AVS1996 Session AS+BI-WeP: Aspects of Biomaterial Characterization
Wednesday, October 16, 1996 5:00 PM in Ballroom A
Wednesday Afternoon
Time Period WeP Sessions | Topic AS Sessions | Time Periods | Topics | AVS1996 Schedule
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AS+BI-WeP-1 Characterization of Chemical Interaction of Asbestos Surfaces during Culturing with Lung Cells
S. Seal, S. Krezoski, D. Petering, T. Barr (University of Wisconsin, Milwaukee) The pathogenic nature of asbestoses has become an established fact in the environmental sciences. This is particularly true for the injury of epithelial lung cells. Although speculation exists as to the involvement of the fibrous nature of the asbestos, and/or the adverse oxidative properties of any ferrous components, as of yet no concrete mechanism has been discerned for this pathogenic interaction. It should be apparent, however, that since the silicates are altering the chemical and structural properties of the cells, stoichiometry requires alterations in the properties of the asbestoses. In the present case we report on a variety of interest results centered around the latter "reverse mechanism," when X-ray photoelectron spectroscopy (XPS or ESCA), Atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), and Secondary ion mass spectrometry (SIMS) are employed to track the behavior and alterations of the silicates in select cell cultures. In this regard a unique mechanism is hypothesized involving first selective chemical attachment of the cellular bodies to the tetrahedral silicate layer of the asbestos followed by progressive extraction of some of the Mg and any Fe out of the octahedral layers. Eventually the latter species are found to lodge in the cells where chemical involvement with oxidants produced in the life cycle, (such as H\sub2\O\sub2\), may generate peroxides through a Fenton-type mechanism. |
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AS+BI-WeP-2 Langmuir Film Structure Based on the Construction of a System Response Function for the Analysis of Second Harmonic Signals
P. Trzaskoma-Paulette, N. Garland, S. Lambrakos (Naval Research Laboratory) Optical second harmonic generation is used to investigate the characteristics of a Langmuir film of hematoporphyrin IV dimethyl ester on water. Interfacial molecular orientation is determined by the construction of a system response function based on general and consistent assumptions concerning the distribution of second order nonlinear hypoerpolarizabilities and the second harmonic signal intensity variation for compressed and expanded versions of the film. Two dominant average hyperpolarizability axes are observed for the individual molecules making up the film. Further, it is found that the molecules tend to align towards the vertical as the film is compressed from the maximum mean molecular area of 130 angstroms to the minimum mean molecular area of 70 angstroms. The molecular tilt angle varies from 44 degrees under maximum compression to 71 degree under full expansion. These results show good quantitative agreement with previous investigations of Langmuir films of similar molecules. |
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AS+BI-WeP-3 In Situ AFM Studies of Surface Morphology and Growth Kinetics in Thaumatin Crystallization
A. Malkin, Y. Kuznetsov, A. McPherson (University of California, Riverside) Surface morphology and growth kinetics of protein thaumatin crystals in supersaturation range (0\<=\s\<=\1.65) were investigated using in situ AFM. At s \<=\0.7 growth steps were produced by screw dislocations and 2D nuclei. At higher supersaturations growth proceeded exclusively by 2D nucleation. Adsorption of 3D clusters on the surfaces of growing crystals which resulted in the formation of multilayer stacks which then grew tangentially was observed. Strong directional kinetic anisotropy in the tangential step growth rates in different directions was also seen. From the supersaturation dependence of tangential step rates, the kinetic coefficient of steps \beta\ was determined to be 2 x 10\super -4\cm\sec. The supersaturation dependence of the rate of 2D nucleation was measured, and this yielded the supersaturation dependence of the normal growth rate. From these data the surface free energy of the step edge \alpha\ was calculated to be 0.4 erg cm\super-2\ for supersaturation s \>=\ 1.2 and 0.2 erg cm\super-2\ for s \<=\ 1.2. It was suggested that at s \<=\ 1.2, 2D nucleation was not homogeneous and occurred at sites more active than normal, e.g. at defects or sites of impurity incorporation. Similiar values of \alpha\ were also obtained based on the sizes of critical nuclei, both for growth on dislocations and by 2D nucleation. |
