Effects of Viscosities and Solution Composition on Core-Sheath Electrospun Polycaprolactone(PCL) Nanoporous Microtubes

Vascularization for tissue engineering applications has been challenging over the past decades. Numerous efforts have been made to fabricate artificial arteries and veins, while few focused on capillary vascularization. In this paper, core-sheath electrospinning was adopted to fabricate nanoporous microtubes that mimic the native capillaries. The results showed that both solution viscosity and polyethylene oxide (PEO) ratio in polycaprolactone (PCL) sheath solution had significant effects on microtube diameter. Adding PEO into PCL sheath solution is also beneficial to surface pore formation, although the effects of further increasing PEO showed mixed results in different viscosity groups. Our study showed that the high viscosity group with a PCL/PEO ratio of 3:1 resulted in the highest average microtube diameter (2.14 µm) and pore size (250 nm), which mimics the native human capillary size of 1–10 µm. Therefore, our microtubes show high potential in tissue vascularization of engineered scaffolds.

Highly photocatalytic activity of natural halloysite - based material for the treatment of dyes in wastewater

In this study, the halloysite nanotube material will be fabricated from a natural halloysite mineral and used as a support for the photocatalytic activity phase based on TiO2. The material is characterized by modern physicochemical methods such as XRD, SEM, BET, UV - vis spectrum, and EDX. Accordingly, the refined halloysite has a nanoscale with a length of about 1.3 μm and a capillary size of about 5 nm. After the deposition of Ag - TiO2 on the halloysite, the specific surface of the material measured by the BET method was about 60 m2/g, and the structure of the halloysite was intact. The band - gap energy of as - prepared materials is also significantly improved in comparison to pure TiO2, makes the material capable of absorbing longer wavelengths of light in the photocatalytic process. The Photocatalyst based on Halloysite and TiO2 showed very high efficiency, up to more than 95% in the decomposition of typical organic pollutant RR - 195. This result shows great potential in this novel material in environmental treatment applications.

Modeling Unsteady Bénard-Marangoni Instabilities in Drying Volatile Droplets on a Heated Substrate

We study unsteady internal flows in a sessile droplet of capillary size evaporating in constant contact line mode on a heated substrate. Three-dimensional simulations of internal flows in evaporating droplets of ethanol and silicone oil have been carried out. For describing the Marangoni flows we find it necessary to account for the diffusion of vapor in air, the thermal conduction in all three phases and thermal radiation. The equations have been solved numerically by finite element method using ANSYS Fluent. As a result of the simulations, the nonstationary behavior of Bénard-Marangoni (BM) instabilities is obtained. At the first stage, a flower structure of BM cells near the triple line emerge. For smaller contact angles, the cells grow in size and occupy the central region of the droplet surface. Being closely connected with recent experimental and theoretical studies, the results obtained help to analyze and resolve the associated issues.

Capabilities and Limitations of Fire-Shaping to Produce Glass Nozzles

Microfluidic devices for drop and emulsion production are often built using fire-shaped (or fire-polished) glass nozzles. These are usually fabricated manually with inexpensive equipment. The shape limitations and poor reproducibility are pointed as the main drawbacks. Here, we evaluate the capabilities of a new fire-shaping approach which fabricates the nozzle by heating a vertical rotating capillary at the Bottom of a Lateral Flame (BLF). We analyze the effect of the heating conditions, and the capillary size and tolerances. The shape reproducibility is excellent for nozzles of the same size produced with the same conditions. However, the size reproducibility is limited and does not seem to be significantly affected by the heating conditions. Specifically, the minimum neck diameter standard deviation is 3%. Different shapes can be obtained by changing the heating position or the capillary dimensions, though, for a given diameter reduction, there is a minimum nozzle length due to the overturning of the surface. The use of thinner (wall or inner diameter) capillaries allows producing much shorter nozzles but hinders the size reproducibility. Finally, we showed an example of how the performance of a microfluidic device is affected by the nozzle shape: a Gas Dynamic Virtual Nozzle (GDVN) built with a higher convergent rate nozzle works over a wider parametric range without whipping.

FORMALIZATION OF THE CONCEPT OF A SLIT CAPILLARY TAKING INTO ACCOUNT THE CONTACT ANGLE OF WETTING

Расчеты процессов распределения и переноса жидкости в пористых средах осуществляют, принимая во внимание ее капиллярные свойства в поровом пространстве. С учетом выведенной нами ранее расчетной формулы для предельного размера капилляра с круглым поперечным сечением, краевого угла смачивания и параметра удельного поверхностного натяжения получена расчетная формула предельного размера для капилляров с щелевым и кольцевым сечением. Установлено, что полученные расчетные формулы предельных размеров для трубчатых капилляров щелевого плоского и кольцевого сечения с учетом краевого угла смачивания идентичны. Отличие формул для капилляров с щелевым и кольцевым сечением от формулы для капилляра круглого поперечного сечения определено только функцией, зависящей от краевого угла смачивания. Значения предельных размеров капилляров с щелевым сечением на 10–17,5% меньше, чем капилляра с круглым сечением. Поверхность отклика позволила оценить влияние удельного поверхностного натяжения и функции краевого угла смачивания на изменение величины предельного размера капилляров. Результаты исследований могут быть использованы для повышения эффективности расчетов тепломассообмена в пористых средах в пищевых производствах и других аналогичных задач. The calculations of the processes of saturation and transfer of fluid in porous media are based on taking into account of its capillary properties in the pore space. Given our previously derived formulas for the maximum amount of capillary with a circular transverse section, wetting angle and parameter specific surface tension obtained calculation formula size limit for capillaries with a slit and annular transverse section. It is established that the obtained calculation formulas of the limit sizes for tubular capillaries of slotted flat and annular section with the account of the wetting edge angle are identical. The difference between the formulas for capillaries with slotted and annular section and the formula for a capillary with a circular transverse section is determined only by a function that depends on the wetting edge angle. The values of the limit sizes of capillaries with a slotted transverse section are 10–17,5% less than those of a capillary with a circular transverse section. The response surface allowed us to evaluate the effect of specific surface tension and the function of the wetting edge angle on the change in the capillary size limit. The research results can be used to improve the efficiency of calculations of heat and mass transfer in porous media in food production and other similar tasks.

Hydrodynamics of Liquid Motion in Straight-Line Capillaries

The paper considers the mathematical model of liquid motion in straight-line capillaries. The proposed mathematical model shows the liquid motion in slit-like capillaries, with regard to the density, viscosity and surface tension of liquids, the capillary size, and the angle of capillary inclination to the horizontal. The modeling results are proved by full-scale experiments.