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/cm² to 2.40 × 10⁻⁷ A/cm² 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.     

Study on crystalline to amorphous structure transition of Cr coatings by magnetron sputtering

The influence of deposition rate on crystalline to amorphous microstructure transition of Cr coatings was studied through preparation of Cr coatings deposited onto silicon wafers using magnetron sputtering technique. The microstructure and morphology of Cr coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results show that Cr coating prepared at 400 W exhibits dense columnar crystalline structure and the crystallite size and crystallization rate are increased expressly in the initial 5 min. When the deposition rate achieved to the maximum, Cr coating shows a case of infinite periodic renucleation where new crystals are assumed to be nucleated periodically on the surfaces of growing crystals and strong persistence of the columnar growth morphology is apparent. However, Cr coating exhibits overall microstructure of amorphous phase mixed with a few nano-crystal grains as the deposition rate decreases to the minimum.     

In vitro biological performance of nano-particles on the surface of hydroxyapatite coatings

The biocompatibility of a kind of heat-treated bilayer hydroxyapatite (HA) coatings with nano-particles was investigated, mainly in terms of the immersion in simulated body fluid (SBF) and osteoblast adhesion. Scanning electron microscopy (SEM) was used to observe the morphology of coatings and cellular adhesion. The phases present in the coatings were determined by X-ray diffraction (XRD). Calcium ion (Ca²⁺) concentration in SBF was measured by Atomic absorption spectrophotometer. The results show nano-HA heat-treated at 650 °C for 0.5 h (BBCs) is comparatively stable during immersion in SBF and favor of the adhesion of osteoblasts. Cellular filopodia adhere firmly to the nano-particles and stretch in various direction.     

Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti-29Nb-5Zr alloy for biomaterials

Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti-29Nb-5Zr alloy for biomaterials have been investigated by several experimental methods. The nanotubular structure was formed by anodizing the Ti-29Nb-5Zr alloy in 1 M H₃PO₄ electrolytes with 1.0 wt.% NaF at room temperature. Hydroxyapatite (HA)/titanium nitride (TiN) films were deposited on Ti-29Nb-5Zr alloy specimens using a magnetron sputtering system. The HA target was made of human tooth-ash by sintering at 1300 °C for 1 h, and the HA target had an average Ca/P ratio of 1.9. The HA/TiN depositions were performed, using the pure HA target, on Ti-29Nb-5Zr alloy following the initial deposition of a TiN buffer layer coating. Microstructures and nanotubular morphology of the coated alloy specimens were examined by FE-SEM, EDX, XRD, and XPS. The Ti-29Nb-5Zr alloy substrate had small grain size and preferred orientation along the drawing direction. The HA/TiN coating was stable with a uniform morphology at the tips of the nanotubes.     

Deposition of thick and adherent Teflon-like coating on industrial scale stainless steel shell using pulsed dc and RF PECVD

A unique combination of pulsed dc and radio frequency (RF) discharge deposition was used to deposit thick (∼5 μm) and adherent (2-4 MPa) Teflon-like coatings on a stainless steel (SS) shell of 2 m diameter size, through plasma enhanced chemical vapor deposition (PECVD). The details of deposition on such a big industrial scale component are reported for the first time. In this method, highly adherent thin interface layers were grown on SS shell that was electrically grounded, using pulsed dc discharge, followed by RF discharge deposition to build up the required coating thickness. The fluorocarbon precursor molecules, required for the deposition of Teflon-like coating, are generated indigenously by pyrolyzing the Teflon powder. The deposited coating was studied for its chemical bond state, surface roughness (Ra), morphology, thickness, and adhesive strength. These studies were carried out by using XPS, AFM, SEM, etc. The adhesive strength of the coating was measured by pin-pull test as per ASTM D4541 standard test. The coatings deposited with pulsed dc discharge were observed to have higher adhesive strength when compared with those deposited with RF discharge.     

