title: Characterization of parylene C as an encapsulation material for implanted neural prostheses.
abstract: The applicability of parylene C as an encapsulation material for implanted neural prostheses was characterized and optimized. The adhesion of parylene C was tested on different substrate materials, which were commonly used in neural prostheses and the efficiency of different adhesion promotion methods was investigated. On Si(3)N(4), platinum, and on a first film of parylene C, a satisfactory adhesion was achieved with Silane A-174, which even withstood standard steam sterilization. The adhesion to gold and polyimide could not be improved sufficiently with the tested methods. Furthermore, tensile tests and measurements of the degree of crystallinity were performed on untreated, on steam sterilized, and on annealed parylene C layers to investigate the influence of thermal treatment. This led to more brittle and stiffer films due to an increase in the crystalline portion in the parylene layers. Finally, an electrochemical impedance spectroscopy was used to test if a parylene C layer was able to protect a metallic structure against corrosion on a Si(3)N(4) substrate. The results indicated that this could be only possible by treating the substrate with Silane A-174. To receive parylene C layers with a good encapsulation performance, it is important to consider the materials, which are used in the neural prosthesis, to find the best suited process parameters.
authors.affiliation: Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering-IMTEK, University of Freiburg, Freiburg, Germany. hassler@imtek.de
authors.forename: Christina
authors.initials: C
authors.lastname: Hassler
authors.forename: Rene P
authors.initials: RP
authors.lastname: von Metzen
authors.forename: Patrick
authors.initials: P
authors.lastname: Ruther
authors.forename: Thomas
authors.initials: T
authors.lastname: Stieglitz
mesh_terms: D000268:Adhesiveness; D000818:Animals; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003343:Corrosion; D003460:Crystallization; D017097:Electric Impedance; D004563:Electrochemistry; D004567:Electrodes, Implanted; D066298:In Vitro Techniques; D008422:Materials Testing; D009420:Nervous System; D019635:Neurosurgical Procedures; D010984:Platinum; D011108:Polymers / Q000737:chemistry*; D019736:Prostheses and Implants; D012821:Silanes; D017655:Silicon Compounds; D013499:Surface Properties; D013718:Tensile Strength; D014961:X-Ray Diffraction; D014992:Xylenes / Q000737:chemistry*
chemical_list: D020099:Coated Materials, Biocompatible; D011108:Polymers; D012821:Silanes; D017655:Silicon Compounds; D014992:Xylenes; C011055:parylene; D010984:Platinum; C032734:silicon nitride