Type I collagen production by osteoblast-like cells cultured in contact with different bioactive glasses

Bioactive glasses are silica-based, surface-active bone substitutes that have shown good biocompatibility both in bone and in soft tissue and are used in oral and maxillofacial bone augmentation. Previous in vitro studies showing that bioactive glasses support the growth and maturation of rat osteoblast-like cells and promote the expression and maintenance of the osteoblastic phenotype have suggested that there is both a solution-mediated and a surface-controlled effect on cell activity. In this study, we investigated the behavior of human primary osteoblast-like cells cultured in contact with three different bioactive glasses and compared them with amorphous silica (SiO2) used in the form of granules. The specific activity of alkaline phosphatase determined biochemically was significantly higher at 2 and 4 days on the bioactive glass with 46.1 mol % silica content (45S5 Bioglass) cultures than in the control cultures and in the bioactive gel-glass cultures, which had 60 mol % (58S) and 80 mol % (77S) silica content. Osteoblasts synthesize collagen type I, which is subsequently mineralized. Immunoblot and biochemical studies showed increased collagen release from osteoblast-like cells cultured in contact with bioactive glasses over that of controls. Among the three bioactive glasses, 45S5 is the highest inducer of osteoblast-like cell collagen release; moreover, mRNA for type I collagen was stimulated approximately three- to fivefold after 45S5 treatment. 77S bioactive glass similarly increased type I collagen synthesis even though alkaline phosphatase was not higher. These results suggest that 45S5 Bioglass not only induces osteogenic differentiation of human primary osteoblast-like cells, but can also increase collagen synthesis and release. The newly formulated bioactive gel-glass 77S seems to have potential applications for tissue engineering, inducing increased collagen synthesis.     

In vitro osteogenesis on a highly bioactive glass-ceramic (Biosilicate)

One of the strategies to improve the mechanical performance of bioactive glasses for load-bearing implant devices has been the development of glass-ceramic materials. The present study aimed to evaluate the effect of a highly bioactive, fully-crystallized glass-ceramic (Biosilicate) of the system P(2)O(5)-Na(2)O-CaO-SiO(2) on various key parameters of in vitro osteogenesis. Surface characterization was carried out by scanning electron microscopy and Fourier transform infrared spectroscopy. Osteogenic cells were obtained by enzymatic digestion of newborn rat calvarial bone and by growing on Biosilicate discs and on control bioactive glass surfaces (Biosilicate) parent glass and Bioglass(R) 45S5) for periods of up to 17 days. All materials developed an apatite layer in simulated body fluid for 24h. Additionally, as early as 12 h under culture conditions and in the absence of cells, all surfaces developed a layer of silica-gel that was gradually covered by amorphous calcium phosphate deposits, which remained amorphous up to 72 h. During the proliferative phase of osteogenic cultures, the majority of cells exhibited disassembly of the actin cytoskeleton, whereas reassembly of actin stress fibers took place only in areas of cell multilayering by day 5. Although no significant differences were detected in terms of total protein content and alkaline phosphatase activity at days 11 and 17, Biosilicate supported significantly larger areas of calcified matrix at day 17. The results indicate that full crystallization of bioactive glasses in a range of compositions of the system P(2)O(5)-Na(2)O-CaO-SiO(2) may promote enhancement of in vitro bone-like tissue formation in an osteogenic cell culture system.     

The influence of novel bioactive glasses on in vitro osteoblast behavior

Implant success requires a direct bond between bone and implant surface. Bioinert implants, such as titanium alloys, are commonly plasma-spray-coated with a bone-bonding, bioactive material such as hydroxyapatite. Such coatings tend to be chemically and topographically inhomogeneous without reproducible properties. A family of bioactive glasses that can be enameled and reliably adheres to titanium alloy has been developed. In this study the cytocompatibility of two of these glass compositions was tested in the as-cast condition. The effects of these glasses on the early and late events of osseous tissue formation in vitro were determined with MC3T3-E1.4 mouse osteoblast-like cells. MC3T3-E1.4 cells were cultured on glasses containing 55 and 50 wt % SiO(2), with titanium alloy (Ti6Al4V) and tissue culture polystyrene as controls. Cellular adhesion and proliferation, and alkaline phosphatase activity were studied over 5 to 15 days in culture. Qualitative and quantitative assays of mineralization were conducted. The osteoblast-like cells showed increased proliferation when grown on a bioactive glass containing 50 wt % silica. However, the adhesion, differentiation and mineralization behavior were similar on both glass compositions used in this study. These bioactive glasses proved to be cytocompatible substrata for osteoblast-like cell culture, and yielded higher cellular proliferation than titanium alloy.     

