Non-Newtonian Droplet Generation in a Cross-Junction Microfluidic Channel

A two-dimensional CFD model based on volume-of-fluid (VOF) is introduced to examine droplet generation in a cross-junction microfluidic using an open-source software, OpenFOAM together with an interFoam solver. Non-Newtonian power-law droplets in Newtonian liquid is numerically studied and its effect on droplet size and detachment time in three different regimes, i.e., squeezing, dripping and jetting, are investigated. To understand the droplet formation mechanism, the shear-thinning behaviour was enhanced by increasing the polymer concentrations in the dispersed phase. It is observed that by choosing a shear-dependent fluid, droplet size decreases compared to Newtonian fluids while detachment time increases due to higher apparent viscosity. Moreover, the rheological parameters—n and K in the power-law model—impose a considerable effect on the droplet size and detachment time, especially in the dripping and jetting regimes. Those parameters also have the potential to change the formation regime if the capillary number (Ca) is high enough. This work extends the understanding of non-Newtonian droplet formation in microfluidics to control the droplet characteristics in applications involving shear-thinning polymeric solutions.

Postoperative Macular Proliferative Vitreoretinopathy: A Case Series and Literature Review

Premacular membranes developing following pars plana vitrectomy (PPV) can cause significant anatomical and functional deficits to the macula. Recent reports showed that postoperative premacular membranes are a localized presentation of macular proliferative vitreoretinopathy (mPVR). Here, we report retrospectively a case series of 5 patients with severe mPVR which developed following uneventful PPV and were followed up to 32 months in the Department of Ophthalmology, Hadassah-Hebrew University Medical Center, Jerusalem, between October 2016 and February 2020. All patients underwent primary repair of rhegmatogenous retinal detachment (RRD) before mPVR developed. Mean best-corrected visual acuity (BCVA) at presentation was 20/76 Snellen (0.58 LogMAR). Median duration of the retinal detachment time until surgery was 1.5 days (range 1–21 days). Mean interval time from last normal follow-up exam to diagnosis of mPVR was 19 days (range 10–28). BCVA dropped from a mean of 20/38 Snellen (0.28 LogMAR) prior to mPVR development to 20/166 Snellen (0.92 LogMAR) following its development, recovering to 20/57 Snellen (0.45 LogMAR) after peeling of membranes. Mean central macular thickness measured by optical coherence tomography decreased from 711 to 354 μm postsurgery. In conclusion, short-term mPVR is a different entity from macular pucker in terms of rapid development, structural distortion, and visual compromise. Surgical treatment significantly restores macular function and anatomy.

Effects of tilt angle on droplets condensation on hydrophobic surface

Condensation surface modification was an important research direction to realize droprise condensation and erhance heat transfer. In order to explore the condensation process and mechanism of droplets on the hydrophobic surface, the condensation process of droplets on the natural Donghu lotus leaves with tilt angle of 30°,60° and 90° were studied. The results show that the tilt angle had a significant effect on the droplets condensation behavior on Donghu lotus leaves hydrophobic surface. Increasing the tilt angle would short the detachment time of condensate droplets. The growth rate of droplets increased with the increase of hydrophobic surface tilt angle. And the condensation droplets diameter also decreased with the increase of incl ination angle.

In vivo, ex vivo and in vitro Mucoadhesive Strength Assessment of Potential Pharmaceutical Bio-resource Polymer from Diospyros melonoxylon Roxb seeds

