Publicação
Bone cements: development of partially degradable ionomer cements
| Resumo: | The first glass-ionomer cement (GIC) was developed by Wilson and Kent in 1971. GICs are usually prepared through the mixing of a fluoroaluminosilicate glass powder, polyacrylic acid (PAA) and water. The PAA attacks the glass particles that leach some of its cations (e.g. Al3+ and Ca2+) to the cement matrix. These cations cross-link the PAA chains yielding the final cement structure. GICs possess as main advantage the ability to bind to hydroxyapatite present in the dentin and bone. These systems have been mainly used in the dentistry field (non-systemic application). Applications that induce a systemic uptake of the cement components (e.g. bone cements) have been discarded due to the presence of aluminium (a known neurotoxin) on the GIC formulations. The present thesis targets the development of new glass-ionomer cement (GIC) formulations with potential to be applied as bone cements. To this purpose, new aluminium-free glass compositions of general formula 0.340SiO2 : 0.300ZnO : (0.250-xy) CaO : xSrO : yMgO: 0.050Na2O : 0.060P2O5 (where x and y = 0.000 or 0.125) were synthesised and tested in the formulation of GICs through their mixing with PAA and water. The different parameters that influence the GIC mechanical performance (e.g. glass particle size, molecular weight of PAA, proportion of the constituents, etc.) were optimized. The GIC prepared with the developed glass compositions where in vitro tested for their bioactivity. To this purpose, GIC samples were immersion in SBF and their ability to form a surface apatite layer was evaluated by: 1) determination of the concentration of the calcium and phosphorous in the SBF (executed by ICP); 2) quantification of the calcium and phosphorous present at the surface of the cements (executed by EDS) and 3) morphological analysis (executed by SEM). Micro-CT was also used to evaluate the spatial distribution of the polymeric and inorganic phases. Finally, in an attempt to enhance the GIC biodegradability it was incorporated starch in the cement formulations, at different weight percentages (5% and 25%). The results obtained under this thesis proved the suitability of some of the developed glass compositions (e.g. 0.34SiO2: 0.30ZnO: 0.125CaO: 0.125SrO: 0.05Na2O: 0.06P2O5) to prepare GICs in accordance with its use as bone cements, including: suitable mechanical performance (compressive strength, CS=25 MPa; compressive modulus, CM=492 MPa) for non-load bearing applications; bioactivity; and 35 % porosity. Moreover, after the 8th week of degradation under enzymatic medium it was detected reducing sugars in the degradation solutions of the starch-containing formulations confirming its biodegradation potential at a longer timeframe. |
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| Autores principais: | Gomes, Filipa Oliveira |
| Ano: | 2011 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The first glass-ionomer cement (GIC) was developed by Wilson and Kent in 1971. GICs are usually prepared through the mixing of a fluoroaluminosilicate glass powder, polyacrylic acid (PAA) and water. The PAA attacks the glass particles that leach some of its cations (e.g. Al3+ and Ca2+) to the cement matrix. These cations cross-link the PAA chains yielding the final cement structure. GICs possess as main advantage the ability to bind to hydroxyapatite present in the dentin and bone. These systems have been mainly used in the dentistry field (non-systemic application). Applications that induce a systemic uptake of the cement components (e.g. bone cements) have been discarded due to the presence of aluminium (a known neurotoxin) on the GIC formulations. The present thesis targets the development of new glass-ionomer cement (GIC) formulations with potential to be applied as bone cements. To this purpose, new aluminium-free glass compositions of general formula 0.340SiO2 : 0.300ZnO : (0.250-xy) CaO : xSrO : yMgO: 0.050Na2O : 0.060P2O5 (where x and y = 0.000 or 0.125) were synthesised and tested in the formulation of GICs through their mixing with PAA and water. The different parameters that influence the GIC mechanical performance (e.g. glass particle size, molecular weight of PAA, proportion of the constituents, etc.) were optimized. The GIC prepared with the developed glass compositions where in vitro tested for their bioactivity. To this purpose, GIC samples were immersion in SBF and their ability to form a surface apatite layer was evaluated by: 1) determination of the concentration of the calcium and phosphorous in the SBF (executed by ICP); 2) quantification of the calcium and phosphorous present at the surface of the cements (executed by EDS) and 3) morphological analysis (executed by SEM). Micro-CT was also used to evaluate the spatial distribution of the polymeric and inorganic phases. Finally, in an attempt to enhance the GIC biodegradability it was incorporated starch in the cement formulations, at different weight percentages (5% and 25%). The results obtained under this thesis proved the suitability of some of the developed glass compositions (e.g. 0.34SiO2: 0.30ZnO: 0.125CaO: 0.125SrO: 0.05Na2O: 0.06P2O5) to prepare GICs in accordance with its use as bone cements, including: suitable mechanical performance (compressive strength, CS=25 MPa; compressive modulus, CM=492 MPa) for non-load bearing applications; bioactivity; and 35 % porosity. Moreover, after the 8th week of degradation under enzymatic medium it was detected reducing sugars in the degradation solutions of the starch-containing formulations confirming its biodegradation potential at a longer timeframe. |
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