Advances in Additive Manufacturing and Microfabrication

Abstract

Additive manufacturing (AM), aided by enhanced computing, unprecedented connectivity, and monumental advances in material science, has been hailed as the "fourth industrial revolution". Despite this prestigious accolade, AM-manufactured products still only represent a tiny fraction of total production. Uncompetitive fabrication speeds and directionally-dependent material properties have historically plagued AM - hindering its adoption to only a few limited applications in niche markets. Continuous stereolithographic (SL) AM offers significant improvements in fabrication speed while delivering parts with uniform material properties. This work focuses on the development of a dual-wavelength initiation and inhibition system for continuous AM. Using a visible light initiator and novel UV-active photo-inhibitor molecule we are able to generate photo-inhibited dead zones and enable continuous AM. Dead zones created in this way are large, easy-to-control and enable the fastest reported vertical print speeds for continuous SL-AM. Dual-wavelength AM methods may, through increases in fabrication rates, make AM a viable alternative manufacturing technology. A challenge in continuous AM methods is a trade-off that exists between vertical 'resolution' and speed. In order to more accurately reproduce parts, vertical resolution is typically improved (at the expense of print speed) by addition of absorbing dyes. We develop a dose-based model and correction algorithm to modify exposures in continuous AM. The algorithm uses physical properties of the system and chemical properties of the resin to calculate the cumulative dose and, through a series of constraints, optimizes the projection images used during printing to improve the resolution of the printed part. This method is verified experimentally in a number of test models and actual parts and found to achieve up to 85% reduction in unwanted gelation while maintaining high print speeds up to 750 mm/hr. Multilayer microfluidic devices are useful in a wide range of applications. Fabrication of these devices, however, is often a tedious, time-consuming and expensive process. We develop a protocol for multilayer microfluidic device fabrication using our dual-wavelength initiation and inhibition system. Using grayscale patterning of the initiating light we are able to pattern microfluidic channels in a two to three short (< 30 s) exposures. This protocol is demonstrated in multilayer microfluidic device fabrication with channels of sub-millimeter height in less than a minute compared with hours or days previous methods require. Fabrication in this way may lower the barrier-to-entry of microfluidic technology for research and commercial applications. Finally we investigate a technique for fabricating variable height microfluidic channels. The fabrication technique uses controlled non-uniform exposure to an etchant solution to create channels of arbitrary height that vary from the inlet to the outlet. Channels that vary in height are shown to effectively and reproducibly separate particles by size and red blood cells by their deformability. The macroscopic visualization of microparticle separation in these devices in addition to their ease of use, simple fabrication, low cost, and small size suggest the viability of such a device in point-of-care diagnosis with multiplexed microparticle assays.