Synthesis, characterization and in vitro bioactivity of sol-gel-derived SiO2–CaO–P2O5–MgO bioglass

Bioactivity of Sodium Free Fluoride Containing Glasses and Glass-Ceramics

The bioactivity of a series of fluoride-containing sodium-free calcium and strontium phosphosilicate glasses has been tested in vitro. Glasses with high fluoride content were partially crystallised to apatite and other fluoride-containing phases. The bioactivity study was carried out in Tris and SBF buffers, and apatite formation was monitored by XRD, FTIR and solid state NMR. Ion release in solutions has been measured using ICP-OES and fluoride-ion selective electrode. The results show that glasses with low amounts of fluoride that were initially amorphous degraded rapidly in Tris buffer and formed apatite as early as 3 h after immersion. The apatite was identified as fluorapatite by 19F MAS-NMR after 6 h of immersion. Glass degradation and apatite formation was significantly slower in SBF solution compared to Tris. On immersion of the partially crystallised glasses, the fraction of apatite increased at 3 h compared to the amount of apatite prior to the treatment. Thus, partial crystallisation of the glasses has not affected bioactivity significantly. Fast dissolution of the amorphous phase was also indicated. There was no difference in kinetics between Tris and SBF studies when the glass was partially crystallised to apatite before immersion. Two different mechanisms of apatite formation for amorphous or partially crystallised glasses are discussed.

In vitro response of human osteoblasts to multi-step sol-gel derived bioactive glass nanoparticles for bone tissue engineering

A multi-step sol-gel process was employed to synthesize bioactive glass (BG) nanoparticles. Transmission electron microscopy (TEM) revealed that the BG nanoparticles were spherical and ranged from 30 to 60 nm in diameter. In vitro reactivity of the BG nanoparticles was tested in phosphate buffer saline (PBS), Tris-buffer (TRIS), simulated body fluid (SBF), and Dulbecco's modified Eagle's medium (DMEM), in comparison with similar sized hydroxyapatite (HA) and silicon substituted HA (SiHA) nanoparticles. Bioactivity of the BG nanoparticles was confirmed through Fourier transform infrared spectroscopy (FTIR) analysis. It was found that bone-like apatite was formed after immersion in SBF at 7 days. Solutions containing BG nanoparticles were slightly more alkaline than HA and SiHA, suggesting that a more rapid apatite formation on BG was related to solution-mediated dissolution. Primary human osteoblast (HOB) cell model was used to evaluate biological responses to BG nanoparticles. Lactate dehydrogenase (LDH) cytotoxicity assay showed that HOB cells were not adversely affected by the BG nanoparticles throughout the 7day test period. Interestingly, MTS assay results showed an enhancement in cell proliferation in the presence of BG when compared to HA and SiHA nanoparticles. Particularly, statistically significant (p<0.05) alkaline phosphatase (ALP) activity of HOB cells was found on the culture containing BG nanoparticles, suggesting that the cell differentiation might be promoted by BG. Real-time quantitative PCR analysis (qPCR) further confirmed this finding, as a significantly higher level of RUNX2 gene expression was recorded on the cells cultured in the presence of BG nanoparticles when compared to those with HA and SiHA.

The use of carbon nanotubes to reinforce 45S5 bioglass-based scaffolds for tissue engineering applications

Bioglass has been used for bone-filling material in bone tissue engineering, but its lean mechanical strength limits its applications in load-bearing positions. Carbon nanotubes (CNTs), with their high aspect ratio and excellent mechanical properties, have the potential to strengthen and toughen bioactive glass material without offsetting its bioactivity. Therefore, in this research, multiwall carbon nanotube (MWCNT)/45S5 Bioglass composite scaffolds have been successfully prepared by means of freeze casting process. 45S5 Bioglass was synthesized by the sol-gel processing method. The obtained material was characterized with X-ray powder diffraction (XRD). The mechanical properties of the scaffolds, such as compression strength and elastic modulus, were measured. Finally, compared with the scaffolds prepared by 100% 45S5 Bioglass powders, the addition of 0.25 wt.% MWCNTs increases the compressive strength and elastic modulus of 45S5 Bioglass scaffolds from 2.08 to 4.56 MPa (a 119% increase) and 111.50 to 266.59 MPa (a 139% increase), respectively.

Fabrication and in vitro biological evaluation of photopolymerisable hydroxyapatite hydrogel composites for bone regeneration

The aim of this study was to improve the bioactive and compressive properties of photopolymerisable polyethylene glycol hydrogels with the incorporation of hydroxyapatite at different loadings. The synthesis of pure hydroxyapatite was verified through Fourier transform infrared spectroscopy (FTIR) analysis by the complete reaction of all constituents. The formation of a bioactive layer of the hydrogel based composites was confirmed through the formation of carbonate hydroxyapatite after soaking the samples in simulated body fluid. The incorporation of hydroxyapatite into the system resulted in an increase in Young’s modulus from 4.36 to 12.73 MPa and an increase in the stress at limit value from 1.20 to 4.42 MPa. This was due to the hydroxyapatite absorbing the compressive load, the polymer matrix distributing the load, a reduction in swelling and the presence of physical crosslinking between both components. Drug dissolution testing showed that the release rate of a drug from the hydrogels was dependent on the molecular weight of the polymer and the type of drug used.

