Pulsed laser deposition of hydroxyapatite on titanium substrate with titania interlayer

Pulsed laser deposition (PLD) has been used to deposit hydroxyapatite (HA) ceramic over titanium substrate with an interlayer of titania. PLD has been identified as a potential candidate for bioceramic coatings over metallic substrates to be used as orthopedic and dental implants because of better process control and preservation of phase identity of the coating component. However, direct deposition of hydroxyapatite on titanium at elevated temperature results in the formation of natural oxide layer along with some perovskites like calcium titanate at the interface. This leads to easy debonding of ceramic layer from the metal and thereby affecting the adhesion strength. In the present study, adherent and stable HA coating over Ti6Al4V was achieved with the help of an interlayer of titania. The interlayer was made to a submicron level and HA was deposited consecutively to a thickness of around one micron by exposing to laser ablation at a substrate temperature of 400°C. The deposited phase was identified to be phase pure HA by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma spectrometry. The mechanical behavior of coating evaluated by scratch test indicates that the adhesion strength of HA coating was improved with the presence of titania interlayer.     

Adhesion study of pulsed laser deposited hydroxyapatite coating on laser surface nitrided titanium

Hydroxyapatite (HA) coatings were fabricated by pulsed laser deposition (PLD) on commercially pure titanium which had been subjected to different types of pre-treatment. These include: (i) 60-grit SiC grinding, (ii) 320-grit SiC grinding, (iii) 1-µm diamond paste mirror-finishing, (iv) etching with Knoll solution, and (v) laser surface nitriding followed by selective etching. The HA coatings were pulsed laser deposited at different water-vapor pressures to determine the optimal processing conditions. The nitrided-etched specimen exhibits a three dimensional TiN dendritic network which promotes the adhesion between HA coating and titanium substrate. Among the specimens with different pre-treatments, the adhesion strength of HA is the highest for the nitrided-etched specimen, reaching about twice that for the mirror-finished specimen. Thin-film X-ray diffraction shows a high degree of crystallinity for the PLD deposited HA. According to energy-dispersive X-ray analysis, the Ca/P ratio of the deposited HA reaches an approximate value of 1.7, similar to that of the HA target. Scanning-electron microscopy reveals that the deposited HA is about 4 μm in thickness. Growth of apatite was rapidly induced on the HA coated specimens when immersed in Hanks' solution for 4 days, indicating that the PLD HA coating is highly bone bioactive. This could be partly due to the high wettability of the PLD HA surface.     

Electrolytic deposition of magnesium-substituted hydroxyapatite crystals on titanium substrate

Electrolytic deposition of magnesium-substituted hydroxyapatite (Mg-HAp) coatings on titanium was investigated and Mg-HAp crystals with up to 2 wt.% Mg²⁺ were deposited in electrolytes with various Mg²⁺ concentration. The incorporation of Mg substantially changed the morphology of the HAp crystals and decreased the crystal size and crystallinity of the HAp. The similarity with natural dentin and bone in composition and the increased specific surface of the Mg-HAp coatings on the Ti substrates were believed to benefit the bioactivity and the drug-carrying properties of the coatings.     

Colloidal characterization and electrophoretic deposition of hydroxyapatite on titanium substrate

Hydroxyapatite (HA) powders were prepared by a modified chemical co-precipitation method and electrophoretically deposited onto a titanium tubular substrate. The zeta potential, electromobility and the particle size of the HA suspension was characterized at various pH values and the most stable and dispersed suspension condition was identified. Electrophoretic deposition of the HA particles on the titanium substrate was then carried out at this optimum suspension condition. Studies on deposition rate and examination on the microstructure of the sintered deposit were performed. The stoichiometry of the HA before and after sintering were also confirmed. The deposition experimental data obtained in the present work was also compared with theoretical model proposed in the literature. Lastly, the adhesion strength of the coating was also quantified using shear strength tests.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

Properties of pulsed laser deposited fluorinated hydroxyapatite films on titanium

Fluorinated hydroxyapatite coated titanium was investigated for application as implant coating for bone substitute materials in orthopaedics and dentistry. Pulsed laser deposition technique was used for films preparation. Fluorinated hydroxyapatite target composition, Ca₁₀(PO₄)₆F_1.37(OH)_0.63, was maintained at 2 J/cm² of laser fluence and 500-600 °C of the substrate temperature. Prepared films had a compact microstructure, composed of spherical micrometric-size aggregates. The average surface roughness resulted to be of 3 nm for the film grown at 500 °C and of 10 nm for that grown at 600 °C, showing that the temperature increase did not favour the growth of a more fine granulated surface. The films were polycrystalline with no preferential growth orientation. The films grown at 500-600 °C were about 8 μm thick and possessed a hardness of 12-13 GPa. Lower or higher substrate temperature provides the possibility to obtain coatings with different fine texture and roughness, thus tayloring them for various applications.     

