BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Types of controlled release devices 3 1. Drug diffusion-controlled release a. Entrapped drug diffuses out of matrix at defined rate (SLIDE Drug diffusion-controlled release Solid matrix b. Can provide release by diffusion out of polymeric matrix or diffusion through a barrier C. Major disadvantages 1. Nondegradable implants i. Diffusion of large molecules such as proteins through the polymer is too slow to be effective Danger of ' dose dumping in barrier systems if membrane is ruptured d. Typically nondegradable polymer i. Poly(dimethylsiloxane)(Norplant contraceptive- 6 flexible tubes filled with levonorgestrel) e. We will see later that eroding polymer release devices can also have diffusion-controlled release over an early timeframe, before degradation has proceeded very far f. Release rates controlled by simple drug diffusion calculations 2. water diffusion-controlled release a. water influx controls release Lecture 5- Controlled Release Devices 3 of 14BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Types of controlled release devices3 1. Drug diffusion-controlled release a. Entrapped drug diffuses out of matrix at defined rate (SLIDE) Solid matrix Drug diffusion-controlled release Barrier release Norplant¨ system b. Can provide release by diffusion out of polymeric matrix or diffusion through a barrier c. Major disadvantages i. Nondegradable implants ii. Diffusion of large molecules such as proteins through the polymer is too slow to be effective iii. Danger of ‘dose dumping’ in barrier systems if membrane is ruptured d. Typically nondegradable polymer i. Poly(dimethylsiloxane) (Norplant contraceptive- 6 flexible tubes filled with levonorgestrel) levonorgestrel e. We will see later that eroding polymer release devices can also have diffusion-controlled release over an early timeframe, before degradation has proceeded very far f. Release rates controlled by simple drug diffusion calculations 2. water diffusion-controlled release a. water influx controls release Lecture 5 – Controlled Release Devices 3 of 14