A chemical means to study the in vitro hydrolytic degradation of poly(glycolic acid)

A chemical means was developed to examine the in vitro hydrolytic degradation of both γ‐irradiated and nonirradiated poly(glycolic acid) (PGA)‐absorbable polymers for the purpose of obtaining information how irradiation affected PGA degradation and how the results related to the previously observed mechanical and morphological data. The method was based on the chemical reaction between the degradation product of the polymer, glycolic acid, and chromotropic acid, and the subsequent measurement of the absorbance of the reaction products by a UV/visible spectrophotometer. It was found that the unirradiated PGA specimens exhibited a two‐stage hydrolytic degradation mechanism. This observation supported the previously hypothesized hydrolytic degradation mechanism on the basis of the level of crystallinity data. As the dosage of irradiation increases, the characteristic two‐stage degradation mechanism becomes less profound and eventually disappears at 20 Mrads. A monotonic degradation profile was then observed at this dosage level. As reported in the literature, the widespread use of mechanical properties to evaluate the degradation phenomena of this class of polymer does not, however, provide the details of the degradation mechanism as revealed by the present study. The interrelationship between tensile strength, level of crystallinity, glycolic acid concentration, and pH levels of the medium, and their changes as hydrolytic degradation proceeds, are discussed for the purpose of elucidating the mechanism in more detail.