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.     

Rheological behavior of aqueous suspensions of hydroxyapatite (HAP)

The aim of this study is to characterize the influence of organic dispersants on the stability of hydroxyapatite (HAP) dispersions, using viscosity measurements, electrokinetic sonic amplitude (ESA) measurements and adsorption isotherms. Colloidal stability of aqueous suspensions of HAP as a function of solids loading and of the type and concentration of deflocculant has been studied. The interaction between particles and dispersant molecules was characterized. Adsorption measurements of the amount of dispersants on the particles surface, viscosity and electrophoretic measurements as a function of the dispersant concentration are correlated. Suspension parameters have been adjusted in order to obtain a high solids loading slurry with a plastic viscosity which will allow its use in colloidal processing.     

Plasma spray of biofunctional(Mg,Sr)-substituted hydroxyapatite coatings for titanium alloy implants

Plasma-sprayed hydroxyapatite(HA) coatings have been widely utilized in load-bearing titanium alloy implants. In this study, Mg, Sr co-substituted HA((Mg, Sr)-HA) nano-scale powders have been synthesized, which are further used to prepare(Mg, Sr)-HA coatings on Ti-6 Al-4 V alloys in order to improve the biological functions. The average size of(Mg, Sr)-HA nano particles is ～75 nm. The average bonding strength for(Mg, Sr)-HA coating and samples after heat treatment at 500°C or 600°C for 3 h are26.17 ± 2.11 MPa, 36.07 ± 4.48 MPa and 37.07 ± 2.95 MPa, respectively. There is a significantly increase of bonding strength likely due to low residual stress after heated treatment. MC3 T3-E1 cells show a high proliferation rate when cultured with(Mg, Sr)-HA coating extract compared to the normal culture medium, which also exhibit large extension and deposition of extracellular matrices when adhered on the coating surfaces. Thus, these(Mg, Sr)-HA coatings show high bonding strength and improved biological functions, which offer promising future applications in the fields of orthopedics and dentistry.     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm⁻². A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Abstract

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm^?2. A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

Bioactive nanocomposite coatings of collagen/hydroxyapatite on titanium substrates

Collagen/hydroxyapatite (HA) nanocomposite thin films containing 10, 20, and 30 wt.% HA were prepared on commercially pure titanium substrates by the spin coating of their homogeneous sols. All of the nanocomposite coatings having a thickness of ∼7.5 μm exhibited a uniform and dense surface, without any obvious aggregation of the HA particles. A minimum contact angle of 36.5° was obtained at 20 wt.% HA, suggesting that these coatings would exhibit the best hydrophilicity. The in vitro cellular assays revealed that the coating treatment of the Ti substrates favored the adhesion of osteoblast-like cells and significantly enhanced the cell proliferation rate. The cells on the nanocomposite coatings expressed much higher alkaline phosphatase (ALP) levels than those on the uncoated Ti substrates. Increasing the amount of HA resulted in a gradual improvement in the ALP activity. The nanocomposite coatings on Ti substrates also exhibited much better cell proliferation behaviors and osteogenic potentials than the conventional composite coatings with equivalent compositions, demonstrating the greater potential of the former as implant materials for hard tissue engineering.     

Biomechanical evaluation of different hydroxyapatite coatings on titanium for keratoprosthesis

Stable tissue integration is important to keratoprosthesis (KPro). The aim of this study was to evaluate the tissue bonding ability of hydroxyapatite (HAp)-coated titanium KPro. The samples were divided into three groups: test groups (IBAD group and AD group) and Ti control. The coated samples had a HAp layer created by ion beam assisted deposition (IBAD) or aerosol deposition (AD). The surface characteristics were analyzed with SEM, AFM, and XRD. The samples were surgically inserted into the muscles of rabbits. Eight weeks after healing, the attachment to the tissue was tested with a universal test device. The three samples exhibited distinctive surface morphology. The force to remove the HAp implants from the muscles was significantly greater than that of Ti group (P<0.01), with the AD samples requiring the greatest force (P<0.01). After removal, SEM showed that the tissue was firmly attached to the surface of AD samples. Photomicrographs of the peri-implant muscles showed a layer of aligned fibrous tissue without severe inflammation. The AD samples had more fibroblasts. Results indicate that because of enhanced mechanical adhesion of soft tissue to the implants, HAp-coated Ti by AD is a suitable KPro skirt material.     

