The Chemical and Biological Properties of Nanohydroxyapatite Coatings with Antibacterial Nanometals,Obtained in the Electrophoretic Process on the Ti13Zr13Nb Alloy

The risk of an early inflammation after implantation surgery of titanium implants has caused the development of different antimicrobial measures. The present research is aimed at characterizing the effects of nanosilver and nanocopper dispersed in the nanohydroxyapatite coatings, deposited on the Ti13Zr13Nb alloy, and on the chemical and biological properties of the coatings. The one-stage deposition process was performed by the electrophoretic method at different contents of nanomaterials in suspension. The surface topography of the coatings was examined with scanning electron microscopy. The wettability was expressed as the water contact angle. The corrosion behavior was characterized by the potentiodynamic technique. The release rate of copper and silver into the simulated body fluid was investigated by atomic absorption spectrometry. The antibacterial efficiency was evaluated as the survivability and adhesion of the bacteria and the growth of the biofilm. The cytotoxicity was assessed for osteoblasts. The results demonstrate that silver and copper increase the corrosion resistance and hydrophilicity. Both elements together effectively kill bacteria and inhibit biofilm growth but appear to be toxic for osteoblasts. The obtained results show that the nanohydroxyapatite coatings doped with nanosilver and nanocopper in a one-stage electrophoretic process can be valuable for antibacterial coatings.     

A comparative study on the synthesis and properties of suspension and solution precursor plasma sprayed hydroxyapatite coatings

In the present study, hydroxyapatite (HAp) coatings were deposited on Ti-6Al-4V alloy by solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) processes and the properties of the coatings were compared. The feedstock powder for SPS method was prepared by coprecipitation technique and characterized for phase and morphology. The obtained HAp coatings were characterized by X-ray diffractometry, Raman spectroscopy and FT-IR spectroscopy. The biocompatibility of the coatings was evaluated using osteoblast like cells. Both the SPS and SPPS hydroxyapatite coatings exhibited similar crystallinity. Interestingly, the HAp-SPS coating showed marginally higher biocompatibility compared to HAp-SPPS and control samples. The wear and corrosion behavior of these coatings was also studied in Hanks' medium. The hydroxyapatite coating fabricated from SPS technique exhibited better corrosion and wear resistance compared to SPPS coating.     

Effect of suspension medium on the electrophoretic deposition of hydroxyapatite nanoparticles and properties of obtained coatings

The suspensions of hydroxyapatite (HA) nanoparticles were prepared in different alcohols. The zeta potential of HA nanoparticles was the highest in butanolic suspension (65.65 mV) due to the higher adsorption of RCH₂OH₂⁺ species via hydrogen bonding with surface P3OH group of HA. Electrophoretic deposition was performed at 20 and 60 V/cm for different times. Deposition rate was faster in low molecular weight alcohols due to the higher electrophoretic mobility of HA nanoparticles in them. The coating deposited from butanolic suspension had the highest adhesion strength and corrosion resistance in SBF solution at 37.5 °C. The surface of this coating was covered by apatite after immersion in SBF solution for 1 week.     

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.     

Porous hydroxyapatite scaffolds produced by the combination of the gel-casting and freeze drying techniques

A technique combining gel-casting and freeze drying methods is introduced to prepare porous hydroxyapatite scaffolds which allow for better control of the scaffold microstructure and have improved mechanical properties. A monomeric system which is known to be a suitable gelling agent for setting ceramic suspensions into dense forms was selected to produce ceramic foams. Different concentrations of sodium lauryl sulphate solution were added into the hydroxyapatite gel suspension as a pore former. The effect of the solid content on the mechanical properties of the scaffold was also investigated. Rapid freezing with liquid nitrogen was performed according to the freeze drying technique and the porous structure and morphology of the scaffolds were analyzed by scanning electron microscopy. The mechanical properties of the hydroxyapatite scaffolds were determined by testing compressive strength using a universal testing machine. The prepared scaffolds were characterized by well-defined pore connectivity along with directional, uniform and completely open porosity. The maximum compressive strength of about 17?MPa obtained from the suspension consisted of 50% solid content with 20% concentration of sodium lauryl sulphate solution. The results show that sodium lauryl sulphate solution plays a significant role in changing the pore structure of hydroxyapaite scaffolds in systems having high solid content.     

