Development of Sr-Substituted Bioactive Glasses as a Dental Pulp Regenerative Material
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Background: Vital pulp therapy (VPT) is a treatment modality to promote healing and repair of damaged dental pulp. Strontium containing bioactive glass (BAG) has the potential to modulated cellular activities and induce hydroxyapatite (HA) formation. The aim was to develop a Sr-BAG material for VPT. Objectives: 1) To develop a highly reactive Sr-containing BAG in a suitable carrier medium for clinical application. 2) To investigate the proliferation and differentiation of human dental pulp stem cell (hDPSC) to this novel material in order to assess its potential as a therapeutic material for VPT. Method: Seven phospho-silicate glasses with high phosphate content with the basic formulations of 36.4SiO2 - 6P2O5 – 53CaO/SrO - 2.25CaCl2 - 2.25CaF2 (%mol) and 38.1SiO2 – 6.3P2O5 – 55.5SrO (%mol) were synthesised by the melt-quench route. In the first formulation, the halogen (CaX2 where X was F or Cl) containing group, SrO was used to substitute for the CaO in proportion of 0, 5, 10, 25, 50 and 100 %mol. The characteristics of the glasses were investigated by DSC, FTIR, XRD and SEM. The bioactivity in 37°C Tris buffer (TB) was examined up to 168 hours. The BAGs were then incorporated in 4% Alginate medium (BAG/Alg). The DNA fluorescence, MTT activity and ALP activity of hDPSCs at 3, 5, 7, 10 and 14 days after exposure to four BAG/Alg mixtures from 0, 50 and 100 Sr-substitutional BAGs and Ca-free BAG (All Ca, Sr50, Sr100 and All Sr respectively) were quantified. The differences among the samples were statistically analysed using two-way ANOVA with Bonferroni’s post hoc multiple comparison test. The differences were considered significant at p-value lesser than 0.05 (p<0.05). Results: The CaX2 had a pronounced effect on the thermodynamic transitions of the glass even though a small amount (5 mol%) was presented. However, the Tg reduction across Sr-substitutional glasses was less when Sr content was over 0.46. In all the glasses, the pH change, and the increase in the concentration of ions in TB were found from the first hour of immersion. The FTIR traces of all the glasses had the split bands at around 560 cm-1 and 1000-1020 cm-1, attributing to the presence of PO43-. In Sr-substitutional glasses, the Ca2+ and Sr2+ ratios in the solution and in the glass were directly proportional over all the time points. Additionally, the XRD traces exhibited the diffraction peaks around 24.6-26.1°θ and 30.7-32.1°θ, corresponding to Ca-HA, Sr-HA and their solid solutions. However, the XRD trace of Ca-free BAG presented the diffraction peak at 30.6°θ which did not match to any known compounds containing Sr and PO43-. The mixtures of BAG/Alg from all the seven BAGs were shown to have a viscoelastic and injectable hydrogel nature. The All Ca, Sr50, Sr100 and All Sr-Alg hydrogel composite were shown to have hDPSCs upregulation effects. The metabolism, proliferation and differentiation of hDPSCs increased when the cells were cultured with the BAGs-Alg. The MTT activity and DNA fluorescence in control group (CT) were much lower than all testing BAGs-Alg (p<0.05). Sr50 was found to promote high hDPSCs proliferation. All Ca group was found to induce ALP activity from the early day of culture. On day 7-10, ALP activity in All Ca was significantly highest (p<0.05). While the Sr50, Sr100 and All Sr groups increased ALP activity over time constantly. Conclusion: The in vitro bioactivity of Sr-substituted phospho-silicate glass with high phosphate content containing CaF2/CaCl2 was firstly investigated in this study. Sr substitution was found to have an effect on the Tg of the BAG network, facilitated dissolution, but did not cause any significant alteration in the glass structure. It suggested that Ca2+ in the apatite was being substituted randomly and not preferentially by Sr2+ both in the glass and the apatite. The novel mixtures of BAG/Alg containing the Sr-BAGs had potentials for clinical application. All four tested BAG/Alg hydrogels could enhance hDPSCs activities especially when both Ca2+ and Sr2+ were present. Hence this novel hydrogel would have the potential to be developed as a material for VPT.
Authors
Prutthithaworn, SCollections
- Theses [4125]