Synthesis,characterization and biocompatibility evaluation of sol–gel derived bioactive glass scaffolds prepared by freeze casting method

In this study, a new class of bioactive glass scaffolds was prepared through freeze casting method for bone tissue engineering applications. After analyzing the structural characteristics of the scaffolds, in vitro biological evaluations were assessed through monitoring alkaline phosphatase (AP) activity of osteoblast cells and soaking in simulated body fluid (SBF) for different time intervals. It was shown that the scaffolds consisted of bioactive glass plates with interconnected pores between them, aligned along the ice growth direction. The ability of the scaffolds for supporting the growth of human fetal osteoblastic cells (hFOB 1.19) was approved. Moreover, inductively coupled plasma-atomic emission spectrometry (ICP-AES) showed meaningful compositional changes of calcium, phosphorus and silicon in SBF solution, indicating the apatite forming ability of the scaffolds. The present investigation revealed that freeze casting could be an effective method for the preparation of highly bioactive scaffolds. In addition, the scaffolds proved to be highly compatible for the proposed works in vivo.     

Powder characteristics,sintering behavior and microstructure of sol–gel derived ZTA composites

A series of alumina/zirconia composites of varying compositions of zirconia were prepared through the sol–gel technique. Precursors were calcined at different temperatures ranging from 300 to 1400°C and sintered at 1530°C for 3 h. Compacts made from the powder calcined at 950°C yielded density up to >99% of theoretical density by pressureless sintering. Pore size distribution and the densification behavior were explained with respect to calcination temperature. Microstructural analysis of the sintered compacts revealed the uniform distribution of the zirconia grains in the alumina matrix. It is also observed that the faceted intergranular zirconia grains are at the grain junctions and the corners of the alumina matrix.     

The effect of acid and base catalysts on phase purity and dissolution behavior of sol–gel derived in situ silica coated apatite composite nanopowders

Synthesis conditions of biomaterials have a key role on their final properties, which affect their performance in the human body. So, the aim of this study was to evaluate the effect of acid and base catalysts used in processing of silica synthesis, on phase purity and dissolution behavior of the in situ silica coated apatite composite nanopowders prepared via the sol–gel method. Composite nanopowders were synthesized in the presence of 0.1 N HNO₃ and acetic acid as the acid catalyst (A-S-AP composite nanopowder) and ammonium hydroxide as the base catalyst (B-S-CP composite nanopowder). The prepared composite nanopowders were characterized by XRD, FTIR, TEM, and BET techniques, acid dissolution test, and AAS spectroscopy. Results indicated that the base catalyst, rather than the acid catalyst, induced a nano-scale phase separation, which paved the way for the creation of a new crystalline phase (whitelockite) along with HA. In addition, the results of dissolution behavior evaluations in physiological saline solution showed that A-S-AP composite nanopowder, rather than B-S-CP composite nanopowder, had more calcium ions release and faster in vitro biomineralization, which are very important for bone repair and regeneration.     

Characterization,antibacterial and in vitro compatibility of zinc–silver doped hydroxyapatite nanoparticles prepared through microwave synthesis

We investigated the possibility of enhancing hydroxyapatite (HA) bioactivity by co-substituting it with zinc and silver. Zn–Ag–HA nanoparticles were synthesized by using the microwave-assisted wet precipitation process, and their phase purity, elemental composition, morphology, and particle size were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). FTIR, XRD, and EDX results showed the characteristic peaks of the Zn–Ag–HA structure, while SEM results demonstrated that the nanoparticles were of spherical shape with a particle size of 70–102 nm. Antibacterial tests of the nanoparticles revealed their antibacterial activity against Staphylococcus aureus and Escherichia coli. By using simulated body fluid (SBF), an apatite layer formation was observed at 28 days. In vitro cell adhesion assay confirmed the cell attachment of normal human osteoblast (NHOst) cells to the disc surface. MTT [(3(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyltetrazolium bromide] assay indicated that the cells were viable, and the cells proliferated faster on the disks than on the control surface due to the presence of metal ions. In conclusion, the novel Zn–Ag–HA nanoparticles were found to be compatible with in vitro experiments and having potential antibacterial properties. Therefore these nanoparticles could be a promising candidate for future biomedical applications.     

