HA Films Research Articles

Morphology change of HA films on highly ordered nanotubular Ti–Nb–Hf alloys as a function of electrochemical deposition cycle

The aim of this study was to investigate the morphology change of HA films on highly ordered nanotubular Ti–Nb–Hf alloys as a function of electrochemical deposition cycle. The Ti–25Nb–xHf alloys were manufactured by vacuum arc-melting, heat treated for 12h at 1000°C, and water quenched. The HA deposition was carried out using a cyclic voltammetry method with a potential range from −1.5V to 0V (vs. SCE) in Ca(NO3)2·4 H2O+NH4H2PO4 at 80°C±1°C (number of cycles: 5, 10, 20, and 50). The morphology changes were observed by OM, FE-SEM, XRD, EDS and image analyses. The microstructures of the Ti–25Nb–xHf alloys were transformed from α″ phase to β phase, and from a needle-like structure to an equiaxed structure as the Hf content increased. The average length of the TiO2 nanotubes increased, and the nanotubes became more highly ordered, as the Hf content increased. The fraction of the alloy surface area covered by the nanotubes decreased from 81% to 73% with increased Hf content. The nucleation of HA was initiated, and the HA precipitates subsequently agglomerated, at the nanotube interspace area for a low number of deposition cycles. The HA precipitates on the nanotube-formed Ti–Nb–Hf alloy surfaces exhibited a needle-like particle morphology, which had different shapes and larger sizes with an increasing number of deposition cycles. Based upon a scratch test, the adhesion of the deposited layer to the titanium alloy was similar for all samples, and a critical load of approximately 6.0N was required to detach the layer. The HA-deposited surface after nanotube formation on the Ti–Nb–Hf alloys should provide improved cell proliferation at a higher rate than on the nanotubular and bulk titanium alloy surfaces.

501 スパッタリング法によるマグネシウム置換HA薄膜の作製とマグネシウム置換量の評価(OS5-(1),OS5 オーガナイズドセッション《ライフサポートにおける工学技術》)

Magnesium substituted hydroxyapatite (Mg-HA) thin films were prepared using rf-magnetron sputtering method. The Mg-HA films were coated onto a titanium (Ti) substrate from a mixed HA/MgO powder target. The molar ratio of Mg to Ca in the mixture target was varied in the ratio of 0:10, 2:8, 4:6, 6:4 and 8:2. The Mg-HA films were heated or subjected to hydrothermal treatment. The chemical compositions of the Mg-HA films were determined by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The crystal lattice parameters from XRD patterns of Mg-HA films were calculated. The chemical analysis by XPS showed that the non-heated, heated, subjected to hydrothermal treatment Mg-HA films contained Mg. The XRD patterns showed that the heated Mg-HA films composed of HA, beta-tricalcium phosphate (β-TCP) and MgO. The subjected to hydrothermal treatment Mg-HA films composed of HA and MgO. The lattice parameters of the HA in the heated and subjected to hydrothermal treatment Mg-HA films (Mg:Ca=2:8, 4:6, 6:4, 8:2) were smaller than that in the heated and subjected to hydrothermal treatment HA films (Mg:Ca=0:10).

The biocompatibility of hydroxyapatite film deposition on micro-arc oxidation Ti6Al4V alloy

Among the titanium alloys employed as implant materials, the Ti6Al4V alloy is still widely used. Micro-arc oxidation (MAO) was used to prepare ceramic oxide layer containing calcium and phosphor on surface of Ti6Al4V alloy and then the specimens were hydrothermal synthesis (HS) treated, and then a thin hydroxyapatite ((Ca10(PO4)6(OH)2, HA) film was deposited on the surface. The biocompatibility of Ti6Al4V alloy, MAO alloy and sample treated by hydrothermal synthesis were evaluated. The biocompatibility of three specimens was tested using anti-hematolysis tests, anti-coagulation tests, anti-platelet adhesion and cytotoxicity tests. Specimens coated with HA film exhibited significant improved anti-hemolytic reaction, and the hematolysis ratio was 0.994% (less than 5%), which indicated that this type of samples could not induce acute hematolysis. And coagulation did not occur within 50min on the HA layer. There was almost no platelet adhered on the surface. The toxicity was ranked as 0 grades which indicated that it could not induce the cytotoxic effect. This demonstrates that the HA film can significantly improve the biocompatibility properties.

