Erodible polymeric delivery systems

Major activity in the area of protein delivery from synthetic degradable matrices has focused on the use of aliphatic polyesters, prinicipally owing to their readily manipulated polymer characteristics and the favorable toxicology of their degradation products. However, the development of new polymers and polymeric delivery systems where drug release is predominantly controlled by surface polymer hydrolysis is also desirable. Poly(ortho esters) (POE), of the general structure 3, are an example of this class of synthetic erodible polymers and have been under extensive development for approximately 20 years. 

Any sol-gel phase reversible system described above can be used as an erodible matrix system. All the components of the system in the sol state are essentially in the dissolved state, and thus they can be released to the environment in the absence of protecting membranes. During the process of gel to sol transition by the addition of glucose, the incorporated insulin can be released as a function of glucose concentration. There are of course other polymeric systems which can be used in glucose-sensitive erodible insulin delivery. 

Polymeric materials for continuous long-term release of entrapped substances (excipients) have been utilized extensively in the last two decades in drug delivery systems. These polymers can be classified into two major groups as shown in Table I. The non-erodible carriers, such as polyacrylamide, polyvinyl alcohol and poly(2-hydroxy methacrylate) have been used widely in sensor preparation mainly as supports for physical or chemical immobilization of fluorescent molecules or enzymes. As discussed above, EVA has been shown to be appropriate as a reservoir polymer for sensor development. 

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