Effect of borate glass composition on its conversion to hydroxyapatite and on the proliferation of MC3T3-E1 cells

Glasses containing varying amounts of B(2)O(3) were prepared by partially or fully replacing the SiO(2) in silicate 45S5 bioactive glass with B(2)O(3). The effects of the B(2)O(3) content of the glass on its conversion to hydroxyapatite (HA) and on the proliferation of MC3T3-E1 cells were investigated in vitro. Conversion of the glasses to HA in dilute (20 mM) K(2)HPO(4) solution was monitored using weight loss and pH measurements. Proliferation of MC3T3-E1 cells was determined qualitatively by assay of cell density at the glass interface after incubation for 1 day and 3 days, and quantitatively by fluorescent measurements of total DNA in cultures incubated for 4 days. Higher B(2)O(3) content of the glass increased the conversion rate to HA, but also resulted in a greater inhibition of cell proliferation under static culture conditions. For a given mass of glass in the culture medium, the inhibition of cell proliferation was alleviated by using glasses with lower B(2)O(3) content, by incubating the cell cultures under dynamic rather than static conditions, or by partially converting the glass to HA prior to cell culture.     

Influence of physicochemical reactions of bioactive glass on the behavior and activity of human osteoblasts in vitro

Bioactive glasses are characterized by a bond to bone with a hydroxyl carbonate apatite layer. They enhance bone tissue formation and for this purpose are used in orthopedic surgery and in dental implantology. In the current work, we studied the biological response of human osteoblasts with a bioactive glass. This bioactive glass is based on 50% Si0(2), 20% Na(2)O, 16% CaO, 6% P(2)O(5), 5% K(2)0, 2% Al(2)O(3) and 1% MgO and designated A9. Cracks and irregularities were observed on the material surface when it was immersed in the culture medium. In addition, energy dispersive X-ray analyses highlighted a selective release of the elements at the surface of the bioactive glass, such as Na(+) and K(+) ions, released from the first day, contrary to the Si, Al, Ca, P, and Mg elements, which were released more slowly. Cell proliferation kinetics, total protein synthesis, and DNA content of the osteoblasts in contact with bioactive glass were similar to control cells. The morphological studies by light and scanning electron microscopy revealed an increasing cellular density in culture with bioactive glass without contact inhibition. The immunohistochemical studies highlighted the expression of types I, III, and V collagens by osteoblasts cultured in the presence of bioactive glass. The pH measurement of the culture medium in the presence of bioactive glass demonstrated a slight alkalinization. We thus conclude that human osteoblasts preserve their properties in the presence of bioactive glass (A9).     

Characterization of microrough bioactive glass surface: surface reactions and osteoblast responses in vitro

The current study characterized the in vitro surface reactions of microroughened bioactive glasses and compared osteoblast cell responses between smooth and microrough surfaces. Three different bioactive glass compositions were used and surface microroughening was obtained using a novel chemical etching method. Porous bioactive glass specimens made of sintered microspheres were immersed in simulated body fluid (SBF) or Tris solutions for 1, 6, 24, 48, or 72 h, and the formation of reaction layers was studied by means of a scanning electron microscope/energy dispersive X-ray analysis (SEM/EDXA). Cell culture studies were performed on bioactive glass disks to examine the influence of surface microroughness on the attachment and proliferation of human osteoblast-like cells (MG-63). Cell attachment was evaluated by means of microscopic counting of in situ stained cells. Cell proliferation was analyzed with a nonradioactive cell proliferation assay combined with in situ staining and laser confocal microscopy. The microroughening of the bioactive glass surface increased the rate of the silica gel layer formation during the first hours of the immersion. The formation of calcium phosphate layer was equal between control and microroughened glass surfaces. In cell cultures on bioactive glass, the microrough surface enhanced the attachment of osteoblast-like cells but did not have an effect on the proliferation rate or morphology of the cells as compared with smooth glass surface. In conclusion, microroughening significantly accelerated the early formation of surface reactions on three bioactive glasses and had a positive effect on initial cell attachment.     

