Effects of electrophoretic deposition times and nanotubular oxide surfaces on properties of the nanohydroxyapatite/nanocopper coating on the Ti13Zr13Nb alloy

Load-bearing implants are developed with a particular emphasis placed on an application of ceramic hydroxyapatite coatings in order, to enhance the bioactivity of titanium implants and to shorten the healing time. Therefore, thin, fully crystalline coatings that are, highly adhesive, hydrophilic and demonstrating antibacterial properties are ly looked for. The aim of this research was to develop and characterize the properties of (nano)hydroxyapatite coatings implemented with nanocopper particles and obtained by the electrophoretic method. The deposition was carried out on the Ti13Zr13Nb alloy, either on a bare surface or a nanotubular oxide layer. The deposition was made for 1 or 2 min. The chemical composition, phase composition, coating structure, homogeneity, thickness, nanoindentation and nanomechanical properties, adhesion determined by a nanoscratch test, and wettability measured by a contact angle were investigated. The presence of nanotubular oxide layers caused no significant change in nanoindentation and nanomechanical propertie and an increase in adhesion strength and a decrease in the contact angle. The increase in deposition time resulted in an increased thickness, a decreased hardness, an increased adhesion strength and wettabilty. The observed effects in the composite (nano)HAp/Cu – (nano)TiO₂ coatings are attributed to the change in the structure of coatings following the increasing deposition time and coating thickness.     

Electrophoretic deposition (EPD) of nanohydroxyapatite - nanosilver coatings on Ti13Zr13Nb alloy

Titanium and its alloys are the biomaterials most frequently used in medical engineering, especially as parts of orthopedic and dental implants. The surfaces of titanium and its alloys are usually modified to improve their biocompatibility and bioactivity, for example, in connection with the deposition of hydroxyapatite coatings.The objective of the present research was to elaborate the technology of electrophoretic deposition (EPD) of nanohydroxyapatite (nanoHAp) coatings decorated with silver nanoparticles (nanoAg) and to investigate the mechanical and chemical properties of these coatings as determined by EPD voltage and the presence of nanoAg. The deposition of nanoHAp was carried out at two voltage values, 15 and 30 V. The decoration of nanoHAp coatings with nanoAg was carried out using the EPD process at a voltage value of 60 V and a deposition time of 5 min. The thickness of the undecorated coatings was found to be 2.16 and 5.14 µm for applied EPD voltages of 15- and 30-V, respectively. The release rate of silver nanoparticles into an artificial saliva solution increased with exposure time and EPD voltage. The corrosion current, between 1 and 10 nA/cm², was significantly higher for undecorated nanoHAp coatings and close to that of the substrate for decorated nanoHAp coatings. The hardness of the undecorated nanoHAp coatings obtained at 15 and 30 V of EPD voltage attained 0.2245±0.036 and 0.0661±0.008 GPa, respectively. Resistance to nanoscratching was higher for thicker coatings. The wettability angle was lower for coatings decorated with nanoAg.     

Tribological behaviour of RF-magnetron sputter deposited hydroxyapatite coatings in physiological solution

The aim of the paper is to explore the tribological performance of hydroxyapatite (HA) coatings deposited by radio frequency (RF) magnetron sputtering on AZ31 magnesium alloy (96% Mg, 3% Al, 0.7% Zn, 0.3% Mn) for biomedical applications. In this study, the position of the samples on a substrate holder, relative to a target erosion zone was taken into consideration in order to elucidate its impact on the coating characteristics, such as composition, morphology, surface topography and tribology. Substrate rotation and arc-movement were foreseen in the experimental set-up to increase the uniformity of thin film properties. The deposited HA thin films were revealed to exhibit an increase of the Ca/P ratio from 1.83 to 1.97, a decrease of (002) texture and thickness, as the samples were shifted towards the target erosion zone. By coatings, the roughness of Mg alloy was decreased (R_{a Mg alloy}=31.3 nm; R_{a coating}=29 nm and 21 nm). The coating placed in the centre of the substrate holder showed high hardness and Young's modulus (H =8.3±0.9 GPa; E=89±10 GPa) than the coating prepared under the target erosion zone (H =6.9±1.1 GPa; E=75±6 GPa). The coating deposited under target erosion zone exhibits superior friction behaviour in simulated body fluid environment, with the friction coefficient (μ) of 0.184, while the sample located in the centre of the substrate holder possesses the friction coefficient (0.306) comparable to the AZ31 substrate (0.307). The low wear rate was determined in the case of coating deposited under target erosion zone (4.83×10⁻⁵ mm³ N⁻¹ m⁻¹) than uncoated AZ31 substrate (0.00518 mm³ N⁻¹ m⁻¹) or than coating placed in the centre of the substrate holder (0.00294 mm³ N⁻¹ m⁻¹).     

