In this work, a glucose fuel cell was fabricated using microfabrication processes assigned for microelectromechanical systems. The fuel cell was equipped with a microchannel to flow an aqueous solution of glucose. The cell was fabricated on a flexible polyimide substrate, and its porous carbon-coated aluminum (Al) electrodes of 2.8 mm in width and 11 mm in length were formed using photolithography and screen printing techniques. Porous carbon was deposited by screen printing of carbon black ink on the Al electrode surfaces in order to increase the effective electrode surface area and to absorb more enzymes on the electrode surfaces. The microchannel with a depth of 200 μm was fabricated using a hot embossing technique. A maximum power of 0.45 μW at 0.5 V that corresponds to a power density of 1.45 μW/cm 2 was realized by introducing a 200 mM concentrated glucose solution at room temperature.

In this study, we fabricated a flexible, stretchable glucose-biofuel cell with silver nanowires (AgNWs) on a dimethylpolysiloxane substrate. The biofuel cell investigated consists of a porous carbon anode (area of 30 mm 2 ) modified by glucose oxidase and ferrocene, and a cathode (area of 30 mm 2 ) modified by bilirubin oxidase. The anode and the cathode were connected with AgNWs. The maximum power of 0.29 μW at 180 mV, which corresponds to a power density of 0.98 μW/cm 2 , is realized by immersing the biofuel cell in a phosphate buffer solution with a glucose concentration of 100 mM, at room temperature.

We used microelectromechanical system techniques to fabricate a miniature ascorbic acid fuel cell (AAFC) equipped with a microchannel for the circulation of ascorbic acid solution (AAS). The fuel cell was fabricated on a flexible polyimide substrate, and a porous carbon-coated aluminum (Al) anode with the dimensions of 2.8 ×1 mm 2 and a porous carbon-coated Al cathode with the dimension of 2.8 ×10 mm 2 were fabricated using photolithography and screen-printing techniques. The porous carbon was deposited by screen-printing carbon-black ink onto the Al electrode surfaces in order to increase the effective electrode surface areas and to absorb more enzymes (bilirubin oxidase) on the cathode surface. No enzyme was deposited on the carbon coated anode surface. The microchannel with a dimension of 3 ×11× 0.2 mm 3 was fabricated using a hot-embossing technique. The maximum power of 0.60 µW at 0.58 V, with a corresponding power density of 1.96 µW/cm 2 , was realized by introducing a 200 mM concentrated AA solution at the flow rate of 30 ml/min at room temperature. No degradation of the anode and cathode was observed up to the radius of curvature of 7.5 mm, which suggests the flexibility of the AAFC.

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The transfer printing of Au micropatterns onto a polyimide (PI) film was investigated, and the optimum transfer conditions were obtained. In this study, micropatterns with widths of 25 μm and 75 μm were successfully transferred onto a PI film at a molding temperature of 150 °C for 5 s under a molding pressure of 2.5 MPa. This technique is expected to provide simplified processes in fabricating wiring patterns in microelectromechanical systems.

Improved fabrication processes of a micro electroosmotic flow pump using hot embossing are described. The microchannels in the micropump were fabricated by hot embossing on a polymethylmethacrylate (PMMA) substrate. A silicon micromachined mold was pressed into the PMMA substrate at a temperature of 145 °C to form microchannel patterns on the substrate. The depth and width of the microchannels were 50 μm and 100 μm, respectively. Aluminum electrodes were deposited using thermal vacuum deposition. A UV ozone treatment was performed to improve adhesion between the PMMA substrate and a PMMA capping layer. This UV ozone treatment enhanced adhesion and resulted in the reduction of the adhesion temperature as low as 70 °C, and nearly no deformation of the microchannels was observed. As a result, the electroosmotic flow pump exhibited the flow rate of 0.5 μl/min when a voltage of 50 V was given between the electrodes separated 8 mm each other.

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