Silica-based bioactive glasses modulate expression of bone morphogenetic protein-2 mRNA in Saos-2 osteoblasts in vitro

A chemical exchange of the silica gel layer forming on the surface of bioactive glasses is thought to be the principal reaction for bone-bioactive glass bonding. The contribution of biological molecules on cell-bioactive glass interaction is largely unknown. To further analyze the mechanisms involved in efficient bone bonding to bioactive glass, Saos-2 osteoblastic cells with proven osteogenic phenotype were cultured for 4, 7 and 14 days on two bioactive glasses with different Si contents. Culture plates and dishes made of bioactive (BAG, 53 % SiO2), biocompatible (BCG, 58% SiO2) and control (GO) glasses were extensively conditioned with phosphate buffer and DMEM medium before seeding the cells. Northern hybridization was used for analysis of mRNA levels of collagen type I (Col-I), alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). A significant increase was observed in Col-I mRNA levels in cells grown on the two bioactive glasses when compared with those grown on controls at 4 and 7 days (p < 0.04). The mRNA level for ALP in the cultures of bioactive glasses-made plates and dishes was also increased over control at 7 days (p < 0.02) and remained this way between BAG and G0 at 14 days. Striking differences in BMP-2 mRNA levels existed between BAG and G0 plates and dishes at 7 days (p < 0.05). BMP-2 mRNA level in BAG group was higher than in BCG group at 4, 7 and 14 days, but without statistical significance. Saos-2 osteoblastic cells with strong ALP staining were mostly seen on BAG plates under a light microscope. In confocal microscopy, a bright FITC-stained F-actin ring was present in the cytoplasm of cells grown on BAG dish, demonstrating an active functional status. Stimulation of the expression of BMP-2 and other bone mRNAs by bioactive glasses in osteoblastic cells suggests biological involvement of bone related growth factors, peptides and cytokines in bone-bioactive glass bonding.     

Differential alkaline phosphatase responses of rat and human bone marrow derived mesenchymal stem cells to 45S5 bioactive glass

Bioactive glass is used as both a bone filler and as a coating on implants, and has been advocated as a potential osteogenic scaffold for tissue engineering. Rat-derived mesenchymal stem cells (MSCs) show elevated levels of alkaline phosphatase activity when grown on 45S5 bioactive glass as compared to standard tissue culture plastic. Similarly, exposure to the dissolution products of 45S5 elevates alkaline phosphatase activity and other osteogenic markers in these cells. We investigated whether human MSCs grown under the same laboratory conditions as rat MSCs would exhibit similar responses. In general, human MSCs produce markedly less alkaline phosphatase activity than rat MSCs, regardless of cell culture conditions, and do not respond to the growth factor BMP-2 in the same way as rat MSCs. In our experiments there was no difference in alkaline phosphatase activity between human MSCs grown on 45S5 bioactive glass or tissue culture plastic, in samples from five different orthopaedic patients, regardless of culture media composition. Neither was there any consistent effect of 45S5 dissolution products on human MSCs from three different donors. These results suggest that the positive effects of bioactive glass on bone growth in human patients are not mediated by accelerated differentiation of mesenchymal stem cells.     

