Microfluidics and Nanofluidics最新文献

Sedimentation is the settling of solid particles in a liquid medium driven by gravity. This phenomenon poses significant challenges in experimental lab-on-chip (LOC) applications, as they often involve a biological sample to be loaded inside a syringe for prolonged periods (e.g. 3D bioprinting, microfluidic cytometers). Mitigating solutions such as mechanical agitators or buffer adjustments exist, but increase the complexity and cost of the setup. In this work, we developed a model of particle sedimentation inside a horizontal syringe, which highlights the importance of several parameters: syringe radius, particle terminal velocity in the buffer, syringe outlet position, and flow-rate. The model provides a simple way to estimate the concentration half-life (({t}_{1/2})), i.e. the time required for the concentration to halve, which is useful during the experiment design process. The model was initially tested numerically and then validated experimentally. Additionally, the applicability of the model to predict sedimentation of biological particles was experimentally demonstrated. Lastly, the model was used to develop guidelines for the design of setups with minimized sedimentation.

Insulator-based dielectrophoresis (iDEP) technology manipulates particles by creating a non-uniform electric field using insulating microchannel structures. It offers advantages such as high operability and electrode-free fabrication. However, the fluid driving and construction of non-uniform electric fields based on iDEP currently mainly relied on direct current (DC), which can easily lead to water electrolysis and the generation of a large amount of Joule heat. In this study, we used two metal tubes as electrodes to apply the AC and inlet/outlet to provide stable liquid flow based on the syringe pump, ensuring stable flow and achieving the focusing of particles and blood cells. Through numerical simulation, a ratchet structure with semicircular tooth surfaces was selected. This structure provides a more uniform distribution of high-field strength regions and can withstand higher flow rates. Subsequently, experiments were conducted to determine the focusing characteristics of particles under different conditions within this chip. Cell focusing throughout improved by nearly 3 times of magnitude compared to that of similar iDEP focusing techniques. Finally, the visualization experiment realized the defined morphology focusing of blood cells, and the optimal focusing ratio reached 7.27, and the focusing characteristics of blood cells were studied. This study is expected to promote the application of dielectrophoresis technology in clinical, biological and other aspects.

Capillary imbibition in periodically constricted tubes (PCTs) plays a critical role in multiple natural and technological processes, where the control of autonomous flows is intrinsically linked to the geometric architecture of the imbibition space. Here we present analytical expressions for the effective radius ((r_{eff})) of PCTs with different wave shapes and analyze how geometric parameters influence the infiltration dynamics. Our analysis reveals that (r_{eff}) is strongly dependent on the ratio of maximum to minimum radii ((alpha)) and, for stepped geometries, on the relative segment length proportion ((gamma)). Increasing (alpha) enhances (r_{eff}) up to a critical value, beyond which a strong reduction is observed: for (alpha >>) 2, approximately, the infiltration velocity progressively decreases. This counterintuitive behavior arises from the interplay between hydrodynamic resistance and capillary driving forces. We evaluated the effect on different geometries, achieving different (r_{eff}) that can be analytically predicted by closed-form expressions. The model was also validated against previously reported experimental data. These findings underline the potential of geometric design to optimize capillary-driven flows, providing a framework for tailoring PCTs to specific applications in microfluidics, porous media, and related fields.

Recycling of thermosetting material with low energy is still a significant challenge due to their stable and strong chemical bonds existed. In this work, we proposed a super-pressure microchannel liquid collision approach that combined microchannel with super-pressure driving and liquid collision to explore the physical and chemical change of crosslinked polyethylene (XLPE), by which the large bond breaking energy can be obtained and imposed on XLPE particles. Here, a super-pressure microchannel liquid collision generator (SP-MLCG) with 300 MPa input pressure and ~600 m/s output speed was designed to obtain the promising collision energy that calculated from the required energies of breaking the crosslinked bonds in XLPE. The particle size, the surface morphology, the molecular weight, the thermal stability, and the melting properties were evaluated step-by-step by optical image, SEM, GPC, TG, and DSC. By using the SP-MCLG, the size of XLPE particles decreased to ~50 μm. Meanwhile, SP-MLCG can lead to the decrease in the proportion of chains with high molecular weight, and in turn produce the reduction of thermal stable, glass transition temperature and melting temperature of XLPE particles. Especially, melt enthalpy can decrease from −89.65 to −64.14 J·g⁻¹. Hence, our proposed technique might be regarded as a promising method that is able to achieve the recycling and reuse of XLPE due to the considerable transformation of its physical and chemical properties.

