Biomedical subjects

Mark A Arnold

Publications and source records attributed to Mark A Arnold.

6 recordsLinked to original sources

PubMed2003

Continuous oxygen monitoring of mammalian cell growth on space shuttle mission STS-93 with a novel radioluminescent oxygen sensor.

A compact, flow-through oxygen sensor device based on luminescence quenching was used to monitor dissolved oxygen levels during mammalian cell growth on the STS-93 mission of the Columbia space shuttle. Excitation of an oxygen-sensitive ruthenium complex was provided by a radioluminescent light source (0.9 mm in diameter, 2.5 mm long), and the intensity of the resulting luminescence was measured by a simple photodiode detector. The use of radioluminescence for the excitation light source is a unique approach that provides many features important for long-term and remote monitoring applications. For the spaceflight experiment, human lung fibroblast cells (WI-38) were grown in hollow-fiber bioreactors. Oxygen concentration was measured in the flow path both before and after the bioreactor cartridge in order to gain information about the metabolism of the cells. The sensor was found to be nonperturbing to cell growth and withstood the challenging physical conditions of shuttle launch and landing while maintaining a stable calibration function. In addition, the sensor provided physically meaningful oxygen predictions.

Aerospace Medicine↗

PubMed2002

Calibration standardization algorithm for partial least-squares regression: application to the determination of physiological levels of glucose by near-infrared spectroscopy.

Calibration standardization methodology for near-infrared (near-IR) spectroscopy is described for updating a partial least-squares calibration model to take into account changes in instrumental response. The guided model reoptimization (GMR) algorithm uses a transfer set of eight samples to characterize the new response and a database of previously acquired spectra used to develop the original calibration model. The samples in the transfer set need not have been measured under the old instrumental conditions, making the algorithm compatible with samples that change over time. The spectra comprising the transfer set are used to guide an iterative optimization procedure that (1) finds an optimal subset of samples from the original database to use in computing the updated model and (2) finds an optimal set of weights to apply to the spectral resolution elements in order to minimize the effects of instrumental changes on the computed model. The optimization relies on an alternating grid search and stepwise addition/deletion steps. The algorithm is evaluated through the use of combination region near-IR spectra to determine physiological levels of glucose in a synthetic biological matrix containing bovine serum albumin and triacetin in phosphate buffer. The ability to update a calibration to account for changes in the response of a Fourier transform spectrometer over four to six years is examined in this study. Separate spectral databases collected in 1994 and 1996 are used with a transfer set and separate test set of spectra collected in 2000. With the 1994 database, the standardization algorithm achieves a standard error of prediction (SEP) of 0.69 mM for the 2000 test set. This compares favorably to SEP values > 2 mM when the original 1994 calibration model is used without standardization. A similar improvement in the prediction performance of the 2000 test set is obtained after standardization with the 1996 database (SEP = 0.70 mM).

Algorithms↗

PubMed2002

Multivariate calibration models for lysozyme from near-infrared transmission spectra in scattering solutions of monodisperse microspheres.

The ability to quantify lysozyme is demonstrated for a series of aqueous samples with different degrees of scattering. Near-infrared spectra are collected for two sets of lysozyme/scattering solutions. In both sets of samples, the solutions are composed of lysozyme dissolved in acetate buffer with suspended monodisperse latex microspheres of polystyrene. The diameter of the microspheres is 6.4 microm for the first set and 0.6 microm for the second. For each set, the amount of microspheres range from 0.005 to 0.998 wt %, the lysozyme concentrations range from 0.834 to 28.6 mg/mL, and solution compositions are designed to minimize correlations between the concentration of lysozyme and percentage of microspheres. Near-infrared spectra are collected individually for each set of solutions. Single-beam spectra are collected over the combination spectral range (5000-4000 cm(-1), 2.0-2.5 microm) by transmitting the incident radiation through a 1.5-mm-thick sample that is maintained at 21 degrees C. Partial least-squares calibration models are evaluated individually for each data set both with and without wavelength optimization. Results indicate that models from raw, nonmodified, single-beam spectra are incapable of extracting lysozyme concentration from these highly scattering solutions. Accurate concentration measurements are possible, however, by implementing either a multiplicative scatter correction to the single-beam spectra or by taking the ratio of these single-beam spectra to an appropriate reference spectrum. In addition, digital Fourier filtering of these spectra enhances model performance. The best calibration model in the presence of 6.4-microm microspheres is obtained from multiplicative scatter corrected single-beam spectra over the 4550-4190-cm(-1) spectral range. The mean percent error of prediction (MPEP) and standard error of prediction (SEP) for this model are 2.2% and 0.28 mg/mL, respectively. Likewise, the multiplicative scatter corrected spectra with wavelength optimization provided the best calibration model for the 0.6-microm data set. In this case, the MPEP and SEP are 2.3% and 0.44 mg/mL, respectively. In addition, the ability to predict lysozyme concentrations is evaluated for the situation where the degree of scattering is greater in the predication samples compared to the calibration samples. Differences in the prediction ability are noted between the 6.4- and 0.6-microm data sets.

