Electrospray deposition as a method to fabricate functionally active protein films

Electrospray ionization is a routine method in MS analysis of proteins and other biopolymers. Deposition of the electrospray products onto a conductive electrode is suggested here as a means to manufacture functionally active protein films. Recovery of the specific hydrolytic activity of the electrosprayed alkaline phosphatase (AP) was used as a probe for preservation of protein intactness in the electrospray deposition (ESD). It was shown that protein inactivation upon ESD is highly dependent on voltage and current used. Humidity and the presence of protective substances in solution also affect the process. Complete preservation of the enzyme activity was observed when the ESD was performed at low current and humidity in the presence of disaccharides.     

Electrostatic Spray Deposition of Biomimetic Nanocrystalline Apatite Coatings onto Titanium

Titanium (Ti) and its alloys are widely used to manufacture orthopedic and dental implants due to their excellent mechanical properties and corrosion resistance. Although these materials are bioinert, improvement of biological properties (e.g., bone implant contact) can be obtained by the application of a coating made of nanostructured apatite. The aim of this study was to investigate the applicability of the electrostatic spray deposition (ESD) technique for the deposition of nanostructured apatite coatings onto commercially pure (cp) Ti substrates at room temperature. To that end, poorly crystalline, nano‐sized, carbonate‐apatite plate‐like particles with dimensions similar to the nanocrystals present in bone were synthesized using wet‐chemical precipitation techniques and their physicochemical properties were subsequently characterized thoroughly. The apatite suspensions were optimized for the ESD process in terms of dispersion, aggregation, and stability. Furthermore, relevant ESD processing parameters, including nozzle‐to‐substrate distance, relative humidity in the deposition chamber and deposition time were varied in order to study their effects on coating morphology. Porous films made of agglomerates of nano‐sized apatite particles of ≈50 nm were generated, demonstrating the feasibility of the ESD technique for the deposition of thin apatite coatings with a nano‐sized surface morphology onto titanium substrates. The ability of these nanocrystals to bind therapeutic agents for bone diseases and the capability of ESD to produce coating at physiological conditions makes this work a first step toward the set‐up of coatings for bone implants based on surface‐activated apatite with improved functionality.     

In vitro response of primary rat osteoblasts to titania/hydroxyapatite coatings compared with transformed human osteoblast-like cells

The biocompatibility of titania/hydroxyapatite (TiO₂HA) composite coatings, at different ratio obtained by sol–gel process, was investigated studying the behavior of primary cultures of rat osteoblastic cells, isolated by femoral trabecular bone tissue. Moreover, the results have been compared with the response of human osteoblast-like MG63 cell line. Cytotoxicity of coatings was assessed by lactate dehydrogenase activity (LDH). The cellular behavior was analyzed by the cell proliferation (MTT test), cell morphology (SEM) and the biochemical markers evaluation of osteoblastic phenotype, such as alkaline phosphatase activity (ALP) and osteocalcin production. The results showed that TiO₂/HA coatings have no toxic effects and seemed to be a good support for cell adhesion and proliferation. Moreover, these materials allowed the differentiation of osteoblasts, stimulating the expression of alkaline phosphatase activity. The responses of the primary rat osteoblasts and human osteoblast-like MG63 cell line grown onto these coatings were similar in terms of proliferation and ALP activity. Differences were found considering the osteocalcin production. The results show that these coatings, thanks to their chemical composition and the deposition technique, are very promising for the potential orthopedic and dental applications.     

HF-CVD of diamond coatings onto Fluidized Bed (FB) treated CrN interlayers

In the present investigation, Fluidized Bed (FB) treatment is applied to pre-treat CrN interlayers onto WC-Co substrates to promote the growth on them of highly adherent diamond coatings. During FB treatment, the CrN interlayers are submitted to high speed impacts of loose abrasives. The action of their cutting edges is able to deeply change the starting morphology of the as-deposited Physical Vapour Deposition (PVD) CrN interlayers, thus promoting the establishment of a highly corrugated surface on which to grow Hot Filament-Chemical Vapour Deposition (HF-CVD) diamond coatings.Growth, morphology, adhesion and wear resistance of the CVD deposited diamond coatings onto the FB treated and just seeded CrN interlayers were looked into and compared to diamond coated WC-Co substrates with the untreated CrN interlayers or pre-treated with a two-step chemical etching (Murakami's reagent and Caro's acid, MC-treatment) or with FB.FB treatment proved to be an effective technique to tailor the surface morphology and roughness of CrN films deposited by PVD-arc technique, and was found to be very useful in improving the adhesion and wear resistance of CVD diamond onto the CrN interlayers.     

