title: Enzymatic surface erosion of high tensile strength polycarbonates based on natural phenols.
abstract: Surface erosion has been recognized as a valuable design tool for resorbable biomaterials within the context of drug delivery devices, surface coatings, and when precise control of strength retention is critical. Here we report on high tensile strength, aromatic-aliphatic polycarbonates based on natural phenols, tyrosol (Ty) and homovanillyl alcohol (Hva), that exhibit enzymatic surface erosion by lipase. The Young's moduli of the polymers for dry and fully hydrated samples are 1.0 to 1.2 GPa and 0.8 to 1.2 GPa, respectively. Typical characteristics of enzymatic surface erosion were confirmed for poly(tyrosol carbonate) films with concomitant mass-loss and thickness-loss at linear rates of 0.14 ± 0.01 mg cm(-2) d(-1) and 3.0 ± 0.8 μm d(-1), respectively. The molecular weight and the mechanical properties of the residual films remained constant. Changing the ratio of Ty and Hva provided control over the glass transition temperature (T(g)) and the enzymatic surface erosion: increasing the Hva content in the polymers resulted in higher T(g) and lower enzymatic erosion rate. Polymers with more than 50 mol % Hva were stable at 37 °C in enzyme solution. Analysis on thin films using quartz crystal microbalance with dissipation (QCM-D) demonstrated that the onset temperature of the enzymatic erosion was approximately 20 °C lower than the wet T(g) for all tested polymers. This new finding demonstrates that relatively high tensile strength polycarbonates can undergo enzymatic surface erosion. Moreover, it also sheds light on the connection between T(g) and enzymatic degradation and explains why few of the high strength polymers follow an enzyme-meditated degradation pathway.
authors.affiliation: The New Jersey Center for Biomaterials, Department of Chemistry and Chemical Biology, Rutgers - The State University of New Jersey , 145 Bevier Rd., Piscataway, New Jersey 08854, United States.
authors.forename: Sven D
authors.initials: SD
authors.lastname: Sommerfeld
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zhang
authors.forename: Marius C
authors.initials: MC
authors.lastname: Costache
authors.forename: Sebastián L
authors.initials: SL
authors.lastname: Vega
authors.forename: Joachim
authors.initials: J
authors.lastname: Kohn
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry; D006719:Homovanillic Acid / Q000737:chemistry*; D008049:Lipase / Q000737:chemistry*; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives* / Q000737:chemistry; D011076:Polycarboxylate Cement / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength
chemical_list: D001672:Biocompatible Materials; D011076:Polycarboxylate Cement; D011091:Polyesters; C532664:homovanillic alcohol; C011867:4-hydroxyphenylethanol; C005506:polycarbonate; D008049:Lipase; D010626:Phenylethyl Alcohol; D006719:Homovanillic Acid