Mirosław M. Bućko

Enzymatic mineralization of gellan gum hydrogel for bone tissue-engineering applications and its enhancement by polydopamine

Interest is growing in the use of hydrogels as bone tissue‐engineering (TE) scaffolds due to advantages such as injectability and ease of incorporation of active substances such as enzymes. Hydrogels consisting of gellan gum (GG), an inexpensive calcium‐crosslinkable polysaccharide, have been applied in cartilage TE. To improve GG suitability as a material for bone TE, alkaline phosphatase (ALP), an enzyme involved in mineralization of bone by cleaving phosphate from organic phosphate, was incorporated into GG hydrogels to induce mineralization with calcium phosphate (CaP). Incorporated ALP induced formation of apatite‐like material on the submicron scale within GG gels, as shown by FTIR, SEM, EDS, XRD, ICP‐OES, TGA and von Kossa staining. Increasing ALP concentration increased amounts of CaP as well as stiffness. Mineralized GG was able to withstand sterilization by autoclaving, although stiffness decreased. In addition, mineralizability and stiffness of GG was enhanced by the incorporation of polydopamine (PDA). Furthermore, mineralization of GG led to enhanced attachment and vitality of cells in vitro while cytocompatibility of the mineralized gels was comparable to one of the most commonly used bone substitute materials. The results proved that ALP‐mediated enzymatic mineralization of GG could be enhanced by functionalization with PDA. Copyright

Generation of composites for bone tissue-engineering applications consisting of gellan gum hydrogels mineralized with calcium and magnesium phosphate phases by enzymatic means.

Mineralization of hydrogels, desirable for bone regeneration applications, may be achieved enzymatically by incorporation of alkaline phosphatase (ALP). ALP‐loaded gellan gum (GG) hydrogels were mineralized by incubation in mineralization media containing calcium and/or magnesium glycerophosphate (CaGP, MgGP). Mineralization media with CaGP:MgGP concentrations 0.1:0, 0.075:0.025, 0.05:0.05, 0.025:0.075 and 0:0.1 (all values mol/dm3, denoted A, B, C, D and E, respectively) were compared. Mineral formation was confirmed by IR and Raman, SEM, ICP‐OES, XRD, TEM, SAED, TGA and increases in the the mass fraction of the hydrogel not consisting of water. Ca was incorporated into mineral to a greater extent than Mg in samples mineralized in media A–D. Mg content and amorphicity of mineral formed increased in the order A < B < C < D. Mineral formed in media A and B was calcium‐deficient hydroxyapatite (CDHA). Mineral formed in medium C was a combination of CDHA and an amorphous phase. Mineral formed in medium D was an amorphous phase. Mineral formed in medium E was a combination of crystalline and amorphous MgP. Youngs moduli and storage moduli decreased in dependence of mineralization medium in the order A > B > C > D, but were significantly higher for samples mineralized in medium E. The attachment and vitality of osteoblastic MC3T3‐E1 cells were higher on samples mineralized in media B–E (containing Mg) than in those mineralized in medium A (not containing Mg). All samples underwent degradation and supported the adhesion of RAW 264.7 monocytic cells, and samples mineralized in media A and B supported osteoclast‐like cell formation. Copyright

Electrical properties of stoichiometric and non-stoichiometric calcium zirconate

Stoichiometric calcium zirconate and calcium zirconate with calcia or zirconia excess sintered bodies were prepared. Electrical properties of these materials were investigated at 950 °C using the dc four-probe and ac impedance spectroscopy methods. XRD analysis was used to determine the changes of cell parameters. The Rietveld method was used to refine calcium zirconate structure. The emf measurements of galvanic cells were used to determine the ionic transference numbers in the selected samples. Stoichiometric calcium zirconate appeared to be a rather poor and mixed electron-oxygen ion conductor, whereas calcium zirconate samples with excess of calcia or zirconia exhibit purely oxygen ion conductivity. In both cases, introduction of a respective cation excess led to the significant enhancement in conductivity. The simple point defect model for calcium zirconate with calcia or zirconia excess was proposed.

Barium zirconate ceramic powder synthesis by the coprecipitation–calcination technique

The coprecipitation technique was used to prepare an intimate mixture of barium carbonate and hydrous zirconia gel. A part of barium ions became incorporated in the zirconia gel structure. Heat treatment of the system results in the crystallisation of the BaO in ZrO2 solid solution of tetragonal symmetry. The solid solution, when heated without contact with BaCO3, decomposes at elevated temperatures. It results in the formation of BaZrO3 and monoclinic zirconia solid solution. No solid solution of monoclinic symmetry appears when barium carbonate is present in the system. In this case, the reaction of the tetragonal solid solution with BaCO3 leads to the synthesis of BaZrO3. The highest sintering ability is observed in the powder, a small part of which remains unreacted.

