3D-Printed Microrobots with Integrated Structural Color for Identification and Tracking

The implementation of two-photon polymerization (TPP) in the microrobotics community has permitted the fabrication of complex 3D structures at the microscale, creating novel platforms with potential biomedical applications for minimizing procedure invasiveness and diagnosis accuracy. Although advanced functionalities for manipulation and drug delivery tasks have been explored, one remaining challenge is achieving improved visualization, identification, and accurate closed-loop control of microscale robots. To enable this, distinguishable identifying and trackable features must be included on the microrobot. Toward this end, the construction of micro- and nanoscale patterns using TPP is demonstrated for the first time on microrobot surfaces with the intent of mimicking color-expressing nanostructures present on beetles or butterflies. The patterns provide identification and tracking targets due to their vivid color expression under visible light. Helical and rectangular microrobots are designed with the topical patterns and further functionalized with magnetic materials to be externally actuated by magnetic fields. Vision-based tracking of a 20 mu mx30 mu m colored feature on a 100 mu m-long helical microrobot using a fixed angular position light source during microrobotic motion is shown. This versatile structural color patterning approach shows great potential for the visual differentiation of various microrobots and tracking for improved closed-loop control.