The Research Of Degradation And In-situ Tension SAXS/WAXS Of Medical Biodegradable Polymer Blends

At present,the research and application of medical biodegradable polymer materials is one of the most popular issues in the domestic and overseas.As the two common medical biodegradable polymer materials,Poly(β-hydroxybutyrate)(PHB)and poly-lactide(PLA)have excellent mechanical properties,biodegradability,biocompatibility,etc.Therefore they have broad development prospects in the field of tissue engineering and received widespread attention with wide use in orthopaedics,internal fixation material,microcapsule drug release system,tissue repair materials and surgical suture.Due to the poor toughness and slow degradation,the applications of pure PLA were restricted as biodegradable polymer materials.Modifying it with physical,chemical or biology methods to enhance its properties is one of the generic methods at present.In this paper,proper physical modification of pure PLLA was conducted for its high crystallinity,poor toughness,slow degradation and other shortcomings.PHB and PLLA were blended in solvent to gain a series ratio of blending materials that then were compressed into film.Physical and chemical properties study,in vitro degradation process and the internal structure research were conducted with the synchrotron radiation small Angle/wide Angle(SAXS/WAXS)characterization methods in Chinese academy of sciences,Shanghai institute of applied physics,Shanghai Synchrotron Radiation Facitity(SSRF).And the relationship between the crystal structure changes and mechanical properties in PLLA/PHB blend materials before and after degradation was explored and developed from three aspects respectively:(1)preliminary preparation of blending materials and characterization of SAXS/WAXS technology;(2)the influence of in-situ tensile process on the blending material crystal structure;(3)the influence of in-situ tensile process on the blending material crystal structure after different degradation cycle.Results show that with the increase of PHB proportion,the physical properties,biocompatibility and degradation rate of the blending material have different degrees of improvement.Compared with pure PLLA,the yield stress and tensile strength of PLLA/PHB(50/50)blend decreased 55%,while breaking elongation ratio increased by 60%.Parts of the crystal in the blending material are destroyed during the stretching process and some amorphous structure gradually oriented orderly with the thickness of the mesophase increasing.The degradation studies for each ratio PLLA/PHB blends were conducted in 37℃standard phosphate buffer solution(PBS)/lysozyme which was simulated body environment.The structural change of blending materials in the degradation process was well studied by observing mass loss periodically and in-situ tension SAXS/WAXS.Results show that the degradation rate of amorphous PLLA was faster than that of PHB,after 90 days degradation,blending materials showed varying degrees of destruction with the internal crystalline structure,resulting in breaking elongation ratio falling by 76%and the tensile strength and yield stress getting different degree of decline.