Electrodeposition of poly(o-anisidine) coatings onto copper

Abstract

Uniform and strongly adherent poly(o-anisidine) (POA) coatings have been successfully electrodeposited onto copper (Cu) substrates from the aqueous bath containing sodium oxalate and o-anisidine by using cyclic voltammetry (CV). CV, UV visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements were used to characterise these coatings, which indicates that the aqueous sodium oxalate solution is a suitable medium for the formation and deposition of POA onto Cu substrates. It is observed that the electrodeposition of POA coatings takes place after the passivation of the Cu substrate via formation of copper oxalate (CuC₂O₄.H₂O) layer, which is confirmed by XRD measurement. The optical absorption spectroscopy study reveals the formation of the mixed phase of pernigraniline base (PB) and emeraldine salt (ES) forms of POA. The surface morphology of the coating is uniform, compact and featureless as revealed by SEM imaging.     

Topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite coatings on carbon fibre-reinforced poly(etheretherketone)

In the present study, topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite (HA) coatings on carbon fibre-reinforced polyetheretherketone (CF/PEEK) was performed. VPS-Ti coatings with high roughness values (Ra=28.29±3.07 m, Rz=145.35±9.88 m) were obtained. On this titanium, intermediate layer HA coatings of various thicknesses were produced. With increasing coating thickness, roughness values of the HA coatings decreased. A high increase of profile length ratio, Lr, of the VPS-Ti coatings (Lr=1.45) compared to the grit-blasted CF/PEEK substrate (Lr=1.08) was observed. Increasing the HA coating thickness resulted in a reduction of the Lr values similar to the roughness values. Fractal analysis of the obtained roughness profiles revealed that the VPS-Ti coatings showed the highest fractal dimension of D=1.34±0.02. Fractal dimension dropped to a value of 1.23–1.25 for all HA coatings. No physical deterioration of the CF/PEEK substrate was observed, indicating that substrate drying and the used VPS process parameter led to the desired coatings on the composite material. Cross-section analysis revealed a good interlocking between the titanium intermediate layer and the PEEK substrate. It is therefore assumed that this interlocking results in suitable mechanical adhesive strength. From the results obtained in this study it is concluded that VPS is a suitable method for manufacturing HA coatings on carbon fibre-reinforced PEEK implant materials.     

Interaction of hydroxyapatite with titanium nickelide and titanium

It has been established that the interaction of hydroxyapatite with titanium nickelide and titanium results in the formation of new phases whose physicomechanical properties and biocompatibility are unknown. After hydroxyapatite has been resorbed, these phases come in contact with tissue and near-tissue fluids and influence the result of the implant. Pis’ma Zh. Tekh. Fiz. 24, 41–44 (December 26, 1998)     

Tribochemical structuring and coating of implant metal surfaces with titanium oxide and hydroxyapatite layers

The sandblasting process with corundum is used for cleaning, roughening and activating of metal surfaces in dentistry and orthopaedics. The high local energy transfer at the impact point originates the displacement of particles in the surface. In principle, this method can be used for coating surfaces by sandblasting. In this work, we present a newly developed technique, which allows the coating of metal surfaces with titanium dioxide (TiO₂) and hydroxyapatite (HA) using a sandblasting process. The blasting material is a composite ceramic consisting of an alumina core (carrier material) covered with a porous shell of titanium dioxide or hydroxyapatite. The technique is applied to titanium substrates; the surface roughness, morphology and composition of the samples are analysed. The procedure results in an averaged surface roughness of 10–15 μm. Energy dispersive X-ray analysis (EDX) indicates the formation of a thin layer consisting of coating material on the metal surface. Furthermore, the traces of corundum crystals, which are inevitable by using the common technique, i.e. sandblasting with single-component grains, are clearly decreased. X-ray diffraction analysis (XRD) indicates mainly the existence of crystalline rutile and hydroxyapatite/β-tricalcium phosphate (β-TCP) on the surface. Therefore, the presented method would be suitable for simultaneously roughening, coating and optimizing the biocompatibility of metal implant surfaces in dentistry and endoprosthetics.     

Tribotechnical properties of coatings on titanium alloys

We compare the antifriction properties of different types of coatings on titanium alloys under conditions of boundary friction as applied to parts of the hydraulic cylinders of an aircraft. We show that gasthermal titanium carbide coatings cladded with nickel and with both copper and nickel have better antifriction characteristics than ones obtained by chrome electroplating, nickel chemoplating, thermooxidation, anodization, etc. Kiev International University of Civil Aviation; J.S.S.T.C. “Antonov,” Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 55–62, March–April, 1998.     

