In vivo degradation of polymers. I. Change of mechanical properties in polyethylene pacemaker lead insulations during long-term implantation in the human body.

The results of mechanical testing and microscopic examination of explanted clinically-used polyethylene pacemaker lead insulations are presented. An experimental set of 98 lead insulations implanted for times ranging from 7 d to 11 yr was evaluated for changes in mechanical properties during clinical use. The results showed that the polyethylene tubing suffered a gradual structural change, due to its exposure to the physiological environment of the human body. The decline of the mechanical properties with implantation time is described by empirical formulae. Abrasive deterioration was also observed and is discussed.