New/Surface-Modified Biocompatible Polymer for ICD Lead Insulation

The average lifetime of an implanted pacemaker or defibrillator cable (lead) is approximately 10 years. One of the main lead failure mechanisms is deterioration of the insulation, which can be caused by chemical, biological, and mechanical processes. Each time lead failure occurs, an operation for its prompt replacement is required, in order to guarantee the patients' well-being. Since lead failure poses a health risk for the patients, and replacement operations are costly, this study aims at the improvement of one of the materials which is used by the cardiac pacing industry. Silicone polymers are commonly used for pacemaker and defibrillator lead insulation. Previous studies showed that some modified polyurethane polymers exhibit very different as well as favorable mechanical surface properties, as compared to their unmodified counterparts. This was due to the fact that polymeric blocs within the network can migrate to the materials' surface, and thereby act as surface-modifying end-groups (SMEs). In this study, a commercially available silicone system was modified by introducing two different SMEs and using two different approaches. In one approach the SMEs were covalently bonded to the silicone backbone, and in the second approach carrier molecules with the SMEs attached to them were admixed to the silicone. The carriers themselves had a siloxane backbone. The tensile properties, tear strength, and hardness were measured in order to describe the material as compared to commercially available mixtures, and to improve the mixing ratio of the components. Protein adhesion, water uptake, and surface wettability were evaluated to investigate the effect of the SMEs on the surface properties of the novel silicone formulations. While the mechanical properties of the silicone mixtures are comparable to but not competitive with the commercially available materials, contact angle measurement showed a significant reduction of the surface hydrophobicity: The initial contact angle of ∼114° could be reduced to ∼55°. It was concluded that the two novel SMEs can be used in order to make initially hydrophobic silicone hydrophilic.