Femtosecond pulsed laser ablation and deposition of titanium carbide

In this work we have evaporated a titanium carbide target by an Nd:glass laser with 250 fs pulse duration. The plasma produced from the ablation has been characterized by Intensified Coupled Charge Device (ICCD) fast imaging, optical emission spectroscopy and quadrupole mass spectrometry, while X-ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS) and Scanning and Transmission Electron Microscopy have been used to study the deposited film morphology and composition. The plume shape and front velocity are very similar to those found in other systems and are typical of femtosecond ablation. In particular the front velocity is 1.1 × 10⁷ cm s^− 1 at a laser fluence of 1.9 J cm^− 2, while the value of the cosine exponent is 4.5 in the same conditions. In the TiC system a delayed emission, found by ICCD imaging and emission spectroscopy, is also present. In fact, although the emission involved in the “traditional” plume ends after about 1 μs, the target is still hot and gives origin to another emission, expanding with a velocity that is about two orders of magnitude lower compared to that of the traditional plume (2.2 × 10⁴ cm s^− 1 at a laser fluence of 1.9 J cm^− 2).The results of the analysis of both the gaseous plume and the deposited films seem to indicate that in the case of TiC system the presence of a large number of particles ejected from the target is responsible for the formation of the films. XPS and EDX data indicate that the stoichiometry of the target is preserved in the films, while XRD analysis shows that the films are amorphous in structure.     

Bioceramic coating of hydroxyapatite on titanium substrate with Nd-YAG laser

The ability to bond to bone tissue is a unique property of bioactive ceramics. Hydroxyapatite (HAp) is one of the potential bioceramics candidates due to its superior bio-compatibility. Significant effort has been devoted to coat HAp ceramics on metallic substrates. Most of these processes, such as ion-beam sputter coating, thermal spraying, and flame spraying, are high temperature line of sight processes, which suffer from undesirable phase formation and weak metal/HAP bonding strength. This paper presents a unique process to coat HAp powders on titanium substrates at low temperature and enhance the coating/substrate interface by laser surface engineering. Nd-YAG laser transmits HAp powders and the laser power is absorbed by titanium substrate to produce a thin layer of molten region. During coating process, HAp powders are kept at low temperature before they are entrapped in metallic layer. Scanning electron microscope (SEM) was used to investigate the microstructure of coating; the chemical composition of the coating is determined by energy dispersive spectrometry (EDS). Mechanical properties of the interface between coating and Ti substrate were investigated by nanoindentation.     

Nano-cube MgO formed on silicon substrate using pulsed laser deposition

Nano-cube MgO particles were formed on Si substrates by deposition of an MgO target using pulsed laser deposition method. An epitaxial film grows on Si(001) substrate with its contraction of lattice constants. In this study, expecting high quality MgO film, the MgO film prepared in the oxygen pressure ranging from 75-400 mTorr at the high temperature of -750 degrees C. The deposited MgO showed the growth of (001) preferred orientation on the Si(001) substrate. However, X-ray Photoelectron Spectroscopy (XPS) indicated the MgO film did not form a continuous film on the Si surface. Interestingly, the surface morphology observed by an Atomic Force Microscopy (AFM) showed nano-cube MgO particles scattered on the smooth surface of Si substrate. After annealing the nano-cube MgO, the shape of MgO particles were changed from nano-cube to round shaped particles. The AFM image of the surface showed round shaped MgO nanoparticles scattered on rough surface. X-ray Diffraction (XRD) revealed the epitaxial growth of MgO(001) with cubic on cubic arrangement on the Si(001) substrate (MgO[100] parallel to Si[100]).     

Pulsed laser deposition of hydroxyapatite on nanostructured titanium towards drug eluting implants

Titania nanotubes grown on titanium substrates by electrochemical anodization in glycerol–ammonium fluoride–water system were used to develop efficient drug carrying implants upon coating hydroxyapatite (HA) ceramic. The nanostructured surfaces achieved by anodization were caped with HA crystallites by pulsed laser deposition. The implant substrates were studied for their drug carrying capacity using gentamicin as a model. The nano-tubular surface with HA coating had better drug loading capacity of about 800 μg/cm² gentamicin while the bare anodized substrate carried less than 660 μg/cm². The HA coating alone stored as low as 68 μg/cm² and released the drug within the initial burst period itself. The ceramic coated anodized substrates were found to be more efficient in controlled delivery for longer than 160 h with a drug release of 0.5 μg/cm² even towards the end. The substrate with nanostructuring alone delivered the whole drug within 140 h. This study proposes the application of laser deposition of HA over nanostructured titanium, which proves to be promising towards controlled drug eluting bioceramic coated metallic prostheses.     

