3D printing technique for microfluidics provides a rapid and cost-effective manufacturing method in one step without considering the complex three-dimensional structures. Because of the layer-by-layer printing process, the microchannel was characterized with rough surface while lacking research on it. Currently, the surface roughness of microchannels is improved mainly by etching (solvent vapor or wet chemical etching), which has two disadvantages: material selectivity and channel openness. In this study, the Polydimethylsiloxane (PDMS) coating method was employed to improve the surface quality of 3D printed microchannels to address the problems mentioned above. The adhesion strength of PDMS on 3D printed substrate was tested. The method proposed in this paper not only reduced the surface roughness of the microchannel effectively (40 fold for circular microchannels) but also reduced the pressure drop of the PDMS coated microchannel by 63.7% and reduced the leakage rate of the 3D printed microvalve by 67%. Moreover, cell viability was tested to validate the feasibility of the method for biomedical and cell analysis applications. Due to the good adhesion properties of PDMS to most materials used in microfluidics, the surface treatment method proposed in this paper can be expanded to other rapid fabrication techniques for low-cost and high-quality microfluidics.

Electrical control toolkits for microlens arrays are available to some extent, but for applications in environments with strong electromagnetic fields, radiation, or deep water, non-electrical actuation and control strategies are more appropriate. An integrated digital microfluidic zoom actuating unit with a logic addressing unit for a built-in membrane lens array, e.g., a flexible bionic compound eye, is developed and studied in this article. A concave–convex membrane fluidic microvalve, which is the component element of the logic gate, actuator, and microlens, is proposed to replace the traditional solenoid valve. The functions of pressure regulation and decoding can be obtained by incorporating microvalves into fluidic networks according to equivalent circuit designs. The zoom actuating unit contains a pressure regulator to adjust the focal length of lenses with three levels, and the logic addressing unit contains a decoder to choose a typical lens from a hexagonal lens array. The microfluidic chip control system is connected flexibly to the actuating part, a membrane lens array. It is shown from a simulation and experimental demonstration that the designed and fabricated system, which is composed of a whole microfluidic zoom unit, addressing technology, and a microlens array, works well. Because these components are constructed in the same fabrication process and operate with the same work media and driving source, the system can be made highly compatible and lightweight for applications such as human-machine interfaces and soft robots.

Passive fluid control has mostly been used for valves, pumps, and mixers in microfluidic systems. The basic principle is to generate localized losses in special channel structures, such as branches, grooves, or spirals. The flow field in two-dimensional space can be easily calculated using the typical Stokes formula, but it is challenging in three-dimensional space. Moreover, the flow field with periodic variable cross-sections channeled of polyhedral units has been neglected in this research field due to previous limitations in manufacturing technology. With the continuous progress of 3D printing technology, the field of microfluidic devices ushered in a new era of manufacturing three-dimensional irregular channels. In this study, we present finite analysis results for a periodic nodular-like channel. The experiments involve variations in the Reynold number (Re), periodic frequency, and comparative analyses with conventional structures. The findings indicate that this variable 3D cross-section structure can readily achieve performance comparable to other passive fluid control methods in valve applications. A 3D model of the periodic tetrahedron channel was fabricated using 3D printing to validate these conclusions. This research has the potential to significantly enhance the performance of passive fluid control units that have long been constrained by manufacturing dimensions.

The development of electronic skin, soft robots, and smart wearables has significantly driven advances in flexible pressure sensing technology. However, traditional multilayer solid-structure flexible pressure sensors encounter challenges at temperatures between 100 °C and 150 °C due to high-temperature modal distortion. Changes in the conductivity of the sensor’s conductive components interfere with accurate pressure measurement. In this research, a flexible pressure sensor with a convective liquid metal sensitive layer is proposed. The sensor uses a cyclic self-cooling mechanism to lower the temperature of its conductive components, reducing the impact of external high temperatures on the pressure measurement accuracy. At a 2.8 W thermal load, the flexible sensor, with liquid metal circulating at 2.0 mL/min, exhibits a sensitivity of 0.11 kPa⁻¹ within the pressure range from 0 to 12.5 kPa, and its maximum measurable pressure is 30 kPa. In addition, the resistance of the sensor is 18.5 mΩ less than that of a stationary liquid metal sensor, representing a 38.1% reduction. The sensor proposed in this research introduces a novel strategy for pressure measurement in high-temperature applications, extending the application scope to aircraft, special robots, and hydraulic oil circuits.

To address the issue of significant torque ripple in axial flux permanent magnet stepper motors with multi-air-gap coupling structures, a torque ripple suppression method based on the coordinated adjustment of rotor misalignment and structural parameters is proposed. Focusing on a dual-stator, triple-rotor, three-phase axial flux permanent magnet stepper motor, a three-dimensional finite-element model is established to analyze the phase superposition relationship of torque components in multiple working air gaps and their impact on the overall output torque ripple. First, the misalignment angle between adjacent rotors is utilized as the primary optimization variable to study the peak-shifting superposition effect of torque components under different misalignment angles. Subsequently, parameter scanning and stepwise optimization are conducted for the air gap distribution, the inner-to-outer diameter ratio of the stator core, the radial width ratio of the permanent magnet to the stator teeth, and the pole arc coefficient. The results demonstrate that by utilizing the phase offset effect of torque in multiple air gaps, combined with the modification of key structural parameters, the torque smoothness of the dual-stator, triple-rotor axial flux permanent magnet stepper motor can be significantly improved; the torque ripple rate is reduced from 62.67% to 19.32%. This study provides a reference for the low-vibration and smooth operation design of this type of motor.