Biohybrid Microrobots

Thanks to millions of years of evolution, living beings have developed complex mechanisms for sensing, actuation, and adaptation to the surrounding environment. Biohybrid robots exploit these mechanisms by embedding living components and combining them with nonliving elements. This allows overcoming some of the issues affecting entirely artificial devices, such as difficult scalability to small scales, inability to self-heal, and possible immunogenicity. In this chapter, biohybrid microrobots based on bacteria or other single cells (e.g., sperm cells, erythrocytes, neutrophils) are described. The most relevant examples reported in the state-of-the-art are analyzed, focusing on their specific sensing and actuation mechanisms. Relying on the use of a complete and autonomous living organism, they must be considered examples of a top-down approach, which needs to find ways of adequately controlling them. Specific applications of these systems are also described, with a particular focus on clinical ones. Then, muscle-based multicellular robots are introduced. Such systems are based on a bottom-up approach, through which single contractile units (skeletal muscle cells, cardiomyocytes, or insect-derived cells) are assembled and integrated with materials supporting them, to achieve effective locomotion and other functions. The main applications and challenges related to multicellular biohybrid microrobots are described, mentioning among others, modeling issues and the need for implementing multiple degrees of freedom, yet keeping high controllability by an external user