沉积温度对多孔钛表面仿生制备羟基磷灰石的影响

为研究沉积温度对羟基磷灰石涂层生长的影响,制备了不同温度条件下成分恒定的仿生沉积液,并采用纯钛和不同孔径的多孔钛做基体,在其表面仿生沉积羟基磷灰石涂层,再将得到的涂层试样浸泡在标准模拟体液中检测其生物活性.通过X射线衍射仪(XRD)分析涂层物相结构,用金相显微镜、环境扫描电子显微镜(ESEM)表征涂层形貌,利用能谱分析仪(EDS)计算钙磷比.研究表明:基体孔径增大,有利于沉积液进入到孔隙且表面粗糙度相对增大,从而使得HA涂层变得均匀致密;沉积温度由30℃升高至37℃,会加快HA涂层致密均匀的生长,但温度升高到44℃时,HA晶粒变粗大,涂层变得疏松化;模拟体液浸泡后,Ti/HA涂层试样表面有新的HA生成,且Ca/P比接近标准的1.67,表明该Ti/HA涂层试样具有良好的生物活性.适当增大钛基体孔径,提高沉积液温度,可以得到均匀致密的HA生物活性涂层.     

Sol-gel derived hydroxyapatite coatings on titanium substrate

Biomaterials, in particular those used for orthopaedic prostheses, consist of a metallic substrate, exhibiting excellent mechanical properties, coated with a ceramic layer, which guarantees resistance to the corrosion and an elevated bioactivity. In this paper the preparation of sol-gel films of hydroxyapatite, HA (Ca₁₀(PO₄)₆(OH)₂), on titanium substrate is described. The samples were obtained through the dip-coating method, starting from a colloidal suspension of hydroxyapatite. In order to increase the adhesion between the HA film and the metallic substrate, the same substrate has been preliminarily coated either with titanium oxide, TiO₂ (in the anatase or rutile phase), or calcium titanate, CaTiO₃ (perovskite). Also these latter films have been deposited from a sol-gel solution. The characterization of the films through XRD, SEM, and AFM gave good results for the crystallinity of the deposited HA; for what concerns the sample morphology, the films turned out to be homogeneous and crack-free.     

Martensitic transformation in TiNi alloy after surface modification done by hydroxyapatite layer deposition

ABSTRACT

A hydroxyapatite (HAp) layer was deposited on the surface of an NiTi alloy using a spark plasma technique. The effects of spraying conditions on the martensitic transformation were investigated in three heat-affected zones: the zone under the handle, the transition zone and in a representative zone with HAp coverage. In the representative area, a reduction in the amount of non-transformable phases was observed. A part of the sublayer showed a nanocrystalline or completely amorphous structure. This sublayer was approximately 30?µm thick. Structural changes contributed to the reduction of the temperature of the reverse martensitic transition down to 25°C. Moreover, modification of the surface revealed a positive influence on the transformation course by narrowing its temperature range and increasing its enthalpy.

This paper is part of a thematic issue on Titanium.     

Laser surface modification of 316 L stainless steel with bioactive hydroxyapatite

Laser-engineered net shaping (LENS?), a commercial additive manufacturing process, was used to modify the surfaces of 316 L stainless steel with bioactive hydroxyapatite (HAP). The modified surfaces were characterized in terms of their microstructure, hardness and apatite forming ability. The results showed that with increase in laser energy input from 32 J/mm² to 59 J/mm² the thickness of the modified surface increased from 222 ± 12 μm to 355 ± 6 μm, while the average surface hardness decreased marginally from 403 ± 18 HV_0.3 to 372 ± 8 HV_0.3. Microstructural studies showed that the modified surface consisted of austenite dendrites with HAP and some reaction products primarily occurring in the inter-dendritic regions. Finally, the surface-modified 316 L samples immersed in simulated body fluids showed significantly higher apatite precipitation compared to unmodified 316 L samples.     

Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate

The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 °C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO₂ film grew at the interface during annealing in moist air, while a TiO₂ layer diffused into the HA films when directly sputtered at 550 °C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.     

