Showing papers by "James P. Butler published in 2008"

Measuring surface-area-to-volume ratios in soft porous materials using laser-polarized xenon interphase exchange NMR

Abstract: We demonstrate a minimally invasive nuclear magnetic resonance (NMR) technique that enables determination of the surface-area-to-volume ratio (S/V ) of soft porous materials from measurements of the diffusive exchange of laser-polarized 129 Xe between gas in the pore space and 129 Xe dissolved in the solid phase. We apply this NMR technique to porous polymer samples and find approximate agreement with destructive stereological measurements of S/V obtained with optical confocal microscopy. Potential applications of laser-polarized xenon interphase exchange NMR include measurements of in vivo lung function in humans and characterization of gas chromatography columns. 81.05.Rm, 82.56.Lz, 68.47.Mn

Distribution and Quantity of Contractile Tissue in Postnatal Development of Rat Alveolar Interstitium

Abstract: Alpha–smooth muscle actin (α-SMA) -expressing cells are important participants in lung remodeling, during both normal postnatal ontogeny and after injury. Developmental dysregulation of these contractile cells contributes to bronchopulmonary dysplasia in newborns, and aberrant recapitulation in adults of the normal ontogeny of these cells has been speculated to underlie disease and repair in mature lungs. The significance of airway smooth muscle has been widely investigated, but contractile elements within the pulmonary parenchyma, although also of structural and functional consequence in developing and mature lungs, are relatively unstudied and little quantitative information exists. Here, we quantify the areal density of α-SMA expression in lung parenchyma and assess changes in its spatiotemporal distribution through postnatal ontogeny. Using an antibody against α-SMA, we immunofluorescently labeled contractile elements in lung sections from a postnatal growth series of rats. Images were segmented using thresholded pixel intensity. Alpha-SMA areal density in the alveolar interstitium was calculated by dividing the area of α-SMA–positive staining by the tissue area. The areal density of α-SMA in 2-day neonates was 3.7%, almost doubled, to 7.2% by 21 days, and decreased to 3% in adults. Neonates had large, elongate concentrations of α-SMA, and α-SMA localized both at septal tips and within the interstitium. In adults, individual areas of α-SMA expression were smaller and more round, and located predominately in alveolar ducts, at alveolar ends and bends. The results are consistent with increasing α-SMA expression during the period of peak myofibroblast activity, corresponding to the phase of rapid alveolarization in the developing lung. Anat Rec, 291:83–93, 2007. © 2007 Wiley-Liss, Inc.

The Cytoskeleton of the Living Cell as an Out-of-Equilibrium System

Abstract: In a remarkably broad range of eukaryotic cell types, the cytoskeleton exhibits physical properties and remodelling dynamics strongly reminiscent of soft inert condensed systems, although with important differences as well. This unexpected intersection of condensed matter physics and cytoskeletal biology suggests that trapping, intermittency, and approach to kinetic arrest represent central mesoscale features linking underlying molecular events to integrative cellular functions such as crawling, contraction and remodelling.

A Potential Elastohydrodynamic Origin of Load-Support and Coulomb-Like Friction in Lung∕Chest Wall Lubrication

Abstract: BACKGROUND: During normal breathing, the mesothelial surfaces of the lung and chest wall slide relative to one another Experimentally, the shear stresses induced by such reciprocal sliding motion are very small, consistent with hydrodynamic lubrication, and relatively insensitive to sliding velocity, similar to Coulomb-type dry friction Here we explore the possibility that shear-induced deformation of surface roughness in such tissues could result in bidirectional load supporting behavior, in the absence of solid-solid contact, with shear stresses relatively insensitive to sliding velocity METHOD OF APPROACH: We consider a lubrication problem with elastic blocks (including the rigid limit) over a planar surface sliding with velocity U , where the normal force is fixed (hence the channel thickness is a dependent variable) One block shape is continuous piecewise linear (V block), the other continuous piecewise smoothly quadratic (Q block) The undeformed elastic blocks are spatially symmetric; their elastic deformation is simplified by taking it to be affine, with the degree of shape asymmetry linearly increasing with shear stress RESULTS: We find that the V block exhibits nonzero Coulomb-type starting friction in both the rigid and elastic case, and that the smooth Q block exhibits approximate Coulomb friction in the sense that the rate of change of shear force with U is unbounded as U → 0 ; shear force ∝U(1/ 2) in the rigid asymmetric case and ∝U(1/ 3) in the (symmetric when undeformed) elastic case Shear-induced deformation of the elastic blocks results in load supporting behavior for both directions of sliding CONCLUSIONS: This mechanism could explain load-supporting behavior of deformable surfaces that are symmetrical when undeformed, and may be the source of the weak velocity dependence of friction seen in the sliding of lubricated, but rough, surfaces of elastic media such as the visceral and parietal pleural surfaces of the lung and chest wall