Lactic-glycolic acid copolymers, controlled

As pointed out by Heller (2), polymer erosion can be controlled by the following three types of mechanisms (1) water-soluble polymers insolubilized by hydrolytically unstable cross-links (2) water-insoluble polymers solubilized by hydrolysis, ionization, or protonation of pendant groups (3) hydrophobic polymers solubilized by backbone cleavage to small water soluble molecules. These mechanisms represent extreme cases the actual erosion may occur by a combination of mechanisms. In addition to poly (lactic acid), poly (glycolic acid), and lactic/glycolic acid copolymers, other commonly used bioerodible/biodegradable polymers include polyorthoesters, polycaprolactone, polyaminoacids, polyanhydrides, and half esters of methyl vinyl ether-maleic anhydride copolymers (3). 

Ogawa Y, Yamamoto M, Takada S, Okada H, Shimamoto T. Controlled-release of leuprolide acetate from polylactic acid or copoly(lactic/glycolic) acid microcapsules Influence of molecular weight and copolymer ratio of polymer. Chemical and Pharmaceutical Bulletin. April 1988 36(4) 1502-1507. PubMed PMID 3138032. 

The development of a bioerodible implant capable of releasing controlled amounts of a contraceptive steriod from a subcutaneous implant for periods of time ranging from three months to about a year has been in progress for many years. The three principal bioerodible polymers currently in use are copolymers of lactic and glycolic acid (25), poly(e-caprolactone) (26), and poly (ortho esters) (14). The desire to develop such a contraceptive system was the principal motivation for the initial development of the poly(ortho ester) polymer system. 

Kissel T, Li YX, Volland C. Properties of block- and random-copolymers of lactic acid and glycolic acid. Proc Int Symp Control Rel Bioact Mater 1993 20 127-128. 

Drug delivery microspheres, in particular smart systems with controlled release, have been developed with PLA and its copolymers with glycolide to produce poly[(D,L-lactic acid)-co-(glycolic acid)]. Since the 80 s up until the present, many publications have reported on the various applications in the pharmaceutical field for using PLA and copolymers and polymers for their sustained release parenteral formulations and performance in drug release in a controlled manner from microspheres [200, 201]. 

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