Surface reactivity of glasses and glass-ceramics for medical applications

P7 Surface reactivity of glasses and glass-ceramics for medical applications MHV Fernandes, RN Correia, JR Frade, JM Oliveira, C Queiroz, M Ferro, S Cachinho, N Almeida Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal In the several projects(1) within the scope of this subject it is aimed to contribute in some way for the understanding of the mechanisms governing the precipitation and adhesion of the apatite layers formed on the surface of glasses and glass-ceramics when immersed in synthetic plasmatic solutions. The surface reactivity of glasses and glass-ceramics, correlated with the characteristics of the in vitro apatite layers, is related with parameters such as the rate of glass dissolution, the extent of crystallization and the nature of crystalline phases within the glass-ceramics. The rate of glass dissolution depends on the composition of the glass matrix but it is mostly determined by the main silicate structure of the glass, namely by the kind of network modifiers present, which can have quite distinct disrupting characters. By another side the extent of crystallization and the nature of the crystalline phases within the glass-ceramics affect the adhesion of the apatite layer to the base material. Studies under way on the effect of glass structure on the surface reactivity are being carried out on glasses of the systems SiO2-CaO-P2O5-MgO and SiO2-Na2O-MgO. Experimental techniques involve NMR, FTIR, Raman, complemented by ICP, XRD, SEM and AFM. The results indicate that there is a relationship between reactivity and relative amount of silicate Qn units in the base glass structure, a higher dissolution being observed for the Q structural units of lower n. The relative amount of Q units can be controlled by the network disrupting effect of different modifying oxides, namely Na2O and MgO. Studies on the effect of crystallization on surface reactivity are being carried out with compositions of the SiO2-P2O5-CaO-MgO-K2O system. Glass ceramics (GCs) are obtained from glasses submitted to different time-temperature schedules and the respective microstructures assessed by SEM with the objective of understanding their crystallization behaviour. In vitro tests in simulated fluids allow to relate composition, microstructure and surface reactivity. The results suggest that in vitro apatite layers precipitated on GCs samples exhibit improved adhesion to the base material, compared with the apatite layers deposited on the respective parent glasses. When comparing different crystallized materials the Kfree GCs show looser apatite layers than the K-containing GCs. Together with parameters such as composition of the glassy and crystalline phases, others such as topography and local roughness of the virgin material and of the precipitated apatite, help to explain those findings. 44 ______________________________________________________________________ _____ (1) - Effect of magnesium on the structure and surface reactivity of silica-based glasses for biomedical applications (POCTI/CTM/46251/2002) - Cinética da cristalização de biomateriais vitrocerâmicos e efeitos no seu desempenho (Doutoramento) - Técnicas de microscopia para estudo da reactividade superficial de vidros e vidros cerâmicos bioactivos (Mestrado) 45 1 a s Jo rn a d a s 1 9 > 2 0 d e De z e m b ro d e 2 0 0 3 Com ple xo Pe da gógico Cie n tífico e Te cn ológico Un ive rs ida de de Ave iro u n iv e rs id a d e d e a v e iro 3 0 a n o s a p ro je ct a r fu t u ro s Co m is s ã o Org a n iz a d o ra : Pro f. Do u t o ra Pa u la Vila rin h o Pro f. Do u t o r Pa u lo Rib e iro Cla ro Ag ra d e c im e n t o s : Re it o ria d a Un id a d e d e Ave iro De p a rt a m e n t o d e Qu ím ica d a Un ive rs id a d e d e Ave iro De p a rt a m e n t o d e Fís ica d a Un ive rs id a d e d e Ave iro De p a rt a m e n t o d e En g e n h a ria Ce râ m ica e Vid ro La b o ra t ó rio Ce n t ra l d e An á lis e s FCT PRODEP FEDER RAIZ Ca ixa Ge ra l d e De p ó s it o s ii