Inkjet Assisted Electroforming and Swarm Actuation of Magnetic Micromotors
Authors: Bernasconi Roberto , Nova Anna , Pané Salvador , Magagnin Luca 
Published: December 2024

In the last few decades, untethered microrobots have been widely investigated for a wealth of potential applications, including high precision manipulation at the microscale, drug delivery, in-situ microsurgery or bacteria cleaning [1]. Most of the works available in literature, however, address these applications by actuating a relatively small number of devices. In order to fully exploit their potential, realistic applications inevitably require the use of a great number of single devices. In this way, the capabilities of the single device are multiplied and enhanced by the cooperation with hundreds or thousands of similar entities. As a natural consequence of this simple consideration, the control of large swarms of independent microdevices is acquiring a great practical relevance [2].
Not only the coordinated actuation of a great number of devices but also their manufacturing is challenging. Current state of the art approaches make large use of techniques derived from the electronic industry like traditional lithography or sputtering. These are often costly or characterized by a limited flexibility, whereas microrobotic swarms manufacturing requires the development of highly tailored, adaptable and low-cost strategies. A possible answer to this need of innovative fabrication routes is the use of additive manufacturing techniques [3]. These include not only the family of technologies that goes under the colloquial name “3D printing” but also direct writing or inkjet printing. The latter, in particular, is relatively unexplored for the fabrication of microdevices [4]. Nevertheless, it is characterized by many advantages (low cost, flexibility, high resolution) that can be attractive for the efficient manufacturing of untethered microdevices.
Starting from these considerations, we manufactured magnetically controlled swarms of discoidal micromotors and we tried to tackle the challenges for their production by exploiting a novel technique that we called “inkjet assisted lithography” (IAL). With respect to a standard lithographic process, IAL offers a considerably higher customizability of the transferred pattern at a lower cost. IAL resembles standard lithography, but in this case the photomask is directly applied on the SU-8 resist by inkjet printing an ink containing UV opaque nanoparticles. The development step removes not only the uncured resist but also the mask itself, leaving patterned templates. These templates are subsequently filled with metal via electrodeposition. The resulting magnetic disks are then released by dissolving the substrate and collectively actuated under controlled magnetic fields, investigating their swarming behavior. The influence of the actuation parameters, the viscosity of the environment and the magnetic properties of the material constituting the disks are determined and discussed. Finally, in order to provide a potential applicative perspective, some disks are also coated with polypyrrole and transformed into drug delivery vehicles.
[1] R. Wu, Y. Zhu, X. Cai, S. Wu, L. Xu and T. Yu, MDPI Micromachines 13(9), 1473 (2022)
[2] L. Yang and L. Zhang, Annu. Rev. Control Robot. Auton. Syst. 4, 509-534 (2021)
[3] J. Li and M. Pumera, Chem. Soc. Rev. 50, 2794-2838 (2021)
[4] R. Bernasconi, D. Carniani, M.-S. Kim, S. Pané and L. Magagnin, ACS Appl. Mater. Interfaces 15(1), 2396-2408 (2023)