The biomimetic deposition of carbonate apatite induced by titanium base calcium enriched silica films

Abstract

In order to obtain a fast biomimetic coating on titanium substrates, calcium enriched silica films were prepared on pure titanium substrates by sol–gel method under the following conditions: pH?=?3 and the molar ratio of tetraethyl orthosilicate (TEOS)/H₂O/EtOH/Ca²⁺?=?1∶4∶11∶0·08. The titanium base calcium enriched silica film is soaked in a slightly supersaturated Ca/P solution, with the concentration of calcium ion and phosphate group being 1·5 times of that of simulated body fluid, for seven days, a uniform apatite layer is precipitated onto the surfaces of calcium enriched silica films, which is quite rapidly. The investigation adopted SEM, EDX, Fourier transform infrared spectroscope and XRD to indicate that the coating was carbonate hydroxyapatite. The results show that it is a feasible way to obtain carbonate hydroxyapatite through functionalising the pure titanium substrates by preparing calcium enriched silica films on it from a sol–gel method.     

Fabrication of a 12-tungstophosphate and cadmium oxide composite film and its properties

A multilayer composite film of the 12-tungstophosphate H₃[PW₁₂O₄₀]³⁻ (PW₁₂) and cadmium oxide nanoparticles (CdO) was fabricated on quartz and silicon by the layer-by-layer (LBL) self-assembly method. The film was characterized by UV–vis spectroscopy, atomic force microscopy (AFM) and luminescence spectra. The proposed composite film exhibits higher photocatalytic activity toward methyl orange (MO) solution at pH 3.5, compared to single PW₁₂ and CdO films. The degradation rate was affected by initial concentration of PW₁₂, pH value of MO solution, inorganic ions concentration and type in MO solution. In addition, the composite film displays luminescent property and reversible electrochromic property with fast response time.     

A novel biodegradable nicotinic acid/calcium phosphate composite coating on Mg–3Zn alloy

A novel biodegradable composite coating is prepared to reduce the biodegradation rate of Mg–3Zn alloy. The Mg–3Zn substrate is first immersed into 0.02 mol L^? 1 nicotinic acid (NA) solution, named as vitamin B₃, to obtain a pretreatment film, and then the electrodeposition of calcium phosphate coating with ultrasonic agitation is carried out on the NA pretreatment film to obtain a NA/calcium phosphate composite coating. Surface morphology is observed by scanning electron microscopy (SEM). Chemical composition is determined by X-ray diffraction (XRD) and EDX. Protection property of the coatings is evaluated by electrochemical tests. The biodegradable behavior is investigated by immersion tests. The results indicate that a thin but compact bottom layer can be obtained by NA pretreatment. The electrodeposition calcium phosphate coating consists of many flake particles and ultrasonic agitation can greatly improve the compactness of the coating. The composite coating is biodegradable and can reduce the biodegradation rate of Mg alloys in stimulated body fluid (SBF) for twenty times. The biodegradation process of the composite coating can be attributed to the gradual dissolution of the flake particles into chippings.     

Layer-by-layer assembled graphene oxide/polydiallydimethylammonium chloride composites for hydrogen gas barrier application

Poly(diallyldimethylammoium chloride) (PDDA)/acid or base modified graphene oxide (MGO) composite (PDDA/MGO)-based gas barrier films were prepared by layer-by-layer (LBL) assembly method on polyethylene terephthalate (PET) substrate using a spray coating assisted deposition. The effect of pH on the hydrogen gas permeability (H₂GP) values of the different MGO-based films was investigated to determine the optimum pH value of the MGO solution for the preparation of PDDA/MGO-based LBL assembly. Accordingly, the different numbers of bilayers based LBL-assembled films were prepared using alternate deposition of PDDA and MGO solutions and the H₂GP values were measured for those assemblies. The films were characterized by XRD, FT-IR, and Raman spectroscopy analyses. The morphology of the LBL-assembled film was observed by cross-sectional field emission scanning electron microscopy which confirms densely packed layered structure. The H₂GP of six bilayers PDDA/MGO composite film is 5.7 cc/m²?d?atm, which is much lower than that of pure PET substrate (170.7 cc/m²?d?atm), indicating 96.7% decrease in H₂GP. This result suggests that the PDDA/MGO composite film could be used as a potential candidate to fabricate hydrogen gas barrier coating material.     

