One-step in situ construction of anisotropic bilayer hydrogel with high sensitivity and wide detection range for adaptive tactile sensing

Abstract

As an excellent human body signal receptor, the skin of the human body can accurately sense changes in the surrounding environment, transmit the signal to the brain and allow the muscles to make timely feedback. Based on this, bionic pressure sensors have received extensive attention. However, for traditional pressure sensors, it is still facing severe challenges to achieve wide range and high sensitivity at the same time. Therefore, this work utilized a simple and efficient in-situ polymerization strategy to construct a bilayer hydrogel consisting of a soft layer and a tough layer, achieving high sensitivity (62.7 kPa−1) under 0–5 kPa and a wide sensing range (up to 600 kPa). In addition, the sensitivities at 5–100 kPa, 100–250 kPa, and 250–600 kPa were 23.6 kPa−1, 9.63 kPa−1, and 0.42 kPa−1, respectively. The soft layer introduces low-density monomers to induce weak chemical cross-linking to improve sensitivity, while the tough layer introduces high-density monomers and nano-scale polyacrylamide to form a high-density chemical/physical double cross-linking network, thereby improving the pressure monitoring range. The effects of monomer density, nano-polyacrylamide, and the thickness ratio of the soft and tough layers in the bilayer gel were simulated by finite element simulation, and the results were in good agreement with the experimental results. On this basis, the hydrogel is assembled on the mechanical arm as a pressure sensor, and forms a tactile feedback system simulating human skin-brain-muscle system with the controller and computer. The system can adaptively and self-feedback grasp soft and tough objects without causing damage to the objects. This work provides new strategies and research directions for bionic robots, bioinspired soft materials, artificial skin, intelligent sensing and other fields.