Effect of particulate bioactive glasses on human macrophages and monocytes in vitro

Bioactive glasses, originally developed to promote tissue adhesion, are finding an increasing array of biomedical applications. The aim of the current study was to assess the ability of silicate- and zinc phosphate-based bioactive glasses to modulate the secretion of cytokines from activated human macrophages and monocytes. Human macrophages and monocytes were isolated and cultured on surfaces coated with a range of quantities of the bioactive glasses. Nontoxic concentrations of the glasses were selected and assessed further for their ability to modulate the secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-10 and -6, in the presence or absence of the stimulant lipopolysaccharide. 45S5 glass produced a significant reduction to the amount of TNF-alpha (p<0.05) and IL-6 (p<0.01) secreted by stimulated cells compared with cells stimulated in the absence of bioactive glass. A significant reduction in IL-6 secretion was also observed with the other silicate- and zinc phosphate-based glasses tested. IL-10 secretion was increased (but not significantly) in presence of all glasses tested. TNF-alpha and IL-6 secretion from stimulated cells was lower in presence of the silicate glasses compared with the zinc phosphate glasses, indicating that this system of bioactive glass might be of clinical use in conditions associated with inflammation.     

In vivo evaluation of a bioactive scaffold for bone tissue engineering

Revision cases of total hip implants are complicated by the significant amount of bone loss. New materials and/or approaches are needed to provide stability to the site, stimulate bone formation, and ultimately lead to fully functional bone tissue. Porous bioactive glasses (prepared from 45S5 granules, 45% SiO2, 24.5% Na2O, 24.5% CaO, and 6% P2O5) have been developed as scaffolds for bone tissue engineering and have been studied in vitro. In this study, we investigated the incorporation of tissue-engineered constructs utilizing these scaffolds in large, cortical bone defects in the rat simulating revision conditions. With implantation times of 2, 4, and 12 weeks the results were compared to those using the bioactive ceramic scaffold alone. Two tissue-engineered constructs were studied: osteoprogenitor cells that were either seeded onto the scaffold prior to implantation ("primary") or those that were culture expanded to form bonelike tissue on the scaffold prior to implantation ("hybrid"). Defects treated with the hybrid had the greatest amount of bone in the available pore space of the defect over all other groups at 2 weeks (p < 0.05). For both the primary and hybrid groups, woven and lamellar bone was present along the interface of the scaffold and the host cortex and within the porous space of the scaffold at 2 weeks. By 4 weeks, very uniform, lamellar bone was present throughout the scaffold for both tissue-engineered groups. The amount of bone significantly increased over time for all groups while the bioactive ceramic gradually resorbed by 40% at 12 weeks (p < 0.05). Structural properties of the treated long bones improved over time. Long bones treated with the hybrid had an early return in torsional stiffness by 2 weeks. Both tissue-engineered constructs achieved normal torsional strength and stiffness by 4 weeks as compared to the scaffold alone, which achieved this by 12 weeks. Porous, surface modified bioactive ceramic is a promising scaffold material for tissue-engineered bone repair.     

The ionic products of bioactive glass particle dissolution enhance periodontal ligament fibroblast osteocalcin expression and enhance early mineralized tissue development

This study resulted in enhanced collagen type 1 and osteocalcin expression in human periodontal ligament fibroblasts (hPDLF) when exposed to bioactive glass conditioned media that subsequently may promote early mineralized tissue development. Commercial Bioglass? (45S5) and experimental bioactive coating glass (6P53-b), were used to make a glass conditioned media (GCM) for comparison to control medium. ICP-MS analysis showed increased concentrations of Ca(2+), PO(4) (3-), Si(4+), and Na(+), for 45S5 GCM and Mg(2+), K(+), Ca(2+), PO(4)(3-), Si(4+), and Na(+) for 6P53-b GCM (relative to control medium). Differentiating hPDLF cultures exposed to 45S5 and 6P53-b GCM showed enhanced expression of collagen type 1 (Col1α1, Col1α2), osteocalcin, and alkaline phosphatase gene expression. These GCM also enhanced osteocalcin protein expression. After 16 d of culture, 45S5 and 6P53-b GCM treated cells showed regions of deep red Alizarin staining, indicating increased Ca within their respective extracellular matrices (ECM), while control-treated cells did not exhibit these features. SEM analysis showed more developed ECM in GCM treated cultures, indicated by multiple tissue layering and abundant collagen fiber bundle formation, while control treated cells did not exhibit these features. SEM analysis showed polygonal structures suggestive of CaP in 45S5 GCM treated cultures. These results indicate the osteogenic potential of bioactive coating glass in periodontal bone defect filling applications.     