镀锌层无铬钼酸盐钝化液的研究进展及思考

镀锌层无铬钼酸盐钝化液的研究进程经历了由钼酸盐+磷酸盐体系发展到该体系加添加剂(无机或有机化合物)的钝化液体系的过程.为了增加钝化膜的膜厚,封闭微裂纹,达到高耐蚀的目的,列举了将无机盐和有机化合物复配以获得复合钝化膜的钝化工艺.其中较为成功的钝化液是钼酸盐与硅烷的复配体系,所获得的钝化膜的性能已接近、达到或超过了铬酸盐钝化膜的耐蚀水平.最后提出了一些尚待解决的问题.     

Exponential growth of LBL films with incorporated inorganic sheets

The fastest growth pattern of layer-by-layer (LBL) assembled films is exponential LBL (e-LBL), which has both fundamental and practical importance. It is associated with "in-and-out" diffusion of flexible polymers and thus was considered to be impossible for films containing clay sheets with strong barrier function, preventing diffusion. Here, we demonstrate that e-LBL for inorganic sheets is possible in a complex tricomponent film of poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA), and Na(+)-montmorillonite (MTM). This system displayed clear e-LBL patterns in terms of both initial accumulation of materials and unusually thick individual bilayers later in the deposition process with film thicknesses reaching 200 microm for films composed of 200 pairs of layers. Successful incorporation of MTM layers was observed by scanning electron microscopy and thermo-gravimetric analysis. Surprisingly, the growth rate was found to be nearly identical in films with and without clay layers, which suggests fast permeation/reptation of polyelectrolytes between the nanosheets during the "in-and-out" diffusion of polymer. In considering these findings, e-LBL growth property is expected for a wide array of available inorganic nanoscale components and have a potential to greatly expand the e-LBL field and LBL field altogether. The large thickness and rapid growth of the films affords fast preparation of nanostructured materials which is essential for multiple practical applications ranging from optical devices to ultrastrong composites.     

BCP coatings on pure titanium plates by CD method

Ca–P coatings on pure titanium plates were precipitated in this work by a cathode deposition (CD) method and showed several differences from other reported works. The fast calcification solution (FCS) and revised simulation body fluid (R-SBF) were used as electrolytes. A significant difference in sizes of crystals and thickness of the precipitated coatings was observed between the bioactive calcium phosphate (BCP) coatings precipitated from FCS and from R-SBF. The possible reason of this difference was ascribed to that the ion concentrations of Ca²⁺ and HPO₄²⁻ and some inhibitors of Ca–P crystals growth such as Mg²⁺ and CO₃²⁻ ions and pH of electrolytes. The crystalline structure and composition of BCP coatings are of special importance to applications of the BCP coatings. The characterization has been fulfilled by the use of XRD, FTIR, SEM and TEM. The results of this study made it clear that the precipitates on the Ti plates by cathode deposition method in different electrolytes were not the hydroxyapatite (HA) but octacalcium phosphate (OCP) and some carbonate-containing amorphous calcium phosphate apatite, and a few of precipitates changed to needle-like HA after immerged in a 0.1 M NaOH solution at 60 °C for 48 h. The present study confirms that CD method is a more convenient and fast way to prepare BCP coatings on titanium implants than the reported works.     

Preparation of Nanocrystalline ZrO2 Film Using a Zirconium Naphthenate and In Vitro Formation of Calcium Phosphate

Bioactive nanocrystalline ZrO₂ coatings were prepared onto (100) Si substrates by using a chemical solution deposition with a zirconium naphthenate as a starting material. Precursor sol was spin-coated onto the substrates and prefired at 500°C for 10 min in air. Formation of crystalline ZrO₂ film was observed at 800°C by X-ray diffraction. Surface morphology and surface roughness of the film were characterized by field emission-scanning electron microscope and atomic force microscope. After soaking for 5 days in a simulated body fluid, formation of the calcium phosphate was observed on ZrO₂ film annealed at 800°C by energy dispersive X-ray spectrometer. Fourier transform infrared spectroscopy revealed that carbonate was substituted into the calcium phosphate.     

An electrodeposition method of calcium phosphate coatings on titanium alloy

Calcium phosphates coatings were deposited onto titanium alloy discs via en electrodeposition method. Titanium alloy discs were blasted with calcium phosphate particles, then etched in a mixture of nitric and fluoric acids and rinsed in demineralized water. The titanium alloy disc (cathode) and platinum mesh (anode) were immersed in a supersaturated calcium phosphate electrolyte buffered at pH 7.4 and connected to a current generator. The microstructure, chemical composition and crystallinity of the electrodeposited coatings were studied as function of time 10–120 min, temperature 25–80°C, current density 8–120 mA/cm², magnesium and hydrogen carbonate amounts (0.1–1 mM). Uniform calcium phosphate coatings were obtained in 30 min but coating thickness increased with deposition time. Raising the temperature of electrolyte resulted in more uniform coatings as ionic mobility increased. Low current density was preferable due to hydrogen gas evolving at the cathode, which disturbed the deposition of calcium phosphate crystals on titanium. The amounts of magnesium and hydrogen carbonate ions affected both the homogeneity and morphology of the coatings. This study showed that the electrodeposition method is efficient for coating titanium with osteoconductive calcium phosphate layers.     

