PALPABLE: enhanced bending stiffness and proprioception in soft actuators for laparoscopic palpation

The assessment of tissue properties via direct palpation is essential for localizing abnormalities during surgery. However, Minimally Invasive Surgery (MIS) eliminates this tactile feedback, creating a critical sensory gap. To address this, the EU Horizon project PALPABLE is developing novel fiber-optic sensing modalities for stiffness assessment. Successful integration of this technology requires an articulation interface that balances high maneuverability with the structural stability necessary for deflection-free tissue palpation. We present a single-degree-of-freedom (DOF) soft silicone actuator integrated with a modular, bioinspired passive stiffening element. Mechanical loading tests, motion tracking, and Finite Element Method (FEM)-guided design iterations validate the stiffening strategy and actuator performance. The design achieves a substantial increase in bending stiffness, improving the stiffness-pressure response by 8-fold relative to the unstiffened actuator under critical loading (normal force at a 90° bend). Furthermore, we developed a compact, custom pneumatic syringe pump with closed-loop pressure control to ensure precise, safe operation in surgical environments. By combining embedded fiber-optic sensing with machine-learning models, the system achieves free-space full-shape reconstruction with approximately 1% error. This work delivers a compact, load-capable, and sensorized soft actuator tailored for PALPABLE's probe manipulation requirements, enabling safe, controllable, and data-rich tissue palpation in confined anatomical spaces.