Gold nanoparticles developed in sol–gel derived apatite—bioactive glass composites

The study is focussed on synthesis and characterisation of a new sol–gel derived composite system consisting of nanocrystalline apatite, bioactive glass and gold nanoparticles, which are of interest both for regenerative medicine and for specific medical applications of the releasable gold nanoparticles. Samples dried at 110°C and then heat treated for 30 min at 300 and 500°C were investigated by thermal analysis (DTA/TG), X-ray diffraction (XRD), UV–VIS–NIR, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Photoelectron(XPS) spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Gold nanoparticles and nanocrystalline apatite are developed already after heat treatment at 300°C. XPS analysis clearly revealed the presence of both metallic and ionic gold species. The development of gold nanoparticles was evidenced by UV–VIS–NIR and TEM analysis, and their size increased from few nanometers to 25 nm by increasing the treatment temperature from 300 to 500°C. The bioactivity of the samples immersed in simulated body fluid was demonstrated by XRD and SEM results.     

Effect of hydrolysis on the phase evolution of water-based sol–gel hydroxyapatite and its application to bioactive coatings

In a previous report, we demonstrated a successful synthesis of crystalline hydroxyapatite (HA) through the use of a water-based sol–gel process. It was shown that the apatite can be obtained at temperatures generally below 400 °C, providing a great advantage for practical bioactive coating purposes. The influence of hydrolysis of phosphorus sol solution on the phase evolution of the resulting HA is the focus of this investigation. Experimental results show that, in the absence of acid catalyst, a long-term hydrolysis, i.e. >4 h, is required for better evolution of apatitic phase. Such a phase evolution is mainly attributed to an increased concentration of apatitic phase, rather than improved crystallinity in the calcined gels. With the aid of acid catalyst, we found that a well-crystalline HA can be synthesized over a time period shorter by 2–3 orders of magnitude than those without catalyst, i.e. a few minutes. In almost all cases, a small amount of tricalcium phosphate (TCP) was detected, which may be explainable by the formation of oligomeric derivatives of the phosphorus sol during synthesis, where calcium phosphate derivatives with lower Ca/P ratio than stoichiometry can be developed. By selecting an optimal sol as a dipping source, highly-porous dental root specimens were coated and a thin, dense, adhesive (upon finger-nail scratching test) coating was achieved after calcinations at 375 °C. An in vitro test also shows a bioactive character of the coating.     

Compaction and sintering behaviour of glass–alumina composites

The effects of Al₂O₃ additions on the compaction and sintering behaviour of a leadborosilicate glass (LG) have been investigated. LG powder was prepared by melting, fritting and milling a glass of the composition: 77PbO, 10B₂O₃, 10SiO₂, 2Al₂O₃ and 1P₂O₅ (wt.%). The mean particle sizes of the powders were: LG, 6.5 μm and Al₂O₃, 3.3 μm. The compaction behaviour of LG–Al₂O₃ powder mixtures can be represented by a new compaction equation: [(D_g−D₀)/(1−D₀)]=(P/P_f)ⁿ, where D_g is the relative green density, D₀ the relative tap density and n and P_f are material constants. The exponent n decreases from 0.192 to 0.065 as the Al₂O₃ content is increased from 0 to 100 vol.%. The Frenkel equation for isothermal shrinkage has been found to be valid. It is shown that in the glass matrix composites the minimum sintering temperature can be determined by measuring the dilatometric deformation temperature. The presence of Al₂O₃ in excess of 15 vol.% has been found to strongly retard the sintering kinetics. An addition of 45 vol.% Al₂O₃ increases the activation energy for sintering from 67 to 112 kcal mol⁻¹. The presence of Al₂O₃ particles also induced a partial crystallisation in LG matrix.     

Antibacterial and bioactive silver-containing Na2O·CaO·2SiO2 glass prepared by sol–gel method

The antibacterial effect of addition of silver oxide to Na2O x CaO x 2SiO2 glass have been studied. Silver containing and silver free Na2O x CaO x 2SiO2 glasses have been prepared by sol-gel synthesis using tetramethil orthosilicate, sodium ethoxide, calcium nitrate tetrahydrate and silver nitrate as starting materials and methyl ethyl ketone as solvent. The gel was examined by differential thermal analysis, thermo gravimetric analysis, FTIR spectroscopy and X-ray diffraction analysis. Antibacterial and bioactive tests on gel glass powders, obtained after a heat treatment of 2 h at 600 degrees C of the dried gel, were carried out. High antimicrobial effects of samples against Escherichia coli and Streptococcus mutans were found. FTIR measurements and SEM micrographs have ascertained the formation of a hydroxyapatite layer on the surface of samples soaked in a simulated body fluid for different times.     

