Alexandre Antunes Ribeiro

Hydroxyapatite Nanoparticles: Synthesis by Sonochemical Method and Assessment of Processing Parameters via Experimental Design

Hydroxyapatite (HAp) has been synthesized by different techniques, and sonochemical methods have shown to be useful in the HAp nanopartcicles production for biomedical applications such as bone graft substitute. In addition, experimental design is an appropriate tool for planning and evaluating a study to meet specified objectives. Then, this work aimed to synthesize HAp nanosized powders by a sonochemical method and assess the processing parameters via experimental design, in order to obtain dense samples. HAp nanopowders were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope/Field Emission Gun (SEM/FEG). For densification analysis, HAp samples were processed with different parameters, such as: compaction pressure (200 or 400 MPa), sintering temperature (900 or 1100°C), sintering heating rate (2 or 20 °C/min), and sintering time (2 or 4 hours). The samples were analyzed by SEM/FEG, whereas the linear shrinkage and density were considered the response variables for the experimental design. The results indicated that the sonochemical method successfully produced HAp nanoparticles with sphere-like morphology. Further, the experimental design showed that sintering temperature was the variable that most influenced the densification of samples.

Study on Processing and Characterization of Calcium Phosphate Bioceramics

The calcium phosphate bioceramics are widely used for the bone reconstruction because of their mineralogical similarities. This work aimed to obtain a biphasic calcium phosphate from hydroxyapatite nanoparticles synthesized by sonochemical technique and processed under two different conditions. The samples were uniaxially cold-pressed at 200MPa and sintered at 900°C/2h (CP900) and 1000°C/2h (CP1000) with heating rates of 2°C/min and 5°C/min, respectively. The characterizations were performed by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and theoretical elastic modulus. From the geometric method, the relative density, porosity and linear shrinkage were measured. The results showed that the studied processing conditions were useful for achieving samples formed by a biphasic calcium phosphate with 80% β-tricalcium phosphate and 20% hydroxyapatite. The CP900 and CP1000 samples presented a theoretical elastic modulus of 34.7 GPa and 53.1 GPa, respectively, which are higher than that found to the compact bone. In addition, the sintering at 900oC was sufficient to promote neck formation and particle coalescence, maintaining adequate porosity (47.5%) for bone tissue ingrowth into pores.

Different Synthesis Routes for Hydroxyapatite Nanoparticles by Mechanical Stirring

Nanosized hydroxyapatite (HA) with crystallinity and composition similar to bone apatite has been widely investigated in the last years, due to their excellent biocompatibility in bone replacement applications. This bioceramic can be synthesized by many wet chemical and mechanochemical methods. In this paper, nanosized hydroxyapatite powders were synthesized by two wet chemical routes using mechanical stirring method. The first route was used for HA synthesis from CaCl2.2H2O and Na3PO4.12H2O solutions and the second route was from Ca (OH)2 and H3PO4 solutions. The synthesized HA nanoparticles were characterized by Dynamic Light Scattering, BET Surface Area analysis, X-ray Diffraction, Infrared Spectroscopy, chemical analysis and Scanning Electron Microscopy. The results indicated that HA nanoparticles were successfully synthesized by both wet chemical precipitation routes and all powders presented a Ca/P ratio similar to stoichiometric HA, nanoneedles morphology and single HA crystalline phase.

Sodium Ions Uptake by Hydroxyapatite from Bovine Bone

The negative impact of soil salinity on agricultural yields is disturbing and significant, especially when related to agricultural plants, whose sensitivity to salinity is frequently, but not exclusively, associated with the abundance of Na+ in the soil, which in excess becomes toxic for plants. This work aims to propose an alternative for the control of Na+ present in waters from saline soils, by the possibility of applying bovine hydroxyapatite as a way to remedy this problematic. Hydroxyapatite powders were processed from bovine bone. The powders were characterized by X-ray diffraction analyses. Preliminary experiments were performed in batches at room temperature, adding together 5g hydroxyapatite and a dilute solution of sodium chloride. Liquid samples were analyzed by atomic absorption spectrophotometry. The results showed that the hydroxyapatite could be a promising alternative for the reduction of Na+ concentration in waters from saline soils.

Effect of Sonochemical Technique on the Morphology and Crystallinity of Hydroxyapatite Nanoparticles

Hydroxyapatite (HA) is the main mineral component of bones and teeth, and for this reason its synthetic analogous has been used with excellent clinical results as bone substitute. The biological apatite is typified as a poorly crystalline carbonate apatite (CHA) formed by nanosized particles with a great superficial area. This work aimed to study the influence of ultrasound technique on the morphology and crystallinity of nanoHA synthesized by chemical precipitation method. The nanoHA particles were obtained from CaCl2·2H2O and Na3PO4·12H2O raw solutions and a powerful ultrasonic sound (UP400S) was used at different conditions during the synthesis. X-ray Diffraction, Infrared spectroscopy, Chemical Analysis and Scanning Electron Microscopy were used to characterize the synthesized nanoHA particles. The results indicated that HA nanoparticles with nanorods morphology were obtained in all conditions. By Scherrer`s formula, the crystallite size was determined and it was found that the increasing in ultrasound amplitude enhances the nanoparticles crystallinity.