Fabrication of mesoporous carbonated hydroxyapatite/carbon nanotube composite coatings by microwave irradiation method

Carbonated hydroxyapatite/carbon nanotube composite coatings (MHCs) with mesoporous structures were fabricated by electrophoretic deposition of nacre powders and carbon nanotubes on Ti6Al4V substrates followed by treatment with a phosphate buffer solution (PBS) by microwave irradiation method. The carbon nanotubes are dispersed uniformly on the whole MHCs. The conversion mechanism of the crack-free nacre/carbonate nanotube composite coatings (NCCs) to MHCs is a dissolution-precipitation reaction. After soaking in PBS, calcium ions are released from the nacre powders and react with phosphate ions to form carbonated hydroxyapatite nanoparticles. These nanoparticles aggregate to form mesopores with the pore sizes of ~ 3.9 nm among them. Simulated body fluid (SBF) immersion tests reveal that MHCs have a good in vitro bioactivity.     

Dynamic aspects of films prepared by a sequential deposition of species: perspectives for smart and responsive materials

The deposition of surface coatings using a step-by-step approach from mutually interacting species allows the fabrication of so called "multilayered films". These coatings are very versatile and easy to produce in environmentally friendly conditions, mostly from aqueous solution. They find more and more applications in many hot topic areas, such as in biomaterials and nanoelectronics but also in stimuli-responsive films. We aim to review the most recent developments in such stimuli-responsive coatings based on layer-by-layer (LBL) depositions in relationship to the properties of these coatings. The most investigated stimuli are based on changes in ionic strength, temperature, exposure to light, and mechanical forces. The possibility to induce a transition from linear to exponential growth in thickness and to change the charge compensation from "intrinsic" to "extrinsic" by controlling parameters such as temperature, pH, and ionic strength are the ways to confer their responsiveness to the films. Chemical post-modifications also allow to significantly modify the film properties.     

Effects of protein incorporation on calcium phosphate coating

The incorporation of proteins into calcium phosphate (Ca–P) coatings is expected to alter their properties. The aim of this work is, therefore, to study the effect of protein concentration on the formation of Ca–P film. A biodegradable blend of corn starch/ethylene vinyl alcohol (SEVA-C) was used as substrate and bioactive glass (45S5 Bioglass^®) was used as a nucleating agent. Bovine serum albumin (BSA) and α-amylase were added, separately, at a concentration of 0.5, 1, and 5 mg/mLto simulated body fluid (SBF) solutions, at the nucleation stage.The incorporation of protein molecules was shown to affect the properties of Ca–P coatings in terms of morphology, composition and crystallinity. Both proteins seem to inhibit in some extent and/or retard the growth of Ca–P nuclei at 0.5 and 5 mg/mL concentrations. FTIR analyses revealed the presence of phosphate and carbonate groups, confirming the formation of a Ca–P layer. The characteristic groups of protein molecules were also detected on the IR spectra, which indicate the efficient incorporation of the proteins into the coatings. When α-amylase was added to the SBF solution the production of reducing sugars was detected, proving the retention of enzyme activity. These results suggest the carrier potential of Ca–P coatings for the sustained delivery of other biologically active proteins and consequently with a strong potential for inducing bone tissue regeneration.     

Calcium phosphate formation on titanium by low-voltage electrolytic treatments

Electrochemical treatments are expected to be effective for the coating of calcium phosphate ceramics to a titanium substrate. In the present study, two types of chronoamperometry with a step potential and a cyclic wave potential at low voltage (up to 2.0 V) and low current density were performed in Hanks’ solution to modify the surface characteristics of titanium. Titanium oxide film formed by self-passivation, that formed as reconstructed film during electrochemical treatments, and a calcium phosphate layer precipitated through treatments were characterised by X-ray photoelectron spectroscopy. The thickness and compositions of the surface films and layers were quantified from the XPS results. Calcium phosphate formation during immersion in Hanks’ solution for 1.0 Ms was evaluated by scanning electron microscopy with energy-dispersive X-ray spectrometry. The results confirmed that the electrolytic treatments in this study were effective to accelerate calcium phosphate formation on titanium in Hanks’ solution in spite of their lower voltage than conventional methods. The results also suggested that the hydroxyl group in the surface oxide film might contribute to the formation of calcium phosphate. This technique is a promising process for the treatment of thin titanium materials.     

