Study on antibacterial effect of 45S5 Bioglass®

Previous studies have shown that bioactive glasses possessed antibacterial effect on common bacteria due to the high aqueous pH value caused by the bioactive glass dissolution. In the present study, the efficiency of the antibacterial effect of 45S5 Bioglass (45S5 BAG) against S. aureus, S. epidermidis and E. coli and its mechanism were investigated. The results showed that 45S5 BAG exhibited a strong antibacterial effect against the bacteria, and the sensitivity of gram-negative and gram-positive bacteria to Bioglass was different. Furthermore, a dose-dependent bacterial adhesion on 45S5 BAG particles and the formation of needle-like Bioglass debris were observed, which resulted in the damage of cell walls and inactivation of bacteria. The results suggested that both the high pH and bioglass debris on the surface of bacteria may be the possible mechanisms of the antibacterial effect of 45S5 BAG particulates.     

Conversion of melt-derived microfibrous borate (13-93B3) and silicate (45S5) bioactive glass in a simulated body fluid

Microfibrous bioactive glasses are showing a considerable capacity to heal soft tissue wounds, but little information is available on the mechanism of healing. In the present study, the conversion of microfibrous borate bioactive glass (diameter = 0.2–5 μm) with the composition designated 13-93B3 (5.5 Na₂O, 11.1 K₂O, 4.6 MgO, 18.5 CaO, 3.7 P₂O₅, 56.6 B₂O₃ wt%) was evaluated in vitro as a function of immersion time in a simulated body fluid (SBF) at 37 °C using structural and chemical techniques. Silicate 45S5glass microfibers (45 SiO₂, 24.5 Na₂O, 24.5 CaO, 6 P₂O₅ wt%) were also studied for comparison. Microfibrous 13-93B3 glass degraded almost completely and converted to a calcium phosphate material within 7–14 days in SBF, whereas >85 % of the silica remained in the 45S5 microfibers, forming a silica gel phase. An amorphous calcium phosphate (ACP) product that formed on the 13-93B3 microfibers crystallized at a slower rate to hydroxyapatite (HA) when compared to the ACP that formed on the 45S5 fibers. For immersion times >3 days, the 13-93B3 fibers released a higher concentration of Ca into the SBF than the 45S5 fibers. The fast and more complete degradation, slow crystallization of the ACP product, and higher concentration of dissolved Ca in SBF could contribute to the capacity of the microfibrous borate 13-93B3 glass to heal soft tissue wounds.     

Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37°C. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO₂ with B₂O₃. Higher B₂O₃ content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO₂ in a Na-depleted core. The concentration of Na⁺ in the phosphate solution increased with reaction time whereas the PO₄^3– concentration decreased, both reaching final limiting values at a rate that increased with the B₂O₃ content of the glass. However, the Ca²⁺ concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K₂HPO₄ and K₂CO₃ produced a carbonate-substituted HA but the presence of the K₂CO₃ had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.     

Synthesis and characterization of titanium-45S5 Bioglass nanocomposites

Titanium-45S5 Bioglass nanocomposites were synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vicker’s microhardness as high as 770 HV_0.2 for Ti-20 wt.% 45S5 Bioglass, which is more than three times higher than that of a conventional microcrystalline titanium (225 HV_0.2). Additionally, titanium-10 wt.% of 45S5 Bioglass nanocomposites (i_c = 1.20 × 10⁻⁷ A/cm², E_c = −0.42 V vs. SCE) were more corrosion resistant than microcrystalline titanium (i_c = 2.27 × 10⁻⁶ A/cm², E_c = −0.36 V vs. SCE). In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti-10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. Mechanical alloying and powder metallurgy process for the fabrication of titanium-45S5 Bioglass nanocomposites with a unique microstructure, higher hardness, lower Young’s modulus and better corrosion resistance, in comparison to microcrystalline titanium, were developed. On the other hand, Ti-10 wt.% 45S5 Bioglass composites posses higher fracture toughness compared to 45S5 Bioglass. The proper modification of chemical composition and microstructure of Ti-bioceramic nanocomposites can expand the use of titanium in the biomedical fields.     

