Structural study of Al2O3-Na2O-CaO-P2O5 bioactive glasses as a function of aluminium content

Abstract

Calcium phosphate based biomaterials are extensively used in the context of tissue engineering: small changes in composition can lead to significant changes in properties allowing their use in a wide range of applications. Samples of composition (Al 2 O 3 ) x (Na 2 O) 0.11-x (CaO) 0.445 (P 2 O 5 ) 0.445 , where x = 0, 0.03, 0.05, and 0.08, were prepared by melt quenching. The atomic-scale structure has been studied using neutron diffraction and solid state 27 Al MAS NMR, and these data have been rationalised with the determined density of the final glass product. With increasing aluminium concentration the density increases initially, but beyond about 3 mol. % Al 2 O 3 the density starts to decrease. Neutron diffraction data show a concomitant change in the aluminium speciation, which is confirmed by 27 Al MAS NMR studies. The NMR data reveal that aluminium is present in 4, 5, and 6-fold coordination and that the relative concentrations of these environments change with increasing aluminium concentration. Materials containing aluminium in 6-fold coordination tend to have higher densities than analogous materials with the aluminium found in 4-fold coordination. Thus, the density changes may readily be explained in terms of an increase in the relative concentration of 4-coordinated aluminium at the expense of 6-fold aluminium as the Al 2 O 3 content is increased beyond 3 mol. %.

Yttrium doped phosphate-based glasses: structural and degradation analyses

“…Furthermore, the average P• • • P coordination number (Npp) and average phosphate chain length (L) can be determined from the NMR Q-species [7,49]. In addition, the N PP is equal to the average number of bridging oxygen (N BO ) [50]. The N BO and L are calculated using equations 2 and 3 and the results are presented in Table 3.…”

“…In addition, the number of BO in phosphate tetrahedral units can be evaluated by O/P ratio [50] and calculated using the equation 6 below:…”

Structural and physico-chemical analysis of calcium/strontium substituted, near-invert phosphate based glasses for biomedical applications

“…However, although several studies on the structure of phosphate based glasses have been conducted [37][38][39][40][41][42][43][44], very little is known about the effect of cation substitution on the structure of complex, multicomponent, lower phosphate containing glasses (i.e. for phosphate glasses close to invert glass formulations).…”

Effect of CaO and Al2O3 addition on the properties of K2O–Na2O–P2O5 glass system

“…27 Al MAS NMR spectroscopy also reveals that octahedral Al is the most abundant moiety in (50‐2 x )MO x Al 2 O 3 (50 + x ) P 2 O 5 glasses (with M = Mg or Ba), but that the fraction of AlO 4 and AlO 5 species increases as the ionicity of the modifier‐oxygen bond decreases . Smith et al analyzed samples of composition (Al 2 O 3 ) x (Na 2 O) 0.11 − x (CaO) 0.445 (P 2 O 5 ) 0.445 , where x = 0, 0.03, 0.05, and 0.08. Their NMR results indicate that initially, with low concentrations of Al, Al is predominantly sixfold coordinated.…”

“…The relationship between glass composition and Al coordination happens to be much more complex in phosphate glasses than in silicate glasses. But irrespective of their CN, Al atoms induce some cross‐linking between the phosphate chains via the formation of Al–O–P linkages with a covalent character, hence giving rise to considerable network strengthening …”