3D Microelectronics for Biomedical Devices via Aerosol Jet Printing: from Fundamental Materials Science & Toolpath Strategies to Realizing Next-Generation Brain-Computer Interfaces

 Additive Manufacturing (AM), also called 3D printing, of electronic circuits is an emerging area of research where devices are fabricated via jetting of functional materials in the form of liquid dispersions. Amongst the various techniques for electronics AM, Aerosol Jet (AJ) nanoparticle printing offers the highest resolution and an ability to print on nonplanar surfaces. While electronics AM was limited to planar 2D structures in the past, recent work from our group has extended this capability to 3D shapes, where fluid dynamics of microdroplets is used to rapidly build 3D microarchitected structures without any auxiliary support. These structures are difficult, if not impossible, to make using conventional 2D lithography, and open an entirely new design space that enabled electronic devices in a wide array of application areas to function at previously impossible efficiencies.

The work in this thesis focuses on expanding and harnessing AJ printing of 3D microarchitectures to address a critical gap in the field of neuroscience – the ability to record action potentials from user-specified 3D brain regions at high recording densities. Specifically, we introduce CMU Array, a new class of brain computer interfaces (BCIs) fabricated using AJ printing with full customizability and an ability to record microvolt and millisecond-level neuron-to-neuron electrical signals at densities up to 2600 channels/cm³. This is the first such tool that can record neuronal signals from throughout the 3D volume of the brain at high density. The manufacturing process, from printing to post-processing, is described, along with difficulties encountered during its development. Specifically, an in-depth study of geometric distortions during the sintering of 3D, freestanding nanoparticle structures (e.g., the micropillar arrays of the BCIs) was carried out. The root cause of the shape distortion, namely a hitherto unknown mass transport mechanism, was identified, and an engineering solution was implemented to print and sinter such structures without distortion. Utilizing this solution, the BCIs were manufactured and characterized. The BCIs were then tested in vivo, in anesthetized mice, in the Yttri lab at CMU. The BCIs showed minimal damage to the brain during insertion and recorded electrical signals with an excellent SNR of 8.6. Additionally, a manufacturing study was carried out to identify the effect of toolpath strategies on the build-up of 3D microarchitectures involving sharp and curved sections. This study further opens up the fabrication and design space for numerous exciting applications.