Synthesis,characterization and in-vitro biocompatibility of electrophoretic deposited europium-doped calcium silicate on titanium substrate

Europium (Eu) has attracted attention to be incorporated as biologically active ions to achieve different biological and functional properties of biomaterials. In this study, calcium silicate (CS) coatings doped with different amount of Eu (up to 10 mol%) were successfully formed on titanium substrates via electrophoretic deposition. A low amount of Eu (2.5 mol%) gave a relatively denser coating and improved coating adhesion strength (～3.3 N). All Eu–CS coatings provided good apatite forming ability, yet lower degradation rate, as compared to CS coating. Moreover, it was observed that the human fetal osteoblast (hFOB) cells could attach and proliferate on all Eu–CS coatings, suggesting their biocompatible nature. Eu2.5CS not only showed comparable cell proliferation with CS, but also enhanced the osteogenic activity of the CS coating. All results suggested that Eu2.5CS coatings are promising coating materials for biomedical implants, particularly bone tissue engineering applications.     

Magnetic and microwave absorptive properties of electrophoretically deposited nano-CoFe2O4 as a 3D structure on carbon fibers

Cobalt ferrite nanoparticles were successfully deposited on carbon fibers as a 3D structure using electrophoretic method to study magnetic and microwave absorption properties. Three well stabilized suspensions from cobalt ferrite nanoparticles were prepared in acetone, ethanol and acetone-ethanol media: and iodine was used as a stabilizing agent. Constant voltage and time were taken into account to investigate their influence on coating morphology and thereafter microwave absorption property. Field-Emission Scanning Electron Microscopy, Differential Thermal Analysis and X-ray Diffractometer were employed to study morphology, thermal behavior and structure of powder, respectively. To investigate magnetic and reflection loss properties, Vibrating Sample Magnetometer and Vector Network Analyzer were used. Particle size distribution and zeta potential was obtained by Dynamic Light Scattering device. It was observed that by optimizing voltage amount and time to 25 V and 6 min, respectively; uniformity of coating was improved and this led to the highest attenuation of −10.25 dB in vicinity of 8–12 GHz.     

Signal amelioration of electrophoretically deposited whole-cell biosensors using external electric fields

This paper presents an integrated whole-cell biochip system where functioning cells are deposited on the solid micro-machined surfaces while specially designed indium tin oxide electrodes that can be used to apply controllable electric fields during various stages; for example during cell deposition. The electrodes can be used also for sensing currents associated with the sensing mechanisms of electrochemical whole-cell biosensors. In this work a new approach integrating live bacterial cells on a biochip using electrophoretic deposition is presented. The biomaterial deposition technique was characterized under various driving potentials and chamber configurations. An analytical model of the electrophoretic deposition kinetics was developed and presented here. The deposited biomass included genetically engineered bacterial cells that may respond to toxic material exposure by expressing proteins that react with specific analytes generating electrochemically active byproducts. In this study the effect of external electric fields on the whole-cell biochips has been successfully developed and tested. The research hypothesis was that by applying electric fields on bacterial whole-cells, their permeability to the penetration of external analytes can be increased. This effect was tested and the results are shown here. The effect of prolonged and short external electric fields on the bioelectrochemical signal generated by sessile bacterial whole-cells in response to the presence of toxins was studied. It was demonstrated that relatively short 10 ms external DC electric pulse improves the performance of bacterial biosensors by 15% relative to un-biased biosensors. The application of prolonged 1 h external alternating electric fields deteriorated the whole-cell performance in the presence of toxins. In this paper we present the electrode apparatus and methods, as well as the characterization results, e.g. signal vs. time and induction factor, of such chips and discussing the highlight and problems of this new concept.     

Influence of processing parameters on the surface quality of electrophoretically deposited alumina coatings on foam ceramics

Previous work showed that the electrophoretic deposition of coatings with aligned pore channels is technically feasible on Al₂O₃-C foams. In the next step, the amount and size of cracks in the sintered coatings should be reduced. The study revealed the drying conditions, alumina raw materials used, the chemistry of the foam skeleton and the sintering conditions as significant influences. The best drying procedure was freeze drying after sudden freezing in liquid nitrogen. Three alumina raw materials with different particle size distributions were tested with regard to linear shrinkage, number of cracks and number of channel-like pores. The CT 9 and CL 370 showed a low number of cracks, however CT 9 possessed almost no pores. The Al₂O₃-C foam skeletons electrophoretically coated with CL 370 and sintered at 1600 °C in air showed the best results with a low number of small cracks and high number of channel-like pores.     