Preparation and in vitro characterization of aerosol-deposited hydroxyapatite coatings with different surface roughnesses

Hydroxyapatite (HA) coatings with different surface roughnesses were deposited on a Ti substrate via aerosol deposition (AD). The effect of the surface roughness on the cellular response to the coating was investigated. The surface roughness was controlled by manipulating the particle size distribution of the raw powder used for deposition and by varying the coating thickness. The coatings obtained from the 1100 °C-heated powder exhibited relatively smooth surfaces, whereas those fabricated using the 1050 °C-heated powder had network-structured rough surfaces with large surface areas and were superior in terms of their adhesion strengths and in vitro cell responses. The surface roughness (R_a) values of the coatings fabricated using the 1050 °C-heated powder increased from approximately 0.65 to 1.03 μm as the coating thickness increased to 10 μm. The coatings with a rough surface had good adhesion to the Ti substrate, exhibiting high adhesion strengths ranging from 37.6 to 29.5 MPa, depending on the coating thickness. The optimum biological performance was observed for the 5 μm-thick HA coating with an intermediate surface roughness value of 0.82 μm.     

Preparation and characterization of boron nitride coatings on carbon fibers from borazine by chemical vapor deposition

Boron nitride (BN) coatings were deposited on carbon fibers by chemical vapor deposition (CVD) using borazine as single source precursor. The deposited coatings were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The effect of temperatures on growth kinetics, morphology, composition and structure of the coatings was investigated. In the low temperature range of 900 °C-1000 °C, the growth rate increased with increasing temperature complying with Arrhenius law, and an apparent active energy of 72 kJ/mol was calculated. The coating surface was smooth and compact, and the coatings uniformly deposited on individual fibers of carbon fiber bundles. The growth was controlled by surface reaction. At 1000 °C, the deposition rate reached a maximum (2.5 μm/h). At the same time, the limiting step of the growth translated to be mass-transportation. Above 1100 °C, the growth rate decreased drastically due to the occurrence of gas-phase nucleation. Moreover, the coating surface became loose and rough. Composition and structure examinations revealed that stoichiometric BN coatings with turbostratic structure were obtained below 1000 °C, while hexagonal BN coatings were deposited above 1100 °C. A penetration of carbon element from the fibers to the coatings was observed.     

Comparative study of hydroxyapatite and octacalcium phosphate coatings deposited on metallic implants by PLD method

The aim of the presented study was an analysis of two apatite coatings: hydroxyapatite (HA) and octacalcium phosphate (OCP) as coatings materials for metallic implants. Both layers were deposited by means of the PLD method. As a target material, synthetic, powdered and pressed hydroxyapatite was used. HA was deposited on 316L steel substrate in two temperature ranges for obtaining different coatings: 150±30°C and 430±30°C for OCP and HA, respectively. As an intermediate layer, the nanocrystalline diamond layer (NCD) was deposited. Examined calcium phosphate layers were tested for adhesion of osteoblast cell culture (MG-63). Analytical methods (AFM, FTIR) showed the usefulness of the PLD method for deposition of the apatite layers on metallic implants. Both examined layers showed biocompatibility with human osteoblast cells and presented favorable conditions for their proliferation.     

Microstructure, mechanical properties, and oxidation resistance of nanocomposite Ti-Si-N coatings

Ti-Si-N coatings with different silicon contents (0-12 at.%) were deposited onto Si(1 0 0) wafer, AISI M42 high speed steel, and stainless steel plate, respectively. These coatings were characterized and analyzed by using a variety of analytical techniques, such as XRD, AES, SEM, XPS, nanoindentation measurements, Rockwell C-type indentation tester, and scratch tester. The results revealed that the hardness was strongly correlated to the amount of silicon addition into a growing TiN film. The maximum hardness of 47.1 GPa was achieved as the Si content was 8.6 at.%. In the mechanical and oxidation resistance measurements, the Ti-Si-N coatings showed three distinct behaviors. (i) The coatings with Si contents of no more than 8.6 at.% performed good adhesion strength quality onto the HSS substrates. (ii) The fracture toughness of the coatings decreased with the increase in Si content. (iii) The Ti-Si-N coating with 8.6 at.% Si showed the excellent oxidation resistance behavior. The cutting performance under using coolant conditions was also evaluated by a conventional drilling machine. The drills with Ti-Si-N coatings performed much better than the drills with TiN coating and the uncoated drills.     

