Hydrolytic Degradation of Low Molecular Weigh Poly(Lactic Acid)s and Their Drug Eluting Behavior
Yasuharu NAGAI, Jun Jae Lee, and Hideki YAMANE
Abstract:Poly(L-lactic acid)s with molecular weights ranging from 500 to 43,000 were synthesized by the direct polycondensation of L-lactic acid. Both initial and total hydrolytic degradation rates in a buffer solution increased with decreasing Mw. Poly(L-lactic acid) with the lowest Mw showed a significantly high degradation rate. This may be due to its Tg lower than the temperature of degradation experiment at which the water molecules easily diffuse into the matrix. Although the hydrolytic degradation can be theoretically described by the first-order reaction, the weight loss of the low Mw poly(L-lactic acid) in the buffer solution deviated from the behavior predicted. The rate of the drug elution from the film showed a maximum at the first day, irrespective of the Mw of poly(L-lactic acid) suggesting that the drug dispersed near the film surface elutes most rapidly. The drug elution rate from the film with the highest Mw was not significantly different from those from low Mw films. This may be due to the similar degree of crystal to those of the low Mw film. These results indicate that the drug elution behavior is affected not only by the molecular weight but also the degree of crystal of the matrix poly(L-lactic acid). Key Words:Poly(lactic acid), Hydrolytic degradation, Drug elution behavior