In this study, an oral bio-based mucoadhesive polymer was developed from Diospyros melonoxylon Roxb (Ebenaceae) seed mucilage and evaluated for mucoadhesive strength. The mucilage showed shear stress results (0.140 ± 0.0007N), with comparable adhesiveness to HPMC E5 (0.098 ± 0.0008N). Force of adhesion required to detach the seed mucilage and HPMC E5 tablets from the mucin of intestinal tissue were 0.0509 ± 0.0007 (N) and 0.0049 ± 0.0006 (N). Seed mucilage revealed significant higher detachment time, erosion time, in vitro wash off time and ex vivo residence compared to HPMC E5 and lactose tablets (p<0.01). In vivo test indicated that seed mucilage tablets possessed good mucoadhesive strength compared to HPMC E5 and resisted disintegration for ≤ 8 h. The swelling index and wetting time showed comparable results between the mucilage and synthetic polymer tablets. Mucilage demonstrated high moisture absorption, percentage hydration, and matrix erosion of 20.0 ± 0.037, 53.66 ± 0.127, and 20.00 ± 0.077 compared to HPMC E5 10.0 ± 0.079, 36.00 ± 0.089, and 1.26 ± 0.085. The mucoadhesive properties of seeds mucilage were comparable to guar gum and HPMC E5. Thus, seed mucilage of D. melonoxylon can be exploited for usage as pharmaceutical excipient in oral bioadhesive drug delivery systems.

Numerical Study of Formation of a Series of Bubbles from an Orifice by Applying Dynamic Contact Angle Model

The dynamic contact angle model is applied in the formation process of a series of bubbles from Period-I regime to Period-II regime by using the VOF method on a 2D axisymmetric domain. In the first process of the current research, the dynamic contact angle model is validated by comparing the numerical results to the experimental data. Good agreement in terms of bubble shape and bubble detachment time is observed from a lower flow rate Q = 150.8 cm3/min (Re = 54.77, Period-I regime) to a higher flow rate Q = 603.2 cm3/min (Re = 219.07, Period-III regime). The comparison between the dynamic contact angle model and the static contact angle model is also performed. It is observed that the static contact angle model can obtain similar results as the dynamic contact angle model only for smaller gas flow rates (Q ≤ 150.8 cm3/min and Re ≤ 54.77)). For higher gas flow rates, the static contact angle model cannot produce good results as the dynamic contact angle model and has larger relative errors in terms of bubble detachment time and bubble shape.

Bio-based Polymer Isolated from Seeds of Buchanania lanzan Spreng with Potential Use as Pharmaceutical Mucoadhesive Excipient

This study was aimed to develop an oral bio-based mucoadhesive polymer from seeds mucilage of Buchanania lanzan spreng, belongs to family anacardiaceae. Isolated mucilage was evaluated for mucoadhesive strength and compared with existing polymer. The mucilage showed shear stress results (0.099 ± 0.0001N), with comparable adhesiveness to methocel E5 (0.098 ± 0.0008N). Force of adhesion required to detach the seed mucilage and methocel E5 tablets from the mucin of intestinal tissue were 0.0276 ± 0.0019 (N) and 0.0049 ± 0.0006 (N), respectively. Seed mucilage revealed significant (P<0.01) higher detachment time, erosion time, in-vitro wash-off time and ex-vivo residence compared to methocel E5 and lactose tablets. In vivo test indicated that seed mucilage tablets possessed good mucoadhesive strength compared to methocel E5 and resisted disintegration for ≤ 8 h. The swelling index and wetting time showed comparable results between the mucilage and synthetic polymer tablets. Mucilage demonstrated high moisture absorption, percentage hydration, and matrix erosion of 18.57 ± 0.036, 50.00 ± 0.051, and 8.30 ± 0.155 compared to methocel E5 10.0 ± 0.079, 36.00 ± 0.089, and 1.26 ± 0.085, respectively. Mucoadhesive properties of seeds mucilage were comparable to guar gum and methocel E5, thus seed mucilage of B. lanzan can be potentially exploited for usage as a bioadhesive pharmaceutical excipient.

An Investigation on Mechanism of Droplet Generation in High Inertial Gaseous Flow

Droplet generation involving high inertial gas flow in a T-junction microchannel was experimentally and numerically studied in this work. The effect of high inertial flow on the water droplet generation was investigated based on the obtained results. At various gas Reynold (Re) numbers and liquid Capillary (Ca) numbers, the unique flow regime mapping including squeezing, dripping and jetting was observed. It was found that stable aqueous droplets are generated in the squeezing and dripping flow regimes. Visualization experiment shows that the morphology of droplets generated in the water-gas system is different from that in the traditional water-oil system. As the Re number increases or the Ca number decreases, the droplet length decreases. Increasing both Re number and Ca number can increase the detachment frequency. Based on the 3D VOF simulations, the droplet attachment to one of the channel wall during the pinch-off period and the rebound of liquid phase after droplet detachment was observed. Droplet size, detachment time and droplet generation frequency were then analyzed for the droplet generation. The dominant detachment mechanism during the whole droplet generation process was also discussed in this work.