Synthesis of mesoporous hydroxyapatite thin films using F127 as templates for biomedical applications

Mesoporous materials with large specific surface area and pore volume have attracted much attention in the biomedical field. In this study, the uniform mesoporous hydroxyapatite (meso-HA) thin films were prepared on the glass substrates by a sol–gel technique using different concentrations of non-ionic surfactant Pluronic F127 as the template. Nitrogen adsorption–desorption measurements indicated that the pore size distribution in the meso-HA samples were mainly sized ∼3.0nm. As compared to the non-mesoporous HA film, the meso-HA samples have remarkably greater surface area and surface wettability owing to the introduction of mesopores. Using MC3T3-E1 cells as the models, the enhanced cell spreading was observed on the meso-HA films after 4 days of culture.

Preparation, surface properties, and MC3T3-E1 cell response of mesoporous hydroxyapatite thin films

Mesoporous hydroxyapatite (meso-HA) thin films were fabricated by a sol–gel method using cetyltrimethyl ammonium bromide as the template. The phase, surface morphology, and mesoporous structure of the meso-HA films were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The uniform thin films consisted of meso-HA spherical particles with different pore size (2.0 or 3.1 nm) were prepared on the glass substrate at different pH value (pH 3.0 or 7.0). The introduction of mesopores would enhance the surface area of HA. Water contact angle was also measured on the non-mesoporous and meso-HA thin films, revealing the promotion of surface wettability in the mesoporous ones. In vitro cytocompatibility of HA films were evaluated by cell adhesion and proliferation tests using MC3T3-E1 cells. After 3 days of culture on the samples, the cells spread in an elongated shape and were well adhered to the surface of the meso-HA films. Moreover, the cells proliferation on the meso-HA films was higher than that on the non-mesoporous films. There are significant differences in the cell density between the control group and the meso-HA films with the pores sized in 2.0 nm after being cultured for 2 and 3 days (P < 0.05). The results suggested that the presence of mesopores could influence the surface and biological properties of HA films, and the mesoporous structure would enhance the cell response of HA.

Formation of Nano-Phase Hydroxyapatite Film on TiO&lt;SUB&gt;2&lt;/SUB&gt; Nano-Network

Nano- and micro-phase HA film formed on TiO2 nano-network surface by simple electrochemical treatment. The range of lateral pore size of the network specimen was about 10-120 nm on Ti surface by anodized in 5 M NaOH solution at 0.3 A for 10 min. Nano-network TiO2 surface were formed by this anodization step which acted as templates and anchorage for growth of the HA during subsequent pulsed electrochemical deposition process at 85 degrees C. The phase and morphologies of deposits HA were influenced by the electrolyte concentration. The nano needle-like precipitates formed under low SBF concentration were identified to be HA crystals orientated parallel to the c-axis direction. Increasing electrolyte concentration, needle-like deposits transferred to the plate-like and micro plate like precipitates in the case of high SBF concentration.

Proposed model for growth preference of plate-like nanohydroxyapatite crystals on superhydrophilic vertically aligned carbon nanotubes by electrodeposition

For the first time, the mechanism of growth of plate-like n-HA electrodeposited on superhydrophilic vertically aligned multi-walled carbon nanotubes (VACNT) is presented and a model for the specific growth preference is discussed. Results show that the carboxyl (carboxylic acid)/carboxylate functional groups directly attached on VACNT tips after oxygen plasma treatment were essential for the acceleration of the OH− formation and the deposition of plate-like HA crystals. FEG-SEM, EDX and XRD showed that a homogeneous highly crystalline HA film, stoichiometric and with preferential growth in the (002) plane direction, was formed.

Preparation and characterization of biomimetically and electrochemically deposited hydroxyapatite coatings on micro-arc oxidized Ti–13Nb–13Zr

Surface properties and corrosion resistance analyses of Ti-13Nb-13Zr coated by an oxide film (obtained by micro-arc oxidation at 300V) or an oxide/hydroxyapatite (HA) film are reported. HA films were biomimetically or electrochemically deposited on the alloy/oxide surface, and their properties compared. Both the biomimetic and the electrochemical method yielded rough and globular apatite surfaces (10-20μm globules for the former and 1-2μm for the latter). As inferred from XRD data, the electrochemical method yielded more biologic-like HA films, while the biomimetic method yielded films containing a mixture of calcium phosphate phases. Coated Ti-13Nb-13Zr samples were immersed in an aerated PBS solution and continuously analyzed during 49days. Considering that, after immersion, the biomimetically deposited films presented smaller variations in thickness and morphology and higher electric resistance (determined by electrochemical impedance spectroscopy), they clearly provide significantly better protection to the Ti-13Nb-13Zr alloy when in PBS solution.

