Susan J. Muller

Roles of epithelial cell-derived periostin in TGF-β activation, collagen production, and collagen gel elasticity in asthma

Periostin is considered to be a matricellular protein with expression typically confined to cells of mesenchymal origin. Here, by using in situ hybridization, we show that periostin is specifically up-regulated in bronchial epithelial cells of asthmatic subjects, and in vitro, we show that periostin protein is basally secreted by airway epithelial cells in response to IL-13 to influence epithelial cell function, epithelial–mesenchymal interactions, and extracellular matrix organization. In primary human bronchial epithelial cells stimulated with periostin and epithelial cells overexpressing periostin, we reveal a function for periostin in stimulating the TGF-β signaling pathway in a mechanism involving matrix metalloproteinases 2 and 9. Furthermore, conditioned medium from the epithelial cells overexpressing periostin caused TGF-β–dependent secretion of type 1 collagen by airway fibroblasts. In addition, mixing recombinant periostin with type 1 collagen in solution caused a dramatic increase in the elastic modulus of the collagen gel, indicating that periostin alters collagen fibrillogenesis or cross-linking and leads to stiffening of the matrix. Epithelial cell-derived periostin in asthma has roles in TGF-β activation and collagen gel elasticity in asthma.

An interlaboratory comparison of measurements from filament-stretching rheometers using common test fluids

Following development of a filament-stretching extensional rheometer at Monash University, similar rheometers have been designed and built in other laboratories. To help validate the basic technique, a collaborative program was undertaken to compare results from several instruments. First, three test fluids prepared at the University of California at Berkeley were characterized in steady and transient shear flows there and at the Massachusetts Institute of Technology (M.I.T.), and then tested in extensional rheometers at M.I.T., Monash and the University of Toronto. Each fluid is a constant-viscosity solution of narrow-molecular-weight-distribution polystyrene dissolved in oligomeric polystyrene. The solute molecular weights are 2.0, 6.5, and 20 million g/mol, and the polymer concentration in each fluid is 0.05 wt. %. From linear viscoelastic measurements, the Zimm relaxation times of the fluids are found to be 3.7, 31, and 150 s, respectively. The scaling of relaxation times with molecular weight indicat...

Wettability of silicone-hydrogel contact lenses in the presence of tear-film components

Introduction. Modern application of soft contact lenses demands safe and comfortable wear over extended time periods up to one month. Lenses that exhibit and sustain complete water wetting allow thick tear-film deposition, minimize film rupture, and permit smooth tear recovery upon lid closure. Water contact angles determined using an air bubble captive on a lens best gauge the in-vivo wetting state. To achieve highly water wetting lenses demands that contact-angle hysteresis be eliminated and that the advancing and receding angles both approach zero. Since lens wear exposes the anterior surface to tear proteins, lens wettability should be measured in the presence of tear-film components. Methods. A captive-bubble technique is applied to measure the advancing and receding contact angles of two commercial silicone-hydrogel lenses: PureVision (PV) and Focus Night & Day (CF) and a standard HEMA (hydroxethyl-methacrylate) hydrogel lens: Acuvue (AV). In the captive-bubble method, an air bubble immersed in aqueous solution is brought into contact with the contact lens. The contact angle through water during bubble expansion yields the receding angle. Bubble contraction gives the water advancing angle. Contact-angle hysteresis is the difference between the advancing and receding angles. Results. In isotonic solution, all three lenses display considerable contact-angle hysteresis with advancing angles of almost 90°. When lysozyme and/or mucin were added to the aqueous solution, hysteresis was eliminated, and equivalent and high water wetting was achieved for the three lenses. Only the advancing angle in isotonic solution provided discriminating evidence for differences in surface chemistry. Covalent attachment of polyethyleneglygol (PEG) to the PV lens surface achieved complete water wetting independent of the presence of tear protein in the solution. Conclusions. The captive-bubble technique provides contact angles that are relevant to on-eye lens wear. Both advancing and receding contact angles are important to lens wettability performance. When lysozyme and/or mucin are present in the solution, PV, CF, and AV lenses display low advancing and receding contact angles indicative of equivalent wettability performance. This result is due to molecular adsorption of the proteins onto the lens external surface. Covalently attached PEG on the PV lens not only provides complete water wetting but also minimizes or even eliminates protein adsorption.

