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Bionic electronic skin with human sensory capabilities has attracted extensive research interest, which has been applied in the fields of medical health diagnosis, wearable electronics, human–computer interaction, and bionic prosthetics. Electronic skin tactile pressure sensing required high sensitivity, good resolution and fast response for sensing different pressure stimuli. In particular, there were still great challenges in the detection of wide pressure and the preparation of sensitive unit microstructures. Here, the direct-write printing of Weissenberg principle to fabricate GNPs/MWCNT filled conductive composite flexible pressure sensors on PDMS substrates was proposed. The effects of platform moving speed, microneedle rotation speed and the number of direct-write times on the line width of the pressure sensitive structure were investigated based on orthogonal experiments, and the optimal direct-write printing parameters were obtained. The performance of the S-shaped polyline pressure sensor was tested, in which the sensitivity could reached 0.164 kPa−1, and the response/recovery time was 100 ms and 100 ms respectively. The capture cases of objects of different quality and objects with flat/curved surfaces were successively demonstrated to exhibit its excellent sensitivity, stability and fast response performance. This work may paved the road for future integration of high-performance electronic skin in smart robotics and prosthetic solutions.

Micro-ultrasonic machining (MUSM) is an effective way of processing microstructures made from hard and brittle materials, although controlling the fluctuation of the machining force during processing is difficult. To control the quality of micro-holes fabricated in hard and brittle materials, MUSM with force control (MUSMFC) is used to study the edge chipping rate (ECR) and material removal rate (MRR) during micro-hole fabrication. The process is controlled using a force sensor and a processing control strategy. Various experiments are designed to assess the processing efficacy. Comparative experiments indicate that the ECR with MUSMFC is superior to that with traditional MUSM. Single-factor experiments show that the ultrasonic power and the fluctuation of the machining force exert a significant influence on the ECR. The influence of the spindle speed on the ECR is small. Orthogonal experiments show that the fluctuations of the machining force and ultrasonic power have large impacts on the MRR. The spindle speed has a significant impact on the MRR as well, whereas the mass fraction has little effect. The best combination of ECR and MRR is obtained using a spindle speed of 500 rpm, a machining-force fluctuation of 0.1 N, an ultrasonic power of 50 W, and a mass fraction of 10%.

Traditional micromilling leaves burrs and has a high surface roughness in the workpiece, which compromises the microstructural machining quality. Electrophoresis-assisted ultrasonic micromilling machining (EUMM) is proposed to solve this problem. An electrophoresis assisted electric field is applied to attract abrasive particles into the machining gap. Combined with the ultrasonic vibrations of the workpiece, the impact and grinding effect of these abrasive particles in the machining gap removes burrs that are generated during machining and reduces the surface roughness of the microstructure. Micro channels were generated for this study to verify the proposed method. The experimental results show that the EUMM significantly reduces burr formation during microchannel milling. The EUMM also decreases the surface roughness (Ra); the bottom roughness using the EUMM (0.33 µm) is lower than that with either the ultrasonic micromilling (UMM) or traditional micromilling. The EUMM also improves the sidewall roughness since the grinding and particle impacts significantly smooth the sidewalls. The particles during EUMM ensure a low surface roughness of 0.34 µm for the vertical sidewalls. Furthermore, the EUMM has a lesser effect on the width of the micro channels; as the spindle speed increases, the microchannel width only increases from 486 to 498 µm.

Electrophoresis-assisted micro-ultrasonic machining (EPAMUSM) is an effective method for solving the problem of using traditional micro-ultrasonic machining (MUSM) to fabricate micro-holes in materials that are hard and brittle, namely the low utilization ratio of abrasive particles. EPAMUSM uses an electric field to attract the abrasive particles to the processing area during processing, which is useful for improving both the utilization ratio of abrasive particles and the processing quality. Numerical simulations of the concentration distributions of abrasive particles in MUSM and EPAMUSM show that the abrasive concentration on the tool surface is much higher in EPAMUSM. The concentration increases rapidly from 1 mol/m3 to 4.68 mol/m3 after 10 s in EPAMUSM. Comparative experiments show that EPAMUSM has advantages over MUSM under the same processing conditions: the EPAMUSM edge chipping rate (0.03) is much less than the MUSM one (0.22) and the EPAMUSM material removal rate (1.916 × 10−4 mm3/min) is marginally better than the MUSM one (1.718 × 10−4 mm3/min). Single-factor experiments are used to study how varying certain parameters (namely DC voltage, ultrasonic power, and spindle speed) affects EPAMUSM manufacturing quality and efficiency. Finally, the processing parameters are optimized by means of response-surface experiments, and the optimum EPAMUSM processing parameters are determined (namely an applied voltage of 7.5 V, an ultrasonic power of 22.5 W, a spindle speed of 300 rpm, and a mass fraction of 10%).

Conventional 3D printing methods often require supporting structures to maintain the structure of the suspended parts in the manufacture of metamaterials, micronano arrays, micro-channels. The remaining uncured resin in the microstructure and the removal of the sacrificial layer material by post-processing are a key challenge for structural molding. Therefore, we propose a free-form-based direct writing 3D printing technology for manufacturing flexible microstructures without self-supporting materials. We proved that the 3D printed microstructure can withstand the bending moment it generates to prevent the collapse of the flexible microstructure. This method provides a new way for the manufacture of flexible microstructure devices such as soft robots, flexible sensing, biological tissues, micro-nano fluidics, and metamaterials.

Tactile sensors with high flexibility have attracted great interest because of their huge potential in various applications including smart robots, smart prostheses, human-machine interfaces, and biological monitoring electronic devices. However, it remains a critical challenge to develop tactile sensors with both high sensitivity and flexibility. In this work, a flexible 8 × 8 array pressure sensors with GNPs/MWCNT filled conductive composite material on PDMS substrates was proposed using direct-write printing. The printing technology based on the Weissenberg effect had the advantages of rapid supply of fluid and avoiding needle clogging in the printing process, which was suitable for large-area manufacturing of sensor sensitive units. The sensitivity of PDMS-based flexible array pressure sensors in the pressure range of 0–25 kPa and 25–75 kPa reached ∼5.09 MPa−1 and ∼0.0209 kPa−1, respectively. Response/recovery time reached ∼150 ms and ∼200 ms, respectively. When 1000 cycles were performed in the 0–75 kPa pressure range, the PDMS substrate flexible array pressure sensor had high stability and repeatability. These superior properties are indicative of their great potential in applications such as intelligent robotics, artificial palpation, prosthetics, and wearable devices.