Synthesis of calcium-silica composites: a route toward an in vitro model system for calcific band keratopathy precipitates.

Calcific band keratopathy (CBK) is a degenerative condition resulting in the deposition of calcium salts in the superficial layers of the cornea and causing significant visual disturbance and pain of the affected eye. Unfortunately, the amount of CBK precipitates recovered from the affected eye is very small therefore; it would be beneficial to prepare a synthetic material mimicking CBK material to further the development of therapeutics. Analyses of biological samples recovered from patients show the presence of silicon in addition to calcium, as well as a distinctive fused spherical morphology. This prompted us to study the reaction of various sources of silicon (fumed silica, silicic acid, and silicone oil) with CaCO(3) under a range of reaction conditions to gain an understanding of the formation of CBK. A silicon source alone was not found to be responsible for the fused spherical morphology, and a third component, a polar surfactant-like molecule such as sodium dodecyl sulfate or tetradecylphosphonic acid, was also required. The effects of silicon:calcium ratio and reaction time have been studied. The reaction of fumed silica with CaCO(3) in presence of sodium dodecyl sulfate results in the formation of spherical shapes resembling the structures and chemical composition observed in the eye samples, while no such structures were observed in the absence of silicon. Samples closely resembling human samples were also formed from the reaction of silicone oil with CaCO(3) in the presence of tetradecylphosphonic acid. Samples were characterized by SEM, XRD, and XPS and Raman spectroscopy.