Effect of suspension stability on electrophoretic deposition of hydroxyapatite coatings

In order to prepare densely packed hydroxyapatite (HAp) coating onto titanium substrate through electrophoretic deposition (EPD), it is highly desirable to produce stable HAp suspension. In this study, nano-HAp particles prepared by hydrothermal method were employed for EPD. The stability of HAp suspensions in various primary aliphatic alcohols (C1–C4) has been studied by measurement of sedimentation tests and electricity conductivity. Furthermore, to make a stable suspension, a dispersant [triethanolamine (TEA)] was added. Maximum stability is observed for the suspension containing n-butanol as the dispersion medium and TEA as the dispersant. The HAp coating deposited in this suspension was observed to be a crack-free and densely packed coating through scanning electron microscopy examination. The shear strength and nano-indention tests have confirmed the good adhesion between the coating and the substrate.     

Colloidal characterization and electrophoretic deposition of hydroxyapatite on titanium substrate

Hydroxyapatite (HA) powders were prepared by a modified chemical co-precipitation method and electrophoretically deposited onto a titanium tubular substrate. The zeta potential, electromobility and the particle size of the HA suspension was characterized at various pH values and the most stable and dispersed suspension condition was identified. Electrophoretic deposition of the HA particles on the titanium substrate was then carried out at this optimum suspension condition. Studies on deposition rate and examination on the microstructure of the sintered deposit were performed. The stoichiometry of the HA before and after sintering were also confirmed. The deposition experimental data obtained in the present work was also compared with theoretical model proposed in the literature. Lastly, the adhesion strength of the coating was also quantified using shear strength tests.     

Precipitation of hydroxyapatite nanoparticles: Effects of precipitation method on electrophoretic deposition

Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (HA) coatings on metal implants with a broad range of thicknesses, from < 1 m to > 500 m. As for many other HA coating techniques, densification of electrophoretically deposited coatings involves heating the coated metal to temperatures above 1000 C. Metal substrates tend to react with HA coatings at such temperatures inducing decomposition at temperatures below 1050 C (decomposition for pure HA normally occurs above 1300 C). Therefore, densification of these coatings needs to be conducted at temperatures lower than 1050 C, and this necessitates the use of high-surface-area HA nano-precipitates, rather than commercially available pre-calcined powders, which densify at temperatures typically higher than 1200 C. HA nano-precipitates were prepared by three methods and deposited on metal substrates by electrophoresis: (1) the acid base method, which produced plate-like nano-particles with a 2.5:1 aspect ratio, and severely cracked coatings; (2) the calcium acetate method, which produced needle-like nano-particles with a 10:1 aspect ratio, and slightly cracked coatings; (3) the metathesis method, which produced rounded nano-particles with a 2:1 aspect ratio, and high-quality crack-free coatings. The results suggested that the less equiaxed the nano-particles, the more cracked the coatings obtained by the electrophoretic deposition technique.     

Carbon nanotube-nanocrystal heterostructures fabricated by electrophoretic deposition

Alternating layer, carbon nanotubes-nanocrystal composite films, comprising multi-walled carbon nanotubes (MWCNTs) and iron oxide (Fe(3)O(4)) nanocrystals, have been fabricated via electrophoretic deposition (EPD) on stainless steel and gold substrates. Low field-high current and high field-low current EPD schemes were integrated to produce the composite films. The low field-high current EPD approach produced porous mats from an aqueous suspension of the MWCNTs, while the high field-low current EPD approach produced tightly packed nanocrystal films from a dispersion of the nanocrystals in hexane. Large electric fields applied during the nanocrystal EPD and strong van der Waals interactions among the nanocrystals facilitated the formation of tightly packed nanocrystal films atop the MWCNT mats to create CNT mat-nanocrystal film composites. The surface coverage and homogeneity of the nanocrystal films improved with repeated deposition of the nanocrystals on the same mat. The assembly of nanotube mats on top of the CNT mat-nanocrystal film composite confirmed the feasibility of multilayered CNT mat-nanocrystal film heterostructures suitable for a range of devices. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were employed to characterize the surface coverage, homogeneity, and topology of these composite films.     

