Dissolution properties of different compositions of biphasic calcium phosphate bimodal porous ceramics following immersion in simulated body fluid solution

Biphasic calcium phosphate (BCP) bimodal porous ceramics were prepared from a mixture of fine powders of hydroxyapatite (HAp) and beta-tricalcium phosphate (β-TCP) with varying HAp/β-TCP ratios. Two types of HAp powders and one type of β-TCP powder were used to produce porous BCP bioceramics with HAp/β-TCP weight ratios of 20/80, 40/60, and 80/20. Dissolution tests were performed to compare the dissolution properties of BCP-based bioceramics with different structural properties. Porous ceramic samples of approximately 0.5 g were individually soaked in 30 ml of simulated body fluid (SBF) solution at 36.5 °C for 1, 3, 7 and 10 days, respectively. The calcium content of the SBF solution was analyzed by ICP. The porous bodies were filtered, dried, and characterized using SEM, XRD, and FT-IR. The results indicate that the sample structural properties seem to have a greater effect than the storage environment on the dissolution properties.     

The nucleation, crystallization and dispersion behavior of PET-monodisperse SiO2 composites

To more accurately investigate the nucleation, crystallization and dispersion behaviors of silica particles in polymers, the composites of PET with monodisperse SiO₂-PS core-shell structured particles were prepared with SiO₂ size from 380 nm to 35 nm.For these SNPET samples, DSC results showed that the nucleation rate of silica particles increased as their size decreased, in which 35 nm SiO₂ particles produced the most obvious nucleation effect. At 2.0 wt.% load of 35 nm silica, Avrami equation proved that the isothermal crystallization rate G of SNPET was ca. 30% higher than that of pure PET and the crystallization activation energy for SNPET was −218.7 kJ mol⁻¹ lower than −196.1 kJ mol⁻¹ for PET. While, the non-isothermal crystallization ΔE for SNPET was −199.8 kJ mol⁻¹ lower than −185.5 for PET.On non-isothermal crystallization, Jeziorny equation presented the primary and secondary crystallization stages in PET and SNPET, in which nano SiO₂ accelerated the crystallization rate. Their Ozawa number m was from 2.1 to 2.7, which was smaller than that of Avrami number n.The nucleation and dispersion behaviors of SiO₂ particles were directly observed. POM results demonstrated that SNPET samples crystallized more quickly from melt and their crystallization rate increased as silica load increases but accelerated at 2-3 wt.%. The spherulites grew well in PET but their size was smaller in SNPET due to the silica barrier on their growth. SEM and TEM observed the homogeneous silica dispersion morphology and the vivid ordered patterns formed in SNPET. The monodisperse particles are highly expected to give more accurate and valuable references than multi-scale ones in obtaining novel advanced PET composites.     

Synthesis and characterization of novel UV-curable polyurethane–clay nanohybrid: Influence of organically modified layered silicates on the properties of polyurethane

Nanohybrids based on UV-curable polyurethane acrylate (PU) and cloisite 20B (C-20B) have been synthesized by solution blending method using different loading levels of C-20B. The structures of PU/C-20B nanohybrids were confirmed by Fourier transform infrared spectroscopy (FTIR) while X-ray diffraction and transmission electron microscopy (TEM) showed the intercalation of PU into layer silicates. The thermal properties of PU and PU/C-20B nanohybrids were investigated by thermal gravimetric analysis (TGA) and differential scanning calorimetric (DSC). TGA tests revealed that the thermal decomposition temperature (T_d10%) of the nanohybrid containing 5 wt% of C-20B increased significantly, being 61 °C higher than that of pure PU while DSC measurements indicated that the introduction of 5 wt% of clay increased the glass transition temperature from 89.7 to 101 °C. Accordingly, the mechanical and anti-water absorption properties proved also to be enhanced greatly as evidenced by nanoindentation anylsis and water absorptions data in which the nanohybrid containing 5 wt% of clay have highest elastic modulus (4.508 GPa), hardness (0.230 GPa) and lowest water absorption capacity. Thus the formations of nanohybrids manifests through the enhancement of thermal, mechanical and anti-water absorption properties as compared with neat PU due to the nanometer-sized dispersion of layered silicate in polymer matrix.     

