3D Micromolding of Small-Scale Biological Robots

Abstract

Small-scale robots are widely applicable for use in biological environments. Robots operating in these workspaces require non-cytotoxic and biodegradable architectures. Traditional methods of manufacturing millimeter or micrometer scale robots inherently preclude the use of many naturally-derived biological materials which fulfill these requirements. Fabrication via micromolding presents a practical method to incorporate these materials into the small-scale robot design space. In this work, we investigate the development of helical-shaped soft, micro bio robots (SMBRs) which are composed of naturally-derived, water-based hydrogels infused with iron oxide and are propelled using uniform, rotating magnetic fields. By incorporating a humectant into the molding process, we are able to create robots that are $\pmb{3-10}\times\ \mathbf{smaller}$ in characteristic dimensions and more than $\pmb{50}\times$ smaller in volume from our previous work. We explore the limitations of using stereolithography and two-photon polymerization printing processes to create molds, and demonstrate that our method can be used across length scales. We demonstrate and characterize the swimming behavior of microscale molded robots at a range of applied magnetic field frequencies, and compare their swimming velocity to their millimeter-scale counterparts. This work enables robot fabrication using functional biological materials, such that these robots can be used for biomedical tasks such as cellular and chemical cargo delivery.