This paper describes the design, simulation, fabrication and characterization of a polymeric microgripper with integrated thermal actuators. The microgripper was fabricated by a polymeric surface micromachining process, which utilizes SU-8 as the functional material and silicon as the sacrificial material. A thin double layer of titanium and platinum was evaporated on the gripper structure and served as the electrically conducting and heat dissipating material. The polymeric microgripper offers the advantage of large displacement and gentle handling forces, which may be ideal for handling bioparticles such as cells. Furthermore, an operating temperature below 100 • C allows the handling of living cells and tissues. The unique characteristic that SU-8 does not soften at elevated temperature allows the use of thermal actuation for the microgripper. To the best knowledge of the authors, the presented device is the first polymeric microgripper with integrated actuators. Each thermal actuator consists of two thin arms and one thick arm. Heat is generated by electrical current passing through the thin titanium/platinum on top of the 100 µm thick SU-8 structure. Based on an electrical/thermal/structural coupled simulation, the gripper can operate in both normally closed mode and normally open mode. The different electrical configurations of the gripper arms allow this flexibility. Results of the simulation and the measurement are also presented in this paper.

This paper describes the design, simulation, fabrication and characterization of micro checkvalves suitable for integration into polymeric microfluidic devices such as micropumps or test cartridges for biomedical analysis. The valves are fabricated by a polymeric surface micromachining process, which utilizes SU-8 as the functional material. The devices are assembled with the lamination technique. A micro checkvalve consists of 3 layers: an inlet layer, a valve layer and an outlet layer. The valve is a disc of 1-mm diameter. The disc is suspended on folded beams, which act as valve springs. Both valve disc and springs are fabricated in a 100-µm SU-8 layer. The valves prove a clear flow rectification function. Relatively low pressure is required for opening the valve. The valves were tested and characterized with water. One of the valves are successfully integrated into a polymeric micropump. These valves prove the facile and reliable lamination technology for fabrication complex polymeric microfluidic devices for biomedical analysis.

This paper presents the fabrication and characterization of a silicon-based optofluidic device for switching and splitting of a core stream with fluorescent dyes. The dye laser was created in the core, which is excited by a blue wavelength. The streams in the microchannel also form a liquid-core/liquid-cladding wave guiding system. The core is a glycerol solution, while the cladding is formed by two sheath streams of deionized water. The higher refractive index of the glycerol solution keeps the laser light inside the liquid core through total internal reflection. Keeping the flow rate of the core stream constant, splitting and switching was realized by controlling the flow rate ratio between the two sheath streams. The width of the core was controlled by hydrodynamic spreading or by the ratio between the core stream and the sheath streams. The fastest switching speed was about 300 ms, which is limited only by the response time of the pumping system. The wave guiding capability of this system was tested by coupling laser signals in and out of the fluidic system and measuring their intensity. The concepts and devices presented in this paper are suitable for applications with hydrodynamic focusing, sorting and optical detection for feed-back control.

This paper reports the improvement of rectification effects in diffuser/nozzle structures with viscoelastic fluids. Since rectification in a diffuser/nozzle structure with Newtonian fluids is caused by inertial effects, micropumps based on this concept require a relatively high Reynolds numbers and high pumping frequencies. In applications with relatively low Reynolds numbers, anisotropic behavior can be achieved with viscoelastic effects. In our investigations, a solution of dilute polyethylene oxide was used as the viscoelastic fluid. A microfluidic device was fabricated in silicon using deep reactive ion etching. The microfluidic device consists of access ports for pressure measurement, and a series of ten diffuser/nozzle structures. Measurements were carried out for diffuser/nozzle structures with opening angles ranging from 15°to 60°. Flow visualization, pressure drop and diodicity of de-ionized water and the viscoelastic fluid were compared and discussed. The improvement of diodicity promises a simple pumping concept at low Reynolds numbers for lab-on-a-chip applications.

One of the current problems of micro-optofluidics is the choice of a suitable liquid with a high refractive index (RI). We report the use of a low-RI liquid in a biconcave liquid-core liquid-cladding lens for focusing light. For the characterization of the lens, a telescope system was constructed from polydimethylsiloxane lenses to collimate and expand a light beam emitted from an optical fiber. The tunable optofluidic biconcave lens focuses the parallel beam. Fluorescent dye diluted in an index-matching liquid was used for the visualization of the light rays in a beam-tracing chamber. The focused beam is tuned by adjusting the flow rate ratio between core and cladding streams.