Comparative study of the hydroxyapatite coatings prepared with/without substrate bias

The aim of this paper is to prepare the hydroxyapatite by Ion Beam Assisted Deposition and to investigate in terms of its elemental and phase composition, roughness and in vitro corrosion resistance. The coatings were prepared with and without applying bias on substrate, in order to find the effect of bias on the chemical, structural, morphological and anti-corrosive properties. The biased coatings exhibited Ca/P ratio closer to the value of the stoichiometric HAP (1.67). The phase composition is not affected by the bias evolution. The adhesion of both coatings is still satisfactory for biomedical applications, irrespective of the bias. Hydroxyapatite deposited without bias presented the best corrosion resistance in SBF at 37 °C, probably due to its smooth surface and low porosity. Moreover, this coating proved to have the highest protection ability at the SBF corrosive attack.     

Nanoindentation study of microplasma sprayed hydroxyapatite coating

The microplasma sprayed (MPS) hydroxyapatite (HAP) coating on surgical grade SS316L, is an emerging material for bio-ceramic based implant application involving higher reliability. For this purpose, a 200 μm thick MPS-HAP coating was developed on SS316L substrate and characterized by XRD, SEM and FE-SEM techniques. The local mechanical properties of the coating, e.g. nano-hardness and Young's modulus were evaluated by nanoindentation technique carried out with a Berkovich indenter at various depths in the range of about 170–3000 nm on a polished top surface. The characteristic values of nano-hardness (1.5–5 GPa) and Young's modulus (∼60–100 GPa) obtained through the application of Weibull statistics to the experimentally measured data revealed a strong indentation size effect (ISE). Attempts were made to explain the genesis of ISE on the basis of some existing and some new concepts.     

In-vitro corrosion inhibition mechanism of fluorine-doped hydroxyapatite and brushite coated Mg–Ca alloys for biomedical applications

Magnesium alloys have received great attention as a new kind of biodegradable metallic biomaterials. However, they suffer from poor corrosion resistance. In this study, Mg–Ca alloy was coated with nano-fluorine-doped hydroxyapatite (FHA), and brushite (DCPD); via electrochemical deposition (ED). Coatings were characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results revealed that nano-fluorine-doped hydroxyapatite coating produced more dense and uniform coating layer, compared to the brushite coating. The compression tests of the ED-coated Mg alloy samples immersed in simulated body fluid for different time periods showed higher yield strength (YS) and ultimate tensile strength (UTS), compared to those of the uncoated samples. The degradation behavior and corrosion properties of the ED-coated Mg alloy samples were examined via electrochemical measurements and immersion tests. The results showed that FHA coating could effectively induce the precipitation of more Ca²⁺ and PO₄³⁻ ions than DCPD coating, because the nanophase can provide higher specific surface area. It was also found that FHA and DCPD coatings can significantly decline the initial degradation rate of the alloy. A corrosion mechanism of the ED-coated alloy is proposed and discussed in this paper.     

Preparation of the reticulated hydroxyapatite ceramics using carbon-coated polymeric sponge with elongated pores as a novel template

This paper proposes a novel, simple way to improve the compressive strength of reticulated porous hydroxyapatite (HA) ceramics using carbon-coated polymeric sponges with elongated pores as a novel template. This template allowed samples to have two interconnected pore networks with a preferential orientation, in which an addition pore network was newly formed by removing the carbon-coated polymeric struts, while preserving the pre-existing pore network. The compressive strength of the sample was as high as 2.9 ± 0.3 MPa with a porosity of 76% when tested parallel to the direction of pore elongation. In addition, the in vitro cell test using a pre-osteoblast cell line revealed the samples to have good biocompatibility.     

Comparative investigation of antibacterial yet biocompatible Ag-doped multicomponent coatings obtained by pulsed electrospark deposition and its combination with ion implantation

