Polyurethane High flex life Uncertain molecular structure- Range of mechanical properties property relationships Surface radically different from ulk(high mobility of"soft segments") Low MW contaminants Subject to hydrolysis, oxidation, d calcification Hydrogel P-HEMA Low reactivity Low strength Absorbable PLA/PGA Programmable absorption Uncertain biological response to Metabolizable degradation products bolus-release of metabolites Collag Replicates eCm components Immunogenicity Halt Replicates ECM component U Chitosan Substitutes for GAG(e.g, hyaluronan) Unproven PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene PET polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone; PDMS polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGAPolyurethane High flex life Uncertain molecular structure￾Range of mechanical properties property relationships Surface radically different from bulk (high mobility of "soft segments") Low MW contaminants Subject to hydrolysis, oxidation, and calcification Hydrogel P-HEMA Low reactivity Transparent Absorbable PLA/PGA Programmable absorption Metabolizable degradation products Natural Collagen Replicates ECM components Hyaluronan Replicates ECM component Low strength Uncertain biological response to bolus-release of metabolites Low strength Immunogenicity? Unproven Chitosan Substitutes for GAG (e.g., hyaluronan) Unproven PTFE polytetrafluoroethylene, UHMWPE, ultra high molecular weight polyethylene PET polyethylene terephthalate; PMMA, polymethyl methacrylate; PSF, polysulfone; PEEK, polyetheretherketone; PDMS, polydimethyl siloxane; P-HEMA, poly hydroxyethyl methacrylate; PLA, polylactic acid; PGA, polyglycolic acid