Effect of surface capping on targeting potential of folate decorated poly (propylene imine) dendrimers

Objective: The objective of the present investigation was to assess and compare the effect of surface capping by different groups (-OH, -COOH and -NH₂) on tumor targeting potential of folate conjugated poly (propylene imine) (PPI) (F-PPI) dendrimers using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay.

Materials and methods: The synthesized nanoconjugates (F-PPI, F-COOH-PPI, F-OH-PPI and F-CONH-PPI) were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (¹H-NMR) and transmission electron microscopic (TEM) studies. The formulations were evaluated for drug entrapment, in vitro drug release and hemolytic toxicity, and cytotoxicity was evaluated on HeLa and SiHa cell line using MTT assay.

Results: In case of all surface capped formulation, Methotrexate (MTX) loading was found to increased; however MTX release rate was found to decrease as compared to unmodified formulation. Further, F-COOH-PPI displayed highest tumor targeting potential as compared to other formulations. This is the first study to explore the effect of surface capping on the targeting potential of folate-conjugated fifth generation (5.0?G) PPI dendrimer.

Conclusions: In conclusion, the targeting potential of all the formulations (anticancer activity) for both HeLa and SiHa cells follows in the following order: F-COOH-PPI?>?F-OH-PPI?>?F-CONH-PPI?>?F-PPI.     

Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young’s modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200–250 μ m were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.     

Effects of coatings on the mechanical properties of carbon fiber reinforced HAP composites

The HAP/carbon-fiber composite for bone re-construction was prepared and its mechanism of interfacial interaction between HAP and carbon fibers was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area diffraction (SAD) in this paper. Results show that composite reinforced by carbon fibers with a layer of β-TCP coatings exhibits significantly better biomechanical properties, comparing these composites with non-coated fibers. It can be explained that the existence of β-TCP coatings, changing the surface properties of carbon fibers into hydrophilic, greatly enhance the interfacial bonding strength by adhering to the HAP matrix directly. On the other hand, the β-TCP coatings, as a mid-layer between HAP and carbon fibers, can reduce the gradient of thermal stress on its phase boundary with HAP matrix, which can eliminate the cracking problems during cooling of sintered. Consequently causing improvement of mechanical properties of composites.     

The process of electrochemical deposited hydroxyapatite coatings on biomedical titanium at room temperature

Calcium phosphate (CaP) ceramics, especially hydroxyapatite (HA), have received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several methods for preparing HA coating, electrochemical deposition is a relatively new and possible process. However, documented electrochemical processes were conducted at elevated temperature. In this study, uniform HA coatings have been directly deposited on titanium at room temperature. X-ray diffractometry (XRD) results demonstrated that dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) was the main component of the coating deposited at lower current densities (1 and 5 mA/cm²). HA structure was obtained at current density above 10 mA/cm² and remained stable after heat treatment at 100–600 °C for 1 h. Part of HA phase was transformed into β-TCP and became a biphasic calcium phosphate coating after annealing at 700 °C. Scratch tests showed that HA coating was not scraped off until a shear stress of 106.3 MPa. Coatings deposited at room temperature exhibited stronger adhesion than those at elevated temperature. HA coating revealed a dense inner layer and rough surface morphology which could fulfill the requisition of implant materials and be adequate to the attachment of bone tissue.     

Abrasive wear of ion-plated titanium nitride coatings on plasma-nitrided steel surfaces

The abrasive wear of ion-plated titanium nitride coatings on hardened tool steel and on hardened and plasma-nitrided tool was studied. Wear tests were made with a dry sand-rubber wheel set-up, and the initial surface roughness of the specimen was one of the test parameters.A wear mechanism for hard coatings on softer substrates under abrasive wear conditions was suggested. The wear initiates on the tops of the asperities where the base material is exposed first. Wear proceeds with the formation of craters at these sites and the growth of these crystals by fractures on the ridges formed by the coating material.The wear rate of coated steel increases with increasing initial surface roughness. A considerable increase takes place when the scale of the surface roughness is of the same order of magnitude as the coating thickness. This increase can be shifted to a higher surface roughness if a subsurface hardening process, in this case plasma nitriding, is used.