The fabrication and characterization of barium titanate/akermanite nano-bio-ceramic with a suitable piezoelectric coefficient for bone defect recovery.

In recent years, due to the controllable mechanical properties and degradation rate, calcium silicates such as akermanite (Ca2MgSi2O7) with Ca-Mg and Si- containing bio-ceramics have received much more attention. In addition, the piezoelectric effect plays an important role in bone growth, remodeling and defect healing. To achieve our objective, the porous bioactive nano-composite with a suitable piezoelectric coefficient was fabricated by the freeze-casting technique from the barium titanate and nano-akermanite (BT/nAK) suspension. The highest d33of 4pC/N was obtained for BT90/nAK10. The compressive strength and porosity were for BT75/nAK25 and BT60/nAK40 at the highest level, respectively. The average pore channel diameter was 41 for BT75/nAK25. Interestingly enough, the inter-connected pore channel was observed in the SEM images. There was no detectable transformation phase in the XRD pattern for the BT/nAK composites. The manipulation flexibility of this method indicated the potential for the customized needs in the application of bone substitutes. An ((3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide)) MTT assay indicated that the obtained scaffolds have no cytotoxic effects on the human bone marrow mesenchymal stem cells.

Enhanced osteoconductivity of polyethersulphone nanofibres loaded with bioactive glass nanoparticles in in vitro and in vivo models.

OBJECTIVES: There is growing need for new scaffold constructions for synthetic bone graft substitutes to repair large bone lesions. A very promising and important class of new implants for tissue engineering is based on three-dimensional scaffolds and bioceramics. MATERIALS AND METHODS: In this study, after investigation of mechanical properties of polyethersulphone (PES) nanofibres, fabricated by electrospinning methodology and coated with bioactive glass (BG), cells of the MG-63 line were cultured on surfaces of these scaffolds. Their capacity to support MG-63 proliferation was also investigated in vitro by MTT assay. Osteoconductivity on these scaffolds was investigated by the common osteogenic markers alkaline phosphatase (ALP) activity, calcium mineral deposition and bone-related gene activation. Next, a bone reconstruction of rat critical-size defects model was evaluated using radiographic imaging analysis (digital mammography), computed tomography and histological examination. RESULTS: In vitro results indicated that biocompatibility and osteogenic markers of MG-63 cells were significantly enhanced after coating PES with BG. Based on in vivo results, new bone formation in the defect site was enhanced in implanted rats in comparison with a control group. The highest reconstruction was observed in animals implanted with BG-coated nanofibres. CONCLUSIONS: Osteoconductivity of PES nanofibres was markedly enhanced after coating them with BG, and introduction of this construct as new bone-graft substitute for bone loss and defects is indicated.

Reorientation of elongated particles at density interfaces.

Density interfaces in the water column are ubiquitously found in oceans and lakes. Interaction of settling particles with pycnoclines plays a pivotal function in nutrient transport between ocean layers and settling rates of marine particles. We perform direct numerical simulations of an elongated particle settling through a density interface and scrutinize the role of stratification on the settling dynamics. It is found that the presence of the density interface tends to turn the long axis of an elongated particle parallel to the settling direction, which is dramatically different from its counterpart in a homogeneous fluid. Although broadside-on settling of the elongated particle is enhanced upon approaching the interface, the long axis rotates toward the settling direction as the particle passes through the interface. We quantify turning couples due to stratification effects, which counteract the pressure-induced torques due to the fluid inertia. A similar behavior is observed for different initial orientations of the particle. It is shown that the reorientation of an elongated particle occurs in both sharp and linear density stratifications.

Interaction between a pair of particles settling in a stratified fluid.

The anisotropic structure of fluidized suspensions is governed by their microstructures which are in turn determined by the dynamics of particle pair interactions. Here, we present a numerical simulation of particle interaction in linearly stratified fluids. It is shown that unlike homogeneous fluids, stratification results in the attraction of particles settling abreast. The attraction between the particles is characterized by the combined effects of buoyancy, inertia, and diffusion. The interaction of the particles settling in tandem can be fundamentally altered due to the presence of the background density gradients and the drafting-kissing-tumbling behavior in a homogeneous fluid can be replaced by drafting-kissing-separation or drafting-separation phenomenon depending on the strength of the stratification. In the case of weak stratification, drafting-kissing-tumbling occurs, however, a prolonged kissing time is observed and the rate of change of the orientation of particles is reduced. It is shown that the formation of the buoyancy-induced vortical structures and the generation of stratified jets behind the particles are the fundamental mechanisms in governing the dynamics of the particle pair interaction in stratified fluids.

Direct cytotoxicity evaluation of 63S bioactive glass and bone-derived hydroxyapatite particles using yeast model and human chondrocyte cells by microcalorimetry.

In this study, the cytotoxicity evaluation of prepared 63S bioactive glass and bone-derived hydroxyapatite particles with yeast and human chondrocyte cells was carried out using isothermal micro-nano calorimetry (IMNC), which is a new method for studying cell/biomaterial interactions. Bioactive glass particles were made via sol-gel method and hydroxyapatite was obtained from bovine bone. Elemental analysis was carried out by XRF and EDXRF. Amorphous structure of the glass and completely crystalline structure of HA were detected by XRD analysis. Finally, the cytotoxicity of bioactive glass and bone-derived HA particles with yeast and cultured human chondrocyte cells was evaluated using IMNC. The results confirmed the viability, growth and proliferation of human chondrocyte cells in contact with 63S bioactive glass, and bone-derived HA particles. Also the results indicated that yeast model which is much easier to handle, can be considered as a good proxy and can provide a rapid primary estimate of the ranges to be used in assays involving human cells. All of these results confirmed that IMNC is a convenient method which caters to measuring the cell-biomaterial interactions alongside the current methods.