J.L. Arias

Hydroxyapatite coatings: a comparative study between plasma-spray and pulsed laser deposition techniques

A comparative study between hydroxyapatite coatings produced by two different techniques, plasma spray (PS) and pulsed-laser deposition (PLD) was carried out. Plasma spray is currently commercially used for coating dental and orthopaedical implant devices, and pulsed-laser deposition (or laser-ablation deposition) gave good results in the field of high critical temperature superconductive thin films, and is being applied to produce calcium phosphate coatings for biomedical purposes. X-ray diffraction was used to control the crystallinity of the coatings, scanning electron microscopy for the surface and cross-sectional morphology, and the pull test to determine the tensile strength of the coatings. This study reveals that the pulsed-laser deposition technique appears to be a very good candidate to replace the plasma spray in many biomedical applications, because it overcomes most of the drawbacks of the plasma spray.

Physicochemical properties of calcium phosphate coatings produced by pulsed laser deposition at different water vapour pressures.

Calcium phosphate coatings were produced by pulsed laser deposition from targets of non-stoichiometric hydroxyapatite (Ca/P = 1.70) at a substrate temperature of 485 degrees C and different processing pressures of water vapour: 0.15, 0.30, 0.45, 0.60 and 0.80 mbar. The physicochemical properties of these coatings were studied using Fourier-transform IR spectroscopy (FT-IR) and energy dispersive X-ray analysis (EDX). A minimum pressure of water vapour was necessary in order to obtain a crystalline coating, as deduced from the FT-IR spectroscopy of these coatings. This analysis also revealed that when the deposition pressure of water vapour was further increased, the coatings were less crystalline and the content of hydroxyl groups, the carbonate substitution for phosphate, and the Ca/P ratio, as measured by EDX, were lower. These effects can be explained by a combined substitution of carbonate and HPO4(2-) for phosphate, being predominant the carbonate substitution at low pressures and the HPO4(2-) substitution at high pressures.

Effect of heat treatment on pulsed laser deposited amorphous calcium phosphate coatings

Amorphous calcium phosphate coatings were produced by pulsed laser deposition from targets of nonstoichiometric hydroxyapatite (Ca/P = 1.70) at a low substrate temperature of 300 degrees C. They were heated in air at different temperatures: 300, 450, 525 and 650 degrees C. Chemical and structural analyses of these coatings were performed using X-ray diffraction (XRD), FTIR, and SEM, XRD analysis of the as-deposited and heated coatings revealed that their crystallinity improved as heat treatment temperature increased. The main phase was apatitic, with some beta-tricalcium phosphate in the coatings heated at 525 and 600 degrees C. In the apatitic phase there was some carbonate substitution for phosphate and hydroxyl ions at 450 degrees C and almost solely for phosphate at 525 and 600 degrees C as identified by FTIR. This was accompanied by a higher hydroxyl content at 525 and 600 degrees C. At 450 degrees C a texture on the coating surface was observable by SEM that was attributable to a calcium hydroxide and calcite formation by XRD. These phases almost disappeared at 600 degrees C, probably due to a transformation into calcium oxide.

Production of calcium phosphate coatings on Ti6Al4V obtained by Nd:yttrium–aluminum–garnet laser cladding

Among the various techniques that have been investigated to produce Hydroxyapatite (HA) coatings in order to promote fixation and osteointegration of cementless prosthesis, the plasma spray (PS) technique is the most popular method commercially in use. PS presents some disadvantages such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, an approach on how to bind HA to the Ti alloy will be introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding. Different techniques were applied to characterize the coated samples, including x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis.

Structural analysis of calcium phosphate coatings produced by pulsed laser deposition at different water-vapour pressures.

Calcium phosphate coatings have been produced by pulsed laser deposition (PLD) at different water-vapour pressures. Rietveld refinement of X-ray diffraction (XRD) data allows us to determine that the structure of these coatings is apatitic with carbonate substitution for phosphate. The carbonate substitution decreases when the chamber pressure is raised, a fact that has been corroborated by Fourier transform–infrared (FT–IR) spectroscopy. Carbonate concentrations between 5 and 17 wt% have been calculated for the crystalline samples. Amorphous coatings are produced at the lowest and highest pressures due to the high carbonate concentration in the first case, and possibly to another type of substitution (Mg2+, HPO2-4, P2O4-7) or the inherent kinetics of the PLD process, in the second case.

Alloying of hydroxyapatite onto Ti6Al-4V by high power laser irradiation.

In the biomedical field, the synthetic hydroxyapatite [Ca10(PO)4(OH)2], with similarity to the inorganic component of bone but brittle, has been considered as the appropriate coating on stronger implant materials, such as metallic implants, for presenting a surface which is conductive to bone formation. Many industrial and laboratory techniques were developed to apply hydroxyapatite onto metallic substrates, such as electrophoretic deposition, ion sputtering, hot isostatic pressing, pulsed laser deposition and the only widely used method commercially available: plasma spraying. This work presents a new approach on how to bind calcium phosphate (CaP) to the Ti alloy with a well-known technique in the metallurgical field: laser surface alloying, in order to overcome the drawbacks of plasma spraying. The analysis of the results obtained and the description of the phenomena that take place in the coating process will complete this explorative study.

Stoichiometric transfer in pulsed laser deposition of hydroxylapatite

Abstract Hydroxylapatite (HA, Ca10(PO4)6(OH)2) is a calcium phosphate used as coating for dental and orthopaedical implants because its composition and structure is similar to the mineral part of bone. As an alternative to traditional plasma sprayed coating technique, pulsed laser deposition (PLD) has been applied due to its ability to reproduce complex stoichiometries. A hydroxylapatite target was ablated with an ArF laser in a water vapor atmosphere to investigate in which range of fluences the stoichiometric transfer to a titanium substrate is possible. The Ca/P ratio of the coatings was measured by energy dispersive spectroscopy (EDS), while their OH− and CO32− content was evaluated by Fourier transform infrared spectroscopy (FT-IR) spectroscopy. The irradiated target surface was analyzed by scanning electron microscopy (SEM) and the ablation rate measured with a profilometer. While at higher fluences all the target material is congruently ablated and stoichiometry is transferred to the coatings, at lower fluences (