Effect of pH and carbon nanotube content on the corrosion behavior of electrophoretically deposited chitosan–hydroxyapatite–carbon nanotube composite coatings

In the first stage, chitosan (CH)–hydroxyapatite (HA)-multiwalled carbon nanotube (MWCNT) composite coatings were synthesized by electrophoretic deposition technique (EPD) on 316L stainless steel substrates at different levels of pH and characterized by X-ray diffraction (XRD), Raman spectroscopy, FTIR and field emission scanning electron microscopy (FESEM). A smooth distribution of HA and MWCNT particles in a chitosan matrix with strong interfacial bonding was obtained. In the next stage, effects of pH and MWCNT content of the suspension on the corrosion behavior and deposition mechanism were studied. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) curves revealed that increasing pH level of the suspension increases the corrosion protection properties of the deposited composite coating in simulated body fluid (SBF). Furthermore, Nyquist plots showed that increasing MWCNT content of the suspension resulted in higher amounts of R_p, but because of the capillary properties of MWCNTs and degradability of the chitosan matrix, corrosion protection level of the coatings containing HA–CH–MWCNT was lower than those of coatings containing solely HA–CH. Amperometric curves in different pH levels of the suspension revealed that the system is diffusion controlled at elevated pH values.     

A study of the electrophoretic deposition of bioactive glass-chitosan composite coating

Bioactive glass is coated on implant's surface to improve corrosion resistance and osseointegration, when placed in the body. Bioactive glass particles were synthesized through a sol-gel process and deposited along with chitosan to form a composite coating on a stainless steel substrate using electrophoretic deposition technique. Stable suspensions of chitosan-bioactive glass were prepared using bioactive glass particles (<1 μm) and 0.5 g/l chitosan solution. The influence of ethanol-water ratio on deposition yield was investigated. For all process conditions, best results were achieved with suspension of 30 vol% water in ethanol-water containing 2 g/l bioactive glass. FTIR studies showed that chitosan was absorbed on ceramic particle surface via hydroxyl and amid bonds. In order to evaluate the coating, its structure and electrochemical properties were studied. It was concluded that increasing the process voltage led to an increase in particle size and porosity, but induced cracks in the coating. In the presence of the polymer-bioactive glass coating, current density in artificial saliva was decreased by 52% and corrosion potential shifted toward more noble values.     

溶液中钙离子对玻璃颗粒电泳沉积的影响

研究了玻璃颗粒在乙醇溶液中对Ca^2 的选择吸附，反转了玻璃颗粒在乙醇中的荷电性质，使玻璃颗粒能够在乙醇中与羟基磷灰石发生共沉积。讨论了不同离子浓度下电泳沉积的沉积量与沉积电流的变化情况，并以此对Ca^2 在电泳沉积中的作用进行了分析。实验结果证实：悬浮液中Ca^2 或吸附到玻璃颗粒上，改变其荷电性质；或留在溶液中，作为电泳沉积过程中电流的主要承载者。离子浓度对电泳沉积的效果有重要的影响，离子浓度太低或太高都易使涂层出现缺陷。分析了不同沉积条件下电泳沉积所得涂层的各种缺陷及其成因。     

Effect of Particle Size on the Electrophoretic Deposition of Hydroxyapatite Coatings: A Kinetic Study Based on a Statistical Analysis

This work reports on the effect of particle size on the electrophoretic deposition (EPD) kinetics of submicrometer and nano‐sized hydroxyapatite (HA) employing a design of experiments strategy namely as response surface methodology (RSM). Zeta potential measurements and particle size analysis were used to study the electrostatic interaction between HA particles in an ethanol‐based suspension. The results of deposition kinetics under constant DC voltages showed a lower deposition rate for nano‐sized HA coating. Furthermore, the effects of voltage and time on EPD kinetics of HA coatings were quantified via RSM based on a central composite design (CCD).     

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.     

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.     

Influence of deposition conditions on the protective behavior of tetraethyl orthosilicate sol–gel films on AA5754 aluminum alloy

The aim of this work is to compare the effect of two deposition methods, dip-coating and electrophoretic deposition, on the characteristics of tetraethyl orthosilicate (TEOS) sol–gel films on AA5754 aluminum alloy, especially in what concerns to their resistance against corrosion. The influence of pH bath on the hydrolysis of the system was analyzed. Moreover, the effect of some experimental parameters, such as deposition time and deposition voltage, was also evaluated. The results showed that pre-hydrolysis rate of the orthosilicate bath depends on the solution pH, and that at pH 2 complete hydrolysis of the solution was obtained after only 20 min. Moreover, it was observed that electrodeposited TEOS films provided better corrosion resistance than films obtained by dip-coating. The improved corrosion resistance was ascribed to a higher uniformity and density of the polysiloxane films and to an in situ modification of the aluminum–polysiloxane interface by the cathodic voltage.     