Surface modification of Ti-6Al-4 V alloy for biomineralization and specific biological response: part II,alkaline phosphatase grafting

Titanium and its alloys are the most widespread materials for the realization of orthopaedic and dental implants due to their good mechanical properties and biocompatibility. Surface functionalization of biomaterials aimed to improve and quicken implant integration and tissue regeneration is an active research field. The opportunity to confer biological activity (ability to directly stimulate cells with proper biological signals) to the Ti6Al4 V alloy, previously modified to be bioactive from the inorganic point of view (apatite precipitation), was explored in this research work. The alkaline phosphatase (ALP) enzyme was grafted to metal surface via tresyl chloride activation, maintaining its activity. A synergistic effect between biological functionalization and inorganic bioactivity was observed.     

Porous Titanium Coatings Through Electrophoretic Deposition of TiH2 Suspensions

In the biomedical field, modification of titanium surfaces to improve the osteoinductive and antibacterial behavior is widely investigated. This functionalization can be further ameliorated by providing a porous coating with high loading capacity for bioactive materials and drug delivery carriers at the implant surface. In this work, a new powder metallurgical processing route used to deposit such porous pure titanium coatings on Ti based substrates is presented. The coatings were prepared by electrophoretic deposition (EPD) of TiH₂ powder suspensions followed by dehydrogenation and sintering in vacuum. The use of hydrides allowed to lower the sintering temperature below that of the α–β transition of the Ti6Al4V substrate. Measurement of the tensile bond strength confirmed a strong adhesion of the porous coating. Deposition of powders with different grain sizes resulted in porous titanium coatings with varying thickness, pore morphology, and surface roughness. The possibility to extend this coating technique to complex shaped implants is highlighted.     

Electrospray deposition of nanohydroxyapatite coatings: A strategy to mimic bone apatite mineral

The biological performance of orthopaedic and oral metallic implants can be enhanced significantly by the application of bioactive coatings. In this work, a cost-efficient alternative to the traditional technique to produce a hydroxyapatite (HA) coating with a nanostructured feature onto a metallic implant surface at room temperature via electrospray deposition, is presented. To evaluate the bioactive capacity of these nanoHA (nHA) coatings in vitro, an acellular simulated body fluid soaking experiment and a human osteoblast (HOB) cell culture work were conducted. Under these physiological conditions, the accelerated apatite precipitation process occurred on the nHA-coated titanium surfaces as compared to the uncoated titanium surfaces. HOB cells developed mature cytoskeletons with distinct evidence of actin stress fibres and vinculin adhesion plaques, on these nHA coatings. Hence, this deposition technique holds great potential in producing high quality nHA coatings for biomedical applications.     

High purity biodegradable magnesium coating for implant application

This paper describes efforts to create high purity Mg coating by Physical Vapor Deposition (PVD) technique that is appropriate for implant applications and to improve the interaction between the implant and the biological environment. The in vitro and in vivo tests conducted with Mg coatings that consist of grains with controlled size demonstrated promising properties in terms of lower corrosion and acceptable foreign body reaction which makes them prospective as biodegradable metallic materials.     

Galvanostatic pulse deposition of hydroxyapatite for adhesion to titanium for biomedical purposes

Calcium phosphate coatings, in particular synthetic hydroxyapatite, are applied to the surfaces of titanium and its alloys so as to improve the biocompatibility and biological performance. Currently, plasma spraying is the clinically accepted technique for the deposition of calcium phosphate onto titanium. Electrochemical cathodic deposition is emerging as an alternative technique due to it being a nonline-of-sight technique. In this present study, it is demonstrated that increased thickness, crystallinity and adhesion of calcium phosphate coating on titanium is achieved by periodic pulsed low current densities compared to a constant current deposition method. It is believed that the “off” part of the AC deposition cycle gives the calcium and phosphate ions in the bulk solution sufficient time to diffuse to the titanium's surface maintaining more favourable conditions for HA growth. Unfortunately, although pulsed deposition at high current densities is able to produce thick coatings it cannot avoid problems associated with hydrogen bubbles and thus both AC and DC films deposited at high current densities have low crystallinity and poor adhesion.     