Characterization of Artifact Influence on the Classification of Glucose Time Series Using Sample Entropy Statistics

This paper analyses the performance of SampEn and one of its derivatives, Fuzzy Entropy (FuzzyEn), in the context of artifacted blood glucose time series classification. This is a difficult and practically unexplored framework, where the availability of more sensitive and reliable measures could be of great clinical impact. Although the advent of new blood glucose monitoring technologies may reduce the incidence of the problems stated above, incorrect device or sensor manipulation, patient adherence, sensor detachment, time constraints, adoption barriers or affordability can still result in relatively short and artifacted records, as the ones analyzed in this paper or in other similar works. This study is aimed at characterizing the changes induced by such artifacts, enabling the arrangement of countermeasures in advance when possible. Despite the presence of these disturbances, results demonstrate that SampEn and FuzzyEn are sufficiently robust to achieve a significant classification performance, using records obtained from patients with duodenal-jejunal exclusion. The classification results, in terms of area under the ROC of up to 0.9, with several tests yielding AUC values also greater than 0.8, and in terms of a leave-one-out average classification accuracy of 80%, confirm the potential of these measures in this context despite the presence of artifacts, with SampEn having slightly better performance than FuzzyEn.

Unsteady sheet fragmentation: droplet sizes and speeds

Understanding what shapes the drop size distributions produced from fluid fragmentation is important for a range of industrial, natural and health processes. Gilet & Bourouiba (J. R. Soc. Interface, vol. 12, 2015, 20141092) showed that both the size and speed of fragmented droplets are critical to transmission of pathogens in the agricultural context. In this paper, we study both the size and speed distributions of droplets ejected during a canonical unsteady sheet fragmentation from drop impact on a target of comparable size to that of the drop. Upon impact, the drop transforms into a sheet which expands in the air bounded by a rim on which ligaments grow, continuously shedding droplets. We developed high-precision tracking algorithms that capture all ejected droplets, measuring their size and speed, as well as the detachment time from, and link to, their ligament of origin. Both size and speed distributions of all ejected droplets are skewed. We show that the polydispersity and skewness of the distributions are inherently due to the unsteadiness of the sheet expansion. We show that each ligament sheds a single drop at a time throughout the entire sheet expansion by a mechanism of end-pinching. The droplet-to-ligament size ratio $R\approx 1.5$ remains constant throughout the unsteady fragmentation, and is robust to change in impact Weber number. We also show that the population mean speed of the fragmented droplets at a given time is equal to the population mean speed of ligaments one necking time prior to detachment time.

COMPUTATIONAL DETERMINATION OF THE DETACHMENT TIME OF THE LEUKOCYTE UNDER DIFFERENT KINETIC DISSOCIATION RATE PARAMETERS

Three-dimensional simulation of the leukocyte detachment subjected to blood flow is presented. The initially captured leukocyte is modeled as a sphere adhered to the bottom wall of a cylindrical vessel via receptor/ligand bonds (P-selectin/PSGL-1). Ansys Parametric Design Language is used to create the geometrical model and couple the Navier–Stokes flow solver with structural equations and the Monte Carlo equation to define the stochastic breakage of the bonds. The assumption of equal forces on bonds has been ignored and the force on each bond is obtained from the balance between hydrodynamic forces and cellular viscoelasticity at every time step. In this model, catch-slip behavior of the P-selectin/PSGL-1 is considered by using the two-pathway dissociation model instead of the Bell model to define the rate of dissociation of each bond. Detachment time of the leukocyte is the time elapsed until all the bonds break. The effects of various values of blood inlet velocities, bond stiffness and kinetic properties of the catch bonds on the detachment time of the leukocyte are studied.