Low-firing thick-film piezoresistive sensors for medical instruments

In this work, a low-firing thick-film materials system allowing fabrication of piezoresistive sensors on surgical alloys is presented in detail, with application to a force-sensing surgical instrument. The system comprises a series of individual thick-film dielectric, conductor, resistive and overglaze compositions based on a lead borosilicate glass matrix. The moderate achieved firing temperature, around 625°C, greatly increases compatibility with metallic substrates, allowing the use of high-strength medical alloys with low thermal degradation. Specific fillers for the dielectric layers increase adhesion on steel substrates and allow thermal matching to austenitic and ferritic / martensitic steels, as well as titanium alloys, and preliminary work demonstrating reactive stabilisation of the dielectric layer to achieve an even wider process window is also shown. Finally, the functionality of this materials system is successfully demonstrated here by implementing it into a previously developed ligament-balancing force sensor for total knee arthroplasty (TKA) [1].