Development of a Biohybrid Tendon Interface for Muscle-Powered Robots

Abstract

Unlike metal and plastic, biological materials can communicate with their surroundings, adapt to stimuli, and self-repair damage. Incorporating these materials into engineered systems could foster smarter, more adaptable machines. We have shown that engineered skeletal muscle stretched around an elastomer ‘skeleton’ can generate force and drive locomotion. However, the interface between the biotic and abiotic components of this robotic system are friction-based, leading to inefficient force transmission. In the body, muscle is covalently tethered to bone via tendons, which efficiently transmit force. Thus, we have developed a bioinspired synthetic tendon to act as a biohybrid interface, enabling the design of more modular and adaptive biohybrid machines.

We developed a tough adhesive hydrogel tendon, composed of a poly(acrylic acid) hydrogel functionalized for tissue adhesion with N-Hydroxysuccinimide ester groups, in collaboration with the Zhao Lab at MIT. Muscle tissues were manufactured from C2C12 mouse myoblasts seeded into a fibrin and Matrigel matrix. Peel tests of these differentiated and undifferentiated muscle tissues bound to the synthetic tendon revealed that the biotic-abiotic interface could withstand forces >500mN before breaking. This is significantly greater than those generated from the contraction of engineered muscle (~300uN), demonstrating a robust binding. A cell viability assay and pH exposure test confirmed that the synthetic tendon had no significant impact on muscle health, indicating general biocompatibility.

Furthermore, we have been able to bind strips of mature engineered skeletal muscle tissue between two strips of synthetic tendon, akin to myotendinous junctions in vivo. We have leveraged this tendon-muscle-tendon (TMT) construct as a modular actuator that can be mechanically coupled to robotic skeletons to generate force and produce motion. We are evaluating the effects of varying synthetic tendon stiffness and preload tension on the force production capability of these units, enabling the optimized design and deployment of TMT actuators in untethered machines. In short, we have developed a hydrogel tendon system that serves as a robust biocompatible musculoskeletal interface.