Search Results (1,686)

The development of collagen-based composite materials offers new opportunities for designing bioactive porous structures with tunable properties. This study focuses on sponges or scaffolds fabricated from fish skin-derived tropocollagen combined with detonation nanodiamonds (NDs), aiming to explore how incorporation of NDs and application of radiation, as a potential sterilization method, influence structural and functional characteristics of the material. Freeze-dry methods of sponge fabrication resulted in a bilayered structure of open porosity, with microporosity at the top and a microchannel at the lower part of the material. The sponges demonstrated mechanical properties with relatively low elongation of below 10%, while the maximum stress was reduced by ca. 20% due to irradiation. Hydration and absorption experiments, mimicking the resorption of collagen in physiological conditions of expected application as wound dressing material, demonstrated controllable fluid uptake and gradual material dissolution, taking place over several hours, depending essentially on the irradiation treatment and morphological characteristics of the sponge. These findings highlight the versatility of collagen–nanodiamond composites as platforms, in which structural design and processing parameters control performance. Moreover, they provide a strong indication of the expected behavior of collagen–nanoparticle systems, including those incorporating NDs modified to impart specific biological functionality, such as antimicrobial activity. Full article

Serial flow cytometry was recently introduced as a method that can estimate measurement uncertainty (i.e., imprecision, the coefficient of variation of repeated measurements of individual particles) independent from population characteristics. Replication of light sources and detectors at multiple sites along a flow cytometer’s microchannel requires more equipment and can complicate detector synchronization. Here, we introduce amplitude modulation to encode each region of a serial cytometer with a unique carrier frequency, which enables demultiplexing of the combined signal incident on a single photodetector by fast Fourier transform (FFT) peak magnitude. To facilitate validation of detection, matching, and uncertainty quantification of fluorescence signals, we designed a microfluidic amplitude modulation (AM) serial flow cytometer that has ground truth detectors on individual regions (serial cytometry) in parallel with the combined channel detection for AM demultiplexing. With this report, we present metrics for event detection and dynamic range, prevalence and processing of overlapping detections, region-decoding accuracy, process yield, and uncertainty quantification on a brightness ladder of calibration microspheres. Despite being operated with reduced light intensities, the AM cytometer was capable of high-fidelity performance in comparison to conventional serial cytometry. For events above the detection limit, over 97% were analyzed. Both conventional and AM serial cytometers achieved median imprecisions in the range of 0.53% to 2.1% after outlier removal, which was well below the inherent intensity distribution of any of the microsphere subpopulations. Overall, AM cytometry supports uncertainty quantification and temporal analyses of serial cytometry data with a reduced number of photodetectors, which offers simplification of chip design with multiple measurement regions and wide-field detectors. Full article

Acoustofluidics has emerged as a transformative technology for contact-free manipulation of microparticles and fluids in microscale systems. Although bulk acoustic waves (BAWs) are known to displace inhomogeneous fluids through acoustic radiation force acting at fluid interfaces, the capability of surface acoustic waves (SAWs) to produce analogous relocation phenomena remains largely unexplored. This study addresses a critical gap in acoustofluidic theory by presenting the first comprehensive finite element method investigation of SAW-driven motion of inhomogeneous fluid confined within microchannels of widths equal to one full or one-half SAW wavelength. Unlike BAW-based system that generate uniform pressure fields across channel heights, SAW devices exhibit inherently nonuniform vertical pressure distributions and intense near-boundary streaming—features that fundamentally alter fluid relocation dynamics. Our simulations demonstrate that despite high-frequency operation (6.65 MHz) and strong ARF, standing SAW fields fail to achieve stable fluid relocation in both initially stable and unstable configurations due to vertical pressure stratification and rapid floor-level streaming. Nevertheless, these same characteristics generate vigorous transverse folding flows that enable exceptionally rapid homogenization, offering a distinct acoustofluidic mechanism for on-chip mixing. These findings not only elucidate fundamental physical differences between BAW and SAW actuation in multiphase microfluidic systems but also establish design principles for SAW-induced microfluidic mixers. The results provide crucial theoretical guidance for device optimization where rapid homogenization is desired over stable stratification. Full article

