Micro-Scale Aerosol Jet Printing of Magnetic Materials for Soft Robotics

Small-scale magnetic soft structures that respond to an externally applied magnetic field have attracted wide research interest because of their unique capabilities and promising potential in a variety of fields, especially for applications in soft robotics. Current attempts for their micro-fabrication are largely based on adapted conventional template-driven fabrication processes, <i>e.g.</i> photolithography, template-based electro-deposition, and soft lithography, which require multiple processing steps and complex instrumentation, making them expensive and time-consuming, and do not effectively support mass customisation. Alternatively, digital fabrication technologies such as 3D printing facilitate the manufacturing of soft robots but are often limited by material selection and offer limited printing resolution. Within this framework, aerosol jet printing (AJP) is an emerging digitally driven, non-contact and mask-less printing process that has distinguished advantages over other technologies as it offers direct-write, high-resolution, versatile deposition of a wide range of materials onto a variety of substrates. Although AJP has primarily been used for surface patterning, researchers are beginning to explore its potential for producing 3D microstructures with complex architectures. Moreover, dual-material aerosol jet printing has been successfully demonstrated for the printing of composite structures with variable composition. Such capabilities illustrate the possible value of AJP in this field as an enabling manufacturing process which could introduce new possibilities of producing unique soft magnetic structures at the micro- and meso-scale by harnessing the unique capabilities of the process.<br/>In this work, two different approaches are presented: 1) single material aerosol jet deposition of magnetic nanoparticles (MNPs) on soft/flexible substrates; 2) dual-material aerosol jet deposition of polymer/MNPs free-standing nanocomposite structures. Using the first approach, micro-patterns of MNPs in the region of 20 μm wide were successfully printed onto soft and flexible materials commonly used in soft robotics and biomedical engineering applications, such as polydimethylsiloxane (PDMS) films and poly-L-lactic acid (PLLA) nanofilms. The second approach allows the fabrication of magnetic nanocomposite with tailorable and controllable composition. An MNPs ink and a polymer ink are separately atomized in different atomizers and the resulting aerosols are mixed uniformly and <i>in situ </i>during the AJP process prior to deposition. The mix ratio of the two aerosols determines the MNPs loading in the nanocomposite, which can be used to locally control the magnetic properties of the printed structures, a significant feature that can’t be achieved in traditional multi-materials printing using liquid/liquid or liquid/solid phases. The entire manufacturing process is digitally driven, thereby providing the capability to rapidly alternate and produce different designs, and to do so within time and cost boundaries that would be unachievable by template-based manufacturing approaches.<br/>We believe that the use of this scalable, accurate, and versatile digitally-driven processing technology could enable a route for the development of novel magnetic microstructures.