Predicting the <i>in vitro</i> dissolution rate constant of mineral wool fibers from fiber composition

We developed predictive formulae for the <i>in vitro</i> dissolution rate constant k_dis of acid-soluble synthetic vitreous fibers (SVF), paralleling our earlier work with glass wools, which are typically more soluble at neutral pH. Developing simple models for predicting the k_dis of a fiber can allow prediction of <i>in vivo</i> behavior, aid fiber developers, and potentially reduce <i>in vivo</i> testing. The k_dis of several acid-soluble SVF were determined using high simulant fluid flow/fiber surface area (F/A) conditions <i>via</i> a single-fiber measurement system. Four fluids were employed, varying in base composition and citrate levels. Equations predicting the k_dis were derived from fiber chemistry and dissolution measurements for two of the fluids. Testing of several fibers showed a ∼10× increase in the k_dis when citrate was included in the simulant solution. Data from tests with Stefaniak’s citrate-free Phagoloysosmal Simulant Fluid (PSF) yielded k_dis values aligned with expectations from <i>in vivo</i> results, unlike results from citrate-containing modified Gamble’s solution. Predictive equations relating fiber chemistry to k_dis showed reasonable agreement between the measured and predicted values. Citrate inclusion in the solution under high F/A conditions significantly increased the measured k_dis. This resulted in more biorelevant data being obtained using the PSF fluid with the high F/A method used. The developed predictive equations, sufficient for fiber development work, require refinement before a recommending their use in place of <i>in vivo</i> biopersistence testing. Significant fit improvements are possible through additional measurements under these experimental conditions.