Bioactivity and cytotoxicity of glass and glass-ceramics based on the 3CaO·P₂O₅--SiO₂--MgO system

The mechanical strength of bioactive glasses can be improved by controlled crystallization, turning its use as bulk bone implants viable. However, crystallization may affect the bioactivity of the material. The aim of this study was to develop glass-ceramics of the nominal composition (wt%) 52.75(3CaO·P₂O₅)-30SiO₂-17.25MgO, with different crystallized fractions and to evaluate their in vitro cytotoxicity and bioactivity. Specimens were heat-treated at 700, 775 and 975 °C, for 4 h. The major crystalline phase identified was whitlockite, an Mg-substituted tricalcium phosphate. The evaluation of the cytotoxicity was carried out by the neutral red uptake methodology. Ionic exchanges with the simulated body fluid SBF-K9 acellular solution during the in vitro bioactivity tests highlight the differences in terms of chemical reactivity between the glass and the glass-ceramics. The effect of crystallinity on the rates of hydroxycarbonate apatite (HCA) formation was followed by Fourier transformed infrared spectroscopy. Although all glass-ceramics can be considered bioactive, the glass-ceramic heat-treated at 775 °C (V775-4) presented the most interesting result, because the onset for HCA formation is at about 24 h and after 7 days the HCA layer dominates completely the spectrum. This occurs probably due to the presence of the whitlockite phase (3(Ca,Mg)O·P₂O₅). All samples were considered not cytotoxic.

Optimal Conditions of Electrostatic Spray Deposition (ESD) for Composite Biomaterials Coating for Biomedical Applications

Various types of metals and alloys are used for medical implants due to their excellent mechanical properties and corrosion resistance; however, their lacks of osteoinductive properties bring about the introduction of biomaterials which can help enhancing the bioactivity between the bones and the implants. Hydroxyapatite (Ca10(PO4)6(OH)2, or HA) which is one of the calcium phosphates that has similar mineral constituents of human bone, has been used as coating material to the metals/alloys substrate. Coating HA usually involves high-temperature such as the plasma spraying coating, which can alter the crystal structure of the HA partially become amorphous. The amorphous nature of HA lessen the benefits of coating with the biomaterial HA. Electrostatic spray deposition (ESD) was used in this research due to the fact that this process is simple, economical, and room-temperature operated. The preliminary results showed a promising thickness layer of about 40 μm; however, the adhesion of the coated layer to the stainless steel 316L was improved by mixing the HA powder with phosphate bioglass and cured in the vacuum furnace at 700oC. Taguchi experimental design technique was used for screening several ESD process parameters: powder feed rate, voltage, current, air volume, distances, time, and nozzle types to significant factors to the coated thickness of the ESD process. The results showed that feed rate, air volume, and time were the significant factors and then Full factorial analysis and response surface method was used for obtaining optimal conditions for the coating, as well as the predicted equation for determine the thickness coated layer with significant factors.

AP40 Bioactive Glass Ceramic by Sol-Gel Synthesis: In Vitro Dissolution and Cell-Mediated Bioresorption

In this work, the sol-gel synthesis of AP40 bioactive glass system was reported. The obtained powder was fully characterised in terms of microstructure, composition and thermal behaviour by X-ray diffraction (XRD) measurements, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry and differential thermal analysis (TG-DTA).In vitrodissolution tests were performed in order to assess the degradation behaviour of sol-gel derived AP40 samples thermally treated at different temperatures. Finally, preliminary results on cytocompatibility are reported, based on bioresorption activity of human peripheral blood monocytes differentiated into osteoclasts on sintered disks.

The influence of phosphorus precursors on the synthesis and bioactivity of SiO2-CaO-P 2O 5 sol-gel glasses and glass-ceramics

Bioactive glasses and glass-ceramics of the SiO(2)-CaO-P(2)O(5) system were synthesised by means of a sol-gel method using different phosphorus precursors according to their respective rates of hydrolysis-triethylphosphate (OP(OC(2)H(5))(3)), phosphoric acid (H(3)PO(4)) and a solution prepared by dissolving phosphorus oxide (P(2)O(5)) in ethanol. The resulting materials were characterised by differential scanning calorimetry and thermogravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and by in vitro bioactivity tests in acellular simulated body fluid. The different precursors significantly affected the main steps of the synthesis, beginning with the time required for gel formation. The most striking influence of these precursors was observed during the thermal treatments at 700-1,200 °C that were used to convert the gels into glasses and glass-ceramics. The samples exhibited very different mineralisation behaviours; especially those prepared using the phosphoric acid, which had a reduced onset temperature of crystallisation and an increased resistance to devitrification. However, all resulting materials were bioactive. The in vitro bioactivity of these materials was strongly affected by the heat treatment temperature. In general, their bioactivity decreased with increasing treatment temperature. For crystallised samples obtained above 900 °C, the bioactivity was favoured by the presence of two crystalline phases: wollastonite (CaSiO(3)) and tricalcium phosphate (α-Ca(3)(PO(4))(2)).

Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na 2O-CaO-MgO-P 2O 5-SiO 2

Osteoconductive bioglasses, free of K(2)O and Al(2)O(3) and with content of Na(2)O lower than 10 mol%, were designed based on the ratio (SiO(2) + MgO)/(P(2)O(5) + CaO + Na(2)O) in the system Na(2)O-CaO-MgO-P(2)O(5)-SiO(2). The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12 weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.

Sol-gel derived 45S5 bioglass: synthesis, microstructural evolution and thermal behaviour

In this work, the 45S5 bioactive glass was synthesized through an aqueous sol-gel method. Characteristic functional groups were evidenced by Fourier transform infrared spectroscopy, the thermal behaviour was investigated by thermogravimetric and differential thermal analysis, crystallization kinetics and phase evolution were followed by X-ray diffraction measurements. The sintering behaviour of the sol-gel derived 45S5 was then studied by dilatometry and the microstructural evolution was followed step-by-step, interrupting the thermal cycle at different temperatures. In vitro dissolution tests were performed in order to assess the degradation behaviour of sol-gel derived 45S5 samples thermally treated at different temperatures. A relevant influence of the calcination conditions (namely, dwelling time and temperature) of the as-prepared powder on the phase appearance and its sintering behaviour as well as on the porosity features, in terms of pore dimension and interconnectivity, of the fired materials was stated.

Metallic ions as therapeutic agents in tissue engineering scaffolds: an overview of their biological applications and strategies for new developments

This article provides an overview on the application of metallic ions in the fields of regenerative medicine and tissue engineering, focusing on their therapeutic applications and the need to design strategies for controlling the release of loaded ions from biomaterial scaffolds. A detailed summary of relevant metallic ions with potential use in tissue engineering approaches is presented. Remaining challenges in the field and directions for future research efforts with focus on the key variables needed to be taken into account when considering the controlled release of metallic ions in tissue engineering therapeutics are also highlighted.

Phytic acid derived bioactive CaO-P2O5-SiO2 gel-glasses

The possibility of using phytic acid as a precursor to synthesize CaO-P(2)O(5)-SiO(2) glasses by sol-gel method has been explored and the pseudo ternary phase diagram has been established. It was shown that gel-glasses over a broader range of compositions could be prepared compared to other phosphorus precursors or melt-quenching method. Furthermore, phytic acid was found to assist calcium being incorporated into glass networks. In vitro tests in simulated body fluid (SBF) were performed on the above gel-glasses and it was found that they were bioactive over a much broader compositional range especially at high phosphate content, thus enabling one to design bioactive materials with various degradation rates by adjusting the phosphate content.

A review of the biological response to ionic dissolution products from bioactive glasses and glass-ceramics

Several inorganic materials such as special compositions of silicate glasses, glass-ceramics and calcium phosphates have been shown to be bioactive and resorbable and to exhibit appropriate mechanical properties which make them suitable for bone tissue engineering applications. However, the exact mechanism of interaction between the ionic dissolution products of such inorganic materials and human cells are not fully understood, which has prompted considerable research work in the biomaterials community during the last decade. This review comprehensively covers literature reports which have investigated specifically the effect of dissolution products of silicate bioactive glasses and glass-ceramics in relation to osteogenesis and angiogenesis. Particularly, recent advances made in fabricating dense biomaterials and scaffolds doped with trace elements (e.g. Zn, Sr, Mg, and Cu) and investigations on the effect of these elements on the scaffold biological performance are summarized and discussed in detail. Clearly, the biological response to artificial materials depends on many parameters such as chemical composition, topography, porosity and grain size. This review, however, focuses only on the ion release kinetics of the materials and the specific effect of the released ionic dissolution products on human cell behaviour, providing also a scope for future investigations and identifying specific research needs to advance the field. The biological performance of pure and doped silicate glasses, phosphate based glasses with novel specific compositions as well as several other silicate based compounds are discussed in detail. Cells investigated in the reviewed articles include human osteoblastic and osteoclastic cells as well as endothelial cells and stem cells.

Sol-gel silica-based biomaterials and bone tissue regeneration

The impact of bone diseases and trauma in developed and developing countries has increased significantly in the last decades. Bioactive glasses, especially silica-based materials, are called to play a fundamental role in this field due to their osteoconductive, osteoproductive and osteoinductive properties. In the last years, sol-gel processes and supramolecular chemistry of surfactants have been incorporated to the bioceramics field, allowing the porosity of bioglasses to be controlled at the nanometric scale. This advance has promoted a new generation of sol-gel bioactive glasses with applications such as drug delivery systems, as well as regenerative grafts with improved bioactive behaviour. Besides, the combination of silica-based glasses with organic components led to new organic-inorganic hybrid materials with improved mechanical properties. Finally, an effort has been made to organize at the macroscopic level the sol-gel glass preparation. This effort has resulted in new three-dimensional macroporous scaffolds, suitable to be used in tissue engineering techniques or as porous pieces to be implanted in situ. This review collects the most important advances in the field of silica glasses occurring in the last decade, which are called to play a lead role in the future of bone regenerative therapies.