Hydrolytic and enzymatic incubation of polyhydroxyoctanoate (PHO): A short-term in vitro study of a degradable bacterial polyester

The present study examined the degradation behaviour of poly(beta-hydroxy o ctanoate) (PHO), a bacterial poly(beta-hydroxy alkanoate), following incuba tion tinder hydrolytic or enzymatic conditions in vitro. Solution-cast PHO films were incubated in a citrate buffer solution with and without acid pho sphatase and in an acetate buffer with and without beta-glucuronidase for p eriods ranging from 7 to GO days. The physical characterization of the PHO films was analyzed by SEM and tensile strength studies. In addition. variou s analytical methods were used to detect modifications in the chemical and morphological structure of the PHO, namely, ESCA, FTIR, DSC, X-ray diffract ion, and SEC. The results indicate that the enzymatic conditions selected i n the present study induced no significant surface morphological or chemica l modifications, and no significant weight loss was observed after 60 days of incubation. However, as revealed by weight average molecular weight (M) over bar(w) and number average molecular weight (M) over bar(n) decreases, changes in the bulk structure of the PHO were observed with acid phosphatas e at 28 and 60 days, in contrast to smaller (M) over bar(w) and (M) over ba r(n) decreases recorded in both the buffers and the beta-glucuronidase. The tensile properties had decreased following incubation, yet showed no diffe rence under all of the selected conditions. With no weight loss or surface changes, the PHO films incubated in acid phosphatase showed only a chemical hydrolytic process characterized by (M) over bar(w) and (M) over bar(n) de creases with time of incubation. The present study demonstrated that the de gradation of PHO films is one of slow, chemical hydrolysis only, perhaps re quiring several months of incubation. The hydrophobic nature of the long al kyl pendent chain in PHO may be responsible for this slow process. The inab ility of enzymes to degrade PHO may be attributed to the latter's poor adso rption capacity, due to its hydrophobic nature, and to a lack of specificit y in the catalytic activity of these enzymes.