Narrow Results

This study investigates the optimization of wire electrical discharge machining (WEDM) parameters for microchannel machining of aluminum alloy Al 6061 with improved mechanical properties, which is crucial for various industries. This investigation for microchannel fabrication considers four response parameters: material removal rate (MRR), surface roughness (SR), tool wear rate (TWR), and spark gap (SG), alongside four input parameters: pulse on time (Ton), sparking gap voltage (SGV), wire tension (WT), and wire feed rate (WFR). The selected levels for the experiment are, Ton 105, 115, and 125$\mu$s, SGV 10, 25, and 40 volts, WT 6, 8, and 12kgf, and the WFR 2, 4, and 6m/min. By examining Ton, SGV, WT, and WFR, the research identifies optimal conditions using Taguchi-based grey relational analysis (GRA). The findings highlight the importance of parameters such as Ton of 105$\mu$s, SGV of 40 volts, WT of 8kgf, and WFR of 4m/min for machining Al 6061-based microchannels, offering valuable insights for future manufacturing endeavors. This research also incorporates the morphology study of machined Aluminium alloy microchannel.

Patterning ridges on the surface of microchannels has been found to be a viable strategy to induce mixing in straight channels, despite their characteristically small Reynolds numbers. In order to identify the fundamental characteristics of the advection process, we evaluate the time evolution of the Rényi entropy associated with the spatial distribution of tracers carried by an incompressible fluid moving through such channels. It is found that independent of the channel surface geometry and of the Reynolds number, the time evolution of the Rényi distributive entropy follows a universal behavior described by a logarithmic increase with time, with a slope close to unity. On the other hand, an analysis of the Shannon mixing entropy evaluated from the time evolution of the position of two tracer species moving through the channel, reveals a cross–over between two different mixing mechanisms: one dominated by the stretching of the interface between the flow regions containing different tracers, and the other dominated by chaotic mixing induced by counter-rotating transversal flows.

In this work, the effective average height of the roughness elements, the relative increase of the pressure gradients, the relative decrease of the permeability are derived based on the fractal geometry theory and technique for laminar flow through tree-like branching networks with roughened channels. The relationships among the effective average height, the structural parameters and pressure drops as well as permeability are studied. It is found that the total pressure drop across a tree-like branching network with roughened channels is increased by a factor of $1/{(1-\epsilon )}^4$, and the permeability for the network with roughened channels is decreased by a factor of ${(1-\epsilon )}^2$, where $\epsilon$ is the relative roughness of surfaces of channels, compared to those with smooth channels.

Previous studies have shown that the flow in porous media can be affected by the structure of microchannels. In this paper, the capillary bundle model is used to simplify the complex and irregular structure of porous media, which is assumed to be comprised of tortuous capillaries covered with statistical self-similar conical rough elements. Considering the boundary layer effect, a fractal geometry-based quantitative model has been proposed to investigate the relationship between the hydraulic roughness of capillaries and the micro-flow properties. According to the proposed model, the influence of roughened surfaces on the tortuosity of Stokes flow can be considered as the combination of every individual rough element in 2D flow fields, which is extended to 3D flow fields based on a series of assumptions and approximations. Analytical expressions of tortuosity and permeability of Stokes flow through roughened capillaries are derived. According to the results, the tortuosity of capillary flow increases with a higher relative roughness, while the permeability is inversely proportional to it. Predictions of permeability by the present model are compared with the previous models and experiment data, which show good agreement.

Electrochemical Machining (ECM) and Electric Discharge Machining (EDM) processes have high potential when applied in micro regimes for good accuracy and shape reproduction. But they have a limitation that only electrically conducting materials can be machined by them. To overcome this limitation, a combination of ECM and EDM processes has been conceived, and it is known as "electrochemical spark machining" (ECSM). ECSM is slowly gaining popularity in machining of non-conductive materials. Here, an attempt is made to perform machining at micro-level on quartz. It is piezoelectric in nature, and made up of a lattice of silica (SiO₂) tetrahedral. For micromachining of quartz, the optimal value of voltage and work piece feed are found out. The depth of microchannel is increased to increase the aspect ratio of the microchannels to make them more useful to make the component such as a micromixer. Microchannels of different shapes are also generated. Finally, the microchannels of minimum width of 144 μm are obtained.

This study presents the thermal performance of pulsating heat pipes (PHPs) using distilled water with mini- and microchannels. The PHPs were fabricated with the channels of square cross section which had hydraulic diameters ranged from 1.6 to 3.2 mm in minichannels and from 0.714 to 0.941 mm in microchannels. The performance of the PHPs was measured and analyzed by varying hydraulic diameter, number of turns, filling ratio, and input power. The filling ratio of the working fluid varied from 0% to 100%. The input power was controlled in the range between 3.6 and 150 W. The hydraulic diameter, number of turns, filling ratio, and input power showed strong influence on the performance of the PHP. In the PHP models with mini- and microchannels, optimum working conditions, such as filling ratio and heat input, were quite different according to channel size.

In the last decade microfabrication processes including rapid prototyping techniques have advanced rapidly and achieved a fairly mature stage. These advances have encouraged and enabled the use of microfluidic devices by a wider range of users with applications in biological separations and cell and organoid cultures. Accordingly, a significant current challenge in the field is controlling biomolecular interactions at interfaces and the development of novel biomaterials to satisfy the unique needs of the biomedical applications. Poly(dimethylsiloxane) (PDMS) is one of the most widely used materials in the fabrication of microfluidic devices. The popularity of this material is the result of its low cost, simple fabrication allowing rapid prototyping, high optical transparency, and gas permeability. However, a major drawback of PDMS is its hydrophobicity and fast hydrophobic recovery after surface hydrophilization. This results in significant nonspecific adsorption of proteins as well as small hydrophobic molecules such as therapeutic drugs limiting the utility of PDMS in biomedical microfluidic circuitry. Accordingly, here, we focus on recent advances in surface molecular treatments to prevent fouling of PDMS surfaces towards improving its utility and expanding its use cases in biomedical applications.

Neurocircuits in the human brain govern complex behavior and involve connections from many different neuronal subtypes from different brain regions. Recent advances in stem cell biology have enabled the derivation of patient-specific human neuronal cells of various subtypes for the study of neuronal function and disease pathology. Nevertheless, one persistent challenge using these human-derived neurons is the ability to reconstruct models of human brain circuitry. To overcome this obstacle, we have developed a compartmentalized microfluidic device, which allows for spatial separation of cell bodies of different human-derived neuronal subtypes (excitatory, inhibitory and dopaminergic) but is permissive to the spreading of projecting processes. Induced neurons (iNs) cultured in the device expressed pan-neuronal markers and subtype specific markers. Morphologically, we demonstrate defined synaptic contacts between selected neuronal subtypes by synapsin staining. Functionally, we show that excitatory neuronal stimulation evoked excitatory postsynaptic current responses in the neurons cultured in a separate chamber.