Microfluidics and Nanofluidics最新文献

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.

Lab-on-a-disc (LoD) devices utilize centrifugal force to regulate fluid movement and are widely employed in biochemical applications. LoDs facilitate biochemical analysis by integrating different essential steps such as mixing samples and reagents, separating target components from the sample, and detecting analytes in a single platform. This integration on a single disc substrate enables the miniaturization and automation of various biochemical workflows. However, current LoD systems frequently rely on active valves, which increase complexity and limit versatility. To address these challenges, this study employed 3D printing technology to develop a 3D-structured tilt capillary valve acting as a passive control mechanism. Tilt capillary valves with inclination angles ranging from 50° to 80° were fabricated, and their burst rotational speeds and repeatability were compared with those of conventional capillary and slope valves. The tilt capillary valve demonstrated superior performance, achieving high-speed fluid control with relative standard deviations ranging from 1.5 to 2.1%. This improvement was attained by distributing the effects of centrifugal and gravitational forces along the inclined flow path. Additionally, the capillary structure stabilized the effects of surface tension, further enhancing reproducibility. These findings suggest that the developed tilt capillary valve enhances the LoD system performance, enabling more precise and rapid fluid control. The enhanced passive valve presented in this study can be implemented in advanced microfluidic device designs, presenting considerable potential for biochemical assays, point-of-care applications, environmental monitoring, and food safety testing.

Droplet microfluidics is a rapidly evolving area of research with significant implications in bioengineering, drug delivery, chemical synthesis, environmental monitoring, and micro-scale electronics manufacturing. Recent advancements in droplet generation methods, including the use of electric fields and acoustic waves, have been driven by related technological developments. These innovations have enabled the creation of droplets with a wide range of sizes, shapes, and compositions, opening new frontiers for droplet microfluidic applications. This study reviews recent advances in droplet formation within microfluidic channels, beginning with an overview of droplet microfluidics and followed by an analysis of the various techniques used for droplet formation. The paper examines the impact of channel geometry, fluid flow rates, and channel wall surface properties on droplet formation. Additionally, it discusses the control of microfluidic droplets and the diverse applications of droplet microfluidics. The study also analyzes the morphological changes of droplets in response to variations in different controlling factors and presents an overview of compound droplet microfluidics, highlighting its technological aspects and significance across various applications. The influential factors governing the dynamics of compound droplets and their respective effects are briefly reviewed throughout the study. In conclusion, the paper identifies the major challenges and opportunities associated with microfluidic droplet dynamics and outlines emerging areas based on this technology. Overall, it provides a comprehensive overview of recent developments in droplet formation within microfluidic channels.

To evaluate the potential use of phage-displayed recombinant antibody fragments as biorecognition elements on microfluidic paper-based devices (µPADs), phage-displayed VL and soluble VL antibody fragments were immobilized on the chitosan-modified surface of µPADs to detect glycine-extended gastrin 17 (G17-Gly) an integral peptide biomarker for colorectal cancer. Additionally, the phage shaft displaying the scFv antibody fragment, used as a detection probe, was conjugated with gold nanoparticles (GNPs) and characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV–visible spectroscopy (UV–Vis). Following the microfluidic sandwich immunoassay, the mean intensity of the color spots was quantitatively analyzed using an image analysis program. Peptide calibration curves showed a linear relationship between the intensity of the color spot signal and the logarithm of the peptide concentration within the ranges of 10⁻⁶–5 × 10⁻¹ µM (R² = 0.98) for the phage-VL fragment and 10⁻⁴–1 µM (R² = 0.97) for the soluble VL fragment, with limits of detection (LOD) of 0.9 and 29 pM, respectively. The proposed µPAD-based immunoassay with the desirable LODs without further amplification provides a simple, versatile means for detecting biomarkers and pathogens of interest.

The freezing of droplets is a complex interdisciplinary research topic involving physics, chemistry, and computational science. This phenomenon has attracted considerable attention due to its significant applications in aerospace, meteorology, materials science, cryobiology, and pharmaceutical development. The development of microfluidic technology provides an ideal platform for microscopic physical research. In this study, we designed a spiral-shaped milli-reactor with a T-junction microchannel to generate digital droplets for studying and observing the digital freezing process of droplets. During the study of the recalescence and solidification processes of digital droplets dynamically moving in microchannels, we found that although the digital generation of droplets in our channel aligns well with the literature, achieving the digitalization of the droplet freezing process is very challenging. Even the initial phase of freezing (the recalescence process) exhibits significant randomness. A key feature of the randomness in the freezing process is the nucleation position of droplets within the channel, which significantly impacts the digital characteristics and hinders digital freezing. During the investigation of freezing randomness, we identified five distinct nucleation profiles, which largely determine the evolution of the freezing front and the duration of the recalescence phase. However, upon studying the motion velocity of the freezing front, we found that these velocities are temperature-dependent. This aligns with the results of our phase-field simulations and experimental findings, indicating that the release of latent heat during the recalescence process is stable. Additionally, the randomness in freezing may also stem from the deformation of droplets during the solidification process. In this study, we identified two distinct solidification modes during the freezing phase: one initiating from the droplet’s head or tail and the other starting from the middle, with the latter causing significant droplet deformation. Through statistical analysis, we further explored the influence of flow rate variation on the digital clustering of droplet freezing and discovered flow rate parameters that optimize freezing digitalization. For instance, when the oil phase flow rate is fixed, varying the water phase flow rate initially increases and then decreases the flatness factor, reaching a maximum at a water phase flow rate of (Q_w = 0.5 , text {mL/min}), indicating optimal clustering of droplets. The findings of this study provide new perspectives and approaches for controlling droplet freezing in microfluidic systems, while also offering significant insights into the unique behaviors and phenomena of nucleation and solidification processes at the microscale.

In this paper, we propose a unified framework to describe three key atomic-scale fluid properties-density, viscosity, and slip length-within nanoscale channels. These properties, which deviate significantly from bulk behavior, are expressed using simple power-law models as functions of the nanochannel height. The proposed framework accurately captures experimental and simulation data, providing a more flexible and interpretable alternative to existing complex or disparate models. The key advantage of our model lies in its mathematical properties. Continuity and a continuous derivative ensure seamless implementation into numerical simulations and theoretical predictions, leading to more understandable, stable, and accurate results. Additionally, the model adheres to physical principles, predicting convergence to bulk properties as channel size increases. Further, compared to existing exponential models, the unified power-law modeling approach offers several advantages. It provides flexibility by capturing nonlinear relationships and diverse data curvatures, interpretability through physically meaningful parameters, and adaptability for integration with other functions to model complex phenomena. Its simplicity facilitates easy parameter estimation, model interpretation, and computational efficiency. Moreover, its robustness makes it less sensitive to outliers and noise while maintaining fewer parameters that directly correspond to underlying physics and scaling laws. Hence, the proposed model’s simplicity, smoothness, physical validity, and generality establish it as a significant heuristic tool for the efficient design and optimization of nanoscale devices, utilizing theory and simulations across a wide range of applications.