Durability of glass and ceramic fibres within the lung.

The durability in the lung of inorganic fibrous materials, such as asbestos and man-made mineral fibres, appears to be a major determinant of their pathogenic potential. However, studies have been inadequate in explaining differences in the physiological durability of such inorganic fibres.This study used an iterative approach to determine key factors affecting physiological durability of a soda-lime silicate bulk glass, A-glass, E-glass, Lead-glass, Cemfil and alumino-silicate ceramic fibres. The aims were to develop a) the current theoretical understanding of durability and b) a suitable in-vitro screening test for durability.Materials were exposed to simulations of the lung environment, which included a) exposure to Gamble's fluid, water, serum and other simulated fluids, b) long-term exposure to the intra-macrophage environment and c) exposure to rat lung. Durability was characterised by scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray microanalysis (EDXA). The use of secondary ion mass spectrometry (SIMS) was also explored, though further development was required in this area.Fibre behaviour depended on fibre composition and thenature of the exposure environment. The ceramic was durable in all environments, whilst A-glass, Lead-glass and the soda-lime silicate were prone to nucleophilic attack and leaching. The effects of in-vivo exposure were consistent with the response in-vitro. However, exposure to the intramacrophage environment in-vitro did not affect fibre durability and this surprising result should be investigated. Physiological durability was related to the ability of the fibre to resist nucleophilic attack and a hybridization bonding model was examined in order to explain the behaviour of some silicate glasses. It was recommended that models based on the molecular bonding were developed to encompass a wider range of materials.Occupational exposure and inhalation of asbestos fibre can cause lung disease and although the mechanisms of asbestos pathogenicity remain uncertain, attention has also focussed on the potential effects of other inorganic fibres.Comparative studies on behaviour of these materials in the lung have strongly implicated the durability and hence lifetime of the fibre to be a major determinant of the pathogenic potential. However, durability studies have generally been inadequate in explaining differences in physiological durability of inorganic fibres and hence provision of theoretical models.This study used a novel iterative approach to determine key factors affecting physiological durability of a range of glass and ceramic materials. The objective was to develop the theoretical understanding of the durability of inorganic fibrous materials in the lung and appraise in-vitro methods for determination of fibre durability to validate a suitable screening test.The durability of a range of glass and ceramic materials has been characterised using in-vitro and in-vivo simulations of the human lung environment; novel exposure systems have been developed and durability behaviour has been characterised by application of traditional analytical methods and by development and application of secondary ion mass spectrometry (SIMS) techniques.Appraisal of in-vitro simulations revealed that fibre behaviour depended upon fibre composition and exposure conditions' durability of the fibres in-vitro was related to model fluid pH. Fibre response in-vivo was rationalised by assuming localised pH variation.This work supports the use of a range of in-vitro exposure conditions to identify key determinants of fibre durability and to characterise chemical behaviour, and is critical of the use of single in-vitro screening tests which will reflect fibre behaviour under specific conditions.Resistance of the inorganic fibre network to hydrolytic attack was suggested as a key determinant of durability and a theoretical model was developed to predict this.