Measurement of in vitro size changes for synthetic vitreous fibers

Introduction
Synthetic vitreous fibers (SVFs) include several commercially important mineral fibers. The potential pathogenicity of a specific fiber depends upon the extent to which the fibers can be inhaled and can persist in the lung. Fiber durability may involve processes occurring both within cells and within the extracellular fluids. The aim of this study is the determination of dissolution fibers in saline solution that simulated the physiological fluids using a stationary model in vitro. 

Methods
The studied fibers were glass wool, rock wool, Super wool X607 HT and a rock wool supplied as “soluble rock wool” by a Danish manufacturer. To simulate macrophage environment and extracellular environment we used a Gamble’s solution to two different pH, respectively 4.5 and 7.4. In the stationary test, 60 mg of fibers was added to 100 ml of Gamble’s solution and maintained at 37°C. The test lasted from 1 to 4 weeks and each solution is analyzed at last weekly. After the test the fibers are checked for weight loss and exanimated by scanning electron microscopy (SEM) to observe changes in fiber morphology and dimension. 

Results
The SEM analysis showed a reduction of length-weighted fiber diameter for all fibrous materials. This reduction was larger at pH 4.5 than at pH 7.4. Super wool showed surface precipitates and rock wool showed corroded layers on the surfaces of the fibers. Moreover a mass loss of each sample was estimated dependent on time.

Discussion
The tests show that fiber dissolves or leaches more rapidly under acid than neutral PH. It indicates that there is strong dependency on pH which affects not only total fiber dissolution but also the leaching of specific chemical components. Now we are studying the chemical changes of filtered solution used in the tests resulting from dissolution and leaching process of the fibers.