Hervé Pelletier

Pulsed laser deposition of hydroxyapatite thin films on Ti-5Al-2.5Fe substrates with and without buffer layers

We present a method for processing hydroxyapatite (HA) thin films on Ti-5Al-2.5Fe substrates. The films were grown by pulsed laser deposition (PLD) in vacuum at room temperature, using a KrF∗ excimer laser. The amorphous as-deposited HA films were recrystallized in ambient air by a thermal treatment at 550°C. The best results have been obtained when inserting a buffer layer of ceramic materials (TiN, ZrO2 or Al2O3). The films were characterized by complementary techniques: grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), cross-section transmission electron microscopy (XTEM), SAED, energy dispersive X-ray spectroscopy (EDS) and nanoindentation. The samples with buffer interlayer preserve the stoichiometry are completely recrystallized and present better mechanical characteristics as compared with that without buffer interlayer.

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10−2–10−1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca2P2O7, Ca2P2O9 and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.

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 ) 3 OH, 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.

Characterization of direct laser deposited low modulus Ti-26Nb alloy on Ti-6Al-4V for biomedical applications

After a joint replacement, a stress-shielding phenomenon often appears resulting from Young’s modulus mismatch between the implant and the cortical bone. In accordance with Wolff’s law, it will result in bone resorption and could lead to loosening of the implant.Ti-Nb beta metastable alloys are excellent candidates for biomedical applications because of their very low elastic modulus close to that of cortical bone and their high strength. This material, associated with the direct laser deposition or CLAD® process allows the fabrication of biomimetic implants. Nevertheless, Ti-Nb powders are still rather uncommon, thus the alloy could be utilized as a replacement material for Ti-6Al-4V on the implant surface only, this configuration creating an elasticity gradient.Microstructure and phase analysis of a direct laser deposited Ti-26(at%)Nb wall revealed a fully beta microstructure. Micro-hardness tests refuted the anisotropy of the deposited alloy and tensile tests showed that the elastic properties of the CLAD® material are not far from those of the cast material. EDS analysis of a CLAD® build of Ti-26Nb on a Ti-6Al-4V substrate highlighted the diffusion of the elements of the substrate towards the deposit. Grain growth was studied with EBSD. Moreover, nanoindentation tests highlight an evolution of the elastic modulus from the substrate to the deposit.After a joint replacement, a stress-shielding phenomenon often appears resulting from Young’s modulus mismatch between the implant and the cortical bone. In accordance with Wolff’s law, it will result in bone resorption and could lead to loosening of the implant.Ti-Nb beta metastable alloys are excellent candidates for biomedical applications because of their very low elastic modulus close to that of cortical bone and their high strength. This material, associated with the direct laser deposition or CLAD® process allows the fabrication of biomimetic implants. Nevertheless, Ti-Nb powders are still rather uncommon, thus the alloy could be utilized as a replacement material for Ti-6Al-4V on the implant surface only, this configuration creating an elasticity gradient.Microstructure and phase analysis of a direct laser deposited Ti-26(at%)Nb wall revealed a fully beta microstructure. Micro-hardness tests refuted the anisotropy of the deposited alloy and tensile tests showed that the elastic properties of the C...

Hydroxyapatite thin films growth by pulsed laser deposition: effects of the Ti alloys substrate passivation on the film properties by the insertion of a TiN buffer layer

Hydroxyapatite (HA), Ca5(PO4)3OH, is now widely used in stomatology and orthopedic surgery. Due to a good biocompatibility combined favorable bioactivity make as HA to be considered as a challenge to successful bone repair. We grow HA thin films on Ti-5Al-2.5Fe alloy substrate by pulsed laser deposition (PLD) technique. The films were deposited in vacuum at room temperature using a KrF excimer laser ((lambda) equals 248 nm, (tau) FWHM >= 20 ns). After deposition the HA films were annealed at 550 degree(s)C in ambient air. The insertion of a bioinert TiN buffer layer at the HA film-metallic substrate interface was studied in terms of HA film microstructure and mechanical properties. SEM, TEM and SAED analysis structurally characterized films. The mechanical properties were evaluated by nanoindentation tests in static and scratch modes. Films with TiN interlayer contain uniquely crystalline HA phase and present better mechanical characteristics as compared with those deposited directly on Ti-alloy substrate.

Influence of a TiN interlayer on the microstructure and mechanical properties of hydroxyapatite films grown by pulsed laser deposition

Crystalline hydroxyapatite (HA) thin films grown on metallic substrates is the best choice for bone restoration. This is due to the good biological compatibility of the hydroxyapatite material combined with the good mechanical characteristics of the substrates. We deposit HA thin films by Pulsed Laser Deposition (PLD) in vacuum at room temperature using a KrF* excimer laser ((lambda) equals 248 nm, (tau) FWHM >= 20 ns). The depositions were performed directly on Ti-5Al-2.5Fe or on substrates previously coated with a TiN buffer layer. The HA deposited structures were characterized by complementary techniques: GIXRD, SEM, TEM, SAED, EDS and nanoindentation. Properties of the HA films grown with and without the TiN buffer were discussed in term of microstructure and mechanical behavior. The films with interlayer preserve the stoichiometry, are completely recrystallized and present better mechanical characteristics as compared with those without buffer.