafts might serve as a conduit for nerve regeneration. A 1 cm segment of sciatic nerve was removed bilaterally in 12 Sprague-Dawley rats. On one side the gap was not repaired, and on the other side a segment of femoral vein was used to bridge the nerve gap. Nerve conduction studies and necropsies were performed at intervals. Reconstitution of nerve trunk continuity and healing of plantar ulcers occurred only in the vein-grafted side. Histologic examination revealed orderly growth of nerve fibers within the lumen of the vein grafts as early as 1 month after repair. Most regenerating nerve fibers passed through the proximal junction in an orderly pattern and reached the distal stumps within 2 months after repair. Results of nerve conduction study at 4 months after operation demonstrated restoration of conduction through the vein-grafted sciatic nerves with muscle reinnervation. Nearly normal muscle fibers in the gastrocnemius on the repaired side were confirmed at necropsy. This study demonstrated that autogenous vein grafts can serve as a conduit for nerve regeneration in rodents.

Autogenous vein graft as a conduit for nerve regeneration

The Histology of the Fowl

Transplantation of bone marrow mesenchymal stem cells on collagen scaffolds for the functional regeneration of injured rat uterus.

Microwave Irradiated collagen tubes as a better matrix for peripheral nerve regeneration

Neurotrophic factors play an important modulatory role in axonal sprouting during nerve regeneration involving the proliferation of hematogenous and Schwann cells in damaged tissue. We have exposed lesioned sciatic nerves to a collagen prosthesis with covalently bonded small cell adhesive peptides Arg-Gly-Asp-Ser (RGDS), Lys-Arg-Asp-Ser (KRDS), and Gly-His-Lys (GHK) to study local production of growth factors and cytokines in the regenerating tissues. Western/enzyme-linked immunosorbent assay (ELISA) studies were performed after 10 days of regeneration, when the tubular prosthesis is filled with fibrous matrix infiltrated by hematogenous cells and proliferating Schwann cells with growth factors produced locally. Regeneration was also analyzed by morphometrical methods after 30 days. The quantification of growth factors and proteins by ELISA revealed that there was an enhanced expression of the neurotrophic factors nerve growth factor (NGF) and neurotrophins (NT-3 and NT-4) in the regenerating tissues. This was further established by Western blot to qualitatively analyze the presence of the antigens in the regenerating tissues. Schwann cells were localized in the regenerating tissues using antibodies against S-100 protein. Other growth factors including growth-associated protein 43 (GAP-43), apolipoprotein E (Apo E), and pro-inflammatory cytokine like interleukin-1alpha (IL-1alpha) expression in the peptide groups were evaluated by ELISA and confirmed by Western blotting. Cell adhesive integrins in the proliferating cells were localized using integrin-alpha V. The combined results suggest that the early phase of regeneration of peripheral nerves in the presence of peptide-incorporated collagen tubes results in the enhanced production of trophic factors by the recruited hematogenous cells and Schwann cells, which in turn help in the secretion of certain vital trophic and tropic factors essential for early regeneration. Furthermore, hematogenous cells recruited within the first 10 days of regeneration help in the production of inflammatory mediators like interleukins that in turn stimulate Schwann cells to produce NGF for axonal growth.

Initial upregulation of growth factors and inflammatory mediators during nerve regeneration in the presence of cell adhesive peptide‐incorporated collagen tubes

Non-Invasive, Non-Enzymatic, Biodegradable and Flexible Sweat Glucose Sensor and Its Electrochemical Studies

The interrenal tissue ofthe adrcnal gland was studicd in different age groups of Japanese quail viz juvenile. immature, mature and senile birds. The interrenal tissue or the adrenal cortex was distinguished into a peripheral zone and a central inner zone. The interrenal cells were columnar and differentiated into types 1,2, 3 and 4 cells. The interrenal cells of the subcapsular zone were arranged in the form of loops and were made of type 1 cells. The cells of the central zone were stacked in double row and consisted of type 2 cells, The type 3 cells were distributed in the intermediatc layer between subcapsular zone and the central zone. Type 4 cells werc rarely found in the subcapsular zone. Ultrathin sections of the tissue showed that these interrenal cells were rich in mitochondria, smooth endoplasmic reticulum and lipid droplets. Atrophic changes in the intcrrenal tissue was observed in molting phase and hyperplasIa of the interrenal cells was recorded in senile birds.

Light and electron microscopic studies on the interrenal tissue of the adrenal gland in Japanese quail (Coturnix coturnix japonica)

The age changes in the histomorphology of the adrenal gland was recorded in different age groups of Japanese quail viz. Juvenile, immature, mature and senile birds of about 156 weeks of age. The tissues were collected from the above age groups, fixed in NBF, Bouin’s fluid and Orth fluid and processed by paraffin embedding technique. The adrenal gland of juvenile age group showed a well defined interrenal tissue and the chromaffin tissue. The interrenal tissue of the adrenal gland in one week old birds formed distinct loops in the periphery and cell cords in the inner portion of the gland. In immature age groups, the two zones of the interrenal tissue were well demarcated and medullary cells formed a discontinuous subcapsular layer and also intermingled in between the interrenal tissue in the form of islets. In mature birds the differentiation of interrenal cells into four types and foamy appearance of the inner zone interrenal cells was well established. Birds at molt revealed shrinkage of the interrenal tissue due to atrophic changes while hyperplasia of the interrenal cells and ganglionic transformation of medullary cells were noticed in senile birds.

Sabiha Hayath Basha

Papers

Microwave Irradiated collagen tubes as a better matrix for peripheral nerve regeneration

Initial upregulation of growth factors and inflammatory mediators during nerve regeneration in the presence of cell adhesive peptide‐incorporated collagen tubes

Non-Invasive, Non-Enzymatic, Biodegradable and Flexible Sweat Glucose Sensor and Its Electrochemical Studies

Light and electron microscopic studies on the interrenal tissue of the adrenal gland in Japanese quail (Coturnix coturnix japonica)

Age related changes of the adrenal gland in Japanese quail (Coturnix coturnix japonica).