PEDOT:PSS Fiber-Based Highly Sensitive Strain Gauge Force Sensor for Biohybrid Robots

Integrating biological components of contractile living muscle tissues with careful microstructure design, biohybrid robots have realized various biomimetic behaviors and functions such as swimming, walking, and object manipulation. However, the inherent vulnerability to the stimulation and increased dexterity of biohybrid robots require perception of their function and surroundings for tissue protection and accurate control. Currently, most biohybrid robots are stimulated to output large forces without considering their health status, causing short lifetime and decreased performance. Therefore, biohybrid robots need to be equipped with sensors that can monitor muscle force and length similar to the Golgi tendon and muscle spindle in humans. The feedback signals would help with tuning stimulation parameters to better protect tissues from damage while generating stable and controllable force. This can be realized by incorporating a strain gauge force sensor within the muscle tissue to provide real-time strain and force information.<br/><br/>Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely utilized conducting polymers with diverse applications in bioelectronics, owing to its favorable electrical and mechanical properties, biocompatibility, stability, and commercial availability. By wet spinning of PEDOT:PSS into sulfuric acid bath, we successfully made fibers with diameters ranging 50-100 µm. These fibers remain elastic within 0-0.5% strain range, which is suitable for in vitro muscle strain monitoring. These fibers work like a resistive strain gauge and achieve a gauge factor of ~150 in the elastic range. The high gauge factor indicates a highly sensitive strain gauge from a single PEDOT:PSS fiber. We are able to incorporate the fiber-based strain gauge into a standard two-pillar muscle culture polydimethylsiloxane (PDMS) platform and calibrate it with a force transducer to generate the strain-force relationship. The PDMS platform can then be used to culture skeletal muscle tissues and measure the muscle strain and force production in real-time. This research sheds light on the perception and control of biohybrid robots.