Development of a Novel In-vivo Setting Bone Graft Substitute From Bioactive Glass

Abstract

Calcium phosphate cements are in-vivo setting, injectable calcium phosphate based biomaterials. They are made of calcium phosphate salts which when mixed with water react to form apatite, the mineral phase of bones and teeth. This study investigates a novel way of forming calcium phosphate cements using bioactive glasses. The aim of the work was to discover a novel route of synthesis using a silicate bioactive glass. Fifteen glass compositions were produced designed to investigate P2O5 content, CaF2 content and calcium to sodium ratio within the glass. Glasses were produced via a melt-quench route before being milled and sieved to below 38 μm. The bioactive glass and Ca(H2PO4)2 powders were mixed in an overall calcium to phosphate ratio of 1.67. The cement powder was then reacted with a 2.5 % solution of Na2HPO4. The paste was then mixed and then placed into cylindrical moulds. Eight samples were immersed into Tris buffer solution for 1 hour, 1 day, 7 days or 28 days. The compressive strength was measured for each specimen as well as SEM performed and the setting times for each composition was studied using the Gilmore needle test. The cement phase was analysed using 31P & 19F MAS-NMR, FTIR and XRD. The results showed that both compressive strength and setting time was dependent upon glass composition. As sodium content was increased both the initial and final setting times decreased. Increased fluoride addition caused a decrease in the setting time. In the fluoride free compositions octacalcium phosphate was identified in all compositions. The cement setting reaction for these compositions followed a similar reaction of first forming dicalcium phosphate dihydrate which transformed to octacalcium phosphate then eventually hydrolysing to hydroxyapatite. When fluoride was incorporated into the cement the phases formed were fluoridated-apatite and DCPD. In conclusion a novel method of producing calcium phosphate cements was discovered using a bioactive glass as a reactive precursor. It was shown that the cement phase, setting time and compressive strength could all be altered by changing the glass composition.