Microfluidics and Nanofluidics最新文献

The current research focuses on investigating the influence of magnetic forces and differently shaped nanoparticles within diverging tapering arteries afflicted with stenoses, utilizing a blood flow model. A notable aspect of this study is the exploration of metallic nanoparticles of various shapes within a water-based fluid medium, a research area that remains largely unexplored. To simulate blood flow dynamics, a radially symmetric yet axially non-symmetric stenosis configuration is employed, providing insights into the complex flow patterns within diseased arteries. A significant contribution of our research lies in the analysis of the symmetrical distribution of wall shearing stresses and their correlation with resistive impedance. Moreover, we investigate the progressive rise of these quantities in tandem with stenosis severity. Through numerical simulations, we evaluate several flow parameters, including velocity, temperature, resistance impedance, boundary shear stress, and shearing stress at the stenosis throat. These assessments provide a comprehensive understanding of the multifaceted effects of nanoparticle shape and magnetic forces on blood flow characteristics within tapered arteries. Furthermore, our study explores the graphical representation of various flow quantities across a spectrum of relevant parameters for Cu-blood systems. By examining different types of tapered arteries, particularly diverging tapering configurations, we gain insights into the intricate interplay between arterial geometry, fluid rheology, and nanoparticle behavior.

With developments of nanofluidics, understanding the behavior of fluids confined in nanospaces becomes important. Particle tracking is an efficient approach, but in nanospaces, it often suffers from the finite temporal resolution, which causes the Brownian displacement of nanoparticles, and the finite spatial resolution due to the decreased signal-to-noise ratio of nanoparticle images, both of which are factors that can cause artifacts. Therefore, in the present study, we simulated nanoparticle tracking velocimetry based on the particle dynamics given by the Langevin equation to evaluate the artifacts. The results revealed that for measurement of the velocity distribution of pressure-driven flow in a 400 nm nanochannel utilizing 60 nm tracer nanoparticles, high-speed (temporal resolution: Δt ≤ 360 µs) and super-resolution (spatial resolution: Δz ≤ 25 nm) measurement is required for errors less than 10%, while insufficient resolution causes an artifact that results in a flattened velocity distribution compared with the original flow profile. The proposed resolutions were experimentally verified by defocusing nanoparticle tracking velocimetry developed by our group. As the simulation predicted, at longer temporal resolution and larger spatial resolution, the measured nanoparticle velocity distribution in the nanochannel indicated a parabolic flow profile but became flattened because of the artifacts. In contrast, at measurement resolutions within the proposed range, the velocity distribution close to the profile given by the Hagen-Poiseuille equation, which was considered to be the actual flow profile, was successfully obtained. This work provides a guideline for nanoscale flow measurements and will accelerate the understanding of specific transport phenomena in nanospaces.

Single-cell analysis provides a groundbreaking avenue for exploring cell-to-cell variation, the heterogeneity of cell responses to stimuli, and the impact of DNA sequence variations on cell phenotypes. A crucial facet of this analytical approach involves the refinement of techniques for effective single-cell trapping and sustained culture. This study introduces a microfluidic platform based on micropillars for hydrodynamic trapping and prolonged cultivation of individual cells. The proposed biochip design, termed three-micropillars based microfluidic (3µPF) structure, incorporates interleaved trap units, each featuring three-micropillars based microfluidic structure strategically designated to trap single cells, enhance the surface area of cells exposed to the culture medium, and enable dynamic culture, continuous waste removal. This configuration aims to mitigate adverse effects associated with bioparticle collisions compared to conventional trap units. The study employs finite element method to conduct a comprehensive numerical investigation into the operational mechanism of the microfluidic device. The simulation results show that the filled trap unit demonstrates a low-velocity magnitude, reducing shear stress on cells and facilitating extended culture. The hydrodynamic single-cell trap mechanism of the proposed device was also verified. The insights derived from this work are pivotal for optimizing the device and guiding future experimental examinations, thus contributing significantly to the progression of single-cell analysis techniques.

The separation of particles such as cells and bacteria in viscoelastic fluids has significant applications in biomedical fields. At present, one of the main challenges that limit the application of microfluidic technology is to separate particles in the viscoelastic fluids with different rheological properties. For instance, most existing microfluidic devices can only work in the fluid with a specific rheological property, resulting in the requirement of time-consuming design, manufacturing, testing, and optimization of different devices to separate particles in the fluids with different rheological properties. In this work, a novel hybrid three-stage microfluidic device that was made up of a micropore structure and two gradually contracted microchannels was designed to achieve efficient continuous separation of particles in the viscoelastic fluid over a wide range of rheological properties (0.07 < El < 340.41). Different separation strategies including first focusing, then initial separation, and then precise separation (FISPS) and initial separation and then precise separation (ISPS) were found. The separation strategy ISPS occurred at El < 0.14 while the separation strategy FISPS occurred at El > 8.43. In addition, the transformation of the separation mechanism from ISPS to FISPS was found under different flow conditions in the fluid with the transitional rheological properties (0.21 < El < 1.10). The effect of the flow rate and the rheological property of the fluid on microparticle separation were systematically studied by the experiment. With simple structure, easy operation, high separation efficiency, the present microfluidic device would have great potentials in the biomedical and clinical applications, such as the separation of cells for different patients.

