ABSTRACT
Calcium phosphate coatings were deposited by pulsed laser ablation with a radiation of 355 nm from a Nd:YAG laser. All the coatings were obtained at the same conditions, but deposition was stopped after different number of pulses to get coatings with different thickness. The influence of thickness in the structural and mechanical properties of the coatings was investigated. Coatings structure was characterised by scanning electron microscopy, grazing incidence X-ray diffractometry and Raman spectroscopy. The mechanical properties were evaluated by scratch test. The morphology of the coatings is dominated by the presence of droplets. The coatings are composed mainly of hydroxyapatite, alpha tricalcium phosphate and amorphous calcium phosphate. Thinner coatings withstand higher loads of failure in the scratch test.
Subject(s)
Calcium Phosphates/chemistry , Calcium Phosphates/metabolism , Neodymium/chemistry , Biocompatible Materials/pharmacology , Durapatite/chemistry , Lasers , Microscopy, Electron, Scanning , Spectrum Analysis, Raman , Surface Properties , Temperature , Tensile Strength , X-Ray DiffractionABSTRACT
The growth of hydroxyapatite coatings obtained by KrF excimer laser ablation and their adhesion to a titanium alloy substrate were studied by producing coatings with thicknesses ranging from 170 nm up to 1.5 microm, as a result of different deposition times. The morphology of the coatings consists of grain-like particles and also droplets. During growth the grain-like particles grow in size, partially masking the droplets, and a columnar structure is developed. The thinnest film is mainly composed of amorphous calcium phosphate. The coating 350nm thick already contains hydroxyapatite, whereas thicker coatings present some alpha tricalcium phosphate in addition to hydroxyapatite. The resulting coating to substrate adhesion was evaluated through the scratch test technique. Coatings fail under the scratch test by spallating laterally from the diamond tip and the failure load increases as thickness decreases, until not adhesive but cohesive failure for the thinnest coating is observed.
Subject(s)
Durapatite/chemistry , Fluorides/chemistry , Krypton/chemistry , Lasers , Alloys , Biocompatible Materials/chemistry , Calcium Phosphates , Materials Testing , Microscopy, Electron, Scanning , Surface Properties , Time Factors , Tissue Adhesions , Titanium/chemistry , X-RaysABSTRACT
The electrochemical synthesis of magnetic nanoparticles of new Sr-Fe and Sr-Co-Fe oxides using an undivided cell with two Fe electrodes is reported in this work. These materials are collected as precipitates by electrolyzing acidic solutions containing mixtures of chlorides and nitrates of Sr2+, Fe3+ and, optionally, Co2+ at temperatures between 40 degrees C and 80 degrees C. Sr-Fe oxides are produced with energy costs lower than 2.7 kWh kg-1 in the pH range 2.0-6.0 at 50 mA cm-2, whereas Sr-Co-Fe oxides are obtained with a cost of 3.0 kWh kg-1 at pH 1.5 and at 35 mA cm-2. Inductively coupled plasma analysis of materials and energy dispersive X-ray microanalysis of single particles confirm that they are composed of pure mixed oxides, without metallic Fe impurities. All synthesized compounds crystallize as inverse cubic spinels, with structures similar to those of maghemite and magnetite. They are formed by round-shape nanoparticles with sizes lower than 50 nm, as observed by transmission electron microscopy. Thermal desorption spectrometry allows us to detect the presence of hydrogen and volatiles proceeding from water decomposition in their lattices. After heating the electrogenerated materials at 300 degrees C during 1 h to eliminate such species, Sr-Co-Fe oxides with similar magnetic properties to those of hard ferrites are obtained, but magnetic Sr-Fe oxides only behave as soft ferrites.
Subject(s)
Cobalt/chemistry , Electrochemistry/methods , Iron/chemistry , Magnetics , Oxides/chemical synthesis , Strontium/chemistry , Crystallography/methods , Electrolysis/methods , Materials Testing , Microspheres , Molecular Conformation , Nanotechnology/methods , Oxides/chemistry , Particle Size , Quality Control , Surface Properties , TemperatureABSTRACT
Amorphous calcium phosphate and crystalline hydroxyapatite coatings with different morphologies were deposited onto Ti-6Al-4V substrates by means of the laser ablation technique. The strength of adhesion of the coatings to the substrate and their mode of fracture were evaluated through the scratch test technique and scanning electron microscopy. The effect of wet immersion on the adhesion was also assessed. The mechanisms of failure and the critical load of delamination differ significantly depending on the phase and structure of the coatings. The HA coatings with granular morphology have higher resistance to delamination as compared to HA coatings with columnar morphology. This fact has been related to the absence of stresses for the granular morphology.
Subject(s)
Calcium Phosphates/chemistry , Hydroxyapatites/chemistry , Lasers , Materials Testing , Microscopy, Electron, Scanning , Spectrum Analysis, Raman , X-Ray DiffractionABSTRACT
A dissolution test was performed with pulsed laser (Nd: YAG, 355 nm)-deposited calcium phosphate coatings composed of hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) in different proportions, as a result of the use of different deposition rates. During immersion in a Ca2+-free Hank's solution, the dissolution kinetics were determined while other structural and compositional properties of the coatings were derived. It was possible to infer that the alpha-TCP is distributed uniformly and that the coating is of a non-columnar compact grain structure. The mass ratio of the phases for each coating was also determined and was related to the X-ray diffraction intensities. When incomplete, the hydroxylation level of the HA in the coatings is completed after immersion.
Subject(s)
Calcium Phosphates/chemistry , Durapatite/chemistry , Prostheses and Implants , Isotonic Solutions , Kinetics , Lasers , Microscopy, Electron, Scanning , Solubility , X-Ray DiffractionABSTRACT
Pulsed laser deposited calcium phosphate coatings on titanium alloy have been tested under simulated physiological conditions in order to evaluate the changes in morphology, composition and structure. The coatings were deposited under different conditions to obtain different crystalline structures, ranging from amorphous and mixed crystalline phases to pure crystalline hydroxyapatite (HA). The coated samples were immersed in a Ca-free Hank's balanced salt solution for up to 5 days. Characterization of the coatings was performed by X-ray diffraction, scanning electron microscopy and Fourier-transform Raman spectroscopy before and after immersion. Their dissolution behaviour was also monitored through their mass loss and calcium release. Coatings of pure HA preserve their morphology and structure during the exposure time in solution. In multiphasic coatings, consisting of HA with tetracalcium phosphate (TetraCP) or beta-tricalcium phosphate (beta-TCP) with a-tricalcium phosphate (alpha-TCP), microporosity is induced by the complete dissolution of TetraCP or gamma-TCP. Amorphous calcium phosphate coatings totally dissolve.
