Partial Substitution Of Ca Research Articles

Enhanced dielectric response and non-Ohmic properties of Cd-doped Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics

In this study, Na1/3(Ca1−xCdx)1/3Bi1/3Cu3Ti4O12 (x = 0, 0.2, 0.4, 0.8, and 1.0) ceramics were prepared via solid-state method. Effects of substitution of Ca2+ with Cd2+ on the microstructure, dielectric response, and non-Ohmic properties of Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics were studied systematically. Results showed that all samples possessed single perovskite phase, in which grain size increased with the increase in Cd2+ doping content. Energy band gaps and activation energy first increased and then decreased, achieving their maxima (4.22 and 0.642 eV, respectively) at x = 0.2. Besides, dielectric constant of doped samples increased with the decrease in dielectric loss in frequency range of 40–106 Hz. Moreover, improvement in non-Ohmic properties was also observed with Cd2+ doping. The optimal dielectric properties (dielectric constant of ∼12,500, dielectric loss of ∼0.032 at 10 kHz, nonlinear coefficient of ∼3.42, and breakdown strength of ∼2.7 kV·cm−1) were achieved at x = 0.2. Dielectric response mechanism of ceramics followed internal barrier layer capacitor model while nonlinear ohmic properties were derived from Schottky barrier structure. Dielectric relaxation peaks at high temperatures (120 °C–220 °C) were associated with grain boundaries. Therefore, partial substitution of Ca2+ with Cd2+ can improve simultaneously dielectric and non-Ohmic properties of Na1/3Ca1/3Bi1/3Cu3Ti4O12 ceramics, which is conducive to their application in high-energy-density storage capacitors and varistors.

Sr-substitution effects on crystal structure and thermoelectric properties of misfit layered cobaltate, [Ca2CoO3]pCoO2

Misfit-layered cobaltate [Ca2CoO3]pCoO2 is a promising thermoelectric (TE) material that can operate at high temperature in air. Partial substitution of Ca with Sr has been suggested to enhance TE properties. To comprehend the unresolved effects of Sr-substitution on the TE properties, we have prepared single-phase polycrystalline samples of Sr-substituted [Ca2CoO3]pCoO2, i.e., [(Ca1-xSrx)2CoO3]pCoO2, using a spark plasma sintering (SPS) method followed by O2 annealing. We analyzed the crystal structure by powder X-ray diffraction, evaluated the average valence state of Co ions by X-ray photoelectron spectroscopy, and measured temperature-dependent TE properties. Upon Sr-substitution, the average valence state of Co ions slightly increased. The electrical resistivity perpendicular to the SPS pressing direction increased, while that along the SPS pressing direction was almost unchanged. The Seebeck coefficient and the thermal conductivity were less affected by the Sr-substitution. The figure-of-merit zT perpendicular to the SPS pressing direction tended to decrease with Sr-substitution, reflecting the increase in electrical resistivity.

Preparation and Characterization of Mono- and Biphasic Ca1-xAgxHPO4·nH2O Compounds for Biomedical Applications.

This study aimed to explore the effects of the full-scale replacement (up to 100%) of Ca2+ ions with Ag1+ ions in the structure of brushite (CaHPO4·2H2O). This substitution has potential benefits for producing monophasic and biphasic Ca1-xAgxHPO4·nH2O compounds. To prepare the starting solutions, (NH4)2HPO4, Ca(NO3)2·4H2O, and AgNO3 at different concentrations were used. The results showed that when the Ag/Ca molar ratio was below 0.25, partial substitution of Ca with Ag reduced the size of the unit cell of brushite. As the Ag/Ca molar ratio increased to 4, a compound with both monoclinic CaHPO4·2H2O and cubic nanostructured Ag3PO4 phases formed. There was a nearly linear relationship between the Ag ion ratio in the starting solutions and the wt% precipitation of the Ag3PO4 phase in the resulting compound. Moreover, when the Ag/Ca molar ratio exceeded 4, a single-phase Ag3PO4 compound formed. Hence, adjusting the Ag/Ca ratio in the starting solution allows the production of biomaterials with customized properties. In summary, this study introduces a novel synthesis method for the mono- and biphasic Ca1-xAgxHPO4·nH2O compounds brushite and silver phosphate. The preparation of these phases in a one-pot synthesis with controlled phase composition resulted in the enhancement of existing bone cement formulations by allowing better mixing of the starting ingredients.

