On the role(s) of additives in bioinspired silicification.

Biological organisms are able to direct the formation of patterned and hierarchical biomineral structures. Extractable organic materials have been found entrapped in diatom, sponge and plant biosilica, some of which have been isolated by selective chemical dissolution methods and their composition and structure studied. Information gained from the bioextracts has inspired materials chemists to design biomimetic analogues and develop bioinspired synthetic schemes for silica formation. The results obtained from bioinspired silicification investigations are hypothesised to arise from specific modes of action of the organic additives, which are described in this review. Specifically, additives in bioinspired silicification act either as catalysts, aggregation promoting agents or structure-directing agents or more typically, exhibit a combination of these behaviours.