XPS and bioactivity study of the bisphosphonate pamidronate adsorbed onto plasma sprayed hydroxyapatite coatings

This paper reports the use of X-ray photoelectron spectroscopy (XPS) to investigate bisphosphonate (BP) adsorption onto plasma sprayed hydroxyapatite (HA) coatings commonly used for orthopaedic implants. BPs exhibit high binding affinity for the calcium present in HA and hence can be adsorbed onto HA-coated implants to exploit their beneficial properties for improved bone growth at the implant interface. A rigorous XPS analysis of pamidronate, a commonly used nitrogenous BP, adsorbed onto plasma sprayed HA-coated cobalt-chromium substrates has been carried out, aimed at: (a) confirming the adsorption of this BP onto HA; (b) studying the BP diffusion profile in the HA coating by employing the technique of XPS depth profiling; (c) confirming the bioactivity of the adsorbed BP. XPS spectra of plasma sprayed HA-coated discs exposed to a 10 mM aqueous BP solution (pamidronate) for periods of 1, 2 and 24 h showed nitrogen and phosphorous photoelectron signals corresponding to the BP, confirming its adsorption onto the HA substrate. XPS depth profiling of the 2 h BP-exposed HA discs showed penetration of the BP into the HA matrix to depths of at least 260 nm. The bioactivity of the adsorbed BP was confirmed by the observed inhibition of osteoclast (bone resorbing) cell activity. In comparison to the HA sample, the HA sample with adsorbed BP exhibited a 25-fold decrease in primary osteoclast cells.     

Influence of TaCl5 partial pressure on texture structure of TaC coating deposited by chemical vapor deposition

TaC was deposited on graphite substrate with different TaCl₅ partial pressure at 800 °C and 1200 °C by chemical vapor deposition. Microstructures and texture structures of the prepared coatings were researched with X-ray diffraction and scanning electronic microscopy. When the coating deposition process is controlled by surface reaction kinetics (800 °C), TaCl₅ partial pressure had little influence on the microstructure and texture structure of the coating. When the coating formation process is controlled by diffusion kinetics (1200 °C), the microstructure, texture structure of the prepared TaC grains vary greatly with TaCl₅ partial pressure. In the diffusion controlled process, the increasing of TaCl₅ partial pressure will result in the changing of gas supersaturation, and then the occurrence of secondary nucleation, which is the main reason for the changing of coating morphology and texture structure. With the help of competitive growth in (1 0 0) and (1 1 1) directions, the formation mechanism of the different texture coatings are discussed in detail. In addition, a diffusion model of deposition species around step-edge-corner was also proposed to explain the growth mechanism of the texture coatings.     

Si，Ag，F离子共修饰HA纳米生物薄膜的制备与表征

采用单电流阶跃电化学沉积技术,在商业纯钛(CP-Ti)表面构建硅、银、氟离子共修饰羟基磷灰石(Si-Ag-F-HA)纳米复合薄膜。Ag+的持续释放可以提供有效的抗菌性,Si4+作为生物活性元素可以有效地抵消Ag+的潜在细胞毒性。采用电感耦合等离子体质谱法(ICP-MS)测定涂层中硅和银元素的释放规律。采用傅里叶变换红外光谱(FTIR)、扫描电子显微镜(SEM)、能量弥散X射线谱(EDS)、X-射线衍射(XRD)等技术对得到的材料进行了表征。结果表明：Si,Ag和F三种元素均匀地掺杂到了HA的晶体结构中。Si-Ag-F-HA为纳米级的针状晶体结构,薄膜整体致密且均匀。Si-Ag-F-HA纳米生物薄膜可以在一周内很好地诱导类骨磷灰石的形成,具有优异的生物活性。塔菲尔曲线测试结果证实涂层的耐SBF腐蚀性较好。ICP-MS测试结果表明Si-Ag-F-HA纳米生物薄膜可以提供持续的Si和Ag离子释放。FTIR 和ICP-MS等光谱技术为开发新型抗菌硬组织修复材料提供了高效快速的检测手段。     

