For the past few decades, many researches have been devoted to study and develop new biocompatible materials for medical implants. MgCa1 and TiAl6V4 are examples of such materials. It is possible to adjust their physical and chemical parameters by coating the surface with calcium phosphates (CaP). In turn, exposing materials to UV radiation influencing the surface charge may contribute to cell immobilization and thus materials biocompatibility. The purpose of this study was to investigate how UV radiation influences the immobilization of yeast cells on the surfaces of Mg- and Ti- originated alloys and their CaP coatings. MgCa1 and TiAl6V4 samples with different coatings (uncoated, CaP, Ca+ and variations doped with Zn or Ga) were used. Surface roughness, FTIR spectras and surface electric potential (via electron work function measurements) were assessed before and after UV irradiation (for 30 and 60 min). S. cerevisiae were immobilized on the surfaces of samples and assessed its coverage using fluorescent microscopy. Adherence of yeast cells was found to be more prominent for Ti samples, than to Mg samples. There was no conclusive link discovered between the samples’ surface roughness and yeast cells’ adherence to it. UV irradiation does not affect the chemical structure of the samples. Overly, UV irradiation has improved the cell immobilization on Mg- and Ti-originated alloys with different CaP coating, exceptions are only coatings with Zn or Ga dopings. Non-coated Mg- and Ti- originated alloys showed the best adherence of yeast cells.

The structural and physical properties of hydroxyapatite (HAP) with the substitution of Sr/Ca and Mg/Ca are studied. The changes in the HAP properties are studied by various methods of density functional theory calculations. The calculation of the lattice constants upon substitution of Sr/Ca in HAP compared with the experimental data shows similar increase in these parameters after substitution of Sr/Ca. The values of bulk modulus, band gap E (g), and the work function Delta phi before and after both substitutions of Sr/Ca and Mg/Ca are calculated. The changes in piezoelectric properties upon Mg/Ca substitution are obtained.

The purpose of this study was to investigate the effect of Zn doped CaP coatings prepared by micro-arc oxidation method, as a possible approach to control MgCa1 alloy degradation. All the prepared coatings comprised a calcium deficient CaP phase. The control in this evaluation was performed with undoped CaP coating in SBF solution at body temperature (37 ± 0.5⁰C). The investigation involved determination of microchemical, mechanical, morphological, properties along with anticorrosive, cytocompatibility and antibacterial efficacy. The effect of sterilization process on the properties of the surfaces was also investigated. The results showed that the addition of Zn into CaP increased the corrosion resistance of MgCa1 alloy. Moreover, the adhesion strength of the coatings to MgCa1 alloy was enhanced by Zn addition. In cytotoxicity testing of the samples, extracts of the samples in MEM were incubated with L929 cells and malformation, degeneration and lysis of the cells were examined microscopically after 72 h. The results showed that all samples were cytocompatible. The degradation of MgCa1 alloy in the simulated body fluids (SBF) or DMEM was decreased by coating with CaP. Moreover, the degradation rate of CaP was further decreased by adding a small amount of Zn into the CaP matrix. The samples having CaP coatings and Zn doped CaP coating demonstrated antibacterial efficacy against E.coli. As a result, coating of magnesium alloy with Zn-doped CaP decreased the degradation rate, increased the corrosion resistance, cytocompatibility and the antibacterial effects of the alloys.

В работе рассмотрены модели, приведены результаты расчетов и проанализированы структурные и физические свойства ГАП как исходного чистого, так и с дефектами типа вакансий и замещений атомов Ca на другие атомы (Sr, Mg, Fe, др.).Моделирование и расчеты свойств ГАП проводились методами теории функционала плотности в различных приближениях в комбинации c квантовыми полуэмпирическими методами расчета PM3, PM7, PM6-D3H4.Изучены изменения структурных, механических и оптических свойств при различных дефектах: рассчитаны постоянные решетки, значения упругих, полярных, пьезоэлектрических, электронных и оптических характеристик; данные колебательных вибрационно-ротационных спектров; методами молекулярной динамики дана оценка температурного поведения ГАП.Все полученные результаты анализируются в сравнении

