BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 er acid ifies Water penetrates into device degrades sHow pht Fig. 2. Theoretical pulsatile release of a drug from a surface- oding polymeric system. The time between initial release and booster release is determined by the erosion of the drug free layer refs for theory: J Contr Rel 20, 201(1992); J Cont Rel 18, 159(1992 Regulated release devices: case example-drug delivery microchips work from M. Cima and R. Langer labs Lecture 5- Programmed Drug Delivery 3 of 12BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Polyanhydride layer acidifies Water penetrates into device Model drug release profiles: environment as it degrades: COO- O C O￾COO- O C O￾COO- O C O- Low pH Polyphosphazene only degrades quickly at neutral/basic pH : • refs for theory: J Contr Rel 20, 201 (1992); J Cont Rel 18, 159 (1992) Regulated release devices: case example- drug delivery microchips • work from M. Cima and R. Langer labs: 4 Lecture 5 – Programmed Drug Delivery 3 of 12