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Degradation of polymeric systems aimed at temporary therapeutic applications : structure-related complications
Research Centre for Artificial Biopolymers, UMR CNRS 5473, University of Montpellier 1, Faculty of Pharmacy, Montpellier, France
During the last 10 years, many novel polymeric compounds have been introduced in literature as degradable or biodegradable polymers. However studies generally stopped at the level of the synthesis. It is now well known that the degradation of polymer chains can be achieved via various processes, namely cell-mediated degradation and abiotic chemical or enzymatic degradation. Considering the hydrolytic degradation of aliphatic polyesters derived from lactic and glycolic acids one can realized that degradation is very much dependent on chain structures, especially in the case of copolymers and stereocopolymers. The present understanding of water-sensitive polymers and copolymers will be recalled. It will be shown that the degradation of copolymer chains leads to deviation from cleavage at random, thus resulting in composition changes, formation of crystalline residues and of degradation products that are more resistant than partially degraded precursors of intermediate molecular weights. The cases of various copolymers and stereocopolymers will be presented, namely PLA stereocopolymers, PLAGA copolymers and poly(malic acid-co-benzyl malate) copolymers. A special attention will be paid to the effect of attaching a label to a degradable macromolecule in order to monitor the degradation mechanism. It will be shown that radioactive labelling by hydrogen-tritium isotopic exchange and labelling by binding a fluorescent dye to polymer chains do not lead to comparable results. The use of a chemical label can be the source of dramatic misinterpretation because of the influence of the dye on the physicochemical behaviour of partially degraded by-products. The chain structure-dependence also exists in the case of enzymatic degradation. It will be shown that selective enzymatic degradation can be used to create porous structures and to investigate the intimate structure of blends of enzymatically degradable polymers.
Presentation: invited oral at E-MRS Fall Meeting 2004, Symposium B, by Michel Vert
See On-line Journal of E-MRS Fall Meeting 2004
Submitted: 2004-04-14 17:34 Revised: 2009-06-08 12:55