Study On Degradation Of Radiation Crosslinked PCL

Poly( ε -caprolactone) (PCL) is a kind of well biodegradable biocompatible polymer material. After PCL undergoing degradation in body, the finally metabolized resultants are carbon dioxide and water. There is no residue remaining in main organs. Linear PCL can be crosslinked by radiation. The crosslinked PCL has better heat resistance and exhibits shape meory effect, which has important applications in the field of biomedical engineering and issue engineering. As biomedical material, its degradable mechanism must be known. So, it is very necessary to investigate the biodegradability and degradable dynamics of the radiation crosslinked PCL. The hydrolysis and enzyme-catalyzed degradation of uncross-linked PCL and cross-linked PCL were studied in this paper as follows:PCL samples were cross-linked by γ-rays at room temperature. The gel-content result showed that the gel content increased with the increasing of radiation dose. The tensile strength and the elongation at break decreased as the increasing of radiation dose. The uncross-linking PCL and cross-linking PCL were degraded in the buffer solution of pH 7.4 at 37±1℃. The results showed that the loss weight of the samples increased with the time increasing. The tensile strength and the elongation at break of the samples decreased with the time increasing. The loss weight and tensile strength and the elongation at break of the samples were increased with the gel content increasing. The samples were characterized by SEM. SEM showed that the surface of the samples got rough. The kinetics of hydrolysis suggested that degradation of 300 and 400kGy crosslinked PCL was following zero-order reaction kinetics.The enzyme degradation of the uncross-linked and cross-linked PCL by lipase AK and porcine lipase was investigated. The degradation of PCL and cross-linking PCL by porcine lipase was reveals: the loss weight of the samples was increased with the time increasing. The tensile strength and the elongation at break of the samples decreased with the time increasing. The loss weight of the samples increased with the gel-content increasing. The tensile strength and the elongation at break increased with the gel-content increasing. The samples were characterized by SEM. SEM showed that the surface of the samples got rough. It could be conclude that the porcine lipase has little effect on the degradation of uncross-linking PCL and cross-linking PCL.The result of degradation of PCL by lipase AK showed that the concentration of the lipase and degradation temperature and gel-content of the sample and pH value of the buffer solution were important factors. The degradation rate of PCL got faster withthe increasing of lipase concentration. The better temperatures for degradation of the uncross-linked and cross-linked PCL were around 50°C and 52°C, respectively. With the gel content increasing, the degradation rate of samples slower. The better pH value of the buffer solution for degradation of PCL was around 6.2. DSC revealed that the melting point decreased with the loss weight increasing for both uncross-linked and cross-linked PCL. The crystallinity increased slightly with the weight loss increasing for uncross-linked PCL and crystallinity decreased with the weight loss increasing for cross-linked PCL. SEM showed that degradation was surface degradation obviously.The kinetics of enzymatic degradation behavior of uncross-linked and cross-linked PCL was studied. The result showed that the concentration of product in the solution increased with the time and substrates concentration increasing. The degradation kinetics of uncross-linked and cross-linked PCL followed Mechaelis- Menten equation. The degradation parameter of the PCL powder was 1.14 mg/ml for Km and 0.39ml/h for Vmax, respectively. The degradation parameter of cross-linked PCL particulate was 71.95 mg/ml for Km and 0.96 ml/h for Vmax, respectively. Finally, the Arrhenius equation of PCL degradation by lipase AK was calculated: lnk=-44.98/T+2.815.