Background: PurSil^®35 is a silicone-urethane copolymer evaluated as a cardiac lead insulation with an overall composition of approximately 35wt% silicone. PurSil^®35 uses the same raw materials as Elasthane^® polyurethane, already used as insulation in production leads, with the addition of silicone polymers. Silicone is incorporated into the polymer backbone and, in addition, the ends of some of the copolymer chains are terminated with silicone Surface-Modifying End Groups™ (SME). Polyurethane SME materials have been shown to enhance biostability and provide desirable surface characteristics (e.g., lubricity, reduced cellular adhesion and proliferation).

Purpose: Excellent accelerated environmental stress cracking (ESC) and metal ion oxidation (MIO) performance in 2-year rabbit studies has previously been summarized. This evaluation presents the PurSil^®35 biostability results from two and five year canine studies conducted on lead insulations of various prototype configurations including coaxial, overlay and multilumen, representative of future product. 

Methods:  The first canine study evaluated an overlay configuration. Twenty-seven leads were implanted in nine canines. The second canine study evaluated co-axial and multilumen configurations. Twenty-eight leads were evaluated from ten canines after two years of implant and twenty-four leads were evaluated from eight canines after five years of implant.  Explanted leads were analyzed by visual observation, SEM, tensile testing, GPC, FTIR, and DSC.

Summary:  The results demonstrated that PurSil^®35 biostability in a variety of lead body configurations is comparable to high modulus 55D polyurethane controls. 

Conclusions:  The incorporation of silicone within the backbone of the polymer and on the chain ends results in a copolymer that possesses a more desirable lower modulus with comparable biostability to high modulus 55D polyurethane materials. A lower modulus lead insulation material translates into a lead that is more compliant (better handling, steerability).  This PurSil^®35 material also provides unique surface properties improving lubricity and chronic cellular response to the implanted lead.