Programmable biodegradable implants.

Pulsatile release implants were developed that release substances up to 58 days post implantation. With a cylindrical size of 2 mm diameter and 1.8 mm height the matrices can carry as much as 1 mg of drug and allow even for intracranial implantation into a rodent model. The matrices are made of materials that have been used for parenteral applications in humans before such as surface eroding polyanhydrides and bulk eroding poly(D,L-lactic acid) or poly(D,L-lactic acid-co-glycolic acid). The onset of drug release is controlled by the degradation of bulk eroding polymers which are known to exhibit a certain stability over a defined period of time and which start eroding after they reach a critical degree of degradation. The time of drug release onset was found to depend on the molecular weight and the chemical state of the carboxylic acid end of the polymer chain. For testing the onset of release in vivo a nude mouse model was developed where the release of Evan's blue could be observed visually after subcutaneous application. By combining individual matrices with different release onset, a therapeutic system can be composed that releases drugs after implantation at predetermined time points in a preprogrammed way. Potential applications for such matrices is vaccination and local tumor therapy.