Modified in-vitro AATCC-100 procedure to measure viable bacteria from wound dressings.

Chronic wounds are reoccurring healthcare problems in the United States and cost up to $50 billion annually. Improper wound care results in complications such as wound debridement, surgical amputation, and increased morbidity/ mortality due to opportunistic infections. To eliminate wound infections, many antimicrobial dressings are developed and submitted to FDA for evaluation. AATCC-100 is a standard method widely used to evaluate cloth wound dressings. This method, requires enrichment, followed by culturing to measure the concentration of culturable organisms; a caveat to this method could result in neglected viable but nonculturable (VBNC) bacteria and overestimate the antimicrobial properties of wound dressings. Therefore, the objectives of this study were to assess this accepted protocol with quantitative real-time polymerase chain reaction (qRT-PCR), to measure time dependent antimicrobial efficacy of wound dressing, and to examine for potential viable bacteria but non-culturable as compared with traditional plating methods. The test organisms included opportunistic pathogens: Pseudomonas aeruginosa (ATCC 15692) and Staphylococcus aureus (ATCC 43300). To mimic a wound dressing environment, samples of commercially available wound dressings (McKesson Inc.) with silver ion (positive control) and dressings without silver ion (positive control) were assessed under sterile conditions. All samples were examined by the original protocol (the extended AATCC-100 method) and qRT-PCR. The expression of specific housekeeping genes was measured (proC for P. aeruginosa and 16s rRNA for S. aureus). Based on these tests, log reduction of experimental conditions was compared to identify time dependent and precise antimicrobial properties from wound dressing samples. These results showed antimicrobial properties of wound dressings diminished as incubation days are increased for both methods from day 1 PCR result of 4.31 ± 0.54 and day 1 plating result of 6.31 ± 3.04 to day 3 PCR result of 1.22 ± 0.97 and day 3 plating result of 5.89 ± 2.41. These results show that data from qRT-PCR generally produced lower standard deviation than that of culture methods, hence shown to be more precise. Complementary parallel analysis of samples using both methods better characterized antimicrobial properties of the tested samples.

Pattern of adsorption isotherms in Ono-Kondo coordinates.

The Ono-Kondo lattice density functional theory is used to analyze adsorbate-adsorbate interactions for supercritical systems. In prior work, this approach has been used to study intermolecular interactions in subcritical adsorbed phases, and this has included the study of adsorbate-adsorbate repulsions in the regime of adsorption compression. In this paper, we present the general pattern of adsorption isotherms in Ono-Kondo coordinates; this has not been done in the past. For this purpose, experimental isotherms for adsorption of supercritical fluids (including nitrogen, methane, and carbon dioxide) are plotted in Ono-Kondo coordinates. In addition, we performed Grand Canonical Monte Carlo simulations of adsorption for Lennard-Jones molecules and plotted isotherms in Ono-Kondo coordinates. Our results indicate a pattern of isotherms with regimes of adsorbate-adsorbate attractions at low surface coverage and adsorbate-adsorbate repulsions at high surface coverage. When the generalized Ono-Kondo model is used over a wide range of pressures - from low pressures of the Henry's law regime to supercritical pressures - the slope of the isotherm varies from positive at low pressures to negative at high pressures. The linear sections of these graphs show when the adsorbate-adsorbate interaction energies are approximately constant. When these linear sections have negative slopes, it indicates that the system is in a state of adsorption compression.

Thermodynamic driving force for diffusion: comparison between theory and simulation.

In previous work, lattice density functional theory equations have been recast into differential form to determine a property whose gradient is universally proportional to the diffusive flux. For color counter diffusion, this property appears as the impingement rate onto vacancies and molecules of a species whose density gradient can be influenced by diffusion. Therefore, the impingement rate of a diffusing molecule depends on the mobility of its surroundings. In order to determine the validity of this finding, molecular dynamics simulations of color counter diffusion were performed in which the mobility of the solvent was varied to determine if the flux of the diffusing species responded to the change when all other factors, such as density gradient, available volume, and temperature are held constant.

Anisotropic mean free path in simulations of fluids traveling down a density gradient.

Hard sphere molecular dynamics simulations are used to study the mean free path of molecules traveling down a density gradient at fluid densities ranging between 0.05sigma(-3) and 0.7sigma(-3). Gradients are developed using semipermeable boundaries in the x-direction and, as a result, a net flow develops in the positive x-direction. Over the course of the simulation, the free paths of colliding molecules are calculated and it was determined that the mean free path in the positive x-direction is greater than the mean free path in the negative x-direction at each density studied. These results are compared to the mean free paths in the positive and negative y- and z-directions (in which there is no net flow) and the distribution of free paths for molecules traveling in the positive and negative x-directions gives insight into the physics of the system. In addition, the dependency of the mean free path on speed is studied and compared to kinetic theory predictions. The results have application in the modification of the classical model of diffusion for low density systems undergoing flow in which the mean free path is finite, large, and can be anisotropic.

