Influence of the packing heterogeneity on the performance of liquid chromatography supports

Vegetable waste scaffolds for 3D-stem cell proliferating systems and low cost biosensors

Vegetable wastes represent an inexpensive and sustainable source of valuable bioproducts for several applications. Natural micro-porous and fibrous materials can be obtained from a very cheap and abundant cellulosic bio-waste. Here we demonstrated that vegetable waste derivatives can be suitable as scaffolds for biosensors and 3D cell growth. Many studies have been addressed to fabricate biocompatible 3D scaffolds for mammalian stem cells cultures and develop novel systems able to reproduce the complexity of the in vivo microenvironment. Many of these products are proprietary, expensive or require chemical synthesis. The recycling and revaluation of vegetable derived tissues to fabricate scaffolds for analytical biosensors 3D stem cell cultures platforms may represent a very low-cost approach for toxicological and environmental analyses. In this approach, potential applications of vegetable-derived tissue for biosensing and 3D stem cell cultures were investigated. Micro-structured scaffolds from stalk of broccoli, named BrcS, were either functionalized for production of enzymatic 3D-biosensors or preconditioned to be used them as 3D-scaffolds for human mesenchymal stem cells cultures. The conditions to fabricate 3D-biosensors and scaffolds for cell growth were here optimized studying all analytical parameters and demonstrating the feasibility to combine these two properties for an innovative solution to ennoble vegetable wastes.

Performance evaluation of different design alternatives for microfabricated nonporous fused silica pillar columns for capillary electrochromatography

An experimental study comparing the performance of different designs for microfabricated column structures for microchip capillary electrochromatography is presented. The work is a follow-up to our previously published modeling and simulation study on the same topic. Experiments were performed using fused silica microchips with and without octadecyltrimethoxysilane coating for nonretained and retained modes of operation, respectively. Showing the same trends as the modeling results, the foil shape produces a significant decrease in plate height with an increase of around 15% in mobile phase velocity in nonretained measurements of Coumarin 480 (C480). Measured plate heights at 1 kV/cm applied electric field were 0.77, 1.33, and 1.42 μm for foil, diamond, and hexagon, respectively. Chromatographic runs of C480 yielded minimal plate height values of 1.85 and 3.28 μm for foil and diamond, respectively. The optimization of the shape and placement of the structures appeared to have a considerable impact on the achievable performance.

Experimental study of the effect of disorder on DNA dynamics in post arrays during electrophoresis

We used top-down fabrication techniques to create both an ordered hexagonal array and a disordered array of 1 μm diameter cylindrical posts in a silicon dioxide microchannel with the same number of posts per unit area. The electrophoretic mobility and dispersion coefficient of λ DNA in each of the arrays were obtained as a function of the electric field using ensembles of DNA molecules in a double channel device that minimizes experimental artifacts. To deepen our understanding of the transport, we also used fluorescence microscopy to examine the dynamics of single DNA molecules as they interact with the arrays at a fixed value of the electric field. Based on the results of these two types of experiments, we conclude that the electrophoretic mobility is not dependent on the array order but that band broadening in the device is greater in the disordered array.

The dependency of solute diffusion on molecular weight and shape in intact bone

Solute transport through the bone lacunar-canalicular system (LCS) is essential for osteocyte survival and function, but quantitative data on the diffusivity of various biological molecules in the LCS are scarce. Using our recently developed approach based on fluorescence recovery after photobleaching (FRAP), diffusion coefficients of five exogenous fluorescent tracers (sodium fluorescein, dextran-3k, dextran-10k, parvalbumin, and ovalbumin) were measured in murine tibiae in situ. These tracers were chosen to test the dependency of solute diffusion on molecular weight (376-43,000 Da) and shape (linear vs. globular). Among the five tracers, no fluorescence recovery (and thus mobility) was detected for dextran-10k and the diffusion coefficients (D(LCS)) of the other four tracers were 295+/-46, 128+/-32, 157+/-88, 65+/-21 microm(2) s(-1) in the LCS, respectively. Overall, the rate of solute diffusion in the bone LCS showed strong dependency on molecular size and shape. Diffusivity decreased with increasing molecular weight for both linear and globular molecules, with the linear molecules decreasing at a faster rate. Compared with free diffusion (D(free)) in aqueous solutions, the relative diffusivities (D(LCS)/D(free)) of the four tracers were not significantly different for sodium fluorescein, dextran-3k, parvalbumin, and ovalbumin (55.0+/-8.6%, 68.1+/-17.0%, 79.7+/-44.7%, 61.0+/-19.6%, respectively). This result did not agree with the homogenous molecular sieve model proposed for the osteocytic pericellular matrix structure. Instead, a heterogeneous porous model of the pericellular matrix may account for the observed solute transport in the LCS. In summary, the present study provides quantitative data on diffusion of various nutrients and signaling molecules in the LCS that are important for bone metabolism and mechanotransduction.

