Local structure and thermodynamic properties of model fluids containing rod-like polymers: a comparison of theory and Monte Carlo simulation

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.Rigid rod polymers are an interesting and commercially important class of materials. To manipulate these materials on the macroscopic scale, one must understand their behavior on the molecular level. This research investigated model fluids containing rigid rods in two ways. First, Monte Carlo computer simulations were done for mixtures of rigid rods and solvent. Rods were modeled by linear tangent hard spheres, and solvent was modeled by simple monatomic hard spheres. The compressibility factor, Z, excess solvent chemical potential [ ], solvent insertion probability pm, order parameters, and monomer-monomer, rod-monomer, and rod-rod radial distribution functions, g(r), were calculated. Simulations were run over a range of densities (from 11=0. I to 11=0.43) and polymer mole fractions (x=0.5 to x=1.O). Results were compared to theoretical calculations to assess the accuracy of two promising theories which have not been previously applied to rigid rod solutions. The Generalized Flory Dimer Theory (GF-D) was used to predict the compressibility factor, excess solvent chemical potential, and monomer insertion probability. Distribution functions were calculated using the Polymer Reference Interaction Site Model (PRISM) with a Percus-Yevick closure, using an iterative Picard method. GF-D Theory does an excellent job of predicting pn, and m and does almost as well for PVT properties, especially at lower densities. Error increases slightly with both increasing density and increasing polymer mole fraction, since the monomeric solvent is easier to model. PRISM, however, is less accurate at lower densities. For monomer-monomer g(r), PRISM underestimates the contact value relative to simulation results, especially at higher densities, but is qualitatively very similar. For rod-monomer and rod-rod g(r)'s, it overpredicts the contact value, except at high packing fractions, and more importantly, predicts different peaks than simulation results. PRISM calculations show peaks at integer multiples of the hard sphere diameter, while simulations show prominent peaks at @3 (y, and F7(y, and very small peaks at 2.0(y only in some systems. These values are not surprising based on the system geometry. Earlier studies demonstrated that PRISM does quite well for flexible chain systems. However, this research indicates it is less reliable for stiff chains, and loses much of its predictive power

Assessing recruitment of lung diffusing capacity in exercising guinea pigs with a rebreathing technique

Noninvasive techniques for assessing cardiopulmonary function in small animals are limited. We previously developed a rebreathing technique for measuring lung volume, pulmonary blood flow, diffusing capacity for carbon monoxide (DlCO) and its components, membrane diffusing capacity (DmCO) and pulmonary capillary blood volume (Vc), and septal volume, in conscious nonsedated guinea pigs at rest. Now we have extended this technique to study guinea pigs during voluntary treadmill exercise with a sealed respiratory mask attached to a body vest and a test gas mixture containing 0.5% SF6 or Ne, 0.3% CO, and 0.8% C2H2 in 40% or 98% O2. From rest to exercise, O2 uptake increased from 12.7 to 25.5 ml·min−1·kg−1 while pulmonary blood flow increased from 123 to 239 ml/kg. The measured DlCO, DmCO, and Vc increased linearly with respect to pulmonary blood flow as expected from alveolar microvascular recruitment; body mass-specific relationships were consistent with those in healthy human subjects and dogs studied with a similar technique. The results show that 1) cardiopulmonary interactions from rest to exercise can be measured noninvasively in guinea pigs, 2) guinea pigs exhibit patterns of exercise response and alveolar microvascular recruitment similar to those of larger species, and 3) the rebreathing technique is widely applicable to human (∼70 kg), dog (20–30 kg), and guinea pig (1–1.5 kg). In theory, this technique can be extended to even smaller animals provided that species-specific technical hurdles can be overcome

Inhalational delivery of induced pluripotent stem cell secretome improves postpneumonectomy lung structure and function.