Gallium-containing phospho‐silicate glasses: Synthesis and in vitro bioactivity

A series of Ga-containing phospho-silicate glasses based on Bioglass 45S5, having molar formula 46.2SiO₂·24.3Na₂O·26.9CaO·2.6P₂O₅·xGa₂O₃ (x = 1.0, 1.6, 3.5), were prepared by fusion method. The reference Bioglass 45S5 without gallium was also prepared. The synthesized glasses were immersed in simulated body fluid (SBF) for 30 days in order to observe ion release and hydroxyapatite (HA) formation. All Ga-containing glasses maintain the ability of HA formation as indicated by main X-ray diffractometric peaks and/or electronic scanning microscopy results. HA layer was formed after 1 day of SBF soaking in 45S5 glass containing up to 1.6% Ga₂O₃ content. Moreover, gallium released by the glasses was found to be partially precipitated on the glass surface as gallium phosphate. Further increase in gallium content reduced the ion release in SBF. The maximum of Ga³⁺ concentration measured in solution is ~ 6 ppm determined for 3.5% Ga₂O₃ content. This amount is about half of the toxic level (14 ppm) of gallium and the glasses release gallium till 30 days of immersion in SBF. Considering the above results, the studied materials can be proposed as bioactive glasses with additional antimicrobial effect of gallium having no toxic outcome.     

Microstructure and in vitro behaviour of 45S5 bioglass coatings deposited by high velocity suspension flame spraying (HVSFS)

The high-velocity suspension flame spraying technique (HVSFS) was employed in order to deposit 45S5 bioactive glass coatings onto titanium substrates, using a suspension of micron-sized glass powders dispersed in a water + isopropanol mixture as feedstock. By modifying the process parameters, five coatings with different thickness and porosity were obtained. The coatings were entirely glassy but exhibited a through-thickness microstructural gradient, as the deposition mechanisms of the glass droplets changed at every torch cycle because of the increase in the system temperature during spraying. After soaking in simulated body fluid, all of the coatings were soon covered by a layer of hydroxyapatite; furthermore, the coatings exhibited no cytotoxicity and human osteosarcoma cells could adhere and proliferate well onto their surfaces. HVSFS-deposited 45S5 bioglass coatings are therefore highly bioactive and have potentials as replacement of conventional hydroxyapatite in order to favour osseointegration of dental and prosthetic implants.     

Nanostructured titanium-45S5 Bioglass scaffold composites for medical applications

Titanium–10 wt.% 45S5 Bioglass scaffold nanocomposites were synthesized by the combination of mechanical alloying and by a “space-holder” sintering process. The porous structure and corrosion properties were investigated. In vitro biocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the disks of the materials and cell growth was examined. The morphology of the cell cultures obtained on Ti–10 wt.% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. On the other hand, on porous scaffold, the cells adhered with their whole surface to the insert penetrating the porous structure, while on the polished surface, more spherical cells were observed with a smaller surface of adhesion. The present study has demonstrated that titanium–10 wt.% 45S5 Bioglass scaffold nanocomposite is a promising biomaterial for bone tissue engineering.     

Primary bone-derived cell colonization of unconditioned and pre-conditioned Bioglass 45S5 surfaces in vitro

Samples of Bioglass 45S5, a bioactive glass that reacts chemically on immersion in an aqueous environment and following implantation can bond with bone, were immersed in culture medium with foetal calf serum as a source of proteins for periods of 1–11 days. Energy dispersive spectroscopy (EDS) revealed that over 11 days immersion, the Bioglass surface was rich in Si relative to Ca and P and scanning electron microscopy (SEM) showed that the Bioglass developed surface reaction layers. Samples conditioned in culture medium and previously untreated samples were used as substrates for primary osteoblast or periosteal cell cultures, to allow comparison of the effects of different Bioglass surface development, on subsequent cell attachment. SEM examination revealed that pre-conditioned Bioglass was a more suitable substrate for osteoblast colonization than previously undeveloped Bioglass, whereas periosteal cells colonized all samples equally well and more rapidly than osteoblasts.     

