Degradable copolymers were synthesized by ring opening polymerization of lactide in the presence of poly(ethylene glycol) (PEG), using CaH2 as a biocompatible initiator. The resulting PLA/PEO/PLA triblock copolymers were dissolved in a biocompatible solvent, namely tetraglycol. Physically crosslinked hydrogels were then prepared by introducing small amounts of water into the thus obtained solutions. Hydrolytic degradation of the highly swollen hydrogels was realized in 0.13 M pH=7.4 phosphate buffer, while the enzymatic degradation was carried out in 0.05 M pH=8.6 Tris buffer containing a PLA-degrading enzyme, proteinase K. In both cases, degradation was initially very fast with dramatic weight loss. The LA/EO ratio of the remaining material increased rapidly, in agreement with the release of PEO-rich segments. In a second phase, the degradation rate slowed down. The presence of proteinase K strongly accelerated the degradation rate of the hydrogels, indicating that the enzyme was able to penetrate inside and attack the PLA domains which constituted nanometric nodes in the gel network.
This paper describes the hydrolytic degradation of three stereoregular poly(ester amides) which were obtained by polycondensation reaction of 1-amino-1-deoxy-2,3,4-tri-O-methyl-5-O-[(pentachlorophenoxy)succinyl]-L-arabinitol, 1-amino-1-deoxy-2,3,4-tri-O-methyl-5-O-[(pentachlorophenoxy)glutaryl]-L-arabinitol, and 1-amino-1-deoxy-2,3,4-tri-O-methyl-5-O-[(pentachlorophenoxy)succinyl]-D-xylitol hydrochlorides. The degradation study was carried out at 37 °C in bidistilled water and/or in buffered salt solution at pH 7.4, and was monitored by mass loss, GPC, SEM, and FAB-MS, IR, and NMR spectroscopies. The hydrolytic degradation of these poly(ester amides) occurs by hydrolysis of the ester linkages and is characterized by rapid rates of hydrolysis. The differences in degradation rates are ascribed to differences in crystallinity and hydrophilicity of the polymers. Our results show that the poly(ester amides) derived from succinic anhydride degrade to a final monomeric product in which a succinimide ring has been formed.
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