PalpAid: Multimodal Pneumatic Tactile Sensor for Tissue Palpation

TL;DR

This work addresses the sensory gap in robot-assisted surgery by introducing PalpAid, a modular multimodal pneumatic tactile sensor that converts contact force into internal pressure changes while capturing acoustic signals via an onboard microphone. The device integrates a compliant silicone palpator, a pressure sensor, and a MEMS microphone mounted on a UR3e manipulator, enabling tissue classification through simultaneous pressure events and acoustic signatures. Experiments demonstrate the ability to distinguish hard 3D-printed PLA infills from ex vivo soft tissues using MFCC features with an SVM classifier, achieving varying levels of accuracy across materials (e.g., 100% for certain soft tissues, 75–100% for PLA infills). PalpAid offers a low-cost, compact solution for real-time tissue delineation with potential for easy sterilization and robotic-handheld deployment, while highlighting avenues for refinement in closed-loop control and higher spatial resolution.

Abstract

The tactile properties of tissue, such as elasticity and stiffness, often play an important role in surgical oncology when identifying tumors and pathological tissue boundaries. Though extremely valuable, robot-assisted surgery comes at the cost of reduced sensory information to the surgeon; typically, only vision is available. Sensors proposed to overcome this sensory desert are often bulky, complex, and incompatible with the surgical workflow. We present PalpAid, a multimodal pneumatic tactile sensor equipped with a microphone and pressure sensor, converting contact force into an internal pressure differential. The pressure sensor acts as an event detector, while the auditory signature captured by the microphone assists in tissue delineation. We show the design, fabrication, and assembly of sensory units with characterization tests to show robustness to use, inflation-deflation cycles, and integration with a robotic system. Finally, we show the sensor's ability to classify 3D-printed hard objects with varying infills and soft ex vivo tissues. Overall, PalpAid aims to fill the sensory gap intelligently and allow improved clinical decision-making.

Figures (6)

• Figure 1: PalpAid: Multimodal pneumatic tactile sensor with adaptive palpator for compliance with soft tissue. The presence of a microphone and a pressure sensor in a connected confined air cavity allows for extracting rich tool-tissue contact interaction, allowing tissue delineation in a surgical setting prakash2025biorender.
• Figure 2: System Overview: (a) Exploded view of PalpAid assembly with major components highlighted, (b) System architecture diagram of robot-mounted sensor with data acquisition and pressure control components.
• Figure 3: Sensor Fabrication: (a) A 1:1 ratio EcoFlex mixture was poured into a two-part mold, (b) EcoFlex was cured at room temperature for a minimum of 4 hours before integrating it with the palpator enclosure prakash2025biorender.
• Figure 4: Pressure Stability: (a) Effect of valve opening time on pressure and resultant palpator height; (b) Gradual pressure reduction with time in relaxed state at palpator initial height of $4$ mm over a span of $20$ minutes.
• Figure 5: Data: (a) Example of time-synced pressure and acoustic data collected over a series of palpation events in pork. The temporal regions extracted for downstream tasks are highlighted based on peaks detected from pressure signal (b) Single palpation event showing clear palpator contact with surface (1), full compression with deflation (2), and retraction with inflation (3) ; (c) corresponding visuals for PLA $20 \%$ and pork tissue corresponding to (b).