In vitro bioactivity assessment and mechanical properties of novel calcium titanate/borosilicate glass composites

Bioactive calcium titanate/borosilicate glass composites were developed. Powder mixtures of borosilicate glass and 10, 20 or 30 wt% of potassium polytitanate particles were uniaxially pressed and sintered at 850 °C for 1 h. After heat treatment the reaction between potassium polytitanate and borosilicate glass produced composites consisting of calcium titanate particles embedded in a B-rich amorphous phase. For the in vitro bioactivity assessment sintered samples were immersed in a simulated body fluid (SBF) for 21 days under physiological conditions of pH and temperature. The compressive strength of the composites was also evaluated. A homogeneous and thick apatite layer was formed on all the materials tested. Furthermore, an appropriate compressive strength was observed (68-85 MPa). These results indicate that these composites are potential materials for bone tissue replacement and regeneration.     

Preparation of Pt/CeO2/HCSs anode electrocatalysts for direct methanol fuel cells

Hollow carbon spheres (HCSs) were prepared through a simple hydrothermal method using silica particles and glucose as the template and carbon precursor, respectively. HCSs used as supports for platinum catalysts deposited with cerium oxide (CeO₂) were prepared for application as anode catalysts in direct methanol fuel cells. The composition and structure of the samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the as-prepared catalysts for methanol oxidation were investigated by cyclic voltammetry (CV). The Pt/CeO₂/HCSs catalyst heated at 550 °C for 1 h exhibited the best catalytic activity for methanol oxidation.     

Microstructure and dielectric properties control of Ba4(Nd0.7Sm0.3)9.33Ti18O54 microwave ceramics

Microwave ceramics of Ba₄(Nd_0.7Sm_0.3)_9.33Ti₁₈O₅₄ with 0–3 wt% Ag additions were synthesized by a citrate sol–gel method. The BaO–B₂O₃–SiO₂ glass was also added into the sol–gel derived BNST ceramic powders as sintering aids. The undoped, Ag- and BaBS-doped samples can be sintered at 1250 °C, 1150 °C and 1000 °C, respectively. The microstructure and dielectric properties were then controlled by doping Ag or BaBS glass. Near isoaxial grains with about 250 nm and typical columnar grains were obtained for the silver-doped and BaBS-doped samples, respectively. For the <1 wt% silver-doped samples, the dielectric constant and Q × f retained unaltered but τ_f decreased from 9 ppm/°C to 1.4 ppm/°C. With increasing silver content from 1 wt% to 3 wt%, the dielectric constant and τ_f significantly increased but Q × f decreased. For the BaBS-doped samples, both dielectric constant and Q × f decreased but τ_f increased with increasing BaBS content.     

Nucleation of Hydroxyapatite Crystal through Chemical Interaction with Collagen

The nucleation of hydroxyapatite (HAp) crystal through chemical interaction with collagen was investigated. A collagen membrane was soaked in a supersaturated simulated body fluid (1.5 SBF) solution with ion concentrations at 1.5 times that of normal simulated body fluid (1.0 SBF). A few carbonate-containing HAp crystals were formed mostly on the edge-side of the collagen membrane after 4 weeks. In the Fourier-transform infrared spectometry (FTIR) results, the carboxylate band of the collagen membrane showed red chemical shifts after the formation of HAp crystals, which coincided well with the decrease of the calculated bond orders of the carboxylate group when chelated with a calcium ion, which emulated the first-step nucleation of HAp crystal on the carboxylate group of collagen. The result implies that the binding of a calcium ion to the carboxylate group of collagen is one of the key factors for the nucleation of HAp crystals in a 1.5 SBF solution.     

