The manufacture of manipulators able to work wirelessly on a micrometric scale is one of the most interesting topics in microfabrication. Such devices, called microrobots, are expected to deeply change some aspects of modern surgery and to make in particular some medical treatments less invasive. Possible applications include localized drug delivery or confined modification of living tissues. Since motion in fluids at the microscale usually happens in low Reynolds number regime, the shape of microrobots is in general inspired by natural structures like bacterial flagella [1] or other propulsion apparatus of living cells well adapted to such conditions. For this reason shapes like rods, flagella [1] and helixes [2] have been tested in the existing literature. The most used method to control the motion of the devices is the application of a magnetic field [3], and due to this the microswimmers must have at least a part made of a metallic magnetic alloy.

Microrobots are nowadays realized using standard lithographic techniques, with high costs and poor flexibility of the production process. From this point of view the introduction of a manufacturing route based on additive manufacturing can introduce significant advantages. In the present work the possibility to directly 3D print the microrobots employing stereolithography (SLA) as technique is investigated. Typical designs like rods and helixes are employed. Since the SLA printing of metals is problematic, photocurable resins are used to produce the devices and the obtained samples are metallized via electroless plating to obtain the magnetic coating necessary for magnetic actuation. The quality of the 3D printed microrobots is evaluated, while the electroless process is first characterized from the general point of view and subsequently applied to the metallization of the devices. A first layer of a pure metal like copper is applied as flash layer, followed by a thicker layer of a suitable magnetic alloy. Finally the microdevices thus obtained are actuated in a controlled magnetic field and the motion at low Reynold number regime is studied.

[1] R. Mhanna et al.; Small 10, 1953 (2014)

[2] K. E. Peyer et al.; Chem. Eur. J. 19, 28 (2013)

[3] S. Kim et al.; Adv. Mater. 25, 5863 (2013)