Sergey Kulkov

Porous alumina, zirconia and alumina/zirconia for bone repair: fabrication, mechanical and in vitro biological response

Zirconia (ZrO2) and alumina (Al2O3) based ceramics are widely used for load-bearing applications in bone repair due to their excellent mechanical properties and biocompatibility. They are often regarded as bioinert since no direct bone-material interface is created unless a porous structure intercedes, leading to better bone bonding. In this regard, investigating interactions between cells and porous ceramics is of great interest. In the present study, we report on the successful fabrication of sintered alumina A-61, zirconia Z-50 and zirconia/alumina composite ZA-60 ceramics with medium porosities of 61, 50 and 60%, respectively, indicating a bimodal pore size distribution and good interconnectivity. They exhibit elastic moduli of 3-10 GPa and compressive strength values of 60-240 MPa, similar to those of human cortical bone.We performed in vitro cell-material investigations comparing the adhesion, proliferation and differentiation of mouse pre-osteoblasts MC3T3-E1 on the three porous materials. While all three ceramics demonstrate a strong cell attachment, better cell spreading is observed on zirconia-containing substrates. Significantly higher cell growth was quantified on the latter ceramics, revealing an increased alkaline phosphatase activity, higher collagen production and increased calcium biomineralization compared to A-61. Hence, these porous zirconia-containing ceramics elicit superior biological responses over porous alumina of similar porosity, promoting enhanced biological interaction, with potential use as non-degradable bone grafts or as implant coatings.

Porous composite materials ZrO2(MgO)-MgO for osteoimplantology

The pore structure and phase composition of ceramic composite material ZrO2(Mg)-MgO at different sintering temperatures were studied. The main mechanical characteristics of the material were determined and it was shown that they are close to the characteristics of natural bone tissues. It was shown that material structure has a positive effect on the pre-osteoblast cells proliferation. In-vitro studies of pre-osteoblast cells, cultivation on material surface showed a good cell adhesion, proliferation and differentiation of MMSC by osteogenic type.

Hydrogen adsorption on low-index surfaces of the PdFe alloy

The adsorption of hydrogen on the (001) and (110) surfaces of the PdFe alloy has been investigated using the projector-augmented-wave method within the generalized gradient Perdew-Burke-Ernzerhof (PBE) approximation for the exchange-correlation functional. The most preferred sites of hydrogen adsorption on the two surfaces have been determined. It has been shown that the hydrogen adsorption in hollow sites is more preferred on the (001) surface independently of its termination. The hydrogen adsorption in B1 bridge sites is energetically more favorable on the palladium-terminated (110) surface, whereas B2 bridge sites are more preferred on the iron-terminated (110) surface. The inclusion of the magnetism in the calculation leads to a decrease in the adsorption energy of hydrogen on the (001) and (110) surfaces, regardless of their termination, but does not change the tendencies revealed in variations of the binding energy in the nonmagnetic calculation. In general, the magnetism affects the position of hydrogen with respect to the surface layer and decreases the negative relaxation of interlayer distances in the cases of iron terminations of both surfaces, while hydrogen, in turn, decreases the magnetic moment of the nearest neighbor iron atoms. The paths of hydrogen diffusion from the surface deep into the material have been analyzed.

Influence of Impurities on Grain Boundaries Cohesion in B2-TiMe

The effect of interstitial and substitutional impurities on grain boundary (GB) cohesion in the series of B2-TiMe alloys is studied from first principles using pseudopotential approach. It is shown that the TiMe Σ5(310) symmetrical tilt GB cohesion is reduced by the segregation of hydrogen while it is increased due to boron or carbon segregation. We analyze also the combined and accumulation effect of interstitial B (C) and H impurities on the change of the Griffith work.

Porosity and biocompatibility study of ceramic implants based on ZrO2 and Al2O3

The work studies ZrO2(MexOy)-based porous ceramics produced from the powders consisting of hollow spherical particles. It was shown that the structure is represented by a cellular framework with bimodal porosity consisting of sphere-like large pores and pores that were not filled with the powder particles during the compaction. For such ceramics, the increase of pore volume is accompanied by the increased strain in an elastic area. It was also shown that the porous ZrO2 ceramics had no acute or chronic cytotoxicity. At the same time, ceramics possess the following osteoconductive properties: adhesion support, spreading, proliferation and osteogenic differentiation of MSCs.