Detection of alkaline phosphatase using surface-enhanced Raman spectroscopy

A new approach was developed to detect the activity of alkaline phosphatase (ALP) enzyme at ultralow concentrations using a surface-enhanced Raman scattering (SERS) technique. The approach is based on the use of gold nanoparticles as a SERS material whereas 5-bromo-4-chloro-3-indolyl phosphate (BCIP) is used as a substrate of ALP. The enzymatic hydrolysis of BCIP led to the formation of indigo dye derivatives, which were found to be highly SERS active. For the first time, we were able to detect ALP at a concentration of approximately 4 x 10(-15) M or at single-molecule levels when ALP was incubated with BCIP for 1 h in the Tris-HCl buffer. The same technique also was successfully employed to detect surface-immobilized avidin, and a detection limit of 10 ng/mL was achieved. This new technique allows the detection of both free and labeled ALP as a Raman probe in enzyme immunoassays, immunoblotting, and DNA hybridization assays at ultralow concentrations.     

Bioactive glass–ceramic coated titanium implants prepared by electrophoretic deposition

Surface modification of Ti alloys towards an improved osteoinductive behaviour is one of the major challenges in orthopaedic implant technology nowadays. One way to achieve this is by applying a bioactive coating which can increase the rate of osseointegration and chemical bonding of surrounding bone to the implant. In the present work, the production of a bioactive glass–ceramic coating on flat Ti alloys by electrophoretic deposition is demonstrated. The coatings are applied by cathodic deposition from non-aqueous suspensions followed by sintering in vacuum, avoiding uncontrolled oxidation of the Ti substrates. The use of non-aqueous suspensions both allowed to reduce the deposition time and yielded homogeneous coatings with a uniform thickness of 8 μm. Evaluation of the coating adhesion confirmed the good mechanical performance of the coatings with a tensile bond strength of 41.0 ± 11.1 MPa. Additionally, a feasibility study demonstrated the potential of electrophoretic deposition as a coating technique for commercial complex implants.     

电沉积非晶Ni-Fe-P涂层析氢催化性能研究

采用直流电镀技术,通过改变电沉积电流密度制备了不同的非晶Ni-Fe-P涂层。采用稳态极化技术比较不同电流密度下电镀Ni-Fe-P合金涂层电化学催化析氢活性,发现电流密度200A/m2电沉积的Ni-Fe-P合金涂层的电化学催化析氢性能最好。通过XRD分析镀层相结构,SEM观察涂层表面的微观结构及EDX分析表面成分,研究影响非晶Ni-Fe-P合金涂层的析氢电催化活性原因。结果表明,影响非晶Ni-Fe-P合金涂层电催化活性的主要因素是镀层中Fe、P元素含量。当Fe的含量最大18.63%(原子分数),P的含量最小13.14%(原子分数)时,非晶Ni-Fe-P涂层电催化析氢活性最好。2     

Electrochemical study of hydroxyapatite coatings on stainless steel substrates

Hydroxyapatite coatings were synthesized electrochemically onto stainless steel. In this study, the composition and morphology of the coatings changed with the deposition and sintering conditions. The electrolyte was kept close to the composition of simulated body fluid with an adjusted pH of 8.0. Deposition temperature affected the purity of the deposits with higher temperatures (65 °C) giving better coatings. The sintering techniques were also shown to affect the deposits, with x-ray diffraction patterns showing well-defined peaks for hydroxyapatite when sintering under vacuum conditions. Coating density and corrosion resistance was improved when applying a double-layer coating technique versus a single-layer. Grain sizes were 30 to 40 nm even after sintering of these coatings in air. The formed coatings were characterized by powder x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy.     

