Strontium and Copper Co-Doped Multifunctional Calcium Phosphates: Biomimetic and Antibacterial Materials for Bone Implants.

ß-tricalcium phosphate (ß-TCP) is a promising material in regenerative traumatology for the creation of bone implants. Previously, it was established that doping the structure with certain cations can reduce the growth of bacterial activity. Recently, much attention has been paid to co-doped ß-TCP, that is explained by their ability, on the one hand, to reduce cytotoxicity for cells of the human organism, on the other hand, to achieve a successful antibacterial effect. Sr, Cu-co-doped solid solutions of the composition Ca9.5-xSrxCu(PO4)7 was obtained by the method of solid-phase reactions. The Rietveld method of structural refinement revealed the presence of Sr2+ ions in four crystal sites: M1, M2, M3, and M4. The M5 site is completely occupied by Cu2+. Isomorphic substitution of Ca2+ → (Sr2+and Cu2+) expands the concentration limits of the existence of the solid solution with the ß-TCP structure. No additional phases were formed up to x = 4.5 in Ca9.5-xSrxCu(PO4)7. Biocompatibility tests were performed on cell lines of human bone marrow mesenchymal stromal cells (hMSC), human fibroblasts (MRC-5) and osteoblasts (U-2OS). It was demonstrated that cytotoxicity exhibited a concentration dependence, along with an increase in osteogenesis and cell proliferation. Ca9.5-xSrxCu(PO4)7 powders showed significant inhibitory activity against pathogenic strains Escherichia coli and Staphylococcus aureus. Piezoelectric properties of Ca9.5-xSrxCu(PO4)7 were investigated. Possible ways to achieve high piezoelectric response are discussed. The combination of bioactive properties of Ca9.5-xSrxCu(PO4)7 renders them multifunctional materials suitable for bone substitutes.

Synthesis and Functional Characterization of CoxFe3-xO4-BaTiO3 Magnetoelectric Nanocomposites for Biomedical Applications.

Nowadays, magnetoelectric nanomaterials are on their way to finding wide applications in biomedicine for various cancer and neurological disease treatment, which is mainly restricted by their relatively high toxicity and complex synthesis. This study for the first time reports novel magnetoelectric nanocomposites of CoxFe3-xO4-BaTiO3 series with tuned magnetic phase structures, which were synthesized via a two-step chemical approach in polyol media. The magnetic CoxFe3-xO4 phases with x = 0.0, 0.5, and 1.0 were obtained by thermal decomposition in triethylene glycol media. The magnetoelectric nanocomposites were synthesized by the decomposition of barium titanate precursors in the presence of a magnetic phase under solvothermal conditions and subsequent annealing at 700 °C. X-ray diffraction revealed the presence of both spinel and perovskite phases after annealing with average crystallite sizes in the range of 9.0-14.5 nm. Transmission electron microscopy data showed two-phase composite nanostructures consisting of ferrites and barium titanate. The presence of interfacial connections between magnetic and ferroelectric phases was confirmed by high-resolution transmission electron microscopy. Magnetization data showed expected ferrimagnetic behavior and σs decrease after the nanocomposite formation. Magnetoelectric coefficient measurements after the annealing showed non-linear change with a maximum of 89 mV/cm*Oe with x = 0.5, 74 mV/cm*Oe with x = 0, and a minimum of 50 mV/cm*Oe with x = 0.0 core composition, that corresponds with the coercive force of the nanocomposites: 240 Oe, 89 Oe and 36 Oe, respectively. The obtained nanocomposites show low toxicity in the whole studied concentration range of 25-400 µg/mL on CT-26 cancer cells. The synthesized nanocomposites show low cytotoxicity and high magnetoelectric effects, therefore they can find wide applications in biomedicine.

Effect of Piezoelectric BaTiO3 Filler on Mechanical and Magnetoelectric Properties of Zn0.25Co0.75Fe2O4/PVDF-TrFE Composites.

Polymer-based multiferroics, combining magnetic and piezoelectric properties, are studied experimentally-from synthesis to multi-parameter characterization-in view of their prospects for fabricating biocompatible scaffolds. The main advantage of these systems is facile generation of mechanical deformations and electric signals in response to external magnetic fields. Herein, we address the composites based on PVDF-TrFE polymer matrices filled with a combination of piezoelectric (BaTiO3, BTO) and/or ferrimagnetic (Zn0.25Co0.75Fe2O4, ZCFO) particles. It is shown that the presence of BTO micron-size particles favors stripe-type structuring of the ZCFO filler and enhances the magnetoelectric response of the sample up to 18.6 mV/(cm∙Oe). Besides that, the admixing of BTO particles is crucial because the mechanical properties of the composite filled with only ZCFO is much less efficient in transforming magnetic excitations into the mechanical and electric responses. Attention is focused on the local surfacial mechanical properties since those, to a great extent, determine the fate of stem cells cultivated on these surfaces. The nano-indentation tests are accomplished with the aid of scanning probe microscopy technique. With their proven suitable mechanical properties, a high level of magnetoelectric conversion and also biocompatibility, the composites of the considered type are enticing as the materials for multiferroic-based polymer scaffolds.

Boosting Magnetoelectric Effect in Polymer-Based Nanocomposites.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (αME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO3 particles. Developed strategies allow us to increase the αME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe2O4 nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures.

Direct Magnetoelectric Effect in a Sandwich Structure of PZT and Magnetostrictive Amorphous Microwires.

The magnetoelectric (ME) response in a trilayer structure consisting of magnetostrictive Fe77.5B15Si17.5 amorphous microwires between two piezoelectric PZT (PbZr0.53Ti0.47O3) layers was investigated. Soft magnetic properties of wires make it possible to operate under weak bias magnetic fields below 400 A/m. Enhanced ME voltage coefficients were found when the microwires were excited by ac magnetic field of a frequency of 50-60 kHz, which corresponded to the frequency of electromechanical resonance. The as-prepared microwires were in a glass coat creating a large thermoelastic stress and forming a uniaxial magnetic anisotropy. The effect of glass-coat removal and wire annealing on ME coupling was investigated. The glass coat not only affects the wire magnetic structure but also prevents the interfacial bonding between the electric and magnetic subsystems. However, after its removal, the ME coefficient increased slightly less than 10%. Refining the micromagnetic structure and increasing the magnetostriction by stress release during wire annealing (before or after glass removal) strongly increases the ME response up to 100 mV/(cm×Oe) and reduces the characteristic DC magnetic field down to 240 A/m. Although the achieved ME coefficient is smaller than reported values for multilayered films with layers of PZT and soft magnetic alloys as Metglass, the proposed system is promising considering a small volume proportion of microwires.

High Entropy Oxide Phases with Perovskite Structure.

The possibility of the formation of high entropy single-phase perovskites using solid-state sintering was investigated. The BaO-SrO-CaO-MgO-PbO-TiO2, BaO-SrO-CaO-MgO-PbO-Fe2O3 and Na2O-K2O-CaO-La2O3-Ce2O3-TiO2 oxide systems were investigated. The optimal synthesis temperature is found between 1150 and 1400 °C, at which the microcrystalline single phase with perovskite structure was produced. The morphology, chemical composition, crystal parameters and dielectric properties were studied and compared with that of pure BaTiO3. According to the EDX data, the single-phase product has a formula of Na0.30K0.07Ca0.24La0.18Ce0.21TiO3 and a cubic structure.