An Inchworm-Inspired Soft Intestinal Robot with Anisotropic Frictional Feet Enabling Low-Voltage Locomotion

This study presents an inchworm-inspired soft intestinal robot powered by a Functionalized Carboxylated Bacterial Cellulose (FCBC)-based ionic actuator and anisotropic frictional feet to enable low-voltage locomotion. A bending ionic electroactive actuator composed of FCBC, Polypyrrole (PPy), and an Ionic Liquid (IL) was fabricated and denoted as FCBC–PPy–IL. The 30 × 6 × 0.8 mm actuator was equipped with silicone anchoring feet patterned with 45° inclined conical protrusions to generate directional friction. Material structure, electrochemical behavior, and cytocompatibility were characterized. Friction was measured on moist ex vivo colonic tissue (0.5–1.5 V, 0.1–10 Hz; end load 0–400 mg). Locomotion was evaluated in confined channels, on colonic surfaces, and within an ex vivo colon lumen. The actuator exhibited reversible, millimeter-scale bending at 0.1–10 Hz with stable output and no cytotoxicity. With anchoring feet, the robot showed pronounced frictional anisotropy, with \(\:{\mu\:}_{\text{r}}\) ≈ 24 (reverse/locking) and \(\:{\mu\:}_{\text{s}}\) ≈ 4 (forward/sliding). Under confinement at ≤ 1.5 V, the robot achieved consistent inchworm-like propulsion, with single-cycle step lengths of 0.031–0.11 mm and a speed of ~ 0.06 \(\:{\text{m}\text{m}\cdot \:\text{s}}^{-1}\) on flat tissue. Free locomotion on inclined surfaces and intraluminal locomotion were further demonstrated at 2.0 V as feasibility demonstrations (~ 0.04 \(\:{\text{m}\text{m}\cdot \:\text{s}}^{-1}\) on a 30° incline). This approach provides an early-stage low-voltage strategy for compliant propulsion and anisotropic-friction anchoring on colonic tissue, supporting future development of soft endoluminal robots.