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Synthesis of chemically modified or ion-substituted hydroxyapatite (HA) as a bioactive bone replacement material is of great interest since the main component of hard tissues in vertebrates is a substituted apatite. The most abundant species in natural bone mineral other than calcium and phosphate ions is carbonate ions. Carbonate ions can be substituted at 2 distinct sites in the HA lattice; the hydroxide (OH) site and the phosphate (PO4) site. Synthetic silicate substituted HA (SiHA) and carbonate-substituted HA (CHA) have each previously been shown to enhance new bone formation when compared to HA in vivo. The positive bioactive properties that result, individually, from carbonate or silicate substitution led to the hypothesis that simultaneous co-substitution of these two ions in to the HA lattice would lead to further improved bioactivity. A range of novel silicate and carbonate co-substituted HA (SiCHA) materials were prepared with silicate substitution of up to 12.5 wt% (3.8 wt% Si) and carbonate substitution up to 8.2 wt%. These compositions were characterised extensively, examining both their chemical and physical attributes. These compositions were single phase after sintering in a wet CO2 atmosphere to near-theoretical density, and contained carbonate ions on both hydroxide and phosphate sites. The grain sizes of these ceramic specimens of these compositions were intermediate between those of CHA and SiHA controls. Further controlled synthesis demonstrated that carbonate and silicate ions could be substituted in non-equimolar quantities, and increased amounts of carbonate could be substituted independently on to the hydroxide site of the SiCHA samples. The biological response to these materials was assessed by completing direct and indirect cell culture experiments using both the MG-63 osteoblast-like cell line and primary human osteoblast (pHOB) cells. The silicate and carbonate co-substituted materials and their dissolution products were not toxic to either of the cell lines, and cell proliferation was observed with all materials studied. The effect of the synthesis route on the purity of silicate-substituted hydroxyapatite (SiHA) was also assessed, with a particular focus on the role of tetraethyl orthosilicate (TEOS) as the source of silicate. The outcomes of this study showed that the final composition of SiHA was strongly dependent on how and when the tetraethyl orthosilicate (TEOS) solution was incorporated during the precipitation reaction.

Mode of access: World Wide Web. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 94-111). / Electronic reproduction. / Also available by subscription via World Wide Web / xv, 111 leaves, bound ill. (some col.) 29 cm

Thesis (PhD)--University of South Australia, 1997

The search for a new environmentally friendly construction material that will match the durability of ancient concrete has stimulated interest in geopolymerisation in recent times. Despite extensive research that has been conducted on various aspects of geopolymerisation, especially in enhancing the properties of resultant binders and understanding the chemical mechanisms involved, a number of questions remain to be answered. The role of calcium in geopolymerisation is one of them. It is known that the presence of a moderate amount of calcium in a geopolymeric binder will improve the resultant compressive strength. However, it is still unclear whether calcium will play a charge-balancing role within the aluminosilicate structure (to maintain electro-neutrality in a similar way as alkali metal cations, Na+ or K+, or perhaps an alternative role). In addition, the role of calcium in geopolymerisation is of great interest because it is proposed for the first time that calcium links geopolymer chemistry to, and distinguishes it from, ordinary Portland cement (OPC). (For complete abstract open document)

Thesis (Ph.D.)--McMaster University (Canada), 1989. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.

Th. univ.--Chim. théorique et informatique--Paris 6, 1994. / 1995 d'après la déclaration de dépôt légal. Bibliogr. p. 185-196. Résumé en français et en anglais.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Albert E. Stiegman, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Sept. 24, 2004). Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 71-76).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. Description based on print version record. Includes bibliographical references.