Self-assembly of T-structures in molecular fluids.

A lattice density functional approach is used to describe the equilibrium assembly of three types of anisotropic patchy particles into a T-structure. The T-structure is comprised of one three-patch, three two-patch, and three one-patch particles. All patches are positioned orthogonal to each other. Temperature, particle concentration, and interaction energy ranges are determined that lead to T-structure formation. T-structure formation is investigated for two types of two-patch particles: Case 1 uses two identical patches and Case 2 employs two differing patches. Sets of parameters leading to T-structure assembly are determined for both cases. We find that in Case 1 the symmetric two-patch particle enforces T-structure formation, while the asymmetric two-patch particle in Case 2 leads to formation of chains, dimers, and incorrect and extended T-structures in addition to the T-structure. Synthetic strategies for both cases are discussed and reveal that Case 2 presents the more straightforward synthetic route.

Modeling fluid diffusion using the lattice density functional theory approach: counterdiffusion in an external field.

The dependence of the diffusivity on temperature, pressure, and composition is not understood well; consequently, data is preferred significantly over correlations in most practical situations. Even in dilute gases, the contributions of attractions and repulsions to the diffusivity are difficult to understand on a molecular level without performing simulations. We have developed a Lattice Density Functional Theory (LDFT) approach for modeling diffusion to supplement existing methods that are very rigorous but computationally demanding. The LDFT approach is analogous to the van der Waals equation in how it accounts for molecular interactions in that it has first-order corrections to ideal behavior; it is an extension of the Equilibrium LDFT for adsorption and phase behavior. In this work, the LDFT approach is presented and demonstrated by modeling the problem of color counterdiffusion in an externally-applied potential field. This potential field, in combination with the intermolecular potential function, creates a diffusion regime in which repulsions cause oscillations in the density profile. Using the LDFT approach, the oscillations were described and attributed to nearest-neighbor and next nearest-neighbor interactions. The LDFT approach gives qualitative and quantitative agreement with dual control-volume Grand Canonical Molecular Dynamics simulations.

Cosorption effect in gas chromatography: flow fluctuations caused by adsorbing carrier gases.

Adsorbing carrier gases have a number of advantages in analytical and preparative gas chromatography, such as clearer detector signals and higher column efficiencies. This work shows that adsorbing carrier gases also may be useful because they cause the mobile phase flow rate to become unsteady after injecting a small amount of sample. This work shows that a 100 microL sample of helium can liberate enough carbon dioxide carrier gas from a zeolite 5A packed column at 373 K, that the departure from the steady-state flow rate had an upper lobe area of 586 microL of carrier gas. This was confirmed by coupling a modified Langmuir kinetic model with the Ergun equation.

Lattice density functional theory of molecular diffusion.

A density functional theory of diffusion is developed for lattice fluids with molecular flux as a functional of the density distribution. The formalism coincides exactly with the generalized Ono-Kondo density functional theory when there is no gradient of chemical potential, i.e., at equilibrium. Away from equilibrium, it gives Fick's first law in the absence of a potential energy gradient, and it departs from Fickian behavior consistently with the Maxwell-Stefan formulation. The theory is applied to model a nanopore, predicting nonequilibrium phase transitions and the role of surface diffusion in the transport of capillary condensate.

Adsorption-Energy Distribution of Heterogeneous Surfaces Predicted by Projections onto Convex Sets.

The method of projections onto convex sets (POCS) is used to calculate the adsorption-energy distribution function from the adsorption integral (using a modified Langmuir local isotherm) for energetically heterogeneous surfaces. The POCS method, originally developed in the 1960s, has been successfully applied for many years to estimation problems, mainly in the fields of image processing, signal recovery, and optics. It allows one to incorporate into an iteration scheme available information about the experimental data and the measurement error as well as a priori constraints (such as nonnegativity) based on physical reasoning. It is important to note that the POCS method does not lead to a unique "optimum" solution. Rather, a feasible solution that is consistent with all imposed contraints is found within a "solution space". The "size" of this solution space depends on how large the measurement errors are; it also depends on the accuracy of the error statistics and the number and significance of a priori constraints used. In several examples, the POCS method is used to recover energy distributions from simulated adsorption data containing normally distributed errors. The excellent recoveries obtained demonstrate the value of the POCS method as a robust and reliable tool for adsorption-integral inversions. Copyright 2001 Academic Press.