PHBV Nerve Conduits Prepared By Electrospinning

The restoration, regeneration and functional recovery in peripheral nerve injury have been a hot subject of the neuroscience. The emergence of tissue engineering provides a new way for the restoration of nerve injury. Currently, the nerve conduit has become one of the ways for the regeneration of peripheral nerve injury. How to prepare neural tubes that provide an environment for nerve regeneration, differentiation and growth has been the difficulty of neural tissue engineering scaffold. Nanofibers scaffolds with high porosity and large surface area prepared by electrospinning, that could imitate the natural extracellular matrix from the nano-scale, can be used as a porous scaffold to promote cell migration and proliferation.In this paper, poly(hydroxybutyrate-hydroxyvalerate)(PHBV), polyethylene glycol (PEG), poly(ε-caprolactone) (PCL) were chosed as the scaffold materials. Nerve conduit with three layers of aligned electrospun fibers was preparaed by electrospinning, melt spinning and plasma modification. It is characterized in that the inner tube made of electrospun PHBV/PEG aligned sub-micron fiber membrane, the middle layer prepared by woven mesh tube of PCL monofilament and the outer tube made of electrospun PHBV with high surface area and high porosity. The morphology, fiber arrangement, crystallization properties, orientation and mechanical properties of PHBV fibers prepared by electrospinning were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized infrared spectroscopy and universal testing machine. The morphology, fiber arrangement, compatibility, crystallization and crystal morphology of PHBV/PEG fiber were characterized by SEM, dynamic mechanical (DMA), thermogravimetric analysis (TG), DSC, WAXD, Fourier transform infrared spectroscopy (FTIR), polarized light microscopy (PLM). The surface morphology, mechanical properties and hydrophilicity of nerve conduits were characterized by SEM, universal testing machine and contact angle test. The main results were listed as follows: (1) PHBV could be electrospun with chloroform/DMF (10/1) as solvent systems, the best process parameters of the electrospinning were as follows:concentration of 6%, pushing speed at 0.5ml/h and voltage at 12KV.(2) During electrospinning of aligned PHBV fibers in which rotating target is used, the fiber arrangement, the orientation degree of crystalline region, molecular orientation degree, crystallinity and mechanical strength of fibers increase with the surface speed increasing, and reach at the maximum when the surface speed is 10.5m/s, but decrease subsequently. The rotating target has a role of stretch for the electrospun fibers so that the average fiber diameter and crystallite size reduce. The necking phenomena is not obvious after the yield point during stretching of electrospun aligned PHBV fibers, strain decrease until complete rupture as increasing of stress.(3) Using chloroform/DMF (10/1) as solvent, the optimum spinning parameters of electrospinning prepared PHBV/PEG fibers are:concentration of 8%, voltage at 10KV, receiving distance up to 18cm and the sample rate of 0.8ml/h. When the PEG is less than 50wt%, PHBV/PEG blends will have better spinnability and smooth surface, and the fibers will be more uniform in diameter, and increased to 70wt%, PHBV/PEG solution could still spin, but with a lot of breakages. The best surface speed for preparing PHBV/PEG electrospinning aligned fiber is 9.5m/s, while the fiber arrangements have a less degree than the pure PHBV.(4) DMA and FTIR analysis showed that the PHBV and PEG were incompatible. In nitrogen atmosphere, PEG improves the thermal stability of PHBV. In the air atmosphere, when the PEG content was more than 50%, the thermal stability of the blend decrease. The melting point, the grain size and the crystallization temperature of PHBV decreased with the PEG content increased by DSC, XRD, and POM analysis. When the PEG content not more than 50%, crystallinity of PHBV was unchanged, but decreased significantly after more than 50%.(5) During the weaving of PHBV/PEG inner tube, the PHBV/PEG membrane was better with 5 layers, each thickness is about 8μm. The best weaving parameters of the middle layer was: 21.65tex,8 spindles. The outer tube with a lower fiber arrangement of outer surface has the higher the porosity of 81%. Water contact angle measurement results showed that PHBV/PEG membrane are more hydrophilic with the increasing of PEG content, the hydrophilicity of outer tube increased significantly after the plasma modified.