Bioactivity of gel-glass powders in the CaO-SiO2 system: a comparison with ternary (CaO-P2O5-SiO2) and quaternary glasses (SiO2-CaO-P2O5-Na2O)

Bioactive glasses react chemically with body fluids in a manner that is compatible with the repair processes of the tissues. This results in the formation of an interfacial bond between the glasses and living tissue. Bioactive glasses also stimulate bone-cell proliferation. This behavior is dependent on the chemical composition as well as the surface texture of the glasses. It has been recently reported that gel-derived monolith specimens in the binary SiO2 - CaO are bioactive over a similar molar range of SiO2 content as the previously studied ternary CaO-P2O5-SiO2 system. In this report, the preparation and bioactivity of the binary gel-glass powder with 70 mol % SiO2 is discussed and its bioactivity is compared with the melt-derived 45S5 (quaternary) Bioglass and sol-gel-derived 58S (ternary) bioactive gel-glass compositions. Dissolution kinetic parameters K(1) and K(2) were also computed based on the silicon release for all glass powders. It was shown that the simple two-component SiO2-CaO gel-glass powder is bioactive with comparable dissolution rates as the clinically used melt-derived 45S5 Bioglass powder and extensively studied sol-gel-derived 58S gel-glass powder.     

High phosphate content significantly increases apatite formation of fluoride-containing bioactive glasses

Bioactive glass-containing toothpastes for treating dentine hypersensitivity work by precipitating hydroxycarbonate apatite (HCA) onto the tooth surface, but concerns exist over the long-term durability of HCA in the mouth. Fluoride-containing bioactive glasses form fluorapatite (FAp) in physiological solutions, which is more chemically stable against acid attack. The influence of phosphate content on apatite formation was investigated by producing a low-phosphate (about 1 mol% P(2)O(5)) and a high-phosphate (about 6 mol%) series of melt-derived bioactive glasses in the system SiO(2)P(2)O(5)CaONa(2)O; increasing amounts of CaF(2) were added by keeping the ratio of all other components constant. pH change, ion release and apatite formation during immersion in Tris buffer at 37°C over up to 7 days were investigated. Crystal phases formed in Tris buffer were characterized using infrared spectroscopy, X-ray diffraction and solid-state nuclear magnetic resonance (NMR) spectroscopy. An increase in phosphate or fluoride content allowed for apatite formation at lower pH; fluoride enhanced apatite formation due to lower solubility of FAp compared to hydroxyapatite or HCA. High phosphate content glasses formed apatite significantly faster (within 6h) than low phosphate content glasses (within 3 days). In addition, an increase in phosphate content favoured apatite formation rather than fluorite (CaF(2)). (19)F magic angle spinning NMR showed the apatite formed by fluoride-containing glasses to be FAp, which makes these glasses of particular interest for dental applications. This study shows that by varying the phosphate content, the reactivity and apatite formation of bioactive glasses can be controlled successfully.     

Effect of degradation rates of resorbable phosphate invert glasses on in vitro osteoblast proliferation

Four resorbable phosphate invert glasses for use as bone replacement were synthesized in the system P2O5--CaO--MgO--Na2O. TiO2 and SiO2 were added at concentrations of 1 and 5.5 mol % to control solubility and crystallization. Both bulk glasses and samples with an open porosity of 65% and pore sizes of 150 to 400 microm were produced using a salt sintering process. Addition of TiO2 decreased the solubility in water and simulated body fluid, while the glass with addition of SiO2 showed a higher dissolution rate than did the original glass. The hypothesis that dissolution rates of the glasses will affect cell proliferation of osteoblastlike cells was tested using a MC3T3-E1.4 murine preosteoblast cell line. Cells were cultured on nonporous polished and porous glasses with tissue culture polystyrene (TCPS) as control. Cell proliferation was studied over 24 and 72 h in culture. Cells proliferated on all polished glasses, but proliferation on porous glasses showed variations with glass composition. Cell proliferation increased with decreased solubility of the glass. It is suggested that resorbable implant materials require the adjustment of dissolution rate so as to facilitate cell adhesion and proliferation and thus a gradual transition from artificial implant to new bone structure.     