The Effect of Full-Scale Exchange of Ca2+ with Co2+ Ions on the Crystal Structure and Phase Composition of CaHPO4·2H2O

The influence of ionic substitution in the Ca1−xCoxHPO4·nH2O compound was studied systematically for the first time. Among the fascinating features of these biomaterials is that they can be easily tailored for specific applications, for example, as biocements and bioceramics. Different molar concentrations of Co(NO3)2·6H2O, Ca(NO3)2·4H2O, and NaH2PO4·2H2O compounds were employed in determining the starting solutions utilized in the present study. The experimental findings reveal that, when the Co/Ca molar ratio is below 0.67 (BCo4), Co doping (the partial substitution of Ca by Co) takes place in brushite as a monophase. However, in the Co/Ca 0.67–1.5 molar ratio range (BCo4–BCo6), biphasic Co3(PO4)2·8H2O/CaHPO4·2H2O crystals start to precipitate. Full Ca replacement by Co results in the precipitation of nanostructured monoclinic cobalt phosphate and orthorhombic ammonium cobalt phosphate hydrate. Subsequent X-ray photoelectron spectroscopy (XPS), powdered X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses, along with thermogravimetric analysis (TGA), confirmed that the starting solution ratio of Co/Ca had a significant influence on the material’s microstructure, while tuning this ratio ultimately tailored the desired properties of the material for the intended applications.

Degradation-controlling mechanisms in natural organic acid solutions of CaO–Al2O3–SiO2–B2O3 glass-ceramics by partially substituting Ca2+ with Ba2+ and Sr2+

The degradation of environmentally friendly CaO–Al2O3–SiO2–B2O3 (CASB) glass-ceramics, which consist of anorthite and glass phase, was investigated in three natural organic acid solutions. The results indicated that citric acid had the most significant effect on the degradation of CASB glass-ceramics. While the chemical stability of anorthite is relatively poor, the glass phase also contributed significantly to the effective degradation of CASB glass-ceramics. Subsequently, Ba2+ or Sr2+ was used for full or partial substitution of Ca2+ in CASB glass-ceramics, and the degradation-controlling mechanism of the substituted CASB glass-ceramics was further researched. The full substitution of Ca2+ in CASB glass-ceramics by the two cations resulted in the occurrence of borate [BO4] units in the glass phases, and the interlinkage of [BO4] with broken silicate [SiO4] network structures caused a complementary network effect. Consequently, the degradation of CASB glass-ceramics by organic acids was reduced due to the improvements in the chemical stability of the modified glass-ceramics. Additionally, degradation control can also be achieved based on a mixed-alkali effect, originating from the partial substitution of Ca2+ in CASB glass-ceramics by Ba2+ or Sr2+. The degradable glass-ceramics have the potential to be applied in low-temperature co-fired ceramic technology because of their good physical properties, which include a dielectric constant of 3–5, a dielectric loss as low as 10−3, a coefficient of thermal expansion of 3–9 × 10−6/°C, and an average bending strength of about 47 MPa. Noticeably, the development of the degradable glass-ceramics is helpful to the low-cost and pollution-free recycling of valuable metal electrodes, which is significant for the sustainable development of electronic packaging technologies.

Effect of calcium doping on Sm1–xCaxBaCo2O5+δ cathode materials for intermediate-temperature solid oxide fuel cells

Here, Sm1–xCaxBaCo2O5+δ (x = 0–0.4; SCBC) oxygen-deficient perovskites were synthesized by a sol–gel method and studied as potential novel cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). As an effective doping strategy, partial substitution of Ca for Sm in SmBaCo2O5+δ could reduce the thermal expansion coefficient (TEC) and improve the conductivity and catalytic activity of the oxygen reduction reaction (ORR). The x = 0–0.2 samples obtained after sintering at 1100 °C crystallized in an orthorhombic structure with the space group Pmmm and had good chemical compatibility with CeO2-based electrolytes at 1000 °C for 10 h. The TECs of the SCBC samples decreased from 20.2 × 10−6 K−1 (x = 0) to 17.7 × 10−6 K−1 (x = 0.2). The area-specific resistances (ASRs) of the x = 0–0.4 cathodes were 0.163, 0.114, 0.075, and 0.090 Ω cm2 at 700 °C. Additionally, the x = 0.2 cathode showed good electrochemical stability in a CO2-containing atmosphere. All results clearly indicated that double perovskite SCBC (x = 0–0.3) are promising cathode materials for IT-SOFCs.

