Pulsed Laser-deposited Hydroxyapatite Research Articles

Effect of Er:YAG Pulsed Laser-Deposited Hydroxyapatite Film on Titanium Implants on M2 Macrophage Polarization In Vitro and Osteogenesis In Vivo.

In a previous study, we successfully coated hydroxyapatite (HAp) onto titanium (Ti) plates using the erbium-doped yttrium aluminum garnet pulsed-laser deposition (Er:YAG-PLD) method. In this study, we performed further experiments to validate the in vitro osteogenic properties, macrophage polarization, and in vivo osseointegration activity of HAp-coated Ti (HAp-Ti) plates and screws. Briefly, we coated a HAp film onto the surfaces of Ti plates and screws via Er:YAG-PLD. The surface morphological, elemental, and crystallographic analyses confirmed the successful surface coating. The macrophage polarization and osteogenic induction were evaluated in macrophages and rat bone marrow mesenchymal stem cells, and the in vivo osteogenic properties were studied. The results showed that needle-shaped nano-HAp promoted the early expression of osteogenic and immunogenic genes in the macrophages and induced excellent M2 polarization properties. The calcium deposition and osteocalcin production were significantly higher in the HAp-Ti than in the uncoated Ti. The implantation into rat femurs revealed that the HAp-coated materials had superior osteoinductive and osseointegration activities compared with the Ti, as assessed by microcomputed tomography and histology. Thus, HAp film on sandblasted Ti plates and screws via Er:YAG-PLD enhances hard-tissue differentiation, macrophage polarization, and new bone formation in tissues surrounding implants both in vitro and in vivo.

Surface morphology, bioactivity, and antibacterial studies of pulsed laser deposited hydroxyapatite coatings on Stainless Steel 254 for orthopedic implant applications

Coating of hydroxyapatite using the pulsed laser deposition technique, on medical grade UNS S31254 stainless steel (254SS), to yield a biomaterial for potential orthopedic implant applications, is unreported so far in the literature. In this paper, the pulsed laser deposition process was used to improve the physiological response of 254SS. The surface morphology of the deposited hydroxyapatite coatings was characterized using scanning electron microscopy and atomic force microscopy, while the phase composition of the deposited hydroxyapatite coatings was determined using the X-ray diffraction method. The thickness and adhesive strength of the hydroxyapatite coatings were determined using an ellipsometer and a tensometer, respectively. The antibacterial efficacy of the deposited hydroxyapatite coatings was confirmed using the modern technique of fluorescence-activated cell sorting. Finally, the bioactivity of hydroxyapatite coatings was investigated by conducting immersion test in simulated body fluid environment. The scanning electron microscopy and atomic force microscopy results revealed higher (∼8 nm) average surface roughness, which is likely to facilitate better osseointegration. X-ray diffraction analysis confirmed that postdeposition annealing is essential to achieve the desired crystallinity and uniformity of coatings. Tensile pull-out tests confirmed adhesive strength of hydroxyapatite coatings beyond the standard expected values. Immersion tests inferred high bioactivity of pulsed laser deposition hydroxyapatite coatings. The promising results obtained in this research signify the potential application of hydroxyapatite coatings in orthopedic implants.

Crack Propagation Resistance of α-Al2O3 Reinforced Pulsed Laser-Deposited Hydroxyapatite Coating on 316 Stainless Steel

Hydroxyapatite (HA) is a widely used bioceramic known for its chemical similarity with that of bone and teeth (Ca/P ratio of 1.67). But, owing to its extreme brittleness, α-Al2O3 is reinforced with HA and processed as a coating via pulsed laser deposition (PLD). Reinforcement of α-Al2O3 (50 wt.%) in HA via PLD on 316L steel substrate has shown modulus increase by 4% and hardness increase by 78%, and an improved adhesion strength of 14.2 N (improvement by 118%). Micro-scratching has shown an increase in the coefficient-of-friction from 0.05 (pure HA) to 0.17 (with 50 wt.% Al2O3) with enhancement in the crack propagation resistance (CPR) up to 4.5 times. Strong adherence of PLD HA–Al2O3 coatings (~4.5 times than that of HA coating) is attributed to efficient release of stored tensile strain energy (~17 × 10−3 J/m2) in HA–Al2O3 composites, making it a potential damage-tolerant bone-replacement surface coating.