Growth of calcium phosphate on ion-exchange resins pre-saturated with calcium or hydrogenphosphate ions: an SEM/EDX and XPS study

Calcium phosphate formed on the surfaces of ion-exchange resins pre-saturated with either Ca²⁺ or HPO₄ ^2- ions has been studied using a combination of scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). Calcium phosphate was formed at a temperature of 36.5°C via two methods. On Ca²⁺ or HPO₄ ^2--saturated resins, 1.5xSBF (simulated body fluid) solution was used while on Ca²⁺-saturated resins only, a novel biomimetic growth medium using the alkaline phosphatase-catalysed hydrolysis reaction of disodium p-nitrophenylphosphate as a source of inorganic phosphate was employed. SEM micrographs showed that the use of 1.5xSBF growth medium solution led to extensive coverage of the resins with calcium phosphate. In contrast, calcium phosphate coatings formed via the alkaline phosphatase-catalysed reaction were of a more variable quality whose morphology could be influenced by adding albumin and collagen to the growth medium. Average Ca:P ratios determined by EDX for coatings formed from the 1.5xSBF growth medium were in the range 1.62–1.74 suggesting that hydroxyapatite had formed. In contrast, Ca:P ratios for the calcium phosphate compounds formed on resins from the alkaline phosphatase reaction were lower at 1.50 suggesting that calcium-deficient hydroxyapatite had formed which was confirmed by inductively coupled plasma (ICP) analysis and X-ray diffraction of isolated amorphous and crystallized powder samples, respectively. Evidence from X-ray photoelectron studies supports a mechanism of formation of the coatings which involves diffusion of the ion out of the interior of the resin to create a high local concentration at the surface thus stimulating precipitation of the coating material on the resin beads.     

Layer-by-layer assembled PVA/Laponite multilayer free-standing films and their mechanical and thermal properties

Structural arrangements of nanoplatelets in a polymer matrix play an important role in determining their properties. In the present study, multilayered composite films of poly(vinyl alcohol) (PVA) with Laponite clay are assembled by layer-by-layer (LBL) deposition. The LBL films are found to be hydrated, flexible and transparent. A facile and solvent-free method-by depositing self-assembled monolayers (SMA) of a functional silane on substrates-is demonstrated for preparing free-standing LBL films. Evolution of nanostructures in LBL films is correlated with thermal and mechanical properties. A well-dispersed solvent-cast PVA/Laponite composite film is also studied for comparison. We found that structurally ordered LBL films with an intercalated nanoclay system exhibits tensile strength, modulus and toughness, which are significantly higher than that of the conventional nanocomposites with well-dispersed clay particles and that of pure PVA. This indicates that clay platelets are oriented in the applied stress direction, leading to efficient interfacial stress transfer. In addition, various grades of composite LBL films are prepared by chemical crosslinking and their mechanical properties are assessed. On account of these excellent properties, the LBL films may find potential use as optical and structural elements, and as humidity sensors.     

Determination of differences in tribological behavior and surface morphology between electrodeposited and traditional phosphate coatings

Traditional phosphate coatings are formed by submersing iron or steel in an aqueous solution of phosphoric acid and other chemicals without applying an axternal voltage. In contrast, the newly developed electrocoated iron phosphate films described in this paper are deposited electrochemically from an oil containing mixed organic phosphates. The friction characteristics and surface morphology of the electrodeposited iron phosphate films on piston ring specimens were compared with those of traditional phosphate coatings. The electrodeposited film consists of an amorphous structure and provides lower friction than does either traditional crystalline manganese or iron phosphate coatings. These results indicate that surface morphology has a strong influence on friction-reducing film formation mechanisms.     