The aim of this work is to obtain antibacterial yet biocompatible coatings using pulsed electrospark deposition (PED). For this purpose new composite electrodes were fabricated from reaction mixtures Ti–C–20%Fe-10%Ca₃(PO₄)₂–3.4%Mg–X%Ag with different amount of antibacterial component (X = 0, 0.5, 1.0, 1.5 and 2.0 at% of Ag) using self-propagating high-temperature synthesis method. The electrodes consisted of TiC grains surrounded by TiFe₂ and TiFeP intermetallic matrix, CaO and MgO inclusions, and Ag-based phase. The influence of Ag content on the electrode mass transfer kinetics was studied by comparing the total substrate weight gain and electrode mass loss during PED. The structure, elemental composition, and surface roughness of coatings were studied by means of X-ray diffraction, scanning electron microscopy, and optical profilometry. The coatings were characterized in terms of Ag⁺ ion release, mechanical and electrochemical properties, as well as biocompatibility. The antibacterial characteristics of Ag-doped PED coatings were compared with those obtained by PED using Ag-free electrode and then implanted with Ag⁺ ions. The results indicated that an increase in the Ag content in electrode leads to a decrease in electrode erosion and substrate weight gain, but the efficiency of the PED process increases. Doping with a small amount of Ag (≤ 1 at%) resulted in 100% antibacterial effect against both gram-positive S. aureus and gram-negative E. сoli bacteria. In addition, the dynamics of МС3Т3-Е1 cell proliferation on the surface of PED coatings with 0.6–0.7 at% of Ag was similar to that in control samples, hereby indicating their biocompatibility. The coating biological characteristics were discussed based on the results of Ag⁺ ion release and electrochemical tests.     

Studies on plasma sprayed bi-layered ceramic coating on bio-medical Ti-13Nb-13Zr alloy

Biomedical Ti alloys are prone to undergo degradation due to the combined effect of wear and corrosion. To overcome these problems, surface modification techniques are being used. In this paper, the biomedical Ti alloy Ti-13Nb-13Zr was plasma sprayed with nanostructured Al₂O₃-13 wt%TiO₂, yttria stabilized zirconia powders and bilayer containing alternate layers of the two coatings to improve the corrosion resistance and microhardness of the substrate. The plasma sprayed coatings were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The microstructure, microhardness and surface roughness of the coatings were investigated. The corrosion resistance of the coatings was studied in simulated body conditions. The results show improved corrosion resistance for the bilayered coating compared to the individual plasma sprayed coatings on biomedical Ti-13Nb-13Zr alloy substrate.     

Effects of deposition temperature on the crystallinity of Ba0.5Sr0.5TiO3 epitaxial thin films integrated on Si substrates by pulsed laser deposition method

Epitaxial Ba_0.5Sr_0.5TiO₃ (BSTO) thin films were grown on TiN buffered Si (0 0 1) substrates by PLD method and the effects of deposition temperature on their crystallinity and microstructure were studied. BSTO thin films were prepared with substrate temperature ranging from 350 to 650 °C. The BSTO films grown at below 400 °C showed amorphous phase and the film grown at 450 °C showed mixed phase of crystalline and amorphous, where crystalline phase was observed only at the top surface portion of the film. The BSTO films with fully crystalline phase were obtained in the samples deposited at above 500 °C. The (0 0 l) preferred orientation and the crystallinity of the BSTO films were improved with increasing the temperature. The dielectric constant, measured at 100 kHz and at room temperature, of the BSTO film grown at 650 °C was measured to be as high as 1129.     

Structure of the hydroxyapatite plasma-sprayed coatings deposited on pre-heated titanium substrates

Plasma spraying is the most commonly used thermal spray method for the application of hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂) coatings. In the present study, the HA coatings were plasma spraying deposited onto plates of titanium pre-heated to 20 °C, 300 °C and 550 °C. The obtained HA coatings were investigated by means of X-ray diffraction and scanning electron microscopy. It is found that the coatings, in addition to HA, contain the tetracalcium phosphate (TTCP, (Ca₄(PO₄)₂O) phase (~10%) and a small amount of CaO (<2%). Crystal structure of HA in the coatings is revealed to be distorted. The PO4 tetrahedrons are deformed (Baur distortion coefficient D1(TO) ~0.2). The distances Ca1-O1 and Ca1-O2 are changed as compared to these in stoichiometric hydroxyapatite. These distortions are considered as a result of internal stresses, which are demonstrated in the broadening of peaks on X-ray diffraction pattern of HA. Microstructure of coatings consisting of flattened splats was formed by fully molten particles. The axial base texture was developed in the coatings. Ultrastructure is columnar with a preferred orientation of c-axes of the crystals parallel to the normal of plane coating n. The heating of substrate has a marked effect on the ultrastructure of coatings: the domain size increases from 790 to 1100 Å, the strain Δ decreases from 1.6·10^-3 to 1,2·10^–3, TTCP content diminishes from 12% to 7%. These results show that the effects due to heating of the substrate may be associated with partial recovery of HA microstructure.     