Nano-crystalline pulsed laser deposition hydroxyapatite thin films on Ti substrate for biomedical application

Hydroxyapatite (HA) thin coating has been coated on titanium substrates by pulsed laser deposition (PLD). Structural and morphological studies by transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed. The HA film is polycrystalline and irregular with a range size of particulates from 100 nm to 1 μm. Adhesion of the HA films to the Ti substrates was excellent as observed by cross-scanning electron microscopy (X-SEM) and transmission electron microscopy (XTEM). The residual stresses state determined on uncoated Ti substrates was compressive. After deposition of thin PLD HA on titanium substrates at 400°C the residual stress state was in a very low tensile state.

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.

Implant Surface Modification Using Laser Guided Coatings: In Vitro Comparison of Mechanical Properties

Plasma-sprayed hydroxyapatite (HA)-coated implants show failures along the coating-substrate interface due to poor bond strength. We analyzed HA coatings obtained by pulsed laser deposition (PLD) and compared them to commercially used plasma-sprayed coatings with respect to their bond strength to titanium alloy (Ti-6Al-4V), as well as surface roughness alterations produced by each of the two deposition methods. Twelve titanium alloy disks were plasma-sprayed under commercial implant coating conditions, and 24 titanium alloy disks were coated using PLD. All coatings were characterized by the presence of the different calcium phosphate (CaP) phases. The plasma-sprayed coatings (n = 12) were predominantly HA, and the pulsed laser-deposited coatings were hydroxydyapatite (n = 12) and HA coating with a tetra calcium phosphate (TTCP) phase (n = 12). The surface roughness was analyzed before and after the coating processes to assess roughness changes to the surface by the coatings. The adhesive bond strengths of these coatings to the substrate titanium alloy was tested and compared. Scheffé's test was used to analyze the statistical significance of the data. The surface roughness alteration following PLD was a decrease of 0.2 mum, whereas following plasma spraying the decrease was 1.0 microm. Bond strengths were as follows [mean (SD) in MPa]: pulsed laser-deposited HA coatings: 68.3 (17.8); pulsed laser-deposited HA with tetra-CaP: 55.2 (21.1); plasma-sprayed HA 17.0 (2.8). The multivariate Scheffé's test revealed that HA coatings obtained by PLD had significantly increased bond strengths compared with the plasma sprayed ones (p<or= 0.05). HA coatings obtained by PLD showed greater adherence to titanium alloy. PLD offers an alternative method to produce thinner coatings with better adherence properties, along with precise control over the deposition process.

HYDROXYAPATITE THIN FILMS ON TITANIUM DEPOSITED BY KrF LASER

Pulsed laser deposition (PLD) is being investigated as an alternative technique to prepare hydroxyapatite coatings. In this research we studied the microstructure and phase composition of the PLD hydroxyapatite films. The surface morphology of the films is composed of droplets for which size ranges from hundreds of nanometers to a few micrometers. The cross-sectional morphology of the films shows that the films adhere to the substrate well and there are no microcracks, pores and other defects between substrate and films. The X-ray diffractometer results show that the deposited films are amorphous and the post heat treatment films consists of crystalline HA and TiO 2.