Droplet microfluidics, a subset of microfluidics, focuses on the controlled generation, manipulation, and transport of micro- to femto-scale droplets. In the last three decades, this technology has become essential in high-throughput applications across biological and chemical analyses, enabling advances in areas such as cell encapsulation, drug screening, digital PCR, and protein crystallization along with applications in chemical mixing, chemical kinetics and chromatography. This review systematically classifies droplet generation methods into classical and contemporary techniques to discuss the technological evolution in droplet generation practice, and further subdivision into passive and active methods based on their operational principles. The paper further discusses about centrifugal microfluidic platform and its applications. Furthermore, the review briefly discusses recent trends in closed-loop feedback based droplet generation methods. By comparing the strengths, limitations, and applications of these techniques, this review provides information on the selection of droplet generation methods for specific applications and highlights potential directions for future research and technological development.

The convection analysis of nanofluid flow under the effect of Marangoni convection, provides important insights into thermal control and fluid dynamics. This phenomenon is critical in many applications, including electronic cooling, heat exchangers, solar thermal collectors, and enhancement in oil recovery by improving fluid flow and promoting controlled crystallization during material processing. Inspired by applications mentioned above, the present research focuses on the couple stress nanofluid flow across a stretching surface while accounting the Marangoni convection, magnetic field, nanoparticles shape factors and thermal radiations. Blood based nanofluid, with the considerations of nanoparticles (gold(Au) and iron-oxide(Fe₂O₃)) is supposed for the present research. Boundary layer assumptions and conservation laws are utilized to model a governing mathematical system for the assumed problem. The emerging partial differential equations (PDEs) of the supposed problem is transformed to the ordinary differential equations (ODEs) by utilizing the appropriate similarity transformations. The numerical outcomes are generated in MATLAB using the bvp4c (approach is designed to solve boundary value problems) solver. Results indicates that the increasing estimates of Marangoni number leads the enhancement in the velocity profile and temperature shows a declining trend in the considered scenarios. It is also observed that the velocity-distribution diminishes for the increasing values of magnetic parameter. The temperature profile of the studied nanofluid is decreasing when the Prandtl number and couple stress parameter increases. The effects of the emerging dimensionless parameters on skin friction and Nusselt number are also revealed in the tabulated form. Research may substantially improve the design of nanofluid-based systems, drug delivery techniques, renewable energy technologies, materials engineering, and electronic cooling systems.

Experimental research on microfluidic devices requires adequate control over surface parameters like wettability. Plasma has already been proven to be a promising tool for the control and alteration of the wettability of solid surfaces, yet its propagation in microfluidic devices and treatment stability remains challenging. Our idea is to produce and propagate an atmospheric pressure helium plasma directly into closed micrometer-size glass channels for in situ wettability treatment. This approach enables better control over the treatment parameters compared to conventional treatments in low-pressure chamber-type plasma reactors. With a homemade kHz dielectric barrier discharge-like setup, we successfully propagated plasma through a (4,hbox {cm}) long rectangular microchannel of uniform depth ((100,upmu hbox {m})) and variable width (250–500 (,upmu hbox {m})). Results obtained by in situ contact angle measurement on images indicate uniform wettability treatment with increased hydrophilic properties after only 1 min of treatment. The wettability achieved on a glass with our setup offers stability for up to 70 days depending on the plasma treatment and storage parameters. Contact angle results are further supported with X-ray photoelectron spectroscopy (XPS) surface analysis which revealed that the two effective mechanisms for wettability alteration are cleaning and surface functionalization.

