Flexible and insulative Plasmalene wire coatings for biomedical applications

A novel polymeric material, Plasmalene, was synthesized and tested as a functional hermetic polymer coating on Gold, Platinum, and MP35N wire substrates. The flexible Plasmalene polymer coatings were synthesized onto wire substrates by vacuum processes which included radio frequency (RF) initiated plasma polymerization and thermal vapor deposition of methane and xylylene monomers. Mechanical and electrical tests were performed on 75 micron wires coated with either Plasmalene, Parylene, or Teflon polymers. The coated wire substrates were mounted on a flex testing machine that was submerged in a saline bath. A +5VDC electrical bias was continuously applied between the wire substrates and the bath. The flex testing machine mechanically stressed the coatings for 50,000 cycles with tensile and compressive loadings of up to 11% strain. The cyclic strain was applied through a total flexural arc of 170 degrees. Electrical leakage currents were measured through the polymer films to the saline bath at +5VDC versus a Ag/AgCl reference electrode. Analysis of the leakage current data for the Parylene and Teflon coated wires indicated that there was a significant (alpha = 0.05) increase, up to microampere levels, in leakage currents through the films as a result of repeated cyclic stressing. Plasmalene coated wires showed no significant increase in initial picoampere leakage currents with cycling and therefore, demonstrated that a superior insulative and mechanically durable film can be synthesized as a wire encapsulant.