Roboticists aim to mimic what natural biological entities have achieved — actions like moving, adapting to the environment, or sensing. Beyond traditional rigid robots, the field of soft robotics has recently emerged using compliant, flexible materials capable of adapting to their environment more efficiently than rigid ones. With this goal in mind, scientists have been working in the field of biohybrid robots or biobots. These generally are composed of muscle tissue, either cardiac or skeletal, and an artificial scaffold that can achieve crawling, grasping, or swimming. Unfortunately, current biobots are unable to emulate the performance of natural entities in terms of mobility and strength.
Researchers have overcome both challenges by using bioengineering tools. They applied 3D bioprinting and engineering design for the development of biobots at the centimeter range that can swim and coast like fish with unprecedented velocities. The key is the use of the spontaneous contraction of muscle cell-based materials with a very compliant skeleton.
Rather than working with stiff or tethered scaffolds to prepare artificial robots, the researchers used biological robots based on a flexible serpentine spring made of a polymer called PDMS, which was designed and optimized via simulations and then printed using 3D printing technology. The advantage of this innovative scaffold lies in the improved training and development of the tissue through mechanical self-stimulation upon spontaneous contractions, which creates a feedback loop due to the restoring force of the spring. This self-training event leads to enhanced actuation and larger contraction force. Such serpentine springs have not been included before in a soft robotic living system. Besides the capacity to self-train, the biohybrid swimmers based on skeletal muscle cells moved at speeds 791 times faster than current skeletal muscle-based biobots and were comparable with other cardiomyocyte-based bioswimmers (based on heart cells).
The new biobots were also able to perform other movements. They were able to coast when placed near the bottom surface, resembling the swimming style of certain fish characterized by sporadic bursts followed by coasting phases.
The work also has applications in drug delivery and development of bionic prosthetics.