Aspects of the in vitro bioactivity and antimicrobial properties of Ag(+)- and Zn (2+)-exchanged 11 A tobermorites.

11 A tobermorite, Ca(5)Si(6)O(16)(OH)(2) . 4H(2)O, is a layer lattice ion exchange mineral whose potential as a carrier for Ag(+) and Zn(2+) ions in antimicrobial, bioactive formulations has not yet been explored. In view of this, the in vitro bioactivity of Ag(+)- and Zn(2+)-exchanged 11 A tobermorites and their bactericidal action against S. aureus and P. aeruginosa are reported. The in vitro bioactivity of the synthetic unsubstituted tobermorite phase was confirmed by the formation of bone-like hydroxycarbonate apatite (HCA) on its surface within 48 h of contact with simulated body fluid. The substitution of labile Ag(+) ions into the tobermorite lattice delayed the onset of HCA-formation to 72 h; whereas, the Zn(2+)-substituted phase failed to elicit an HCA-layer within 14 days. Both Ag(+)- and Zn(2+)-exchanged tobermorite phases were found to exhibit marked antimicrobial action against S. aureus and P. aeruginosa, two common pathogens in biomaterial-centred infections.