Cynthia L. Stokes, Ph.D., Assistant Professor, Chemical Engineering, UH
Our long-term objective is to obtain an understanding of the mechanisms that regulate the distribution of drugs and biological chemicals throughout tissues, with emphasis on the effects of cellular pharmacology. UH investigation will aid in the development of improved therapeutic drugs and methods of delivery. This research can be applied to medical therapies on earth. It also provides an inexpensive means of studying the effects of altered physiology during space flight caused by zero gravity on drug delivery. The specific goal of the research team was to develop an in vitro experimental assay to study the effects of transport, binding, and intracellular trafficking mechanisms on movement of targeted drugs in tissues. The project team tested many of the predictions of a previously developed mathematical model of this system.
Our experimental assay consists of a "model tissue" (cells- embedded in agarose) apposed to a "drug source" (transferrin in agarose) in an assay chamber on the microscope. The movement of the fluorescently labelled "drug" through the model tissue was recorded and measured via video microscopy and image analysis. Our model system is transferrin as the drug, labeled with either FITC or Texas Red fluorophores, with SKMEL or HeLa tumor cells embedded in the agarose. The use of two fluorophores which are differently sensitive to intracellular conditions has enabled us to estimate the fraction of internalized transferrin.
Experimental results now confirm many of the predictions of the mathematical model. Results with both cell lines demonstrate that there is significant internalization of transferrin, resulting in internal trapping of the drug (see figure, point a). This trapping is a double-edged sword for drug delivery and efficacy. If intracellular action is required for drug efficacy, then cells which internalize drug will be "treated" better than those that do not; on the other hand, the model predicts also that the trapping of drug by cells near the source prevents further penetration by the drug into the tissue, decreasing the "treatment" of cells further from the source. A pseudo-steady state analysis of our mathematical model predicts (1) that the distribution of cell-associated drug (surface-bound plus internalized drug) is dependent only on the probability of drug binding to the cells, as is the total drug in the tissue (extracellular, surface-bound, and internalized) and (2) that the degree of internal trapping of drug is a product of the probability of binding and the probability of internalization of bound drug.
These probabilities are defined in terms of the rate constants of the endocytic cycle for a cell type. The cell lines used have different probabilities of internalization but the same probability of binding. A comparison of the experiments using FITC-transferrin with both cell lines demonstrates the validity of prediction (2) (see figure, point b). Comparing results from the HeLa cells with preliminary data from the SKMEL cells (experiments ongoing) also supports prediction (1). These results demonstrate that the probabilities of binding and internalization are useful descriptors of how cellular pharmacology will affect transport through a tissue. Hence, a priori knowledge of these probabilities for a drug/cell system, obtained from simple cell biological measurements, will allow accurate prediction of the movement of the drug through a tissue (e.g., a tumor) predominated by that cell type.
TRANSFERRIN ASSAY--Representative assay results showing normalized [transferrin] in
the "model tissue" versus distance from the transferrin source (x = 0). Owing to
the pH-dependence of the fluorophore used as the transferrin label, the Texas
Red-transferrin (TXR-tf) result represents all of the transferrin in the tissue
(extracellular, cell-surface and intracellular) whereas the FITC-transferrin (f-tf)
results represent only the extracellular plus cell-surface transferrin.
Point a. Comparing the TXR-tf/HeLa cell curvewith the f-tf/HeLa cell curve shows that a
significant fraction of transferrin is internalized. The difference between the two curves
represents the internalized concentration of transferrin in the system.
Point b. Comparing the f-tf/HeLa result with the f-tf/SKMEL cell result demonstrates that
there is less internalization of transferrin by SKMELs than HeLas, consistent with the
probabilities of internalization being about 0.3 and 0.5 for the two cell lines,
respectively.