Preparation of manganese oxide - graphite electrodes by electrophoretic deposition

Manganese oxide is a promising active material for supercapacitors (SCs) with pseudocapacitance due to its high capacitance and its environmentally friendly character. This paper deals with the preparation of electrodes for supercapacitors consisting of manganese oxide supported onto graphite by electrophoretic deposition. Manganese oxide powders were characterized and dispersed in water by controlling the colloidal and rheological behavior in order to obtain stable suspensions. Optimized manganese oxide suspensions were deposited onto graphite electrodes by electrophoretic deposition. The deposited mass per unit area in the electrodes was optimized by controlling the applied current density and the deposition time. It has been demonstrated that the introduction of a binder helped to improve the adherence to graphite; otherwise the deposit thickness obtained by EPD is limited and no films can be obtained by simply dipping. These conditions allowed us to obtain more homogeneous deposits with higher specific energy than without binder.     

Microscopic and spectroscopic evidences for multiple ion-exchange reactions controlling biomineralization of CaO.MgO.2SiO2 nanoceramics

This study is focused on the mechanism of in vitro biomineralization on the surface of CaO.MgO.2SiO₂ (diopside) nanostructured coatings by scanning electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma spectroscopy assessments. A homogeneous diopside coating of almost 2 µm in thickness was deposited on a medical-grade stainless steel by coprecipitation, dipping and sintering sequences. After soaking the sample in a simulated body fluid (SBF) for 14 days, a layer with the thickness of 8 µm is recognized to be substituted for the primary diopside deposit, suggesting the mineralization of apatite on the surface. Investigations revealed that the newly-formed layer is predominantly composed of Ca, P and Si, albeit with a biased accumulations of P and Si towards the surface and substrate, respectively. The variations in the ionic composition and pH of the SBF due to the incubation of the sample were also correlated with the above-interpreted biomineralization. In conclusion, the multiple ion-exchange reactions related to Ca, Mg, Si and P were found to be responsible for the in vitro bioactivity of nanodiopside.     

Two-step modification process to improve mechanical properties and bioactivity of hydroxyfluorapatite scaffolds

Porous ceramic scaffolds are synthetic implants, which support cell migration and establish sufficient extracellular matrix (ECM) and cell-cell interactions to heal bone defects. Hydroxyapatite (HA) scaffolds is one of the most suitable synthetic scaffolds for hard tissue replacement due to their bioactivity, biocompatibility and biomimetic features. However, the major disadvantages of HA is poor mechanical properties as well as low degradability rate and apatite formation ability. In this study, we developed a new method to improve the bioactivity, biodegradability and mechanical properties of natural hydroxyfluorapatite (HFA) by applying two-step coating process including ceramic and polymer coats. The structure, morphology and bioactivity potential of the modified and unmodified nanocomposite scaffolds were evaluated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS). The scaffold with optimized mechanical properties was HFA-30?wt%HT (HT stands for hardystonite) with a total porosity and pore size of 89?±?1 and 900–1000?µm, respectively. The compressive modulus and strength of HFA (porosity ~ 93?±?1) were improved from 108.81?±?11.12–251.45?±?12.2?MPa and 0.46?±?0.1–1.7?±?0.3?MPa in HFA-30?wt%HT sample, respectively. After applying poly(ε-caprolactone fumarate) (PCLF) polymer coating, the compressive strength and modules increased to 2.8?±?0.15 and 426.1?±?15.14?MPa, respectively. The apatite formation ability of scaffolds was investigated using simulated body fluid (SBF). The results showed that applying the hardystonite coating improve the apatite formation ability; however, the release of ions increased the pH. Whereas, modified scaffolds with PCLF could control the release of ions and improve the apatite formation ability as well.     

Porous boron nitride nanofibers/PVA hydrogels with improved mechanical property and thermal stability

Polyvinyl alcohol (PVA) hydrogel is a promising material possessing good chemical stability, high water absorption, excellent biocompatibility and biological aging resistant. However, the poor mechanical performance of PVA hydrogel limits its applications. Here we report the utilization of one-dimensional (1D) BN nanofibers (BNNFs) as nanofillers into PVA matrix to prepare a novel kind of BNNFs/PVA composite hydrogel via a cyclic freezing and thawing method. For comparison, the composite hydrogels using spherical BN nanoparticles i.e. BN nanospheres (BNNSs) as fillers were also prepared. The mechanical properties, thermal stabilities and swelling behaviors of the composite hydrogels were investigated in detail. Our study indicates that the mechanical properties of the hydrogels can be improved by adding of BNNFs. After loading of BNNFs into PVA with content of 0.5?wt%, the compressive strength of the composite hydrogel increases by 252% compared with that of pure PVA hydrogel. The tensile performance of BNNFs/PVA composite hydrogels has also been improved. Impressive 87.8% increases in tensile strengths can be obtained with 1?wt% BNNFs added. In addition, with the increase of BNNFs content, the thermal stability and the swelling ratio of hydrogels are increased gradually. The swelling ratio of hydrogel increases by 56.3% with only 1?wt% BNNFs added. In comparison, the improvement effects of the BNNS fillers on the mechanical strengths and swelling ratios are much weaker. The enhanced effects of BNNFs can be ascribed to the strong hydrogen bond interaction between BNNFs and PVA. The high aspect ratios of the nanofibers should also be took into account.     