Nano-scratch study of pulsed laser-deposited hydroxyapatite thin films implanted at high energy with N+and AR+ions

In this study we report a method to improve the adherence of hydroxyapatite (HA) thin films, using an ion beam implantation treatment. Crystalline HA films were grown by a pulsed laser deposition technique (PLD), using an excimer KrF* laser. The films were deposited at room temperature in vacuum on Ti-5Al-2.5Fe alloy substrates previously coated with a ceramic TiN buffer layer and then annealed in ambient air at (500–600)°C. After deposition the films were implanted with N+ and Ar+ ions accelerated at high energy (1–1.5 MeV range) at a fixed dose of 1016 cm−2. The intrinsic mechanical resistance and adherence to the TiN buffer layer of the implanted HA films have been evaluated by nano-scratch tests. We used for measurements a spherical indenter with a tip radius of 5 μm. Different scratch tests have been performed on implanted and unimplanted areas of films to demonstrate the effects of N+ and Ar+ ion implantation process on the films properties. Results show an enhancement of the dynamic mechanical properties in the implanted zones and influence of the nature of the implanted species. The best results are obtained for films implanted with nitrogen. The modes of failure of the films under loading are described.

Determination of mechanical properties of pulsed laser-deposited hydroxyapatite thin film implanted at high energy with N+and Ar+ions, using nanoindentation

Hydroxyapatite (HA) is extensively studied for various applications in bone implantology. We report here a comparison between the effects of ion beam implantation treatment using nitrogen and argon ions, on the mechanical characteristics of HA films grown by pulsed laser deposition. We used for deposition a KrF* excimer laser. Crystalline and stoichiometric HA films were grown on Ti-5Al-2.5Fe alloy substrate, previously coated with a TiN buffer layer. After deposition, the film were implanted with ions of N+ and Ar+ of high energy (1–1.5 MeV range) and dose set at 1016 at cm−2. The hardness and elastic modulus were determined by nanoindentation tests using a spherical tipped nanoindenter with a 5 μm-tip radius. From the load-displacement curves, we put into evidence an enhancement of the mechanical characteristics of the HA films after implantation, especially for those implanted with N+ ions. This improvement of the mechanical characteristics is related to the changes of surface morphology and the densification of the HA layer after ion treatment.

Mechanical properties of pulsed laser-deposited hydroxyapatite thin films implanted at high energy with N + and Ar + ions. Part II: nano-scratch tests with spherical tipped indenter

In this study we report a method to improve the adherence of hydroxyapatite (HA) thin films, using an ion beam implantation treatment. Crystalline HA films were grown by pulsed laser deposition technique (PLD), using an excimer KrF * laser. The films were deposited at room temperature in vacuum on Ti–5Al–2.5Fe alloy substrates previously coated with a ceramic TiN buffer layer and then annealed in ambient air at (500–600) °C. After deposition the films were implanted with N + and Ar + ions accelerated at high energy (1–1.5 MeV range) at a fixed dose of 10 16 cm −2. The intrinsic mechanical resistance and adherence to the TiN buffer layer of the implanted HA films have been evaluated by nano-scratch tests. We used for measurements a spherical indenter with a tip radius of 5 μm. Different scratch tests have been performed on implanted and unimplanted areas of films to put into evidence the effects of N + and Ar + ion implantation process on the films properties. Results show an enhancement of the dynamic mechanical properties in the implanted zones and influence of the nature of the implanted species. The best results are obtained for films implanted with nitrogen.

Mechanical properties of pulsed laser-deposited hydroxyapatite thin film implanted at high energy with N + and Ar + ions. Part I: nanoindentation with spherical tipped indenter

We report here a comparison between the effects of ion beam implantation treatment using nitrogen and argon ions, on the mechanical characteristics of HA films grown by pulsed laser deposition, using a KrF ∗ excimer laser. Crystalline and stoichiometric HA films were grown on Ti–5Al–2.5Fe alloy substrate, previously coated with a TiN buffer layer. After deposition, the film were implanted with ions of N + and Ar + of high energy (1–1.5 MeV range) and dose set at 10 16 at cm −2. From the load–displacement curves determined by nanoindentation tests using a spherical tipped nanoindenter ( R=5 μm), we put into evidence an enhancement of the mechanical characteristics (hardness and elastic modulus) of the HA films after implantation, especially for those implanted with N + ions. Moreover, using various applied normal loads (ranging from 1 to 100 mN) in different implanted areas, a good reproducibility of nitrogen implantation effect are observed.

