Synthesis And Character Of Degradable Poly-(Amino Acid Ester) Phosphazene Hybrid Materials

At present, biomaterials are widely used in the fields of artifical organ, drug-controlled system and tissue engineering, and the applications have always been expanding, for whose excellent biocompatibility and degradability. Biomaterial research and development are transferring from the generation of 1^st and 2^st, with the character of degradable or bioactive, to the 3^st with the degradable and cell and /or gene activated properties. Synthesized materials and natural polymers commonly have deficiencies in composite properties more or less and disenable to meet the different requires for clinic uses. And generally needed to modify by the ways of ray treatment, copolymerization, blending and molding, etc. to lever the characters.In this study, several polyphosphazenes were synthesized and modified with amylose or gelatin by crosslinking or blending, to improve the hydrophilicity and rates of degradability. A serials of polyphosphazenes nanofibers with different surface wettability were also obtained by electrospinning.1. A kind of novel hybrid material was prepared by crosslinking poly[(glycino ethyl ester)_0.6(alanino ethyl ester)_1.2(chororide)_0.2 phosphazene] (PAGP₁) with amylose. The results showed that the residual P-C1 groups in PAGP₁ could be nucleophilic substituted by hydroxyl groups of amylose in the form of R-ONa. The obtained hybrid polymeric film exhibited no obvious phase separation, which commonly occurred in polymer blends. The crosslinked hybrid material had better mechanical properties than the blended poly(glycino ethyl ester)_0.33 (alanino ethyl ester)_0.67 phosphazene (PAGP₂) /amylose with similar composition, and was more hydrophilic than pure PAGP₂.2. Effect of parameters in the glutaraldehyde vapour crosslinking process on the properties of the degree of crosslinking, water absorption and mechanical strength of lyophilized porous gelatin films was studied by the orthogonal test, and the optimal crosslinking method firstly gained. The results proved that the compression modulus, water absorption and water-resistant character of porous gelatin films have all improved. The glutaraldehyde steam crosslinking was more homogeneous and controllable than that of the glutaraldehyde solution treatment, and the porous structures of gelatin films could be maintained.3. For the next-step research in the electrospinning of functional polyphosphazene/gelatin nanofibers, effect of voltage, concentration and temperature on the morphologies and diameter distributions of PAGP fibers was discussed. The analysis of SEM demonstrated that the morphologies and average diameters of PAGP fibers were directly influenced by the solution concentration, and bead free fibers could not formed when the concentration was below 15 w/v%TFE. When the temperature was too low, there could be amalgamation during the fibers, and the fluid channel would be jammed and caused the electrospinnability of the PAGP polymer fell if the temperature was too high. Temperature directly influenced the viscosity and conductivity of poly(methoxylethoxyl)phosphzene (MEEP) and gelatin blended solution, and the crosslinking modification by glutaraldehyde vapour would help to improve the water resistant ability of as-electrospun MEEP/gelatin nanofibers.4. Two kinds of biodegradable polymer, poly(s-caprolactone) (PCL) and poly[(alanino ethyl ester)_0.67 (glycino ethyl ester)_0.33 phosphazene] (PAGP), were electrospun, respectively, by using four different solvents. All PCL nanofibrous mats had similar surface water contact angles (WCAs) independent of solvents. However, it was found that the WCAs of PAGP nanofibrous mats were 102.2±2.3°, 113.5±2.2°, 115.8±1.4°and 119.1±0.7°, respectively, as trifluoroethanol (TFE), chloroform (TCM), dichloromethane (DCM) and tetrahydrofuran (THF) were employed. This difference was supposed mainly due to phosphorous and nitrous atoms in PAGP being dragged to fiber surface with solvent evaporation during the solidification of nanofibers, because of the strong interaction between positive phosphorous atoms and electronegative atoms in solvents. This interaction was confirmed by FT-IR, and the accumulation of phosphorous and nitrous atoms in the solvent-casting PAGP film surface was identified by XPS analysis. PCL samples did not show the solvent-controlled surface wettability since it contained fewer polar atoms.5. Composite nanofibers were made by co-dissolving PAGP and gelatin in TFE and firstly co-electrospinning. The co-electrospun composite from different mixing ratios (0, 10, 30, 50, 70 and 90 wt%) of gelatin to PAGP consisted of nanoscale fibers with a mean diameter ranging from approximately 300 nm to 1 urn. An increase in gelatin in the solution resulted in the increase of average fiber diameter. Transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDS) measurements showed that gelatin core-PAGP shell structural nanofibers had been formed when the content of gelatin in the hybrid was below 50 wt%. But homogeneous PAGP/gelatin composite nanofibers were obtained as the mixing ratios of gelatin to PAGP were 70 and 90 wt%. Contact angle measurement indicated that the homogeneous PAGP/gelatin composite fibrous membrane exhibited more favorable wettability than that obtained from PAGP alone.