A new technology of microdispersed silver in polyurethane induces antimicrobial activity in central venous catheters

Metal ions or metal ions in complexes or compounds ha,ve been used for cent uries to disinfect fluids, solids and tissues. The biocidal effect of silve r,er, with, its broad spectrum of activity, including bacterial, fungal and \iral agents, is particulal lg well known,in and the term "oligodynamic ac tivity, nas coined for this phenomenon,Silver ions ha,re an affinity to sul fhydryl groups in enzyme systems of the cell,wall, through which they inter fere with the transmembranous energy transfer and electron transport of bac terial mieroorganisms. Silver,er ions also block the respiratory chain of m icroorganisms reversibly in low concentrations and irreversibly in higher c oncentrations. Binding to the DIVA of bacteria and fungi increases the stab ility of the bacterial double helix and thug inhibits proliferation. There is no cross resistance with antibiotics and also no induction of antimicrob ial resistance by silver ions. The concentrations required for bactericidal activity are in the range 10(-9) mol/l, These concentrations can be achiev ed in solution by the interaction of metallic silver with electrolytes only if there is a large enough surface of silver,. BS a no, el technology, met allic silver, is distributed in submicron particles in polyurethane and res ults in a concentration of 0.8% in an active surface of 450 cm(2)/g polyure thane. Polyurethane is hygroscopic and rapidly attracts,vater; the interact ion of electrolyte solutions with the estremely finely distributed silver t hroughout the polyurethane releases bactericidal concentrations of silver c er ions over a period of years to the surface of the material. The electron egatively, charged surface of bacteria attracts the positively, charged sil ver ions, The concentrations released from the polyurethane are far below t he toxic concentrations for humans.