Convergence of a regularization method for creeping flow of a Bingham material about a rigid sphere

Abstract Creeping flow around a solid sphere is solved numerically using two regularized constitutive equations that approximate a Bingham material. The yield surface cannot be easily established from contours of the yield stress obtained with finite values of the regularization parameter due to numerical constraints. The outer yield surface can be estimated from the values of the normalized second invariant of the deformation rate that are invariant with respect to the regularization parameter, and the limiting solution for creeping flow of a Bingham material about a rigid sphere appears to be achieved.

Microfluidic four-roll mill for all flow types

A microfluidic four-roll mill device that can cover the entire spectrum of flow types including purely rotational flow was designed using pseudo-three-dimensional simulations. In experiments using high aspect ratio devices etched in silicon, the authors observed the whole range of flow type by changing only the flow rate ratio. This microfluidic four-roll mill device can be applied to examining microdrop deformation and the dynamics of single molecules in a mixed flow or to enhancing mixing efficiency by sinusoidal changes of the inlet flow rate.

Ex Vivo Sputum Analysis Reveals Impairment of Protease-dependent Mucus Degradation by Plasma Proteins in Acute Asthma

RATIONALE Airway mucus plugs, composed of mucin glycoproteins mixed with plasma proteins, are an important cause of airway obstruction in acute severe asthma, and they are poorly treated with current therapies. OBJECTIVES To investigate mechanisms of airway mucus clearance in health and in acute severe asthma. METHODS We collected airway mucus from patients with asthma and nonasthmatic control subjects, using sputum induction or tracheal aspiration. We used rheological methods complemented by centrifugation-based mucin size profiling and immunoblotting to characterize the physical properties of the mucus gel, the size profiles of mucins, and the degradation products of albumin in airway mucus. MEASUREMENTS AND MAIN RESULTS Repeated ex vivo measures of size and entanglement of mucin polymers in airway mucus from nonasthmatic control subjects showed that the mucus gel is normally degraded by proteases and that albumin inhibits this degradation. In airway mucus collected from patients with asthma at various time points during acute asthma exacerbation, protease-driven mucus degradation was inhibited at the height of exacerbation but was restored during recovery. In immunoblots of human serum albumin digested by neutrophil elastase and in immunoblots of airway mucus, we found that albumin was a substrate of neutrophil elastase and that products of albumin degradation were abundant in airway mucus during acute asthma exacerbation. CONCLUSIONS Rheological methods complemented by centrifugation-based mucin size profiling of airway mucins in health and acute asthma reveal that mucin degradation is inhibited in acute asthma, and that an excess of plasma proteins present in acute asthma inhibits the degradation of mucins in a protease-dependent manner. These findings identify a novel mechanism whereby plasma exudation may impair airway mucus clearance.

Flow visualization of the elastic Taylor-Couette instability in Boger fluids

Flow visualization is performed on an elastically-dominated instability in several similar Boger fluids in Taylor-Couette flow. The onset and evolution of secondary flow are observed over a range of shear rates using reflective mica platelet seeding. Sequences of ambiently and sheet-illuminated images were digitally processed. Rotation of the inner cylinder was ramped from rest to its final value over a time on the order of a polymer relaxation time. Dilute solutions of high molecular weight polyisobutylene in oligomeric polybutene manifest a flow transition at a Deborah number, Des = λs γ ≈ 1.5 with a Taylor number of 0.00022 in a cell with dimensionless gap ratio δ = 0.0963. At this transition, simple azimuthal shearing is replaced by steady, roughly square, axisymmetric counter-rotating vortices grossly similar to the well-known Taylor vortex flow that is observed at Des = 0, Ta = 3612. At Des = 3.75, Ta = 0.0014, an axisymmetric oscillatory secondary flow develops initially but is replaced by the steady vortices. At Des = 7.5, Ta = 0.0054, the oscillatory and vortex flow coexist and possess an irregular cellular cross-section. A wide span of growth rates is observed: the ratio of onset to polymer relaxation time ranges from 170000 at Des= 1.5 to O(10) at Des > 5. The role of inertia was explored through changing the solvent viscosity. A transition similar to the one that occurs at Des = 3.75, Ta = 0.0014, from the base azimuthal shearing flow to axisymmetric vortices, was also observed with a much lower viscosity fluid at Des = 3.3, Ta = 74.