Biological response of a recently developed nanocomposite based on calcium phosphate cement and sol–gel derived bioactive glass fibers as substitution of bone tissues

Calcium phosphate cements (CPCs) have been used in a number of medical and dental procedures due to their excellent osteoconductivity and bone replacement capability. However, the low mechanical properties of CPCs prohibit their usage in many unsupported defects and stress bearing locations. Bioactive glass fiber (BGF) reinforced-CPC with enhanced mechanical property has been recently developed [Nezafati et al. 2011, Ceramics International]. In the present study, the in vitro bioactivity and cellular properties of the CPC optimally reinforced with 15 vol% BGFs were evaluated and compared with a control group, i.e. unreinforced CPC. The samples were soaked in simulated body fluid (SBF) for different time intervals and were then characterized by various techniques. Carbonate substituted apatite crystals with oriented plate-like morphology were also found on the surface of the samples. Furthermore, rat-derived osteoblastic cells were seeded on the samples for different times and evaluated in terms of proliferation, morphology and alkaline phosphatase (ALP) activity. In addition, the proliferation of osteoblastic cells on samples and increasing in level of alkaline phosphatase enzyme were observed as a function of time. The obtained results indicated that the reinforced composite made of CPC and BGFs could be considered as a highly bioactive material for bone tissue defect treatment after successful passage of in vivo experiments.     

Preparation and antibacterial activity of Ag/SiO2 thin film on glazed ceramic tiles by sol–gel method

In the present study, silver-doped silica thin films on glazed surface of ceramic tiles were well prepared by sol–gel method to achieve antibacterial activity. Thermal treatment was done in the air at 1100 °C for two hours. The Ag/SiO₂ thin films were investigated through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and wavelength dispersive spectrometry (WDS). Atomic absorption spectroscopy (AAS) was used for the quantitative determination of the silver ion concentration being released from Ag/SiO₂ films over a 24 day period. The antibacterial effects of Ag/SiO₂ thin films against Escherichia coli and Staphylococcus aureus were also examined. From the analysis results, it was found that high temperature treated coating consists of two phases of SiO₂ and Ag based on the trapping of the Ag phase in the silica matrix. The presence of Ag elements on the surface of the coated tiles, were also observed. Thermal treatment at high temperatures caused sharp XRD peaks and high crystallinity in this system. Ag⁺ ions were released constantly and the mean release rate (±SD) was 0.104 ±0.01 μg/ml during 24 days. Coating films exhibited an excellent antibacterial performance against both bacterium.     

Effects of formulation properties on sol–gel behavior of chitosan/glycerolphosphate hydrogel

Chitosan solution containing glycerolphosphate disodium salt (Gp) is an injectable thermosensitive in situ gel-forming system which undergoes sol–gel transition under certain physiological pH and temperature conditions. When a drug-incorporated chitosan/Gp solution is injected into the body, it forms a three-dimensional gel at 37 °C, which allows the drug to be released in a sustained manner. This hydrogel can be used as a drug delivery system for prolonged release of peptides and glycopeptides. The objective of this work was to investigate the effect of different excipients on the sol–gel behavior of this thermosensitive hydrogel. Chitosan polymeric solutions (2 % w/v) containing Gp and different excipients, such as hydroxypropyl methyl cellulose (HPMC), polyethylene glycol (PEG) with two different molecular weights (PEG200 and PEG1000), and poloxamer (F127) in various concentrations, were prepared, and the pH, sol–gel transition time, and syringeability of the final solutions were evaluated. The obtained results point to HPMC as the best additive for chitosan/Gp solutions in developing an in situ gel-forming drug delivery system with optimum gelling time. A significant decrease was noted in the sol-to-gel transition time (from 90 to 60 s) when HPMC was added to the system. This may have been due to the HPMC structure which acted as a viscosity-enhancing and gel-promoting agent. The in vitro release of vancomycin hydrochloride from chitosan/Gp/HPMC hydrogel was also studied. Vancomycin release studies showed a sustained release profile for over 20 days. It can be concluded that combining chitosan/Gp and HPMC is a promising strategy for preparing a thermally reversible in situ gel-forming delivery system with an optimized gelation time.     