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AS+BI-WeP-4 Thickness and/or Energy Dependence of Secondary Ion Emission from Langmuir-Blodgett Films and Self-assembled Monolayer Films
M. Kudo (Seikei University, Japan); T. Hoshi (ULVAC-PHI, Inc., Japan); S. Yamada (Seikei University, Japan); S. Yoshida, T. Watanabe (University of Tokyo, Japan); Z. Liu (RIKEN, Japan) Langmuir-Blodgett(LB) films and self-assembled monolayers can be regarded as suitable samples for the basic study of the secondary ion emissions in Static Secondary Ion Mass Spectrometry(S-SIMS), due to the flexibility for desired sample preparations. In this study, the intensity variations versus the number of monolayers and/or the primary ion energy were investigated for various kind of secondary ion species by Time-of-Flight (TOF) SIMS and Quadrupole SIMS. Samples used for the experiments were cadmium arachidate LB films formed on a Si or a silver film/Si, and alkanethiol monolayers formed on a Au(111)/mica. The investigation on the film thickness dependence of the secondary ion intensities from the LB films showed that the total secondary ion intensities decreased as the film thickness increased, whereas Cd+ and C3H5+ intensities did not show much correlation with film thickness. The quasi-molecular secondary ion [(M+H)+,(M+Cd)+] intensities decreased with f! ilm thickness, which showed the hi ghest ion intensity at the single layer sample. The investigation on the primary ion energy dependence was also carried out using one layer LB film and a self-assembled monolayer sample. In the case of LB film on a Si substrate, it was found that the highest secondary ion yield for quasi-molecular ions were observed with the lowest primary ion energy(2 keV). These results are interpreted with respect to the escape process of the formed secondary ion species as well as the energy loss process of the primary ion beam in the organic films and at the film-substrate interface. |
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AS+BI-WeP-5 Structural Characterization of Langmuir Blodgett (LB) Films by Time-of-Flight (TOF) SIMS and XPS
M. Anderle, R. Canteri, S. Ferrari, G. Speranza (Centro Materiali e Biofisica Medica, Italy) Structure of perfluorinated fatty acids LB films were examined by means of an high lateral resolution TOF SIMS and a small spot XPS. The spatial distribution of chemical elements constituting the film and contaminants were analyzed to understand possible causes of structural disorder in LB films. The degree of sample porosity was examined by TOF-SIMS measuring the shilding capability of the LB layers respect to the substrate ions. XPS was employed to infer the LB structure. Conventional, angle dependent and X-E measurements were used to understand the physical and chemical charateristics of the LB deposited films. |
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AS+BI-WeP-6 Particle Electrophoresis of 45S5 Bioactive Glass Granules in a Simulated Body Fluid
H. Lu, S. Pollack, P. Ducheyne (University of Pennsylvania) The present study is part of an ongoing investigation into the mechanism of bioactivity of 45S5 bioactive glass (BG). Bioactivity is defined as the ability of an already biocompatible material to enhance bone formation and to bond to surrounding bone. In vivo, BG undergoes a series of ion exchange, dissolution and precipitation reactions which lead to the formation of a biologically equivalent calcium phosphate (Ca-P) layer. We hypothesize that BG surface charge plays an important role in the events leading to the formation of this Ca-P layer. We have determined BG surface charge as a function of immersion time in a simulated body fluid (SBF) via particle electrophoresis (PE), and we have characterized the various stages of the bioactive surface using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA), and Fourier Transform Infrared Spectroscopy (FTIR). BG surface was negative at the beginning of immersion, and there was a tendency toward establishing a less negative surface within the first 24 hours of immersion. The long term BG surface was negative in charge. Surface analysis results indicated the formation of a silica rich layer during the first 24 hours of immersion. An amorphous Ca-P layer was detected after 1 day, and it later matured into a crystallized Ca-P layer at 3 days after immersion. It is clear that PE results combined with SEM, SEM+EDXA and FTIR data allow the monitoring of dynamic reactions occurring at the BG surface as it develops into a Ca-P layer. Further work focuses on the effects of protein presence on BG surface charge and the formation of Ca-P layer, as well as cellular response to the changing BG surface. |