Mechanical properties of pulsed laser-deposited hydroxyapatite thin films for applications in biomedical implants

ABSTRACTWe have obtained nanostructured hydroxyapatite thin films on titanium alloy substrates by pulsed laser deposition. Deposition was carried out using a KrF excimer laser (248 nm) with the energy density of 4 – 7 J/cm2 at substrate temperatures in the 550°C - 650°C range. The crystallinity of the coatings was probed by X-ray diffraction. Phase transitions from hydroxyapatite to other calcium phosphate compounds were observed with varying the substrate temperature during the growth process. Scanning electron microscopy revealed thin films made up of partially sintered nanoscale grains. The average size of nanoscale grains increased significantly with film thickness, suggesting a growth mechanism involving the coalescence of nanoscale grains. As the laser energy density increases, the hydroxyapatite crystallites in the coatings are oriented preferentially along the c-axis perpendicular to the substrate. Mechanical properties of the highly c-axis oriented coatings such as hardness and Young's modulus were studied by using nanoindentation technique.

Mechanical properties improvement of pulsed laser-deposited hydroxyapatite thin films by high energy ion-beam implantation

Major problems in the hydroxyapatite (HA), Ca 5(PO 4) 3OH, thin films processing still keep the poor mechanical properties and the lack in density. We present a study on the feasibility of high energy ion-beam implantation technique to densify HA bioceramic films. Crystalline HA films were grown by pulsed laser deposition (PLD) method using an excimer KrF ∗ laser ( λ=248 nm , τ FWHM ≥20 ns ). The films were deposited on Ti–5Al–2.5Fe alloys substrates previously coated with a ceramic TiN buffer layer. After deposition the films were implanted with Ar + ions at high energy. Optical microscopy (OM), white light confocal microscopy (WLCM), grazing incidence X-ray diffraction (GIXRD) and Berkovich nanoindentation in normal and scratch options have been applied for the characterization of the obtained structures. We put into evidence an enhancement of the mechanical characteristics after implantation, while GIXRD measurements confirm that the crystalline structure of HA phase is preserved. The improvement in mechanical properties is an effect of a densification after ion treatment as a result of pores elimination and grains regrowth.

Structural characterization of pulsed laser-deposited hydroxyapatite film on titanium substrate

Pure, crystalline hydroxyapatite (HA) films with thicknesses of roughly 10 μm have been deposited on titanium substrate using the pulsed laser deposition (PLD) technique. Experimental results indicate that the structure and properties of the PLD-HA films varied with deposition parameters. The PLD process used in the present study did not induce significant amounts of calcium phosphate phases other than apatite, or significant changes in the behaviour of hydroxyl or phosphate functional groups. Broad face scanning electron microscopy showed that HA coating was comprised of numerous essentially spheroidal-shaped particles of different sizes, while the lateral morphology indicated that columnar and dome-shaped structures both existed in the film. Many pinholes and crevices observed on coating surfaces were linked to the original substrate surface crevices/craters. The adhesion strength of the coating, mostly in the range of 30–40 MPa, was found to be closely related to the fractography of the tested specimen. The fracture surfaces of specimens with higher bond strengths were usually accompanied by a higher degree of deformation and coating-substrate debonding, while the fracture of specimens with lower bond strengths occurred more frequently within HA coatings in a more brittle manner. The energy dispersive spectroscopy-determined Ca P ratios of raw HA powder (1.78) and sintered HA target for PLD (1.79) were very close, indicating that the sintering process used in the present study essentially did not change the Ca P ratio of HA. After the PLD process, the Ca P ratio of the HA film increased to 1.99. Cross-sectional scanning electron microscopy-energy dispersive spectroscopy point analysis indicated that the value of the Ca P ratio was significantly higher in the region near the surface, particularly near the coating-substrate interface, than in the coating interior.