In vitro osteogenesis on fluorcanasite glass-ceramic with three different chemical compositions

This study aimed at investigating in vitro osteogenesis on three fluorcanasite glass-ceramic compositions with different solubilities (K3, K5, and K8). Osteoblastic cells were obtained from human alveolar bone fragments and cultured under standard osteogenic condition until subconfluence. First passage cells were cultured on K3, K5, and K8 and on Bioglass((R)) 45S5 (45S5-control). Cell adhesion was evaluated at 24 h. For proliferation and viability, cells were cultured for 1, 4, and 10 days. Total protein content and alkaline phosphatase (ALP) activity were measured at 7, 14, and 21 days. Cultures were stained with Alizarin red at 21 days, for detection of mineralized matrix. Data were compared by ANOVA followed by Duncan's test. Cell adhesion, cell proliferation, viability, total protein content, and ALP activity were not affected by fluorcanasite glass-ceramic composition and solubility. Bone-like formation was similar on all fluorcanasite glass-ceramics and was reduced compared to 45S5. The changes in the chemical composition and consequently solubility of the fluorcanasite glass-ceramics tested here did not significantly alter the in vitro osteogenesis. Further modifications of the chemical composition of the fluorcanasite glass-ceramic would be required to improve bone response, making this biomaterial a good candidate to be employed as a bone substitute.     

An extended X-ray absorption fine structure investigation on the local environment of niobium ions in Nb2O5-doped SrTiO3 glass ceramics

The dielectrical properties of glass ceramics derived from SrO–B2O3–Al2O3–TiO2 glasses are improved by doping the starting material with Nb2O5 and judicious choice of heat treatment conditions. In order to understand this effect the local environment of the niobium ions is studied by EXAFS (extended X-ray absorption fine structure) investigations at the Nb-K edge. For comparison purposes Ti-K and Sr-K EXAFS spectra have also been measured. The experiments suggest that the niobium ions are incorporated onto titanium sites in the crystalline SrTiO3 phase formed during the thermal treatment. This revised version was published online in November 2006 with corrections to the Cover Date.     

Historic and current strategies in bone tissue engineering: Do we have a hope in Hench?

Professors Larry Hench and Julia Polak formed the Tissue Engineering and Regenerative Medicine Centre (TERM) at Imperial College London to foster collaborations between biologists and materials scientists. Early work at the center elucidated the biomolecular interactions between primary human osteoblasts and 45S5 Bioglass . As research efforts expanded, the team discovered that the dissolution products of both 45S5 Bioglass and 58S sol-gel bioactive glasses had osteoblastic stimulatory properties. To address the shortage of appropriate cells for bone tissue engineering applications, TERM scientists also demonstrated the differentiation of embryonic stem (ES) cells to osteoblasts when treated with the dissolution products of bioactive glasses. They also found that the soluble factors ascorbic acid, beta -glycerophosphate, and dexamethasone preferentially differentiated ES cells to osteoblasts, and their combination with the dissolution products of bioactive glasses stimulated differentiation even further. Taken together, these results demonstrate the suitability of bioactive glasses as scaffolds for bone tissue engineering as they not only provide an osteoconductive and osteoproductive substrate, but also actively stimulate cells to express appropriate osteoblastic phenotypes. Professor Hench's vision to pioneer regenerative medicine research continues with the aim of developing novel therapeutics to treat musculoskeletal disability.     

Scalable,fluorine free and hot water repelling superhydrophobic and superoleophobic coating based on functionalized Al_2O_3 nanoparticles

Hot water droplet and oils induced air cushion failure, intensively used fluorine-containing chemicals,tedious preparation process, etc. are the main bottlenecks of the current artificially fabricated superhydrophobic materials, restricting their large-scale production and real-world applications. Herein, a facile,scalable, fluorine-free spray-coating strategy was employed to achieve superhydrophobic and superoleophobic polymerized organosilanes/Al2O3 nanoparticles(POS/Al₂O₃ NPs) coatings. The POS/Al₂O₃ NPs coating was achieved through hydrolytic condensation of tetraethyl orthoilicate(TEOS) and hexadecyltrimethoxysilane(HDTMS) in the presence of Al2O3 NPs. A variety of analytical techniques including scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), energy dispersive X-ray photoelectron spectroscopy(EDS) were used to investigate the fabricated coatings. The POS/Al₂O₃ NPs coating features high contact angle(>158°) and low sliding angle(<5°) for water, glycerol, and ethylene glycol droplets with different surface tensions, verifying both superhydrophobic and superoleophobic properties. Moreover, the coatings present extremely low surface adhesion force, excellent liquid-driven self-cleaning ability, and hot water repellency. The superamphiphobic POS/Al₂O₃ NPs coating exhibits promising applications in various fields including self-cleaning, corrosion resistance, and preventing scald as this strategy is applicable on various substrates.     

