James E. Maneval

NMR imaging in the study of diffusion of water in foods

Abstract Most studies of moisture transport in foods and related polymeric materials have of necessity been integral experiments, for instance, the characterization of the drying of a food from the drying rate data only. Integral data are often insufficient to allow the investigation of the underlying physics of moisture transport, particularly in heterogeneous systems such as foods. Magnetic resonance imaging makes it possible to resolve spatially and temporally both moisture saturation and water self-diffusion coefficients. This information can then be used to determine effective transport coefficients, material structure, and material properties, and additionally to assist in the study of physicochemical processes. Classical characterizations of moisture transport in food systems have employed integral techniques such as sorption-desorption or gravimetric analysis. These studies have proven useful for control of industrial processes, although they have failed to provide detailed insight or information on the role of material structure and properties in moisture transport. Magnetic resonance imaging is a new technology capable of providing measurements of component saturations and material properties on a spatially resolved basis. Through analysis and interpretation of magnetic resonance imaging measurements it is possible to map internal structure, internal variations in transport rates, and internal variations in material properties such as membrane permeabilities. Nuclear magnetic resonance and magnetic resonance imaging can be utilized to measure the transport of mass by measuring molecular diffusion coefficients and/or by measuring internal gradients in component saturations. These two different data sets can then be applied to estimating the structure and properties of the material under study. This paper presents an introduction to magnetic resonance and outlines the strategy for characterizing moisture transport in food materials using magnetic resonance saturation profiles and self-diffusion measurements.

NMR velocity phase encoded measurements of fibrous suspensions

Nuclear magnetic resonance (NMR) imaging is a noninvasive technique that allows velocity measurement in systems where classical techniques are not suitable due either to opacity or the presence of a solid phase. NMR velocity phase encode measurements for the flow of fiber suspensions yield quantitative data for the average flow field in the suspensions and qualitative information on the microscopic nature of the flow. Bulk translational motion causes modulation of the phase of the sample magnetization which provides information on the average velocity field within the sample. Motions on spatial and time scales that are small relative to the measurement scales cause damping of the magnetization, as reflected by signal attenuation.

Influence of adsorption on phenol transport through soil-bentonite vertical barriers amended with activated carbon.

The potential for enhanced containment of phenol by soil-bentonite (SB) vertical barriers amended with activated carbon (AC) was investigated. Results of batch equilibrium adsorption tests on model SB backfills amended with 0-10 wt.% granular AC (GAC) or powdered AC (PAC) illustrate that the backfills exhibited nonlinear adsorption behavior that was described well by both the Freundlich and Tóth adsorption models. The AC amended backfills exhibited enhanced phenol adsorption relative to unamended backfill due to hydrophobic partitioning to the AC. Adsorption capacity increased with increasing AC content but was insensitive to AC type (GAC versus PAC). Results of numerical transport simulations based on the measured adsorption behavior show that the Tóth model yielded similar or lower phenol breakthrough times than the Freundlich model for the range of source concentrations (C(o)) considered in the simulations (0.1-10 mg/L). Breakthrough time decreased with increasing C(o) but increased with increasing AC content. Predicted breakthrough times for an SB vertical barrier amended with 2-10 wt.% AC increased by several orders of magnitude relative to the theoretical case of a nonreactive (non-adsorbing) barrier. The findings suggest that AC may be a highly effective adsorption amendment for sustaining the containment performance of SB vertical barriers.

Critical review of coupled flux formulations for clay membranes based on nonequilibrium thermodynamics

Extensive research conducted over the past several decades has indicated that semipermeable membrane behavior (i.e., the ability of a porous medium to restrict the passage of solutes) may have a significant influence on solute migration through a wide variety of clay-rich soils, including both natural clay formations (aquitards, aquicludes) and engineered clay barriers (e.g., landfill liners and vertical cutoff walls). Restricted solute migration through clay membranes generally has been described using coupled flux formulations based on nonequilibrium (irreversible) thermodynamics. However, these formulations have differed depending on the assumptions inherent in the theoretical development, resulting in some confusion regarding the applicability of the formulations. Accordingly, a critical review of coupled flux formulations for liquid, current, and solutes through a semipermeable clay membrane under isothermal conditions is undertaken with the goals of explicitly resolving differences among the formulations and illustrating the significance of the differences from theoretical and practical perspectives. Formulations based on single-solute systems (i.e., uncharged solute), single-salt systems, and general systems containing multiple cations or anions are presented. Also, expressions relating the phenomenological coefficients in the coupled flux equations to relevant soil properties (e.g., hydraulic conductivity and effective diffusion coefficient) are summarized for each system. A major difference in the formulations is shown to exist depending on whether counter diffusion or salt diffusion is assumed. This difference between counter and salt diffusion is shown to affect the interpretation of values for the effective diffusion coefficient in a clay membrane based on previously published experimental data. Solute transport theories based on both counter and salt diffusion then are used to re-evaluate previously published column test data for the same clay membrane. The results indicate that, despite the theoretical inconsistency between the counter-diffusion assumption and the salt-diffusion conditions of the experiments, the predictive ability of solute transport theory based on the assumption of counter diffusion is not significantly different from that based on the assumption of salt diffusion, provided that the input parameters used in each theory are derived under the same assumption inherent in the theory. Nonetheless, salt-diffusion theory is fundamentally correct and, therefore, is more appropriate for problems involving salt diffusion in clay membranes. Finally, the fact that solute diffusion cannot occur in an ideal or perfect membrane is not explicitly captured in any of the theoretical expressions for total solute flux in clay membranes, but rather is generally accounted for via inclusion of an effective porosity, n(e), or a restrictive tortuosity factor, τ(r), in the formulation of Ficks first law for diffusion. Both n(e) and τ(r) have been correlated as a linear function of membrane efficiency. This linear correlation is supported theoretically by pore-scale modeling of solid-liquid interactions, but experimental support is limited. Additional data are needed to bolster the validity of the linear correlation for clay membranes.