Silica nanofilms deposited by atmospheric pressure plasma liquid deposition

Silica coatings were deposited onto pure silicon surfaces by a deposition technique known as atmospheric pressure plasma liquid deposition using liquid tetraethylorthosilicate (TEOS) as a precursor. Deposition parameters were varied, including power, TEOS flow rate, helium flow rate, and substrate distance, in order to assess their influence on the growth rates and refractive index as well as the formation of surface particulates and organic content of the coatings. Growth rates were accurately controlled in the range of 0.5 nm s^− 1 to 7.2 nm s^− 1, with thin-films having refractive indices ranging from 1.1 to 1.4, indicative of layers with different levels of porosity. The results suggest that, with careful selection of deposition parameters, this (atmospheric pressure) plasma-based deposition technique could be used to achieve coherent, particulate free, smooth dense inorganic silica coatings.     

Characterization of Plasma Enhanced Chemical Vapor Deposition-Physical Vapor Deposition transparent deposits on textiles to trigger various antimicrobial properties to food industry textiles

Textiles for the food industry were treated with an original deposition technique based on a combination of Plasma Enhanced Chemical Vapor Deposition and Physical Vapor Deposition to obtain nanometer size silver clusters incorporated into a SiOCH matrix. The optimization of plasma deposition parameters (gas mixture, pressure, and power) was focused on textile transparency and antimicrobial properties and was based on the study of both surface and depth composition (X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), as well as Transmission Electron Microscopy, Atomic Force Microscopy, SIMS depth profiling and XPS depth profiling on treated glass slides). Deposition conditions were identified in order to obtain a variable and controlled quantity of ~ 10 nm size silver particles at the surface and inside of coatings exhibiting acceptable transparency properties. Microbiological characterization indicated that the surface variable silver content as calculated from XPS and ToF-SIMS data directly influences the level of antimicrobial activity.     

Exploring the Nickel–Graphene Nanocomposite Coatings for Superior Corrosion Resistance: Manipulating the Effect of Deposition Current Density on its Morphology,Mechanical Properties,and Erosion‐Corrosion Performance

The use of graphene‐based composite as anti‐corrosion and protective coatings for metallic materials is still a provocative topic worthy of debate. Nickel–graphene nanocomposite coatings have been successfully fabricated onto the mild steel by electrochemical co‐deposition technique. This research demonstrates the properties of nickel–graphene composite coatings influenced by different electrodeposition current densities. The effect of deposition current density on the; surface morphologies, composition, microstructures, grain sizes, mechanical, and electrochemical properties of the composite coatings are executed. The coarseness of deposited coatings increases with the increasing of deposition current density. The carbon content in the composite coatings increases first and then decreases by further increasing of current density. The improved mechanical properties and superior anti‐corrosion performance of composite coatings are obtained at the peak value of current density of 9 A dm^?2. The incorporation of graphene sheets into nickel metal matrix lead to enhance the micro hardness, surface roughness, and adhesion strength of produced composite coatings. Furthermore, the presence of graphene in composite coating exhibits the reduced grain sizes and the enhanced erosion–corrosion resistance properties.

     

Nanostructured self-lubricating CrN-Ag films deposited by PVD arc discharge and magnetron sputtering

CrN-Ag nanostructured coatings are deposited onto low-alloy steel substrates by means of Physical Vapour Deposition (PVD) reactive magnetron sputtering and PVD reactive arc discharge evaporation. The two different kinds of film have been characterized morphologically, chemically and tribologically. Depending on the used technique, as-deposited film shows different morphology, but in both cases, Ag nano-clusters are present on the surface. The annealing leads to coarsening of superficial Ag clusters and segregation out of the CrN matrix, depending on the temperature. After 600 °C annealing the surface is covered by an almost continuous layer of Ag, no matter which deposition technique is used. Tribological tests at different temperatures show that the lowest coefficient of friction appears at 600 °C for both coatings. The analysis of the wear tracks reveals that such a low friction is related to continuous Ag segregation out-of-CrN matrix, which enables self-lubrication.     

