Preparation, structural characterisation and antibacterial properties of Ga-doped sol-gel phosphate-based glass

A sol-gel preparation of Ga-doped phosphate-based glass with potential application in antimicrobial devices has been developed. Samples of composition (CaO)(0.30)(Na2O)(0.20-x) (Ga2O3) (x) (P2O5)(0.50) where x = 0 and 0.03 were prepared, and the structure and properties of the gallium-doped sample compared with those of the sample containing no gallium. Analysis of the P-31 MAS NMR data demonstrated that addition of gallium to the sol-gel reaction increases the connectivity of the phosphate network at the expense of hydroxyl groups. This premise is supported by the results of the elemental analysis, which showed that the gallium-free sample contains significantly more hydrogen and by FTIR spectroscopy, which revealed a higher concentration of -OH groups in that sample. Ga K-edge extended X-ray absorption fine structure and X-ray absorption near-edge structure data revealed that the gallium ions are coordinated by six oxygen atoms. In agreement with the X-ray absorption data, the high-energy XRD results also suggest that the Ga3+ ions are octahedrally coordinated with respect to oxygen. Antimicrobial studies demonstrated that the sample containing Ga3+ ions had significant activity against Staphylococcus aureus compared to the control

In vitro bioactivity of titanium-doped bioglass

Previous studies have suggested that incorporating relatively small quantities of titanium dioxide into bioactive glasses may result in an increase in bioactivity and hydroxyapatite formation. The present work therefore investigated the in vitro bioactivity of a titanium doped bioglass and compared the results with 45S5 bioglass. Apatite formation was evaluated for bioglass and Ti-bioglass in the presence and absence of foetal calf serum. Scanning electron microscopy (SEM) images were used to evaluate the surface development and energy dispersive X-ray measurements provided information on the elemental ratios. X-ray diffraction spectra confirmed the presence of apatite formation. Cell viability was assessed for bone marrow stromal cells under direct and indirect contact conditions and cell adhesion was assessed using SEM

Non-hexagonal neural dynamics in vowel space

Are the grid cells discovered in rodents relevant to human cognition? Following up on two seminal studies by others, we aimed to check whether an approximate 6-fold, grid-like symmetry shows up in the cortical activity of humans who "navigate" between vowels, given that vowel space can be approximated with a continuous trapezoidal 2D manifold, spanned by the first and second formant frequencies. We created 30 vowel trajectories in the assumedly flat central portion of the trapezoid. Each of these trajectories had a duration of 240 milliseconds, with a steady start and end point on the perimeter of a "wheel". We hypothesized that if the neural representation of this "box" is similar to that of rodent grid units, there should be an at least partial hexagonal (6-fold) symmetry in the EEG response of participants who navigate it. We have not found any dominant n-fold symmetry, however, but instead, using PCAs, we find indications that the vowel representation may reflect phonetic features, as positioned on the vowel manifold. The suggestion, therefore, is that vowels are encoded in relation to their salient sensory-perceptual variables, and are not assigned to arbitrary gridlike abstract maps. Finally, we explored the relationship between the first PCA eigenvector and putative vowel attractors for native Italian speakers, who served as the subjects in our study

A multinuclear solid state NMR study of the sol-gel formation of amorphous Nb2O5-SiO2 materials

Multinuclear 1 H, 13C, 17O, 29Si MAS and 93Nb static NMR is reported from a series of sol–gel prepared (Nb2O5)x(SiO2)1x materials with x ¼ 0:03; 0.075 or 0.30. 13C NMR shows that by 500 1C the organic precursor fragments have been removed although some residual carbon remains as a separate phase. The 29Si NMR typically shows three Q-species (Q2,3,4) in the initial gels, and that with increasing heat treatment the average n of the Qn -species increases as the organic fragments and hydroxyl groups are removed. 17O shows unequivocally that the x ¼ 0:03 and 0.075 samples are not phase separated, while at the much higher niobia-content of x ¼ 0:30 Nb–O–Nb signals are readily detected, a definite indication of the atomic scale phase separation of Nb2O5. Th e x ¼ 0:03 and 0.075 samples heated to 750 1C are thus representative of amorphous niobium silicates. Comparison is made to other sol–gel prepared metal silicates especially with another Group Va metal tantalum. The effects of tantalum and niobium on the silica network are very different and it is suggested here that most of the niobium is present as NbO4, forming part of the silicate network

The use of advanced diffraction methods in the study of the structure of a bioactive calcia:silica sol-gel glass

Sol-gel derived calcium silicate glasses may be useful for the regeneration of damaged bone. The mechanism of bioactivity is as yet only partially understood but has been strongly linked to calcium dissolution from the glass matrix. In addition to the usual laboratory-based characterisation methods, we have used neutron diffraction with isotopic substitution to gain new insights into the nature of the atomic-scale calcium environment in bioactive sol-gel glasses, and have also used high energy X-ray total diffraction to probe the nature of the processes initiated when bioactive glass is immersed in vitro in simulated body fluid. The data obtained point to a complex calcium environment in which calcium is loosely bound within the glass network and may therefore be regarded as facile. Complex multistage dissolution and mineral growth phases were observed as a function of reaction time between 1 min and 30 days, leading eventually, via octacalcium phosphate, to the formation of a disordered hydroxyapatite (HA) layer on the glass surface. This methodology provides insight into the structure of key sites in these materials and key stages involved in their reactions, and thereby more generally into the behaviour of bone-regenerative materials that may facilitate improvements in tissue engineering applications