麻省理工学院 生物材料课程 Lecture 4 Biomaterials Surfaces Chemistry Polymer Hydrolysis.pdfVIP

3.051J/20.340J 1 Lecture 4 Biomaterials Surfaces: Chemistry Like metallic implants, some polymers used in biomaterials applications are susceptible to chemical reactions that lead to degradation through hydrolysis. In many cases, a polymer is specifically chosen for its ability to degrade in vivo. Polymer Hydrolysis Polymer hydrolysis involves the scission of susceptible molecular groups by reaction with H2O. ¾ May be acid, base or enzyme catalyzed ¾Not surface-limited if water penetrates bulk a) Molecular Structural Factors Influencing Hydrolysis ¾Bond Stability ¾Hydrophobicity: ↑ hydrophobicity ⇒↓ hydrolysis ¾MW architecture: higher MW ⇒↓ hydrolysis ¾Morphology • crystallinity ↓ hydrolysis • porosity ↑ hydrolysis ¾T : less mobility ⇒↓ hydrolysis g Bond Stability Susceptible linkages at bonds where resonance stabilized intermediates are possible… O O • Esters: R-C-O-R’ + H2O → R-C-OH + HO-R’ 3.051J/20.340J 2 Example 1: poly(lactide-co-glycolide) Properties: rapid degradation, amorphous, Tg ~ 45-55°C Uses: bioresorbable sutures, controlled release matrices, tissue engineering scaffolds O O (-O-CH(CH )-C -) -r-(-O-CH -C-) 3 x 2 y lactic acid glycolic acid Example 2: polyethylene terephthalate (Dacron) Properties: very slow hydrolysis, semicrystalline, Tg~ 69°C Uses: vascular grafts, arterial patches, heart pumps O O [-O C C O- CH - CH -] 2 2 N base-catalyzed polyester hydrolysis: OH— O C ••