Electro-spark deposition of Fe-based amorphous alloy coatings

A simple and effective surface coating technique, electro-spark deposition (ESD), has been used to produce amorphous alloy coatings. Fe-Cr-Mo-Gd-C-B amorphous alloy rods produced by copper mould casting were used as electrode to produce coatings onto 304 stainless steel substrate. Classical X-ray diffraction (XRD), glancing angle XRD (GAXRD), and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis indicate that the coatings have an average thickness of ∼ 30 μm, show an amorphous structure, and are metallurgically bonded to the substrate. Microhardness tests showed that the coating layer has a high hardness of 1542 kg/mm², implying a much improved wear resistance on surface of stainless steels.     

Chemical vapour deposition of coatings

Chemical Vapour Deposition (CVD) of films and coatings involve the chemical reactions of gaseous reactants on or near the vicinity of a heated substrate surface. This atomistic deposition method can provide highly pure materials with structural control at atomic or nanometer scale level. Moreover, it can produce single layer, multilayer, composite, nanostructured, and functionally graded coating materials with well controlled dimension and unique structure at low processing temperatures. Furthermore, the unique feature of CVD over other deposition techniques such as the non-line-of-sight-deposition capability has allowed the coating of complex shape engineering components and the fabrication of nano-devices, carbon-carbon (C-C) composites, ceramic matrix composite (CMCs), free standing shape components. The versatility of CVD had led to rapid growth and it has become one of the main processing methods for the deposition of thin films and coatings for a wide range of applications, including semiconductors (e.g. Si, Ge, Si_1-xGe_x, III-V, II-VI) for microelectronics, optoelectronics, energy conversion devices; dielectrics (e.g. SiO₂, AlN, Si₃N₄) for microelectronics; refractory ceramic materials (e.g. SiC, TiN, TiB₂, Al₂O₃, BN, MoSi₂, ZrO₂) used for hard coatings, protection against corrosion, oxidation or as diffusion barriers; metallic films (e.g. W, Mo, Al, Au, Cu, Pt) for microelectronics and for protective coatings; fibre production (e.g. B and SiC monofilament fibres) and fibre coating. This contribution aims to provide a brief overview of CVD of films and coatings. The fundamental aspects of CVD including process principle, deposition mechanism, reaction chemistry, thermodynamics, kinetics and transport phenomena will be presented. In addition, the practical aspects of CVD such as the CVD system and apparatus used, CVD process parameters, process control techniques, range of films synthesized, characterisation and co-relationships of structures and properties will be presented. The advantages and limitations of CVD will be discussed, and its applications will be briefly reviewed. The article will also review the development of CVD technologies based on different heating methods, and the type of precursor used which has led to different variants of CVD methods including thermally activated CVD, plasma enhanced CVD, photo-assisted CVD, atomic layer epitaxy process, metalorganic assisted CVD. There are also variants such as fluidised-bed CVD developed for coating powders; electrochemical vapour deposition for depositing dense films onto porous substrates; chemical vapour infiltration for the fabrication of C-C composites and CMCs through the deposition and densification of ceramic layers onto porous fibre preforms. The emerging cost-effective CVD-based techniques such as electrostatic-aerosol assisted CVD and flame assisted CVD will be highlighted. The scientific and technological significance of these different variants of CVD will be discussed and compared with other vapour processing techniques such as Physical Vapour Deposition.     

Hybrid plasma CVD of diamond-like carbon (DLC) at low temperatures

Diamond-like carbon coatings have been deposited onto various substrates at 100–150°C using a hybrid plasma assisted chemical vapour deposition technique activated by radio frequency at 13.56 MHz. The coatings have been characterized using a number of techniques including scanning electron microscopy, Raman spectroscopy, thermoanalysis and pin-on-disc wear testing. Results show the films to be diamond like, with the addition of nitrogen (prior to deposition) promoting the formation of crystallites. In addition the condition and type of substrate have been found to have a strong influence on the structural characteristics of the deposited diamond-like films. SEM analysis of diamond-like carbon coatings deposited onto metal matrix composite materials such as Si-Al MMC is reported. The hybrid CVD technology enabled films to be deposited evenly onto the porous MMC structure. Commercially manufactured drills, coated with DLC and titanium nitride (TiN), have been compared to examine their cutting wear resistance characteristics. This revised version was published online in November 2006 with corrections to the Cover Date.