The effect of ceramic nanoparticles on tribological properties of alumina sol–gel thin coatings

Thin alumina coatings containing zirconia or alumina nanoparticles having diameter of ～20–30 nm were deposited by the sol–gel dip-coating process on silicon wafers. The mass content of nanoparticles in the alumina coating was fixed at 15% in relation to the theoretical mass of alumina matrix resulted from the amount of the applied precursor. Atomic force microscopy (AFM) was used to image the surface topography of as-made coatings and find out the wear level after frictional tests. Tribological tests were performed with the use of a microtribometer operating in the load range of 30–100 mN. It was found that the presence of α-alumina (corundum) or zirconia nanoparticles enhances the tribological performance of alumina layers annealed at 100 °C by decreasing the average wear rate by 20% and 63% for zirconia and corundum nanoparticles, respectively. No wear was observed for samples containing both types of nanoparticles annealed at 500 °C.     

The effect of zirconia ions on corrosion performance of sol–gel coated galvanized steel

Currently, galvanized steel is treated with hexavalent chrome passivation. Sol–gel coating has been found to be a potential replacement for the hazardous hexavalent chrome passivation treatment. The aim of this work is to study the effect of zirconyl nitrate on corrosion behavior of sol–gel coating. Aminopropyl-trimethoxysilane and 3-glycidoxypropyltrimethoxysilane were employed as precursors to prepare the sol–gel-based silane coating. The sol–gel film was deposited on galvanized steel sheet by dip coating method. The chemical properties of sol–gel solution and coated films were analyzed by infrared spectroscopy. Morphology of the film was characterized by scanning electron microscope. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray test. The results indicated that zirconia-doped coatings have better corrosion resistance in comparison with their undoped counterparts. The coating doped with 0.5% zirconyl nitrate provides better corrosion protection due to the inhibitive action of zirconia ion.     

Influence of the sintering temperature on the structural feature and bioactivity of sol–gel derived SiO2–CaO–P2O5 bioglass

A sol–gel method was utilized to synthesize the gel with the composition of 58 mol% SiO₂–38 mol% CaO–4 mol% P₂O₅. The thermal properties were studied using thermogravimetric and differential thermal analysis (TG/DTA). Then the gels were sintered at 700, 900, 1000 and 1200 °C. The structure features were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), in addition in vitro assays were carried out in simulated body fluid (SBF). The results revealed that at sintering temperature above 900 °C, crystallization occurred and glass-ceramics with pseudowollastonite and wollastonite were formed. Furthermore with the increase of sintering temperature, the amount of pseudowollastonite decreased while that of wollastonite increased. In vitro tests indicated that the crystallization did not inhibit the samples bioactivity. After soaking in SBF, the formation of apatite was confirmed on glass and glass-ceramics surface, and the bioactivity of the glass-ceramics was based on the formed pseudowollastonite and wollastonite.     

A comparative study of the effect of Pd-doping on the structural,optical, and photocatalytic properties of sol–gel derived anatase TiO2 nanoparticles

Pd-doped anatase TiO₂ nanoparticles were synthesized by a modified sol–gel deposition technique. The synthetic strategy is applicable to other transition and post-transition metals to obtain phase-pure anatase titania nanoparticles. This is important in the sense that anatase titania forms the most hydroxyl radicals (compared to other polymorphs like rutile, brookite, etc.) for better photocatalytic performance. XRD and Raman data confirm the phase-pure anatase formation. Doping of Pd²⁺ into Ti⁴⁺ sites (for substitutional doping) or interstitial sites (for interstitial doping) creates strain within the nanoparticles and is reflected in the XRD peak broadening and Raman peak shifts. This is because of the ionic radii difference between Ti⁴⁺(∼68 pm) and Pd²⁺(∼86 pm). XPS data confirm the formation of high surface titanol groups at the nanoparticle surface and a large number of loosely bound Ti³⁺–O bonds, both of which considerably enhance the photocatalytic activity of the doped nanoparticles. A comparative study with other metal doping (Ga) shows that TiO₂: Pd nanoparticles have more Ti³⁺–O bonds, which enhance the charge transfer rate and hence improve the photocatalytic activity compared to other transition and post-transition metal-doped titania nanostructures.     

