BEH.462/3.962J Molecular Principles of Biomaterials Spring 2003 Lecture 2: Molecular Design and Synthesis of Biomaterials I: Biodegradable Materials Chemistry of Biodegradable Materials: I. Hydrolytically degraded biomaterials Common hydrolytically unstable linkages: Ester amide (STRUCTURES) Example polymers explored for use as biomaterials: (STRUCTURES) PLGA polypeptides Poly(D,L-lactide) Poly(L-lactide) Poly(ε-caprolactone) Polyanhydrides Stereochemistry of lactides: L- vs. D- vs. D/L DRAWINGS OF STEREOSTRUCTURE, 3D animation? Chemistry of hydrolysis: Physical chemistry of hydrolysis: -hydrolysis requires water to access the bonds: so structure has a strong effect on hydrolysis rates! -Factors influencing hydrolysis rates: 1. Hydrophobicity a. Degradation rate of PCL < PLA < PLGA 2. steric interference 3. crystallinity Controlling degradation behavior of solids for devices by choosing the right chemical structure: Given the above factors in degradation rate, it is not surprising that biodegradable solids may have differing modes of degradation: ETC ETC ETC II. Enzymatically degraded biomaterials 1 of 1