Phospholipid bilayer formation on hydroxyapatite sol–gel synthesized films

Lipid bilayers supported by porous biomaterials are being explored as models for cell membranes. Hydroxyapatite is a relevant material currently being used extensively for biomedical applications. In this study, hydroxyapatite films produced via a sol–gel chemistry route have been characterized and explored as a scaffolding material for lipid membranes. The hydroxyapatite has been characterized using XRD, SEM, and AFM, followed by vesicle-fusion of lipids characterized by fluorescence microscopy and fluorescence recovery after photobleaching (FRAP) to determine the diffusion coefficient of this system. The HA films produced in this work were found to produce slow lateral diffusion and, in the two-phase lipid systems, some domains were observed. The low lateral diffusion coefficients were believed to be a result of the large undulations present on the hydroxyapatite film surface.

Fabrication and characterization of rod-like nano-hydroxyapatite on MAO coating supported on Mg–Zn–Ca alloy

The poor corrosion resistance of magnesium alloys is a dominant problem that limits their clinical application. In order to solve this challenge, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys and then electrochemical deposition (ED) was done to fabricate rod-like nano-hydroxyapatite (RNHA) on MAO coating. The cross-section morphology of the composite coatings and its corresponding energy dispersion spectroscopy (EDS) surficial scanning map of calcium revealed that HA rods were successfully deposited into the pores. The three dimensional morphology and scanning electron microscopy (SEM) image of the composite coatings showed that the distribution of the HA rods was dense and uniform. Atomic force microscope (AFM) observation of the composite coatings showed that the diameters of HA rods varied from 95 nm to 116 nm and the root mean square roughness (RMS) of the composite coatings was about 42 nm, which were favorable for cellular survival. The bonding strength between the HA film and MAO coating increased to 12.3 MPa, almost two times higher than that of the direct electrochemical deposition coating (6.3 MPa). Compared with that of the substrate, the corrosion potential of Mg–Zn–Ca alloy with composite coatings increased by 161 mV and its corrosion current density decreased from 3.36 × 10 −4 A/cm 2 to 2.40 × 10 −7 A/cm 2 which was due to the enhancement of bonding strength and the deposition of RNHA in the MAO pores. Immersion tests were carried out at 36.5 ± 0.5 °C in simulated body fluid (SBF). It was found that RNHA can induce the rapid precipitation of calcium orthophosphates in comparison with conventional HA coatings. Thus magnesium alloy coated with the composite coatings is a promising candidate as biodegradable bone implants.

Carbon nanotube–hydroxyapatite–hemoglobin nanocomposites with high bioelectrocatalytic activity

In this paper, carbon nanotubes–hydroxyapatite (MWCNTs–HA) composite were synthesized by self-assembling technique, and investigated by X-ray diffraction, scanning electron microscopy (SEM) and FT-IR spectroscopy. Hemoglobin (Hb) immobilized in MWCNTs–HA film not only retained its similarly native conformations, but also achieved the direct electron transfer. The apparent heterogeneous electron transfer rate constant ( k s) was evaluated as (5.05 ± 0.41) s − 1 according to Laviron's equation, and the surface coverage ( Γ*) was estimated as (9.25 ± 0.69) × 10 − 10 mol cm − 2 . Moreover, the Hb immobilized in MWCNTs–HA film exhibited remarkable bioelectrocatalytic activity for the electrochemical reduction of H 2O 2. The amperometric response of the biosensor varied linearly with the H 2O 2 concentration ranging from 0.5 μM to 2 μM, and the results showed a detection limit of 0.09 μM. Furthermore, the Hb-immobilized MWCNTs–HA film exhibited the excellent catalytic reactivity toward trichloroacetic acid (TCA).

Carbon nanotube–hydroxyapatite nanocomposite: A novel platform for glucose/O2 biofuel cell

This study demonstrates a novel carbon nanotubes-hydroxyapatite (CNTs–HA) nanocomposite-based compartment-less glucose/O2 biofuel cell (BFC) with the glucose oxidase (GOD) as the anodic biocatalysts and the laccase as the cathodic biocatalysts. CNTs–HA nanocomposite prepared by the self-assembly method via an aqueous solution reaction has been used as the co-immobilization matrix to incorporate biocatalysts, i.e. GOD and laccase successfully. Moreover, the three-dimensional configuration of the CNTs–HA films electrode would be advantageous to the glucose oxidation on the bioanode and O2 electroreduction on the biocathode of BFC. The maximum power density delivered by the assembled glucose/O2 BFC could reach 15.8μWcm−2 at a cell voltage of 0.28V with 10mM glucose. The results indicate that the CNTs–HA nanocomposite is believed to be very useful for the development of novel BFC device.