Characterization of Titanium Powders Processed at Different Temperatures

Titanium is the most adequate metallic material for orthopedic or dental implants fabrication, due to a very favorable combination of properties, when compared with other metals, such as good corrosion resistance, good mechanical properties, relatively low density, elasticity modulus close to that of bone and good biocompatibility, which assures good adhesion/integration to bone. Powder metallurgy has been used for titanium based implants fabrication due to advantages such as the production of more complex shapes and reduction of machining operation. In this work, compacted pure titanium powders, consolidated by rolling at different temperatures, were characterized by means of optical microscopy, Field Emission Scanning Electron Microscopy (FESEM) with Electron Back Scattering Diffraction (EBSD) analysis, automatic image analysis and hardness tests. The hardness of rolled samples increased from 200 to 400oC , which indicated that 300 to 400°C is the most adequate temperature range for this processing route, since it allowed obtaining low porosity with satisfactory and relatively high hardness.

TITANIUM SUBSTRATE SURFACES COATED WITH HYDROXYAPATITE BY MAGNETRON SPUTTERING

The deposition of hydroxyapatite coatings on titanium via sputtering techniques has been quite studied on commercial dense substrates, for use as a biomaterial. In this work, porous titanium samples produced by powder metallurgy and commercially dense titanium sheet, used as control, were used as substrates. The coatings were deposited by radio frequency magnetron sputtering using a hydroxyapatite target in argon atmosphere with different deposition times. Samples characterization was performed by Optical Microscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy and low-angle X-ray Diffraction. Hydroxyapatite coating depositions were obtained on both titanium substrates. The results indicated the potential of this methodology for titanium substrates with homogeneous hydroxyapatite coatings.

Characterization of Porous Ti-35Nb Alloy Sintered at Different Temperatures for Implant Applications

Studies show that porous titanium alloys improve osseointegration at the implant-bone interface, since they induce new bone tissue formation inside the pores providing a better mechanical stability. In this work, porous Ti-35Nb samples were manufactured by powder metallurgy for orthopedic implant application. The titanium and niobium powders were mixing with a pore former additive and then uniaxially and cold-isostatically compacted. The samples sintering were performed at 1200oC and 1300oC. Samples characterization was performed by Scanning Electron Microscopy with Energy Dispersive X-Ray (SEM/EDS), X-Ray Diffractometry (XRD) and Optical Microscopy (OM). Moreover, ultrasound test and Quantitative Analysis by Optical Metallography (QAOM) were conducted to obtain the modulus of elasticity and total porosity, respectively. The results indicated that the used processing parameters made it possible to obtain homogeneous microstructures throughout the length of the sample.

Quantitative Analysis of Titanium Samples by Means of the Pore-Throat Network Code Application

Several studies about porous biomaterials indicate that surgical implants success is directly linked to its surface morphology and structural characteristics. Porous implants improve osseointegration at the implant-bone interface, since they induce new bone tissue formation inside the pores providing a better mechanical stability. One of the most important parameters is the size of the pores. However, if the connectivity among the pores is not large enough for good blood irrigation, the osteocytes cells cannot reach the pores, no matter its size. The aim of this work is to analyze the porous structure of titanium samples fabricated by powder metallurgy, by characterizing pores and connections separately. This kind of structure characterization is important to improve the design of porous biomaterials. To accomplish it, a numerical code which converts 3D images into a pore-throat network structure was adopted. With this code, parameters such as size, frequency and quantity of pores and their connections can be determined. To acquire the 3D images of the samples, X-ray microtomography was used. Two samples were analyzed with distinct pore morphological types. The main result showed marked differences between the structures related to the connections radius, which suggests the one with better blood permeability.

Study of Sol-Gel/Powder Metallurgy Technique for Processing Titanium Parts

The powder metallurgy processing of titanium devices for biomedical applications has complex steps. In order to introduce a new processing route, this work studied a sol-gel technique combined with powder metallurgy for producing porous titanium samples. The process involves the mixture of titanium powders with sodium alginate suspension, which undergoes reticulation by calcium salt solution contact, forming a titanium/calcium alginate hydrogel in granule shape. Later, the hydrogel granules were dried and sintered in a high vacuum furnace for titanium particles consolidation and calcium alginate removal. The samples characterization was performed by scanning electron microscopy, optical microscopy, metallographic analysis, semi-quantitative X-ray fluorescence spectroscopy and X-ray diffraction. The results showed that the methodology used is adequate for producing porous titanium parts, since the samples presented no contamination, a uniform shape, particle consolidation and interconnected porosity. The research continues aiming to obtain samples with different bulk morphology, like, discs or bars for surgical implant applications.