Understanding and design of existing and future chromatographic support formats

The present contribution reviews the use of alternative support formats as a means to surpass the chromatographic performance of the packed bed of spheres. First, a number of idealized structures are considered to obtain a general insight in how the performance of a chromatographic support depends on its shape and size, using the isocratic peak-capacity generation speed as the main performance indicator. Using this criterion, it is found that the packing density or, equivalently, the external porosity, is the most important of all geometrical shape factors. Depending on whether the sample consists of weakly or strongly retained components, the optimal external porosity can be expected to vary between 60% and a value near 100%. The optimal exploitation of a high external porosity, however, also requires overall shrinkage of the domain size, towards and into the sub-micron range. With the current fabrication technologies, this requirement seems difficult to achieve. In the presence of a lower limit on the characteristic support size, each range of desired plate numbers or peak capacities has its own optimal external porosity, ranging from a very low value (high packing density) for high speed, small peak capacity applications, to very high external porosities (low packing density) for applications requiring a very large peak capacity. Subsequently, the obtained theoretical insights are used to review and discuss the past and current research on alternative support formats. Finally, a number of emerging micro- and nano-fabrication technologies are introduced and their potential for the future production of supports with improved shape and homogeneity is discussed.

Pressure-driven reverse-phase liquid chromatography separations in ordered nonporous pillar array columns

Building upon the micromachined column idea proposed by the group of Regnier in 1998, we report on the first high-resolution reversed-phase separations in micromachined pillar array columns under pressure-driven LC conditions. A three component mixture could be separated in 3 s using arrays of nonporous silicon pillars with a diameter of approximately 4.3 microm and an external porosity of 55%. Under slightly retained component conditions (retention factor k' = 0.65-1.2), plate heights of about H = 4 microm were obtained at a mobile phase velocity around u = 0.5 mm/s. In reduced terms, such plate heights are as low as hmin = 1. Also, since the flow resistance of the column is much smaller than in a packed column (mainly because of the higher external porosity of the pillar array), the separation impedance of the array was as small as E = 150, i.e., of the same order as the best currently existing monolithic columns. At pH = 3, yielding very low retention factors (k' = 0.13 and 0.23), plate heights as low as H = 2 microm were realized, yielding a separation of the three component mixture with an efficiency of N = 4000-5000 plates over a column length of 1 cm. At higher retention factors, significantly larger plate heights were obtained. More experimental work is needed to investigate this more in depth. The study is completed with a discussion of the performance limits of the pillar array column concept in the frame of the current state-of-the-art in microfabrication precision.

Domain Size-Induced Heterogeneity as Performance Limitation of Small-Domain Monolithic Columns and Other LC Support Types

We have computed the band broadening and the flow resistance in a series of apparently self-similar porous LC support structures, all having the same mean geometric ratios and external porosity, but with a decreasing scale and disturbed by a scale-independent variance on the size and position of the porous solid zone elements. The study shows in a general and qualitative way that each type of LC support that is produced using a manufacturing process displaying a fixed (i.e., domain-size independent) variance on the size and position of the produced solid zone elements will eventually encounter a limit beyond which a further reduction of the domain size can no longer be expected to yield a significant gain in separation speed. This is currently observed in practice for silica monoliths and could also compromise the performance of photolithographically etched columns.