Biofunctionalization of porous titanium coatings through sol–gel impregnation with a bioactive glass–ceramic

In implant technology, open porous Ti coatings are applied as functional surface layers on prosthetic devices to improve osseointegration. Since a successful clinical performance strongly depends on the (initial) quality of bone ingrowth in the porous structure, surface functionalization of the porous Ti to incorporate an additional osteoconductive capacity is recommended. In this paper, a bioactive glass–ceramic coating is applied into the open porous network of Ti coatings with a pore throat size of 1–20 μm through a sol–gel process. Using an all-alkoxide precursor route, homogeneous amorphous powders of three- (SiO₂–CaO–P₂O₅) and four-component (SiO₂–CaO–Na₂O–P₂O₅) bioactive glass compositions are prepared. By sol impregnation followed by a heat treatment, it is possible to deposit a micrometer thin bioactive glass–ceramic layer on the walls of the internal pore surface, while the original porosity and the open pore structure of the Ti coatings are maintained. The tensile adhesion strength of the Ti/bioactive glass–ceramic composite coatings is 22 to 29 MPa, suggesting a good mechanical adhesion.     

Modifying a dental ceramic by bioactive glass via the sol–gel route: Characterization and bioactivity investigation

The modification of a widely used dental ceramic by a bioactive glass via sol–gel method resulted in the fabrication of novel dental ceramic composites with bioactive behavior. The presence of leucite (Lt), apatite (Ap), various calcium silicate phases (CS) and a glassy aluminosilicate matrix were detected, while after sintering the predominance of wollastonite (W) among the other calcium silicate phases was observed, along with further crystallization of apatite. Concerning the bioactivity, the onset of the apatite formation was directly dependent on the bioactive glass amount, while a delay of the sintered specimens compared to the raw powders was also observed.     

Development of injectable biocomposites from hyaluronic acid and bioactive glass nano-particles obtained from different sol–gel routes

Bioactive glass nano-powders with the same chemical composition and different particle characteristics were synthesized by acid-catalyzed (the glass is called BG1) and acid–base catalyzed (BG2) sol–gel processes. Morphological characteristics of powders were determined by TEM and BET methods. The powders were separately mixed with 3% hyaluronic acid solution to form a paste. In vitro reactivity of pastes was determined by soaking them in simulated body fluid. Rheological behaviors of paste in both rotation and oscillation modes were also measured. The results showed that BG1 particles was microporous with mean pore diameter of 1.6 nm and particle size of ~ 300 nm while BG2 was mesoporous with average pore diameter of 8 and 17 nm and particle size of 20–30 nm. The paste made of BG2 revealed better washout resistance and in vitro apatite formation ability than BG1. According to the rheological evaluations, both pastes exhibited shear thinning but non-thixotropic behavior, meanwhile paste of BG2 had higher viscosity than BG1. The oscillatory tests revealed that the pastes were viscoelastic materials with more viscous nature. Both pastes could be completely injected through standard syringe using low compressive load of 5–50 N. Overall, The biocomposites can potentially be used as bioactive paste for the treatment of hard and even soft tissues.     

PLD bioactive ceramic films: the influence of CaO–P2O5 glass additions to hydroxyapatite on the proliferation and morphology of osteblastic like-cells

This work consists on the evaluation of the in vitro performance of Ti6Al4V samples PLD (pulsed laser deposition) coated with hydroxyapatite, both pure and mixed with a CaO–P₂O₅ glass. Previous studies on immersion of PLD coatings in SBF, showed that the immersion apatite films did not present the usual cauliflower morphology but replicated the original columnar structure and exhibited good bioactivity. However, the influence of glass associated to hydroxyapatite concerning adhesion, proliferation and morphology of MG63 cells on the films surface was unclear. In this study, the performance of these PLD coated samples was evaluated, not only following the physical–chemical transformations resulting from the SBF immersion, but also evaluating the cytocompatibility in contact with osteoblast-like MG63 cells. SEM and AFM confirmed that the bioactive ceramic PLD films reproduce the substrate’s surface topography and that the films presented good adherence and uniform surface roughness. Physical–chemical phenomena occurring during immersion in SBF did not modify the original columnar structure. In contact with MG63 cells, coated samples exhibited very good acceptance and cytocompatibility when compared to control. The glass mixed with hydroxyapatite induced higher cellular proliferation. Cells grown on these samples presented many filipodia and granular structures, typical features of osteoblasts.     

