The dissolution of silver–sodium–calcium–phosphate glasses for the control of urinary tract infections

Cast tubes of silver–sodium–calcium–phosphate controlled release glasses have been developed for the delivery of a constant concentration of silver ion in aqueous flow systems. In the solid glasses calcium ions are preferentially located at the ends of polyphosphate chains and randomly at middle-group sites. The polyphosphate anions that persist after dissolution have been analyzed by two-dimensional NMR methods; a range of linear ions can be detected but the predominant species is cyclo-hexaphosphate. With water as flow medium the concentration of silver in the effluent depends on the glass composition. When the flow medium is simulated urine, which contains, among other constituents, chloride, urea and creatinine, the concentration of silver is controlled by the equilibrium between solid silver chloride and the bis(creatinine)silver cation.