Xanthippi Chatzistavrou

Copper-releasing, boron-containing bioactive glass-based scaffolds coated with alginate for bone tissue engineering

The aim of this study was to synthesize and characterize new boron-containing bioactive glass-based scaffolds coated with alginate cross-linked with copper ions. A recently developed bioactive glass powder with nominal composition (wt.%) 65 SiO2, 15 CaO, 18.4 Na2O, 0.1 MgO and 1.5 B2O3 was fabricated as porous scaffolds by the foam replica method. Scaffolds were alginate coated by dipping them in alginate solution. Scanning electron microscopy investigations indicated that the alginate effectively attached on the surface of the three-dimensional scaffolds leading to a homogeneous coating. It was confirmed that the scaffold structure remained amorphous after the sintering process and that the alginate coating improved the scaffold bioactivity and mechanical properties. Copper release studies showed that the alginate-coated scaffolds allowed controlled release of copper ions. The novel copper-releasing composite scaffolds represent promising candidates for bone regeneration.

Hydroxy Carbonate Apatite Formation on Particulate Bioglass In Vitro as a Function of Time

The mechanism of bonding of bioactive glasses with living tissues has been reported to be associated with the development of a layer consisting of carbonate-containing hydroxyapatite similar to that of bone on the surface of the materials. This layer is also formed in vitro, in solutions with ion concentrations similar to those of human blood plasma, like SBF (Simulated Body Fluid). The development of HCAp (Hydroxy carbonate apatite) layer on the surface of a commercially available Bioglass® Synthetic Bone Graft Particulate (Perioglas®) after immersion in SBF solution using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with associated Energy Dispersive Spectroscopy (EDS). PerioGlas® powder with particle size 20-63μm, pressed in a vacuum press in order to produce pellets. The pellets were soaked in SBF for 12, 18, 24 and 48 hours at 37°C. Results revealed the formation of an amorphous CaO-P 2 O 5 - rich layer on the surface of the specimens after 12 hours in the solution and a well crystalline HCAp layer after 24 hours immersion time.

Fabrication and characterization of bioactive and antibacterial composites for dental applications

There is an increasing clinical need to design novel dental materials that combine regenerative and antibacterial properties. In this work the characterization of a recently developed sol-gel-derived bioactive glass ceramic containing silver ions (Ag-BG) is presented. The microstructural characteristics, ion release profile, zeta potential value and changes in weight loss and pH value as a function of the immersion time of Ag-BG in Tris buffer are evaluated. Ag-BG is also incorporated into natural extracellular matrix (ECM) hydrogel to further enhance its regenerative properties. Then, the micro and macro architectures of these new composites (ECM/Ag-BG) are characterized. In addition, the antibacterial properties of these new composites are tested against Escherichia coli and Enterococcus faecalis, a bacterium commonly implicated in the pathogenesis of dental pulp infections. Cell-material interaction is also monitored in a primary culture of dental pulp cells. Our study highlights the benefits of the successful incorporation of Ag in the bioactive glass, resulting in a stable antibacterial material with long-lasting bactericidal activity. Furthermore, this work presents for the first time the fabrication of new Ag-doped composite materials, with inductive pulp-cell proliferation and antibacterial properties (ECM/Ag-BG). This advanced composite made of Ag-BG incorporated into natural ECM possesses improved properties that may facilitate potential applications in tooth regeneration approaches.

Designing dental composites with bioactive and bactericidal properties.

OBJECTIVES The aim of this work was to fabricate and evaluate new antibacterial and bioactive composites capable of strictly controlling oral bacteria, enhancing apatite layer formation and retaining their mechanical properties. METHODS A new Ag-doped bioactive glass (Ag-BG) was incorporated into flowable dental composite (COMP) in different concentrations (1, 5, and 15 wt.%) in order to fabricate new combined bioactive and antibacterial composite materials (Ag-BGCOMPs). The antibacterial properties, bioactivity, and total bond strength of the Ag-BGCOMPs were evaluated. RESULTS The bioactivity of the Ag-BG was confirmed after its immersion in simulated body fluid (SBF). The total bond strength between the surrounding tooth tissue and the new composites or the control (dental composite alone) has not shown any statistically significant difference in the performed pilot study. Antibacterial activity was observed against Escherichia coli (E. coli) and Streptococcus mutans (S. mutans) for the Ag-BGCOMP 5 wt.% and 15 wt.% but not for the Ag-BGCOMP 1 wt.% or the control. CONCLUSIONS This work contributes to our long term aim which is the fabrication of dental materials capable of reducing bacteria invasion and enhancing remineralization of the surrounding dental tissues. SIGNIFICANCE We anticipate that these new composites could ultimately prevent restoration failure by inhibiting the formation of secondary caries and by remineralizing the hard tissues surrounding tooth lesions.

