Engineering Synthetic Soft Tissue for Accurate Human-Exoskeleton Interaction Testing

In the field of wearable robotics, assessing physical human-exoskeletons interaction (pHEI) is of critical importance in the development of wearable assistive devices. However, in the early stages of development of such devices, involving human testing could raise safety and ethical concerns. To address those limitations, we developed an active dummy leg named Leg Replica. Yet, the realism for pHEI was not adequate when mimicking soft-tissue behavior (compression and shear). The work presented here focused on identifying synthetic soft tissue simulants to enhance the fidelity of the Leg Replica, resulting in responses under compressive and shear stresses similar to those observed in human subjects. A novel approach is proposed in this work as a testing method for mechanical characterization of compressive and shear stresses of human soft tissues that is coherent with the specific application of wearable lower limb exoskeletons. The testing methodology was applied to 10 human subjects as well as the Leg Replica enhanced with three different platinum-catalyzed silicone material of varying hardness and thickness. One of the tested materials, with a thickness of 3 cm, demonstrated a mechanical behavior under compression and shear stresses comparable to that observed in human tissue. This study demonstrates the ability of the proposed methodology to objectively benchmark the adequacy of the Leg Replica combined with a new tissue simulant to mimic the biomechanical behavior of the human leg.