Despite earlier claims of biological stability, there is growing evidence from case histories, in vitro testing, and implant retrieval programs that poly(ethylene terephthalate) fibers experience some degradation when implanted in humans as arterial prostheses.

Previously, this was of minor significance when prognoses were of limited duration. Today these devices are being implanted in a wider spectrum of patients with the expectation of longer service lifetimes. There is growing urgency, therefore, to identify the rate and cause of this degradative behavior.

The authors have previously reported a progressive loss in the bursting strength of commercial polyester arterial prostheses with increasing times of implantation in humans. They have suggested that physical factors, such as the changes in the geometry of the knitted and woven structures have contributed to this loss of mechanical performance. This paper reports additional findings from an implant retrieval program. After residency periods from a few hours to 14 years, the chemical properties of the explanted devices have been analyzed. The results are compared with those from unused controls in order to determine the nature and extent of the chemical changes to the polymer during implantation. Losses in bursting strength are accompanied by losses in molecular weight and increases in carboxyl group concentration, suggesting that a chemical mechanism is also responsible for the degradative process. The kinetics of this chain scission reaction approximate a logarithmic decay model rather than that expected from autocatalytic initiation or a simple random or end-group mechanism with or without diffusion control of the initiator. It is estimated that 25% of the initial bursting strength is lost after 162 ± 23 months and 25% of the initial molecular weight is lost after 120 ± 15 months of implantation in humans.