Vibrational features of phospho-silicate glasses: Periodic B3LYP simulations

Mesoporous 45S5 bioactive glass: synthesis, in vitro dissolution and biomineralization behavior

The development of a new generation of biomaterials includes a sol-gel process to obtain glass foams, which is a well established method for CaO-SiO₂-P₂O₅ compositions, but is not yet recognized for Bioglass® containing sodium oxide. In this study, we report, for the first time, the synthesis of a mesoporous 45S5 bioactive glass with superior textural characteristics and its in vitro dissolution and biomineralization behavior. Wormhole-like bioactive mesostructured 45S5 glass has been synthesized by an acid assisted sol-gel method followed by an evaporation induced self-assembly process. The virgin mesoporous 45S5 bioactive glass has been characterized by various analytical methods before and after soaking in simulated body fluid (SBF). The factors affecting the glass formation have been discussed in terms of the critical micelle concentration (CMC) at a particular temperature followed by a specified time interval. In vitro studies on the mesostructured 45S5 glass sample reveal the rapid formation of carbonated hydroxyapatite (HCA) with nano sized crystals. The mesostructured glass showed an excellent cell proliferation response without toxicity up to the concentration of 50 μg ml^-1. Furthermore, we show that the 45S5 glass with superior textural parameters is extremely useful within the family of bioactive materials as it has accelerated formation kinetics of the apatite phase as compared to other bioactive glass compositions.

Bioactivity of Sodium Free Fluoride Containing Glasses and Glass-Ceramics

The bioactivity of a series of fluoride-containing sodium-free calcium and strontium phosphosilicate glasses has been tested in vitro. Glasses with high fluoride content were partially crystallised to apatite and other fluoride-containing phases. The bioactivity study was carried out in Tris and SBF buffers, and apatite formation was monitored by XRD, FTIR and solid state NMR. Ion release in solutions has been measured using ICP-OES and fluoride-ion selective electrode. The results show that glasses with low amounts of fluoride that were initially amorphous degraded rapidly in Tris buffer and formed apatite as early as 3 h after immersion. The apatite was identified as fluorapatite by 19F MAS-NMR after 6 h of immersion. Glass degradation and apatite formation was significantly slower in SBF solution compared to Tris. On immersion of the partially crystallised glasses, the fraction of apatite increased at 3 h compared to the amount of apatite prior to the treatment. Thus, partial crystallisation of the glasses has not affected bioactivity significantly. Fast dissolution of the amorphous phase was also indicated. There was no difference in kinetics between Tris and SBF studies when the glass was partially crystallised to apatite before immersion. Two different mechanisms of apatite formation for amorphous or partially crystallised glasses are discussed.

DFT modeling of 45S5 and 77S soda-lime phospho-silicate glass surfaces: clues on different bioactivity mechanism

The reactivity of bioglasses, which is related to the dissolution of cations and orthosilicate groups in the physiological fluid, strongly depends on the key structural features present at the glass surfaces. On the basis of the composition and the synthetic routes employed to make the glass, surfaces with very different characteristics and thus presenting different mechanisms of dissolution can be observed. In this paper, the surface structures of two very different bioglass compositions, namely 45S5 (46.1 SiO2, 24.4 Na2O, 26.9 CaO, and 2.6 P2O5 mol %) and 77S (80.0 SiO2, 16.0 CaO, and 4.0 P2O5 mol %), have been investigated by means of periodic DFT calculations based on a PBE functional and localized Gaussian basis set as encoded in the CRYSTAL code. Our calculations show that the two glass surfaces differ by the relative amount of key structural sites such as NBOs, exposed ions, orthosilicate units, and small rings. We have demonstrated how the number of these sites affects the surface stability and reactivity (bioactivity).

Silica Aerogel Improves the Biocompatibility in a Poly-ε-Caprolactone Composite Used as a Tissue Engineering Scaffold

Poly-ε-caprolactone (PCL) is a biodegradable polyester that has received great attentions in clinical and biomedical applications as sutures, drug delivery tool, and implantable scaffold material. Silica aerogel is a material composed of SiO2that has excellent physical properties for use in drug release formulations and biomaterials for tissue engineering. The current study addresses a composite of silica aerogel with PCL as a potential bone scaffold material for bone tissue engineering. The biocompatibility evaluation of this composite indicates that the presence of silica aerogel effectively prevented any cytotoxic effects of the PCL membrane during extended tissue culture periods and improved the survival, attachment, and growth of 3T3 cells and primary mouse osteoblastic cells. The beneficial effect of silica aerogel may be due to neutralization of the acidic condition that develops during PCL degradation. Specifically, it appears that silica aerogel to PCL wt/wt ratio at 0.5 : 1 maintains a constant pH environment for up to 4 weeks and provides a better environment for cell growth.