The migration and proliferation of cancer cells within the extracellular matrix play a critical role in cancer metastasis, enabling cancer cells to move between the blood and lymph vessels and surrounding tissues and form tumors. The heterogeneous oxygen conditions in the tumor microenvironment (TME) also affect cancer cell behaviors. However, the behaviors of cancer cells in the extremely low oxygen concentration gradients in the TME are poorly understood. The present study evaluated the behaviors of cultured cancer cells using microfluidic devices capable of precise oxygen concentration control. MDA-MB-231 cells mixed within a collagen gel were placed in the device and observed for 24 h under various oxygen concentration gradients with different oxygen levels and slopes. The cell distribution changed depending on the oxygen concentration gradient, with cell proliferation being the primary factor, with some contribution of aerotaxis. Aerotaxis directed the migration of MDA-MB-231 cells toward higher oxygen concentrations within the 2–6% O₂ range and lower oxygen concentrations within the 7–12% O₂ range. These results demonstrate the utility of microfluidic devices for analyzing cancer cell behaviors under oxygen concentration gradients at oxygen levels similar to those in the TME and show that cancer cells exhibit different aerotactic behaviors at specific oxygen concentrations.

Zoledronic acid (ZA), the third-generation nitrogen-containing bisphosphonate, is one of the most effective bisphosphonates and is used as a highly potent inhibitor of bone resorption with no adverse effects on bone mineralization. It is also used to treat multiple cancers, such as lung cancer, bone cancer, breast cancer, and prostate cancer. A microfluidic system can generate an adjustable flow rate and pressure inside multiple channels with the desired shape and dimensions, which are often fabricated from PDMS polymer. Among the advantages of these systems are precise control of environmental conditions, reduction of user intervention, and reduced time and reagent volumes. The microfluidic method, as a simple and cost-effective process with high capability, leads to particle size control, narrow size distribution, and the spherical shape of nanoparticles. With the rapid development of microfluidic technology, the preparation of particles with controlled size, morphology, and composition would be possible with this approach. In this study, to the best of our knowledge, the evaluation of the cytotoxic activity of microfluidic synthesized chitosan-zoledronic acid (CS-ZA) nanoparticles has been investigated for the first time in order to develop new cancer therapy strategies by using pharmaceutical nanotechnology. A microfluidic synthesis of nanoparticles with a narrow size distribution and uniform morphology through the ionic gelation of chitosan (CS) with ZA without a crosslinker was explained in detail in the previous article (Khayati et al., Int J Biol Macromol 234, 2023). This study aimed to evaluate the cytotoxic effect of the best microfluidic synthesized nanoparticles with ZA solution as core flow, CS as sheath flow, and flow ratios of ZA/CS = 0.5 (denoted by MFCSZA0.5) along with synthesized bulk nanoparticles (BCSZA) on the A549 lung cancer cell line through an MTT cell viability assay and a flow cytometric apoptosis assay. The results indicate that MFCSZA0.5 demonstrated significantly greater antitumor activity compared to BCSZA and free ZA. The in vitro drug release from MFCSZA0.5 microfluidic synthesized nanoparticles depicted a gradual, sustained release profile compared to BCSZA synthesized in bulk conditions. However, both of these nanoparticles exhibit promising carriers for intracellular delivery of ZA molecules, which ultimately affect cancer cell viability. The microfluidic method demonstrated a high drug entrapment efficiency compared to the bulk method, and it showed a more controlled in-vitro release of the drug. The synthesized nanoparticles in both microfluidic and bulk methods were found to have an anticancer effect comparable to the free ZA drug.

Graphical abstract

A microfluidic system for immunohistochemistry providing improved staining uniformity and more convenient operation is designed, prototyped, and tested. The chip is comprised of two parts: a plastic (polycarbonate PC) sliding cover that forms a chamber over a glass slide with a mounted sample tissue section. Staining reagents and labeled antibodies are successively pipetted into the chamber and flow over the tissue section by gravity. Staining uniformity is improved in channel design optimization. The plastic cover includes structural features to modify the flow field and reduce the mixing of successive loadings. Flow characteristics are optimized using finite element modeling. The approach shows substantially more uniform staining, as demonstrated quantitatively by image processing of stained samples.