Advances in microelectronics manufacturing can be utilized to enable next generation devices in several critical areas. Printed electronics is one such microfabrication method that allows rapid changes to design, use of a large number of functional materials, and novel device geometries. Printed electronics, however, has been largely confined to 2D structures on 2D or 3D substrates. In this work, we extend nanoparticle printing into three dimensions, where controlled condensation and solvent evaporation in microdroplets is used to realize a new class of three-dimensional (3D) micro-architected materials without any support materials. A precise arrangement of nanoparticles in 3-D space is achieved to fabricate structures such as highly intricate 3-D micro-lattices, pillars, and spirals. Theories of dropwise condensation and evaporation are developed and validated through experiments.
We then use this printing method to realize Brain-Machine Interface (BMI) devices having recording densities of > 5000 sites/cm2, which is an order of magnitude higher than the current state of the art devices. The BMIs were successfully inserted into mouse and macaque brains. Low electrochemical impedance of the printed electrodes led to a successful recording of action potentials from the brain of anesthetized mice with a high signal to noise ratio. We also demonstrate highly sensitive strain, temperature, and touch sensors via the printing method developed in the lab. Lastly, we show that the printed 3D microlattice structures can be used as Li-ion batteries with 2x the areal density compared to conventional block electrodes.