In this study, nanopatterned Nafion microelectrode arrays for in vitro cardiac electrophysiology are reported. With the aim of defining sophisticated Nafion nanostructures with highly ionic conductivity, fabrication parameters such as Nafion concentration and curing temperature are optimized. By increasing curing temperature and Nafion concentration, the replication fidelity of Nafion nanopatterns when copied from a polydimethylsiloxane master mold are controlled. It is also found that cross‐sectional morphology and ion current density of nanopatterned Nafion strongly depends on the fabrication parameters. To investigate this dependency, current‐voltage analysis is conducted using organic electrochemical transistors overlaid with patterned Nafion substrates. Nanopatterned Nafion is found to allow higher ion current densities than unpatterned surfaces. Furthermore, higher curing temperatures are found to render Nafion layers with higher ion/electrical transfer properties. To optimize nanopattern dimensions, electrical current flows, and film uniformity, a final configuration consisting of 5% nanopatterned Nafion cured at 65 °C is chosen. Microelectrode arrays (MEAs) are then covered with optimized Nafion nanopatterns and used for electrophysiological analysis of two types of induced pluripotent stem cell‐derived cardiomyocytes (iPSCs‐CMs). These data highlight the suitability of nanopatterned Nafion, combined with MEAs, for enhancing the cellular environment of iPSC‐CMs for use in electrophysiological analysis in vitro.
The positive-displacement micropumps push out fluid into one direction by expanding and decreasing a cavity volume with various actuation mechanisms. However, the volume change of the cavity is repeated periodically to supply the fluid, which causes a periodic flow rate change, resulting in a pulse flow. Such pulsations are not suitable for use in specific applications that require stable fluid delivery, such as microsensors [12][13][14] and droplet microfluidic devices. [15,16] For example, in the application of mechanosensors that utilize bending displacements to measure the adsorption of biomolecules on cantilever surface, pulse flow can vibrate the cantilever, generating noise in the output signal. [17,18] In contrast to the positive-displacement micropumps, nonmechanical micropumps that generate pulseless flow have also been developed by using thermo-pneumatic actuation, [19,20] chemical reactions, [21] and capillary force. [22][23][24] However, there are limitations in the thermo-pneumatic actuation due to heat damage to biomaterials, while micropumps using chemical reactions or capillary force have difficulties to actively control the flow rate.As an alternative approach to supply fluids, commercially available syringe pumps are widely used in microfluidic devices. Bulky syringe pumps have disadvantages for use with microfluidic devices due to 1) the large dead volume associated with the large bore of the syringe and its connecting tubes, and 2) difficulty in inserting the whole system into an incubator. Although miniaturizing the conventional bulky syringe is in a growing demand for microfluidic devices, it is challenging due to the difficulty in fabricating and assembling complex 3D microcomponents as well as the scaling law of the mechanical sliding parts in microscale. Since the stick-slip phenomenon occurs in the micro-sized piston-cylinder, it is crucial to avoid any mechanical sliding parts to realize on-chip microsyringe pumps. Also, it is necessary to develop on-chip power sources having not only high output power density but also no mechanical sliding parts.Considering these demands, we focus on utilizing an electroconjugate fluid (ECF) for the development of on-chip microsyringe pumps. The ECF, a functional fluid, can generate an active flow (ECF jet) between a pair of electrodes when a high DC voltage is applied to the electrodes in the ECF. The ECFs are
Powered microvalves are necessary for a variety of microfluidic applications such as on-demand droplet generators and droplet capture systems. Currently, a central challenge for these microvalve systems is the miniaturization of bulky power sources and control components, for example, air compressors, hydraulic pumps, solenoid valves, and regulators. In this paper, we propose a polydimethylsiloxane (PDMS)-based microvalve integrated with an on-chip power source, an electro-conjugate fluid (ECF) micropump. The assembled PDMS membrane of the device deforms and then blockades the port in the microchannel via fluidic pressure generated by the ECF micropump with the application of high DC voltage. Following finite element method simulations, we utilized 15 electrode pairs for the on-chip ECF micropump. By combining a MEMS process and the bonding process, we successfully realized the designed device and proceeded to evaluation of its performance characteristics. First, we evaluated the performance of the ECF micropump, which showed a maximum output pressure and a flow rate of 49.7 kPa, 87.3 mm3 s−1, respectively, at an applied voltage of 2.0 kV. Second, we found that the minimum sealing pressure of the microvalve was 10 kPa without any load condition. Third, we investigated the cracking pressures, which were 20 kPa and 50 kPa at the applied voltages of 1.5 kV and 2.0 kV to the ECF micropump, respectively. This study experimentally demonstrated the feasibility of the proposed microvalve device and its potential to be integrated into other microfluidic devices for precision control of liquid volumes.
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