In vivo degradation of polymers. II. Change of mechanical properties and cross-link density in silicone rubber pacemaker lead insulations during long-term implantation in the human body.

The results of mechanical testing, microscopic examinations and swelling of the explanted clinically used silicone rubber pacemaker lead insulations are presented. An experimental set of 100 lead insulations implanted for times ranging from 3 d to 11 yr were evaluated for change of mechanical properties and cross-link density during clinical use. The results show that the silicone rubber tubing suffers a gradual structural change due to its exposure to the physiological environment of the human body. A spiral deformation pattern due to the permanent set of the silicone rubber tubing in contact with the electrode leading wire was observed.