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 i ntracranial implantation into a rodent model. The matrices are made of mate rials that have been used for parenteral applications in humans before such as surface eroding polyanhydrides and bulk eroding poly(D,L-lactic acid) o r poly(D,L-lactic acid-coglycolic acid). The onset of drug release is contr olled by the degradation of bulk eroding polymers which are known to exhibi t 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 releas e 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 r elease in vivo a nude mouse model was developed where the release of Evan's blue could be observed visually after subcutaneous application. By combini ng individual matrices with different release onset, a therapeutic system c an 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. (C) 2001 Elsevier Science B.V. All ri ghts reserved.