Abstract
Micro–nano robots represent an exciting area in robotics research, involving tiny devices capable of navigating and interacting within the nano-scale world. The field of micro robotics has advanced with breakthroughs in microfluidic research over the past few decades. Non-invasive access to smaller spaces, parallel controllability, and biocompatibility of these units can benefit many biomedical applications. In this research, we developed multi-functional microbots that can be actuated with tightly focused laser beams for targeted drug delivery, cell poking, and cell characterization studies. The experimental setup included a modular optical tweezer system, a stage top incubator unit for cell studies, and a quadrant photodiode (QPD) sensor for measuring optical trap displacements. Microbots were batch-fabricated using the biocompatible photoresistIp-Dip2 via two photon polymerization (TPP), a 3D direct laser writing technique. They feature15nm-thick gold layers deposited within their bodies to induce convective microfluidic flows for the manipulation of microscale cargo. Their performance was evaluated through numerical simulations with Multiphysics software. We also demonstrated the loading and unloading of microparticles experimentally, using silica beads with a 2 µm diameter as cargo. By analyzing camera feedback, the motion of the beads was studied to verify the proposed technique. Furthermore, microbots were used as tools for micro-scale force measurements with living cells. These force measurements help evaluate the mechanical properties of cells as part of cell characterization studies. The ability to operate in closed microfluidic channels and higher force sensitivity gives microbot-assisted techniques a comparative advantage over conventional Atomic Force Microscopy. In our experiments, human malignant melanoma (A375) cancer cells were mechanically probed by translating the microbot across the surface to which the cells were attached. Microbots were controlled with optical traps, and the relative displacements between the traps and the microbot handles were measured with the QPD sensor for contact force estimation. Trap displacement data, combined with a harmonic spring model, were used to estimate piconewton-scale contact forces on live cells. The optical tweezer setup with an incubator environment provided an ideal setting for cell experiments. Our study utilized QPD sensor data with a multi-trap model, surpassing video microscopy-based techniques and demonstrating significant potential for real-time force measurements in vitro cellular studies.