Investigation Of Preparation And Properties Of Microporous Silk-fibroin Composite Nanofibrous Scaffold

The electrospun nanofibrous scaffolds is similar to the extra-cellular matrix(ECM)of biological cell growth environment in fiber size and structure,so that it is widely used in skin,cornea,cartilage,nerve tissue engineering fields.However,fiber are closely packed in the nanofibrous scaffolds and pore size among fibers is too small.Therefore,cell is difficult to grow and infiltrate in and a thick tissue is difficult to constituted.In this paper,we focuses on the improvement on the thickness and pore size and porosity of nanofibrous scaffold,using the electrospinning technology combined with two methods of removing sacrificial material and using specific collector connected with negative voltage,to prepare microporous nanofibrous scaffolds which resembles the biological size of cells.This paper chose the concentration of 20wt% PEG dissolved in chloroform solution as an electrospraying solution,the PEG molecular chain of in this concentration are in the range of semi-dilute solution of moderate entanglement system.In this concentration,shapes and morphology of electrospraying PEG microspheres were the most stable and electrospraying can be used by adjusting the flow rate in a relatively large range.In the system,even the flow rate is below 4 m L/h,PEG microspheres can be collected in stable morphology.PEG microspheres with stable size and morphology were obtained by studying the water-soluble PEG microspheres with diameters of about 10 microns.With the method of removing sacrificial material,SF/Gelatin composite scaffold entrapped with PEG microspheres were collected on roller receiving device by the simultaneously electrospraying and electrospinning.Different contents of polyethylene glycol(PEG)microspheres were embedded into the SF/gelatin nanofibrous membranes by varying the content of PEG microsphere in preparation of nanofibrous scaffolds with different pore size and porosity.The pore size and porosity of composite nanofibrous scaffold further increase after removing water-soluble PEG microspheres within nanofibrous scaffold.After removing the PEG microspheres,the average pore size of composite nanofibrous scaffolds can reach more than 20 ?m with the high content of PEG microspheres.However,the mechanical strength of electrospun scaffolds significantly decreased with the increasing content of PEG.In order to improve the thickness and pore size of nanofibrous scaffold,a special electrospinning setup can effectively reduce collecting area of nanofibers that specific collector of copper plate were covered with a self-designed PMMA mask and the plate is connected to a negative voltage power supply.A power supply of +15 kV high voltage is connected to the needle and the negative high voltage is connected to circular copper plate.By this method,3 mm thick SF/PCL nanofibrous scaffold can be prepared.The coordinate system is established to analyze the electric field distribution between the needle and the center of circular metal plate and the electric field distribution on PMMA plate.It can be seen that electric field strength increases when it closes to the hole of collecting plate,the time and electric field force of fiber diffusion outward is reduced,resulting in more nanofibers concentrated towards a hole in the PMMA mask connected to a negative voltage.Finally,it can be found that pore size increases with the increasing thickness of quite thick nanofibrous scaffold from the analysis of cross-section SEM sample photo.The pore size can reach 25 ?m or more in the area of nanofibrous scaffold thickness more than 600 ?m.