In vitro assessment of biodurability: acellular systems.

The assessment of biodurability of man-made vitreous fibers is essential to the limitation of health hazards associated with human exposure to environments in which respirable fibers are present. In vitro acellular systems provide effective test methods of measuring fiber solubility provided care is taken to select the most suitable solvent and test conditions for the specific fiber type and dimension.

SEM-EDS analysis of glass fibers corroded in physiological solutions by dynamic tests with variable flow rates.

The dissolution of mineral fibers has been studied in simulated physiological fluids using a dynamic testing procedure. Fibers of different chemical composition and obtained by different processes with a mean diameter of about 1 micron, have been characterized with respect to their solubility under various test conditions of flow-rate. The surfaces were analyzed using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction techniques. SEM examinations show the formation of various corrosion patterns: porous, gel-like outer layers; precipitation zones and even, in some cases, no modification of the surface aspect. EDS analyses performed on the fibers, on the fiber surface layers, or on the deposits show three types of chemical composition: areas enriched in Al, in Ca and P, or in Al, Ca, and P. These surface compositions can be found for the same type of fiber tested, depending on the flow rate of the solution. Surface changes depend strongly on the initial composition of the glass and on the test conditions, particularly the flow rate. It is of particular interest to characterize the remaining surfaces (if any) obtained at the end of the in vitro test run and to compare them with surface analysis of the recovered fibers from the in vivo tests to assess the validity of the in vitro tests.

In vitro dynamic solubility test: influence of various parameters.

This article discusses the dissolution of mineral fibers in simulated physiological fluids (SPF), and the parameters that affect the solubility measurement in a dynamic test where an SPF runs through a cell containing fibers (Scholze and Conradt test). Solutions simulate either the extracellular fluid (pH 7.6) or the intracellular fluid (pH 4.5). The fibers have various chemical compositions and are either continuously drawn or processed as wool. The fiber solubility is determined by the amount of SiO2 (and occasionally other ions) released in the solution. Results are stated as percentage of the initial silica content released or as dissolution rate v in nm/day. The reproducibility of the test is higher with the less soluble fibers (10% solubility), than with highly soluble fibers (20% solubility). The influence of test parameters, including SPF, test duration, and surface area/volume (SA/V), has been studied. The pH and the inorganic buffer salts have a major influence: industrial glasswool composition is soluble at pH 7.6 but not at pH 4.5. The opposite is true for rock- (basalt) wool composition. For slightly soluble fibers, the dissolution rate v remains constant with time, whereas for highly soluble fibers, the dissolution rate decreases rapidly. The dissolution rates believed to occur are v1, initial dissolution rate, and v2, dissolution rate of the residual fibers. The SA of fibers varies with the mass of the fibers tested, or with the fiber diameter at equal mass. Volume, V, is the chosen flow rate. An increase in the SA/V ratio leads to a decrease in the dissolution rate.(ABSTRACT TRUNCATED AT 250 WORDS)