ABSTRACT
This chapter considers some of the factors which must be taken into account in the design of biodegradable delivery systems. It reviews the literature on polymer biodegradation in vivo, with emphasis placed on polyesters and results obtained in the authors’ laboratories. Polymers which function by virtue of slow dissolution in the body are not strictly biodegradable, although enteric coatings have long been used by the pharmaceutical industry as a means of extending the duration of oral medication. Polymers with hydrolytically labile ortho ester linkages form the basis of two drug delivery systems which function by constant surface erosion of a polymer implant. The biodegradation of nylon-6 is characterized by the appearance of surface cracks soon after implantation, bulk aqueous amide cleavage, and enzyme-catalyzed surface erosion. The nonenzymatic nature of the initial chain scission has been demonstrated by the observation of the same process in vitro.
