Electrospinning Of Modified PLLA, And Structure And Properties Of Its Fibrous Membranes

Tissue engineering scaffolds material is the current research hotspot, especially the electrospun fibrous membranes are expected to have wide applications in tissue engineering field. In this dissertation, the biodegradable poly(L-lactide) (PLLA)was used as the research object, and it was modified with copolymerization, blending and composite. The electrospinning process, the structure and properties of the fibrous membranes were investigated. In order to improve the hydrophilic of the fibrous membranes, chondroitin sulfate (CS) and chitosan (CHS) were selected as the polyelectrolyte to deposit on the fibrous membranes substrate via the electrostatic assemble technique, which will expand their application in biomedical fields. The main contents and resuluts of this dissertation are as follows:(1)PLLA/PCL, PLLA/PEG multiblock copolymers were synthesized from diol-terminated PLLA (PLLA-diols), as hard segments and PCL, as soft segments. The PLLA/PCL fibrous membranes were fabricated by electrospinning. The crystalline of PLLA, the morphology of the fibers and mechanical properties of the fibrous membranes were investigated. The results showed that the crystalline phase is mainly PLLA phase in these block copolymers, and high crystallinity in all copolymers with the higher PLLA ratios. The fiber diameter of copolymers decreased with decreasing solution concentration and increasing PCL, PEG content. Comparing with the electrospun PLLA membrane, the electrospun fibrous membranes of the copolymers demonstrated an enhanced elongation with still high tensile strength and Young's modulus.(2) The electrospun PLLA/PCL blend fibers could be optimally prepared with a 1/1 ratio of PLLA/PCL blend under a solution concentration of 10 wt%, an applied voltage of 20 kV and a TCD of 15cm. The porosity, crystalline, mechanical properties and biocompatibility of the fibrous membranes were investigated. The results showed that with increasing the content of PCL, the tensile strength and Young's modulus decreased gradually but the elongation at break increased. The high porosity and large ductility characteristics of the electrospun PLLA/PCL (1/1) blend fibrous membrane have made it a strong candidate for use as tissue scaffolds. The morphology and interactions between ADSCs and PLLA/PCL blend fibrous scaffolds were examined by using IPCM and SEM. With increasing seeding time, an increasing number of cells grow along the fiber orientation direction, forming a three-dimensional network with a fibrous pattern. The results of MTT assay demonstrated that the electrospun PLLA/PCL blend fibrous scaffolds provide ADSCs with a supportive interface to survive. Furthermore, the multi-lineage differentiation of ADSCs on such scaffold indicated the prospect to replace the native ECM for tissue engineering.(3) Aligned PLLA/PCL/F-MWNT composite fibrous membranes were fabricated with strong-acid oxidized MWNTs by electrospinning. The morphology, structure, porosity, crystalline, thermal stability, bio-degradation, mechanical properties and biocompatibility of the fibrous membranes were investigated. The results showed that F-MWNTs are oriented along the fiber axis. With the incorporation of F-MWNTs, the PLLA/PCL/F-MWNT composite fibers become thinner due to the increment in conductivity. PLLA/PCL/F-MWNT composite fibrous membranes show good thermal stability and bio-degradation. During electrospinning, F-MWNTs hinder the crystallization of PLLA/PCL blend, but during cold crystallization, the F-MWNTs act as nucleation sites to enhance the crystallization of PLLA. Moreover, the 1.25 wt% F-MWNTs toughen the electrospun PLLA/PCL blend fibrous membrane. MTT assay indicates that the electrospun PLLA/PCL/F-MWNT composite fibrous scaffolds have no toxic effect on proliferation of ADSCs.(4) CS/CHS multiplayer were selected as the polyelectrolyte to deposit on the PLLA/PCL, PLLA/PCL/F-MWNT fibrous membranes via the electrostatic assemble technique. The results verified the chemical reaction between 1,6-diaminohexane and PLLA, and more CS/CHS adsorption on the fibrous membranes. As CS/CHS multiplayers increase, the hydrophilic of the membranes increase gradually.