The effect of true human synovial fluid on the functionality of an in vivo pressure sensor element

This paper presents a study on the feasibility of packaging a sensor element by a thin biocompatible coating. The goal of the work was twofold; Firstly to investigate the possible impact of the coating on sensor element performance; Secondly to examine the sensor element functionality after soaking into true human synovial fluid for more than 30 days. Sensor elements with two different structures of TiO₂, the amorphous and the anatase, were examined and compared to uncoated elements. The device under test was a piezoresistive pressure sensor element designed for in vivo applications. Pressure characteristics were measured before and after Atomic Layer Deposition of the TiO₂ coatings. Sensor signals were examined and visual inspection of the sensor element surfaces were done after more than 30 days soaking in true human synovial fluid. Throughout the soaking period the shift in output signal was higher and varied more for uncoated elements than for coated ones. Our results indicate that a 20 nm thick TiO₂ coating can provide good protection towards the harsh synovial fluid.