The High-Frequency Ultrasound Detection of Rat Sciatic Nerve in a Crushed Injury Model.

OBJECTIVE: This study aimed to visualize sciatic nerve injury in rats using ultrasound imaging in a crushed injury model. METHODS: Adult male Sprague-Dawley rats were subjected to a left sciatic nerve crush operation. Then, high-frequency ultrasound was used to image both sciatic nerves at 2 days and at 1, 2, 3, 4, and 6 weeks after surgery. RESULTS: Normal uninjured nerves have uniform thickness, display a smooth epineurium and inner adventitia, and are oblong in transverse sections. After the crush operation, nerve thickness increased, the inner echo signal decreased, the image of the epineurium became obscured and coarse before becoming smooth again, and transverse sections of the nerve fibers changed from being semicircular to oval in shape before becoming elliptical again. These observations were consistent with pathological changes associated with nerve injury. CONCLUSIONS: High-frequency ultrasound is capable of capturing dynamic changes in rat sciatic nerves in a crushed injury model. This can be used as an auxiliary method of evaluation in traditional peripheral nerve injury experiments.

Novel conductive polypyrrole/silk fibroin scaffold for neural tissue repair.

Three dimensional (3D) bioprinting, which involves depositing bioinks (mixed biomaterials) layer by layer to form computer-aided designs, is an ideal method for fabricating complex 3D biological structures. However, it remains challenging to prepare biomaterials with micro-nanostructures that accurately mimic the nanostructural features of natural tissues. A novel nanotechnological tool, electrospinning, permits the processing and modification of proper nanoscale biomaterials to enhance neural cell adhesion, migration, proliferation, differentiation, and subsequent nerve regeneration. The composite scaffold was prepared by combining 3D bioprinting with subsequent electrochemical deposition of polypyrrole and electrospinning of silk fibroin to form a composite polypyrrole/silk fibroin scaffold. Fourier transform infrared spectroscopy was used to analyze scaffold composition. The surface morphology of the scaffold was observed by light microscopy and scanning electron microscopy. A digital multimeter was used to measure the resistivity of prepared scaffolds. Light microscopy was applied to observe the surface morphology of scaffolds immersed in water or Dulbecco's Modified Eagle's Medium at 37°C for 30 days to assess stability. Results showed characteristic peaks of polypyrrole and silk fibroin in the synthesized conductive polypyrrole/silk fibroin scaffold, as well as the structure of the electrospun nanofiber layer on the surface. The electrical conductivity was 1 × 10-5-1 × 10-3 S/cm, while stability was 66.67%. A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay was employed to measure scaffold cytotoxicity in vitro. Fluorescence microscopy was used to observe EdU-labeled Schwann cells to quantify cell proliferation. Immunohistochemistry was utilized to detect S100ß immunoreactivity, while scanning electron microscopy was applied to observe the morphology of adherent Schwann cells. Results demonstrated that the polypyrrole/silk fibroin scaffold was not cytotoxic and did not affect Schwann cell proliferation. Moreover, filopodia formed on the scaffold and Schwann cells were regularly arranged. Our findings verified that the composite polypyrrole/silk fibroin scaffold has good biocompatibility and may be a suitable material for neural tissue engineering.

A partition-type tubular scaffold loaded with PDGF-releasing microspheres for spinal cord repair facilitates the directional migration and growth of cells.