Ultrahigh energy storage density of Ca2+-modified PLZST antiferroelectric ceramics prepared by the tape-casting method

High energy density is the goal pursued by energy storage dielectric capacitors. Lead-based antiferroelectric ceramics are the most promising material system. Herein, the improved recoverable energy storage of 14.5 J/cm3 and efficiency of 77.1 % are obtained at x = 0.02 in Ca2+-modified Pb0.97-xCaxLa0.02(Zr0.93Sn0.05Ti0.02)O3 (PCLZST) antiferroelectric ceramics, which are fabricated by the tape-casting method. It is proved that the partial substitution of Ca2+ to Pb2+ at A-site can effectively strengthen the antiferroelectricity due to the reduced tolerance factor. Besides, the addition of Ca2+ can refine the grains and increase the breakdown strength, up to 448 kV/cm vs 376 kV/cm for PLZST ceramics. In addition, the discharge energy density and time are 11.6 J/cm3 and 5.09 μs, respectively. These characteristics indicate that Pb0.95Ca0.02La0.02(Zr0.93Sn0.05Ti0.02)O3 ceramic is a potential energy storage material for pulsed power systems.

Lattice engineering by Sr-substitution leads to high piezoelectric performance of (SrxCa1-x)3TaAl3Si2O14 single crystals

In this work the partial substitution of Ca by Sr in the known langasite single crystal Ca3TaAl3Si2O14 is investigated from the point of view of crystal growth in order to improve the piezoelectric properties. For it, a (SrxCa1-x)3TaAl3Si2O14 (SCTAS) single crystal with x = 0.25 was grown by the Czochralski method. The grown crystal was strongly faceted, highly transparent, and of a high crystalline quality, as indicated by a full width at half maximum of the X-ray rocking curve as small as 31 arcsec. On the other hand, the crystal exhibited a high resistivity, with a value over 1010 Ω cm at 400 °C. Temperature dependent piezoelectric measurements confirmed the effective enhancement of the d11 piezoelectric coefficient at any temperature, while maintaining the dielectric loss below 1% up to 600 °C. Therefore, SCTAS exhibits superior properties compared with other piezoelectric materials for high temperature applications.

Influence of Ca substitution on microstructure and microwave dielectric properties of BaCu2V2O8 ceramics

The Ba1−xCaxCu2V2O8 (x = 0–0.20) ceramics were synthesized by using the traditional solid-phase reaction sintering method. The effects of partial substitution of Ca2+ for Ba2+ on the sintering, microstructure, relative density, crystalline phase composition, and microwave dielectric properties were studied. It is expected that by adding CaO, the τf value of ceramics will be increased to nearly zero. The results show that the BaCu2V2O8 phase was the main crystalline phase of ceramics. However, in the samples with more CaO content, a new BaV2O6 phase was detected. The appearance of the BaV2O6 phase directly leaded to the decrease of the relative dielectric constant and the deterioration of the Qf value. The Ba0.8Ca0.2Cu2V2O8 ceramic calcined at 725 °C for 6 h showed the following properties: er = 11.8, Qf = 22300 GHz, τf = − 7.9 ppm/°C. The results show that the microwave device made of this ceramic has the possibility of application in the high-frequency field.

Fe and Zn co-substituted beta-tricalcium phosphate (β-TCP): Synthesis, structural, magnetic, mechanical and biological properties.

In the present work, Fe3+ and Zn2+ co-substituted β-tricalcium phosphate (β-TCP) has been synthesized by wet co-precipitation method. Co-substitution level in the range from 1 to 5mol% has been studied. Thermal decomposition of as-prepared precipitates was shown to be affected by introducing of foreign ions, decreasing the decomposition temperature of precursor. It was determined that partial substitution of Ca2+ by Fe3+ and Zn2+ ions leads to the change in lattice parameters, which gradually decrease as doping level increases. Lattice distortion was also confirmed by means of Raman spectroscopy, which showed gradual change of the peaks shape in the Raman spectra. Rietveld refinement and electron paramagnetic resonance study confirmed that Fe3+ ions occupy only one Ca crystallographic site until Fe3+ and Zn2+ substitution level reaches 5mol%. All co-substituted samples revealed paramagnetic behavior, magnetization of powders was determined to be linearly dependent on concentration of Fe3+ ions. Cytotoxicity of the synthesized species was estimated by in vivo assay using zebrafish (Danio rerio) and revealed non-toxic nature of the samples. Preparation of ceramic bodies from the powders was performed, however the results obtained on Vickers hardness of the ceramics did not show improvement in mechanical properties induced by co-substitution.

