Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications.

Effective manipulation of liquids on open surfaces without external energy input is indispensable for the advancement of point-of-care diagnostic devices. Open-surface microfluidics has the potential to benefit health care, especially in the developing world. This review highlights the prospects for harnessing capillary forces on surface-microfluidic platforms, chiefly by inducing smooth gradients or sharp steps of wettability on substrates, to elicit passive liquid transport and higher-order fluidic manipulations without off-the-chip energy sources. A broad spectrum of the recent progress in the emerging field of passive surface microfluidics is highlighted, and its promise for developing facile, low-cost, easy-to-operate microfluidic devices is discussed in light of recent applications, not only in the domain of biomedical microfluidics but also in the general areas of energy and water conservation.

Post-Impact Behavior of a Droplet Impacting on a Permeable Metal Mesh with a Sharp Wettability Step.

The impact of liquid droplets on permeable substrates is important for a number of applications, such as fog collection, liquid atomization, and interaction of liquids with filters and textiles. When a water droplet impacts a wettable mesh, it penetrates the mesh easily with a part of the liquid remaining pinned. On the other hand, when striking a superhydrophobic mesh, part of the water droplet may penetrate and detach from the parent droplet, depending upon the impact velocity and the relative length scales of the droplet and the mesh. In most cases, the remaining droplet would rebound from the top of the superhydrophobic mesh. In this work, we study the impact of a water droplet on a wettability-patterned mesh, with the droplet centrally impacting the wettability-contrast line between the superhydrophobic and superhydrophilic semi-infinite domains. Half of the droplet seeing the superhydrophobic domain responds to it in a fashion that differs from the half hitting the superhydrophilic mesh side. This creates a wide range of post-impact scenarios, depending on the impact conditions and the relative characteristics of the droplet and the mesh. The difference in mesh wettability leads to a net unbalanced surface-tension force that makes the droplet rebound with a horizontal momentum component directed from the non-wettable to the wettable side. Some part of the droplet may even detach during such directional rebounding (i.e., vectoring). Along with the experimental results, a simplified analytical model is presented, which differentiates the cases of detachment or no detachment during vectoring.

Efficacy evaluation of ethanolic extract of Tamarindus indica L. leaves as possible alternate therapy in septic arthritis model of rabbit.

BACKGROUND: Our previous study exhibited free radicals scavenging and antioxidant activities of ethanolic and aqueous extracts of Tamarindus indica L. leaves in chronic sodium fluoride poisoning in rats. Tamarindus indica L. seed extract was also reported to have anti-arthritic efficacy by inhibiting cartilage and bone degrading factors. Therefore, an attempt was made to evaluate the effects of ethanolic extract of Tamarindus indica L. leaves in septic arthritis. METHODS: The safety study was performed by oral dosing of ethanolic extract of the plant leaves at 2 g kg- 1 for consecutive 28 days in rabbits. Septic arthritis was induced in rabbits by single intra-articular inoculation of 104 c.f.u. of Staphylococcus aureus to the left stifle joint and was monitored by bacterial colony count, some relevant biochemical parameters and histopathological interpretation of the affected joint. For efficacy evaluation in septic arthritis, linezolid at 75 mg kg- 1 twice daily for 10 days and the ethanolic extract of Tamarindus indica L. at 500 and 1000 mg kg- 1 for consecutive 14 days were administered orally to the rabbits after 48 h of induction of arthritis. RESULTS: In sub-acute toxicity study of Tamarindus indica L. leaves ethanolic extract, no significant change between days was found for aspertate aminotransferase, alanine transaminase, alkaline phosphatase, blood urea nitrogen and creatinine compared to day 0 values of the same group. The bacterial colony count of synovial fluid following Staphylococcus aureus inoculation to left stifle joint was found to be 1.08 ± 0.47 and 1.19 ± 0.29 c.f.u. mL- 1 in ethanolic extract low dose and high dose groups respectively, on day 2 which was reduced to 0.057 ± 0.036 c.f.u. mL- 1 and nil on day 16. The test extract was also found to markedly reduce simultaneous glucose difference, total protein ratio of serum and synovial fluid, joint radius and joint narrowing. CONCLUSION: Ethanolic extract of Tamarindus indica L. leaves at 500 mg kg- 1 and 1000 mg kg- 1 produced anti-arthritic effects against S. aureus induced septic arthritis in rabbits. However, the ethanolic extract at 1000 mg kg- 1 orally for consecutive 14 days showed better effects in septic arthritis.

Scaling Laws in Directional Spreading of Droplets on Wettability-Confined Diverging Tracks.

Spontaneous pumpless transport of droplets on wettability-confined tracks is important for various applications, such as rapid transport and mixing of fluid droplets, enhanced dropwise condensation, biomedical devices, and so forth. Recent studies have shown that on an open surface, a superhydrophilic track of diverging width, laid on a superhydrophobic background, facilitates the transport of water from the narrower end to the wider end at unprecedented rates (up to 40 cm/s) without external actuation. The spreading behavior on such surfaces, however, has only been characterized for water. Keeping in mind that such designs play a key role for a diverse range of applications, such as handling organic liquids and in point-of-care devices, the importance of characterizing the spreading behavior of viscous liquids on such surfaces cannot be overemphasized. In the present work, the spreading behavior on the aforementioned wettability-patterned diverging tracks was observed for fluids of different viscosities. Two dimensionless variables were identified, and a comprehensive relationship was obtained. Three distinct temporal regimes of droplet spreading were established: I), a Washburn-type slow spreading, II) a much faster Laplace pressure-driven spreading, and III), a sluggish density-augmented Tanner-type film spreading. The results offer design guidance for tracks that can pumplessly manage fluids of various viscosities and surface tensions.