Study of the friction, adhesion and mechanical properties of single crystals, ceramics and ceramic coatings by AFM

This paper reviews commonly used methods of analyzing and interpreting friction, adhesion and nanoindentation with an AFM tip test data, with a particular emphasis of the testing of single crystals, metals, ceramics and ceramic coatings. Experimental results are reported on the friction, mechanical and adhesion properties of these materials.The popularity of AFM testing is evidenced by the large quantity of papers that report such measurements in the last decade. Unfortunately, a lot of information about these topics is scare in the literature. The present paper is aimed to present the basic physical modelling employed and also some examples using each technique.     

Characterization and properties of microarc oxidized coatings containing Si, Ca and Na on titanium

To form bioactive microarc oxidized (MAO) coatings on titanium, the exploration for introducing various elements into the TiO₂-based MAO coatings has been continually noticed. In this work, novel MAO coatings containing Si, Ca and Na (SCN) elements were prepared on titanium. The elemental composition, mechanical properties, corrosion resistance and apatite-forming ability of TiO₂-based MAO coatings containing SCN were investigated. The surface hardness, elastic modulus, elastic recovery and corrosion resistance of the MAO coatings containing SCN were improved obviously by increasing the applied voltages. And the effect of applied voltage on the wetting ability of MAO coatings containing SCN is not significant. The current results indicated that the MAO coating containing SCN possesses good apatite-forming ability. The apatite-bonding structure is highly dependent on the chemical reactivity of the materials surface in simulated body fluid.     

Properties of calcium phosphates ceramic composites derived from natural materials

In this study, ceramics containing mixed phases of hydroxyapatite/beta-tricalcium phosphate (HA/β-TCP) were fabricated by a solid-state reaction technique. The HA powder was synthesized from cockle shells while the β-TCP powder was synthesized from egg shells. Pure HA and β-TCP fine powders were successfully obtained. The HA and β-TCP were mixed and subjected to a thermal treatment up to 1100 °C. To form the mixed phase ceramics, the resulting powders were sintered at 1350 °C. Effects of HA concentration on the properties of the studied ceramic were investigated. X-ray diffraction analysis revealed that all samples presented multiphase of calcium phosphate compounds. Average grain size of the ceramics decreased with the HA additive content. The 75 wt% HA ceramic showed the maximum hardness value (5.5 GPa) which is high when compared with many calcium phosphate ceramics. In vitro bioactivity test indicated that apatite forming increased with the HA additive content. To increase antibacterial activity, selected ceramics were coated with AgNO₃. Antibacterial test suggested that an Ag compound coating on the ceramics could improve the antibacterial ability of the studied ceramics. In addition, the antibacterial ability for the Ag coated ceramics depended on the porosity of the ceramics.     

Biomineralization,strength and cytocompatibility improvement of bredigite scaffolds through doping/coating

Coprecipitation-derived, sacrificial polymeric (urethane) foam-fabricated bredigite (Ca₇MgSi₄O₁₆) scaffolds were processed by individual and combined treatments of fluoride doping and poly (lactic-co-glycolic acid) (PLGA) coating and then studied in terms of structure, mechanical strength, bioactivity and cell biocompatibility in vitro. According to scanning electron microscopy and Archimedes porosimetry, the geometrical characteristics of pores for all the scaffolds are in the appropriate range for hard tissue regeneration applications. The apatite-formation ability of the samples immersed in a simulated body fluid is improved by doping for both the bare and coated conditions, based on microscopic and energy-dispersive X-ray spectroscopic analyses. Both the treatments advantageously buffer physiological pH changes imposed due to the fast bioresorption of the ceramic. Also, the biodegradable PLGA coating typically enhances the compressive strength of the scaffolds, which is critical for bone tissue engineering. In accordance with the MTT assay on osteoblast-like cells (MG-63) cultures, both the processes individually enhance the cell viability, while the highest improvement is obtained for the combined application of them. It is finally concluded that fluoride doping and PLGA coating are impressive approaches to improve the bioperformance of bredigite-based scaffolds.