Microfluidics and inkjet for biomedical engineering materials

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Inkjet printing is an additive manufacturing (AM) technique used for a wide range of applications, from office printers to single cell dispensing in genomics research. This core technology has many advantages over other AM techniques, including its tunable droplet size (as low as 100 pL), high dispensing rate, and the ability to dispense material onto a wide range of substrates in a non-contact manner. For example, this differs from extrusion-based 3D printing, a slower contact method. As such, inkjet is widely used to pattern organic polymers, conductive inks and biological materials such as proteins or cells. However, fluids with a viscosity above ~ 20 mPa·s are not compatible with inkjet because they cannot achieve successful droplet pinch-off at the nozzle exit. Additionally, fluids with low surface tension present issues because their droplets can wet the outside surface of the inkjet nozzle and cause poor reliability (i.e., sometimes the droplet may not pinch-off) and the unintentional generation of satellite droplets leading to poor print quality. The long-term objective of this research program is to expand the range of materials that are compatible with inkjet printing by designing new nozzles that can reliably print materials with higher viscosity or lower surface tension. To connect printing performance with fundamental understanding, the fluids and dispensing process will be characterized in terms of the relevant dimensionless groups that describe inkjet behaviour, so that an operating space can be mapped for dispensing these fluids within the modified inkjet nozzles for a wide range of materials. Short-term objective (1) is to develop controlled nanotopology at the surface of inkjet nozzles, with the goal to increase the applicability of drop-on-demand inkjet to high viscosity and low surface tension fluids. By creating slip at the fluid/nozzle interface, drag reduction has the potential to permit the dispensing of fluids with higher viscosity. This nanotopology would also reduce fouling on the nozzle face, permitting more reliable droplet printing for low surface tension fluids. Short-term objective (2) is to investigate the use of viscoelastic and other complex polymer solutions as cell-encapsulating fluids in inkjet printing, aiming to narrow the distribution of cells (or particulate analogues) in dispensed droplets (i.e., aiming at one cell per droplet). The effects of ion concentration on the polymer solution rheology, the resultant biocompatibility and the printing results will be investigated. The results of the research will be applicable across a range of inkjet dispensers and materials, including adhesives, polymers and gels, and will reduce the need to tune fluid viscosity and surface tension. This will have significant impact on the field of printed electronics and will enable the development of systems capable of highly accurate, ultra-high speed single cell dispensing for tissue engineering and sequencing.