Surface modification of titanium by nano-TiO2/HA bioceramic coating

A nano-TiO₂/hydroxyapatite composite bioceramic coating was developed and applied to the surfaces of pure titanium discs by the sol-gel method. A TiO₂ anatase bioceramic coating was utilized in the inner layer, which could adhere tightly to the titanium substrate. A porous hydroxyapatite (HA) bioceramic coating was utilized in the outer layer, which has higher solubility and better short-term bioactivity. Conventional HA coatings and commercially pure titanium were used as controls. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the crystallization, surface morphology, and thickness of the coatings. The bioactivities of the coatings were evaluated by in vitro osteoblast cultures. Results showed that the nano-TiO₂/HA composite bioceramic coating exhibited good crystallization and homogeneous, nano-scale surface morphology. In addition, the nano-TiO₂/HA coating adhered tightly to the substrate, and the in vitro osteoblast cultures exhibited satisfactory bioactivity.     

Bioactive glass and hydroxyapatite thin films obtained by pulsed laser deposition

Bioactive glass (BG), calcium hydroxyapatite (HA), and ZrO₂ doped HA thin films were grown by pulsed laser deposition on Ti substrates. An UV KrF^* (λ = 248 nm, τ ≥ 7 ns) excimer laser was used for the multi-pulse irradiation of the targets. The substrates were kept at room temperature or heated during the film deposition at values within the (400-550 °C) range. The depositions were performed in oxygen and water vapor atmospheres, at pressure values in the range (5-40 Pa). The HA coatings were heat post-treated for 6 h in a flux of hot water vapors at the same temperature as applied during deposition. The surface morphology, chemical composition, and crystalline quality of the obtained thin films were studied by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The films were seeded for in vitro tests with Hek293 (human embryonic kidney) cells that revealed a good adherence on the deposited layers. Biocompatibility tests showed that cell growth was better on HA than on BG thin films.     

Influence of NH beam bombarding energy on structural characterization and cell attachment of CNx coating

The carbon nitride (CN_x) coating with its novel properties will be excellent candidate for biomedical applications. CN_x coatings were prepared on the surface of Ti–6Al–4V by ion-beam-assisted deposition (IBAD) with different NHⁿ⁺ beam bombarding energies at low substrate temperature. The coatings were characterized by Scanning electron microscopy (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. The result showed that the wear-resistance of CN_x coatings was better at higher beam bombarding energy. The cell attachment tests also gave interesting results that CN_x coatings exhibited low macrophage attachment and provide desirable surface for the normal cellular growth and morphology of the fibroblasts. Structural analysis showed that NHⁿ⁺ beam bombardment at the energies of 300–400 eV could result in more nitrogen concentration and fraction of sp³CN bonds in the structure of CN_x coatings, which may be responsible for the improvement in the wear-resistance and the cell attachment.     

Effects of mesoporous structure and UV irradiation on in vitro bioactivity of titania coatings

Mesoporous titania coatings (MTCs) with a pore size of 4.75 nm were prepared on Ti6Al4V substrates by a sol-gel process, and then irradiated with UV light at room temperature for 2 h. The effects of mesoporous structure and UV irradiation on the in vitro bioactivity were investigated. Simulated body fluid (SBF) tests reveal that the MTCs exhibit a high apatite-forming ability, which may be attributed to the following reasons: (i) the BET surface area of the MTCs is ∼190 m²/g, resulting in a greater density of Ti-OH groups than that without mesoporous structure; (ii) theoretical analysis reveals that the mesoporous structure can improve the driving force and nucleation rate of apatite precipitation in SBF. As compared with the MTCs, the UV-irradiated coatings do not exhibit any change in phase components and surface morphologies. However, the apatite-forming ability is higher on the UV irradiation coatings than on the MTCs because of the increase of Ti-OH groups and the improvement of wettability after UV irradiation. In addition, the investigation of the MG63 cell proliferation on the both substrates was performed. The results indicate that the MTCs before and after UV irradiation exhibit a good biocompatibility and are fit for the MG63 cell proliferation.     