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Russell G. Thompson, Ph.D. Professor, Decision and Information Sciences, UH
The potential economic impact of lunar solar power on the U. S. economy is under evaluation for implementation as a commercialized technology. DEA Best-Practice methods have been applied to data for the world's ten leading industrial nations--Australia, Belgium, Canada, France, Germany, Italy, Japan, Sweden, the United Kingdom, and the United States. Two measures of efficiency and productivity are estimated, one without a lunar solar power initiative and one with a lunar solar power initiative (LSP). The U. S. alone would pay the full commercialization cost of this initiative, which sum would be paid back in full (plus interest) from LSP commercial power revenues.
LSP is conceptualized as being fully incorporated in the U. S. economy's capital stock, labor employment, and domestic product. This new U. S. economy is evaluated relative to the economy of ten industrial nations, including its fomer self. Based on these concepts, modeling results show that an LSP initiative would significantly increase the efficiency, productivity, and growth of the U. S. economy, relative to its industrial peers and its old self. It would restore economic growth in the U. S. economy to levels observed in the late 1950s and early 1960s. The U. S. economy will continue to lose its competitive edge relative to its peers, if it does not, however, undertake an LSP initiative. Thus, the U. S. has the knowledge and technology to provide world leadership to improve environmental quality, decrease fossil fuel use, and increase economic growth.
| U.S. TFP Economic Growth, %/Yr | ||
| Old U.S. Enon. | New U.S. Econ. | U.S. Price Inflation Rate*2k |
| 2.3 | 6.7 | 5.3 |
| *Implicit GDP deflator rate of change from 1980 to 1990. | ||
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Wayne Wentworth, Ph.D., Professor, Chemistry, UH
This research entails two areas of investigation: (1) a photo-ionization source that replaces the conventional radioactive foil for ionization of the analytes and (2) configuration of the Ion Mobility Spectrometer to utilize the unique features of the pulsed discharge photoionization source. These two issues were under study almost simultaneously at the outset of the research project.
A detailed investigation of the
photoionization source has led to useful findings. In addition to the emission from pure
helium, the research team has considered the following dopants in order to alter the
photoionization spectra: Ar, Kr, H2, N2. The Ar and Kr produced the well known resonance
emissions of the atomic species and broad emissions from Ar2 and Kr2 at longer
wavelengths. These spectra were recorded using a monochromator purged with 6-nines helium.
The monochromator allowed photon transmission from 60-200 nm so all emission spectra,
including that from He2 in the region 70-90 nm, could be observed. We expected N2 and H2
dopants to produce atomic emissions at 120 and 121.5 nm, respectively. However, H2 gave a
very weak atomic emission and N2 gave considerable ionization which increased the
background current to an intolerable level. The Ar and Kr dopants are quite satisfactory
and allow one to use different gas mixtures to obtain selective ionization of analytes.
This would be most useful as an ionization source for ion Mobility Spectrometery.
Two papers have been accepted for publication which describe the use of these photoionization sources for selective ionization of analytes in an ionization detector. The first shows how the photoionization source can be selected simply by positioning a four-port gas stream sampling valve. One of the streams is pure He so that the lines can be purged when the helium photoionization source is desired. The other streams include a low flow of pure Ar or Kr which are directed to the principal He discharge gas (~30mL/Min). The concentration of Ar or Kr can be controlled simply by varying the pressure of the Ar or Kr before it passes through a fixed restrictor prior to the sampling valve. It would appear that the photoionization source can be changed in a minute so conceivably it could be changed during a GC run. The second paper shows how the simultaneous response from three photoionization detectors, He, Ar (5%), Kr (1%) can be used to qualitatively identify a given analyte coming from the GC column. The GC stream is split between the three detectors. The relative response (ratio) of the photoionization detectors is independent of concentration, and the two ratios can be used for qualitative identification. If the two relative photoionization responses were combined with the relative retention time, the three numbers would appear to be unique to each of the analytes investigated.
A third paper recently completed describes a low volume detector (< 24uL) that can use these photoionization sources for selective ionization of analytes coming from a microbore column, commonly used in high speed chromatography.
