Date of Award
Doctor of Philosophy
Department of Manufacturing, Biomedical and Facilities Engineering
Dr. Daniel Boyd
Dr. Helen O'Shea
Dr. Ger Kelly
Calcium silicate ceramics are amongst a group of ceramic materials currently utilised as bone graft materials. However, current calcium silicate grafts offer little therapeutic potential and poor mechanical properties. The objective of this project was to examine the composition-structure-property relationships arising from the incorporation of therapeutic ions of strontium (Sr) and zinc (Zn) into calcium silicate glass-ceramics (GC) in order to allow for healthy bone regeneration and antibacterial efficacy. Five compositions were studied with varying mole fractions of Sr and Zn. The GC’s were characterised using differential scanning calorimetry (DSC), x-ray diffraction (XRD) at room and ascending temperatures, x-ray tomography (XRT) and dilatometry. The evolution of crystalline phases for each GC was investigated up to the materials’ first temperature of crystallisation, where it was established that BTl 10, BTl 11 and BTl 12 comprised of biocompatible materials, namely sodium calcium silicate in the case of BTl 10, calcium silicate in BTl 11, and calcium silicate and sodium silicate in BTl 12. BTl 11 and BTl 12 also contained a Sr rich glass phase within the glass ceramic. Based on the characterisation data, GC foams were fabricated with structures permissive for osseous integration and vascularisation. The foams had an average porosity of 94% and Sr^^ and Zn^^ release was quantified over 1, 7 and 30 days, under normal (NPC) and extreme physiological conditions (EPC) for each GC. The Zn^^ release results at pH 7.4 ranged from lppm-30ppm and indicated that under NPC, all examined Zn-containing GC’s have potential as therapeutic bone grafts, but, under EPC, the high Zn^"^ levels (74ppm-600ppm) may produce cytotoxic effects. Sr-containing GC’s demonstrated Sr release in the range 6ppm-318ppm at pH 7.4 and 138ppm-582ppm at pH 3, and indicated that all GC’s s may have therapeutic potential under both physiological conditions. BTl 10, BTl 11 and BTl 12 sintered disks were found to have biaxial flexural strengths (BFS) in excess of both hydroxyapatite and p-tricalcium phosphate, following incubation in simulated physiological conditions with average maximum values of 120MPa, 149Mpa and 121 Mpa, respectively. The antibacterial activity of BTl 10, BTl 11, and BTl 12 was then assessed by the zone of inhibition test using three bacterial strains commonly associated with orthopaedic implant infections. BTl 12 exhibited a zone of inhibition for all three bacteria used. The radii of the zones of inhibition were as follows - E.faecalis 13 mm ±0.2 mm, MRSA 6.5 mm ±0.2 mm and P. aeruginosa 16 mm±0.2 mm. Also shown in Figure 7(C), BTl 10 demonstrates an inhibitory effect on P. aeruginosa with a halo of inhibition present whose radius was measured at 3.8 mm±0.2 mm. The results of the work carried out indicate that the glass ceramics investigated have excellent potential in both load bearing and non-load bearing application, whilst providing therapeutic benefit at a local level.
Looney, Mark, "Composition - Structure - Property Relationships in Strontium / Zinc Doped Glass-Ceramics." (2011). Theses [online].
Available at: https://sword.cit.ie/allthe/223