Ionic conductivity of CaO–Y2O3–ZrO2 materials with constant oxygen vacancy concentration

Structural modification of the fully stabilised zirconia is a possible way to improve its electrical properties. Electrical properties, especially ionic conductivity, of cubic zirconia solid solutions are strictly related to the ionic radius and valency of cations incorporated into the zirconia structure. Nanopowders with a constant oxygen vacancy concentration of 8 and 10 mol% were prepared by a hydrothermal treatment of co-precipitated zirconia hydrogels in a NaOH environment. The desired oxygen vacancy concentrations were obtained by introducing calcia and yttria, at different ratios, to the zirconia solid solutions. Phase compositions and lattice parameters of the respective phases were determined using X-ray diffraction analysis. Electrical properties of the samples were described on the basis of complex impedance spectroscopy analysis. It has been stated that substitution of calcia for yttria or yttria for calcia in zirconia solid solutions leads to ionic conductivity enhancement. Samples with a cubic structure, close to the stabilisation threshold, had the highest conductivity.

SHS Synthesis of the Materials in the Ti-Al-C-N System Using Intermetallics

Materials in the Ti-Al-C-N system due to their specific heterodesmic structure show pseudo-plastic properties. Direct synthesis of these compounds from respective elements requires high-temperature and long-lasting reaction. Presented work shows attempts to prepare some ternary compounds using self-propagating high-temperature synthesis (SHS). Intermetalic precursors, TiAl and Ti3Al, were used to synthesize fine and sinterable powders of 211 and 312 complex structure materials.

Structural and magnetic properties of GaN/Mn nanopowders prepared by an anaerobic synthesis route†

A new oxygen-free molecular precursor system based on (i) ammonolysis in refluxing/liquid NH3 of selected mixtures of gallium tris(dimethyl)amide Ga(NMe2)3 and manganese bis(trimethylsilyl)amide Mn[N(SiMe3)2]2 (Me = CH3, initial Mn-contents = 0.1, 5, 20, 50 at.%) followed by (ii) pyrolysis under flowing ammonia gas at 500, 700, and 900 °C afforded a range of nanocrystalline powders in the GaN/Mn system. The nanopowders were characterized mainly by powder XRD diffraction, FT-IR spectroscopy, Raman spectroscopy, SEM/EDX morphology examination, and XRF elemental analysis. Magnetization measurements as a function of magnetic field and temperature were carried out with a SQUID magnetometer. Structurally, the materials were shown to be single-phases based on the gallium nitride lattice. The presence of small quantities of residual amorphous Mn/N/Si/C species due to an incomplete transamination/removal of the trimethylsilylamide groups during ammonolysis was deduced from the XRF, FT-IR, Raman, and magnetization data. Magnetic properties for all nanopowders consistently pointed to a paramagnetic GaMnN phase with antiferromagnetic interactions among Mn-centers that under favorable circumstances reached the level of 3.8 at.% Mn. The paramagnetic phase was accompanied by a residual antiferromagnetic phase due to a facile oxidation in air of excessive Mn-containing by-products.

Microstructure evolution and electrical properties of yttria and magnesia stabilized zirconia

The paper contains the results of microstructure and chemical composition analyses of micrograins, which were formed on initial grain boundaries in ZrO2–Y2O3 and ZrO2–Y2O3–MgO systems. It has been found that the micrograins appear in the process of diffusion induced by grain boundary migration (DIGM). The observed processes can be described as both liquid film migration (LFM) and chemically induced grain boundary migration (CIGM). New micrograins had an increased content of Y2O3 and a cubic symmetry. Zirconia–yttria solid solutions with magnesia particulate addition showed an increased amount of migration nuclei and bigger size of new grains. However, no change in the chemical composition of the grains has been detected. The ionic conductivity measurements have shown that the activation energy (Ea) of conductivity at lower temperatures is connected to a DIGM-like process and to the distance of grain boundary migration. In the case of materials with dominating LFM process an increased grain boundary migration distance leads to a lowering of the activation energy of conductivity. Contrary to that, in the materials with dominating CIGM process an increase of migration zone causes increase of Ea values. The data obtained with respect to the type of DIGM process (LFM or CIGM) indicate that the grain boundary conductivity contribution increases with the CIGM distance.

Ceramic Pigments with Perovskite Structure

The results of preliminary investigation on preparation of perovskite pigments by solid state reaction are presented. The effects of different raw materials used as component carriers on formation of colored pigments were examined. Pigment composition, optimum chromophore addition, type of mineralizer and the conditions of synthesis were determined experimentally as well as the resulting color, phase composition and morphology of powders. The wet method of preparation of starting mixtures was also analyzed.

Composite (CaF2 + α-Al2O3) solid electrolytes: Preparation, properties and application to the solid oxide galvanic cells

Abstract Calcium fluoride based composites containing up to 25 mol. % α-Al 2 O 3 disperse phase were prepared. Electrical conductivities of the samples were measured in the temperature range 400–700 °C by the d.c. four-probe method. Dispersions of α-Al 2 O 3 up to 5 m/o were found to enhance the conductivity of pure CaF 2 . The conductivity values were increased two orders of magnitude higher than those of pure CaF 2 and they were dependent on the preparation method of the sample. The maximum conductivity values were observed for 2.5 m/o α-Al 2 O 3 content. The (CaF 2 + α-Al 2 O 3 ) composites appeared to be purely ionic conductors. The materials prepared were applied as electrolytes in solid-state oxide galvanic cells. The Gibbs free energy of formation at 700 °C for calcium metasilicate was determined from electromotive force (emf) measurements in this way.