ABSTRACT
In recent years, the development of new degradable polymers as possible bio materials has attracted considerable attention. One widely studied application of these polymers are implantable drug delivery devices and currently a wide range of new applications for degradable polymers is being investigated. The release of active agents from bioerodible polymeric matrices has been classified by Heller [1,2] into three groups, according to the breakdown mechanism involved: water-soluble polymers which are made insoluble by hydrolytically unstable cross links (mechanism I); linear polymers which are initially water-insoluble and which become solubilized by ionization resulting from hydrolysis, or protonation of pendent groups, but without backbone cleavage (mechanism II); and polymers which are water-insoluble and break down to small soluble products by backbone cleavage (mechanism III). This last category includes poly(ortho esters) (POE), which are hydrophobic polymers that under certain conditions can undergo an erosion (heterogeneous) process that is confined to the polymer-water interface.