Enhancement of the magnetic and magnetocaloric properties by Na substitution for Ca of La0.8Ca0.2MnO3 manganite prepared via the Pechini-type sol–gel process

We report in this work the results of synthesis and characterization of La0.8Ca0.2−xNaxMnO3 (0 ≤ x ≤ 0.2) prepared by the Pechini sol–gel method. We have investigated different effects of replacing Ca by Na on the magnetic properties and magnetocaloric effect of La0.8Ca0.2MnO3 compounds using X-ray diffraction and magnetization measurements. We have observed an evolution from an orthorhombic to a rhombohedral symmetry caused by the addition of Na and that the rhombohedral phase is stable for x ≥ 0.1. The partial substitution of Ca by Na leads to a monotonic increase in the Curie temperature (TC) of the samples from 105 K for x = 0 to 330 K for x = 0.2. A second-order nature of the magnetic phase transition is established in all the prepared compounds with the help of the Banerjee criterion. At an applied field of 5T, the maximum magnetic entropy change (∆SMmax) shows an enhancement with increasing Na+ concentration. Moreover, the relative cooling power (RCP) values are found to vary between 203 and 300.5 J/kg in this series of materials. In order to compare the magnetocaloric performances of the prepared samples, we have used several figures of merit such as the temperature-averaged entropy change (TEC), refrigerant capacity (RC) and normalized refrigerant capacity (NRC). Accordingly, the addition of Na ion greatly increases TEC, RC and NRC and thereby improves the magnetocaloric performance in La0.8Ca0.2−xNaxMnO3 (0 ≤ x ≤ 0.2). These metrics can help in identifying materials with high performance and clearly suggest that the sol–gel-made samples with x ≥ 0.1 can be customized for use in magnetic cooling applications near room temperature.

Autowave Synthesis of TiAl-Based Cast Composite Materials from Thermite-Type Mixtures

TiAl-based composite materials have been produced by spin-casting self-propagating high-temperature synthesis metallurgy methods using thermite-type mixtures, general relationships in the formation of their composition and structure have been investigated, the synthesis conditions have been optimized, a method for obtaining large ingots has been proposed, and their composition and structure have been determined. We have obtained cast Nb- and Cr-doped TiAl-based composite materials using mixtures of Ti, Nb, Cr, and Ca oxides with a combined reducing agent (Al and Ca) under the effect of an overload above 200g. It has been shown that partial Ca substitution for Al in the starting mixture ensures complete reduction of the TiO2, and the resultant metallic phase contains calculated amounts of Ti and Al. Mixtures of optimized composition make it possible to produce a cast composite material similar in composition to alloy 4822.

Effect of partial substitution of Ca for Sr on crystal structure and luminescence of Ce-doped Sr4Al14O25

Monophasic undoped and cerium-doped Sr4Al14O25 samples with partial substitution of calcium for strontium were prepared using conventional solid-state synthesis. Structural studies revealed that substitution of strontium by calcium in Sr4-xCaxAl14O25 up to x = 1.4 is possible without formation of additional phases and that the Sr2 site (of two possible) is more likely to be substituted by the smaller Ca ions. Photoluminescence measurements of Sr4Al14O25:Ce showed emission with double peak (360 and 380 nm) under 330 nm excitation wavelength. The effect of partial substitution of strontium by calcium on the luminescence of Sr4-xCaxAl14O25:Ce (emission, quantum yield, decay) were studied as well.

Investigation of Sm1−xCaxFe0.7Co0.3O3 films (x = 0.0–0.3) prepared by modified sol–gel spin-coating method for carbon monoxide and propane gas sensing