Binary CaO-SiO(2) gel-glasses for biomedical applications

Bioactive materials are routinely used in dental and orthopaedic applications. The concept was first introduced in 1971, with the discovery of 45S5 Bioglass, which is known to develop an interfacial bond between the implant and the host tissue. This glass is composed of SiO(2), CaO, P(2)O(5) and Na(2)O. Since then numerous glasses and glass ceramics with similar compositions have been extensively studied for clinical applications. Until 1990 it was accepted that P(2)O(5) and Na(2)O were necessary components for the glass composition to be bioactive. However, calcium silicate glasses with high SiO(2) content are impossible to produce using the traditional melt-quench method. This is due to the liquid-liquid immiscibility region that is present between 0.02 and 0.3 mole fraction of CaO and in terms of bioactivity, high CaO compositions were inferior to those quaternary bioactive glass compositions already in existence. In the last few years several studies have been reported regarding the production of CaO-SiO(2) glasses via the sol-gel processing technique. This report summarises the findings of the past and the present and also outlines potential of these calcium silicate gel-glasses in the field of biomaterials.     

In vitro dissolution of melt-derived 45S5 and sol-gel derived 58S bioactive glasses

Effects of powder type, particle size (5-20 microm; 90-300 microm; 90-710 microm), and type of dissolution medium on the dissolution behavior of bioactive glasses were investigated in vitro using melt-derived 45S5 and sol-gel derived 58S bioactive glass powders. Dissolution studies were performed in simulated body fluid and in alpha-MEM based cell culture medium at 37 degrees C under dynamic conditions (1 Hz) for periods of 30 min, 1, 2, 4, 8, 17, and 22 h. The concentrations of elements dissolved from the glasses were evaluated using inductively coupled plasma analysis. The reacted powders were analyzed for bioactivity using Fourier transform infrared spectrometry to observe the formation of a calcium phosphate layer on the surface. The non-porous surfaces of melt-derived 45S5 glass powders exhibited lower dissolution rates and rate of surface layer formation than 58S gel-glass powders. The rates of dissolution for both types of powders were lower in culture medium, compared to simulated body fluid, and increased as the particle size decreased. Thus, particle size range, glass type, and powder volume fraction can be used as a means to control the release rate of active ions that stimulate the gene expression and cellular response for tissue proliferation and repair.     

Bioactive glasses with improved processing. Part 1. Thermal properties,ion release and apatite formation

Bioactive glasses, particularly Bioglass® 45S5, have been used to clinically regenerate human bone since the mid-1980s; however, they show a strong tendency to undergo crystallization upon heat treatment, which limits their range of applications. Attempts at improving their processing (by reducing their tendency to crystallize) have included increasing their silica content (and thus their network connectivity), incorporating intermediate oxides or reducing their phosphate content, all of which reduce glass bioactivity. Therefore, bioactive glasses known for their good processing (e.g. 13–93) are considerably less bioactive. Here, we investigated if the processing of 45S5 bioactive glass can be improved while maintaining its network connectivity and phosphate content. The results show that, by increasing the calcium:alkali cation ratio, partially substituting potassium for sodium (thereby making use of the mixed alkali effect) and adding small amounts of fluoride, bioactive glasses can be obtained which have a larger processing window (suggesting that they can be processed more easily, allowing for sintering of scaffolds or drawing into fibres) while degrading readily and forming apatite in aqueous solution within a few hours.     