Incorporation of proteins and enzymes at different stages of the preparation of calcium phosphate coatings on a degradable substrate by a biomimetic methodology

In this work, the possibility of incorporating proteins into calcium phosphate (Ca-P) coatings, prepared on the surface of starch polymeric biomaterials by means of a biomimetic route, was investigated. The morphology, chemical composition and crystallinity of Ca-P coatings was assessed and related to the incorporation of the studied biomolecules. For that, bovine serum albumin (BSA) and α-amylase were added in concentrations of 1 mg/ml to simulated body fluid (SBF) solutions, being both added at the nucleation or growth stages of the biomimetic coating process. A biodegradable blend of corn starch/ethylene vinyl alcohol (SEVA-C) was used as substrate and bioactive glass (45S5 Bioglass®) was used as the nucleating agent. The obtained Ca-P coatings were characterised by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy using an attenuated reflectance device (FTIR-ATR) and thin-film X-ray diffraction (TF-XRD). Additionally, to evaluate the activity of the incorporated enzyme and the stability of the Ca-P films, coated samples were immersed in an SBF solution for different periods of time. The enzyme activity was measured and the morphology of the coating examined by SEM. The results obtained showed that the presence of protein molecules, at the nucleation or growth stages, lead to the formation of a dense Ca-P film presenting different morphologies that were different of the selected coating conditions. FTIR-ATR analysis detected the presence of carbonate and phosphate groups on the Ca-P layer, indicating the formation of a coating similar to the mineral component of vertebrates bone tissue. When proteins were added, amide I and amide II bands, characteristic groups of protein molecules, were also detected, revealing the efficient incorporation of these biomolecules into the Ca-P coatings.Ca-P coatings, with α-amylase incorporated at the nucleation stage, showed no degradation of the film after incubation in SBF for 28 days. The release of increasing concentration of reducing sugars with degradation time revealed that α-amylase was efficiently incorporated in the coating remaining active throughout the coating preparation. This can be a strategy that will allow, in addition of conferring osteoconductive properties to biodegradable polymers, also simultaneously tailoring their degradation kinetics.     

Imposed quasi-layer-by-layer homoepitaxial growth of SrTiO3 films by large area pulsed laser deposition

The homoepitaxial growth of SrTiO₃ (STO) films was investigated by a large-area pulsed laser deposition (PLD), which was in-situ monitored by a high pressure reflective high energy electron diffraction. By combining a conventionally continuous film deposition with a followed interval relaxation, a persistent layer-by-layer (LBL) film growth of more than 100 unit cells STO films was achieved. This interrupted PLD technique could realize persistent LBL film growth at any laser frequency between 1 and 10 Hz and provides an effective way to fabricate high quality complex oxide films on unit cell scale.     

Physical–chemical and biological behavior of an amorphous calcium phosphate thin film produced by RF-magnetron sputtering

This work evaluates the thermal reactivity and the biological reactivity of an amorphous calcium phosphate thin film produced by radio frequency (RF) magnetron sputtering onto titanium substrates. The analyses showed that the sputtering conditions used in this work led to the deposition of an amorphous calcium phosphate. The thermal treatment of this amorphous coating in the presence of H₂O and CO₂ promoted the formation of a carbonated HA crystalline coating with the entrance of CO₃^2 ? ions into the hydroxyl HA lattice. When immersed in culture medium, the amorphous and carbonated coatings exhibited a remarkable instability. The presence of proteins increased the dissolution process, which was confirmed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonated HA coating induced precipitation independently of the presence of proteins under dynamic conditions. Despite this surface instability, this reactive calcium phosphate significantly improved the cellular behavior. The cell proliferation was higher on the Ticp than on the calcium phosphate coatings, but the two coatings increased cellular spreading and stress fiber formation. In this sense, the presence of reactive calcium phosphate coatings can stimulate cellular behavior.     

Preparation and characterization of luminescent nanocomposite film containing polyoxometalate

A nanosized composite film based on polyoxometalate anion [Eu(SiW₁₀VO₃₉)₂]¹⁵⁻ (EuSiWV) and polyethyleneimine (PEI) has been synthesized by layer-by-layer (LBL) self-assembly. The components and growth processes of the film have been determined by X-ray photoelectron spectra and ultraviolet-visible absorption spectra. The results showed that the composite film was formed by the alternate adsorption of EuSiWV and PEI, and the deposition process was quantitative and highly reproducible from layer to layer. Atomic force microscopy images indicated that the surface of the film was relatively uniform and smooth. The EuSiWV salt aggregated into nanoclusters with approximately 10 nm mean grain size, distributing on the surface uniformly. The surface roughness was approximately 2.4 nm. Fluorescence properties of the film were consistent with those of the solid sample, exhibiting obvious activity of fluorescence and incarnating the characteristic luminescence of Eu³⁺. In addition, the electrochemical behavior of the film has also been investigated, demonstrating that the electrochemical property of EuSiW₁₀V was fully maintained in the LBL film.