A comparative study of direct and indirect evaluation of piezoelectric properties of electrophoreticaly deposited (Ba,Ca) (Zr,Ti)O3 lead-free piezoceramics

The development and optimisation of piezoceramics are targeted usually to enhance their piezoelectric properties evaluated by both the direct or indirect measurement methods. The presented work aims to elaborate on the correlation of one direct (Berlincourt) and two indirect (convert and field-dependent) piezoelectric measurement methods on various material states. The role of the ceramic powder treatment by ball milling and electrophoretic deposition (EPD) technique on the determined electric properties as well as basic physical and mechanical properties of (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ceramics (BCZT) was investigated. It was found that the EPD technologically supported by milling allows obtaining thick and dense deposits (>2 mm). After sintering, the BCZT ceramics with a relative density of >95%, hardness in the range of 2.3–2.9 GPa and piezoelectric coefficients of d₃₃* = 940 pm/V, d_33(E=0) = 427 pm/V and d₃₃ = 364 pC/N can be achieved. Reported results also suggest that indirect (field-dependent) and direct (Berlincourt) measurements of the piezoelectric coefficients can be comparable at optimal poling conditions.     

Constrained sintering and thermal ageing behaviour of electrophoretically deposited Yb2Si2O7 environmental barrier coating

The oxidation of SiC and the formation of a thermally grown oxide layer (TGO) limit the lifetime of environmental barrier coatings. Thus, this paper focuses on the deposition of denser Yb₂Si₂O₇ coatings using electrophoretic deposition to reduce the TGO growth rate. The findings showed densification for Yb₂Si₂O₇ can be achieved with an optimized sintering profile (heating/cooling rate, temperature, and time). However, the addition of 1.5 wt% of Al₂O₃ to Yb₂Si₂O₇ promoted densification and lowered the required sintering temperature, 1380 °C using 2 °C/min heating/cooling rate for 10 h provided efficient coating density. Moreover, adding Al₂O₃ reduced the TGO growth rate by more than 70 % compared to the Al₂O₃-free coatings, without cracking in TGO after 150 h of thermal ageing at 1350 °C. Results within this study suggest electrophoretic deposition with Al₂O₃ addition produces promising Yb₂Si₂O₇ environmental barrier coatings on SiC substrate with low oxidation rates and increased lifetime.     

Microstructure and mechanical properties of continuous carbon fiber-reinforced ZrB2-based composites via combined electrophoretic deposition and sintering

A process combining electrophoretic deposition (EPD) with hot pressing (HP) was developed to fabricate continuous carbon fiber-reinforced ZrB₂-based composites (C_f/ZrB₂-based composites). ZrB₂-based ultra-high temperature ceramic (UHTC) particles were uniformly pre-coated on continuous carbon fibers via EPD. Then, the UHTC-coated carbon fibers were stacked and hot pressed to prepare the C_f/ZrB₂-based composites. Microstructure observations revealed that almost no micro-pores were found in the inter-bundle and intra-bundle regions of fibers after HP. The flexural strength, fracture toughness and the work of fracture of the C_f/ZrB₂-based composite were measured as 199 ± 26 MPa, 6.71 ± 1.29 MPa·m^1/2, and 754 ± 58 J/m², respectively. Based on the observations of non-brittle fracture behavior, fractured morphology and crack propagation, the enhanced fracture properties were mainly attributed to the multiple toughening mechanisms, such as fiber pull-out, fiber bridging, crack deflection and branching along the interfaces.     

Fabrication of biphasic calcium phosphates nanowhiskers by reflux approach

Nanowhiskers of biphasic calcium phosphates composed of monetite/hydroxyapatite were fabricated using a cost-effective reflux hydrothermal approach from calcium nitrate and ammonium hydrogen phosphate precursors in presence of urea. The produced nanowhiskers were characterized using, FT-IR-spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron micrograph (TEM) and BET surface area determination. The major phase in Biphasic was (monetite, CaHPO₄.) and their grown crystals were morphologically formed with irregular sizes of well defined rod or whiskers crystal structure. The specific surface area of these fabricated nanowhiskers was found to be 8.48?m²/g according to BET studies. The N₂ adsorption/desorption isotherm of the as prepared monetite calcium phosphate is of type IV indicating that this material has a mesoporous structure. The produced nanowhiskers had 80% of monetite and 20% is hydroxyapatite. By controlling the parameters of the reflux approach it is possible to manipulate the composition and the size of these produced nanowhiskers.     

