Zirconium Ions Up-Regulate the BMP/SMAD Signaling Pathway and Promote the Proliferation and Differentiation of Human Osteoblasts

Zirconium (Zr) is an element commonly used in dental and orthopedic implants either as zirconia (ZrO2) or in metal alloys. It can also be incorporated into calcium silicate-based ceramics. However, the effects of in vitro culture of human osteoblasts (HOBs) with soluble ionic forms of Zr have not been determined. In this study, primary culture of human osteoblasts was conducted in the presence of medium containing either ZrCl4 or Zirconium (IV) oxynitrate (ZrO(NO3)2) at concentrations of 0, 5, 50 and 500 μM, and osteoblast proliferation, differentiation and calcium deposition were assessed. Incubation of human osteoblast cultures with Zr ions increased the proliferation of human osteoblasts and also gene expression of genetic markers of osteoblast differentiation. In 21 and 28 day cultures, Zr ions at concentrations of 50 and 500 μM increased the deposition of calcium phosphate. In addition, the gene expression of BMP2 and BMP receptors was increased in response to culture with Zr ions and this was associated with increased phosphorylation of SMAD1/5. Moreover, Noggin suppressed osteogenic gene expression in HOBs co-treated with Zr ions. In conclusion, Zr ions appear able to induce both the proliferation and the differentiation of primary human osteoblasts. This is associated with up-regulation of BMP2 expression and activation of BMP signaling suggesting this action is, at least in part, mediated by BMP signaling.NHMRC Project grant 63265

A Novel Bone Substitute with High Bioactivity, Strength, and Porosity for Repairing Large and Load-Bearing Bone Defects.

Achieving adequate healing in large or load-bearing bone defects is highly challenging even with surgical intervention. The clinical standard of repairing bone defects using autografts or allografts has many drawbacks. A bioactive ceramic scaffold, strontium-hardystonite-gahnite or "Sr-HT-Gahnite" (a multi-component, calcium silicate-based ceramic) is developed, which when 3D-printed combines high strength with outstanding bone regeneration ability. In this study, the performance of purely synthetic, 3D-printed Sr-HT-Gahnite scaffolds is assessed in repairing large and load-bearing bone defects. The scaffolds are implanted into critical-sized segmental defects in sheep tibia for 3 and 12 months, with bone autografts used for comparison. The scaffolds induce substantial bone formation and defect bridging after 12 months, as indicated by X-ray, micro-computed tomography, and histological and biomechanical analyses. Detailed analysis of the bone-scaffold interface using focused ion beam scanning electron microscopy and multiphoton microscopy shows scaffold degradation and maturation of the newly formed bone. In silico modeling of strain energy distribution in the scaffolds reveal the importance of surgical fixation and mechanical loading on long-term bone regeneration. The clinical application of 3D-printed Sr-HT-Gahnite scaffolds as a synthetic bone substitute can potentially improve the repair of challenging bone defects and overcome the limitations of bone graft transplantation

Micro-poro-elasticity of baghdadite-based bone tissue engineering scaffolds:A unifying approach based on ultrasonics, nanoindentation, and homogenization theory

\u3cp\u3eMicrostructure-elasticity relations for bone tissue engineering scaffolds are key to rational biomaterial design. As a contribution thereto, we here report comprehensive length measuring, weighing, and ultrasonic tests at 0.1 MHz frequency, on porous baghdadite (Ca\u3csub\u3e3\u3c/sub\u3eZrSi\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e9\u3c/sub\u3e) scaffolds. The resulting porosity-stiffness relations further confirm a formerly detected, micromechanically explained, general relationship for a great variety of different polycrystals, which also allows for estimating the zero-porosity case, i.e. Young modulus and Poisson ratio of pure (dense) baghdadite. These estimates were impressively confirmed by a physically and statistically independent nanoindentation campaign comprising some 1750 indents. Consequently, we can present a remarkably complete picture of porous baghdadite elasticity across a wide range of porosities, and, thanks to the micromechanical understanding, reaching out beyond classical elasticity, towards poroelastic properties, quantifying the effect of pore pressure on the material system behavior.\u3c/p\u3

Micro-elasticity of porous ceramic baghdadite : A combined acoustic-nanoindentation approach supported by homogenization theory

Bone tissue engineering aims at repairing damaged bone and restoring its functions with the help of biocompatible materials cultivated with cells and corresponding growth factors [1]. Besides being osteoconductive and osteoinductive, the bone substitute or scaffold should exhibit sufficient porosity for good vascular and tissue ingrowth, while not overly compromising the overall mechanical properties of the implant, i.e. its stiffness and strength. The design process of such scaffolds requires a multitude of in vitro and in vivo experiments and has proven to be a challenging task, thus giving rise to the wish for rational, computer-aided design of biomaterials, regarding not only biological and cell transport aspects, but also mechanics. Highly porous baghdadite (Ca3ZrSi2O9) scaffolds have shown promising biological responses when used for the repair of critical size defects in rabbit radial bones [2]. However, the mechanical properties of these scaffolds require further investigation. Therefore, by using structure-property relations derived from ultrasound and nanoindentation experiments, and on the basis of theoretical and applied micromechanics, the current research aims at applying the state-of-the-art methods in computational biomechanics and biomaterials to this new material to investigate its elastic properties

Zirconium ion promotes HOB proliferation.

<p>(A) The MTT assay was used to determine the HOB viability after HOBs were treated with zirconium solutions with different concentrations for 1, 3 and 7 days. Compared to the control and NaNO3-treated control, higher concentrations of zirconium significantly increased HOB viability. ZrO(NO₃)₂ at 5µM increased cell proliferation at D1 and D3 but not D7, whereas ZrCl₄ at 5µM had no effects on HOB proliferation. However, higher concentrations of both of zirconium solutions significantly increased cell proliferation at D1, D3 and D7. Between the time points, viable cell number in each treatment group are significantly increased (p<0.01). (B) The graph shows the quantification of Ki67 positive cells to total cells. Compared to the control, the proportion of Ki67-positive cells is significantly increased in all treatment groups. There were no significant differences observed between the treatment groups at the different concentrations. (C-J) Representative images from each treatment group following KI67 immunostaining. Arrows indicate the positive staining of cells with the Ki67 antibody (C). Scale bar: 100 µm. Data are Mean±SD of three separate experiments. * p<0.05, **p<0.01 versus control.</p