Improved properties of PTFE composites filled with glass fiber modified by sol–gel method

PTFE/GF(glass fiber) composites are widely applied in high-frequency printed circuit board (PCB) substrate materials due to the excellent dielectric properties of PTFE and the low thermal expansion coefficient of GF. However, the poor interface compatibility between PTFE and GF affects the performance of the composite substrates. In this study, tetraethyl orthosilicate (TEOS) was used as the silicon source, and polydimethylsiloxane (PDMS) was the organic precursor to modify the surface of GF through the sol–gel method to promote the interface compatibility of GF and PTFE. The modified GF noted T-GF was filled in PTFE to prepare PTFE/T-GF composites. SEM, FTIR, XPS, and contact angle confirmed that organic–inorganic hybrids were successfully loaded on GF's surface. Moreover, compared with PTFE/GF and the conventional coupling agent modified GF filled PTFE composites, the PTFE/T-GF exhibited improved dielectric constant (2.305), decreased dielectric loss (9.08E^?4), higher bending strength (21.45 MPa) and bending modulus (522 MPa), better thermal conductivity (0.268 W/m*K) and lower CTE (70 ppm/°C), making it has promising application as the substrate materials for high frequency PCB.

     

Thin hydroxyapatite coatings via sol–gel synthesis

Production of hydroxyapatite coatings using an alkoxide-based sol–gel route requires control of solution aging time and heating schedule. 31P nuclear magnetic resonance spectroscopy was used to investigate the changes during aging of the sol and thermal gravimetric analysis employed to study the behavior of the xerogels as a function of temperature, while final products were determined using X-ray diffraction. Results from 31P nuclear magnetic resonance spectroscopy and thermal analysis revealed that sols must be aged for at least 24 h to complete the reaction of the two reactants. Deposition of the sol for coating production will then yield monophasic hydroxyapatite. Coatings produced from sols aged for less than 24 h yielded calcium oxide in addition to hydroxyapatite. Prefiring is necessary to remove most of the residual organic materials. Final heating up to 800°C produces crystallization at 550°C and removal of the remaining organic constituents for the formation of a thin hydroxyapatite layer. © 1998 Kluwer Academic Publishers     

Composite bone substitute materials based on β-tricalcium phosphate and magnesium-containing sol–gel derived bioactive glass

In the present study, bioceramic composites with improved mechanical and biological properties were synthesized by sintering mixtures of β-tricalcium phosphate and SiO₂–CaO–MgO–P₂O₅ sol–gel derived bioactive glass at 1000–1200°C. The physical, mechanical, structural and biological properties of the composites were evaluated by appropriate experiments such as microhardness, bending strength, XRD, SEM and MTT. The results showed that 1000 and 1100°C were not appropriate temperatures for sintering the composites and in contrast, the microhardness, bending strength and bulk density significantly increased by increasing in quantity of bioglass phase when the samples were sintered at 1200°C. No significant difference was found between the fracture toughness of the composites and pure β-tricalcium phosphate. β-tricalcium phosphate was structurally stable up to 1200°C and did not transform to its alpha form even in the presence of the bioglass phase but migration of magnesium cations from the glass composition into its lattice structure was found by right-shift in XRD patterns, especially when the composite contained higher amount of bioglass component. Calcium silicate was also crystallized in the composition of the composites, which was more detectable in higher sintering temperatures. The results of the MTT test showed that proliferation of human osteosarcoma cells on the composites was considerably better than that of pure β-TCP.     

Fire retardancy of sol–gel derived titania wood-inorganic composites

Sol–gel technology was applied in tailoring novel wood-made-inorganic composites with improved thermal and fire properties. In practice, composites materials were prepared by impregnating pine sapwood wood with nano-scaled precursor solutions derived from titanium(IV) isopropoxide followed by a thermal curing process. Thermal and fire properties were evaluated by thermal analysis and cone calorimetry, whereas flammability was specified by oxygen index (LOI) and UL 94 test. Peak heat release rates were moderately reduced indicating fire retardance potential in terms of flame spread attributed to the appropriate protection layer action of the titania-based depositions. LOI (oxygen index) values of these composites were increased up to 38 vol.% in comparison to 23 vol.% for untreated wood. The flame retardancy performance depends on the fire scenario and is strongly influenced by wood loading and crack-free deposition of the titania layers inside the composite.     