In recent years, passive cell manipulation in microfluidic devices has emerged as a crucial tool for biomedical and biotechnological applications, allowing control over cell positioning and behavior without the need for chemical labels or complex external forces. However, achieving precise and tunable modulation of cell dynamics remains a challenge, particularly with low-cost and non-invasive methods. In this work, we present a novel approach that leverages controlled acousto-mechanical perturbations (AMPs) to modulate cell arrangement and behavior in microchannels. By coupling a smartphone-driven audio speaker with a microfluidic device, acoustic signals are converted into mechanical vibrations of the tubing, generating AMPs that interact with hydrodynamically driven flows. Experiments with yeast cells and silica beads under different flow conditions revealed that acoustic stimulation induced periodic flow dynamics, with yeast cells showing tunable, flow-dependent responses while inert particles exhibited weak and stable modulation. Frequency-domain analysis highlighted a dominant response synchronized with the applied acoustic protocol, accompanied by higher-frequency components characteristic of acoustic actuation. These results demonstrate that simple, low-cost acoustic actuation revealed distinct dynamical responses between rigid inert particles and deformable biological cells and enable label-free cellular manipulation. The proposed platform offers a versatile, non-invasive, and accessible approach for controlled cell manipulation in microfluidics. Full article

This study explores the passive separation of solid particles from liquid suspensions in spiral separators fabricated using fused filament fabrication (FFF) and stereolithography (SLA). Building on prior work, we investigate the effect of microchannel geometry, circular vs. square cross-sections of equal area, and printing method on separation performance. Devices were tested across a wider range of flow rates (150 mL min⁻¹–350 mL min⁻¹), extending into transitional regimes, to examine geometry-induced inertial effects. Separation performance was quantified using the normalized outlet mass difference (Δ) for talc, precipitated calcium carbonate, and quartz. Maximum separation was obtained for quartz sand in the SLA separator at 250 mL min⁻¹ (Δ = 0.2175 g per 100 mL), while talc showed the highest mass difference in the square FFF separator at 300 mL min⁻¹ (Δ = 0.1196 g per 100 mL). For calcium carbonate, the highest separation occurred in the SLA device at 250 mL min⁻¹ (Δ = 0.1721 g per 100 mL), though performance was limited by agglomeration and clogging in FFF devices. Overall, separation was predominantly mass-based rather than strictly size-selective, with channel geometry, flow regime, and fabrication method jointly governing performance. Full article

This study numerically investigates the effects of red blood cell (RBC) volume fraction (hematocrit) and RBC diameter on cell distribution, cell-free layer (CFL) thickness and pressure drop in a microchannel with sudden expansion. Hematocrit levels of 0.2, 0.3, 0.4 and 0.5, together with RBC diameters of 4, 8 and 11 µm, are considered, where deviations from the physiological diameter of 8 μm represent pathological conditions. An Euler–Euler approach is employed to model the multiphase flow, treating RBCs as rigid spherical particles, while the non-Newtonian viscosity of blood is represented using a modified Carreau–Yasuda model. The numerical predictions are validated against existing experimental and numerical data. The effect of volumetric flow rate on RBC distribution is found to be limited; therefore, a representative flow rate of 100 μL/min is adopted for the subsequent analysis. The results show that RBC migration and the resulting cell distribution are strongly governed by RBC size and hematocrit. The pressure drop is primarily influenced by hematocrit, while the effect of RBC size is relatively weak. A minimum value for pressure drop is observed at a hematocrit of 0.3, indicating an optimal hematocrit level for minimizing flow resistance. A parabolic correlation is proposed for predicting the pressure drop as a function of hematocrit, with a maximum relative error of 1.13%. This study contributes to the understanding of pathological RBC size variations and their impact on microscale hemodynamics. Full article

The global effort to mitigate hazardous particulate matter (PM) emissions from diesel engines relies significantly on advances in separations technologies. The diesel particulate filter (DPF) is a critical component designed to trap soot and ash from diesel engine exhaust, ensuring cleaner emissions and compliance with environmental regulations. In the current paper, a gas-particle two-phase flow model in the microchannels of a DPF is developed. A novel statistical approach based on probability sampling is proposed aimed at generating a particle ensemble that adheres to the real-world soot particle size distribution (PSD). The Eulerian-Lagrangian approach is employed to model the soot-laden gas flow, where the gas phase flow field is solved in the Eulerian framework, while the particle phase motion is tracked in the Lagrangian framework. The results demonstrate that the through-wall velocity plays a predominant role in the overall deposition behavior of the mixed-sized particle group. Increasing upstream velocity shifts initial particle deposition positions further from the channel inlet and enhances mass accumulation at the channel’s terminal section. Reduced filtration wall permeability promotes the uniformity of soot deposition along the channel. A permeability of 5 × 10⁻¹³ m² is identified as the critical threshold, below which the soot deposition distribution approaches near-complete uniformity. Full article

