Crocheted artificial tendons and ligaments for the anatomically correct testbed (ACT) hand

In the human hand, tendons and ligaments are important soft tissues that transfer forces from muscles to finger joints and coordinate the complex finger movements. However in conventional robotic hand research, their functions are often simplified by cables and linkages due to biological counterparts' complicated shapes and branching mechanism. In order to better simulate the neuromuscular control strategy of the human hand, we believe that it is important to replicate the salient features of the biological ligaments and tendons using artificial materials. To this end, we design and fabricate the artificial extensor hood for the anatomically correct testbed (ACT) hand via innovative crochet technique. The resulting artificial extensor hood resemble not only the shape and branching mechanism but also the varying fiber orientation in ligaments of its human counterparts. We successfully validate our design efficacy through finger movement experiments and quantitatively test the mechanical properties of the crocheted tendons under different branching conditions. We find that the crocheted ligament has a force-displacement behavior similar to that of the human hand and possesses a five times higher breaking strength on average.