Hydroxyapatite (HAP) belongs to a family of structurally and chemically related, sparingly soluble calcium phosphate (CP) salts , and is the structural prototype for the principal mineral component of bone and teeth . Well-defined synthetic HAP has excellent biocompatibility and is widely exploited as a biomedical material . Furthermore, synthetic HAP is frequently used as a surrogate in studies of calcified tissue, because the latter are complex and highly variable . For an overview of bioceramic applications and materials, see the review by Wilson [Chap. 11, this volume].The adsorption of naturally occurring and synthetic polyelectrolytes (macromolecular ions) on HAP and other CPs is of great fundamental and ppractical interest for biological, medical and industrial applications. Studies have shown that polyelectrolytes impact the solubility [5,6] and surface chemistry [7,8] of HAP, among other properties . Understanding polyelectrolyte adsorption mechanisms on HAP has direct implications for the adhesion of polycarboxylate based resins and composites in dental restoriation [10-16]. Used as antiscalantsis polyelectrolytes inhibit or retard CP precipitation by blocking growth sites on crystal nuclei and via complexation reactions with constitutent ions 117-201. Biological polyelectrolytes, which include polysaccharides and proteins, act as regulators and/or matrices for biomineralization mechanisms in bone and teeth [2,21]. Amelogenin proteins, for instance, modulate calcium phosphate precipitation and growth during the development of tooth enamel, and are the principal components of the developing enamel matrix . Amelogenin exhibits an affinity for specific faces on the growing crystallite via its carboxyl moieties, thus facilitating the high aspect ratios characteristic of tooth enamel crystals. The proteins are proteolytically removed once the matrix is fully formed, leaving behind a mature enamel microstructure composed almost entirely of oriented elongated apatite crystals. In the present chapter we examine the interactions of ionizable polymers with HAP and related CP minerals with a focus on the underlying chemical mechanisms that govern adsorption in an aqueous medium. Furthermore, we examine the resulting impact these interactions have on the chemical composition of the minearal surface and bulk solution.
Polymers in Particulate Systems: Properties and Applications