Effect of cellulose acetate materials on the oxidative burst of human neutrophils.

Following adverse clinical events involving seven patients undergoing renal dialysis using 12-year-old cellulose acetate hemodialyzers, this in vitro study was proposed in an effort to characterize the inflammatory response to the constituent cellulose acetate (CA) fiber materials. Chemiluminescence (CL) and apoptosis assays were used to determine whether human neutrophils were activated by CA fiber materials and/or are sensitive to degradation/alteration of these fibers over time. Furthermore, the study examined in vitro assays with human neutrophils using a CA film, the solvents used in the film preparation and CA resin. The film could be cut to identical sized pieces in an effort to compare hemodialysis material effects in standardized amounts. For the CL assays, 60-min exposure was followed by secondary stimulation with n-formyl-met-leu-phe (fMLP) or phorbol-12-myristate-13-acetate (PMA). Short-term exposure (60-min postintroduction to CA materials) increased the inflammatory response as measured by the respiratory burst of neutrophils (p < or =.05), with CA fiber exposure significantly compared with cells alone. There was a trend toward an increased response with exposure to older fibers with secondary PMA stimulation. Apoptosis was increased 12% with exposure to the more aged fibers versus 2% with the new fibers. The fiber storage component, glycerol, significantly inhibited the oxidative response (p < or =.001; > or =80% suppression with concentrations of 5-20%). The solvents used in film preparation, N,N-dimethylacetamide and tetrahydrofuran, produced greater than a 70% and 60% suppression, respectively, of CL activity for all concentrations > or =1%. More work is needed to determine the specific nature of the interaction of inflammatory cells with CA materials, but early evidence suggests that neutrophils are activated by CA and display an altered response to more aged fibers.

ASTM lights the way for tissue engineered medical products standards: jump start for combination medical products that restore biological function of human tissues.

Everybody hopes for better health and restoration of impaired bodily function, and now that hope is illuminated by the promise of powerful biological tools that make human cells grow and replace human tissue. ASTM Committee F04 on Medical and Surgical Materials and Devices is taking the lead by defining some of those tools as standards that can be used for the development, production, testing, and regulatory approval of medical products.

Biomaterials for tissue engineering: summary.

NASA: This article summarizes presentations and discussion at the workshop "Enabling Biomaterial Technology for Tissue Engineering," which was held during the Fifth World Biomaterials Congress in May 1996. Presentations covered the areas of material substrate architecture, barrier effects, and cellular response, including analysis of biomaterials challenges involved in producing specific tissue-engineered products.^ieng

Human monocyte morphology is affected by local substrate charge heterogeneity.

Cells are sensitive to topological, chemical, and electrical properties of substrates on which they are grown. However, most studies of cell-surface interactions have neglected electrical effects or confounded them with other substrate properties. The use of nanofabrication technology has made it possible to fabricate optically transparent surfaces with controlled chemistry and topology, and with active, controllable surface charge density in domains as small as 1-4 microns. Human monocytes incubated on polystyrene with 3.3 microns-wide strip domains, alternately charged so as to maintain overall charge neutrality, show significant charge density and time-dependent increases (greater than twofold) in cell area and cell perimeter after challenge with a phagocytic trigger (human IgG opsonized zymosan particles). Additional utlrastructural studies on silicon dioxide substrates show charge-density-dependent qualitative morphological differences. These studies clearly demonstrate that human monocytes respond in vitro to local surface-charge heterogeneity in the absence of substrate topology and compositional variation.

Application of quantitative immunofluorescence to clinical serology: antibody levels of Treponema pallidum.

A previously reported method of quantitative immunofluorescence, employing a calibrated photometric system and chemically stabilized fluorescence intensity, was used to replace the subjective, visual method of endpoint determination with a quantitative, calibrated measurement of antibodies to Treponema pallidum in serum. The results of the quantitative immunofluorescence method showed a 90% correlation with the subjective determinations of the visual method.

Application of quantitative immunofluorescence to clinical serology: antibody levels of Toxoplasma gondii.

Methods currently used for immunofluorescent reagent standardization require subjective visual comparison of reagents with control materials. Reactivities of reagents in immunofluorescence test kits vary from manufacturer to manufacturer. To solve these problems, a quantitative immunofluorescence (QIF) method which uses a calibrated photometric system and incorporates reducing agents into the mounting medium to reduce fading was developed to replace the visual method of endpoint determination. A uranyl glass slide was used to calibrate the instrument's voltage measurements, permitting daily comparisons and measurement of the instrument reading fluctuations. The QIF method was initially tailored to the determination of serum antibodies to Toxoplasma gondii by measuring the fluorescence intensity of individual tagged organisms. The nonspecific fluorescence intensity resulting from the counterstain was eliminated by use of a red-suppressing filter. The dilution-correlated polar fluorescence component was removed by subtraction of the intensity for the matching negative control dilution from each sample dilution intensity. The QIF method showed a 94% correlation with the visual comparison method for 62 clinical specimens.

Characterization of instrumentation and calibrators for quantitative microfluorometry for immunofluorescence tests.

The current method for measuring reagents for immunofluorescence microscopy involves a subjective evaluation of the endpoint (titer) with a negative or positive (1+ to 4+) scale. Variability is due to the biological constituents of the reagent, the observer, and the instrumentation. To have reliable methods for evaluation of performance of these products, we are developing a quantitative method that uses photometric measurements of microscopically observed epifluorescence of slide preparations. A computer-controlled microscope-photometer converts the light intensity into a voltage measurement. Our goal is to replace the subjective endpoint determination with an objective, quantitative method. The instrumentation and its operating characteristics are presented in this paper. Selected commercially available fluorescent materials were evaluated as calibrators for the instrumentation. These materials showed consistency in measurement and thus demonstrated their suitability for various levels of calibration. It is possible that they will prove useful as a reference standard for interlaboratory comparisons.

Review of medical biosensors and associated materials problems.

Developers of biosensors as medical devices are using emerging technologies that incorporate chemical assays with fiber optics and semiconductors. These biosensors will eventually become indwelling catheters for monitoring blood analyte concentrations as well as functioning as controlled feedback elements for artificial organs. Materials used in these devices are subject to problems of manufacture and reliability as well as those induced by the human body's response to these "foreign agents." The Division of Mechanics and Materials Science in the Center for Devices and Radiological Health at the Food and Drug Administration has initiated a program to investigate factors that effect sensitivity, selectivity and reliability of sensors used in biological applications. Our group's principle focus is on sensors of chemical processes. This article is an outgrowth of our research efforts and is a review of some of the technologies that are currently available or becoming available for these applications. The goal of our research is to identify factors that will have an impact on the reliability of long-term implanted medical devices with particular attention to sensors used in feedback-controlled therapeutic systems.

Performance characteristics of a new photometer with a moving filter tape for luminescence assay.

The performance characteristics of a new photometer that incorporated a reaction system consisting of a movable filtration tape have been studied for use with the firefly luciferase assay for adenosine 5'-triphosphate. Precision, linearity, and sensitivity are given for measuring a graded series of constant-light emitters, concentrations of adenosine 5'-triphosphate, and washed bacterial cells. Precision ranged from 1 to 10% coefficient of variation. The coefficient of correlation was 0.9985 for 7 X 10(8) to 7 X 10(3) bacteria per ml; however, the accuracy decreased at the low levels. The sample processing time was 2 min for a 1-ml sample. This instrument shows potential for many applications in quantitating small numbers of organisms, e.g., pollution, water monitoring, and clinical infection detection.