The impact of Nb2O5 on in-vitro bioactivity and antibacterial activity of CaF2–CaO–B2O3–P2O5–SrO glass system

This work consists of in vitro bioactivity (in SBF) and antibacterial studies (against S. aureus and E. coli bacteria) of Nb₂O₅ doped bioactive glasses. X-ray diffraction and scanning electron microscopy investigations indicated deposition of Nb-HAp (hydroxyapatite) crystalline layer on the samples after exposing to SBF. The spectroscopy investigations also indicated the deposition of HAp layer on these samples. The magnitude of HAp deposited on the glasses found to be relying on concentration of Nb₂O₅ dopant; this conclusion was drawn by determining weight loss of the glasses due to exposure to SBF and also by assessing the variation of pH of the remnant fluid as functions of Nb₂O₅content. The studies further indicated the maximal content of hydroxyapatite was deposited on the surface the glasses doped with 4.0 mol% of Nb₂O₅. The antibacterial studies (against E. coli and S. aureus bacteria) of these glasses indicated the maximal killing effect of bacteria of the samples admixed with 4.0 mol% of Nb₂O₅. This result is attributed to the occupancy of maximal fraction of Nb ions in NbO₆ structural units (confirmed by IR and Raman spectroscopic results) in this sample that paved the way for easy disintegration of the glass and to act on the bacteria. Overall, the results of bioactivity studies of Nb₂O₅ doped bioglasses indicated that the Nb₂O₅ not only enhanced bioactivity potential but also exhibited antimicrobial activity.     

Influence of annealing temperature on the structural and anti-corrosion characteristics of sol–gel derived,spin-coated thin films

Recently, an aqueous particulate sol–gel process using metallic chloride precursors was introduced to synthesize zirconium titanate. In this paper, the effect of annealing temperature on the structural and corrosion protection characteristics of spin-coated thin films obtained from this sol–gel system was investigated. Based on scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and spectroscopic reflectometry studies, it was found that the flatness and thickness of the thin films were decreased by increasing the annealing temperature. Also, the corrosion protection of stainless steel AISI 316L provided by the prepared coatings, as analyzed by electrochemical potentiodynamic polarization experiments in a simulated body fluid, was improved in this order: 500 °C-annealed sample<900 °C-annealed sample<700 °C-annealed sample, attributed to a compromise between the defect density and the adhesion of the films to the substrate.     

Influence of iron oxide substitution on the magnetic interactions in sol–gel-derived 45S5 bioactive glass–ceramics

Magnetic interactions in sol–gel-derived bioactive magnetic glass–ceramics (MGCs) with compositions of (45 − x)SiO₂·24.5CaO·24.5Na₂O·6P₂O₅ xFe₂O₃ (2 ≤ x ≥ 15 wt.%) have been investigated using electron paramagnetic resonance (EPR), and temperature-dependent magnetic susceptibility and magnetization (M–T) techniques. EPR spectra of the MGC samples revealed strong composition dependence in the intensity and linewidth of resonance absorptions at g ≈ 2.0 and g ≈ 4.3. EPR linewidth analysis showed the dominance of dipole–dipole interaction in MGC samples with iron oxide content ≤4 wt.% and a crossover to super-exchange type interaction in samples with higher iron oxide content. Composition-dependent magnetic interaction in these MGC could be related to Fe²⁺ and Fe³⁺ ion concentrations using high-temperature magnetic susceptibility studies. Zero-field cooled and field cooled M–T curves indicate different magnetic behavior for MGC samples with x ≤ 6 and x ≥ 8 wt.% iron oxide. Although the former show weak magnetic behavior, the latter exhibit superparamagnetic behavior which could be correlated with the percentage of magnetic phases present in each sample. These studies reveal composition-dependent variation in dipolar and super-exchange type interaction in the samples which could help in assessing these MGC for biomedical applications.     

Synthesis and characterization of sol–gel derived calcium hydroxyapatite thin films spin-coated on silicon substrate

The goal of this study was to demonstrate that sol–gel processing route is suitable for the fabrication of calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, CHA) thin films on Si substrate by spin-coating technique. The substrate was spin-coated by precursor sol solution 1, 5, 15 and 30 times. The samples were annealed after each spin-coating procedure at 1000 °C for 5 h in air. In the sol–gel process ethylendiamintetraacetic acid and 1,2-ethandiol, and triethanolamine and polyvinyl alcohol were used as complexing agents and as gel network forming agents, respectively. The coatings were characterized using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) and Raman spectroscopies, profilometry and the contact angle measurements (CAM). It was demonstrated, that properties of calcium hydroxyapatite thin films depend on spinning and annealing times.     

