Aspects of the in vitro bioactivity and antimicrobial properties of Ag+- and Zn2+-exchanged 11 Å tobermorites

11 Å tobermorite, Ca5Si6O16(OH)2 · 4H2O, is a layer lattice ion exchange mineral whose potential as a carrier for Ag+ and Zn2+ ions in antimicrobial, bioactive formulations has not yet been explored. In view of this, the in vitro bioactivity of Ag+- and Zn2+-exchanged 11 Å 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 Zn2+-substituted phase failed to elicit an HCA-layer within 14 days. Both Ag+- and Zn2+-exchanged tobermorite phases were found to exhibit marked antimicrobial action against S. aureus and P.aeruginosa, two common pathogens in biomaterial-centred infections.

Aspects of the in vitro bioactivity of hydraulic calcium (alumino)silicate cement

In response to a burgeoning interest in the prospective clinical applications of hydraulic calcium (alumino)silicate cements, the in vitro bioactivity and dissolution characteristics of a white Portland cement have been investigated. The formation of an apatite layer within 6 h of contact with simulated body fluid was attributed to the rapid dissolution of calcium hydroxide from the cement matrix and to the abundance of pre-existing Si-OH nucleation sites presented by the calcium silicate hydrate phase. A simple kinetic model has been used to describe the rate of apatite formation and an apparent pseudo-second-order rate constant for the removal of HPO42- ions frorn solultion has been calculated (k(2) = 5.8 x 10(-4) g mg(-1)). Aspects of the chemistry of hydraulic cements are also discussed with respect to their potential use in the remedial treatment of living tissue. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 90A: 166-174, 2009

Heritage

This article examines the concepts, definitions, policies, and practices of heritage in a contemporary context. Within recent years, there have been significant shifts in our understandings and applications of heritage concepts and policies in the modern world. ‘Heritage’ emerged as a buzz word in international policy arenas in the 1980s and early 1990s, and has since weathered the vagaries of turbulent definitional and governance–nomenclature storms, as traditional debates about ‘what it is and what it is not’ reverberate around academia and state agencies alike. Policy and funding structures for heritage are determined by the classifications used to define them in various countries. Typically, reference is made to ‘built heritage’, ‘natural heritage’, and ‘intangible heritage’, loosely reflecting buildings, landscapes, and culture. Aspects of heritage are used by the cultural and tourism industries to add economic value, through heritage tourism sites, museums, and other activities. The cultural tourism product is often anchored around notions of heritage, and in postmodern, post-tourist societies, boundaries between culture, (travel) space, and identities are increasingly blurred. Issues of authenticity become important in the representation of heritage, and questions are asked about the validity of nostalgia versus realism. The role of heritage is examined in the context of identity formulation at individual and nation-state levels, and the political aspects of this are also discussed. Finally, heritage conservation is assessed through an examination of UNESCO’s World Heritage Site listing and protection strategy. In a changing world, new constructs of heritage, identity, authenticity, and representation will continue to emerge as meanings are constantly renegotiated over time and space.