Load sensing surgical instruments - Development and characterisation of low firing thick-film materials systems for medical steels

The goal of this project was to develop low-firing thick-film materials systems for the fabrication of piezoresistive sensors on special steels, for the fabrication of instrumented medical devices. To this end, a series of individual thick-film materials and complete systems, based on lead borosilicate glasses, were developed and extensively characterised. These studies allowed us to formulate an optimised system firing at 625°C and applicable to austenitic, ferritic and martensitic steels. The functionality of this system was demonstrated with several steels by manufacturing pressure sensors and – in this report – by successfully instrumenting the previously developed knee-balancing force sensor [1]. The moderate achieved firing temperature strongly reduces compatibility problems with steels, compared to standard thick-film systems that require firing at 850°C: oxidation and annealing of the steel are considerably reduced, and, especially, phase transition problems are eliminated, allowing the use of high-strength martensitic steels as substrates. Finally, preliminary studies were carried out to eliminate lead from our materials, by replacing lead borosilicate glasses by compositions in the bismuth-zinc borosilicate system, with successful proof-of-principle results.