Thermoplastic microfluidic technologies for portable and disposable bioanalytical and diagnostic platforms
Rahmanian, Omid David
DeVoe, Don L
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Portable and cost-effective medical diagnostic technologies that require minimal external infrastructure for their operation are highly desirable for on-field military operations, defense against acts of bioterrorism, and infectious disease screening in resource-limited environments. Miniaturized Total Analysis Systems (µTAS) have the potential to fulfill this un-met need via low-cost, portable, and disposable point-of-care (POC) diagnostic devices. Inherent advantages of µTAS systems can be utilized to transform diagnostic technologies that currently require significant investment in centralized laboratories and highly trained personnel into automated, integrated, and miniaturized platforms. This dissertation addresses the development of microfabrication techniques and resulting component technologies that are realized in low-cost thermoplastic substrates. A thermoplastic microfabrication technique termed orogenic microfabrication, based on a non-reversible solvent-assisted swelling mechanism, is developed to provide unique capabilities for microscale and nanoscale patterning in rigid thermoplastics with minimal infrastructure. Orogenic microfabrication is compatible with multiple masking techniques including photolithography, chemical surface modification, contact and noncontact spotting, and inkjet deposition techniques, with each masking method offering unique influence on resulting orogenic structures that can be applied to microfluidic and µTAS systems. Direct ink masking is further explored as a low-cost rapid prototyping tool for fabrication of simple microfluidic devices where channel formation and bonding are combined into a single step, resulting in fully enclosed microfluidic channels within 30 minutes. Chemical surface passivation by UV-ozone treatment is utilized in combination with orogenic swelling and thermocompression bonding to develop single-use burst valves with tunable burst pressures. In addition to assisting in on-chip fluid manipulation, the normally closed burst valves enable on-chip reagent packaging and hermetic sealing of bioactive material in lyophilized format, and can be used for delivery of stored reagents for a range of disposable point-of-care assays. On-chip integrated micropumps are also developed, using simple fabrication process compatible with conventional thermoplastic fabrication techniques such as direct micromilling or injection molding. Direct displacement of liquid reagents using screw-assisted pumping can be operated either automatically or manually, with on-demand delivery of liquid reagents in a wide range of flow rates typically used in microfluidic applications. Collectively, the technologies developed in this dissertation may be applied to the future development of simple, disposable, and portable diagnostic devices that have the potential to be operated without off-chip instrumentation. On-chip storage of buffers and reagents in either dry or liquid format, and on-demand delivery of liquid reagents is packaged in a miniaturized, portable, and automated platform that can be operated in resource-constrained settings by practitioners with minimal expertise.