Precise Liquid Transport on and through Thin Porous Materials.

Porous substrates have the ability to transport liquids not only laterally on their open surfaces but also transversally through their thickness. Directionality of the fluid transport can be achieved through spatial wettability patterning of these substrates. Different designs of wettability patterns are implemented herein to attain different schemes (modes) of three-dimensional transport in a high-density paper towel, which acts as a thin porous matrix directing the fluid. All schemes facilitate precise transport of metered liquid microvolumes (dispensed as droplets) on the surface and through the substrate. One selected mode features lateral fluid transport along the bottom surface of the substrate, with the top surface remaining dry, except at the initial droplet dispension point. This configuration is investigated in further detail, and an analytical model is developed to predict the temporal variation of the penetrating drop shape. The analysis and respective measurements agree within the experimental error limits, thus confirming the model's ability to account for the main transport mechanisms.

Surface Treatments to Enhance the Functionality of PPEs.

The outbreak of unknown viral pneumonia in Wuhan China in December 2019 led to a new coronavirus (SARS-CoV-2), which attracted worldwide attention, with the related COVID-19 disease quickly becoming a global pandemic. In about 5 months, this disease has led to ~ 4 million cases and claimed more than 200 k deaths as a result of its highly contagious nature. The present understanding is that SARS-CoV-2 is a type of influenza virus that can be transmitted through respiratory droplets and aerosols; Lewis (Nature 580:175, 2020). The primary methodology to prevent the spreading of this disease has been "social distancing" and usage of personal protective equipment (PPE) at the front lines of healthcare and other critical operations. The scale of the disease has led to unprecedented demand for PPEs and increased functionality of the same. This paper focuses on improving PPE functionality in a scalable manner by surface treatment and coating with appropriate materials and other functional enhancements, such as exposure to UV rays or other sterilizing agents (e.g., hydrogen peroxide).

Importance of Body Stance in Fog Droplet Collection by the Namib Desert Beetle.

The fog-basking behavior of the Onymacris unguicularis, a beetle species living in the coastal regions of the Namibian desert, has recently caught the attention of the engineering community, as suggesting a viable biomimetic approach to address the problem of harvesting water in arid regions of the globe. Previous research has focused on observation and analysis of the beetle's elytron properties and how these affect fog-collection rates. The head stance taken by the Onymacris unguicularis when fog basking is well documented. However, how this stance affects droplet collection has not been studied up to now. The present paper addresses this problem from a computational fluid dynamics perspective, where three-dimensional numerical simulations are used to characterize the fog flow properties around a simplified geometry mimicking the beetle's body. The simulations employ two-way coupling between the gas flow and the dispersed fog phase to account for feedback effects of fog droplets on the carrier fluid (air), and assume that droplets are captured after hitting the elytron surface. The study considers several combinations of free-stream velocity and droplet volume fraction. The analysis reveals that there is a range of head-stance angles, corresponding to an inclination of the beetle between 35 deg and 45 deg with respect to the horizon, that maximizes water collection on the beetle's back, in qualitative agreement with observations in nature and laboratory experiments. A rationale is proposed to explain this phenomenon, finding that the specific head stance corresponds to the maximum residence time of fluid particles above the beetle's elytron surface. This, in turn, designates the maximum likelihood for water droplets to be captured in the boundary layer developing over the beetle and subsequently hit the surface where they get captured. The results reveal the importance of the fluid flow pattern around the beetle's body in addition to the microphysical properties of the elytron when reliable predictions of the water droplet collection efficiency are sought.

Burst mode pumping: A new mechanism of drinking in mosquitoes.

Mosquitoes transport liquid foods into the body using two muscular pumps in the head. In normal drinking, these pumps reciprocate in a stereotyped pattern of oscillation, with a high frequency but small stroke volume. Do mosquitoes modulate their neuromotor programs for pumping to produce different drinking modes? More broadly, what are the mechanical consequences of a two-pump system in insects? To address these questions, we used synchrotron x-ray imaging and fluid mechanical modeling to investigate drinking performance in mosquitoes. X-ray imaging of the pumps during drinking revealed two modes of pumping: continuous reciprocation with multiple small strokes, and a newly discovered 'burst mode' involving a single, large-volume stroke. Results from modeling demonstrate that burst mode pumping creates a very large pressure drop and high volume flow rate, but requires a massive increase in power, suggesting that continuous pumping is more economical for drinking. Modeling also demonstrates that, from one mode of pumping to the other, the mechanical role of the individual pumps changes. These results suggest that the advantage of a two-pump system in insects lies in its flexibility, enabling the animal to pump efficiently or powerfully as demanded by environmental considerations.

Surface-Wettability Patterning for Distributing High-Momentum Water Jets on Porous Polymeric Substrates.

Liquid jet impingement on porous materials is particularly important in many applications of heat transfer, filtration, or in incontinence products. Generally, it is desired that the liquid not penetrate the substrate at or near the point of jet impact, but rather be distributed over a wider area before reaching the back side. A facile wettability-patterning technique is presented, whereby a water jet impinging orthogonally on a wettability-patterned nonwoven substrate is distributed on the top surface and through the porous matrix, and ultimately dispensed from prespecified points underneath the sample. A systematic approach is adopted to identify the optimum design that allows for a uniform distribution of the liquid on horizontally mounted substrates of ∼50 cm2 area, with minimal or no spilling over the sample edges at jet flow rates exceeding 1 L/min. The effect of the location of jet impingement on liquid distribution is also studied, and the design is observed to perform well even under offset jet impact conditions.