Study On The Preparation, Characterization And Properties Of Silk Fabroin/Polyurethane Hydrogels

Silk is a natural polymer and has unique properties such as slow biodegradation, superior mechanical properties favorable processability in combination with biocompatibility, have fueled wide interest for a variety of application. Since have structure similarity to protein, polyurethane is evaluated as a potential natural matrix for biological materials. Hydrogels based on polyurethane have been attracting more and more researchers since they combined excellent biocompatibility of hydrogel and property tunable polyurehane which explored their application in biomedical purposes. The major drawbacks of existing hydrogels are poor swelling properties and mechanical strength. In this study, keeping in mind the past work and future potential application as drug carriers, the stimulate responsibility and mechanical strength of hydrogels are being taking into consideration. Silk fibroin/polyurethane(SF/PU) hydrogels are fabricated and characterized to investigated their use as a matrix for sustained drug release.A series of polyurethane(PU) prepolymers were synthesized using polyethylene isophorone diisocyanate(IPDI), glycol(PEG-2000), polypropylene glycol(PPG-2000) as the main materials, Dimethoxypropionic Acid(DMPA) which would offer hydrophilicity and diethylene glycol(DEG) were adopted as extenders. After ionized by triethylamine(TEA), the PU polymers were mixed with self-made silk fibroin(SF) aqueous solutions, thus SF/PU hydrogels were prepared. The prepare technology, micro structure and morphology of SF/PU hydrogels and relationship between their structures and properties were investigated using infrared spectroscopy(FT-IR), scanning electron microscope(SEM) and differential Thermal Analysis(DSC). The study proved that the expected structure were obtained, the two compositions of hydrogels showed good compatibility with each other, increasing amount of used PEG migrate the glass transition temperature to the lower region.On the basis of analysing prepare technology and relationship between structures and properties of SF/PU hydrogels, a series of PU prepolymers were synthesized using IPDI, PEG-2000, PPG-2000 as main materials. They were hybrid with self-made SF aqueous solutions, thus SF/PU hydrogels with 3-dimentional cross-linked structure were fabricated. ATR, SEM were adopted to characterized the structure and micro morphology of obtained hydrogels. The mechanism of swelling behaviour of SF/PU hydrogels was analysed by calculating the swelling ratio and equilibrium water content in various media. SEM images revealed microporous surface with pore size of 10μm around. The obtained SF/PU hydrogels showed excellent pH responsibility, and the equilibrium water content of hydrogels in the alkaline media were much high than that of hydrogels in the acidic media. In the media of pH<7, the swelling ratio were almost the same, while in the media of pH>7, the swelling ratio rise up quickly. When using more DMPA, the swelling ratio increased. However, equilibrium water content decreased as SF/PU composition proportion increased. As the temperature rise up, the equilibrium water content of hydrogels decreased, and the reversibility of swelling ratio hydrogels between 20 and 50 "C. The behaviour of SF/PU hydrogels as drug carrier and drug release was studied, the result showed that the drug release ratio reached 80%. The anti-bacterium image proved that the drug-loaded SF/PU hydrogels have good comprehensive properties as drug carrier.Two types of ionic hydrophilic groups were introduced into the PU prepolymer chain by adopting 2,2-dimethoxypropionic acid(DMPA) and N-methyldiethanolamine(MDEA) as anionic and cationic groups respectively. Then a novel amphoteric SF/PU hydrogel was fabricated by mixing the obtained PU prepolymer with SF aqueous solution. ATR, SEM were used to characterized the structure and microporous surface. SEM images revealed microporous surface with pore size of 15μm around. The swelling ratios of amphoteric hydrogels in media of pH=1～4 and 8～13 were much higher than that of in the media of pH=5-7. Moreover, in the media of pH<7, the amphoteric hydrogels with more MDEA gained higher swelling ratio, while the amphoteric hydrogels with more DMPA got higher swelling ratio in the media of pH>7. The equilibrium water content of amphoteric SF/PU hydrogels in the media of pH=2,12 were much higher than that of pH=7. The study also revealed that the swelling behaviour of amphoteric SF/PU hydrogels in the media of pH=2,12 followed the mechanism of chain relaxation control, however, in the media of pH=7, the swelling behaviour followed the Fickian diffusion mechanism. The mechanical properties was tested by the universal test machine and the result showed that the prepared amphoteric SF/PU hydrogels have good mechanical properties. The maximum compressive strength was 0.577 MPa, while the maximum deformation was 85.8%.