Carbon composite microelectrodes fabricated by electrophoretic deposition

Single-walled carbon nanotubes were deposited on one end of the etched carbon fiber electrodes by an electrophoretic method. The carbon nanotube bundles formed a dense network on the carbon fiber surface. The electrochemical properties of the composite carbon electrodes were studied in the buffered neutral solutions. The results in cyclic voltammetry's characteristic indicate that the electrons on the electrodes transfer very fast. Furthermore, the redox reactions of dopamine (DA) on the composite electrodes show good sensitivity. When the DA concentration was 0.02 mM, the peak current in differential pulse technique reached 1.33 microA after performing the background subtraction. In addition, the simultaneous detection of DA and ascorbic acid (AA) showed that the interference effect was not observed. It was suggested that the carbon composite microelectrodes have potential applications as electrochemical sensors inside a single cell.     

Development of novel bioactive composites by electrophoretic deposition

Electrophoretic deposition (EPD), which is normally available on electric conductive materials, was applied to insulating materials. Wollastonite particles were deposited into the pores of porous alumina and porous ultrahigh molecular weight polyethylene (UHMWPE) substrates by EPD to yield alumina-wollastonite and UHMWPE-wollastonite composites, respectively. These composites were soaked in simulated body fluid (SBF) to evaluate their apatite-forming ability. Apatite was induced from the wollastonite particles, which grew on the surfaces and covered the entire composite surfaces. The bonding strength of the apatite layer to the substrates was as high as 8.9 MPa for alumina and 5.2 MPa for UHMWPE due to an interlocking effect. Thus, the formed alumina-wollastonite and UHMWPE-wollastonite composites should be useful as bone substitutes.     

Electrophoretic deposition of hydroxyapatite

Hydroxyapatite powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V surgical alloy substrates. The powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size distribution and zeta potential measurements. Prior to electrophoretic deposition, anodic films were obtained on Ti6Al4V and studied by the Auger method. It was established that experimental conditions of powder preparation, electric field and stirring have a significant influence on suspension stability and deposit morphology. The deposition yield was studied at various deposition durations and applied voltages. Sintered coatings were studied by SEM and XRD.     

Synthesis and microstructural manipulation of ceramics by electrophoretic deposition

Critical issues of electrophoretic deposition (EPD) and its potential for fabricating high-performance ceramics are reviewed. Deposition kinetics under constant-current and constant-voltage conditions are discussed. The process of submonolayer formation of mono-sized silica particles as a function of deposition time during EPD has been discussed and is shown to have a remarkable similarity with the atomic thin-film growth (10000 times smaller scale) process of Molecular Beam Epitaxial (MBE) process. Ceramic coatings by EPD are described and strategies to avoid cracking are outlined. Discussion on avoiding cracking using the Reaction Bonded Aluminium Oxide (RBAO) process is also described. The versatility of the EPD process towards fabrication of a wide spectrum of composite microstructures is discussed together with references. Potential use of EPD in the fabrication of Micro-Solid Oxide Fuel Cell (SOFC) has also been discussed.     

Fabrication of polystyrene colloidal crystal film by electrophoretic deposition

Proper conditions for the formation of a colloidal crystal film by the electrophoretic deposition process were investigated in detail using monodisperse polystyrene (PS) colloidal spheres. Removal of the ionic contaminants and application of a pulsed current were effective in suppressing the electrolysis of water and obtaining a uniform film, but it was not possible to obtain colloidal crystals in which the particles were closely and periodically packed. Mixing EtOH at a high concentration with an aqueous PS suspension and withdrawing the substrate from the suspension at a moderate rate after the EPD process were found to be the key for the successful fabrication of colloidal crystal films. It was demonstrated that the formation of large area colloidal crystal films by the EPD technique was also possible. The advantage of the EPD process for scale up was successfully shown, taking into account the fast film fabrication rate.     