The transient extensional behavior of polystyrene-based Boger fluids of varying solvent quality and molecular weight

The behavior under transient uniaxial elongation of a homologous series of variable extensibility polystyrene‐based Boger fluids has been investigated in an apparatus similar to that developed by Sridhar and co‐workers. The test fluids are dilute solutions of either 2.0×107 or 2.0×106 g/mol monodisperse polystyrene dissolved in poor, dioctyl phthalate‐based or good, tricresyl phosphate‐based solvents. This rational manipulation of Boger fluid solvent quality (assessed based on previously reported light scattering and intrinsic viscometry measurements) and chain length yields a unique opportunity to correlate viscoelastic extensional response to finite extensibility and molecular interactions: here we search for such effects in transient filament extension between parallel plates, an approximation of purely extensional flow. The test device, which can impart a maximum Hencky strain, e, of 4.5 at rates, e, between 0.3 and 3.0 s−1, is similar to that reported by Sridhar et al. (1991). In agreement with results communicated there and in Tirtaatmadja and Sridhar (1993), large strain hardening is observed for these polymer solutions, as well as certain deviations of the experimental flow from ideal uniaxial extension. As opposed to Tirtaatmadja and Sridhar (1993), no steady‐state extensional viscosities are obtained for the comparatively small strains of our experiment. The transient experimental results are roughly consistent with simple one‐dimensional FENE–P calculations. However, uncertainties due to the nonideal nature of the flow at short times and the sensitivity of the measured extensional stress growth coefficient to the details of the imposed elongation make it difficult to unambiguously assign L based solely on short time filament stretching results. These results are considered in light of the substantial effects solvent quality and molecular weight have on the measured drag in flow past a sphere [Chmielewski et al. (1990); Solomon and Muller (1996b)].

Experimental studies of the onset of oscillatory instability in viscoelastic Taylor-Couette flow

Abstract Laser Doppler velocimetry (LDV) measurements of the flow of a wellcharacterized viscoelastic fluid between concentric cylinders are presented. The results show that the viscoelastic Taylor-Couette instability at vanishing Reynolds number is oscillatory for a Boger fluid; the velocity undergoes a transition from steady to time periodic at a critical Deborah number, De c . The value of De c measured by LDV is in good agreement with earlier mechanical measurements and with the calculations of Shaqfeh et al. for an Oldroyd-B fluid. The frequency of oscillation of the velocity field, however, is considerably higher than the Oldroyd-B prediction. In addition, higher harmonics of the oscillation frequency appear in the power spectrum of the velocity just above the critical condition. This observation is consistent with the calculations of Northey et al. who predict that the flatness of the neutral stability curve with respect to changes in axial wavenumber will lead to nonlinear interactions between families of time-periodic states that are closely spaced in De . Finally, the temporal evolution of the local flow field in the present LDV studies appears qualitatively different from that observed in global flow-visualization studies. This suggests that the flow may depend on the history of the experiment as well as the Deborah number.

Experimental study of shear-induced migration of polymers in dilute solutions

The results of an experimental study into the coupling of mass and momentum transfer for dilute polymer solutions are presented to test the numerous theoretical investigations of this effect. Solutions of high molecular weight, nearly monodisperse, linear polystyrene in oligomeric polystyrene were sheared in the cone‐and‐plate geometry. After long times under shear, the concentration of the high molecular weight species was measured as a function of radial position using a gel permeation chromatography based technique. An increase in polymer concentration of over 200% near the apex of the cone and a depletion of polymer near the edge was measured indicating a migration of polymer as a result of shearing the sample. The time evolution of the nonuniform concentration profile was found to be very slow and a strong function of both the polymer molecular weight and the applied shear rate. The experimental results are compared to theoretical predictions of a dumbbell based model and measured values of the physi...