In this thesis, a new technology and methodology is presented that can be applied to create the next generation of complex in vitro models for a range of high value applications.
Aerosol Jet printing is an emerging direct write technology. It can replace established fine feature patterning techniques with a digitally-driven, agile method. Aerosol Jet printing has advantages over other patterning technologies as it can deposit most liquids, solutions and suspensions in specific customisable designs on planar and non-planar surfaces. By automating the print process and establishing a range of enabling procedures, the technique was applied to pattern acellular structures in freeform patterns. These were used as culture substrates and shown to influence the growth and movement of cells in culture.
The fundamental engineering and validation of the apparatus is presented in this thesis. The design, development and testing of the automation system is reported, as well as the enabling procedures such as substrate production, alignment camera design, and control code generation. The automation system was experimentally proven to be capable of a minimum incremental movement of <10μm and had a backlash of 25μm in the print region. The alignment camera is capable of distinguishing features as small as 5μm. The control code generator was capable of producing high fidelity designs from mathematical equations or digital designs. These digital designs could be updated within hours, compared to a physical template which can take weeks to update if the production is outsourced.
To enable reliable micro-scale printing over long periods the material formulation and operating parameters are established. From an initial choice of three functional materials, an ink based around the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was used as the print feedstock. When using this functional material, pertinent operating parameters were investigated for their effect on the deposit geometry. Increasing the material flow rate through the machine or increasing the size of the nozzle orifice was found to enlarge the deposit, whereas increasing the scanning speed under the print head, or increasing the focusing sheath gas diminished the deposit. During a multivariable design of experiment with a 100μm micron nozzle, the line cross sectional areas were measured between 6 and 10μm2. The two most notable results were that the geometry is enlarged when the atomiser gas was increased, and diminished when the sheath gas was increased.
Finally, this thesis explores the ability for the deposited features to control the tethering and growth characteristics of cells in culture. The primary focus of the experiments was the HCT-116 colorectal cancer cell lines, which were encouraged to grow into the printed shapes including lines, dots, sharp angles, arcs, circles, and different pitched lines. Subsequently, the functionality of this method across eight different cell lines was proved. Baby Hamster Kidney, L929, primary Human Dermal Fibroblasts, HCT-116, RAW, C6, EA.hy 926, and HT-29 cells were all observed to preferentially tether to the deposited patterns and grow into shapes defined by them. The manner of the interaction was dependent on the cell type, however, a preferential response was seen across the full range of endothelial, fibroblast, neuronal and macrophage cells.
Finally, HCT-116 cells were patterned with high fidelity on curved surfaces, and with freeform patterns over areas larger than 2.5mm2. These experiments proved the apparatus is a viable method to produce complex in vitro models used to replicate in vivo conditions in applications such as pre-clinical drug evaluation, tissue engineering and fundamental biological studies.
