Plasma Enhanced Hydrophobicity of Parylene-C Surfaces for a Blood Contacting Pressure Sensor

A bio- and haemocompatible packaging strategy is proposed for an implantable pressure sensor for continuous direct blood pressure monitoring. A commercial sub-millimeter piezoresistive sensor was attached to an alumina substrate and a double coating of PDMS and parylene-C was applied. The packaged device has dimensions of 2.6x3.6x1.8 mm. A surface modification technique using O2 and SF6 plasma has been employed to tune the haemocompatibility of the packaged sensor. By enhancing the intrinsic hydrophobicity of parylene it is possible to increase plasma proteins adsorption and minimize platelets adhesion on the surface. Contact angle measurements were performed on parylene-coated PDMS samples after plasma treatment, using water and whole pig blood. A maximum contact angle of 134° has been achieved. The influence of different plasma exposure times on the surface wettability has been investigated. To study the stability of the plasma treated surfaces, the contact angle was measured immediately and at regular intervals.