Bilayered Biofabrication Unlocks the Potential of Skeletal Muscle for Biohybrid Soft Robots

The emerging field of biohybrid robotics aims to create the next generation of soft and sustainable robots by using engineered biological muscle tissues integrated with soft materials as artificial muscles (bio-actuators). Both cardiac and skeletal muscle cells can be used for biohybrid actuation. Generally, cardiac bio-actuators take the shape of thin cellular films, while locomotive skeletal muscle bio-actuators form bulk tissues. The geometry of a bio-actuator should be optimized for the type of desired motion, e.g., thin film layers are optimal for swimming actuators mimicking fish. Until now, the geometry of skeletal muscle bio-actuators has been constrained to ring- or block-like tissues generally differentiated around a pair of pillars due to the need to oppose the contraction force exerted during the skeletal muscle differentiation process. In this work, we extend the possible geometry of skeletal muscle bio-actuators by demonstrating a bilayered design that mimics the motion of jellyfish. We take advantage of a volumetric printing method, i.e., xolography, which allows us to micropattern poly(ethylene glycol) diacrylate and gelatin methacrylate hydrogels to serve as scaffolds for seeding a layer of the skeletal muscle cell matrix. We demonstrate the locomotion speed of our bio-actuators is 3.4x faster than previously reported counterparts. In addition, our skeletal bio-actuators outperform most cardiac ones. Further optimization of our bilayer biofabrication for improved reproducibility of the maturation process of the skeletal muscle tissue will pave the way for the next generation of performant skeletal muscle-based actuators for biohybrid robots.