Scientists at Harvard University and Emory University have created the first fully autonomous biohybrid robotic fish made from human heart muscle cells, paper and hydrogel. The 25-milligram device recreates the muscle contractions of a beating heart, allowing it to float in water. The results are published in the journal Science.
Scientists have made a device from cardiomyocytes derived from human stem cells that mimics the movement of a zebrafish. The biomechanical robotic fish had a tail fin consisting of two layers (bilayer) of muscle cells. These layers functioned in an antagonistic manner: when one side of the fin was stretched, the other side was compressed. The stretching of the layer led to the opening of mechanosensitive protein channels, which caused subsequent contraction, then stretching, and so on. This closed loop provided 108 days of battery life for the device.
For secondary control of the contraction-stretch cycle, the researchers built an analogue of the sinus node of the heart from cardiomyocytes – the G-node, which sends electrical signals to the fin muscles and acts as a pacemaker. The autonomous G-node and bilayer together generated spontaneous but coordinated rapid body and fin movements. As a result, the G-knotted robotic fish increased its swimming speed to more than one body length per second (15 millimeters per second).
The amplitude of muscle contractions, maximum swimming speed and muscle coordination increased during the first month as cardiomyocytes matured. Eventually, the biohybrid fish achieved swimming speeds comparable to those of zebrafish in the wild.
According to scientists, their technology can serve not only as the foundation for creating complex self-sustaining biomechanical devices, but also improve understanding of the human heart.