Electrophoretic deposition of titania nanostructured coatings with different porous patterns

Titania nanostructured coatings with different porous patterns were fabricated by electrophoretic deposition (EPD) in isopropanolic suspension including different concentrations of carbon active (CA) or carbon black (CB) particles as the porogen additives. Finer and negatively charged CA particles were electrostatically adsorbed on the coarser and positively charged titania particles and formed CA-titania particles. While, finer and positively charged titania particles were electrostatically adsorbed on the coarser and negatively charged CB particles to form titania-CB particles. Both CA-titania and titania-CB particles had the net positive surface charge and so cathodic EPD was applicable. EPD was carried out at optimized conditions of 60?V and 10?s. Thermogravimetry (TG) analysis showed that CA and CB burn out between 450?°C and 600?°C. The higher the carbon content in the suspension the higher was their content in the coating. The coatings were characterized by SEM, AFM, adhesion strength and bioactivity tests. Even coatings with interconnected fine pores and low roughnesses were obtained after the heat treatment of CA-titania coatings. While, rough coatings with coarse and isolated pores were obtained after the heat treatment of titania-CB coatings. The porosity of coating increased as the carbon content increased in the suspension. The hydroxyapatite layer grew on the coatings after their soaking in simulated body fluid for 1week at 37.5?±?1.5?°C.     

Enhanced corrosion resistance and mechanical properties of nanostructured graphene-polymer composite coating on copper by electrophoretic deposition

Composite coating of reduced graphene oxide (RGO) and poly (4-vinylpyridine-co-butyl methacrylate) (PVPBM) on copper was produced by electrophoretic deposition (EPD) technique. The structural and morphological characterizations of the RGO-PVPBM coating were carried out using a Raman spectrometer and a field emission scanning electron microscope, respectively. The thermal stability of the coating was analyzed by thermo-gravimetric analysis, and the corrosion resistance properties were examined by potentiodynamic polarization measurements and electrochemical impedance spectroscopy in 3.5% NaCl solution. At optimal EPD conditions of operating voltage of 5 V and total deposition time of 15 min, a uniform crack-free RGO-PVPBM composite coating is obtained. The microscratch experiment has shown an enhancement in the crack propagation resistance of RGO-PVPBM composite coating up to 3.7 times and adhesive strength increased ~2 times compared to PVPBM coating, thereby making it a potential damage tolerance surface coating on Cu substrate. The potentiodynamic measurements clearly show that RGO-PVPBM acts as a protective coating for Cu in 3.5% NaCl solution. The corrosion inhibition efficiency for RGO-PVPBM coating was calculated to be 95.4% which clearly indicates that the tailored RGO-PVPBM composite is an excellent barrier coating to ion diffusion and corrosive electrolyte with considerably enhanced corrosion resistance.     

2Cr13在浓盐酸中的腐蚀行为研究

针对油气田开发实际,采用高温高压釜模拟2Cr13在盐酸溴化锌加重溶液中的腐蚀过程;利用SEM观察了试样的腐蚀形貌特征,并用EDS和XRD分析腐蚀产物膜的成分。实验结果表明：在实验条件下,2Cr13的腐蚀速率为3.993 mm/a,属欠耐蚀型;其中Cl-、Br-是引起2Cr13腐蚀的主要因素。2Cr13的腐蚀产物膜呈密集多孔性点蚀,出现蜂窝状的腐蚀形貌,蚀孔呈开放式。     

Development of HA-CNTs composite coating on AZ31 Magnesium alloy by cathodic electrodeposition. Part 2: Electrochemical and in-vitro behavior

The carbon nano-tubes (CNTs) reinforced hydroxyapatite (HA), with various functionalized CNTs concentration ranging from 0 to 1.5?wt%, were deposited on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The corrosion resistance of the coatings was tested in simulated body fluid (SBF) using different electrochemical methods such as open circuit potential, polarization and electrochemical impedance spectroscopy. The in-vitro behavior, changes in solution pH as well as the amount of evolved hydrogen of these coatings were also evaluated during five days immersion in SBF. The results indicated that the pulse deposited HA having 1% CNTs coating was the optimum condition which decreased the corrosion current density of AZ31 magnesium alloy from 44.25?µA/cm² to 0.72?µA/cm². Moreover, it stabilized the alkalization behavior of AZ31 alloy and caused a tenfold decrease in the amount of hydrogen generation in SBF. Additionally, the formation of new hydroxyapatite layer on the surface of the pre-exist coatings after five days immersion in SBF was confirmed by SEM characterization.     

