A dynamically deformable microfilter for selective separation of specific substances in microfluidics

Enhancing particle focusing: a comparative experimental study of modified square wave and square wave microchannels in lift and Dean vortex regimes

Serpentine microchannels are known for their effective particle focusing through Dean flow-induced rotational effects, which are used in compact designs for size-dependent focusing in medical diagnostics. This study explores square serpentine microchannels, a geometry that has recently gained prominence in inertial microfluidics, and presents a modification of square wave microchannels for improved particle separation and focusing. The proposed modification incorporates an additional U-shaped unit to convert the square wave microchannel into a non-axisymmetric structure, which enhances the Dean flow and consequently increases the Dean drag force. Extensive experiments were conducted covering a wide range of Reynolds numbers and particle sizes (2.45 µm to 12 µm). The particle concentration capability and streak position dynamics of the two structures were compared in detail. The results indicate that the modified square-wave microchannel exhibits efficient particle separation in the lower part of the Dean vortex-dominated regime. With increasing Reynolds number, the particles are successively focused into two streaks in the lift force-dominated regime and into a single streak in the Dean vortex-dominated regime, in this modified square wave geometry. These streaks have a low standard deviation around a mean value. In the Dean vortex-dominated regime, the location of the particle stream is highly dependent on the particle size, which allows good particle separation. Particle focusing occurs at lower Reynolds numbers in both the lift-dominated and lift/Dean drag-dominated regions than in the square wave microchannel. The innovative serpentine channel is particularly useful for the Dean drag-dominated regime and introduces a unique asymmetry that affects the particle focusing dynamics. The proposed device offers significant advantages in terms of efficiency, parallelization, footprint, and throughput over existing geometries.

Tuning particle inertial separation in sinusoidal channels by embedding periodic obstacle microstructures

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.

PDMS Microfabrication and Design for Microfluidics and Sustainable Energy Application: Review

The polydimethylsiloxane (PDMS) is popular for wide application in various fields of microfluidics, microneedles, biology, medicine, chemistry, optics, electronics, architecture, and emerging sustainable energy due to the intrinsic non-toxic, transparent, flexible, stretchable, biocompatible, hydrophobic, insulating, and negative triboelectric properties that meet different requirements. For example, the flexibility, biocompatibility, non-toxicity, good stability, and high transparency make PDMS a good candidate for the material selection of microfluidics, microneedles, biomedical, and chemistry microchips as well as for optical examination and wearable electronics. However, the hydrophobic surface and post-surface-treatment hydrophobic recovery impede the development of self-driven capillary microchips. How to develop a long-term hydrophilicity treatment for PDMS is crucial for capillary-driven microfluidics-based application. The dual-tone PDMS-to-PDMS casting for concave-and-convex microstructure without stiction is important for simplifying the process integration. The emerging triboelectric nanogenerator (TENG) uses the transparent flexible PDMS as the high negative triboelectric material to make friction with metals or other positive-triboelectric material for harvesting sustainably mechanical energy. The morphology of PDMS is related to TENG performance. This review will address the above issues in terms of PDMS microfabrication and design for the efficient micromixer, microreactor, capillary pump, microneedles, and TENG for more practical applications in the future.