Effect of nanoparticulate bioactive glass particles on bioactivity and cytocompatibility of poly(3-hydroxybutyrate) composites

This work investigated the effect of adding nanoparticulate (29 nm) bioactive glass particles on the bioactivity, degradation and in vitro cytocompatibility of poly(3-hydroxybutyrate) (P(3HB)) composites/nano-sized bioactive glass (n-BG). Two different concentrations (10 and 20 wt %) of nanoscale bioactive glass particles of 45S5 Bioglass composition were used to prepare composite films. Several techniques (Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray) were used to monitor their surface and bioreactivity over a 45-day period of immersion in simulated body fluid (SBF). All results suggested the P(3HB)/n-BG composites to be highly bioactive, confirmed by the formation of hydroxyapatite on material surfaces upon immersion in SBF. The weight loss and water uptake were found to increase on increasing bioactive glass content. Cytocompatibility study (cell proliferation, cell attachment, alkaline phosphatase activity and osteocalcin production) using human MG-63 osteoblast-like cells in osteogenic and non-osteogenic medium showed that the composite substrates are suitable for cell attachment, proliferation and differentiation.     

Bioactive response of Ag-doped tape cast Bioglass® 45S5 following heat treatment

The suitability of Bioglass 45S5 to the tape casting process and the ability of the glass to retain in vitro bioactivity following heat treatment to increase strength has been established. In this research, tape cast Bioglass was doped with silver prior to heat treatment in an effort to impart antimicrobial properties. The effect of initial dopant concentration and processing temperature was investigated. FTIR confirmed the presence of well established hydroxyapatite (HA) surface layers on Ag-doped tape cast Bioglass following heat treatment and simulated body fluid (SBF) immersion. Solution analysis revealed the release of silver ion in concentrations similar to those reported in the literature to have antimicrobial effects. Additionally, mercury porosimetry was used to determine that silver enhanced the densification process relative to that of undoped tape cast Bioglass. Ag-doped tape cast and sintered Bioglass (TCSBG) appears promising for use in situations requiring rapid surface HA formation and antimicrobial properties.     

The Development of Bioactive Glass‐Ceramic Substrates with Biocide Activity

The biocide efficiency of bioactive 45S5 Bioglass® derived glass‐ceramic substrates against common Gram positive and Gram negative bacteria, and also against yeast, is investigated in this study. The results confirm the high bactericidal capacity of this material. Inorganic coatings containing silver nanoparticles on glass‐ceramic substrates are developed in order to ascertain whether the presence of silver enhances the biocide activity. It is found that a coating made of soda‐glass containing silver nanoparticles does not improve the antifungal properties of the 45S5 Bioglass® derived glass‐ceramic substrates.     

Characterisation of bioactive glass coatings on titanium substrates produced using a CO2 laser

Titanium and its alloys are widely used in load-bearing bioinert implants. Bioactive glasses (BAGs) form a chemical bond with bone, but they are not suitable for load-bearing applications. Creating a BAG coating on a titanium implant could combine the best properties of both materials. The results tend to be poor when conventional firing methods are applied to coat titanium with BAG. A local application of heat to melt the glass can be achieved by a CO2 laser. A new method is introduced to create BAG coatings on titanium locally in a controlled manner, with a focused CO2 laser beam. The coatings produced by this method precipitate calcium phosphate in vitro. Processing parameters (number of coated layers, laser power, and processing atmosphere) providing a firm attachment of the glass and good in vitro bioactivity were identified. XRD analysis showed no crystallisation of the glass due to processing with the laser. EDXA indicated the formation of a calcium phosphate layer, which FTIR suggested to be a hydroxyapatite. The results show CO2 laser processing to be a promising technique for the manufacture of 30-40 microm BAG coatings on titanium.     

Physical and biocompatibility studies of novel titanium dioxide doped phosphate-based glasses for bone tissue engineering applications

This study investigated doping titanium dioxide (TiO(2)) into phosphate glasses, 50 P(2)O(5)-30 CaO-20 Na(2)O, to control their degradation rate and enhance their biological response to be suitable scaffolds for bone tissue engineering applications. The thermal and structural properties were analysed using differential thermal analysis and X-ray powder diffraction. The effect of TiO(2) incorporation on degradation rate, ion release, and pH changes was also carried out. In vitro cyto-biocompatibility was assessed through MG63 human osteosarcoma cells attachment and viability using scanning electron microscopy and confocal microscopy, respectively. The results showed that addition of TiO(2) produced a significant increase in density and glass transition temperature. X-ray diffraction analysis showed the presence of NaCa(PO(3))(3) as a main phase of these glasses with titanium phosphate Ti-P(2)O(7) only detected for 5 mol% TiO(2) glasses. The degradation rate, however, was significantly reduced by one order of magnitude with incorporation of 5 mol% TiO(2) which has been reflected in released ions (cations and anions) and the minimal pH changes. Moreover, addition of TiO(2), 3 and 5 mol% in particular, supported the MG63 cells attachment and maintained high cell viability up to 7 days culture comparable to Thermanox. These results suggested that TiO(2) containing phosphate glasses can be a promising substrate for bone tissue engineering applications.     

