Sensor-integrated TPU soft actuators fabricated by foam additive manufacturing

The development of multifunctional soft devices requires materials that combine compliance with integrated sensing, yet most existing solutions rely on rigid sensors or on conductive filaments where anisotropic filler networks and infill-based porosity limit reproducibility. Previous work on foamed PLA has shown density reduction via additive manufacturing, but without functional integration, while conventional conductive TPU remains confined to bulk or patterned infill structures with poor electromechanical consistency. Here we present the first demonstration of Foam Additive Manufacturing (FAM) applied to carbon-black-filled thermoplastic polyurethane (TPU) for the fabrication of lightweight, sensor-integrated soft actuators. By tuning solubilization, desorption, and extrusion conditions, we generate homogeneous microcellular foams with up to 42.2% density reduction while preserving mechanical integrity. The resulting conductive foams exhibit stable and repeatable piezoresistive responses under load. Comparative tests on phalanx- and finger-like specimens confirm enhanced compliance and real-time resistance feedback during grasping and release, outperforming both bulk and infill-matched references. This work establishes FAM as a new route to directly print soft actuators that integrate structure and sensing in a single material, overcoming the anisotropy and scalability limits of previous foamed PLA and conductive TPU approaches. Potential applications span soft robotics, prosthetics, and wearable systems.