Cell-free secretory products (secretome) of human induced pluripotent stem cells (iPSCs) have been shown to attenuate tissue injury and facilitate repair and recovery. To examine whether iPSC secretome facilitates mechanically-induced compensatory responses following unilateral pneumonectomy (PNX), litter-matched young adult female hounds underwent right PNX (removing 55-58% of lung units) followed by inhalational delivery of either the nebulized conditioned media containing iPSCs secretome (iPSC CM) or control cell-free media (CFM); inhalation was repeated every 5 days for 10 treatments. Lung function was measured under anesthesia pre-PNX and 10 d after the last treatment (8 weeks post-PNX); detailed quantitative analysis of lung ultrastructure was performed postmortem. Pre-PNX lung function was similar between groups. Compared to CFM control, treatment with iPSC CM attenuated the post-PNX decline in DLCO and DMCO, accompanied by a 24% larger postmortem lobar volume and distal air space enlargement. Alveolar double-capillary profiles were 39% more prevalent consistent with enhanced intussusceptive angiogenesis. Frequency distribution of the harmonic mean thickness of alveolar blood-gas barrier shifted towards the lowest values while alveolar septal tissue volume and arithmetic septal thickness were similar, indicating septal remodeling and reduced diffusive resistance of the blood-gas barrier. Thus, repetitive inhalational delivery of iPSC secretome enhanced post-PNX alveolar angiogenesis and septal remodeling that are associated with improved gas exchange compensation. Results highlight the plasticity of the remaining lung units following major loss of lung mass that are responsive to broad-based modulation provided by the iPSC secretome

Predicting diffusive alveolar oxygen transfer from carbon monoxide-diffusing capacity in exercising foxhounds

Although lung diffusing capacity for carbon monoxide (DlCO) is a widely used test of diffusive O2 transfer, few studies have directly related DlCO to O2-diffusing capacity (DlO2); none has used the components of DlCO, i.e., conductance of alveolar membrane and capillary blood, to predict DlO2 from rest to exercise. To understand the relationship between DlCO and DlO2 at matched levels of cardiac output, we analyzed cumulative data from rest to heavy exercise in 43 adult dogs, with normal lungs or reduced lung capacity following lung resection, that were studied by two techniques. 1) A rebreathing (RB) technique was used to measure DlCO and pulmonary blood flow at two O2 tensions, independent of O2 exchange. DlCO was partitioned into CO-diffusing capacity of alveolar membrane and pulmonary capillary blood volume using the Roughton-Forster equation and converted into an equivalent DlO2, [DlO2(RB)]. 2) A multiple inert-gas elimination technique (MIGET) was used to measure ventilation-perfusion distributions, O2 and CO2 exchange under hypoxia, to derive DlO2 [DlO2(MIGET)] by the Lilienthal-Riley technique and Bohr integration. For direct comparisons, DlO2(RB) was interpolated to the cardiac output measured by the Fick principle corresponding to DlO2(MIGET). The DlO2-to-DlCO ratio averaged 1.61. Correlation between DlO2(RB) and DlO2(MIGET) was similar in normal and post-resection groups. Overall, DlO2(MIGET) = 0.975 DlO2(RB); mean difference between the two techniques was under 5% for both animal groups. We conclude that, despite various uncertainties inherent in these two disparate methods, the Roughton-Forster equation adequately predicts diffusive O2 transfer from rest to heavy exercise in canines with normal, as well as reduced, lung capacities

Noninvasive quantification of heterogeneous lung growth following extensive lung resection by high-resolution computed tomography

To quantify the in vivo magnitude and distribution of regional compensatory lung growth following extensive lung resection, we performed high-resolution computed tomography at 15- and 30-cmH2O transpulmonary pressures and measured air and tissue (including microvascular blood) volumes within and among lobes in six adult male foxhounds, before and after balanced 65% lung resection (∼32% removed from each side). Each lobe was identified from lobar fissures. Intralobar gradients in air and tissue volumes were expressed along standardized x,y,z-coordinate axes. Fractional tissue volume (FTV) was calculated as the volume ratio of tissue/(tissue + air). Following resection compared with before, lobar air and tissue volumes increased 1.8- to 3.5-fold, and whole lung air and tissue volumes were 67 and 90% of normal, respectively. Lobar-specific compliance doubled post-resection, and whole lung-specific compliance normalized. These results are consistent with vigorous compensatory growth in all remaining lobes. Compared with pre-resection, post-resection interlobar heterogeneity of FTV, assessed from the coefficient of variation, decreased at submaximal inflation, but was unchanged at maximal inflation. The coefficient of variation of intralobar FTV gradients changed variably due to the patchy development of thickened pleura and alveolar septa, with elevated alveolar septal density and connective tissue content in posterior-caudal and peripheral regions of the remaining lobes; these areas likely experienced disproportional mechanical stress. We conclude that HRCT can noninvasively and quantitatively assess the magnitude and spatial distribution of compensatory lung growth. Following extensive resection, heterogeneous regional mechanical lung strain may exceed the level that could be sustained solely by existing connective tissue elements