Microspheres↗

PubMed2002

Nondestructive near-infrared spectroscopic measurement of multiple analytes in undiluted samples of serum-based cell culture media.

An adaptive calibration procedure is used to build selective multivariate calibration models for the measurement of glucose, lactate, glutamine, and ammonia in undiluted serum-based cell culture media. This adaptive procedure removes metabolism-induced covariance between these analytes in a series of calibration samples collected during the cultivation of PC-3 human prostate cancer cells. Partial least-squares calibration models are generated from single-beam near-infrared (NIR) spectra collected over the 4800- to 4200-cm(-1) combination spectral range. Calibration models were generated with both the full spectral range and optimized spectral ranges. In both cases, the number of model factors was optimized and model validity was determined by comparing analyte concentrations predicted from a series of independent and unaltered samples that were obtained during a subsequent cultivation of the PC-3 cells. Similar analytical performance was achieved with fewer model factors when the optimized spectral range was used. The lowest standard errors of prediction were 0.82, 0.94, 0.55, and 0.76 mM for glucose, lactate, glutamine, and ammonia, respectively. Different spectral ranges were optimal for each analyte and the optimized spectral range coincided with the distinguishing spectral features of the analyte. The results of this study demonstrate that NIR spectroscopy can be used effectively in the off-line measurement of important nutrients (glucose and glutamine) and byproducts (lactate and ammonia) in a serum-based animal cell culture medium.

Algorithms↗

PubMedDate not supplied

Monitoring and controlling the dissolved oxygen (DO) concentration within the high aspect ratio vessel (HARV).

A probe-type oxygen sensor was developed utilizing a radioluminescent (RL)-based light source and a ruthenium-based sensing chemistry for monitoring the dissolved oxygen (DO) concentration in a modified version of the NASA-designed high aspect ratio vessel (HARV), a batch rotating wall vessel. This sensor provided the means to monitor the DO concentration in the HARV without influencing the flow pattern, thereby retaining the low shear HARV environment conducive to the formation of 3-dimensional cell aggregates. This sensor lost significant signal as a result of exposure to the first three autoclave cycles, but only minimal change in signal was observed following exposure to subsequent autoclave cycles. A new calibration model requiring only one fitted parameter was developed that accurately fit data over the entire range from 0% to 100% oxygen saturation. The ability for DO concentration control within the vessel was demonstrated by using this sensor to monitor the DO concentration inside the HARV.

Animals↗

PubMedDate not supplied

Evaluating prostate cancer cell culturing methods: a comparison of cell morphologies and metabolic activity.

LNCaP prostate cancer cells were grown under four unique cultivation conditions. Two types of bioreactor systems were used to observe the influence of low-shear culture conditions allowing for three-dimensional growth: a) a perfusion rotating wall vessel (RWV) bioreactor; and b) a high aspect ratio vessel (HARV) RWV bioreactor, with periodic medium exchanges (fed-batch). In addition, two growth methods utilized tissue culture flasks (TCFs): a) unaltered or conventional TCFs; and b) poly(2-hydroxyethyl methacrylate) [poly(HEMA)] coated TCFs, to inhibit cell attachment. Comparisons were drawn based on qualitative observation of cell morphology and quantitative metabolic data. Similar cellular metabolism was demonstrated for cells grown under each condition. The degree of aggregation, however, varies considerably. Spherical shaped aggregates with diameters of 1 to 3 mm were produced when cells were grown within the perfusion-RWV bioreactor. All other growth conditions produced irregular shaped aggregates of various sizes. Quantitative results demonstrated the expected glucose utilization concomitant with lactate accumulation. Immunohistochemical evaluations were unremarkable for all four cultivation conditions. Results demonstrate that use of the perfusion-RWV bioreactor is advantageous in obtaining spherical aggregates, while grown in a controlled environment.

Bioreactors↗