The immobilization of titania nanoparticles on hyaluronan films and their photocatalyticproperties

We have developed a method to bind titania nanoparticles onto hyaluronic films (HA)photoimmobilized on silanized glass. Titania nanoparticles were deposited on the HAfilms from commercially available dispersions by casting and dip-coating methodsat various pH values. XPS was used to monitor the deposition of titania andto estimate the surface coverage of the nanoparticles. The topography of thetitania-modified HA films was investigated by means of AFM. XPS results indicatethat the titania surface coverage depends on the preparation method and thepH of the dispersion. We found that the maximum titania nanoparticle surfacecoverage was obtained by the casting method with the formation of aggregates andmultilayers of particles. The titania surface coverage for the surfaces prepared bythe dip-coating method is pH-dependent. The surfaces prepared at pH 2 show asurface coverage of 65% and a rather uniform distribution of particles. We foundthat titania nanoparticles are anchored in a stable way to the HA substrate in aphosphate buffer solution (PBS) and that the interaction between the HA andthe titania is through the carbonyl group of carboxylates and amidic groups ofthe polymer. AFM images clearly show that titania nanoparticles are uniformlydistributed over the HA films. By measuring the average diameter and the averageheight of the nanoparticles deposited on HA films it appears that the particles arepartially embedded in the polysaccharide films. The results of the study on thephotobleaching of methylene blue indicate that the characteristic photocatalytic activity oftitania is maintained when the nanoparticles are anchored to the HA substrate.

Hydroxyapatite coating on Ti6Al4V alloy by a sol–gel method

Using trimethyl phosphate and calcium nitrate tetrahydrate as the calcium and phosphorus precursors, respectively, HA films were prepared layer by layer by a sol-gel method. The phase constitution, microstructure and calcium/phosphorus (Ca/P) molar ratio of the sol-gel films were studied by X-ray diffraction (XRD) and electronic probe microanalysis (EPMA). The results show that the sol-gel films have high crystallinity and are composed of HA and CaO phases, and the Ca/P ratio is slightly higher than the theoretical value in HA because of the loss of phosphorous element. Two typical cauliflower-like and lamellar structures were observed in the films. Cauliflower-like structure, which increases the biological reactivity of the implant surface towards natural bone, formed mainly at low drying temperature and high calcining temperature, while the lamellar structure formed when the drying temperature is high (500 degrees C or above).

Pulsed laser deposition of silicon substituted hydroxyapatite coatings from synthetical and biological sources

Silicon substituted hydroxyapatite (Si–HA) is a new material with an enhanced bioactibity and it can be produced by chemical synthesis. Nevertheless, the coating of metallic substrates with a bioactive material is a common method nowadays to improve its integration with the receptor bone. Si–HA films were deposited by pulsed laser deposition (PLD), using targets composed of mixtures of HA with different Si containing sources such as SiO 2 and diatomaceous earth. The Si–HA films were characterized in terms of structure and chemical composition by spectroscopic techniques (FTIR, XPS), and several ion beam techniques (RBS, PIXE). The analysis revealed that the Si is successfully incorporated into the HA structure, as well as traces of other elements such as Na, Fe or K.

Hydroxyapatite Films Deposited on TiN and TiO&lt;sub&gt;2&lt;/sub&gt; Buffer Layers by Radio-Frequency Magnetron Sputtering: Comparative Study

A comparative study was presented to demonstrate the clear influence of the different buffer layer (TiN and TiO2) on the HA film. In this study, magnetron sputtering was applied for different film deposition. Nano-indentation was used to examine the mechanical properties of the HA film on both TiN and TiO2 buffer layers. It is found that HA film on TiN buffer layer is harder and the HA film on TiO2 buffers is more rigid. Further more, the simulated body fluid (SBF) soaking test was selected to investigate the properties of the HA/TiN and HA/TiO2 films in the physiological media. The obvious delamination was observed on the surface of HA film on TiN buffer layer, while the surface morphology of HA film on TiO2 buffer layer remained nearly unchanged. The result indicated that TiO2 buffer layer shows a better interfacial bonding to the HA film.

