Synthesis Of PELA And Preparation Of Its Ultrafine Fibers And Microspheres

Poly(L-lactic acid) (PLLA) has become a hot research subject in biomedical area because of its good biocompatibility, biodegradability and low immunogenicity. However, the high hydrophobicity limited its applications at a large scale. Poly(ethylene glycol) (PEG) is also widely used in controlled drug delivery systems. PEG and PLLA could form block copolymers (PELA) and the hydrophilicity/hydrophobicity of PELA block copolymers could be adjusted by changing the fraction of PLLA and PEG. At the same time, the flexibility and mechanical properties of the copolymers could be greatly improved by the introduction of PEG. These advantages make PELA block copolymers become a kind of excellent biomedical polymer materials, and exhibit a good of potential uses in the areas of controlled drug delivery, drug targeting systems, tissue engineering and so on.In this study, a series of PELA were synthesized by the ring-opening polymerization of LA, with Sn(Oct)2 as the catalyst and mPEG as the reaction initiator. The structure and relative molecular mass were investigated by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The contact angle test and differential scanning calorimetry (DSC) indicated that the higher the mPEG content or relative molecular mass was,the more hydrophilic and the lower values of Tg, Tm, Tcc of PELA appeared.Ultrafine fibrous membranes of PELA copolymers, E-PEO/PELA and C-PEO/PELA were prepared by traditional electrospinning, emulsion electrospinning and coaxial electrospinning, respectively. The morphology of ultrafine fibers was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The hydrophilicity of electrospun membranes was investigated by water uptake test in PBS solution and contact angle test. The results indicated that the higher the mPEG content or its relative molecular mass was, the more hydrophilic the PELA membranes appeared; The E-PEO/PELA and C-PEO/PELA membranes exhibited better hydrophilicity than PELA due to the core/shell fiber structures. The mechanical properties of electrospun membranes were evaluated by tensile test, and the results indicated that E-PEO/PELA and C-PEO/PELA membranes had better mechanical properties than PELA membranes. Their Young's moduli were 46.61±13.66MPa, 45.88±1.42MPa, respectively, significantly higher than that of PELA (32.23±11.32MPa). The mechanical properties in the wet state were worse than those in the dry state.Studies on cell adhesion, proliferation and morphology on the fibrous membranes showed that PELA and E-PEO/PELA membranes could both mimic the structure of extracellular matrices (ECMs). The behaviors of cells on E-PEO/PELA membranes were relatively worse than those on PELA membranes due to the existence of PEO.The PELA microspheres were produced by self-assembly. The microspheres'surface morphology and average size were investigated by SEM and a dynamic light scattering (DLS) instrument, respectively. Results indicated that the microspheres surface was smooth, and the longer the PLLA chain, the smaller the mean diameter of microspheres appeared. The mean diameter of the microspheres increased from 517nm to 998nm as the relative molecular mass of mPEG went up from 750 to 2000.