UBC Theses and Dissertations
A microsphere based microfluidic check valve Ou, Kevin
Biomedical applications of Micro-Electro-Mechanical System (MEMS) technology have sprung growth in the field of microfluidic systems and have been attracting much attention from scientific researchers and industry. Implantable drug delivery devices can deliver localized dosage which can reduce the side effects of medication. Such devices can maintain therapeutic concentrations of the drug over extended periods by providing small doses minimizing the risk of systemic toxicity. Recently, ocular drug delivery devices with micropumps using check valves have been demonstrated. The use of external magnetic actuation in a MEMS-based drug delivery device has been verified in reciprocating diaphragm micropumps. However, the magnetic diaphragm generates low pressures resulting in low flow rates (Re<1). This work investigates the use of polystyrene (PS) microspheres as resistive elements in a fluidic channel to create a check valve. The check valve takes advantage of the low profile microsphere and flow channel to rectify flow in low pressure and low flow applications. This makes the check valve ideal for thin planar reciprocating micropumps, which can be used as ocular drug delivery devices, with the conjunctival cul-de-sac being a possible site of implantation. The microspheres form a porous media which acts as variable fluid resistors based on the direction of flow, and also increases tortuosity in the check valve limiting diffusion from the device. Three check valve designs were characterized based on their flow rate and diodicity (ratio of flow in the forward and reverse direction). Pump performance, based on the check valves integrated in series with a deflecting diaphragm actuator, was investigated. Finally, a proof-of-concept diffusion study was conducted using docetaxel (DTX), a low aqueous solubility drug used to treat late stage proliferative retinopathy, as the sample drug to demonstrate the microsphere check valve’s ability to limit diffusion from the micropump.
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