Microstructure and Selected Properties of Advanced Biomedical n-HA/ZnS/Sulfonated PEEK Coatings Fabricated on Zirconium Alloy by Duplex Treatment

In this work, sulfonated polyetheretherketone (S-PEEK)-based coatings, nanocrystalline ZnS and hydroxyapatite (n-HA) particles were developed on Zr-2.5Nb zirconium alloy substrates by electrophoretic deposition (EPD) combined with subsequent heat treatment. The properties of suspensions and deposition kinetics were studied. Cationic chitosan polyelectrolyte ensured the stabilization of the suspension and allowed for the co-deposition of all coating components on the cathode. The heating of the coated samples at a temperature of 450 °C and slow cooling resulted in sulfonation of the PEEK and the formation of dense coatings. The coatings were characterized by high roughness, hardness, modulus of elasticity and adhesion strength. The coatings revealed mild hydrophilicity, improved the electrochemical corrosion resistance of the alloy and induced the formation of hydroxyapatite with a cauliflower-like morphology on its surface during the Kokubo test. This work explored the great development potential of advanced sulfonated PEEK-based coatings, incorporating antibacterial and bioactive components by EPD combined with heat treatment to stimulate the surface properties of zirconium alloy for prospective dental and orthopedic applications. The antibacterial and osteoconductive properties of the obtained coatings should be further investigated.     

Electrophoretic deposition of bioactive glass nanopowders on magnesium based alloy for biomedical applications

To slow down the initial biodegradation rate of magnesium (Mg) alloy, crystalline nano-sized bioactive glass coating was used to deposit on micro-arc oxidized AZ91 samples via electrophoretic deposition (EPD). Zeta potential and conductivity of the bioactive glass suspension were characterized at various pH values to identify the most stable dispersion conditions. The bone-bonding properties of bioactive glass coated samples were evaluated in terms of apatite-forming ability during the immersion in simulated body fluid (SBF) solution. Results revealed that the ability to form a bioactive glass coating via EPD was influenced by the degree of its crystalline phase composition. Moreover, the potentiodynamic polarization tests recorded significant drops in corrosion current density and corrosion rate of the coated samples which implies a good level of corrosion protective behavior. These preliminary results show that this process will enable the development of Mg implants in the later stage of bone healing.     

Preparation of Crystalline-Oriented Titania Photoelectrodes on ITO Glasses from a 2-Propanol–2,4-Pentanedione Solvent by Electrophoretic Deposition in a Strong Magnetic Field

Crystal-oriented and crack-free thin TiO₂ films with a good interfacial adhesion on indium–tin oxide glass substrates for photoelectrodes of dye-sensitized solar cells were fabricated by the constant voltage electrophoretic deposition (EPD) method in a strong magnetic field of 12 T generated by a superconducting magnet. A binder-free suspension for the EPD was prepared by dispersing TiO₂ in a mixture of 2-propanol and 2,4-pentanedione (acetylacetone). The electrical conductivity, sedimentation rate, and the electrophoretic mobility were measured at varying ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO₂ films were characterized by X-ray diffraction and scanning electron microscopic analyses.     

电泳沉积用羟基磷灰石稳定悬浮液的制备

研究了羟基磷灰石粉体粒径、粉体预烧温度、陈化时间、分散溶剂、悬浮液固含量对羟基磷灰石悬浮液稳定性的影响,通过测定Zeta电位,吸光度等参数表征悬浮液稳定性,对悬浮液电泳沉积的涂层进行SEM表面形貌及粘结-拉伸结合强度的表征.结果表明:悬浮液颗粒越小,Zeta电位越高;对羟基磷灰石粉体预烧800℃,Zeta电位明显提高,且有利于涂层与基体的结合;悬浮液陈化48 h后,颗粒荷电性最佳,可得致密均匀的涂层;以乙二醇为分散溶剂可制备稳定的悬浮液,但乙醇溶剂更有利于涂层的电泳沉积;悬浮液固含量控制为20g/L时,涂层质量较好.