Controlled drug release bioerosion

Controlled Drug Release—Because the degradation products of Type III bioerosion are small, water soluble molecules, the principal application of polymers undergoing such degradation is for the systemic administration of therapeutic agents from subcutaneous, intramuscular or intraperitoneal implantation sites. Application of Type III bioerosion to controlled drug release was first described in 1970 (32) and has since then been extensively investigated. The various types of devices currently under development can be classified into (a) diffusional and (b) monolithic (7). 

The biomedical uses of polyphosphazenes mentioned earlier involve chemistry that could in principle be carried out on a classical petrochemical-based polymer. However, in their bioerosion reactions, polyphosphazenes display a uniqueness that sets them apart. This uniqueness stems from the presence of the inorganic backbone, which in the presence of appropriate side groups is capable of undergoing facile hydrolysis to phosphate and ammonia. Phosphate can be metabolized, and ammonia is excreted. If the side groups released in this process are also metabolizable or excretable, the polymer can be eroded under hydrolytic conditions without the danger of a toxic response. Thus, poljnners of this tjT are candidates for use as erodible biostructural materials or sutures, or as matrices for the controlled delivery of drugs. Four examples will be given to illustrate the opportunities that exist. 

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