This paper investigates the optical solitons to the M-truncated fractional $(1+1)$-dimensional nonlinear generalized Bretherton model with arbitrary constants. It is employed to forecast the movement of liquid droplets or gas bubbles in microchannels, which is crucial for drug delivery systems, biomedical diagnostics, and lab-on-a-chip technologies. We obtain optical soliton solutions using the extended hyperbolic function method (EHFM) and the modified extended tanh method (METM). Numerous solutions, such as singular, periodic–singular, bright, and dark optical solitons, are obtained from our investigation. The $2D$ graphical depiction of the solutions shows a variety of wave patterns that change with varied values of $\alpha$ and t. The wave’s amplitude forms become more apparent as $\alpha$ and t increase. Using 2D plots, the comparison of fractional effects for the M-truncated fractional derivative is demonstrated by giving specific values to the fractional parameter. Full article

Virtual impactors are widely used for particulate matter (PM) classification due to their advantages of small cut-off particle size, simple structural design, ease of operation, and high particle handling capability, enabling subsequent analysis based on the desired aerodynamic diameter. Existing studies have mainly focused on the effects of particle size and structural parameters on classification performance, whereas systematic investigations into the regulatory mechanisms of fluid medium properties and ambient temperature variations on cut-off particle size remain relatively limited. Particularly under low-temperature gas conditions, variations in gas dynamic viscosity may significantly influence the dynamics of inertial particle separation, thereby altering the classification performance of virtual impactors. In this study, a low-temperature carbon dioxide-driven virtual impactor is proposed. By regulating the physicochemical properties of low-temperature gas, effective control over the particle inertial separation process is achieved, thereby expanding the tunable range of classification performance in virtual impactors. Numerical simulation results indicate that under low-temperature CO₂ conditions, the virtual impactor can achieve a cut-off particle size classification capability of approximately 1.8 μm for fine particles. Under identical channel dimensions, a comparative analysis between conventional rectangular main channels and trapezoidal main channels was conducted, quantitatively showing that wall loss decreased from 44% to 24%. Based on the trapezoidal main channel configuration, further parametric studies on the horizontal inlet geometric dimensions were performed, revealing their influence on separation efficiency and wall loss. To validate the reliability of the numerical simulation results, particle separation experiments were conducted using polystyrene microspheres with particle sizes of 2 μm and 5 μm. Experimental results demonstrate that the virtual impactor can achieve stable particle separation and confirm the reliability of simulation-predicted particle classification trends. The results further show that, when driven by low-temperature CO₂ combined with trapezoidal main channel structural optimization, the cut-off particle size of the virtual impactor decreases by approximately 26%, from 2.5 μm to about 1.8 μm. The trapezoidal channel structure significantly reduces particle wall loss under specific cut-off particle size conditions, while the low dynamic viscosity characteristic of low-temperature CO₂ lowers the internal gas temperature environment of the microchannel, thereby improving inertial particle separation efficiency. Full article

This study systematically investigates the flow characteristics, mixing efficiency, and concentration gradient generation (CGG) capabilities of three types of vertical-stepped main-channel microfluidic concentration gradient generators—the upward vertical-step (UVS-GG), downward vertical-step (DVS-GG), and straight horizontal channel (SHC-GG)—under different Reynolds numbers (Re) through numerical simulation and comparative analysis. Using numerical simulations, the research reveals the universal transition of flow regimes from diffusion-dominated to convection-dominated and reports the emergence of a “multi-peak oscillatory concentration gradient” phenomenon under stepped geometries and high Re (Re = 100, 200). The results indicate that the SHC-GG can generate monotonic gradients at low Re, making it an ideal baseline configuration. In contrast, UVS-GG and DVS-GG enhance mixing and enable the programming of complex concentration distributions through unique inertia–geometry coupling effects. The synergistic interaction between geometric configuration and Re is identified as the core mechanism for regulating concentration field morphology and device performance. This study provides key theoretical and design foundations for the rational design of microfluidic gradient generators targeting applications such as biological screening, chemical analysis, and material synthesis. Full article

The supercritical carbon dioxide (SCO₂) Brayton cycle presents a promising alternative to the traditional steam Rankine cycle, owing to its superior thermal efficiency, high power density, and compact design. As a key component governing system performance, the heat exchanger requires a highly compact and efficient design. This study proposes a novel additively manufactured (AM) wavy microchannel heat exchanger that achieves a compactness of 1670 m²/m³. The design incorporates adaptive flow channels to accommodate SCO₂’s density variation, along with wavy patterns and ribs to enhance thermal performance. A comprehensive fluid–thermal–mechanical coupling numerical analysis was conducted to evaluate its thermal–hydraulic and mechanical performance. Within the Reynolds number range of about 900–6000, the wavy structures improve the heat transfer rate by 21–58%, compared with the straight channel. The maximum effectiveness (ε = 0.66) occurs at a Reynolds number of 900. Compared with other heat exchangers used in the SCO₂ cycle, the overall performance of the hot and cold channels has improved by 12–44% and 3–89%, respectively. Structural analysis confirms that the average total stress under operating conditions remains below the yield strength of the Inconel 617 material, with thermal stress being the dominant contributor. This work underscores the potential of the proposed AM heat exchanger to deliver a superior combination of compactness, thermal–hydraulic performance, and structural integrity for advanced SCO₂ power cycles. Full article

