Although additive manufacturing emerged about 30 years ago, a large number of researchers have been still working on its processes, materials, and applications due to the unique advantages of low cost, high degree of customization, high complexity, fast lead time, less waste material, and integrated assembly. Additive manufacturing has been widely used in a lot of fields, including aerospace, bioengineering, tissue engineering, optics, medical, and electronics.
A vat-based projection microstereolithography (MSL) has been studied for multi-material fabrication with various applications including drug loaded microneedle array and tissue engineering scaffolds. These studies indicate that MSL is an attracting microfabrication process that can create intricate and complex small structures with a high resolution. However, fabrication limitations exist due to the inherent system configuration and fabrication process. These limitations include the difficulty in using highly viscous materials, considerable material consumption, low fabrication speed, and high oxygen inhibition. This thesis sought a method to improve the fabrication capabilities of the existing MSL process by introducing a liquid bridge (a liquid drop formed between two parallel disks) to replace the vat which is a key element in conventional MSL to hold the liquid polymer.
In this thesis, a novel liquid bridge based microstereolithography (LBMSL) was proposed and developed. The liquid bridge was first introduced into the MSL process by replacing the vat, allowing the entire fabrication process to occur within the liquid bridge. The liquid bridge was studied theoretically and experimentally in order to obtain the stable equilibrium shape and the relationship between the height and the volume of the liquid bridge. The adhesion force between the fabricated part and the top disk as well as the oxygen inhibition during the fabrication process were investigated.
Using the LBMSL process, the fabrication layer thickness of 0.5 µm was reached. This could not be achieved in the vat-based MSL due to the oxygen inhibition to the photopolymer. A highly viscous material with the viscosity of more than 3000 cp, which is hard to be used in the conventional MSL, was tested and promising results were obtained. Compared with the vat-based MSL, the material consumption in LBMSL was reduced at least 2 times and the fabrication speed was improved greatly, especially when using a higher viscous material. In addition, the LBMSL showed a potential for multi-material fabrication and continuous fabrication due to this unique fabrication process.
In summary, improvements of fabrication capabilities with the suggested LBMSL process was proved with various experimental results. The suggested process presented many advantages in terms of the layer thickness, the fabrication speed, oxygen inhibition, and highly viscous material fabrication, which can open a route to develop a new additive manufacturing process.