Influence of sol–gel derived ZrO2 and ZrC additions on microstructure and properties of ZrB2 composites

ZrB₂ powder was coated with 5% ZrOC sol–gel precursor and sintered by SPS. Relative densities >98% were achieved at 1800 °C with minimal grain growth and an intergranular phase of ZrC. Carbon content in the precursor determined the type of reinforcing phase and porosity of the sintered composites. XRD, SEM and EDS studies indicated that carbon deficiency resulted in ZrO₂ retention, improving ZrB₂ densification with oxide particle reinforcement. Excess carbon resulted in ZrC formation as the reinforcing phase, but could yield porosity and residual carbon at grain boundaries. These two types of ZrB₂ composites displayed different densification and microstructural evolution that explain their contrasting properties. In the extreme oxidative environment of oxyacetylene ablation, the composites with ZrC-C maintained superior leading edge geometry; whereas for mechanical strength, a bias towards the residual ZrO₂ content was beneficial. This highlighted the sensitivity of processing carbon-precursors in the initial sol–gel process and the carbon content in ZrB₂-based composite systems.     

Corrosion protection behaviour of sol–gel derived N,N-dimethylthiourea doped 3-glycidoxypropyltrimethoxysilane on aluminium

The present work describes the anticorrosion features of inhibitor doped sol–gel coating on Al metal. Sol–gel coatings were prepared by using 3-glycidoxypropyltrimethoxysilane (GPTMS) as parent precursor. In order to improve the corrosion resistance property of coating, N,N-dimethylthiourea was added into the sol–gel matrix. The corrosion inhibitor doped sol–gel coating on metal was characterized by Fourier transform infrared analysis (FTIR) and scanning electron microscope (SEM). Inhibition effect of N,N-dimethylthiourea doped GPTMS coating on Al substrates in 1% NaCl solution was investigated using electrochemical impedance (EIS) and polarization studies. EIS results showed that the corrosion resistance of sol–gel coating significantly improved upon addition of N,N-dimethylthiourea. The study had outlined the nuances of doping an organic inhibitor to enhance the protection ability of sol–gel coating on Al metal.     

Synthesis of TiO2–Ag nanocomposite with sol–gel method and investigation of its antibacterial activity against E. coli

TiO₂–Ag nanocomposite was prepared by the sol–gel method and an azeotropic distillation with benzene was used for dehydration of the gel. Because of gel dehydration by distillation method a nanopowder with a surface area of 230 m²/g was produced which decreased to 80 m²/g after calcination. TEM micrographs and XRD patterns showed that spherical nanosized Ag particles (≈ 10 nm) were deposited among TiO₂ particles. The antibacterial activity of calcined powder at 300 and 500 °C was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The antibacterial tests confirmed the powder calcined at 300 °C possessed more antibacterial activity than the pure TiO₂, amorphous powder and the powder calcined at 500 °C under UV irradiation. In the absence of UV, the reduction in viable cells was observed only with calcinated powder at 300 °C.     

Fabrication and properties of cordierite based glass/AlN composites by sol–gel and pressureless sintering

In this study, the effect of AlN content on the crystallization behavior of cordierite based glass, was firstly investigated. Results show that μ-cordierite appeared in the composites with high AlN content even at high temperatures, which implied that the AlN may broad the crystallization temperature range of μ-cordierite and depress the transformation of μ→α-cordierite. The crystallization temperature of α-cordierite was about 980 °C for the pure glass and the temperature increased with AlN content for composites, but the crystallization temperature of μ-cordierite had reverse trend. The composites owned excellent bending strength when the AlN content was 20 wt%. With increasing of AlN content, the dielectric loss was increased which was caused mainly by the structural loss and the appearance of μ-cordierite, but the dielectric constant had crosscurrent. It was observed that the composites were beneficial in producing LTCC material which can be highlighted with high strength, low shrinkage and good dielectric properties at 1 MHz.