Rheological evaluations and in vitro studies of injectable bioactive glass–polycaprolactone–sodium alginate composites

Composite pastes composed of various amounts of melt-derived bioactive glass 52S4 (MG5) and polycaprolactone (PCL) microspheres in sodium alginate solution were prepared. Rheological properties in both rotatory and oscillatory modes were evaluated. Injectability was measured as injection force versus piston displacement. In vitro calcium phosphate precipitation was also studied in simulated body fluid (SBF) and tracked using scanning electron microscopy, X-ray diffraction and FTIR analyses. All composite pastes were thixotropic in nature and exhibited shear thinning behavior. The magnitude of thixotropy decreased by adding 10–30 wt% PCL, while further amounts of PCL increased it again. Moreover, the composites were viscoelastic materials in which the elastic modulus was higher than viscous term. The pastes which were just made of MG5 or PCL had poor injectability, whereas the composites containing both of these constituents exhibited reasonable injectability. All pastes revealed adequate structural stability in contact with SBF solution. In vitro calcium phosphate precipitation was well observed on the paste made of MG5 and somewhat on the pastes with 10–40 wt% PCL, however the precipitated layer was amorphous in nature. Overall, the produced composites may be appropriate as injectable biomaterials for non-invasive surgeries but more biological evaluations are essential.     

Synthesis of high purity hydroxyapatite nanopowder via sol–gel combustion process

A polymeric sol–gel combustion method has been used to synthesize nanocrystalline hydroxyapatite (HA) powder from calcium nitrate and triethyl phosphate with the addition of NH₄OH. The sol–gel combustion process generates phase-pure nanocrystalline HA powder, as characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Sintering of the HA powder compact at 1200°C for 2 h leads to a 93% theoretical dense ceramic body. This method offers an easy route for the preparation of phase-pure nanocrystalline HA powder.     

Synthesis of nanocrystalline carbonated hydroxyapatite powder via nonalkoxide sol–gel method

Nanocrystalline hydroxyapatite powder was synthesized via nonalkoxide sol–gel method. Ca(NO₃)₂·4H₂O and P₂O₅ were mixed in ethanol, which led to a stable sol. STA, XRD and FTIR were used to characterize the calcined powders. The degrees of crystallinity and crystallite sizes were thereafter calculated from XRD patterns. The microscopic observations of the powder were performed using SEM and TEM. Results showed that a nanocrystalline hydroxyapatite powder was obtained after being heated at 450 °C for 6 h. Furthermore, increasing the calcining temperature caused both the formation of carbonate bonds and the increase in the crystallite sizes, and the degree of crystallinity.     

Synthesis and dissolution behaviour of CaO/SrO-containing sol–gel-derived 58S glasses

The effect of the substitution of strontium for calcium in the tertiary the SiO₂–CaO–P₂O₅ sol–gel bioactive glass 58S (60SiO₂·36CaO·4P₂O₅, mol%) on its structure and its chemical durability on soaking in simulated body fluids was investigated. 58S was selected as a starting composition, and substitution for calcium was carried out from 0 to 100% with an increment of 25%. A novel phosphate source of diethylphosphatoethyltriethoxysilane, which consists of Si and P connected with ethylene group, was used in this work. XRD and FTIR showed that the gels obtained following drying at 130 °C had a typical sol–gel structure, where a continuous amorphous silica gel network and surface bound mineral salts of Ca(NO₃)₂ and Sr(NO₃)₂. Once the gels were heat stabilised to decompose nitrates and incorporate the cations into the network, samples containing Sr formed a strontium silicate crystalline phase. With increasing levels of Sr in the composition, the overall crystallinity of the glass–ceramic increased, while, at the maximum substitution of 100% SrO, macroscopic phase separation was observed, characterised by needle-like crystals of strontium apatite (Sr₅(PO₄)₃OH) and strontium silicate (Sr₂SiO₄) phases in addition to amorphous regions. Dissolution experiments in Tris-buffered solution showed Sr successfully released into the media even though it existed as a crystalline phase in the glass–ceramic. Further, the glass–ceramics induced nucleation and growth of carbonated hydroxyapatite (HA) on their surface suggesting potential bioactivity of the materials. At higher substitutions (75 and 100% SrO for CaO), HA nucleation was not found to occur this may have been due to low amount of phosphate released from the original glass–ceramic as a result of it being locked up in the strontium apatite phase.     

