Design, Fabrication and Testing of Magnetic Composite Polymer Actuators Integrated With Microfluidic Devices and Systems

Work presented in this thesis demonstrates methods of combining a newly developed magnetic composite polymer (M-CP) with other commonly used polymer microfluidics materials for the creation of complex all-polymer microfluidic systems. To achieve fully integrated microfluidic systems, new fabrication techniques for integration of M-CP structures are developed. Employing the new M-CP material and the novel fabrication techniques, three types of actuators are developed: cilia, flap, and hybrid M-CP/PDMS actuator. All three actuators employ compatible materials, fabrication techniques, and actuation mechanisms. The performance of each of these actuators is characterized for different applications: cilia-based mixers, flap-based valves, and hybrid M-CP/PDMS actuators for applying extracellular stimulation on cell monolayers. The actuators in each of these applications are driven via relatively small external magnetic fields. The M-CP used in these novel actuators is composed of rare-earth magnetic micro-particles (5–10 micrometer) that are embedded in polydimethylsiloxane. The M-CP is patterned into large force, large stroke actuators. The polymer matrix without magnetic particles is employed as the substrate material for passive parts, facilitating integration of the magnetic and non-magnetic materials. The compatible fabrication techniques include a modified soft-lithography technique for hybrid M-CP/PDMS actuators, screen printing via shadow masks for micro-patterning of thin layers of M-CP, and a novel fabrication technique using poly(ethylene glycol) (PEG) as a sacrificial material for the fabrication of ultra-high aspect-ratio and highly flexible M-CP cilia. Microfluidic devices using these actuators show improved performances in their respective fields when compared with existing designs. Microfluidic mixers with 8 cilia show a reduction in mixing time of up to 63 times over diffusion. Flap-based valve arrays effectively switch flows between two microfluidic channels using an array of two valves, and effectively perform as on-off switches for flow control. A valve with a 2.3 mm flap thickness, actuated under an 80 mT magnetic field, is capable of blocking liquid flow at a flow rate of 1 mL/min for pressures up to 9.65 kPa. Microfluidic platforms for stretching/compressing biological cells based on the hybrid M-CP/PDMS actuators achieve large and bi-directional surface deflections. Actuation can be applied cyclically, under both flow and no-flow conditions.