Water-Powered Microfluidic Devices for Diagnostic and Drug Delivery Systems

This dissertation presents the development of water-powered microfluidic devices, including actuators, pumps, pressure-sensitive valves, and flow discretizers, by integrating osmosis, capillarity, microfabrication, and polymer processing technologies at the microscale. By harvesting and coordinating the mechanical actuations driven by chemical potentials and interfacial forces, these water-powered devices can transport flows in pre-programmed manners without consuming any electricity. Because of the significant reduction on electricity, water-powered microfluidic devices provide attractive alternatives for the realization of lower-power diagnostic and implantable drug delivery systems.
The osmotic microactuator, which draws power from water and converts it into mechanical actuation, is made of semipermeable cellulose acetate while sodium chloride (with osmotic pressure of 35.6 MPa) is chosen as the embedded osmotic driving agent. Experimental measurements indicate that constant volumetric displacement rates of 5 to 2500 nl/hr are achieved and desired rates can be synthesized by controlling the dimensions and properties of the semipermeable diaphragm. 
The prototype micropump, which consists of an osmotic microactuator, a reservoir filled with targeted drugs, and a microchannel to control the diffusive flows, functions as a drug delivery system with constant rate and pressure up to 25 MPa to overcome potential blockages. Using oxygen plasma to activate bonding surfaces, the system is assembled and aqueous drugs can be encapsulated in-situ. The prototype has a measured constant delivery rate at 0.2 μl/hr for 10 hours with an accumulated delivery volume of 2 μl. Both delivery rate and volume of the prototype drug delivery system could be altered by changing the design and process parameters for applications of specific disease treatments up to a few years.
To achieve diverse transport profiles, flow discretization mechanisms driven by interfacial forces are integrated. The prototype flow discretizer made of PDMS microfluidic channel with desired hydrophobic/hydrophilic patterns on the surfaces can autonomously digitizes continuous liquid flow into nanoliter segments. With the assistance of geometrical design and hydrophobic/hydrophilic surface patterns, continuous flow has been split into segments with predetermined volume from 10 to 40 nanoliters. As such, this autonomous flow discretizer provides the required metering and manipulation functions for the realization of programmable transport profiles in microfluidic systems.
Publication date: 
May 31, 2003
Publication type: 
Ph.D. Dissertation
Su, Y. (2003). Water-powered Microfluidic Devices for Disgnostic and Drug Delivery Systems. United States: University of California, Berkeley.

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