Innovative Approaches to Regenerate Enamel and Dentin

The process of tooth mineralization and the role of molecular control of cellular behavior during embryonic tooth development have attracted much attention the last few years. The knowledge gained from the research in these fields has improved the general understanding about the formation of dental tissues and the entire tooth and set the basis for teeth regeneration. Tissue engineering using scaffold and cell aggregate methods has been considered to produce bioengineered dental tissues, while dental stem/progenitor cells, which can differentiate into dental cell lineages, have been also introduced into the field of tooth mineralization and regeneration. Some of the main strategies for making enamel, dentin, and complex tooth-like structures are presented in this paper. However, there are still significant barriers that obstruct such strategies to move into the regular clinic practice, and these should be overcome in order to have the regenerative dentistry as the important mean that can treat the consequences of tooth-related diseases.

Study of the Bioactive Behavior of Thermally Treated Modified 58S Bioactive Glass

Thermal treatment of bioactive glasses can affect their microstructure and thus their bioactivity. The aim of this study was the characterization of the thermally treated sol-gel-derived bioactive glass 58S at characteristic temperatures and the dependence of its bioactive behavior on the specific thermal treatment. The thermal behavior of the bioactive glass was studied by thermal analysis (TG/DTA). Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffractometry (XRD) were used for the characterization of the bioactive glass. The bioactive behavior in Simulated Body Fluid (SBF) was examined by Scanning Electron Microscopy (SEM-EDS) and FTIR. The major crystal phases after thermal treatment were Calcium Silicates, Wollastonite and Pseudowollastonite, while all thermally treated samples developed apatite after 48 hours in SBF. A slight enhancement of bioactivity was observed for the samples heated at the temperature range 910-970oC.

A Bioactive Glass/Dental Porcelain System by the Sol Gel Route: Fabrication and Characterization

Melt derived bioactive glass- porcelain system is reported to be bioactive but with a slow rate of bioactivity. The aim of this work is to fabricate and characterize bioactive glass/dental porcelain composites produced by the sol-gel method. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffractometry (XRD) were used to characterize the fabricated materials. The FTIR spectra and the XRD patterns confirm the presence of both constituents in the mixtures, while the dominant crystal phases in bioactive glass/dental porcelain specimens are leucite and wollastonite.

Orai1 expression pattern in tooth and craniofacial ectodermal tissues and potential functions during ameloblast differentiation

Background: Orai1 is a plasma membrane protein that forms the pore of the calcium release activated calcium channel. Humans with mutated Orai1 present with hereditary combined immunodeficiency, congenital myopathy and anhidrotic ectodermal dysplasia. Consistent with the ectodermal dysplasia phenotype, enamel formation and mineralization is also abnormal in Orai1 deficient patients. The expression pattern and potential functions of Orai1 in enamel formation remains unclear. To contribute toward understanding the role of Orai1 in amelogenesis we characterized ORAI1 protein developmental pattern in comparison with other ectodermal organs. We also examined the effects of Orai1 down‐regulation in ameloblast cell proliferation and differentiation. Results: Our data show strong expression of ORAI1 protein during the ameloblast secretory stage, which weans at the end of the maturation stage. In salivary glands, ORAI1 is expressed mainly in acini cells. ORAI1 expression is also found in hair follicle and oral epithelium. Knockdown of Orai1 expression decreases cell proliferation and results in RNA expression levels changes of key ameloblast genes regulating enamel thickness and mineralization. Conclusions: This study provides insights in the anhidrotic ectodermal dysplasia phenotype due to Orai1 mutation and highlights the importance of calcium signaling in controlling ameloblast differentiation and maturation during tooth development. Developmental Dynamics 244:1249–1258, 2015.

Physical Properties of an Ag-Doped Bioactive Flowable Composite Resin

The aim of this work was to study the physical and antibacterial properties of a flowable resin composite incorporating a sol-gel derived silver doped bioactive glass (Ag-BGCOMP). The depth of the cure was calculated by measuring the surface micro-hardness for the top and bottom surfaces. The volumetric polymerization shrinkage was measured by recording the linear shrinkage as change in length, while the biaxial flexural strength was studied measuring the load at failure. The antibacterial properties of the samples were tested against Streptococcus mutans (S. mutans) and Lactobacillus casei (L. casei). The measured values were slightly decreased for all tested physical properties compared to those of control group (flowable resin composite without Ag-BG), however enhanced bacteria inhibition was observed for Ag-BGCOMP. Ag-BGCOMP could find an application in low stress-bearing areas as well as in small cavity preparations to decrease secondary caries. This work provides a good foundation for future studies on evaluating the effects of Ag-BG addition into packable composites for applications in larger cavity preparations where enhanced mechanical properties are needed.

Sintered Hydroxyapatite / Bioactive Glass Composites: Thermal Analysis and Bioactivity

Three-dimensionally ordered materials containing hydroxyapatite (HAp) as well as Bioglass® (BG) have been prepared in form of pellets and have been examined the effects of BG addition -in combination with a heat treatment process- on biological properties of composite HAp/BG. The investigation of the bioactive behavior of sintered and unheated biphasic mixtures and the deviations from pure HAp was performed by FTIR spectroscopy and Differential Thermal Analysis. It was observed the appearance of new phases on sintered composite pellets, while a faster biological HAp layer formation was detected, on the composite unheated pellets’ surface than on pure HAp and sintered composite pellets, currently leading to increased bioactivity.