Chemical modification of titanium immersed in hydrogen peroxide using nanosecond pulsed fiber laser irradiation

This paper addresses chemical alteration of titanium using pulsed Ytterbium fiber laser irradiation. For this study, Hydrogen Peroxide (HP) is used as the medium to study its effect on increasing anatase-titania composition in titanium substrates for samples irradiated by the laser. The variation of anatasei-rutile transformation generated in HP is compared with those generated in air. X-Ray diffraction (XRD) analysis suggests that three titanium dioxide structures - brookite, anatiase, and rutile - are present in the substrates irradiated by the laser beam. Additional peaks appeared in XRD results of HP immersed samples indicating that anatase and a rare titanium oxide structure, Hongquiite, are also produced, whereas these oxides are not detected in the samples generated in air. Energy-dispersive X-ray spectroscopy (EDAX) analysis reveals an increase of the oxide layer on the surface of HP-treated samples.     

Preferred growth of epitaxial TiN thin film on silicon substrate by pulsed laser deposition

Epitaxial TiN thin films on silicon substrates were prepared by pulsed excimer laser (KrF, 34 ns) ablation of a hot-pressed TiN target in nitrogen gas atmosphere. X-ray diffraction (XRD) showed that the preferred orientations of TiN thin films did not change with substrate temperatures, nitrogen gas pressure and film thickness; however, they did change with the orientations of substrates. The epitaxial orientation relationships between high-quality epitaxial TiN thin films and silicon substrates [2 4 2] TiN [2 4 2] Si, (1 1 1) TiN(1 1 1) Si and [3 1 1] TiN [3 1 1] Si, (1 0 0) TiN(1 0 0) Si. The full-width at half-maximum (FWHM) of the rocking curve of XRD and the minimum channelling yield of Rutherford backscattered spectroscopy (RBS) of the epitaxial TiN thin film were estimated to be 0.3 ° and 7.3%, respectively, indicating excellent crystalline quality of the grown film. X-ray photoelectron spectroscopy confirmed that the binding energies of Ti 2p 3/2 and N 1s core levels in epitaxial thin film were 455.2 and 397.1 eV, respectively, corresponding to those of TiN bulk. By calibrating the RBS spectra, the chemical composition of TiN thin films was found to be titanium-rich. The typical surface roughness of TiN thin film observed by scanning probe microscopy was about 1.5 nm. © 1998 Chapman & Hall     

Pulsed laser deposition of hydroxyapatite thin films

Hydroxyapatite is a bioactive ceramic material that mimics the mineral composition of natural bone. This material does not possess acceptable mechanical properties for use as a bulk biomaterial; however, it does demonstrate significant potential for use as a coating on metallic orthopaedic and dental prostheses. This paper reviews recent developments involving pulsed laser deposition of hydroxyapatite thin films for medical and dental applications. The structural, mechanical, and biological properties of hydroxyapatite thin films are described. In addition, future directions in pulsed laser deposition of hydroxyapatite thin films are discussed.     

Pulsed laser deposition of silicon-substituted hydroxyapatite coatings

Thin films of Si-substituted hydroxyapatite (Si-HA) were deposited on Si and Ti substrates by pulsed laser deposition (PLD), in the presence of a water vapour atmosphere. The PLD ablation targets were made with different mixtures of commercial carbonated HA and Si powder, in order to produce the Si-HA thin films. The physicochemical properties of the coatings and the incorporation of the Si into the HA structure was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Si atoms were successfully incorporated into the HA structure, and were found to be in the form of SiO₄⁴⁻ groups, principally displacing carbonate groups off the HA structure.     

Cryogenic pulsed laser deposition of ZnO

The paper deals with the pulsed laser deposition technology and in this special case the substrate was cooled at cryogenic temperature by liquid nitrogen during the deposition process. This approach is proper for growth of highly disordered structures with new physical properties and zinc oxide was applied as experimental example for demonstration. Films were deposited on different substrates: Si (100) and sapphire (0001) and subsequently annealed at different temperatures (200-800 °C). Their properties were investigated by various analytical methods. X-ray diffraction (XRD) proved fully amorphous structure of as-grown ZnO layers which were cooled during the deposition process. Annealing of these amorphous layers changed their properties according to temperature level and annealing time. XRD and scanning electron microscopy (SEM) revealed recrystallized structure. According to the secondary ion mass spectroscopy (SIMS) the layers has homogenous chemical composition along the depth profile with improved homogeneity after annealing.