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Strontium- and calcium-releasing, titanium-stabilised phosphate-based glasses with a controlled degradation rate are currently under development for orthopaedic tissue engineering applications. Ca and/or Sr were incorporated at varying concentrations in quaternary phosphate-based glasses, in order to promote osteoinduction. Ti was incorporated at a fixed concentration in order to prolong degradation. Glasses of the general formula (P2O5)–(Na2O)–(TiO2)–(CaO)–(SrO) were prepared via the melt-quench technique. The materials were characterised by energy-dispersive X-ray spectroscopy, X-ray diffraction, 31P magic angle spinning nuclear magnetic resonance, Fourier transform infrared spectroscopy, differential thermal analysis and density determination. The dissolution rate in distilled water was determined by measuring mass loss, ion release and pH change over a two-week period. In addition, the cytocompatibility and alkaline phosphatase activity of an osteoblast-like cell line cultured on the surface of glass discs was assessed. The glasses were shown to be amorphous and contained Q1, Q2 and Q3 species. Fourier transform infrared spectroscopy revealed small changes in the glass structure as Ca was substituted with Sr and differential thermal analysis confirmed a decrease in crystallisation temperature with increasing Sr content. Degradation and ion release studies also showed that mass loss was positively correlated with Sr content. These results were attributed to the lower electronegativity of Sr in comparison to Ca favouring the formation of phosphate-based mineral phases. All compositions supported cell proliferation and survival and induced at least 2.3-fold alkaline phosphatase activity relative to the control. Glass containing 17.5 mol% Sr had 3.6-fold greater alkaline phosphatase activity than the control. The gradual release of Ca and Sr supported osteoinduction, indicating their potential suitability in orthopaedic tissue engineering applications.

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Gallium-doped phosphate-based glasses (Ga-PBG) were assessed for their impact on Streptococcus mutans and dental mineralisation, firstly by disc diffusion assays followed by biofilms grown on nitrocellulose filter membrane (NFM) and constant-depth film fermentor (CDFF). Short-time exposure (10 min) effects of Ga-PBG on S. mutans biofilm were compared with that of 0.2% chlorhexidine. The effects of Ga-PBG on bovine enamel (which was investigated under pH-cycling condition) and dentine were analysed using transverse microradiography (TMR), profilometry and inductively coupled plasma optical-emission spectrometry (ICP-OES). The disc diffusion assays showed inhibition zones of 24.5 ± 0.5 mm for Ga-PBG compared with controls (C-PBG). Ga-PBG showed statistically significant growth inhibition of S. mutans biofilms on NFM (p = 0.001) and CDFF (p < 0.046) compared with hydroxyapatite (HA) and C-PBG. The CDFF assay revealed a maximum of 2.11 log colony-forming unit (CFU) reduction at 48 h, but short-time exposure effects were comparable with that of 0.2% chlorhexidine only on older biofilms (maximum of 0.59 vs. 0.69 log CFU reduction at 120 h). TMR analyses of the enamel revealed non-significant mineral loss (p = 0.37) only in the case of Ga-PBG samples compared with controls including sodium fluoride. ICP-OES analyses indicated transient gallium adsorption into dentine by calcium displacement. The results confirmed that gallium inhibited S. mutans growth and appears to have the potential to protect the enamel surface under conditions representative of the oral environment. Further work is needed to establish whether it has an application in daily oral hygiene procedures to prevent or reduce caries.

Quaternary phosphate-based glasses in the P 2 O 5 -CaO-Na 2 O-TiO 2 system with a fixed P 2 O 5 and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol-gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised solgel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), 31 P nuclear magnetic resonance ( 31 P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol-gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol-gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly sixfold coordination environment. The 31 P NMR and FTIR results revealed that the glass structure consist of mainly Q 1 and Q 2 phosphate units and the Ti 4+ cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing Na 2 O content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO 2 content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol-gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed.

The production of large quantities of functional vascularized bone tissue ex vivo still represent an unmet clinical challenge. Microcarriers offer a potential solution to scalable manufacture of bone tissue due to their high surface area-to-volume ratio and the capacity to be assembled using a modular approach. Microcarriers made of phosphate bioactive glass doped with titanium dioxide have been previously shown to enhance proliferation of osteoblast progenitors and maturation towards functional osteoblasts. Furthemore, doping with cobalt appears to mimic hypoxic conditions that have a key role in promoting angiogenesis. This characteristic could be exploited to meet the clinical requirement of producing vascularized units of bone tissue. In the current study, the human osteosarcoma cell line MG-63 was cultured on phosphate glass microspheres doped with 5% mol titanium dioxide and different concentrations of cobalt oxide (0%, 2% and 5% mol), under static and dynamic conditions (150 and 300 rpm on an orbital shaker). Cell proliferation and the formation of aggregates of cells and microspheres were observed over a period of two weeks in all glass compositions, thus confirming the biocompatibility of the substrate and the suitability of this system for the formation of compact micro-units of tissue. At the concentrations tested, cobalt was not found to be cytotoxic and did not alter cell metabolism. On the other hand, the dynamic environment played a key role, with moderate agitation having a positive effect on cell proliferation while higher agitation resulting in impaired cell growth. Finally, in static culture assays, the capacity of cobalt doping to induce vascular endothelial growth factor (VEGF) upregulation by osteoblastic cells was observed, but was not found to increase linearly with cobalt oxide content. In conclusion, Ti-Co phosphate glasses were found to support osteoblastic cell growth and aggregate formation that is a necessary precursor to tissue formation and the upregaulation of VEGF production can potentially support vascularization.

The potential of Euglossini bees, especially Euglossa, as biological indicators of organic vs nonorganic coffee farms was studied in Atenas and San Isidro, Alajuela, Costa Rica using 1.8-cineole as lure. Observations were made for three days at each of four farms and complemented with data from a year of observations. Orchid bees were in greater abundance in the organic farms (t-Student test). However, lower abundances suggest that an organic farm may be negatively affected by the proximity of non-organic farms, depending on its size and distance. Orchid bees may be indicators of organic coffee farms. Rev. Biol. Trop. 54 (3): 965-969. Epub 2006 Sept. 29.

The purpose of this study was to determine whether or not the dual constant-depth film fermenter (dCDFF) is able to produce caries-like enamel lesions and to ascertain further information regarding the performance of this fully functional biological caries model. Conditions were defined by the continuation (CF) or cessation (FF) of a saliva-type growth medium supply during 50-mM sucrose exposures (8 times daily). Hydroxyapatite (n = 3) and bovine enamel (n = 3) substrata were included within each condition and samples extracted after 2, 4, 8, and 16 days. Community profiles were generated for fastidious anaerobes, Lactobacillus spp., Streptococcus spp., mutans streptococci (MS), and Veillonella spp. using selective culture techniques and enamel demineralisation assessed by transverse microradiography. Results demonstrated that the dCDFF model is able to produce caries-like enamel lesions with a high degree of sensitivity where reduced ionic strength within the FF condition increased surface layer mineral deposition. Between conditions, biofilm communities did not differ significantly, although MS in the biofilms extracted from the FF condition rose to a higher proportion (by 1.5 log₁₀ units), and Veillonella spp. were initially greater within the CF condition (by 2.5 log₁₀ units), indicating an enhanced ability for the clearance of low-pK_a acids following exposures to sucrose. However, both conditions retained the ability for caries-like lesion formation.