Advancement in the modeling of pressure-flow for the guidance of development and scale-up of commercial-scale biopharmaceutical chromatography

This paper details the advancements made in the modeling of open column and packed bed pressure-flow. The theoretical description is a one-dimensional elasticity model. By accounting for the loss of intra-particle porosity through empiricism, and by systematically selecting the functional form of the elastic modulus from stress-strain data, this model can accurately predict several kinds of large-scale behavior from small-scale data: packed pressure-flow, open column pressure-flow, and critical velocity. The robustness of the model has been demonstrated for MabSelect, SP 650M, Butyl Sepharose 4 FF and several other agarose-based and polymethacrylate-based resins. The predicted critical velocities are on average within +/-5% of observations. A simple modification to the Blake-Kozeny permeability expression allows accurate prediction of packed bed pressure-flow explicitly from compression factor, packed bed height, and settled bed inter-particle porosity. The model provides limits on mobile phase velocity and on operating pressure-flow as a function of bed height, particle size, and resin rigidity, and allows exploration of commercial manufacturing scenarios to identify scalable process time and cycle number.

Mechanical Deformation of Compressible Chromatographic Columns

A one‐dimensional model of mechanical deformation of compressible chromatography columns is presented. The model is based on linear elasticity and continuum mechanics and is compared to a more complete two‐dimensional model and one‐dimensional porosity profiles measured by NMR imaging methods. The model provides a quantitative description of compression and the effects of wall support during scale‐up. A simple criterion for the significance of wall support as a function of both diameter and length is also developed. Although the model accounts only for mechanical deformation, flow compression can be included, and validation presented here suggests that a more complete model may be valuable for anticipating the effects of scale and aspect ratio on pressure‐flow behavior of compressible columns.

Toward a Robust Model of Packing and Scale‐Up for Chromatographic Beds. 2. Flow Packing

We developed and evaluated a model for predicting the flow packing of nonrigid chromatographic resins. The model is based on elasticity theory and accounts for resin rigidity and column diameter. When a modulus determined from a standard mechanical compression (consolidation) test is used, the model captures the primary phenomena of the scale‐up process. However, moduli determined from flow‐packing experiments improve the accuracy of the predictions and show that the apparent rigidity of chromatographic resins is lower for flow packing than for mechanical compression. Using a modulus from flow‐packing experiments provided quantitative scale‐up predictions of flow packing carried out in columns with diameters between 200 and 450 mm at different locations and by different operators.

Magnetic resonance analysis of capillary formation reaction front dynamics in alginate gels

The formation of heterogeneous structures in biopolymer gels is of current interest for biomedical applications and is of fundamental interest to understanding the molecular level origins of structures generated from disordered solutions by reactions. The cation‐mediated physical gelation of alginate by calcium and copper is analyzed using magnetic resonance measurements of spatially resolved molecular dynamics during gel front propagation. Relaxation time and pulse‐field gradient methods are applied to determine the impact of ion front motion on molecular translational dynamics. The formation of capillaries in alginate copper gels is correlated to changes in translational dynamics. Copyright

A Microfluidic Method to Measure Small Molecule Diffusion in Hydrogels

Drug release from a fluid-contacting biomaterial is simulated using a microfluidic device with a channel defined by solute-loaded hydrogel; as water is pumped through the channel, solute transfers from the hydrogel into the water. Optical analysis of in-situ hydrogels, characterization of the microfluidic device effluent, and NMR methods were used to find diffusion coefficients of several dyes (model drugs) in poly(ethylene glycol) diacrylate (PEG-DA) hydrogels. Diffusion coefficients for methylene blue and sulforhodamine 101 in PEG-DA calculated using the three methods are in good agreement; both dyes are mobile in the hydrogel and elute from the hydrogel at the aqueous channel interface. However, the dye acid blue 22 deviates from typical diffusion behavior and does not release as expected from the hydrogel. Importantly, only the microfluidic method is capable of detecting this behavior. Characterizing solute diffusion with a combination of NMR, optical and effluent methods offer greater insight into molecular diffusion in hydrogels than employing each technique individually. The NMR method made precise measurements for solute diffusion in all cases. The microfluidic optical method was effective for visualizing diffusion of the optically active solutes. The optical and effluent methods show potential to be used to screen solutes to determine if they elute from a hydrogel in contact with flowing fluid. Our data suggest that when designing a drug delivery device, analyzing the diffusion from the molecular level to the device level is important to establish a complete picture of drug elution, and microfluidic methods to study such diffusion can play a key role.

Flow velocity maps measured by nuclear magnetic resonance in medical intravenous catheter needleless connectors

&NA; This work explains the motivation, advantages, and novel approach of using velocity magnetic resonance imaging (MRI) for studying the hydrodynamics in a complicated structural biomedical device such as an intravenous catheter needleless connector (NC). MRI was applied as a non‐invasive and non‐destructive technique to evaluate the fluid dynamics associated with various internal designs of the NC. Spatial velocity maps of fluid flow at specific locations within these medical devices were acquired. Dynamic MRI is demonstrated as an effective method to quantify flow patterns and fluid dynamic dependence on structural features of NCs. These spatial velocity maps could be used as a basis for groundtruthing computational fluid dynamics (CFD) methods that could impact the design of NCs.