An Ion Mobility Spectrometer has been structured so that the photoionization source can be used to its best advantage. The unique features of this source are: (1) a very narrow, linelike image resulting from the discharge between the pointed electrodes and (2) a discharge pulsed for a very short period (< 1 usec) at intervals > 300 usec. In order to obtain good resolution from the Ion Mobility Spectrometer, the ions must be initially confined to a narrow sheath perpendicular to the direction of drift. In order to accomplish this characterization with the photoionization source, the discharge is located off axis with the image perpendicular to the flight path. This is shown in the schematic diagram of the Pulsed Discharge Ion Mobility Spectrometer. The light coming from this discharge is further confined to a narrow image as it passes through a narrow slit which is aligned with the discharge.
Since the photoionization source is pulsed, the ions will be produced in a relatively short period of time. Consequently, the ions formed from this configuration should be formed in a narrow sheath within a period of < 1 usec before the ions begin drifting down the drift tube. The drift tube is constructed of alternate insulators (99.99% alumina) and stainless steel electrodes. The electrodes have step-down potentials starting with ~1,000V in order to cause the ions to drift down the tube.
Testing is in progress to see if this light source is a satisfactory replacement for the conventional radioactive foil. The principle problem encountered thus far has been the formation of small particles that have covered the fine slit and, consequently, block the light from entering the ionization region. The source of these particles is unknown at this time, but they appear to arise from the discharge. This problem is being alleviated by splitting the He discharge gas so that some passes through the discharge and some passes through the slit to the Ion Mobility Spectrometer. The He passing through the discharge will then exit external from the Ion Mobility Spectrometer. Thus, particles that may be formed in the discharge would not encounter the fine slit.
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David C. Zimmerman, Ph.D., Associate Professor, Mechanical Engineering, UH
The determination of location and extent of structural damage is of significant importance in many engineering systems ranging from advanced aerospace structures to the nation's civil infrastructure. Inspection of these structures in the past has been based mainly on visual methods, with occasional usage of conventional non-destructive evaluation techniques such as ultrasonics or acoustic emission. However, this methodology is time consuming and costly. It does not necessarily provide a quantitative measure of the extent of structural damage experienced, and it is not applicable to a wide range of advanced aerospace structures. Thus, it is necessary to develop a structural health monitoring system to detect and locate structural damage as it occurs. Our general concept for structural damage detection is depicted in Fig. 1.
With the
assistance of ISSO funding, researchers developed a coupled matrix update/parameter
estimation approach, resulting in an enhanced estimate of the extent of structural damage.
The extent estimate is critically important for mission planners in that the estimated
"remaining strength/life" of the structure will be used in decisions to
"go" or "no-go." The approach used in the matrix updating was the
Minimum Rank Perturbation Theory, although it should be noted that the formulation allows
for the use of other matrix update algorithms. The parameter estimation approach utilizes
a least squares solution procedure. One major problem with matrix updates is that the
final updated matrices are not necessarily finite element consistent. Another major
problem with parameter estimate approaches is the nonlinear relationship between
structural parameters and modal parameters, thus increasing the computational burden. The
proposed hybrid approach circumvents both of these problems, resulting in a
computationally attractive algorithm suitable for real-time implementation.
The methodology consists of two main steps: (1) determine the location of damage, and (2) with a priori knowledge of location, assess the damage. In the first step the location of damaged regions is determined by using the residual vector algorithm. The new contribution of this work is the development of a hybrid algorithm for estimating the extent of damage. In this approach the perturbation matrix (mass and/or stiffness) is first computed using the MRPT algorithm. The difference between this perturbation matrix and the corresponding finite element feasible (FEF) perturbation matrix is minimized with respect to the estimate of structural parameters. The FEF perturbation matrix is then used to estimate the extent of damage.
Experimental studies utilized data obtained from the NASA LaRC 8-Bay Truss Damage Detection Test-Bed. A comparison of the performance of the hybrid algorithm with the industry "standard" Baruch updating technique showed that extent estimate errors were reduced on the average from fifty percent to less than five percent.
Contents
ISSO -- Institute for Space Systems Operations
1994-1995 Annual Report
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