The evaporation of a thin liquid film representative of power-law rheology flowing along an inclined channel wall under the combined influence of gravity and surface tension is investigated using a semi-analytical modelling framework. The evolution of film thickness, heat transfer characteristics, and dry-out behaviour are examined as functions of the power-law exponent, Weber number, and inlet film thickness. The results show that a decrease in the power-law exponent leads to a slower reduction in film thickness, resulting in a significant increase in the dry-out length for a fixed value of consistency. This behaviour is attributed to the large effective viscosity developing near the free surface for shear-thinning fluids, in contrast to the negligible surface viscosity observed for shear-thickening fluids. The local Nusselt number increases gradually along the flow direction, followed by a sharp terminal rise marking the onset of dry-out. The mean Nusselt number decreases with increasing power-law exponent, which is consistent with the dry-out length variation with the power-law exponent. The dry-out length is found to be largely insensitive to surface tension for a fixed normalised inlet film thickness, while exhibiting an approximately linear dependence on the inlet film thickness that is nearly independent of the power-law index. Overall, the study establishes a hierarchy of controlling parameters for evaporating power-law films in inclined micro-channels, demonstrating that inlet film thickness primarily governs the dry-out location, while rheology and surface tension exert secondary influences within the parameter ranges considered. Full article

Integrating functional perovskites on an amorphous microchannel plate (MCP) glass faces challenges regarding the lack of ordered nucleation sites and stringent thermal budgets. Herein, we propose a surface energetics-based atomic layer deposition (ALD) strategy to achieve template-assisted oriented BaTiO₃ growth via a (101)-oriented anatase TiO₂ seed layer. Systematic investigation of the TiCl₄/O₃ process reveals a kinetic-to-thermodynamic transition at 300 °C, triggering a singular (101) preferred orientation. Combined DFT calculations and Wulff construction elucidate that this texture evolution is governed by a thermally activated surface energy minimization mechanism, driven by the intrinsic stability of the (101) facet. Crucially, the optimized seed layer acts as a multifunctional template: it not only transforms BaTiO₃ growth from random polycrystalline morphology to a singular (100) orientation with suppressed bulk carbonate impurities but also ensures excellent conformality and uniformity throughout the high aspect ratio microchannels. This study clarifies the thermodynamic mechanism of oriented growth on amorphous substrates, providing a versatile surface engineering pathway for constructing high-performance MCP-based heterojunction devices. Full article

Abrasive air jet (AAJ) machining is a non-traditional technology used to pattern microstructures on a wide variety of engineering materials. Understanding the material removal mechanisms and the formation of micro-channels produced by AAJ is essential for optimizing process parameters and enhancing machining quality. Therefore, this study develops and validates a discrete element model to simulate abrasive air jet machining of micro-channels on quartz crystals. It shows that the crack network, which consists of opening mode cracks and shearing mode cracks, contributes to the removal of target particles. Opening mode cracks dominate the material removal process. The histories of the number of newly generated cracks and newly removed target particles can be divided into three stages: an incubation stage, a transitional stage, and a stable stage. Both the number of newly generated cracks and the number of newly removed target particles first increase and then decrease as the machining process progresses. An indicator called the “contribution rate” is proposed, showing that damage accumulates in the target substrate during abrasive air jet machining. During the machining of micro-channels, erosion impression appears at first. As the width and depth of the erosion impressions increase, micro-channels gradually form. Full article

Microchannel liquid cooling technology, characterized by high heat-transfer efficiency, represents an effective solution for thermal management in high heat-flux density electronic devices. Existing research has mainly focused on optimizing the structural design of microchannel heat sinks, while neglecting the specific effects of inlet manifold configurations on their heat transfer and flow performance. To obtain more systematic data on microchannel heat transfer performance and internal velocity distribution, this study designed microchannels with single-inlet and triple-inlet configurations. A microchannel cooling performance testing platform was established, and visualization experiments of the internal flow field in straight microchannels were conducted using a particle image velocimetry (PIV) system. The velocity distribution uniformity and heat transfer performance were compared between single-inlet and triple-inlet microchannels with varying channel spacings. The results show that under the same flow conditions, the triple-inlet splitter structure yields a more uniform flow distribution, a lower peak temperature for the heat source chip, and improved heat transfer performance, with its pressure drop reduced to 11.1–26.6% of that of the single-inlet configuration. Furthermore, smaller channel spacings yield improved heat-transfer efficiency in microchannels. Full article