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Inertial microfluidics functions solely based on the fluid dynamics at relatively high flow speed. Thus, channel geometry is the critical design parameter that contributes to the performance of the device. Four basic channel geometries (i.e., straight, expansion-contraction, spiral and serpentine) have been proposed and extensively studied. To further enhance the performance, innovative channel design through combining two or more geometries is promising. This work explores embedding periodic concave and convex obstacle microstructures in sinusoidal channels and investigates their influence on particle inertial focusing and separation. The concave obstacles could significantly enhance the Dean flow and tune the flow range for particle inertial focusing and separation. Based on this finding, we propose a cascaded device by connecting two sinusoidal channels consecutively for rare cell separation. The concave obstacles are embedded in the second channel to adapt its operational flow rates and enable the functional operation of both channels. Polystyrene beads and breast cancer cells (T47D) spiking in the blood were respectively processed by the proposed device. The results indicate an outstanding separation performance, with 3 to 4 orders of magnitude enhancement in purity for samples with a primary cancer cells ratio of 0.01% and 0.001%, respectively. Embedding microstructures as obstacles brings more flexibility to the design of inertial microfluidic devices, offering a feasible new way to combine two or more serial processing units for high-performance separation. [ABSTRACT FROM AUTHOR]

Multiphysics microfluidics, which combines multiple functional physical processes in a microfluidics platform, is an emerging research area that has attracted increasing interest for diverse biomedical applications. Multiphysics microfluidics is expected to overcome the limitations of individual physical phenomena through combining their advantages. Furthermore, multiphysics microfluidics is superior for cell manipulation due to its high precision, better sensitivity, real-time tunability, and multi-target sorting capabilities. These exciting features motivate us to review this state-of-the-art field and reassess the feasibility of coupling multiple physical processes. To confine the scope of this paper, we mainly focus on five common forces in microfluidics: inertial lift, elastic, dielectrophoresis (DEP), magnetophoresis (MP), and acoustic forces. This review first explains the working mechanisms of single physical phenomena. Next, we classify multiphysics techniques in terms of cascaded connections and physical coupling, and we elaborate on combinations of designs and working mechanisms in systems reported in the literature to date. Finally, we discuss the possibility of combining multiple physical processes and associated design schemes and propose several promising future directions. [ABSTRACT FROM AUTHOR]

A liquid marble is a liquid droplet coated with a shell of microparticles. Liquid marbles have served as a unique microreactor for chemical reactions and cell culture. Mixing is an essential task for liquid marbles as a microreactor. However, the potential of liquid marble-based microreactors is significantly limited due to the lack of effective mixing strategies. Most mixing strategies used manual and contact-based actuation schemes. This paper reports the development of a manipulation scheme that induces fluid motion into a liquid marble, leading to enhanced mixing. By inducing rotation on a horizontal axis, we significantly increased the mixing rate by 27.6 times compared to a non-actuated liquid marble and reduced the reaction time by more than 10 times. The proposed method provides a simple, continuous, precise, and controllable high-performance mixing strategy on a liquid marble platform.

Microfluidic technologies have been widely used for single-cell studies as they provide facile, cost-effective, and high-throughput evaluations of single cells with great accuracy. Capturing single cells has been investigated extensively using various microfluidic techniques. Furthermore, cell retrieval is crucial for the subsequent study of cells in applications such as drug screening. However, there are no robust methods for the facile release of the captured cells. Therefore, we developed a stretchable microfluidic cell trapper for easy on-demand release of cells in a deterministic manner. The stretchable microdevice consists of several U-shaped microstructures to capture single cells. The gap at the bottom edge of the microstructure broadens when the device is stretched along its width. By tuning the horizontal elongation of the device, ample space is provided to release particle/cell sizes of interest. The performance of the stretchable microdevice was evaluated using particles and cells. A deterministic release of particles was demonstrated using a mixture of 15 μm and 20 μm particles. The retrieval of the 15 μm particles and the 20 μm particles was achieved with elongation lengths of 1 mm and 5 mm, respectively. Two different cell lines, T47D breast cancer cells and J774A.1 macrophages, were employed to characterise the cell release capability of the device. The proposed stretchable micro cell trapper provided a deterministic recovery of the captured cells by adjusting the elongation length of the device. We believe that this stretchable microfluidic platform can provide an alternative method to facilely release trapped cells for subsequent evaluation.