The effects of annealing on mechanical, chemical, and physical properties and structural stability of Parylene C

Parylene C is one of the established encapsulation polymers for chronic implants. We investigated the influence of annealing Parylene C on its mechanical properties, chemical structure, and on the stability of Parylene C - platinum Parylene C sandwich structures as a model of flexible neural interfaces in 0.9 % saline solution. Films of Parylene C were annealed at 200 degrees C, 300 degrees C, 350 degrees C, and 400 degrees C in nitrogen atmosphere. Temperatures of 350 degrees C and higher as well as annealing in air destroyed the Parylene C layers; films annealed at lower temperatures showed identical infrared spectra. Higher anneal temperatures produced increased values of elongation at break, tensile and yield strength, and yield strain while at the same time Young's modulus was shown to decrease. Crystallinity increased with annealing temperature. The structural stability of sandwich structures benefitted remarkably from annealing. Sandwich structures annealed at 300 degrees C maintained their structural integrity during 320 days in saline solution at 37 degrees C and the insulation capability stayed consistently high.