In Vivo Biocompatibility and Degradation Studies of Polyhydroxyoctanoate in the Rat: A New Sealant for the Polyester Arterial Prosthesis

The present study examined the biocompatibility and degradation properties of poly (β-hydroxy octanoate) (PHO) as an impregnation substrate on arterial prostheses. PHO-impregnated polyester grafts sterilized by ethylene oxide (EO) or gamma (γ) radiation, and polyester Dacron^® prostheses impregnated with fluoropolymer, gelatin, or albumin were implanted subcutaneously in rats for periods ranging from 2 to 180 days. The biocompatibility was assessed by quantifying the alkaline and acid phosphatase secretion while performing histological studies at the tissue/prosthesis interface. The degradation was determined by chemical analysis of the EO and γ-sterilized PHO after implantation using differential scanning calorimetry (DSC), wide angle x-ray diffraction (WAXD), and size exclusion chromatography (SEC). Alkaline phosphatase activity by the sterilized PHO and by the gelatin and albumin grafts was significantly elevated early after implantation in contrast to that of the Dacron and fluoropolymer grafts that occurred later, at 7 and 5 days, respectively The peak of acid phosphatase activity for all of the grafts occurred between 5 and 10 days postimplantation, with the γ-sterilized PHO grafts recording the greatest activity. Histological study revealed that the tissue incorporation into the graft wall was earlier and more complete for the Dacron and fluoropolymer grafts after 6 months than for the gelatin and albumin grafts, because the latter induced important inflammatory reactions during the resorption of the cross-linked protein substrates. The EO and γ-sterilized PHO grafts exhibited a similar healing sequence characterized by the development of a collagenous tissue surrounding the prostheses. However, no infiltration of tissue into the graft wall was observed after 6 months, mainly because of the presence of the PHO. Degradation of the EO and γ-sterilized PHO occurred preferentially by a hydrolytic mechanism as shown by a 30% molecular weight decrease after 6 months. In conclusion, PHO showed good biocompatibility in terms of enzyme activity and tissue reaction. Degradation was a slow, in vivo process controlled primarily by a random hydrolytic reaction and by a local enzymatic attack by macrophages and giant cells.