Influence of artificial body fluids and medical sterilization procedures on chemical stability of Parylene C

Among materials suitable for flexible encapsulation poly-para-xylylene (Parylene C), often chosen as protective coating for biomedical devices and variety of anticorrosion applications due to its favorable chemical and biological resistance, high thermal stability, low water vapor absorption, permeability, high biocompatibility as well as excellent dielectric and mechanical properties, is one of the most promising. In spite of a wide use only few systematic studies on biological and chemical stability of Parylene C have been carried out. In this work the influence of autoclave, electron beam (e-beam), gamma, ethylene oxide (EtO) and H2O2-plasma sterilization procedures as well as influence of in-vitro dynamic loading with artificial blood plasma (ABP) and cerebrospinal fluid (ASCF) and 0.9 % NaCl on chemical resistance and crystallinity of Parylene C were studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The samples, treated with e-beam sterilization, show substantial changes in their chemical content comparing to the untreated state. The XPS-analysis revealed the intrusion of CH- and CN-groups into the polymer structure and formation of inorganic chlorides on the surface of Parylene C. The second effect was also present in the samples after EtO-treatment. No detectable changes in chemical content of polymer films were observed after gamma, plasma and autoclave procedures. The reduction of Cl-concentration in Parylene C, resulted from damaging of its structure, was found in all the samples loaded with fluids. Additionally, after the fluid influence, the already mentioned implantation of nitrogen and formation of inorganic chlorides have been observed. According to the XRD-results, the autoclave sterilization and fluidic treatments caused the significant ride of Parylene C crystallinity grade. Low crystallinity increase was detected after EtO and plasma procedures, while the both irradiation treatments leads to stronger marked amorphism of the studied structures.