Structural changes of hydroxyapatite coating electrophoretically deposited on NiTi shape memory alloy

The surface of the NiTi shape memory alloy was functionalized through the deposition of hydroxyapatite (HAp) coatings using the electrophoretic method (EPD). The electrophoresis carried out at the voltage of 40?V during the time of 120?s did not affect the crystalline structure of the initial HAp powder and, at the same time, ensured obtaining a homogeneous layer without visible cracks or discontinuities. Next, the coatings were subjected to heat treatment at 800?°C for 2?h in vacuum, wherein the applied conditions did not affect the decomposition of the deposited hydroxyapatite. The heat treatment resulted in the formation of carbonate apatite (C-HAp) in the HAp layer and in ceramic particles’ coalescence. Changes in the morphology and roughness of the layer as well as partial decomposition of the NiTi substrate parent phase into Ti₂Ni and Ni₄Ti₃ phases were also observed.     

Enhancing mechanical and biological properties of biphasic calcium phosphate ceramics by adding calcium oxide

There is a big challenge to achieve a balance between mechanical characteristics and biological properties in biphasic calcium phosphate (BCP) ceramics. The present study investigated the effects of calcium oxide (CaO) addition on the sintering behaviors and biological performances of BCP ceramics. The characterizations of surface structure, phase composition and crystal structure demonstrated that the addition of CaO could stabilize calcium-deficient hydroxyapatite (CDHA) phase and reduce grain size in BCP ceramics, so as to better mimic chemical composition and crystal structure of the natural bony minerals. Mechanical tests indicated that the addition of CaO could increase the compressive strength, flexural strength and fracture toughness of BCP ceramics, because of the enhanced crack deflection associated with a transgranular to intergranular cracking. Due to high content of CDHA phase, small grain size and slightly alkali environment, BCP ceramics with appropriate amount of CaO addition (2%) could promote the spreading and osteogenic differentiation of BMSCs. The strong bone-like apatite formation ability predicted a good osteoinductive potential of BCP ceramics with CaO addition. In summary, these findings suggest that the addition of CaO offers a promising strategy for design and fabrication of BCP ceramics with superior mechanical and biological properties.     

Calcium phosphates of biological importance based coatings deposited on Ti-15Mo alloy modified by laser beam irradiation for dental and orthopedic applications

Ti-15Mo alloy samples were irradiated by pulsed Yb:YAG pulsed laser beam under air and atmospheric pressure. Sequentially, calcium phosphate coatings were deposited on the irradiated surfaces by the biomimetic method. The formation of calcium phosphates (CaP) under biological medium and SBF (Synthetic/Simulated Body Fluid) occurs in the presence of Ca²⁺ and PO₄^3- ions, as well as ions such as: Mg^2+, HCO₃^-, K⁺ and Na⁺, which facilitates the mimicking of the biological process. The biomimetic calcium phosphates-based surfaces were submitted to heat treatment conditions at 350?°C and 600?°C. The present study correlates four conditions of fluency (1.91, 3.17, 4.16 and 5.54?J/cm², respectively) as established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric (TiO₂₎ and non-stoichiometric titanium oxides (TiO, Ti₃O, Ti₃O₅ and Ti₆O) with different oxide percentages depending on the fluency applied. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The morphological and physico-chemical analysis indicated the formation of a multiphase coatings depending on the heat treatment temperature performed to 350?°C (ACP1–2, CDHA, HA phases) and 600?°C (CDHA, HA and β-TCP phases). It is worth noting multiphasic bioceramic systems has been gaining attention for biomedical applications. The laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in clinical applications.     

Inorganic cements for biomedical application: calcium phosphate,calcium sulphate and calcium silicate

Inorganic cements have found utility in tissue replacement since the late nineteenth century, one of the first examples being calcium sulphates in the augmentation of bone defects. In the intervening period of time countless formulations of calcium phosphate, sulphate and silicate cement have been researched and as a result, many are now commercially available for a variety of biomedical applications. This review summarises the applications, formulations, advantages and drawbacks of such inorganic cements, suggesting future work that will drive progress in this area into the future of biomaterials research.     

