BEH.462/3. 962J Molecular Principles of Biomaterials Spring 2003 Fig. 1. Scanning electron microscopy of intact(A) and(B) fractured microspheres obtained by double emulsion-solvent evaporation using 20% insulin/ polymer(preparation B2) 1. aq. solution of protein added to organic solution of polymer; emulsify 2. add milky W/O emulsion to large aq. phase containing stabilizer, emulsify to form second emulsion 3. stir and evaporate organic phase to form solid polymer microspheres entrapping aq. droplets of protein solution issues with delivery of protein LOADING EFFICIENCIES TYPICALLY POOR FOR PROTEIN DRUGS Difficult to achieve more than a few by weight protein Escape to aqueous phase during processing o Many fragile proteins denatured or irreversibly bound due to low pH, adsorption to hydrophobic polymer segments We will return to the topic of controlled release device synthesis when we discuss nanoparticle-based Lecture 5- Controlled Release Devices 10 of 14BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 • synthesis: 1. aq. solution of protein added to organic solution of polymer; emulsify 2. add milky W/O emulsion to large aq. phase containing stabilizer, emulsify to form second emulsion 3. stir and evaporate organic phase to form solid polymer microspheres entrapping aq. droplets of protein solution • issues with delivery of protein drugs o LOADING EFFICIENCIES TYPICALLY POOR FOR PROTEIN DRUGS ƒ Difficult to achieve more than a few % by weight protein ƒ Escape to aqueous phase during processing o Many fragile proteins denatured or irreversibly bound due to low pH, adsorption to hydrophobic polymer segments • We will return to the topic of controlled release device synthesis when we discuss nanoparticle-based biomaterials Lecture 5 – Controlled Release Devices 10 of 14