Abstract
A microrobot system comprising an untethered tumbling magnetic microrobot, a two-degree-of-freedom rotating permanent magnet, and an ultrasound imaging system has been developed for in vitro and in vivo biomedical applications. The microrobot tumbles end-over-end in a net forward motion due to applied magnetic torque from the rotating magnet. By turning the rotational axis of the magnet, two-dimensional directional control is possible and the microrobot was steered along various trajectories, including a circular path and P-shaped path. The microrobot is capable of moving over the unstructured terrain within a murine colon in in vitro, in situ, and in vivo conditions, as well as a porcine colon in ex vivo conditions. High-frequency ultrasound imaging allows for real-time determination of the microrobot’s position while it is optically occluded by animal tissue. When coated with a fluorescein payload, the microrobot was shown to release the majority of the payload over a 1-h time period in phosphate-buffered saline. Cytotoxicity tests demonstrated that the microrobot’s constituent materials, SU-8 and polydimethylsiloxane (PDMS), did not show a statistically significant difference in toxicity to murine fibroblasts from the negative control, even when the materials were doped with magnetic neodymium microparticles. The microrobot system’s capabilities make it promising for targeted drug delivery and other in vivo biomedical applications.
Highlights
Recent advances in the design and fabrication of microrobots has made them increasingly viable for biomedical applications [1,2,3]
Microrobots were coated with a solution consisting of a 50:50 ratio of dimethylformamide (DMF):chloroform, 1% poly(lactic-co-glycolic acid) (PLGA), and 1% fluorescein, with fluorescein serving as a mock drug payload
When seeded with murine fibroblasts, all material variants of the microrobot exhibited cell proliferation, with no statistically significant difference in toxicity compared to the negative control samples
Summary
Recent advances in the design and fabrication of microrobots has made them increasingly viable for biomedical applications [1,2,3]. Compared to conventional surgical and drug administration techniques, the use of actively guided microrobots have promise to reduce patient trauma, lower the risk of side effects, and have higher drug retention rates Potential applications such as microsurgery [4], tumor imaging and ablation [5,6], tissue biopsies [7], targeted drug delivery [8,9,10], cell delivery [11,12], and gene silencing [13,14] have recently been explored, with demonstrations of microrobot viability in both in vitro and in vivo conditions. An imaging/actuation combination with high resolution, cross-compatibility, small footprint, and tissue penetration capabilities is necessary for the feasibility of actively guided, minimally invasive in vivo microrobots. We highlight the development of a microrobot system consisting of high-frequency ultrasound imaging, magnetic actuation, and tumbling magnetic microrobots, showing promise for a variety of minimally invasive in vivo biomedical applications
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