Surface Modification of PHBV Films with Different Functional Groups: Thermal Properties and In Vitro Degradation

Polyacrylamide was photografted on solution-cast poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) films (amide-PHBV), on which amide groups were transformed into amine groups through Hofmann degradation reaction (amine-PHBV), followed by collagen coupling reaction to prepare collagen-modified PHBV (collagen-PHBV). Amide-, amine-, and collagen-PHBV had higher water absorption and d-spacing values than PHBV, and melting temperatures and enthalpies decreased in the order of collagen-PHBV < amine-PHBV < amide-PHBV < PHBV. Thermal decomposition kinetics of PHBV component in the films has been investigated by means of nonisothermal thermogravirnetric and derivative thermogravimetric studies. Applying the Avrami-Erofeev equation with index of 2/5 as the probable kinetic function, the suitable activation energy was calculated by the Friedman method through linear fitting (correlation coefficient > 0.98). The activation energy of PHBV was lower than that of amide-PHBV but higher than that of amine- and collagen-PHBV. Being incubated in phosphate-buffered saline at 37 degrees C, the modified PHBV films showed more weight loss than PHBV during 360 days; however, pH of degradation fluids was nearly neutral as the initial pH was recorded at 7.2. The modified PHBV films with different functional groups may provide an improved biodegradation rate for various cytocompatible biomaterials constructs. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 390-398, 2010