Synthesis and structure of nanomaterials in the system K2O-Nb2O5-SiO2

The aim of the present work is synthesis of ferroelectric nanomaterials, in the K2O-Nb2O5-SiO2 system via solgel method and studying the processes of formation and structure of the synthesized ferroelectric nanomaterials. The structure of synthesized materials has been studied by means of the following methods: EDS, XRD, FT-IR, SEM and AFM. The results obtained showed that the structure of the investigated compositions does not depend on the niobium content and all the samples keep their amorphous nature at room temperature. The surface structure shows random distribution of different kinds of aggregates with dimensions about 200–500 nm. The presence of a hybrid nanostructure with well-defi ned nanounits having special geometry is clearly observed

The influence of processing parameters on morphology and granulometry of a wet-milled sol-gel glass powder

A quaternary bioactive sol-gel glass of high silica content was heat treated at different temperatures, and then wet ball milled under different balls-to-powder ratios. A total of sixteen experiments were performed to study in detail the effects of both experimental variables on the structure, morphology, particle size distributions and nitrogen adsorption isotherms. The balls–to–powder ratio exerts a tremendous influence on the final particle size distribution of the powders, while its effects on the pore volume and morphology are minimal. These structural features are mostly governed by the changes in calcination temperature. Therefore, understanding the specific roles of each experimental parameter is of paramount importance towards achieving optimum powders with the desired properties. This work sheds light on the importance of using a suitable combination of these two parameters for tuning the morphology and the granulometry of the sol-gel derived bioactive glass powders.publishe

Enhanced bioactivity of a rapidly-dried sol-gel derived quaternary bioglass

Novel quaternary (67Si-24Ca-10Na-8P) glass powders were successfully synthesised by sol-gel followed by two alternative drying schedules, conventional drying (CD) and an innovative fast drying (FD) process (200 times quicker). The glasses were thermally stabilised at 550 °C, and then characterised by different complementary techniques. The samples showed very similar silica network structures, with the FD one having slightly lower degree of polymerisation than the CD sample. This less polymerised, more open, network structure exhibited an improved bioactivity in simulated body fluid (SBF), probably also due to the apparent presence of poorly crystalline HAp in the stabilised glass powder. In contrast, the CD glass exhibited an unwanted secondary crystalline silica phase. Both glasses showed excellent biomineralisation upon immersion in SBF, being more pronounced in the case of FD with clear evidence of HAp formation after 4 h, while equivalent signs in the CD samples were only noticed after longer immersion periods between 8 h and 1 week.publishe

Robocasting of Cu2+ & La3+ doped sol-gel glass scaffolds with greatly enhanced mechanical properties: compressive strength up to 14 MPa

This research details the successful fabrication of scaffolds by robocasting from high silica sol-gel glass doped with Cu2+ or La3+. The parent HSSGG composition within the system SiO2-CaO-Na2O-P2O5 [67% Si - 24% Ca - 5% Na - 4% P (mol%)] was doped with 5 wt% Cu2+ or La3+ (Cu5 and La5). The paper sheds light on the importance of copper and lanthanum in improving the mechanical properties of the 3-D printed scaffolds. 1 h wet milling was sufficient to obtain a bioglass powder ready to be used in the preparation of a 40 vol% solid loading paste suitable for printing. Moreover, Cu addition showed a small reduction in the mean particle size, while La exhibited a greater reduction, compared with the parent glass. Scaffolds with macroporosity between 300 and 500 µm were successfully printed by robocasting, and then sintered at 800 °C. A small improvement in the compressive strength (7-18%) over the parent glass accompanied the addition of La. However, a much greater improvement in the compressive strength was observed with Cu addition, up to 221% greater than the parent glass, with compressive strength values of up to ∼14 MPa. This enhancement in compressive strength, around the upper limit registered for human cancellous bones, supports the potential use of this material in biomedical applications. STATEMENT OF SIGNIFICANCE: 3D porous bioactive glass scaffolds with greatly improved compressive strength were fabricated by robocasting from a high silica sol-gel glasses doped with Cu2+ or La3+. In comparison to the parent glass, the mechanical performance of scaffolds was greatly improved by copper-doping (>220%), while a modest increase of ∼9% was registered for lanthanum-doping. Doping ions (particularly La3+) acted as glass modifiers leading to less extents of silica polymerisation. This favoured the milling of the glass powders and the obtaining of smaller mean particle sizes. Pastes with a high solid loading (40 vol%) and with suitable rheological properties for robocasting were prepared from all glass powders. Scaffolds with dimensions of 3 × 3 × 4 mm and macro-pore sizes between 300 and 500 µm were fabricated.publishe

The role of calcium (source & content) on the in vitro behaviour of sol–gel quaternary glass series

To highlight the effect of salt precursors on the final properties, bioactivity and biocompatibility, five quaternary (Si–Ca–P–Na) glass compositions were successfully prepared through two distinct rapid sol–gel routes; one using acetate salt precursors (A) catalysed by nitric acid, and the other using nitrate salts (N) and citric acid as a catalyst. The sols dried rapidly, and stabilised at 550 & 800 °C to be characterised by X–ray diffraction (XRD), Magic angle spinning–Nuclear magnetic resonance (29Si MAS–NMR) and Fourier transform infra–red spectroscopy (FTIR). Upon immersion in simulated body fluid (SBF), hydroxyapatite (HAp) formation was initially enhanced by increasing Ca–content up to 40 mol%, but the formation of calcite was favoured with further increments of Ca to 45 and 48 mol%. The A–glasses exhibited lower density and lower network connectivity compared with N–glasses. The chemical surface modifications after 4 h in SBF were more evident for N–glasses in comparison to A–glasses. The biocompatibility is favoured for the samples treated at 800 °C and for the samples of the higher silica contents.publishe