Effects of suspension properties on the fabrication of Yb2Si2O7 coatings using electrophoretic deposition

This study examines the electrophoretic deposition of Yb₂Si₂O₇ particles on SiC substrates to produce Environmental Barrier Coatings. To prepare crack-free and homogeneous green coatings, the effect of the solvent, dispersant concentration, and pH were investigated. Ethanol provided a well-dispersed suspension and crack-free coating which was shown by sedimentation tests and microstructure analysis. The effect of the dispersant concentration was investigated with zeta potential measurement and microstructure analysis with a concentration above 0.5 g/L resulting in higher ionic strength and producing cracked and uneven coatings. The ionic strength was also associated with the powder packing density with larger indentation impressions measured for loosely packed coatings. The deposition rate depended on the suspension properties influenced coating integrity with delamination evidenced by analysing the current density drop during deposition. Sintering of the green coatings having different densities and microstructure showed their importance in the preparation of uniform and dense sintered coatings.     

Evaluation of ascorbic acid-loaded calcium phosphate bone cements: Physical properties and in vitro release behavior

In this study, different concentrations of ascorbic acid (50, 100 and 200 µg/mL) were added to the liquid phase of a calcium phosphate cement (CPC). The cements were immersed in simulated body fluid (SBF) for different intervals and physical, physicochemical and mechanical properties of them were evaluated. The release of added ascorbic acid from CPCs into the SBF solution was also studied. From the results, both setting time and injectability of CPC decreased by adding ascorbic acid, however the compressive strength was sharply increased before soaking in SBF solution. But, the compressive strength values of all cements (with or without ascorbic acid) soaked in SBF solution for more than 7 d duration were comparable. The X-ray diffractometry results showed that in vitro apatite formation ability of cement reactants did not change by adding ascorbic acid. The scanning electron microscopy images indicated that morphology of the formed apatite crystals was nano-needlelike and needle diameter was less than 100 nm. The loaded ascorbic acid was slowly released from CPC into the SBF solution so that about 10% and 20% of the loaded drug was released after 504 h for the cements containing 100 and 200 µg/mL ascorbic acid, respectively. The release rate was increased when the amount of added ascorbic acid decreased by 50 µg/mL.     

Morphological, structural and electrochemical properties of lithium iron phosphates synthesized by Spray Pyrolysis

In the field of materials for lithium ion batteries, the lithium iron phosphate LiFePO₄ has been proven for use as a positive electrode due to its good resistance to thermal degradation and overcharge, safety and low cost. The use of nanostructured materials would improve its efficiency. This work shows the results of the synthesis of nanostructured materials with functional properties for lithium batteries through aerosol techniques. The Spray Pyrolysis method allows synthesizing nanostructured particles with spherical geometry, not agglomerates, with narrow distribution of particle size and homogeneous composition in respect to a precursor solution. Experimental techniques were focused on the morphological (SEM and TEM), structural (XRD and HRTEM-SAED), chemical (EDS) and electrochemical characterization.     

Gelcasting and sintering of hydroxyapatite materials: Effect of particle size and Ca/P ratio on microstructural,mechanical and biological properties

The sintering behaviour and microstructural evolution of two batches of a commercial calcium-deficient hydroxyapatite powder were investigated. First, the sintered density as a function of the starting particle size distribution was studied, and the minimum particle size to get the desired target density was determined. Then, as the two batches were characterized by a slight difference in Ca/P ratio, the role of such ratio on phase and microstructural evolutions during sintering, as well as on mechanical and biological properties was investigated.It was observed that the powder with lower Ca/P ratio underwent significant hydroxyapatite (HA) to β-tricalcium phosphate (β-TCP) decomposition, with a simultaneous formation of tetracalcium phosphate (TTCP). The microstructure of sintered gelcast samples evolved during isothermal sintering at 1300 °C, moving from a starting homogeneous and narrow grain size distribution to a bimodal distribution after 3 h sintering. In fact, over time, large grains decomposed into smaller ones, finally providing a microstructure composed of coarse grains surrounded by plenty of ultra-fine grains. On the contrary, the powder with the higher Ca/P ratio provided a limited HA to β-TCP transformation, and normal grain growth by increasing the sintering time. Such differences lead to different mechanical properties for gelcast samples produced by the two powder batches, as the material with the lower Ca/P ratio affected by lower mechanical strength. Finally, sintered samples from both powders showed in-vitro bioactivity, with a larger surface coverage observed for the lower Ca/P ratio material. The morphology of the apatite layer seemed to be affected by the material composition, too, showing flake-like and needle-like morphologies depending on the Ca/P ratio of the starting powder.     

