Integrated Closed-loop Control of Bio-actuation for Proprioceptive Bio-hybrid Robots

Biohybrid robots are emergent soft robots that combine engineered artificial structures and living biosystems to exploit unique characteristics of biological cells and tissues. Skeletal muscle tissue-based bio-actuators can respond to externally applied stimuli, such as electrical fields. However, current bio-actuation systems rely on open-loop control strategies that lack knowledge of the actuator state. The regulation of output force and position of bio-hybrid robots requires self-sensing control systems that combine bio-actuators with sensors and control paradigms. Here, we propose a soft, fiber-shaped mechanical sensor based on a composite with piezoresistive properties that efficiently integrates with engineered skeletal muscle tissue and senses its contracting states in a cell culture environment in the presence of applied electrical fields. After testing the sensor insulation and biocompatibility, we characterized its sensitivity for typical strains (<1%) and proved its ability to detect motions from contractile skeletal muscle tissue constructs. Finally, we showed that the sensor response can feed an autonomous control system, thus demonstrating the first proprioceptive bio-hybrid robot that can sense and respond to its contraction state. In addition to inspiring intelligent implantable systems, informative biomedical models, and other bioelectronic systems, the proposed technology will encourage strategies to exceed the durability, design, and portability limitations of biohybrid robots and confer them decisional autonomy, thus driving the paradigm shift between bio-actuators and intelligent bio-hybrid robots. ### Competing Interest Statement The authors have declared no competing interest.