From lines to lattices—high-resolution 2D and 3D PDMS microarchitectures via aerosol jet printing

Soft compliant silicone polymers such as Polydimethylsiloxane (PDMS) are widely used in soft robotics, biomedical devices, and microfluidic systems. PDMS, however, exhibits poor printability due to its high viscosity and low surface energy that have long restricted the fabrication of its three-dimensional (3D) freestanding microarchitectures. Such structures are required to achieve 3D microfluidic channels, sensitive actuators, and compliant micro-scale features. We introduce a polymer-based 3D Aerosol Jet Printing (Polymer 3D-AJP) method that fabricates minimally constrained freeform 3D microarchitectures of PDMS without auxiliary support. Our process uses in-situ rapid thermal curing of PDMS droplets to stack them in space, forming self-supporting 3D structures such as hollow and solid micropillars and microlattices in a single processing step. A solvent-diluted long-shelf-life PDMS ink formulation is introduced for our printing process. Modeling-guided experimentation uncovers a unique design space available for fabricating such structures. The approach is further generalized to a range of polymers such as Ecoflex (another silicone), PEDOT:PSS (conductive polymer), SU-8 (UV-curable polymer), and polyimide (stiffer polymer). Our approach is then used to demonstrate applications in areas previously thought impossible. PDMS microlattices exhibit exceptional fatigue resistance, withstanding over 10,000 compression cycles at strains up to 50%. We then show freestanding flexible PDMS microchannels with leak-proof 3D microfluidic paths. Finally, magnetic microactuators are shown by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) in the PDMS micropillars. We thus establish a novel fabrication approach that opens new design spaces for 3D polymer microarchitectures with exciting applications in soft robotics and microfluidics.