| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
The purpose of this project is to elucidate the long-term in vitro hydrolytic degradation behavior and mechanism of PLLA crystalline residues (extended chain crystallites). For this purpose, PLLA crystalline residues were prepared by crystallization of PLLA films and subsequent accelerated hydrolytic degradation at 97℃ for 40 hours and the obtained crystalline residues were hydrolytically degraded at different conditions at pH 7.4 and different temperatures of 37, 50, 70, and 97℃ up to 512 days, at 37℃ at different pH of-0.9, 0.2, 7.4,11.7, and 12.8, and at pH8.6 and 37℃ in the presence of proteinase K. Also, the hydrolytic degradation behavior of L-lactic acid copolymers of poly(L-lactide-co-glycolide) (81:19) [P(LLA-GA)], poly(L-lactide-ε-caprolactone) (77/23) [P(LLA-CL)],and poly(L-lactide-co-D-lactide)] (77:23) (98.8:1.2) [P(LLA-DLA)] and their crystalline residues formed during hydrolytic degradation was monitored. The formation and hydrolytic degradation of the crystalline residu
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es were traced by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The following results were obtained. (1) For all conditions, the crystalline residues are hydrolytically degraded linearly with degradation time from the chain terminals at the folding surface; (2) The activation energy for hydrolytic degradation (ΔE_h) of the crystalline residues at pH 7.4 was estimated to be 75.2 kJ mol^<-1>. This is much higher than 50.9 kJ mol^<-1> of ΔE_h reported for PLLA in the melt and indicates that higher hydrolytic degradation-resistance of the crystalline residues; (3) Acidic and alkaline conditions as well as high temperature enhanced the hydrolytic degradation of the crystalline residues, whereas proteinase K has no catalytic effect, revealing that the insignificant enzymatic activity of proteinase K for the PLLA chains neighboring on the crystalline regions. (4) The crystalline residues were formed and hydrolytically degraded in P(LLA-GA) and P(LLA-CL) films within the periods of 24 weeks, whereas in the case of PLLA and P(LLA-DLA) (98.8:1.2) films, neither formation nor hydrolytic degradation of crystalline residues took place within the degradation period of 50 weeks. Less
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