Bioactive sol–gel glass added ionomer cement for the regeneration of tooth structure

Dental cements including the glass ionomer cement (GIC) have found widespread use in restoring tooth structures. In this study, a sol-gel derived glass (SG) with a bioactive composition (70SiO(2) . 25CaO . 5P(2)O(5)) was added to the commercial GIC (GC, Fuji I) to improve the bioactivity and tooth regeneration capability. The SG powders prepared with sizes in the range of a few micrometers were mixed with GIC at SG/GC ratios of 10 and 30 wt%. The setting time, diametral tensile strength, and in vitro bioactivity of the GC-SG cements were examined. The setting time of the GC-SG cements increased with increasing amount of SG. However, the addition of SG did not significantly alter the diametral tensile strength of the GC. GC-SG induced the precipitation of an apatite bone-mineral phase on the surface after immersion in a simulated body fluid (SBF), showing in vitro bone bioactivity. However, no mineral induction in SBF was observed in the commercial GIC after the immersion. The in vitro cell assay confirmed that the GC-SG samples produced higher cell viability than the GC sample with cell culturing for up to 7 days.     

Physical and cytocompatibility properties of bioactive glass–polyvinyl alcohol–sodium alginate biocomposite foams prepared via sol–gel processing for trabecular bone regeneration

In the present work, biocomposite foams of bioactive glass along with polyvinyl alcohol and sodium alginate are designed and developed as a potential biomaterial for bone regeneration. These biocomposite foams have a low density of 0.92 g/cm³, providing desired property for bone tissue engineering applications. Biocomposite foams were prepared via surfactant foaming. Scanning electron microscopic characterization revealed pore size of 200–500 μm of the biocomposite foams. When these materials were incubated in simulated body fluid, hydroxyapatite layer formation was observed on the material surface. To confirm the cell viability and proliferation on these materials, MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was performed with NIH 3T3 fibroblast cells and the results revealed good biocompatibility with the biocomposite foams. Cell adhesion studies further confirmed the biocompatibility of the scaffolds via cell attachment and ECM production. The optimally synthesized biocomposite foams had a good combination of physical properties with compressive strength of 1.64 MPa and elastic modulus of 18 MPa. In view of the favorable combination of physical and biological properties, the newly developed materials are considered to be suitable for regeneration of trabecular bone.     

Sol–gel derived composite from bioactive glass–polyvinyl alcohol

Investigation of novel biomaterials for bone engineering is based on the development of porous scaffolds, which should match the properties of the tissue that is to be replaced. These materials need to be biocompatible, ideally osteoinductive, osteoconductive, and mechanically well-matched. In the present paper, we report the preparation and characterization of hybrid macroporous scaffold of polyvinyl alcohol (PVA)/bioactive glass through the sol–gel route. Hybrids containing PVA (80, 70 and 60 wt%) and bioactive glass with composition 58SiO₂–33CaO–9P₂O₅ were synthesized by foaming a mixture of polymer solution and bioactive glass via sol–gel precursor solution. PVA with two different degree of hydrolysis (DH), 98.5% (high degree) and 80% (low degree) were also investigated, in order to evaluate the influence of residual acetate group present in polymer chain on the final structure and properties of 3D porous composite produced. The microstructure, morphology and crystallinity of the hybrid porous scaffolds were characterized by X-ray diffraction (XRD), Infrared Fourier Transform spectrometry (FTIR) and Scanning electron microscopy (SEM/EDX) analysis. In addition, specific surface area was assessed by B.E.T. nitrogen adsorption method and mechanical behavior was evaluated by compression tests. Preliminary cytotoxicity and cell viability were also performed by the MTT assay. VERO cell monolayers were grown in 96-well microtiter plates. The results have clearly showed that hybrid foams of polyvinyl alcohol/bioactive glass (PVA/BG) with interconnected macroporous 3D structure were successfully produced. All the tested hybrids of PVA/BG have showed adequate cell viability properties for potential biological applications.     

Low temperature synthesis of hydroxyapatite nano-rods by a modified sol–gel technique

Hydroxyapatite (HAp) nano-rods were successfully synthesized by a modified sol–gel method using a solution of CaCl₂·2H₂O in water, along with a solution of H₃PO₄ in triethylamine and NH₄OH as starting materials. The Ca/P molar ratio was maintained at 1.67. The sol obtained was dried in an oven for 2 days at 100 °C after being dialyzed for 12 h. Pellets were made from the crystalline powders and immersed in simulated body fluid (SBF) to check its biocompatibility after 15, 45 and 180 days of immersion. The HAp powders and pellets were characterized by X-Ray Diffraction crystallography (XRD), Fourier transform Infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The HAp nano-rods had an average diameter of 25 nm and length 110–120 nm. Immersion of the HAp pellets in SBF led to the formation of a highly porous interconnecting HAp layer on the surface. The porosity increased with increase in immersion time.