Development and physicochemical characterization of novel porous phosphate glass bone graft substitute and in vitro comparison with xenograft.

The process of bone regeneration in bone grafting procedures is greatly influenced by the physicochemical properties of the bone graft substitute. In this study, porous phosphate glass (PPG) morsels were developed and their physicochemical properties such as degradation, crystallinity, organic content, surface topography, particle size and porosity were evaluated using various analytical methods. The in vitro cytotoxicity of the PPG morsels was assessed and the interaction of the PPG morsels with Dental Pulp Stem Cells (DPSCs) was studied by measuring cell proliferation and cell penetration depth. The cell-material interactions between PPG morsels and a commercially available xenograft (XG) were compared. The PPG morsels were observed to be amorphous, biocompatible and highly porous (porosity = 58.45%). From in vitro experiments, PPG morsels were observed to be non-cytotoxic and showed better cell proliferation. The internal surface of PPG was easily accessible to the cells compared to XG.

Titanium phosphate glass microcarriers induce enhanced osteogenic cell proliferation and human mesenchymal stem cell protein expression.

In this study, we have developed 50- to 100-µm-sized titanium phosphate glass microcarriers (denoted as Ti5) that show enhanced proliferation of human mesenchymal stem cells and MG63 osteosarcoma cells, as well as enhanced human mesenchymal stem cell expression of bone differentiation markers, in comparison with commercially available glass microspheres at all time points. We also demonstrate that these microcarriers provide superior human mesenchymal stem cell proliferation with conventional Dulbecco's Modified Eagle medium than with a specially developed commercial stem cell medium. The microcarrier proliferative capacity is revealed by a 24-fold increase in MG63 cell numbers in spinner flask bioreactor studies performed over a 7-day period, versus only a 6-fold increase in control microspheres under the same conditions; the corresponding values of Ti5 and control microspheres under static culture are 8-fold and 7-fold, respectively. The capability of guided osteogenic differentiation is confirmed by ELISAs for bone morphogenetic protein-2 and osteopontin, which reveal significantly greater expression of these markers, especially osteopontin, by human mesenchymal stem cells on the Ti5 microspheres than on the control. Scanning electron microscopy and confocal laser scanning microscopy images reveal favorable MG63 and human mesenchymal stem cell adhesion on the Ti5 microsphere surfaces. Thus, the results demonstrate the suitability of the developed microspheres for use as microcarriers in bone tissue engineering applications.

Development, characterisation and biocompatibility testing of a cobalt-containing titanium phosphate-based glass for engineering of vascularized hard tissues.

There is a continuing need to develop scaffold materials that can promote vascularisation throughout the tissue engineered construct. This study investigated the effect of cobalt oxide (CoO) doped into titanium phosphate glasses on material properties, biocompatibility and vascular endothelial growth factor (VEGF) secretion by osteoblastic MG63 cells. Glasses composed of (P2O5)45(Na2O)20(TiO2)05(CaO)30-x(CoO)x(x=0, 5, 10, and 15 mol%) were fabricated and the effect of Co on physicochemical properties including density, glass transition temperature (Tg), degradation rate, ion release, and pH changes was assessed. The results showed that incorporation of CoO into the glass system produced an increase in density with little change in Tg. It was then confirmed that the pH did not change significantly when CoO was incorporated in the glass, and stayed constant at around 6.5-7.0 throughout the dissolution study period of 336 h. Ion release results followed a specific pattern with increasing amounts of CoO. In general, although incorporation of CoO into a titanium phosphate glass increased its density, other bulk and surface properties of the glass did not show any significant changes. Cell culture studies performed using MG63 cells over a 7-day period indicated that the glasses provide a stable surface for cell attachment and are biocompatible. Furthermore, VEGF secretion was significantly enhanced on all glasses compared with standard tissue culture plastic and Co doping enhanced this effect further. In conclusion, the developed Co-doped glasses are stable and biocompatible and thus offer enhanced potential for engineering vascularized tissue.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses.

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

TiO2-doped phosphate glass microcarriers: a stable bioactive substrate for expansion of adherent mammalian cells.

