Study On The Phase Separation Of Poly(Lactide-Co-Glycolide)/Polyphosphazene Blend Film

As an important biodegradable material, poly(lactide-co-glycolide) (PLGA) has been widely studied and applied because of its good biocompatibility and certified by the FDA. However, the acidic degradation products can cause aseptic inflammation and rejection. Currently, one way to solve this problem is to combine PLGA and another biodegradable material to reduce the acidity of degradation products, and biodegradable polyphosphazenes become the choice for the variety of side groups. Polyphosphazenes are hybrid polymers with a backbone of alternating phosphorus and nitrogen atoms containing two organic side groups attached to each phosphorus atom. Biodegradable polyphosphazenes have good biocompatibility and undergo degradation to form neutral and non-toxic products such as phosphates, ammonia and the corresponding ester side groups. This unique property of polyphosphazenes has been recently utilized to form self-neutralizing blend systems by combining polyphosphazenes with PLGA.Up to now, the study on PLGA/polyphosphazene blends usually focuses on the compatibility, the pH of degradation products and the cell affinity. Little has been reported about the phase separation of PLGA/polyphosphazene blend film. It's investigated that the surface morphology, especially the micro and nano structure, plays a very important role to the cell adhesion, proliferation, differentiation, etc. For this reason, a study was carried out regarding the factors including weight ratios, solvents, environmental humidity, film thickness, and substrates on the phase separation of PLGA/polyphosphazene blend film. It's significant to the cell affinity of PLGA/polyphosphazene blend film. Besides, ploy(glycine ethyl ester)phosphazene (PGP) and ploy[(alaine ethyl ester)/(glycine ethyl ester)]phosphazene (PAGP) were chosen as blend materials for the degradation rate matching with PLGA and the degradation products being alkaline.1. PLGA5050, PLGA7030, PGP, PAGP were synthesized by ring-opening polymerization and nucleophilic substitution of side groups. The polymers' composition, molecular weight and hydrophilicity were characterized by 1H-NMR, GPC, etc.2. Using a mutual solvent technique, blend films of PLGA7030/PAGP were prepared at different conditions including weight ratios, solvents, environmental humidity, film thickness and substrates. It was found that compared with dichloromethane (DCM) and tetrahydrofuran (THF), chloroform (CF) was the better solvent to form miscible PLGA7030/PAGP blend films at relatively anhydrous atmosphere. However, in the humid atmosphere, the circular or hexagonal arrangement of holes appeared on the surface of blend films, which dimension and shape was influenced by the weight ratios, film thickness and the property of the substrate.3. The properties of PLGA7030/PAGP blend film prepared in high humidity were characterized by selective removal PAGP component, EDX and XPS. A sandwich-liked structure was formed with the hydrophilic PAGP component at the top and bottom, while the PLGA component in the middle.4. Blend films of PLGA5050/PGP were prepared at different solvents and weight ratios. The morphology of blend films was observed by SEM. In low humid atmosphere, using CF and DCM as solvent can form micro phase separation structure, while THF can only form macroscopic phase separation.5. The phase separation of PLGA-PEG-PLGA (PLGE) blend with PAGP was performed and compared with PLGA7030/PAGP blend film. It was found that the surface morphology (cellular structure) of polymer films has a great relationship to each polymer's hydrophilicity in the high humidity.