Sol-gel electrophoretic deposition of PZT nanotubes

Sol-gel electrophoretic deposition was utilized to grow lead zirconate titanate (PZT) nanotubes through a template-based process, using porous anodic alumina templates and an acetic acid-based PZT sol. The templates were prepared employing various anodizing voltages and times to achieve different pore diameters and lengths. The PZT sol was deposited into the template channels under the influence of a DC electric field. A single-firing process was developed to transform the dried precursor gels into the perovskite PZT phase. Scanning and transmission electron microscopy show the applicability of electrophoresis technique for the deposition of tubular PZT arrays. Electron diffraction patterns also indicate the amorphous nature of the template and polycrystalline structure of the tubes. X-ray diffraction studies indicate the perovskite structure of the grown PZT nanotubes.     

电泳沉积法制备钛酸纳米管膜层

采用水热合成法制备钛酸钠纳米管,然后依次与HNO3,正四丁基氢氧化铵水溶液(TBAOH)离子交换后,经过高速离心,将所得沉淀物分散于无水乙醇溶液中,并应用电泳沉积的方法成功地在不锈钢或导电玻璃表面构筑了钛酸纳米管薄膜.采用TEM、XRD、SEM及EDS等对纳米管薄膜的表面形貌、结构和组成等进行表征.结果表明,电泳沉积法制备钛酸纳米管薄膜致密均匀、厚度可控并与基体结合力良好;经高温烧结后,形貌基本保持不变,可望成为一种新的功能材料.文中还对纳米管薄膜的形成机理进行了讨论.     

Nano-Ag-loaded hydroxyapatite coatings on titanium surfaces by electrochemical deposition

Hydroxyapatite (HA) coatings on titanium (Ti) substrates have attracted much attention owing to the combination of good mechanical properties of Ti and superior biocompatibility of HA. Incorporating silver (Ag) into HA coatings is an effective method to impart the coatings with antibacterial properties. However, the uniform distribution of Ag is still a challenge and Ag particles in the coatings are easy to agglomerate, which in turn affects the applications of the coatings. In this study, we employed pulsed electrochemical deposition to co-deposit HA and Ag simultaneously, which realized the uniform distribution of Ag particles in the coatings. This method was based on the use of a well-designed electrolyte containing Ag ions, calcium ions and l-cysteine, in which cysteine acted as the coordination agent to stabilize Ag ions. The antibacterial and cell culture tests were used to evaluate the antibacterial properties and biocompatibility of HA/Ag composite coatings, respectively. The results indicated the as-prepared coatings had good antibacterial properties and biocompatibility. However, an appropriate silver content should be chosen to balance the biocompatibility and antibacterial properties. Heat treatments promoted the adhesive strength and enhanced the biocompatibility without sacrificing the antibacterial properties of the HA/Ag coatings. In summary, this study provided an alternative method to prepare bioactive surfaces with bactericidal ability for biomedical devices.     

Layer by layer deposition of hydroxyapatite onto the collagen matrix

Layer by layer (LbL) deposition is a useful method for deposition of many inorganic (including metals, oxides and phosphates) and organic (including polymers and proteins) components on a large range of substrates. The LbL deposition of hydroxyapatite (HA) onto a collagen matrix involves HA synthesis on the collagen matrix starting from electrically charged precursors such as Ca²⁺ and PO₄³⁻ at a proper pH to precipitate the desired calcium phosphate.The LbL deposition process was continuously monitored in order to study the amount of HA deposited in each layer. The deposition of the first layers of HA was concluded to be highly influenced by the collagen matrix. When the collagen matrix is crosslinked with glutaraldehyde, the matrix structure is not modified during the deposition, and the porosity will decrease with the number of layers until saturation is reached. Following pore saturation, HA will be only deposited onto the mineralized collagen matrix surface. The obtained composite materials were characterized by XRD, SEM, DTA-TG and FTIR.     

