Encrustation of a metal alloy urinary stent: A mechanistic investigation

Objectives: To investigate the kinetics of encrustation of a metall alloy u rinary stent system in vitro by calcium oxalate and characterize the crysta ls forming from solutions supersaturated with respect to all calcium oxalat e hydrates. Materials and Methods: A section of a metal stent consisting mainly of tant alum coated partially by strongly adhering calcium oxalate monohydrate (COM ) crystals was immersed in supersaturated solutions prepared from calcium c hloride and sodium oxalate at 37 degrees C and ionic strength 0.15 Min NaCl . Results: The COM-coated stent mineralized upon immersion in the supersatura ted solutions. The process was monitored with a calcium ion-selective elect rode and the rates were measured at conditions of sustained solution supers aturation. COM crystals formed on the stent and the rate of COM crystal gro wth yielded a second-order dependence on the solution supersaturation. Conclusions: The deposition of COM crystals on the metal stents coated part ially with COM crystals by adhesive forces was found to be most important f or the acceleration of the encrustation process. The dependence of the rate s on the solution supersaturation suggested absence of secondary nucleation and a surface-controlled process for the encrustation process. Copyright ( C) 2000 S. Karger AG, Basel.