The underpotential deposition of Bi2Te3−ySey thin films by an electrochemical co-deposition method

Bi₂Te_3−ySe_y thin films were grown on Au(1 1 1) substrates using an electrochemical co-deposition method at 25 °C. The appropriate co-deposition potentials based on the underpotential deposition (upd) potentials of Bi, Te and Se have been determined by the cyclic voltammetric studies. The films were grown from an electrolyte of 2.5 mM Bi(NO₃)₃, 2 mM TeO₂, and 0.3 mM SeO₂ in 0.1 M HNO₃ at a potential of −0.02 V vs. Ag|AgCl (3 M NaCl). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to characterize the thin films. XRD and EDS results revealed that the films are single phase with approximate composition of Bi₂Te_2.7Se_0.3. SEM studies showed that the films are homogeneous and have micronsized granular crystallites.     

Creep behavior modeling of silica fume containing Al2O3-MgO refractory castables

Alumina-magnesia refractory castables usually present silica fume in their compositions, due to their ability to induce better flowability and to compensate the expansion related to the in situ spinel formation. In this paper, four compositions containing distinct silica fume content (0-1 wt%) were designed and analyzed by creep resistance and hot mechanical strength. The θ-projection concept coupled with the thermodynamic simulations were used in order to predict the creep behavior and to identify the main mechanism leading to the deformation of the samples. Based on the collected results, a linear correlation between the creep parameters (θ_i) and the silica fume content was attained by analyzing the experimental data, resulting in reliable data and the likelihood to simulate the performance of other compositions in the same system. Moreover, particle sliding assisted by viscous flow was suggested as the dominant creep mechanism in the studied castables.     

Synthesis and solubility of calcium fluoride/hydroxy-fluorapatite nanocrystals for dental applications

As the mineral phase of tooth enamel consists of apatite containing fluoride, the “CaF₂-like” salts are of significant interest in dentistry for their roles as labile fluoride reservoirs in caries prevention. Fluoride ion is required for normal dental development because of its therapeutic ability of osteoporosis healing and stimulating osteoblast activity both in vitro and in vivo. In this research, biphasic Calcium fluoride/fluorinated-hydroxyapatite (CF/FHAp) nanocrystals have been successfully synthesized via co-precipitation method. The synthesized powder was characterized by the commonly used bulk techniques such as chemical analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray powder diffraction (XRD) analyses. The obtained results confirmed the formation of biphasic powder composed of about 46% CF and 54% (w/w%) apatite phase which was a solid solution composed of more than 50% fluorapatite (FAp). In addition, in vitro evaluations of the powder were performed, and for investigating their bioactive capacity they were soaked in simulated body fluid (SBF) at different time intervals. The samples showed significant enhancement in bioactivity within few hours of immersion in SBF solution. Also, the EDS analysis clearly showed dissolution and deposition of calcium and phosphate ions on the surface of synthesized biphasic powder after the first week of immersion in SBF solution.     

Fabrication of corrosion resistant, bioactive and antibacterial silver substituted hydroxyapatite/titania composite coating on Cp Ti

The present work is aimed at developing a bioactive, corrosion resistant and anti bacterial nanostructured silver substituted hydroxyapatite/titania (AgHA/TiO₂) composite coating in a single step on commercially pure titanium (Cp Ti) by plasma electrolytic processing (PEP) technique. For this purpose 2.5 wt% silver substituted hydroxyapatite (AgHA) nanoparticles were prepared by microwave processing technique and were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM) methods. The as-synthesized AgHA particles with particle length ranging from 60 to 70 nm and width ranging from 15 to 20 nm were used for the subsequent development of coating on Cp Ti. The PEP treated Cp Ti showed both titania and AgHA in its coating and exhibited an improved corrosion resistance in 7.4 pH simulated body fluid (SBF) and 4.5 pH osteoclast bioresorbable conditions compared to untreated Cp Ti. The in vitro bioactivity test conducted under Kokubo SBF conditions indicated an enhanced apatite forming ability of PEP treated Cp Ti surface compared to that of the untreated Cp Ti. The Kirby-Bauer disc diffusion method or antibiotic sensitivity test conducted with the test organisms of Escherichia coli (E. coli) for 24 h showed a significant zone of inhibition for PEP treated Cp Ti compared to untreated Cp Ti.     