The acoustic radiation force (ARF) acting on particles measures the performance of microfluidic devices driven by standing surface acoustic waves (SSAWs). However, existing ARF calibration techniques rely on image post-processing or additional equipment. This work proposes a look-up table method to determine the ARF by examining the particle acoustophoresis mode in discrete phase-modulated SSAW fields, where the phase difference between the two counter-propagating SAWs is changed at fixed time intervals. Theoretical analysis indicates that particles in a straight channel migrate laterally either in the “locked” mode or the “drift” mode, while mode switching can be observed when the interval reaches a critical value highly dependent on the ARF amplitude. A look-up table can then be established for a given SSAW device. By observing the particle acoustophoresis modes at different phase-changing intervals, the ARF amplitude can be obtained from the easily determined critical interval. The procedure is demonstrated experimentally in an SSAW acoustofluidic device and compared with the particle tracking protocol to verify the former’s effectiveness and demonstrate its operational simplicity. Inspired by the established theory, a method to improve the efficiency of particle acoustophoresis by optimizing the phase-modulating parameters is also proposed.

The reliable conjugation of antibodies to a solid matrix is crucial for robust immunoassays in microfluidic devices. Various magnetic particles (MPs) have been employed due to their high surface-to-volume ratios and ease of magnetic manipulation, providing a reliable surface for antibody immobilization. However, achieving uniform positioning of MPs across the channel surface has been challenging due to inadequate magnetic forces or magnetic field uniformity. Here, we present the utilization of Halbach magnetic arrays to enable consistent deployment of MPs on the microfluidic surface, thereby facilitating robust immunoassay capabilities. Using finite element method magnetics (FEMM) simulations, we predicted that incorporating Halbach magnetic arrays beneath the microfluidic channels would create more uniform and augmented magnetic flux density gradients over the surface. Subsequently, we applied this platform to assess cancer biomarkers in patients’ blood plasma and achieved statistically reliable results, comparable to those obtained using an FDA-approved device. We detected three cancer biomarkers, including prostate-specific antigen (PSA), alpha-fetoprotein (AFP), and carcinoembryonic antigen (CEA). The limit of detection (LOD) of three biomarkers were < 1 ng/mL, ranging from 0.38–0.95 ng mL⁻¹. This platform provided within-run, between-run, and between-day precisions for the three cancer biomarkers, ranging from 0.37–9.87%. This advancement holds significant promise for improving the accuracy and performance of immunoassays in various microfluidic diagnostic applications.

Mobility manipulation of liquid droplets is an important task of digital imicrofluidics. Acoustic levitation has revolutionised the contactless manipulation of liquid droplets for various applications. Acoustic levitation technique can be effectively used to manipulate droplets to obtain their coalescence. This paper reports a unique, versatile, and material-independent approach for the vertical coalescence of the droplets suspended in an acoustic levitator. The acoustic power of the levitator is carefully engineered to obtain vertical coalescence of two liquid droplets. Water, 20% and 40% glycerol–water solutions are used as the working liquids. The results of the experiments revealed three outcomes during the coalescence. The outcomes are analysed and discussed.

Numerical investigations of high-speed rarefied gas outflow into a vacuum through channels with a forward- or backward-facing step have been conducted using the direct simulation Monte Carlo method. Calculations have been performed for various free-stream Mach numbers, covering transonic, supersonic, and hypersonic flow regimes, and over a wide range of gas rarefaction from free molecular to near hydrodynamic conditions. Mass flow rates through the channel and the gas flow field have been accurately calculated both inside the channel and in the regions upstream and downstream. It has been established that channel geometry, the free-stream velocity, and gas rarefaction strongly influence the gas flow. In the flow field, in front of the channel, a phenomenon known as a detached shock occurs, while inside the channel, a gas recirculation zone may form.

Microfluidic flow control systems are critical components for on-chip biomedical applications. This study introduces a new micropump for on-chip sample preparation and analysis by using an acoustic nozzle diffuser mechanism. The micropump implements a commercially available transducer and control board kit with 3D-printed fluid reservoirs. In this micropump, conic-shaped micro-holes on the metal sheet cover of the transducer are employed as oscillating nozzle diffuser micro arrays to achieve directional flow control. The micropump is shown to efficiently pump water and particle mixtures exceeding flow rates of 515 µl/min at a 12-volt input voltage. In addition, owing to the small size of the nozzle hole opening, larger particles can also be filtered out from a sample solution during fluid pumping enabling a new function. Importantly, the micropump can be fabricated and assembled without needing a cleanroom, making it more accessible. This feature is advantageous for researchers and practitioners, eliminating a significant barrier to entry. By combining commercially available components with 3D printing technology, this micropump presents a cost-effective and versatile solution for on-chip applications in biomedical research and analysis.