Sm1−xCaxFe0.7Co0.3O3 thin film gas sensors with different calcium concentrations (x = 0.0–0.3) were prepared using a modified sol–gel spin-coating method and then annealed at 650 °C for 2 h in air. The thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrical resistance measurements at concentrations from 1 to 200 ppm for carbon monoxide (CO) and from 1 to 500 ppm for propane (C3H8) in the temperature range of 25–300 °C for both gases. The resulting XRD data reveal that a pure phase with perovskite structure was obtained for each substitution in x and corresponds to the orthorhombic system with a Pbnm space group. Topography and roughness of the coating were obtained by AFM; roughness results of the sample do not significantly affect the response of the sensor, but the Ca2+ content does. Morphology of the nanoparticles and the thickness of each doping in calcium were observed by SEM, and the thickness was around 300 nm. The gas-sensing characteristics of the Sm–Ca–Fe–Co–O system were investigated in CO and C3H8 gases. It was found that the electrical resistance and gas-sensing characteristics were influenced by the substitution of Sm2+ by Ca2+ ions. When x was greater than or equal to 0.2 and CO concentration was 200 ppm and operating temperature was 300 °C, there was a higher response of the sensor, reaching up to 100%. For operating temperatures below 100 °C, the response of the Sm1−xCaxFe0.7Co0.3O3-based sensors to CO or C3H8 was < 5% regardless of the degree of substitution of Ca. On the other hand, at temperatures above 100 °C, the response depended on the gas to be sensed. In addition, the partial substitution of Ca in the structure increased the response of the sensor in relation to CO and C3H8 concentrations. It is suggested that this is due to the process of electric valence compensation.

Effect of simultaneous K, and Yb substitution for Ca on the microstructural and thermoelectric characteristics of CaMnO3 ceramics

CaMnO3-based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca2+ by an equimolar mixture of K+ and Yb3+, Ca1-x(K0.5Yb0.5)xMnO3, with x = 0.05, 0.10, 0.15, and 0.20. XRD studies have confirmed that the thermoelectric phase is the major one in all samples. Microstructure has shown the formation of large crystals, and an increasing porosity when the substitution is raised. This evolution has been confirmed through density measurements. Electrical resistivity has been drastically decreased for the 0.10 substituted samples, compared with the 0.05 ones, slightly increasing for higher substitution. On the other hand, absolute Seebeck coefficient and thermal conductivity are lower when the substitution is raised. The best ZT values have been achieved for the 0.10 substituted samples, which are around the typical reported in the literature for higher doping level. These results clearly point out to a decrease of the necessary rare earth dopant content to achieve similar performances in CaMnO3 ceramics, which is of the main economic significance for their industrial production.

Synthesis, Crystal Structure, and Luminescence Properties of Tunable Red-Emitting Nitride Solid Solutions (Ca1-xSrx)16Si17N34:Eu2+ for White LEDs.

A series of nitride solid solutions (Ca1-xSrx)16Si17N34:0.03Eu2+ were successfully synthesized through the conventional solid-state method. The electronic crystal structure and photoluminescence characteristics were studied in detail. The excitation in the near-ultraviolet and blue regions of the samples shows a broad band in the 250-550 nm range, which can match well with the n-UV and blue lighting-emitting diode chips. Partial substitution of Ca2+ by Sr2+ results in a redshift emission, and the impacts of Sr content on the luminescence were researched in detail. Under 410 nm excitation, the phosphor exhibited tunable red emission from 616 to 653 nm by changing the concentration of Sr2+. Based on the crystal data, the emission can be fitted into three distinguished Gaussian components, which are attributed to the different Eu2+ luminescence centers occupied in three disparate Ca2+ (Sr2+) lattice sites. The temperature quenching property of the phosphor was also investigated, and the good thermal stability of the phosphors was analyzed through the activation energy for thermal quenching. And the obtained CCT values from 2642 to 2817 K are suitable for a warm white light region. All the results indicated that the phosphors have possible application in the warm white light-emitting diodes.

Luminescence and Energy Transfer of Dual-Emitting Solid Solution Phosphors (Ca,Sr)10Li(PO4)7:Ce3+,Mn2+ for Ratiometric Temperature Sensing

A series of novel dual-emitting solid solution phosphors, (Ca,Sr)10Li(PO4)7:Ce3+, Mn2+ (CSLP:Ce3+,Mn2+), were synthesized by high-temperature solid-state method. CSLP:Ce3+,Mn2+ exhibits both Ce3+ violet emission and Mn2+ red emission under UV excitation. It is found that Sr2+ partial substitution of Ca2+ could result in enhancement of Mn2+ emission intensity and blue-shift of Mn2+ emission wavelength, which is due to site symmetry reduction and polyhedron expansion, respectively. The Ce3+–Mn2+ energy transfer (ET) is efficient (∼90%), and the ET mechanism is dipole–dipole interaction. The application potential of CSLP:Ce3+,Mn2+ in optical thermometry was studied by exploiting the temperature sensitivity of the fluorescent intensity ratio (violet/red). It is found that the intensity ratio of the Ce3+ and Mn2+ emission peak linearly related to the temperature from 293 to 473 K with sensitivity of 0.40% K–1. These results reveal that CSLP:Ce3+,Mn2+ may be a potential candidate for a luminescent ratiometric t...