In vitro bioactivity of biphasic calcium phosphate silicate glassceramic in CaO-SiO2-P2O5 system

The main purpose of the paper is the evaluation of the influence of chemical composition of the gel of the synthesized 15CaO·0.5P2O5·6SiO2 glass-ceramic on the structure, crystallization behaviour and in vitro bioactivity in static conditions for different periods of time - 3, 9 and 30 days in 1.5SBF. The obtained glass-ceramic was synthesized via polystep sol-gel technique. The structure of the prepared and the one thermally treated at 1200°C for 2 h powder was studied by XRD, 29Si MAS NMR, FTIR and SEM

Sol-gel coatings for metallic prosthesis from methyl-modified alkoxysilanes: balance between protection and bioactivation

The reported osteogenic properties of the hybrid silica sol-gel materials make these compositions perfect candidates for bone tissue engineering applications. The aim of this study was the synthesis and characterisation of hybrid silica coatings, obtained using mixtures of tetraethyl orthosilicate (TEOS) and three different methyl-modified alkoxysilanes: trimethoxymethylsilane (MTMS), dimethyldiethoxysilane (DMDES) or polydimethylsiloxane (PDMS). A comparison of the properties of these materials can reveal the best candidate for the coatings on metallic prostheses. After optimising the synthesis parameters, the developed coatings were characterised using Fourier transform infrared spectrometry (FT-IR), 1H and 29Si solid-state nuclear magnetic resonance (1H-NMR and 29Si-MNR), cross-cut tests, scanning electron microscopy (SEM), contact angle measurements, optical profilometry, hydrolytic degradation tests and electrochemical corrosion analysis. Homogeneous and well-adhering coatings were obtained using the three methyl-modified reagents. However, different degrees of protection against corrosion, different hydrophilicity and varying degradation kinetics were observed for different precursors. The MTMS-based coating showed the highest hydrophilicity and degradation kinetics; these properties can be associated with increased bioactivity (Si release). In contrast, the PDMS and DMDES-based coatings showed augmented resistance to corrosion and lower permeability to water and, consequently, improved protection of metallic surfaces. From the physicochemical point of view, all these materials displayed interesting characteristics, relevant for coatings to be used in biomedical applications

A novel hybrid material with calcium and strontium release capability

The preparation of PDMS–TEOS–CaO hybrid materials by sol–gel techniques has been widely described in previous works. Calcium nitrate is the most common source of calcium used in these preparations. However, to remove possible toxic nitrate by-products a thermal treatment is necessary at temperatures above 500 1C, which leads to the degradation of the polymeric components of the hybrids. Strontium has already shown some promising results in the therapeutic area, being used in cases of osteoporosis and low bone density. In this study a new potential bioactive hybrid material was prepared, by sol–gel techniques, using calcium acetate as a novel calcium source. Also, for the first time, incorporation of strontium in a PDMS–TEOS hybrid system was evaluated. Samples were characterized before and after immersion in Kokubo’s Simulated Body Fluid (SBF) by SEM, EDS, ICP and FT-IR spectroscopy

A biocompatible hybrid material with simultaneous calcium and strontium release capability for bone tissue repair

The increasing interest in the effect of strontium in bone tissue repair has promoted the development of bioactive materials with strontium release capability. According to literature, hybrid materials based on the system PDMS–SiO2 have been considered a plausible alternative as they present a mechanical behavior similar to the one of the human bone. The main purpose of this study was to obtain a biocompatible hybrid material with simultaneous calcium and strontium release capability. A hybrid material, in the system PDMS–SiO2–CaO–SrO, was prepared with the incorporation of 0.05 mol of titanium per mol of SiO2. Calcium and strontium were added using the respective acetates as sources, following a sol–gel technique previously developed by the present authors. The obtained samples were characterized by FT-IR, solid-state NMR, and SAXS, and surface roughness was analyzed by 3D optical profilometry. In vitro studies were performed by immersion of the samples in Kokubo's SBF for different periods of time, in order to determine the bioactive potential of these hybrids. Surfaces of the immersed samples were observed by SEM, EDS and PIXE, showing the formation of calcium phosphate precipitates. Supernatants were analyzed by ICP, revealing the capability of the material to simultaneously fix phosphorus ions and to release calcium and strontium, in a concentration range within the values reported as suitable for the induction of the bone tissue repair. The material demonstrated to be cytocompatible when tested with MG63 osteoblastic cells, exhibiting an inductive effect on cell proliferation and alkaline phosphatase activity

A new approach to the preparation of PDMS-SiO2 based hybrids - A structural study

Due to its elasticity, transparency and biocompatibility, polydimethylsiloxane (PDMS) has been used as an organic component of hybrid materials in different fields of application such as photonics or biomaterials. Typically an acidic medium is used in the sol-gel processing of PDMS-metal oxide systems due to its catalytic effect. Furthermore, when dealing with highly reactive transition metal alkoxides, a chelating agent is pointed out as being necessary to avoid phase separation. In this work a new approach to the preparation procedure of hybrid materials, based on the system PDMS-SiO2-MO2 with M=Ti or Zr, was used. Samples were prepared at different pH values, without water addition and in the presence or absence of a chelating agent (ethyl acetoacetate). All samples were homogeneous and transparent even at high pH. ATR-IR, Si-29-NMR MAS and Si-29-{H-1} CP-MAS were used for the characterization of the obtained samples. According to the 29Si-{H-1} CP-MAS results some differences in the nature of difunctional D ((CH3)(2)center dot SiO2) and tetrafunctional (SiO4) Q structural units were observed. The presence of Ti-O-Si and Zr-O-Si bonds was confirmed by ATR-IR analysis. (C) 2014 Elsevier B.V. All rights reserved