Electrophoretic deposition of ZnCo2O4 spinel and its electrocatalytic properties for oxygen evolution reaction

In this paper, ZnCo₂O₄ was deposited on nickel substrate by electrophoretic deposition (EPD) method as electrocatalyst for the oxygen evolution reaction. The effect of electrophoresis variables including the deposition time, the applied voltages was discussed. XRD, SEM, and electrochemical measurement techniques were used to characterize the deposit and ZnCo₂O₄/Ni electrode. Compared with the ZnCo₂O₄ electrode prepared by nitrate decomposition method, the electrophoretic ZnCo₂O₄ electrodes exhibit better electrocatalytic properties and higher mechanical stability. And the electrode prepared at 10 V for 5 min has the best electrocatalytic properties with the overpotential of only 0.203 V at current density of 100 mA cm⁻².     

Apatitic calcium phosphates used in compression: rationalization of the end-use properties

Different apatitic calcium phosphates used as direct compression excipients have been developed in the last years. The difficulty to obtain reproducible synthesis explains their approximative and irregular composition. TRI-TAB® commercial grade called anhydrous tricalcium phosphate is associated to a chemical formula corresponding to a mixture of tricalcium phosphate (Ca₃(PO₄)₂) and calcium hydroxide (Ca(OH)₂). The chemical analysis shows that it is hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂).

The purpose of this work is to rationalize the chemical and physical natures of apatitic calcium phosphates used in direct compression, and thus their technological properties. Apatitic calcium phosphates differing in their Ca/P molar ratio (from 1.500 i.e. tricalcium phosphate to 1.667 i.e. hydroxyapatite) have been synthesized and their compression properties have been analysed. The results have been compared to those of TRI-TAB®. They pointed out the importance of the chemical nature contribution. Tricalcium phosphate-based materials exhibited an excellent compactibility when not calcined. Uncalcined hydroxyapatite had similar properties than TRI-TAB®, that is intermediate. Calcined tricalcium phosphate and hydroxyapatite showed a low compaction ability. It appears that the perfect chemical and physical control of the material is important in particle design to rationalize and optimise the tablet formulation as well as the process.     

Improving mechanical properties of porous calcium phosphate scaffolds by constructing elongated gyroid structures using digital light processing

The present study reports the manufacturing of a novel type of porous calcium phosphate scaffolds with elongated gyroid structures using digital light processing (DLP), in order to offer significantly enhanced mechanical properties. In particular, solid camphor was employed as the diluent, in order to offer sufficiently low viscosity at high solid loading for conventional layer-by-layer DLP process. Four types of porous CaP scaffolds with different percent elongation (%EL = 0, 20, 40, and 60) were manufactured, and their porous structures and mechanical properties were characterized. All porous CaP scaffolds showed that CaP walls were elongated along the z-direction, while the degree of pore elongation increased with an increase in the designed %EL. Owing to the use of controlled processing parameters, such as layer thickness and exposure time for layer-by-layer photocuring process, and carefully designed debinding process, the photocured layers could be completely bonded together with high densification after sintering at 1,200 °C for 3 h. Such elongation of a gyroid structure offered significantly enhanced mechanical properties ? compressive strengths of 4.33 ± 0.26 MPa and 11.51 ± 1.75 MPa were obtained for the porous CaP scaffold with the %EL of 0 and 60, respectively.     

Pressure dependent mechanical properties of calcium carbides

The mechanical properties of newly synthesized Ca₂C₃ and Ca₂C under pressure have been studied by using the first-principles calculations with generalized gradient approximation. The equilibrium geometry, elastic stiffness constants, various moduli, and Pugh's ratio of the C2/m phase of Ca₂C₃ and the C2/m and Pnma phases of CaC₂ are systematically studied. The elastic stiffness constants of C2/m-Ca₂C₃ under 0–30GPa, C2/m-Ca₂C under 0–7.5 GPa, and Pnma-Ca₂C under 7.5–30 GPa satisfy the Born?Huang mechanical criteria. The three phases of calcium carbides exhibit ductile characteristics. The surface constructions of bulk and Young's moduli illustrate the mechanical anisotropy of Ca₂C₃ and Ca₂C. Our results are consistent with previously obtained experimental and theoretical data and have significant implications for the application of calcium carbides.