Diamond deposition on siliconized stainless steel

Silicon diffusion layers in AISI 304 and AISI 316 type stainless steels were investigated as an alternative to surface barrier coatings for diamond film growth. Uniform 2 μm thick silicon rich interlayers were obtained by coating the surface of the steels with silicon and performing diffusion treatments at 800 °C. Adherent diamond films with low sp² carbon content were deposited on the diffused silicon layers by a modified hot filament assisted chemical vapor deposition (HFCVD) method. Characterization of as-siliconized layers and diamond coatings was performed by energy dispersive X-ray analysis, scanning electron microscopy, X-ray diffraction and Raman spectroscopy.     

Apatite formation on Poly (vinyl alcohol)-coated Poly (?-caprolactone) films by incubation in simulated body fluids

In this study, biodegradable poly (?-caprolactone) (PCL) films were coated with poly (vinyl alcohol) (PVA) and then incubated in a simulated body fluid 1.5SBF to prepare an apatite (HA)/PCL composite. It was found that the bone-like apatite formability of PCL was enhanced by PVA coating. The changes of surface properties induced by PVA coating were effective for apatite formation. The apatite formability increased with increasing coating amount. After 24 h incubation, apatite was formed on PVA-coated PCL film but hardly any apatite was found on uncoated PCL plate. The surface chemistry of the specimens was examined using XPS, FT-IR-ATR. The apatite formed was characterized by using SEM, TF-XRD, FT-IR, EDS. The apatite formed was similar in morphology and composition to that of natural bone. This indicated that simple PVA coating on PCL substrate could serve as a novel way to accelerated apatite formation via biomimetic method.     

Influence of substrate hardness transition on built-up of nanostructured WC-12Co by cold spraying

The ability of cold spray process to retain the feedstock microstructure into coating makes it possible to deposit nanostructured WC-Co coatings. In the present study, the deposition behavior of nanostructured WC-12Co coating was examined through the surface morphology and cross-sectional structure of the deposited single WC-12Co particle impacting on the substrates with different hardness using a nanostructured WC-12Co powder. Substrates included stainless steel, nickel-based self-fluxing alloy coatings with different hardness. It was observed from the top surface and cross-section of individual WC-12Co particles that the penetration leading to particle deposition depends on substrate hardness. When the substrate surface is covered by WC-12Co particles, the hardness of the newly formed substrate, i.e. the coating, increases greatly. The significant increase of the surface hardness leads to the rebounding off of impacting particles and erosion of the deposited particles, which prohibits effective built-up of coating. However, it was found that with spray jet fixed, a deposit with a thickness up to over 700 μm can be built-up. A model involving in substrate hardness transition during deposition is proposed to explain such phenomenon, which can be employed to optimize the conditions to build up a uniform nanostructured WC-12Co coating.     

Hydroxyapatite/titania composite bioactivity coating processed by sol-gel method

Hydroxyapatite/titania composite material was coated onto a titanium (pure Ti) substrate by sol-gel method. The hydroxyapatite (HA) and titania (TiO₂) sol were made from precursor and mixed together. The insertion of TiO₂ enhanced the chemical affinity and the physical consistency between HA and Ti substrate. The HA/TiO₂ composite coating adhered tightly to the Ti substrate. Owing to the insertion of TiO₂, the crystallinity of HA has been delayed. The specimens with HA/TiO₂ composite coatings were soaked into SBF, and displayed good bone-like apatite forming ability. The bioactivity of the composite HA coatings were tested in vitro by cell culture.