This article is focusing on electrical functionalization of biomaterial's surface to enhance its biocompatibility. It is an overview of previously unpublished results from a series of experiments concerning the effects surface electrical functionalization can have on biological systems. Saccharomyces cerevisiae cells were used for biological experiments. The hydroxyapatite (HAp) specimens were used to investigate influence of structural point defects on the surface electrical charge. Threshold photoelectron emission spectroscopy was used to measure the electron work function of HAp and biologic samples. The density functional theory and its different approximations were used for the calculation of HAp structures with defects. It was shown that the electrical charge deposition on the semiconductor or dielectric substrate can be delivered because of production of the point defects in HAp structure. The spatial arrangements of various atoms of the HAp lattice, i.e., PO4 and OH groups, oxygen vacancies, interstitial H atoms, etc., give the instruments to deposit the electrical charge on the substrate. Immobilization of the microorganisms can be achieved on the even surface of the substrate, characterized with a couple of nanometer roughness. This cells attachment can be controlled because of the surface electrical functionalization (deposition of the electrical charge). A protein layer as a shield for the accumulated surface charge was considered, and it was shown that the protein layer having a thickness below 1 µm is not crucial to shield the electrical charge deposited on the substrate surface. Moreover, the influence of surface charge on the attachment of microorganisms, when the surface roughness is excluded, and the influence of controlled surface roughness on the attachment of microorganisms, when surface charge is constant, were also considered.

The results are based on DFT calculations of hydroxyapatite (HAp) structures, pristine and defective, determined by various defects formed by oxygen vacancy depending on the charged states. Ordered hexagonal and monoclinic HAp phases have polarization, while disordered ones do not. These ferroelectric properties are determined by orientation of OH dipoles and cause the piezoelectric and pyroelectric phenomena in such HAp structures. Optical properties of defected HAp are mainly determined by various types of oxygen vacancy defects and can be manifested in the absorption and photocatalysis under ultraviolet illumination.

The report is directed to nanostructured hydroxyapatite (HA) electrically functionalized costing aimed to enhance biocompatibility of the HA originated implants. The reader will be guided from necessity and prerequisites for HA electrical functionalization to its computed designing, characterization technique, fabrication, and biological properties.

Novel composites based on polymer ferroelectrics with graphene (G) and graphene oxide (GO) have many advantages over pristine materials. In this work, the results of the computational molecular modeling of the composite nanostructures are presented and analyzed. The calculations were focused on pyroelectric properties of the composites based on polyvinylidene fluoride (PVDF) films with G/GO layers. The pyroelectric effect was modeled and pyroelectric coefficients were calculated for several models using molecular dynamics simulation with quantum-chemical semi-empirical PM3 method from HyperChem tool. The obtained results present a new prospective for further studies of the ferroelectric polymer-graphene multifunctional nanomaterials and their applications.

Advantages in the studies of new composite nanomaterials based on polymer ferroelectrics and graphene are presented. We analyzed the main results of the computational molecular modeling of nanostructures and the pyroelectric properties of the composites from polyvinylidene fluoride (PVDF) films and graphene layers. The pyroelectric effect was modelled and pyroelectric coefficients were calculated for several models using molecular dynamics simulation with quantum-chemical semi-empirical PM3 method from HyperChem tool. The results obtained provide important insights into our understanding of the mechanisms of pyroelectricity in the new nanocomposites, give us new prospective for further studies of the ferroelectric polymer–graphene multifunctional nanomaterials.

В этой обзорной лекции представлены последние достижения в области компьютерного моделирования, а также сравнение с экспериментальными исследованиями новых нанокомпозитных материалов на основе полимерных сегнетоэлектриков и графена / оксида графена.Основные результаты компьютерного молекулярного моделирования различных наноструктур, его физические свойства, такие как поляризационные изменения и поляризационное переключение, пьезоэлектрические и пироэлектрические свойства таких нанокомпозитов, построенных из тонких пленок поливинилиденфторида (PVDF) / поливинилиденфторида-трифторэтилен) (P(VDF-TrFE

Дефекты в гидроксиапатите: структура и свойства,

Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF), graphene (G) and/or graphene oxide (GO), was performed using the semi-empirical quantum approximation PM3 in the HyperChem software package. The piezoelectric properties of the composites were analyzed and compared with the experimental data obtained for thin films containing poly(vinylidene-fluoride-trifluoroethylene) with graphene oxide (P (VDF-TrFE)/GO). A qualitative agreement was obtained between the simulation results and the experimental measurements of the piezoelectric coefficient, its decrease in the presence of G or GO was revealed. When models containing one or more layers of graphene with 54 carbon atoms were investigated, it was found that the average piezoelectric coefficient was reduced to -9.8 pm/V for the one-sided PVDF/G model and to -18.98 pm/V for the two-sided sandwich model G/PVDF/G in compare with the calculated piezoelectric coefficient for pure PVDF (-42.2 pm/V). After computer modeling for models incorporating one or more layers of 96 carbon atoms in the oxide graphene, it was found that the piezoelectric coefficient was reduced to a value of -14.6 pm/V for a one-sided PVDF / GO model and to a value of -29.8 pm/V for a two-sided sandwich model GO/ PVDF/GO compared to the piezoelectric coefficient for pure PVDF.

