Miniature Compliance Controllable Sensor for Tissue Stiffness Sensing and Palpation

Tissue stiffness can provide key details about the health and type of tissues. This paper presents the creation of a miniaturised soft tissue stiffness sensor with dimensions that make it suitable for palpation in minimally invasive surgery. We introduce the stiffness sensor design and experimentally test its force sensing, elasticity measurement, and dynamic palpation performance. The sensor can measure normal forces with an adjustable range. Angled forces were measured with their magnitude and angles, <inline-formula> <tex-math notation="LaTeX">$\theta _{Y}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\theta _{X}$ </tex-math></inline-formula>, root-mean-square errors (RMSE) of 8.37%, 6.68%, and 13.92% of their respective ranges. Furthermore, samples with an elasticity between 4.20 kPa and 177.62 kPa, which were not in the training set, were measured with an RMSE of 7.79% of the tested range. During palpation, the boundary between the 13.4 kPa elastomer and the 2 mm embedded 29.3 kPa elastomer was located with a signal-noise ratio (SNR) of 77.04:1 and a mean offset of 0.706 mm. This investigation provides new insights into sensing devices capable of fitting trocars while measuring tissue elasticity and force during minimally invasive procedures.