Field Effect Transistor-Like Control of Capillaric Flow Using Off-Valves

An important application area of microfluidics is point-of-care devices. Capillaric circuits are a promising technology to realize such devices. Recently, we introduced a capillary action off-valve which adds preprogrammed autonomous “off”-type valving as a unit operation to capillaric circuits. To date, these devices have only been shown to operate in binary mode. However, due to its conceptual symmetry with electronic junction field effect transistors, it was hypothesized that the off-valve was capable of providing analog resistance control. Using an experimental approach, this work demonstrates for the first time that capillary off-valves can operate in analog resistance mode and that flow control results can be fitted using a modified model of the Shockley transistor equation

Capillaric-Field Effect Transistors

Controlling fluid flow in capillaric circuits is a key requirement to increase their uptake for assay applications. Capillary action off-valves provide such functionality by pushing an occluding bubble into the channel using a difference in capillary pressure. Previously, we utilized the binary switching mode of this structure to develop a powerful set of fundamental fluidic valving operations. In this work, we study the transistor-like qualities of the off-valve and provide evidence that these structures are in fact functionally complementary to electronic junction field effect transistors. In view of this, we propose the new term capillaric field effect transistor to describe these types of valves. To support this conclusion, we present a theoretical description, experimental characterization, and practical application of analog flow resistance control. In addition, we demonstrate that the valves can also be reopened. We show modulation of the flow resistance from fully open to pinch-off, determine the flow rate–trigger channel volume relationship and demonstrate that the latter can be modeled using Shockley’s equation for electronic transistors. Finally, we provide a first example of how the valves can be opened and closed repeatedly

3D printing of porous media at the microstructural scale

What is superficially referred to as ‘packing quality’, a myriad of geometrical parameters governing the interrelations between pores, has only been measured post-hoc in the form of separation efficiency. While several computational studies of chromatography bed microstructures have explored the effects of various packing parameters on dispersion, experimental replication and model validation has remained elusive. Additive manufacturing, or 3D printing, offers the opportunity to manufacture porous media composed of micro-structural elements of different shapes and sizes, and to precisely locate and orient them within the bed. For example, spherical beads with a narrow size distribution can be constructed individually at desired locations within the bed, allowing the creation of specific packing arrangements, i.e. perfectly ordered lattices or random packing mimicking conventionally packed chromatography columns. Further opportunities are to create geometric elements with different shapes or sizes and place them at individual locations within the same bed. Alternatively, the structural focus can shift from the solid-phase to the mobile phase, with the design of complex flow channels within a monolithic bed. These observations led us to propose the use of 3D printing as both a chromatography column production method and as a tool to enable fundamental studies of packed bed microstructures. The main challenges to this approach include achieving sufficient printing resolution to compete with current media in terms of theoretical plate height and developing materials that have appropriate internal porosity and surface functionalities to enable high binding capacity and specificity. Other challenges are as for conventional media, for example good swelling properties, low non-specific adsorption, and the absence of toxicity and leaching. Here, we show examples of progress made to date in creating 3D printed chromatography columns. These include i) micro-structural analyses of columns containing porous beds with a variety of lattice arrangements and channel structures, printed at a maximum current printing resolution of 16 µm and ii) comparison of residence time distributions and flow characteristics for a range of columns, including several printed with different integrated flow distributors and column cross-sections. We demonstrate reasonable fidelity between printed and designed columns and identify current limitations with regard to resolution. Finally, we compare packed beds incorporating deliberately introduced imperfections within packing lattices, including a ‘line defect’ that runs the length of the column and a ‘cluster defect’ consisting of localized voids at various locations within the packing. Experimentally determined reduced plate heights are compared with computational fluid dynamics flow studies

A Numerical Investigation of the Hydrodynamic Dispersion in Novel Chromatographic Stationary Phases

3D printed custom chromatographic stationary phases are now a reality. Using the Lattice Boltzmann Method, we compare the chromatographic performance of random packing of monodisperse spheres, open tubular columns (OTC) and stationary phases based on three triply periodic minimal surfaces (TPMS): Schwarz Diamond (SD), Schoen Gyroid (SG) and Schwarz Primitive (SP). Three performance metrics were employed in this comparison: i) reduced plate height, ii) Darcy number, iii) kinetic performance factor. Each simulated geometry was unconfined with an impermeable stationary phase to remove wall effects and pore diffusion. The performance was studied for macro- porosities in the range 0.2 to 0.8, depending on the geometry. OTCs were found to have superior permeability to both random sphere packing and TPMS structures across the entire porosity range. At porosity greater than 0.366, the Schwarz Diamond medium achieved the lowest levels of band broadening and greatest kinetic performance. The reduced plate height of all stationary phase geometries was shown to increase with bed porosity. The kinetic performance was found to increase with porosity for TPMS structures, decrease with porosity for random packing and be independent of porosity for OTCs. This work illustrates that chromatographic stationary phase geometries based on TPMS structures are theoretically competitive with random packing and open tubular columns and their feasibility for practical chromatography should continue to be explored

The selenium jevels of mothers and their neonates using hair, breast milk, meconium, and maternal and umbilical cord blood in van basin

The objective of the present study is to calculate linear regressions between a mother and her child with respect to their selenium concentration (ng/g) in the following traits: maternal blood and umbilical cord blood, maternal and child hair, maternal milk and child umbilical cord blood, maternal milk and meconium, maternal blood plasma, and child meconium. The data were collected at Research Hospital of the University of Yüzüncü Yıl from 30 pairs of mothers and their newborn baby. The mean maternal serum Se level in 30 mothers was 68.52 ± 3.57 ng/g and cord plasma level was 119.90 ± 18.08 ng/g. The Se concentration in maternal and neonatal hair was 330.84 ± 39.03 and 1,124.76 ± 186.84 ng/g, respectively. The Se concentration of maternal milk at day 14 after delivery was determined as 68.63 ± 7.78 ng/g (n = 13) and the concentration of Se was 418.90 ± 45.49 ng/g (n = 22) for meconium of neonatal. There was no significant difference between maternal blood and milk Se levels. However, hair Se concentration was significantly higher than milk and maternal blood Se level. For each trait comparison, the average absolute difference in log10-transformed Se concentration was calculated between a mother and her child. The observed average absolute difference was compared with a test distribution of 1,000 resampled bootstrap averages where the number of samples was maintained but the relationship between a mother and her child was randomized among samples (α = 0.05).H. Sağmanlıgil Özdemir, F. Karadas, A. C. Pappas, P. Cassey, G. Oto and O. Tunce