Scalable expansion of cells for regenerative cell therapy or to produce large quantities for high-throughput screening remains a challenge for bioprocess engineers. Laboratory scale cell expansion using t-flasks requires frequent passaging that exposes cells to many poorly defined bioprocess forces that can cause damage or alter their phenotype. Microcarriers offer a potential solution to scalable production, lending themselves to cell culture processes more akin to fermentation, removing the need for frequent passaging throughout the expansion period. One main problem with microcarrier expansion, however, is the difficulty in harvesting cells at the end of the process. Therefore, therapies that rely on cell delivery using biomaterial scaffolds could benefit from a microcarrier expansion system whereby the cells and microcarriers are transplanted together. In the current study, we used bioactive glass microcarriers doped with 5% TiO2 that display a controlled rate of degradation and conducted experiments to assess biocompatibility and growth of primary fibroblast cells as a model for cell therapy products. We found that the microcarriers are highly biocompatible and facilitate cell growth in a gradual controlled manner. Therefore, even without additional biofunctionalization methods, Ti-doped bioactive glass microcarriers offer potential as a cell expansion platform.

Structural characterization of titanium-doped Bioglass using isotopic substitution neutron diffraction.

Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglass® is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO(2) into Bioglass® using isotopic substitution (of the Ti) applied to neutron diffraction and X-ray Absorption Near Edge Structure (XANES). We present the first isotopic substitution data applied to melt quench derived Bioglass or its derivatives. Results show that titanium is on average surrounded by 5.2(1) nearest neighbor oxygen atoms. This implies an upper limit of 40% four-fold coordinated titanium and shows that the network connectivity is reduced from 2.11 to 1.97 for small quantities of titanium. Titanium XANES micro-fluorescence confirms the titanium environment is homogenous on the micron length scale within these glasses. Solid state magic angle spinning (MAS) NMR confirms the network connectivity model proposed. Furthermore, the results show the intermediate range order containing Na-O, Ca-O, O-P-O and O-Si-O correlations are unaffected by the addition of small quantities of TiO(2) into these systems.

Titanium phosphate glass microspheres for bone tissue engineering.

We have demonstrated the successful production of titanium phosphate glass microspheres in the size range of ∼10-200 µm using an inexpensive, efficient, easily scalable process and assessed their use in bone tissue engineering applications. Glasses of the following compositions were prepared by melt-quench techniques: 0.5P2O5-0.4CaO-(0.1-x)Na2O-xTiO2, where x=0.03, 0.05 and 0.07 mol fraction (denoted as Ti3, Ti5 and Ti7 respectively). Several characterization studies such as differential thermal analysis, degradation (performed using a novel time lapse imaging technique) and pH and ion release measurements revealed significant densification of the glass structure with increased incorporation of TiO2 in the glass from 3 to 5 mol.%, although further TiO2 incorporation up to 7 mol.% did not affect the glass structure to the same extent. Cell culture studies performed using MG63 cells over a 7-day period clearly showed the ability of the microspheres to provide a stable surface for cell attachment, growth and proliferation. Taken together, the results confirm that 5 mol.% TiO2 glass microspheres, on account of their relative ease of preparation and favourable biocompatibility, are worthy candidates for use as substrate materials in bone tissue engineering applications.

Titanium and strontium-doped phosphate glasses as vehicles for strontium ion delivery to cells.

This study investigated the use of a Ti-containing quaternary phosphate glass system P(2)O(5)-Na(2)O-CaO-TiO(2) as a vehicle for strontium ion delivery to cells. Four glass compositions were manufactured: 0.5P(2)O(5)-0.15Na(2)O-0.05TiO(2)-(0.3 - x)CaO-xSrO (x = 0, 0.01, 0.03, and 0.05). Structural characterization revealed that sodium calcium phosphate is the dominant phase in all the glasses. Degradation studies demonstrated highly linear glass degradation, with Sr-containing glasses degrading at higher rates than the Sr-free glass. Biocompatibility studies using MG63 cells showed that the Sr-containing glasses possess excellent cell attachment and growth, particularly over short periods (~4 days).