Bone-like forming ability of apatite-wollastonite glass ceramic

This research describes the preparation, characterisation and in vitro behavior of a bioactive glass ceramic containing 44.8 wt% apatite, 28.0 wt% wollastonite-2 M and 27.2 wt% of amorphous phase. The biomaterial was obtained by a specific thermal cycle process that caused the devitrification of the Ca₃(PO₄)₂-CaSiO₃ binary system's stoichiometric eutectic composition. Overall, the material combines the properties of a resorbable Si-Ca-rich glass, in addition to bioactive properties of wollastonite and apatite phases. The bioactivity of this material was studied by soaking the samples in a simulated body fluid (SFB) for 3, 7, 14 and 21 days at 36.5 °C. During the soaking, the amorphous phase and also wollastonite-2 M phase underwent steady dissolution by releasing Si and Ca ions into the SBF medium. After 7 days, a porous hydroxy-carbonate apatite (HCA) layer was formed at the SBF-glass ceramic interface. The micro-nanostructured apatite-wollastonite-2 M glass ceramics with improved mechanical properties, in comparison with the parent glass, could serve as a promising platform for hard tissue regeneration.     

Hydrothermal nucleation of hydroxyapatite on titanium surface

Titanium plates were submitted to nucleation and growth of hydroxyapatite (HAp) under hydrothermal conditions. A group of these plates were submitted to nucleation without any previous treatment and another group was treated with NaOH 1 M at 130°C inside an autoclave followed by heat-treatment at 600°C. The nucleation were performed by soaking all these titanium pieces, in a simulated body fluid (SBF) solution, containing calcium, phosphate and other ions, in order to promote the nucleation and growth of hydroxyapatite under hydrothermal conditions on the titanium surface. The results show that hydrothermal nucleation and growth of HAp occurs even on the non-treated titanium surface at 150°C. However, a better uniformity of the hydroxyapatite layer was observed on the pre-treated titanium surface, at 80°C, with the renewal of the SBF solution.     

Thermodynamic evaluation of spinel containing refractory castables corrosion by secondary metallurgy slag

This work addresses the thermodynamic evaluation of different spinel-containing refractory castable compositions in contact with a basic steel ladle slag (CaO/SiO₂ ∼ 9). The main differences among the castable compositions were the amount of silica fume (0 or 1 wt%), the binder source (calcium aluminate cement or hydratable alumina) and the spinel incorporation route (in situ or pre-formed). The interaction of the liquid slag with the refractory was carried out with the help of thermodynamic software (FactSage) and the applied methodology considered the changes in the slag composition due to the interaction with the castable. The theoretical results were compared with the experimental data attained by corrosion cup-tests, pointing out that the thermodynamic calculations were suitable for predicting various aspects observed in the corroded samples by SEM. Therefore, the equilibrium simulations led to parameters that indicated the corrosion resistance trends, complementing the experimental evaluation and reducing further experimental testing.     