Electrochemical studies of cytochrome c on gold electrodes with promotor of humic acid and 4-aminothiophenol

p-Aminothiophenol (PATP) and humic acids (HA or HAs) were applied jointly as the electron transfer accelerants of redox reactions of cytochrome c (Cyt c) on gold electrodes. The electrochemical properties of the modified electrodes were studied by field emission scanning electron microscope, ultraviolet-visible spectroscopy, electrochemical impedance spectroscopy, Raman spectroscopy and cyclic voltammetry. The immobilized Cyt c displayed a couple of stable and well-defined redox peaks with a formal potential of −0.101 V (vs. SCE) in pH 7.0 phosphate buffer solution. Cyt c adsorption is in the form of a monolayer with average surface coverage of 5.28 pmol cm−2. The electron transfer rate constant was calculated to be 2.14 s−1. It indicate that the HA film acted as a good adsorption matrix for Cyt c and an excellent accelerant for the redox of Cyt c. The Cyt c-HA modified gold electrode showed a new couple of well-marked redox peaks when 2,4-dichlorophenol was added to the test solution.

Microwave annealing for preparation of crystalline hydroxyapatite thin films

A sol was spun on single crystal silicon substrates at a spin-rate of 3000-5000 rpm followed by a low temperature cure to form a stable sol-gel/ silicon structure. Good quality crystalline HA films of thickness ~300-400 nm were obtained by anneal- ing the sol-gel/Si structure in a conventional cavity applicator microwave system with a magnetron power of 1300 W, frequency of 2.45 GHz, and at a low processing temperature of 425 � C for annealing times ranging from 2-60 min. X-ray Diffraction and FTIR analysis confirmed that the crystalline quality of the thin films were comparable or better than those heat-treated under the same processing condi- tions (temperature and time) in a Rapid Thermal Annealing (RTA) system. The RBS data suggests a composition corresponding to stoichiometric hydroxyapatite Ca10(PO4)6(OH)2, the major inor- ganic component of bone. The results showed that the HA film thickness decreases with increasing sol spin-rate. The HA films showed good biocompati- bility because little monocyte adhesion occurred and hence no inflammatory response was activated in vitro. The potential of microwave annealing for rapid and low temperature processing of good crystalline quality HA thin films derived from sol-gel is dem- onstrated.

Interfacial characteristic of graded hydroxyapatite and titanium thin film by magnetron sputtering

Graded film of calcium phosphate and titanium (Ti) was prepared on Ti-6Al-4V alloy by radio-frequency magnetron sputtering. Concurrent sputtering of HA and Ti for four times, The area proportions of HA to Ti in the targets are 20%, 50%, 90% and 100% respectively, contributes a gradual distribution of Ca, P, O and Ti across the interface of film and alloy substrate. The graded HA/Ti film is formed by annealing for 1 h at 600 °C water vapour flow. The tensile adhesion strength of graded sputtered and annealed HA/Ti film is approximately 35 Mpa, which is an obvious advantage compared with monolithic HA film. The results obtained from the nanoindentation test show that Young's modulus and microhardness of graded HA/Ti film are also graded distribution and strain reversion was much better than that in the monolithic HA film.

Bacterial adhesion studies on titanium, titanium nitride and modified hydroxyapatite thin films

A qualitative study on adhesion of the oral bacteria Porphyromonas gingivalis on titanium (Ti), titanium nitride (TiN), fluorine modified hydroxyapatite (FHA) and zinc modified FHA (Zn-FHA) thin films is investigated. Ti and TiN thin films were deposited by DC magnetron sputtering and hydroxyapatite-based films were prepared by solgel method. The crystalline structure, optical characteristics, chemical composition and surface topography of the films were studied by XRD, optical transmission, XPS, EDAX and AFM measurements. The predominant crystallite orientation in the Ti and TiN films was along (002) and (111) of hcp and cubic structures, respectively. The Ti : O : N composition ratio in the surface of the Ti and TiN films was found to be 7 : 21 : 1 and 3 : 8 : 2, respectively. The atomic concentration ratio (Zn + Ca) / P in Zn-FHA film was found to be 1.74 whereby the Zn replaced 3.2% of Ca. The rough surface feature in modified HA films was clearly observed in the SEM images and the surface roughness (rms) of Ti and TiN films was 2.49 and 3.5 nm, respectively, as observed using AFM. The film samples were sterilized, treated in the bacteria culture medium, processed and analyzed using SEM. Surface roughness of the films was found to have least influence on the bacterial adhesion. More bacteria were observed on the TiN film with oxide nitride surface layer and less number of adhered bacteria was noticed on the Ti film with native surface oxide layer and on Zn-FHA film.