Study On Biodegradable Polymer Composites With Shape Memory Properties

In this dissertation,the thermo-induced shape memory and biodegradable composites consisted of poly(D,L-lactide)(PDLLA) as polymeric matrix and inorganic particles such as hydroxyapatite(HA),β-tricalcium phosphate(β-TCP) and magnetic iron oxide(Fe₃O₄) were prepared.Moreover,mechanism of shape memory effect,biodegradation and interface action of composites was also analyzed and discussed.The aim of these studies was that the safe and effective composites possessing shape memory effect and biodegradation are designed and a theoretical support for biomedical application can be provided.Firstly,PDLLA/HA composites were studied,which possess biodegradation, biocompatibility and shape memory properties.We could find the result by dynamic mechanical analysis(DMA) that storage modulus at the rubbery state is about two orders of magnitude larger than that at the glassy state,which could indicated that PDLLA/HA composites had desirable shape memory effect.It could also be identified by the shape memory testing and the parameters of shape memory properties.As a result,the shape recovery ratios(Rs) of the PDLLA/HA composites were above 95%.The results could conclude that bioactive HA particles in composites played an important role during the shape memory recovery.So,it was very significant for investigation of the mechanism that the composites of amorphous PDLLA and HA nanoparticles could show well shape memory effect.Based on the analysis of interface action between the molecular segments of polymer and inorganic phase,we revealed the existence of hydrogen bonding in nanocomposites.The PDLLA/HA nanocomposites were prepared by solution mixture and thermal mold-pressure.The results of Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS) indicated that the hydrogen bonding between the C=O in PDLLA and the surface P-OH groups of HA nano-crystalline was formed indeed.The improvement of shape memory properties further implied the existence of hydrogen bonding in nanocomposites.Moreover,a schematic model of the hydrogen bonding was designed on the base of the experimental results,which could clearly explain the memory mechanism of nanocomposites.In addition,the interface action of PDLLA and nano-HA was simulated and computed by Materials Studio(MS) software,so that could compare with previous experiment results.The results of MS simulation could clearly indicate that some interaction between polymer and inorganic phase existed in nanocomposites,which were in agreement with the examined results of experiment.In order to obtain polymer/inorganic composite with well interface,a novel biodegradable polymer-ceramic nanocomposite was prepared by the in-situ biomimetic method,which consisted of Gelatin(Gel),PDLLA and HA nanofibers. The results of XRD and IR showed that the HA nanofibers played an important role on the existence of bridging bond between polymeric Gel and PDLLA in the nanocomposite.The schematic model of two polymeric chains bridged by inorganic nanofibers was designed on the base of the experimental results,which could well show the interaction mechanism of three phases and explain the mechanism of improvement of the shape memory effect.Moreover,the Gel could initiate and regulate the mineral growth of HA crystals along the functional groups of molecular chains of polymer.It was also very signifcant for the investigation on effect of in vitro degradation of PDLLA/β-TCP composites on theirs shape memory properties.Thus, we prepared PDLLA/β-TCP composites with different weight ratios.The shape-memory behaviors of composites during degradation process of 56 days were performed.During degradation,the dispersed morphology,T_g,molecular weight, weight loss and pH change of composites were all changed,which could result in the decrease of reovery ratios of composites.The reaction formulae of crystalline phase transformation could explain that the change of shape memory properties of PDLLA/β-TCP composites might result from the new inorganic particles in degradation.Finally,the biocompatible PDLLA/Fe₃O₄ nanocomposites were prepared and their magnetic-field induced shape memory effect was also investigated.The Fe₃O₄ nanoparticles with an average size of 20 nm were synthesized by chemical co-precipitation method with the modifying of polyethylene glycol(PEG).Moreover, the magnetic-field induced shape memory effect of composites was performed in an alternating magnetic field.As a consequence,PDLLA/Fe₃O₄ nanocomposites displayed excellent shape memory effect.Moreover,the reason of the phenomenon was also further analysed.