ABSTRACT
Achieving polymer surface erosion is one of the holy grails of research in controlled drug release because in such systems, drug release in the absence of diffusion is completely controlled by rate of polymer hydrolysis. Clearly, not all polymers will undergo non-enzymatic surface hydrolysis and most known polymers will undergo bulk hydrolysis where the reaction occurs more or less uniformly throughout the bulk of the material. Such materials can be readilly prepared by the reaction between alcohols and the copolymer of methyl vinyl ether and maleic anhydride. Use of poly (ortho esters) that undergo surface erosion is not limited to short term delivery devices and work to develop a bioerodible implant that can release levonorgestrel for about one year by an erosion controlled process has been in progress for many years. Devices were also explanted at various time intervals and examined by scanning electron microscopy. Polyanhydrides have been extensively investigated as bioerodible matrices for the controlled delivery of therapeutic agents.