Bioactive properties of CuO doped CaF2‒CaO‒B2O3‒P2O5‒MO(M=Ba,Sr, Zn,Mg) glasses

Calcium oxy fluoro boro phosphate glasses with fixed concentration of CuO and mixed with different modifier oxides (viz., BaO, SrO, ZnO and MgO) that play a vital role in collagen deposition, cellular activity, proliferation of osteoblasts and in blood vessel maturation, producing enzymes etc., that are necessary for normal functioning of human body were synthesized. In vitro bioactivity studies indicated the formation of hydroxy apatite (HAp) layer on the surface of the samples. This was confirmed by XRD and SEM photographs and also IR spectral studies. The magnitude of HAp layer formed was evaluated by measuring weight loss of the samples and pH measurements of the residual simulated body fluid (SBF) solutions at specific intervals of time. The analysis of the results of degradability studies together with spectroscopic studies has revealed that BaO is an effective modifier in improving the bioactivity of the host glass, among all the modifiers investigated.     

Studies on nonisothermal crystallization of HDPE/POSS nanocomposites

The nonisothermal crystallization of HDPE/POSS nanocomposites (POSS content varying from 1 to 10 wt%) was studied using differential scanning calorimetry (DSC) technique. The Ozawa approach failed to describe the crystallization behaviour of nanocomposites, whereas the modified Avrami analysis could explain the behaviour of HDPE/POSS (90:10) nanocomposite only. The value of Avrami exponent n for HDPE/POSS (90:10) nanocomposite ranged from 2.5 to 2.9 and decreased with increasing cooling rate. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation while simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n at higher cooling rates. A novel kinetic model by Liu et al. was able to satisfactorily describe the crystallization behaviour of HDPE/POSS nanocomposites. Presence of POSS did not cause significant change in the activation energy for the transport of polymer segments to the growing crystal surface. POSS molecules exhibit nucleation activity only at 10 wt% loading in HDPE and are not effective nuclei at lower loadings.     

Enhancement of antimicrobial and long-term biostability of the zinc-incorporated hydroxyapatite coated 316L stainless steel implant for biomedical application

Antimicrobial hydroxyapatite (HAp) nanoparticles with different concentrations (0, 3, and 6 mol%) of zinc were prepared by the ultrasonication process. The prepared nanoparticles and chitosan (CTS) composite were coated on 316L stainless steel implant by spin coating technique. The powder samples were characterised by particle size analyser, X-ray fluorescence, and X-ray diffraction studies. The morphology of the coating was investigated by scanning electron microscopy. The diameter of the particle size decreased with increase in the concentration of zinc in HAp structure. The structure of the coated implant was found to be uniform without any cracks and pores. Antimicrobial activity of the composites against Bacillus subtilis, Staphylococcus aureus, Klebsiella pneumonia, Salmonella typhi and Pseudomonas aeruginosa was analysed. The results showed that the increase in the concentration of zinc enhances the antimicrobial properties of 316L stainless steel implant. The stability of the implant in physiological environment was characterised by electrochemical impedance spectroscopy and polarisation analysis. The higher concentration of the ZnHAp/CTS composite shows higher corrosion resistance than that of the HAp/CTS-coated implant. This study shows that the coating provides corrosion resistance to the stainless steel substrate in simulated body fluid (SBF). The in vitro bioactivity study of the coated samples immersed in SBF solution confirms the formation of bone-like apatite layer on the surface of the implant. Thus, highly biocompatible ZnHAp/CTS-coated materials could be very useful in the long-term stability of the biomedical applications.     

Influence of Fe2O3 content on the dielectric behavior of aluminous porcelain insulators

Due to the increasing availability of substitute materials for electrical porcelain, research is needed to adapt formulations involving these materials to the current economic realities of the industry. This study assessed the effect of iron oxide concentration (0, 1, 2, 3, 5, and 8 wt%) on the dielectric properties of an aluminous porcelain composition commonly employed for electrical insulation based on different values of temperature and frequency. Samples with iron oxide contents of 0, 3, and 5 wt% were analyzed using dilatometry, X-ray diffraction, and scanning electron microscopy to evaluate the thermal, structural, and microstructural changes related to their Fe₂O₃ concentrations. Both the dielectric constant (ε_r) and the loss tangent (tan δ) were measured and evaluated in every sample. Results indicated that the presence of Fe₂O₃ increased the dielectric constant and loss tangent, which could result in an increase in heating by dielectric losses. Fe₂O₃ contents of up to 5 wt% had no significant effect on the performance of these insulators at room temperature (∼30 °C) and a high frequency (1 MHz), especially when the hematite phase was completely solubilized in the porcelain phases.     

