Improving the Manufacturability of Active Microfluidic Devices using Stereolithography (SL)

Thesis (Master's)--University of Washington, 2016-06Microfluidic devices are instrumental in a variety of scientific and biomedical applications. These devices have revolutionized scientific research in areas ranging from cancer diagnostics to drug discovery and neuroscience. Microfluidic devices are broadly classified as active and passive devices. Passive devices constitute micro flow channels, flow splitters, reaction chambers, gradient generators and mixers. Active devices are essentially microfluidic valves and pumps which allow microfluidic automation. All of the microfluidic devices have traditionally been manufactured using a manufacturing process called soft lithography with a transparent, elastomeric and biocompatible material called poly-dimethyl siloxane (PDMS). Soft lithography is based on PDMS micromolding and it is extremely labor intensive, expensive, and cannot produce complex devices with high yield. That is why many researchers have recently published studies utilizing stereolithography (SL) to manufacture passive microfluidic devices. SL simplifies the complexity of soft lithography and improves the manufacturability of microfluidic devices. However, to date SL has lacked the valving functionality of soft lithography and thus, active microfluidic devices are not shown to be produced using SL. Thus, this research focuses on overcoming the current limitations in manufacturing active microfluidic devices using SL. PDMS like elastomeric resins are essential for active microfluidic device manufacturing using SL. The first part of this research explores, characterizes and optimizes the current commercially available elastomeric SL resin. The optical analysis of the SL microfluidic device manufacturing process is understood using a mathematical model. The limitations of the existing resins are identified. A definite need to synthesize a photocurable PDMS resin for SL is established. The second part of the research develops a chemistry to synthesize photocurable PDMS resin for SL. A highly customized projection stereolithography system using open source electronics is constructed to overcome the limitations of commercial systems. Using extensive experimentation, a protocol to manufacture transparent and elastomeric parts using the synthesized PDMS SL resin is developed. The material properties of these parts are tested. It is proved that the parts made with photocurable PDMS resin using stereolithography are equally transparent as that of parts made using soft lithography and both the parts have Young’s modulus in the same range. Unavailability of PDMS like resin was a major roadblock impeding the use of SL for active microfluidic device manufacturing. This research overcomes this roadblock by synthesizing a photocurable PDMS resin for stereolithography

BaroFuse, a novel pressure-driven, adjustable-throughput perfusion system for tissue maintenance and assessment

Objectives: Microfluidic perfusion systems are used for assessing cell and tissue function while assuring cellular viability. Low perfusate flow rates, desired both for conserving reagents and for extending the number of channels and duration of experiments, conventionally depend on peristaltic pumps to maintain flow yet such pumps are unwieldy and scale poorly for high-throughput applications requiring 16 or more channels. The goal of the study was to develop a scalable multichannel microfluidics system capable of maintaining and assessing kinetic responses of small amounts of tissue to drugs or changes in test conditions. Methods: Here we describe the BaroFuse, a novel, multichannel microfluidics device fabricated using 3D-printing technology that uses gas pressure to drive large numbers of parallel perfusion experiments. The system is versatile with respect to endpoints due to the translucence of the walls of the perifusion chambers, enabling optical methods for interrogating the tissue status. The system was validated by the incorporation of an oxygen detection system that enabled continuous measurement of oxygen consumption rate (OCR). Results: Stable and low flow rates (1–20 μL/min/channel) were finely controlled by a single pressure regulator (0.5–2 psi). Control of flow in 0.2 μL/min increments was achieved. Low flow rates allowed for changes in OCR in response to glucose to be well resolved with very small numbers of islets (1–10 islets/channel). Effects of acetaminophen on OCR by precision-cut liver slices of were dose dependent and similar to previously published values that used more tissue and peristaltic-pump driven flow. Conclusions: The very low flow rates and simplicity of design and operation of the BaroFuse device allow for the efficient generation of large number of kinetic profiles in OCR and other endpoints lasting from hours to days. The use of flow enhances the ability to make measurements on primary tissue where some elements of native three-dimensional structure are preserved. We offer the BaroFuse as a powerful tool for physiological studies and for pharmaceutical assessment of drug effects as well as personalized medicine