Investigation On Biodegradable Shape Memory Polymeric Composites

In this study, we chose chemically crosslinked poly(e-caprolactone) (cPCL) as the base material, polysebacic anhydride (PSA) and functionalized multi-walled carbon nanotubes (MWNTs) as the enhancement materials to prepare biodegradable SMPs. A series of experiments to investigate their properties such as mechanical, shape memory, in vitro biodegradation and cytotoxicity were performed. The aim of this work was to fabricate the shape memory polymer composites with favorable biodegradability, excellent mechanical properties and good biocompatibility.Firstly, we have prepared the drug loaded cPCL/PSA composites (the drug model is paracetamol). We discussed the mechanical, shape memory, in vitro degradation and drug release properties of these samples. The result shows that the composites have fantastic mechanical properties, excellent thermo-responsive shape memory effect. Significantly, we have noticed that the additional PSA could effectively accelerate the biodegradation speed of cPCL. After the drug release experiment, we have known that with the help of PSA, the release accumulation could also be improved.Secondly, a new method was tried to stimulate the shape memory process in consideration of the limitation of thermo-responsive SMPs in biomedical field. In this study, the conducting nano-material MWNTs were introduced into the cPCL matrixin order to prepare a new kind of electro-active SMPs. However, in view of the weak hydrophilic property and high cytotoxicity, the MWNTs must be functionalized. We used acid-oxidation, covalently grafted PEG and biomineralization method to induce the hydroxyl, carboxyl group, polyethylene glycol (PEG) and hydroxyapatite (HA) on the surface of MWNTs, respectively. The resuls illustrated that the PEG was successfully grafted on the surface of MWNTs through covalent bond and the hydrophilic properties and biocompatibility of MWNTs were obviously improved. On the other hand, through the TGA results,the weight of deposited HA on the surface of MWNTs was nearly 80%,and the biocompatibility of the HA functionalized MWNTs was significantly ameliorated. Finally, we used the covalently PEGylated carbon nanotubes to prepare electro-active SMPs. Through a series of investigations, we have got the conclusion that this material could exhibit favourable shape memory effect under 50V constant voltage and the shape memory recovery ratio could remain above 90%. However, compared with the thermo-responsive SMPs, the recovery speed should be improved. After the 16 weeks in vitro biodegradation experiments, the shape memory behaviours, especially the electro-active recovery ability decreased largely. When we applied 50V constant voltage on the biodegradation samples, only 60% recovery ratio could be observed after 120s stimulation. The explanation could be summaried by results of the morphologic feature and gel fraction analysis. The decreasing surface energy which leads the phase separation and the breakage of chemical crosslinked network are main factors resulting in the unfavourable shape memory effect for our composites.