Raman spectroscopic investigation of sodium borosilicate glass structure

Raman spectra of sodium borosilicate glasses with a wide range of Na₂O/B₂O₃ ratios were systematically measured. Variations of the spectra with glass composition were studied to interpret the implied distribution of Na⁺ ions between silicate and borate units. When Na₂O/B₂O₃ is less than 1, all Na⁺ ions are associated with borate units as indicated by the absence of the 1100 cm⁻¹ band of Si-O⁻ non-bridging bond stretching. For the (1−x)Na₂O · SiO₂ ·xB₂O₃ glass withx≦0.4 the peak-height ratio of the 950 cm⁻¹ band to the 1080 cm⁻¹ band was used to analyse semiquantitatively the distribution of the Na⁺ ions between silicate and borate units. Sodium ions are divided between silicate and borate units approximately in proportion to the amount of SiO₂ and B₂O₃ present in these glasses. Some of the high sodium content glasses were crystallized and their spectra were compared with the bulk glass spectra. The distribution of Na⁺ ions in the glass was quite different from their distribution after crystallization. Spectra of high silica glasses that had been heat-treated for phase separation indicated exclusion of borate units from the silica network and the formation of borate groups. For high boron content glasses, no change was observed on heat treatment. Raman bands due to borate groups seem to be little affected by their environments. Also affiliated with the Department of Geosciences.     

Reaction of sodium calcium borate glasses to form hydroxyapatite

This study investigated the transformation of two sodium calcium borate glasses to hydroxyapatite (HA). The chemical reaction was between either 1CaO · 2Na₂O · 6B₂O₃ or 2CaO · 2Na₂O · 6B₂O₃ glass and a 0.25 M phosphate (K₂HPO₄) solution at 37, 75 and 200 °C. Glass samples in the form of irregular particles (125–180 μm) and microspheres (45–90 and 125–180 μm) were used in order to understand the reaction mechanism. The effect of glass composition (calcium content) on the weight loss rate and reaction temperature on crystal size, crystallinity and grain shape of the reaction products were studied. Carbonated HA was made by dissolving an appropriate amount of carbonate (K₂CO₃) in the 0.25 M phosphate solution. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy were used to characterize the reaction products. The results show that sodium calcium borate glasses can be transformed to HA by reacting with a phosphate solution. It is essentially a process of dissolution of glass and precipitation of HA. The transformation begins from an amorphous state to calcium-deficient HA without changing the size and shape of the original glass sample. Glass with a lower calcium content (1CaO · 2Na₂O · 6B₂O₃), or reacted at an elevated temperature (75 °C), has a higher reaction rate. The HA crystal size increases and grain shape changes from spheroidal to cylindrical as temperature increases from 37 to 200 °C. Increase in carbonate concentration can also decrease the crystal size and yield a more needle-like grain shape.     

Interactions between Ti and alumina-based ceramics

Reactive metal coatings have been frequently used on ceramic materials for various purposes. However, little work was done in the past to understand the interactions between coating and ceramic substrates and their effects on the mechanical properties of the ceramics. In this study, titanium coatings were applied to single-crystal (sapphire) and polycrystalline alumina to study the interface reactions. Also, the effect of the coating on the mechanical properties of the substrates was quantified in terms of modulus of rupture (MOR) in four-point bending strength. Reactions between the coating and the Al₂O₃-based substrates at 980°C caused the formation of a new phase, Ti₃Al[O], and a significant decrease (15%–65%) in the MOR strength of the ceramic materials. This study showed that in polycrystalline alumina, interactions between titanium and the glassy grain-boundary phase in the ceramic materials were responsible for reduction in the MOR strength, while the effect of thermal expansion mismatch between titanium and the ceramic substrate appeared to be dominant for singlecrystal alumina.