Rheological behavior of multiwalled carbon nanotube/polycarbonate composites

The rheological behavior of compression molded mixtures of polycarbonate containing between 0.5 and 15 wt% carbon nanotubes was investigated using oscillatory rheometry at 260 °C. The nanotubes have diameters between 10 and 15 nm and lengths ranging from 1 to 10 μm. The composites were obtained by diluting a masterbatch containing 15 wt% nanotubes using a twin-screw extruder. The increase in viscosity associated with the addition of nanotubes is much higher than viscosity changes reported for carbon nanofibers having larger diameters and for carbon black composites; this can be explained by the higher aspect ratio of the nanotubes. The viscosity increase is accompanied by an increase in the elastic melt properties, represented by the storage modulus G′, which is much higher than the increase in the loss modulus G″. The viscosity curves above 2 wt% nanotubes exhibit a larger decrease with frequency than samples containing lower nanotube loadings. Composites containing more than 2 wt% nanotubes exhibit non-Newtonian behavior at lower frequencies. A step increase at approximately 2 wt% nanotubes was observed in the viscosity-composition curves at low frequencies. This step change may be regarded as a rheological threshold. Ultimately, the rheological threshold coincides with the electrical conductivity percolation threshold which was found to be between 1 and 2 wt% nanotubes.     

Isothermal and non-isothermal crystallization behavior of poly(l-lactic acid): Effects of stereocomplex as nucleating agent

The effects of incorporated poly(d-lactic acid) (PDLA) as poly(lactic acid) (PLA) stereocomplex crystallites on the isothermal and non-isothermal crystallization behavior of poly(l-lactic acid) (PLLA) from the melt were investigated for a wide PDLA contents from 0.1 to 10 wt%. In isothermal crystallization from the melt, the radius growth rate of PLLA spherulites (crystallization temperature (T_c)≥125 °C), the induction period for PLLA spherulite formation (t_i) (T_c≥125 °C), the growth mechanism of PLLA crystallites (90 °C≤T_c≤150 °C), and the mechanical properties of the PLLA films were not affected by the incorporation of PDLA or the presence of stereocomplex crystallites as a nucleating agent. In contrast, the presence of stereocomplex crystallites significantly increased the number of PLLA spherulites per unit area or volume. In isothermal crystallization from the melt, at PDLA content of 10 wt%, the starting, half, and ending times for overall PLLA crystallization (t_c(S), t_c(1/2), and t_c(E), respectively) were much shorter than those at PDLA content of 0 wt%, due to the increased number of PLLA spherulites. Reversely, at PDLA content of 0.1 wt%, the t_c(S), t_c(1/2), and t_c(E) were longer than or similar to those at PDLA content of 0 wt%, probably due to the long t_i and the decreased number of spherulites. This seems to have been caused by free PDLA chains, which did not form stereocomplex crystallites. On the other hand, at PDLA contents of 0.3-3 wt%, the t_c(S), t_c(1/2), and t_c(E) were shorter than or similar to those at PDLA content of 0 wt% for the T_c range below 95 °C and above 125 °C, whereas this inclination was reversed for the T_c range of 100-120 °C. In the non-isothermal crystallization of as-cast or amorphous-made PLLA films during cooling from the melt, the addition of PDLA above 1 wt% was effective to accelerate overall PLLA crystallization. The X-ray diffractometry could trace the formation of stereocomplex crystallites in the melt-quenched PLLA films at PDLA contents above 1 wt%. This study revealed that the addition of small amounts of PDLA is effective to accelerate overall PLLA crystallization when the PDLA content and crystallization conditions are scrupulously selected.