Hui You

Embedded 3D printing of hydrophilic hydrogels in aqueous support baths often suffers from filament deformation, positional deviation, and diffusion before complete cross-linking, while practical parameter-selection guidelines for specific material systems remain limited. In this work, an integrated engineering evaluation method was developed to characterize filament formation and early-stage evolution during embedded printing of gelatin/sodium alginate inks in Carbomer support baths. Filament quality was assessed using cross-sectional geometry, contour irregularity, deposition position, and early-stage diffusion ratio. The effects of printing kinematics and material rheology are systematically examined to establish a practical process window for this hydrophilic ink–bath system. The results show that the speed ratio between substrate and ink is a primary factor controlling filament geometry and deposition position, and a ratio close to 1 yields the most balanced cross-sectional morphology without position shift from the printed nozzle. Ink with high viscosity maintains contour irregularity within a narrow range of 0.005–0.009 and suppresses early diffusion, whereas a support bath with high viscosity and ink with high viscosity combination further slows diffusional evolution by about 70%. Based on the identified process window, several three-dimensional hydrogel structures were fabricated successfully. The proposed workflow provides a practical route for process evaluation and parameter selection in hydrophilic embedded printing, especially for continuous filament and tubular structures, and offers engineering guidance for bio-soft material fabrication in applications.

In micro-extrusion and direct ink writing, the nozzle outlet diameter is often used to estimate the deposited line width or free-filament diameter. However, highly loaded conductive silver pastes may exhibit pronounced extrusion swell after leaving the nozzle, resulting in a filament diameter larger than the nozzle inner diameter. To quantify this deviation, this study proposes a single-parameter semi-theoretical correction model based on radial force balance at the nozzle exit, integrating Herschel–Bulkley yield stress–shear-thinning rheology with a finite-deformation description. The exit radial stress is derived from pressure-driven circular tube flow, while the post-exit radial expansion is balanced against atmospheric constraint. A comprehensive correction force constant, C, is introduced to account for wall-induced energy dissipation, particle-structure rearrangement, residual elastic recovery, and model simplifications. After calibration using a transition-swelling nozzle, C was determined as 1.03 × 10⁻² N. The model was applied to six nozzle diameters and four nozzle length–pressure conditions. For Nozzles 1–4 with significant swelling, the mean absolute percentage error was 5.31%, while the overall error for all six nozzles was 11.84%, mainly due to overestimation for the nearly non-swelling Nozzle 6. For varying nozzle lengths, the error was 5.20%, and both experimental and predicted swell ratios decreased with increasing effective nozzle length. The model provides a semi-theoretical tool for estimating free-filament dimensions and analyzing nozzle-length effects, primarily under pronounced-swell conditions. Its predictive capability becomes limited as the swell ratio approaches unity, where additional corrections for wall slip, relaxation, and the zero-swell boundary are required.

High-density interconnection (HDI) printed circuit boards require precise defect control during copper microvia electrodeposition, where levelers play a decisive role in defining the filling window and deposit quality. This work investigates 2-amino-5-mercapto-1,3,4-thiadiazole (G1) as a leveler and compares it with the structurally analogous 2,5-diamino-1,3,4-thiadiazole (G2) to clarify the relationship between molecular structure, interfacial adsorption regulation, and microvia superfilling. Microvia plating experiments, electrochemical characterization, density functional theory (DFT), and molecular dynamics (MD) simulations were combined to reveal the distinct behaviors of G1 and G2. Plating results show that only G1 enables bottom-up superfilling of blind microvias while maintaining low surface roughness and a preferred Cu(220) orientation. Electrochemical measurements demonstrate that G1 exhibits strong cooperative suppression with the suppressor PEP and effectively resists competitive adsorption by the accelerator ZPS, forming a highly inhibiting PEP–ZPS–G1 system with a measurable convection response. In contrast, G2 shows weak synergy with PEP and lacks comparable electrochemical features, explaining its inferior filling performance. DFT calculations indicate that the asymmetric substitution of G1 produces a more heterogeneous charge distribution and enhanced active sites, strengthening its interactions with the cathodic interface and coadditives. MD simulations further confirm that G1 adsorbs more stably on Cu(111), increases PEP surface coverage, and suppresses effective ZPS adsorption, leading to selective interfacial regulation characterized by strong PEP adsorption and weak ZPS adsorption. These results establish a clear structure–function relationship for thiadiazole-based levelers and provide guidance for rational molecular design in advanced copper electrodeposition.

This study developed a technology for precise acoustic flow field manipulation using a variety of microbubble shapes (including circular, elliptical, triangular, and square) through an acoustofluidic chip system. By utilizing advanced fabrication techniques, the microcavity structure was optimally designed to achieve stable microbubble trapping. Employing 2 μm diameter polystyrene particle tracking technology, experimental results demonstrate that elliptical microbubbles can induce stable quadruple-vortex patterns. Unlike the dual-vortex limitation of spherical structures, elliptical structures stably generate quadruple-vortices across a broad frequency range (20–120 kHz), with a maximum velocity gradient of 35/s. The velocity gradient variation in this quadruple-vortex field is significantly smaller than that in dual-vortex patterns of other microbubbles, unlike other shapes that typically produced a dual-vortex pattern. Changes in excitation voltage affected the fluid velocity gradient around the microbubbles, with increased voltage resulting in a higher velocity gradient. Additionally, the choice of excitation frequency significantly impacted the flow field patterns of non-circular microbubbles. The key breakthrough lies in demonstrating that elliptical microbubbles can stably generate quadruple-vortex streaming, with significantly superior maximum velocity gradient and shear uniformity compared to conventional spherical microbubbles, offering additional flexibility for microbubble manipulation. These findings confirm the direct influence of microbubble shape on acoustic flow patterns. Moreover, our results reveal the potential of non-circular microbubbles in acoustic manipulation and introduce a new perspective to acoustic fluid engineering, emphasizing the importance of optimizing microbubble shape and frequency selection for future applications, particularly in drug delivery, cell manipulation, and biochemical analysis. Future research will focus on enhancing the practical efficiency of specific microbubble shapes, optimizing designs, and assessing their long-term environmental impact to promote sustainable development of the technology.

This study presents an innovative wedge-shaped inlet weir-type microfluidic chip designed to address common issues of clogging and inefficiency in microfiltration processes. Driven solely by centrifugal force, the chip integrates a crossflow separation mechanism and enables selective droplet sorting based on size, without the need for external pumps. Fabricated from PMMA, the device features a central elliptical chamber, a wedge-shaped inlet, and spiral microchannels. These structures leverage shear stress and Dean vortices under centrifugal fields to achieve high-throughput separation of droplets with different diameters. Using water-in-oil emulsions as a model system, we systematically investigated the effects of geometric parameters and rotational speed on separation performance. A theoretical model was developed to derive the critical droplet size based on force balance, accounting for centrifugal force, viscous drag, pressure differentials, and surface tension. Experimental results demonstrate that the chip can effectively separate droplets ranging from 0 to 400 μm in diameter at 200 rpm, achieving a sorting efficiency of up to 72% and a separation threshold (cutoff accuracy) of 98.2%. Fluorescence analysis confirmed the absence of cross-contamination during single-chip operation. This work offers a structure-guided, efficient, and contamination-free droplet sorting strategy with broad potential applications in biomedical diagnostics and drug screening.