Quantification of Skeletal Muscle Fatigue in Biohybrid Actuating Systems

Incorporation of biohybrid materials into soft robotics actuation systems leverages the beneficial characteristics of <i>in vivo</i> muscle actuation, such as tuned force output, energy efficiency, self-healing ability, and adaptability. This offers a promising alternative to synthetic-compliant materials such as shape memory alloys or pneumatics. Although proof-of-concept studies have demonstrated small-scale biohybrid actuating systems, many aspects of the system require further optimization before the desired longevity and force output can be achieved. One such aspect is mitigating performance challenges related to muscular fatigue. Metabolic biomarkers such as lactate can be correlated to contractile mechanisms which determine muscular force output. Therefore, integration of a real-time lactate sensing component into a biohybrid actuator could improve system performance by informing stimulation parameters to reduce fatigue. Here we show the development of a sense and actuation platform for skeletal muscle cells, in which two-dimensional (2D) and three-dimensional (3D) skeletal muscle constructs are electrically stimulated. A nanostructured carbon-based electrochemical sensor is used to measure the varying concentration of lactate over time, allowing for system fatigue level determination and control using varying stimulation patterns. The electrochemical sensing device presented here provides a promising alternative to more invasive methods of quantifying fatigue levels in skeletal muscle systems, such as utilizing force gauges to measure changes in output capabilities. The prospective applications of this device into a minimally invasive device for long-term continuous lactate detection could be of great assistance in development of soft robotic systems, as well as in other fields such as clinical care and diagnoses.