Effect of nitridation on the aqueous dissolution of Na2O-K2O-CaO-P2O5 metaphosphate glasses

The use of oxynitride glasses is presented as an alternative for the preparation of bioresorbable phosphate glasses with a controlled dissolution rate. This work describes the design of oxynitride phosphate glasses within the systems of composition (50-x)Na(2)O·xCaO·50P(2)O(5) and (25-(x/2))Na(2)O·(25-(x/2))K(2)O·xCaO·50P(2)O(5) (x=5, 10, 15, 20 mol.%) throughout the processing parameters of the ammonolysis reaction and the glass composition. Mixed-alkali sodium-potassium phosphate glasses with low CaO contents present the best characteristics for nitridation. The dissolution rate has been determined by immersion of glass samples in water, at constant temperature of 37 °C, and has been discussed as a function of both modifiers composition and nitrogen content incorporated in the glasses through ammonolysis. All oxynitride glass compositions dissolve congruently and their dissolution rate decreases by more than three orders of magnitude for the highest nitrogen contents. However, it has been demonstrated that nitrogen contents as low as 2-3 wt.% (i.e. a 0.2N/P ratio) are sufficient to decrease the dissolution rate by one order of magnitude with respect to the pure oxide glasses. Novel oxynitride phosphate glasses with a controlled and congruent dissolution are proposed for future applications in biodegradable composite materials, tissue engineering or host matrices for the controlled release of drugs.     

In vitro studies of calcium phosphate glass ceramics with different solubility with the use of human bone marrow cells

Two glass ceramics in the CaO--P2O5--MgO system with the incorporation of K2O or TiO2 oxides were prepared with the goal of using them as potential bone graft substitutes. The incorporation of TiO2 and K2O led to the preparation of specific crystalline phases in the structure of the glass ceramics, which show different degrees of biodegradation. In fact, the 45CaO--45P2O5--5MgO--5K2O has been previously demonstrated to be much more soluble in aqueous solutions than the 45CaO--37P2O5--5MgO--13TiO2 glass ceramic. The in vitro biological activity of the two calcium phosphate glass ceramics was studied with the use of human bone marrow osteoblast cell cultures maintained for 28 days, and seeded materials were assessed for cell proliferation and function. The Ti-containing glass ceramic showed a stable surface throughout the culture time, on macroscopic and SEM observation. Osteoblast cells proliferated gradually, especially during the third week, with a high alkaline phosphatase activity and formation of a mineralized matrix. On SEM observation, attached cells appeared with a spread-polygonal morphology typical of the osteoblast cells, with extensive cell-to-cell contact. Cell behavior on the seeded material was similar to that found on cultures performed on tissue-culture-grade polystyrene; except for the presence of lower cell numbers during the first 2 weeks. By contrast, the K-containing glass ceramic showed a highly instable surface with dissolution/precipitation processes occurring throughout the culture time. Few cells adhered to the material surface, and subsequent proliferation was also hindered, especially from the first week onwards. Cell numbers were significantly lower than those observed in the Ti-containing glass ceramic during most of the incubation time. Results suggest that the different in vitro biological behavior of these two glass ceramics is mainly due to the significant differences in the surface degradation rate, which is directly correlated to the chemical composition of the mother glass.     

Substitutions of cerium, gallium and zinc in ordered mesoporous bioactive glasses

Ordered mesoporous glasses based on the 80% SiO(2)-15% CaO-5% P(2)O(5) system including up to 3.5% Ce(2)O(3), 3.5% Ga(2)O(3) or 7.0% ZnO (in mol.%) were synthesized by the evaporation-induced self-assembly process using Pluronic? 123 as a surfactant. An ordered hexagonal mesophase was observed in both the unsubstituted glass (denoted in this paper as B: blank) and glasses containing <0.4% of substituent by X-ray diffraction, transmission electron microscopy and electron diffraction. The increase in the amount of substituent led to a decrease in the mesopore order. B glass exhibited good textural properties: S(BET)=515m(2)g(-1), D(P)=4.7nm and V(P)=0.58cm(3)g(-1). With the inclusion of cerium, gallium and zinc oxides the textural properties decreased, but remained in amounts useful for clinical applications. Zinc-containing samples showed the highest decrement in the textural properties. Substituted glasses exhibited a quick in vitro bioactive response except when the ZnO content was over 0.4%. Taking into account the ordered mesoporosity, the quick in vitro bioactive response and the added values of the substituents, this new family of glasses are promising candidates for applications in bone tissue engineering.