The best tissue-engineered spinal cord grafts not only match the structural characteristics of the spinal cord but also allow the seed cells to grow and function in situ. Platelet-derived growth factor (PDGF) has been shown to promote the migration of bone marrow stromal cells; however, cytokines need to be released at a steady rate to maintain a stable concentration in vivo. Therefore, new methods are needed to maintain an optimal concentration of cytokines over an extended period of time to effectively promote seed cell localization, proliferation and differentiation. In the present study, a partition-type tubular scaffold matching the anatomical features of the thoracic 8-10 spinal cord of the rat was fabricated using chitosan and then subsequently loaded with chitosan-encapsulated PDGF-BB microspheres (PDGF-MSs). The PDGF-MS-containing scaffold was then examined in vitro for sustained-release capacity, biocompatibility, and its effect on neural progenitor cells differentiated in vitro from multilineage-differentiating stress-enduring cells (MUSE-NPCs). We found that pre-freezing for 2 hours at -20°C significantly increased the yield of partition-type tubular scaffolds, and 30 µL of 25% glutaraldehyde ensured optimal crosslinking of PDGF-MSs. The resulting PDGF-MSs cumulatively released 52% of the PDGF-BB at 4 weeks in vitro without burst release. The PDGF-MS-containing tubular scaffold showed suitable biocompatibility towards MUSE-NPCs and could promote the directional migration and growth of these cells. These findings indicate that the combination of a partition-type tubular scaffold, PDGF-MSs and MUSE-NPCs may be a promising model for the fabrication of tissue-engineered spinal cord grafts.

The Effect of Low-Intensity Ultrasound on Brain-Derived Neurotropic Factor Expression in a Rat Sciatic Nerve Crushed Injury Model.

Low-intensity ultrasound (LIU) can improve nerve regeneration and functional recovery after peripheral nerve crush injury, but the underlying mechanism is not clear. The objective of this study was to examine the effects of LIU on rat sciatic crush injury and to investigate a possible molecular mechanism. Adult male Sprague-Dawley rats underwent left sciatic nerve crush surgery and were then randomized into two groups: a treatment group that received LIU every other d, and a control group that received sham exposure. Compared with rats in the control group, rats in the treatment group had higher sciatic nerve function indexes, compound muscle action potentials, wet weight ratios of the target muscle and mRNA expression of brain-derived neurotropic factor (BDNF) in the crushed nerve and ipsilateral dorsal root ganglia. Our findings suggest that LIU might promote injured nerve regeneration by stimulating BDNF release.

Angiogenesis in tissue-engineered nerves evaluated objectively using MICROFIL perfusion and micro-CT scanning.

Angiogenesis is a key process in regenerative medicine generally, as well as in the specific field of nerve regeneration. However, no convenient and objective method for evaluating the angiogenesis of tissue-engineered nerves has been reported. In this study, tissue-engineered nerves were constructed in vitro using Schwann cells differentiated from rat skin-derived precursors as supporting cells and chitosan nerve conduits combined with silk fibroin fibers as scaffolds to bridge 10-mm sciatic nerve defects in rats. Four weeks after surgery, three-dimensional blood vessel reconstructions were made through MICROFIL perfusion and micro-CT scanning, and parameter analysis of the tissue-engineered nerves was performed. New blood vessels grew into the tissue-engineered nerves from three main directions: the proximal end, the distal end, and the middle. The parameter analysis of the three-dimensional blood vessel images yielded several parameters, including the number, diameter, connection, and spatial distribution of blood vessels. The new blood vessels were mainly capillaries and microvessels, with diameters ranging from 9 to 301 µm. The blood vessels with diameters from 27 to 155 µm accounted for 82.84% of the new vessels. The microvessels in the tissue-engineered nerves implanted in vivo were relatively well-identified using the MICROFIL perfusion and micro-CT scanning method, which allows the evaluation and comparison of differences and changes of angiogenesis in tissue-engineered nerves implanted in vivo.

Controlling the release of bFGF from silk fibroin membrane.

Since neurotrophic factor is easy to degrade and aggregate, it usually has a short half-life in vitro. To overcome this shortage, neurotrophic factor has been combined with the silk fibroin (SF) membrane to realize less degradation, optimal loading efficiency, sustained release, and good adsorption. By optimizing its binding conditions, main parameters were investigated and its optimal loading efficiency was obtained. bFGF was combined to SF membrane by layer by layer (LbL) static adsorption technique. The natural and nontoxic chondroitin sulfate (CS) was used as a crosslinking agent. Optimization was carried out in three aspects: the concentration of bFGF, the concentration of CS, and the reaction time. This experiment provides a better environment for the growth of cells and offers a new kind material of absorbing neurotrophic factor to meet increasing demand for biological materials.