Novel deposition of nano-sized silicon substituted hydroxyapatite by electrostatic spraying

Suspensions containing nano-sized silicon substituted hydroxyaptite (nSiHA) particles were produced and processed for electrostatic spray deposition. No secondary phases were detected by X-ray diffraction, which indicated that the nSiHA was phase pure. Electrostatic spraying of nSiHA in cone-jet mode was achieved at flow rate of 10⁻⁹ m³s⁻¹ with an applied voltage between the needle and the ring-shaped ground electrode set at 6 to 8 kV. Micrometer- and submicrometer-scaled islands of nSiHA have been deposited on glass and titanium substrates. The surface roughness of such nHA and nSiHA islands was in the range 60 to 80 nm, as measured from atomic force microscopy in tapping mode. The growth of primary human osteoblast (HOB) cells on the nSiHA deposited substrates increased with time during the 4 days of culture, and the increase was related with the Si content in substituted HA, indicating that nSiHA was able to promote and support the growth of HOB cells. Scanning electron microscopy (SEM) revealed that extracellular matrix (ECM) produced by the HOB cells on these nSiHA deposits was well organized. In addition, the presence of Ca and P containing nodules in the ECM were also confirmed by Energy Dispersive X-ray (EDX) analysis, indicating early signs of calcification fronts. The results showed that nSiHA produced by electrostatic spray deposition was able to promote the attachment and the growth of HOB cells. Therefore, electrostatic spray deposition offers great potential for the creation of bioactive surfaces to provide improved interfacial bonding with host tissues.     

电泳沉积制备BG／BG—FHA复合涂层

采用电泳沉积在Ti6A14V钛合金表面制备了以生物玻璃（BG）为中间层,BG与氟取代磷灰石（FHA）复合粉末为表层的BG／BG—FHA涂层。通过XRD、SEM、EDS和电子万能力学试验机对BG／BG—FHA复合涂层的物相结构、微观形貌和涂层结合力进行了分析,优化了涂层的热处理制度,并通过模拟体液浸泡实验研究了涂层的体外...     

Kinetics of electrophoretic deposition ofβ-alumina

The equations describing electrophoretic deposition, proposed by Hamakar Avgustinik and coworkers, have been verified in the case ofβ-alumina suspended in isoamyl alcohol. The variation of electrophoretic yield with (i) concentration of suspension, (ii) extent of grinding the suspension, (iii) temperature of the suspension, and (iv) electrode separation was studied. The effect of addition of glycol monethyl ether was also investigated. The effect of various parameters on the electrical conductivity of the suspension, which in turn influences the yield, was noted.     

Fabrication of material patterns by grid-assisted deposition

We developed a simple patterning approach where a grid with micrometer rule is used in order to control the deposition of a solute. Ordered patterns were obtained, over large areas, in a few seconds. The patterning process we propose here is fast and low cost. It can also be applied to diverse soluble molecular and supramolecular species. We also investigated what parameters have to be changed in order to have total control on the final tridimensional architecture of the material.     

Urea sensing characteristics of titanate nanotubes deposited by electrophoretic deposition method

Urea sensing properties of titanate nanotubes (TNT) are presented here. TNT films were deposited by electrophoretic deposition (EPD) method on aluminum substrate. Prior to EPD, commercial nanoparticles of TiO2 were hydrothermally treated at 70 degrees C for 48 h after sonicating the solution for 8 h. Hydrothermal method resulted in the conversion of particles to tubular structure following the established method. Urease was covalently attached with TNT (by soaking in urease solution for 3 h). In general, conductivity of film increases after urease immobilization. The urease immobilized films were characterized for urea sensing in the concentration range of 1 mM to 500 mM. Three different sensitivity regions are observed viz. (i) lower concentrations (below 10 mM); (ii) linear region up to 100 mM and a (iii) saturation region above 100 mM. Sensors are extremely sensitive in region (i). From the elemental analyses of the films after urease immobilization, urease was found attached with TiO2, as evident by N 1s peak in the photoelectron spectra. Cyclic voltammetric studies indicated surface-confined redox couple is responsible for sensing behavior. A possible sensing mechanism is presented and discussed.