Measurement of in- vitro fibre dissolution rate at acidic pH

Abstract A low biopersistence of man-made vitreous fibres (MMVFs) has often been related to a high in-vitro dissolution rate at near-neutral pH. For some fibre types, however, a low in-vivo biopersistence cannot be explained by the in-vitro dissolution rate in near-neutral physiological fluids. It has been suggested, that the high in-vitro dissolution rate of these fibres at the acidic pH which is found inside the phagolysosomes of the alveolar macrophages could be the reason for the fast in-vivo clearance of such fibres. The aim of this study was, through interlaboratory comparison of in-vitro dissolution measurements at acidic pH, to investigate the causes of variations and to identify key parameters for a measurement method similar to the method used at near neutral pH. Results of in-vitro measurements of different fibre types at acidic pH are presented, and the influence of different test parameters described. The measurements and calculations at acidic pH can be made similar to what is done for measurements at near-neutral conditions. Since incongruent dissolution is often very pronounced, it is relevant to calculate two dissolution rates, one for the network represented by silicon and one for the leaching elements. In order to obtain comparable results it is necessary to use a liquid which is well-defined with respect to type and concentration of buffer system, and to compare only values obtained under similar experimental conditions. The measured dissolution rates differ substantially with different liquids and different experimental conditions. However, the ranking of the different tested fibres with respect to the dissolution rates remains the same as long as they are tested under identical conditions.