Electromagnetically actuated soft hydrogel microrobots for biomedical applications

This paper introduces electromagnetically actuated biomedical microrobots using external stimulus responsive hydrogels. We briefly summarize several research trends using representative magnetic actuated hydrogel microrobots developed to date and introduce our three developed types of magnetic actuated hydrogel microrobots. First, we propose a selective microrobots control method using microclampers consisting of temperature-responsive hydrogel (NIPAAM) blocks and microheaters. Using the selective microrobots control method, multiple microrobots can be independently controlled by an electromagnetic actuation (EMA) system. Second, we developed a self-folding magnetically driven microrobot in which a layer containing magnetic nanoparticles (MNPs) and a temperature-responsive hydrogel layer are laminated. The motion of the magnetically driven microrobot is controlled precisely using magnetic field control and the microrobot performs self-(un)folding motion due to the temperature change. Additionally, the microrobot is able to grab a bead containing a drug and to manipulate it precisely to a desired position. Finally, we developed a spring-shaped hydrogel (NIPAAM) microrobot using drugs and MNPs. By using an integrated system containing an EMA system and a near-infra-red (NIR) light generating device, we demonstrated that the spring-type hydrogel microrobot can move to a desired position and actively release the loaded drug. Thus, it is shown that a variety of magnetically actuated hydrogel microrobots were developed and further in-depth studies are necessary for the development and use of these microrobots in biomedical applications.