Texture-structure-based liquid metal filling for blind-end microchannels and its application on multi-layer chips

Abstract

This research work reports a novel method to achieve fast liquid metal (LM) injection in blind-end microchannels which is especially suitable for multi-layer microfluidic chips. This method is based on a texture-like surface bonding technology. The texture-like surface is fabricated on a polydimethylsiloxane (PDMS) slab with standard soft-lithography technology and bonded with another PDMS slab with microelectrode patterns on it. When injected with LM, the texture-like structure can prevent the LM from entering but allows the air inside to be released during the injection to achieve perfect blind-end complex LM electrodes. The experimental results show that it can achieve fast and perfect LM injection in the blind-end pattern and can also prevent the large area of the flat chamber from collapsing during bonding. We also parametrically studied the texture structure's size for bonding strength between the texture structure and the blank PDMS surface. In addition, we integrate three layers of blind-end complex liquid metal patterns into one multi-layer chip using this technology and later use this structure to realize series connection of two LM-based electroosmotic micropumps (EOP). Compared with the conventional LM-based EOP, the structure of the EOP chip was greatly simplified and resulted in a higher level of integration.

Fig. 1. (a) Texture structure and its chip fabrication process. (b) Schematic representation of two texture structures under the microscope. (Long rectangles and small squares, respectively).

Fig. 2. (a) Comparison of injections with a texture structure and blank PDMS using snowflake-like branching pattern. (b) Comparison of injections with a texture structure and blank PDMS using flat patterns with large aspect ratios. (c) Local magnification under the microscope in Fig. 2(b) “textured PDMS”. The black scale is 2 mm, the pink scale is 500 μm and the white scale is 100 μm.

Fig. 3. Complex blind-end microstructure injection using texture structures. (a) A checkerboard grid structure. (b) Spirals passing through a circular array. (c) Flower patterns in nature. (d) Horse pattern in the Chinese zodiac. (e) Dragon pattern in the Chinese zodiac. (f) Snake pattern in the Chinese zodiac. The black scale is 2 mm and the pink scale is 200 μm.

Fig. 4. (a) Illustration of the concept of unit small square area and bondable area to total area. (b) Results of a parametric study on the effect of texture structure size on the bonding situation. The scale bar is 20 μm.

Fig. 5. (a) Exploded view of the three layers structures. (b) Multilayer chip with blind-end infusion using texture structures. (c) Side view of the chip. (d) Schematic of the three layers of the chip. The black scale is 5 mm.

Fig. 6. Schematic of the EOP (a) schematic of stratification of the EOP. (b) Combination of the EOP. (c) Actual schematic of EOP after injection. The black scale is 5 mm.

Fig. 7. (a) Sequential diagram of the position of fluorescent particles in the flow channel at different times. (b) The flow rate of EOP at different voltages. The white scale is 50 μm.