Dielectric Properties of Eu-Doped CaCu3Ti4O12 with Different Compensation Mechanisms

To get a better understanding of the influence of rare-earth element doping, CaCu3Ti4O12 (CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction. All the ceramics were single phase, while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO. Ca0.875Eu0.1Cu3Ti4O12 (CECT1) exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO, while Ca0.85Eu0.1Cu3Ti4O12 (CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance. The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects. The variation of permittivity is related to the localization of carriers, which, according to the XPS results, should be caused by the presence of oxygen vacancies. The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu+ and Cu2+, which is an important source of the polarization in grain boundaries.

Structural, magnetic and ferroelectric properties of Ho1−x Ca x Mn1−y Co y O3 (x = 0.05, y = 0.05, 0.1)

Polycrystalline Ho1−xCaxMn1−yCoyO3 (x = 0.05, y = 0.05, 0.1) samples were synthesized by solid-state reaction route to study the effect of compositional variation on structural, magnetic and ferroelectric properties. From XRD measurement, it is clearly observed that orthorhombic phase stabilizes completely at y = 0.1. Partial substitution of Ca and Co at Ho and Mn site promotes structural distortion in the lattice which is responsible for suppression of hexagonal structure and stabilization of orthorhombic phase. On the other hand, incorporation of Co2+ cation into the HMO causes the transformation of John–Teller Mn3+ to Mn4+ ion which is not a John–Teller cation. Higher substitution of Co at Mn site enhances the magnetic property and shifts the transition temperature toward higher value (154 K). FC and ZFC curves become more divergent below 154 K for y = 0.1, indicating the presence of weak ferromagnetism below 154 K. M-H curve at 150 K for y = 0.1 shows a ferromagnetic-like behaviour which confirms our observed M-T data. The ferromagnetism in the sample may arise due to the double-exchange interaction between Mn3+ and Mn4+ ions. Values of remanent polarization and coercive field are observed to be 0.25 µC/cm2 and 3.23 kV/cm, respectively. It is quite interesting that substitution of Ca at Ho site and Co at Mn site induced weak ferromagnetism and ferroelectricity in the material. This finding makes the material a potential candidate for future device application.

Novel Nanostructured Zn-substituted Monetite Based Biomaterial for Bone Regeneration

A bone regeneration biomaterial must be biocompatible, osteoconductive and osteoinductive, and be gradually replaced by newly formed bone in the shorter time possible. Nanostructured materials, emulating bone composition and morphology, have shown great potential in bone repair because of their higher reactivity, faster reabsorption and improved biological behavior over microstructured materials. This work was aimed at developing a new biomaterial that meets the requirements for effective bone regeneration. Combination of elements with different solubility such as monetite, hydroxyapatite, amorphous calcium phosphate and silica gel, provided with the means to modulate the rate of material reabsorption of this novel biomaterial were Zn was found to be present as a partial substitution of Ca in the monetite lattice. The biomaterial was obtained by a hydraulic cementing reaction and was characterized by XRD, FTIR, NMR, chemical analysis, N2 adsorption porosimetry, Hg porosimetry, picnometry, SEM, TEM and evaluated in vitro and in vivo. Biomaterial showed a nanometric structure with a very high specific surface area (≈80 m2/g), high surface roughness and high intragranular porosity (50%) ranging from macro to nanopores. All of these are key features for a bone regeneration material. Solubility studies demonstrate the different solubility of its components and the release of Ca, P, Si and Zn. In vivo evaluation showed the effectiveness of the material to regenerate and to maintain 89 ± 9% of the volume of a critical size bone defect in sheep at 16 weeks. In the restored volume residual biomaterial was found to occupy 9 ± 5% of the space while newly formed trabeculae occupied 32 ± 6% of the space. The newly formed bone showed abundant vascularization and osteogenic activity. Biomaterial was estimated to have resorbed by 86 ± 7% with a reduction of 67 ± 8% in diameter and clear signs of cell-mediated resorption.