Contactless Transport and Mixing of Liquids on Self-Sustained Sublimating Coatings

Preparation and Analysis of Structured Color Janus Droplets Based on Microfluidic 3D Droplet Printing

The microfluidic technique for the three-dimensional (3D) printing of Janus droplets offers precise control over their size, orientation, and positioning. The proposed approach investigates the impact of variables such as the volume ratio of the oil phase, droplet size, and the ratio of nonionic surfactants on the dimensions of the structured color apertures of Janus droplets. The findings reveal that structured color apertures modulate accurately. Furthermore, fabricating color patterns facilitates cat, fish, and various other specific shapes using structured color Janus droplets. The color patterns exhibit temperature-sensitive properties, enabling them to transition between display and concealed states. Herein, the adopted microfluidic technique creates Janus droplets with customizable characteristics and uniform size, solving orientation as well as space arrangement problems. This approach holds promising applications for optical devices, sensors, and biomimetic systems.

Poloxamer/Poly(ethylene glycol) Self-Healing Hydrogel for High-Precision Freeform Reversible Embedding of Suspended Hydrogel

Freeform reversible embedding of suspended hydrogel (FRESH) is an additive manufacturing technique enabling the 3D printing of soft materials with low or no yield stress. The printed material is embedded during the process until its solidification. From the literature, FRESH abilities are self-healing, reusability, suspending, thermal stability, and high-precision printing. This study proposes a new support hydrogel bath formulation for FRESH 3D printing. To do so, a poloxamer micellar thermoreversible hydrogel is tuned through the addition of poly(ethylene glycol) (PEG) to adapt rheological properties. PEG macromolecules interact with poly(ethylene oxide) blocks of poloxamer and favor micelle dehydration, and then decreasing the gelation temperature, the yield stress, and the viscosity. Parameters such as the Oldroyd number and the Rayleigh-Plateau instability, both dependent on yield stress, were studied to determine their impact on the FRESH 3D printing resolution and accuracy. It was found that print accuracy of embedded parts increases with increasing yield stress but then the self-healing property gets limited, leading to crevasse formation. The usefulness of this approach is distinctly demonstrated through a six-axis printing of a highly complex silicone anatomical model. Printing fidelity of 96.0 ± 3.58% (5-40 mm printed parts) is thus achieved using the newly formulated FRESH material, while only 56.0 ± 0.76% fidelity is obtained using the standard formulation. The present study thus showed that complex FRESH 3D printing of soft materials is possible in this tunable hydrogel and that parts can be manufactured on an industrial scale, thanks to the reusability of the support bath.

Droplet Self-Propulsion on Superhydrophobic Microtracks

Liquid transport (continuous or segmented) in microfluidic platforms typically requires pumping devices or external fields working collaboratively with special fluid properties to enable fluid motion. Natural liquid adhesion on surfaces deters motion and promotes the possibility of liquid or surface contamination. Despite progress, significant advancements are needed before devices for passive liquid propulsion, without the input of external energy and unwanted contamination, become a reality in applications. Here we present an unexplored and facile approach based on the Laplace pressure imbalance, manifesting itself through targeted track texturing, driving passively droplet motion, while maintaining the limited contact of the Cassie-Baxter state on superhydrophobic surfaces. The track topography resembles out-of-plane, backgammon-board, slowly converging microridges decorated with nanotexturing. This design naturally deforms asymmetrically the menisci formed at the bottom of a droplet contacting such tracks and causes a Laplace pressure imbalance that drives droplet motion. We investigate this effect over a range of opening track angles and develop a model to explain and quantify the underlying mechanism of droplet self-propulsion. We further implement the developed topography for applications relevant to microfluidic platform functionalities. We demonstrate control of the rebound angle of vertically impacting droplets, achieve horizontal self-transport to distances up to 65 times the droplet diameter, show significant uphill motion against gravity, and illustrate a self-driven droplet-merging process.