Shape-programmable Adaptive Multi-material Microrobots for Biomedical Applications

Abstract: Flagellated microorganisms can swim at low Reynolds numbers and adapt to changes in their environment. Specifically, the flagella can switch their shapes or modes through gene expression. In the past decade, efforts have been made to fabricate and investigate rigid types of microrobots without any adaptation to the environments. More recently, obtaining adaptive microrobots mimicking real microorganisms is getting more attention. However, even though some adaptive microrobots achieved by hydrogels have emerged, the swimming behaviors of the microrobots before and after the environment-induced deformations are not predicted in a systematic standardized way. In this work, experiments, finite element analysis, and dynamic modeling are presented together to realize a complete understanding of these adaptive microrobots. The above three parts are cross-verified proving the success of using such methods, facilitating the bio-applications with shape-programmable and even swimming performance-programmable microrobots. Moreover, an application of targeted object delivery using the proposed microrobot has been successfully demonstrated. Finally, cytotoxicity tests are performed to prove the potential for using the proposed microrobot for biomedical applications. One-Sentence Summary: A systematic approach to design shape-programable, dual-function, and adaptive microrobots for biomedical applications. Main Text: INTRODUCTION Microorganisms are capable of swimming with flagella to provide motility (1-3). These microorganisms can adapt their flagella into different shapes or modes by altering gene expression to accommodate environmental changes or for other proposes like nutrition, hosting, and invasion (4). For example, the flagella of a spermatozoon of Echinus esculentus will result in a transition from a planar to a helical shape when the viscosity is increased and back to a quasi-planar shape when it is further increased (5). Moreover, recent investigations show that the flagella can deform to wrap around the cell body to escape from traps or to enhance the efficiency of environmental exploration (6, 7). Inspired by these natural living beings, many microrobots have been fabricated to swim in this microscale world. The two strategies most adopted to achieve motility are the helical structures mimicking the flagella of bacterial E. coli and the flexible body replicating the motion of a spermatozoa (8). In the last decade, various helical-type microrobots are realized with fixed shapes, i.e., the structure will not change once it is fabricated (9-11).