Nanostructured hydroxyapatite (HAP) and its nanoparticles are widely used for implantation into the human organism. The biocompatibility of the implants depends very much on the interaction between the implant and the cells regenerating tissue to be connected to the implant. An implant surface electrical charged density plays an important role in these processes. Possible instruments managing the surface electrical potential of HAP are in the focus of this paper. Both theoretical and experimental results evidence that: - the surface electrical charge density of the nanoparticle depends on its size and shape; - the electrical charge density of HAP could be engineered by contact less technique because of deposition of the electrical charge from the external radiation source, surface couples reconstruction.

Hydroxyapatite (HAp) has structural features that define its basic physical properties, which have an important role at the surface, and it is one of the most used materials in bone implants. In this work, we present a density functional modeling (DFT) study of HAp both as bulk and with special HAp models with various defects, especially oxygen vacancies in HAp surface layers, which can also determine photocatalytic properties, confirmed experimentally. The first-principles calculations of bulk and modified HAp were carried out using local basis (AIMPRO) and plane-wave (VASP) codes. Data obtained are analyzed using both approaches, and compared.

Hydroxyapatite (HAp) was studied from a first principle approach using the local density approximation (LDA) method in AIMPRO code, in combination with various quantum mechanical (QM) and molecular mechanical (MM) methods from HypemChem 7.5/8.0. The data obtained were used for studies of HAp structures, the physical properties of HAp (density of electronic states-DOS, bulk modulus etc) and defects in HAp. Computed data confirmed that HAp can co-exist in different phases-hexagonal and monoclinic. Ordered monoclinic structures, which could reveal piezoelectric properties, are of special interest. The data obtained allow us to characterize the properties of the following defects in HAp: O, H and OH vacancies; H and OH interstitials; substitutions of Ca by Mg, Sr, Mn or Se, and P by Si. These properties reveal the appearance of additional energy levels inside the forbidden zone, shifts of the top of the valence band or the bottom of the conduction band, and subsequent changes in the width of the forbidden zone. The data computed are compared with other known data, both calculated and experimental, such as alteration of the electron work functions under different influences of various defects and treatments, obtained by photoelectron emission. The obtained data are very useful, and there is an urgent need for such analysis of modified HAp interactions with living cells and tissues, improvement of implant techniques and development of new nanomedical applications.

First principle modeling and calculations of hydroxyapatite both native and surface modified and having various defects (OH vacancies, H inter-nodes) were performed. Local Density Approximation method used with calculations of Density of States allows us to analyze the experimental obtained work function data. Molecular modeling was confirmed by photo-electron measurements up to 6.5eV and photoluminescence experimental data from synchrotron DESY up to 30eV. Brief analysis of the influence of heating, microwave radiation, hydrogenation, and synchrotron radiation on hydroxyapatite surface is presented in this work. New data on the structure of modified hydroxyapatite are obtained.

The results are based on the first principal modeling and calculations for hydroxyapatite (HAP) nanostructures as native as well surface modified, charged and having various defects (H and OH vacancies, H internodes).HAP structures having being studied using Local Density Approximation (LDA) method with calculations of Density of States (DOS) allow us analyzing the experimental forbidden energy gap (Eg) and work function data.Molecular modeling by HyperChem is confirmed by photo-electron monochromatic measurements up to 6 eV and photo-luminescence (PL) data from synchrotron DESY experimental data up to 30 eV values.Brief analysis of the influence of heating, microwave radiation, hydrogenation, x-rays and synchrotron radiation on HAP surface is presented in this work.New data of the structure of modified hydroxyapatite are obtained.The determined energy levels for H internodes is EH-int ~ Ev + (1.5-2.0)eV, while for OH vacancy energy is in the range of EOH-vac ~ Ev + (2.9-3.4)eV inside the forbidden zone Eg.The analysis of PL emission allows us to conclude that these energies are close to observed main PL spectral line 420 nm (2.95 eV), and consequently OH vacancy could play the leading role in the surface energy levels changes and charging.But the influence of the inserted hydrogen is revealed too through excitation from most deep valence band levels due to existence of close overlapped molecular orbital with phosphorus atoms in the excited states.Both defects are observed by PL emission spectrum under synchrotron excitation energy in diapason ~8.5-14.5 eV.

The general adhesion theory is the fundament to explain cell attachment to a bioimlplant surface in a human body. Electrical potential of the surface could be employed to control attachment. The paper demonstrates that the electrical potential may be engineered due to hydrogenation of hydroxyapatite. Such the procedure enhance attachment of osteoblast and generation of tissue. The Sr and Si doped hydrohyapatite demonstrates higher ability to be engineered by hydrogenation in contrast with undoped and Ag doped materials.