Meniscus-guided 3D printing with material supplied by the intrinsic capillary replenishment flow: Printing success rate, printed structure size adjustment, and microscale functional device fabrication

Meniscus-guided 3D printing is a microscale ink-based 3D printing technique, which features ease of operation and can print micro/nano functional devices of multiple types of materials at a low cost. However, the customized microscale functional device fabrication challenge remains, because the critical printing conditions for successful printing are complex. Whether the printed device efficiency depends on printing conditions is unclear. Our study shows that there exist clogging and terminated critical pulling speeds in meniscus-guided 3D printing with material supplied by the evaporation-induced capillary replenishment flow, where only the pulling speed is within this range 3D printing could be successfully implemented. The printable ink viscosity can be higher than the previously reported if the pulling speed criterion is satisfied. The critical pulling speeds and the interval between them decrease with the micropipette diameter or ambient humidity. A more comprehensive formulation than the literature reported ones describing the dependence of the 3D-printed micropillar diameter on the micropipette pulling velocity and diameter is derived, which agrees well with the experimentally printed micropillar diameters under different conditions and indicates that 3D-printed micropillar diameter adjustment is governed by the meniscus shape and its evaporation rate. Based on the improved 3D-printed structure adjustment technology, the 3D microbridge humidity sensors and 3D micropillar capacitor electrodes can be fabricated with high repeatability and efficiency. The 3D-printed microscale devices’ efficiencies in this study are superior to most previously reported microscale devices, with their efficiencies adjustable by the relative humidity during the printing process. Furthermore, the 3D-printed humidity sensor is demonstrated to be used as a contactless finger sensor, which shows potential application in preventing disease cross-infection in public facilities. Improvement of the meniscus-guided 3D printing technology on printing success and printed structure size adjustment in this study paves the way for precisely fabricating efficiency-adjustable 3D microscale functional devices.