Papers by Author: Marize Varella de Oliveira

Abstract: In the present work, mechanical properties of a stoichiometric hydroxyapatite (HA), synthesized by hydrothermal method, with 1.66 Ca/P molar ratio are investigated as a function of the processing parameters. Cylindrical samples were processed by uniaxial compacting, followed by sintering, aiming to obtain high density HA samples. Density values were obtained by the geometric method and SEM images were taken from HA samples in order to characterize their topography and to determine the grain size for each set of samples. Vickers micro-hardness was measured for each set of samples. Compressive strength of cylindrical samples with 2.0 mean diameter/height ratio was measured reporting load to failure divided by the cross-sectional area of the samples. Vickers micro-hardness and compaction strength values of the samples were found to be in agreement with the relative density and grain size values.

Abstract: Synthetic Hydroxyapatite (HA) has been used as coating in order to enhance biocompatibility of titanium implants. Osseointegration at the implant-bone interface can be positively affected by the presence of HA coating and other biocompatible calcium phosphates (CaP) deposited on titanium implants, due to the high biocompatibility of these bioceramics. The biomimetic process is based on the nucleation and growth of a bioceramic film onto a substrate immersed in a body fluid solution (SBF) and it can be applied to deposit CaP coatings onto metallic substrates. The present work presents results on the characterization by SEM of CaP coating deposited on porous titanium samples by a biomimetic process.

Abstract: The osseointegration of porous titanium implants was evaluated in the present work. Implants were fabricated from ASTM grade 2 titanium by a powder metallurgy method. Part of these implants were submitted to chemical and thermal treatment in order to deposit a biomimetic coating, aiming to evaluate its influence on the osseointegration of the implants. The implants were characterized by Scanning Electron Microscopy (SEM), Electron Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy. Three coated and three control (uncoated) implants were surgically inserted into thirty albino rabbits’ left and right tibiae, respectively. Tibiae samples were submitted to histological and histomorphometric analyses, utilizing SEM, optical microscopy and mechanical tests. EDS results indicated calcium (Ca) and phosphorous (P) at the surface and Raman spectra exhibited an intense peak, characteristic of hydroxyapatite (HA). Bone neoformation was detected at the bone-implant interface and inside the pores, including the central ones. The mean bone neoformation percentage in the coated implants was statistically higher at 15 days, compared to 30 and 45 days. The mechanical tests showed that coated implants presented higher resistance to displacement, especially after 30 and 45 days.

Abstract: Despite of the wide use of hydroxyapatite (HA) for bone repair and regeneration, its brittleness has limited clinical application to less stressed body parts. Thus, evaluation of HA mechanical properties has been an important research matter. The aim of this study is to assess the compressive strength of a stoichiometric HA with 1.66 Ca/P molar ratio, synthesized by hydrothermal method. Cylindrical samples were processed by uniaxial compacting, followed by sintering. Compressive strength of cylindrical samples with 2.0 medium diameter/height ratio was measured according to ASTM C 1424. Load to failure divided by the cross-sectional area of the samples were reported and microstructural characterization was made by MEV-EDS. The compression strength results were compared to values reported in the literature.

Abstract: In order to improve implant-bone attachment, porous titanium has been used to achieve the ingrowth of bone tissue within the porous structure. Although this biomaterial has shown efficient bone adhesion for orthopedic and dental implants, the ideal surface must have chemical bonds at the implant-bone interface. In this work, samples of pure porous titanium were produced by powder metallurgy technique and submitted to biomimetic process in order to evaluate the material’s bioactivity and to enhance its osteoconductivity. The samples were immersed in modified simulated body fluid (mSBF) which induces the nucleation and growth of a calcium phosphate bioactive film and a chemical bond with titanium. SEM, EDX and FTIR analyses showed that a calcium phosphate deposition occurred without the need of pre-treatments to increase the surface bioactivity. As a result, this research revealed the potential for obtaining a bonelike apatite film on this porous titanium by biomimetic method.

Abstract: In this work, porous titanium samples processed by powder metallurgy and coated with biomimetic coatings, obtained during different periods of immersion in a simulated body fluid (SBF), were tested for corrosion resistance in a phosphate buffer solution (PBS). Uncoated samples were also tested for comparison. The corrosion resistance of both types of titanium samples was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarisation curves. The electrochemical results indicated the formation of a surface film on the porous Ti samples with immersion in the SBF solution and this biomimetic film increased their corrosion resistance. This film helps osteointegration besides increasing corrosion resistance.

Abstract: Porosity and pore size are critical features for biomaterial scaffolds as they play an essential role in bone formation and bone ingrowth in vivo. Therefore, techniques for scaffolds evaluation are of great importance for their design and processing. Porous titanium has been used for grafts and implant coatings as it allows the mechanical interlocking of the pores and bone. In this study, porous titanium samples were manufactured by powder metallurgy. The porosity quantification was assessed by optical quantitative metallographic analysis, and non-destructive gamma-ray transmission and X-ray microtomography techniques, in order to compare their efficacy for porosity evaluation. Pore morphology and surface topography were characterized via scanning electron microscopy. These techniques have demonstrated to be suitable for titanium scaffolds evaluation, and micro-CT was the one that allowed the three-dimensional porosity assessment.

Abstract: Surgical implant coatings and grafts for tissue replacement have been made by porous surface materials to improve the implant to bone attachment. In this work, porous titanium samples were produced via powder metallurgy techniques and submitted to the biomimetic process in order to enhance its osteoconductivity. This process allows a nucleation and growth of a calcium phosphate film which makes a chemical bond with titanium. Therefore, it avoids the looseness of this film from substrate. The samples were chemically treated, heat treated at different temperatures and soaked into a modified body fluid solution (mSBF) during periods of 2 and 7 days. Samples with and without pretreatments and not soaked in mSBF were used as controls. SEM and EDX analyses detected a calcium phosphate phase on the sample surfaces treated at 400°C and 600°C and soaked in mSBF for 2 and 7 days. The results demonstrated the potential of the methodology applied for obtaining a bonelike apatite film on porous titanium samples processed by powder metallurgy.

Abstract: Titanium foams have been used for surgical implants and biomedical engineering because they exhibit inert behavior and good corrosion resistance. Substantial progress has been achieved for metallic foam fabrication techniques, however the porosity characterization methods available haven’t been studied sufficiently. A previous research has developed a powder metallurgy route to produce pure titanium foams attaining the porosity requisites for porous surfaced surgical implants. In this study, titanium foams porosity was evaluated employing different techniques: optical quantitative metallographic analysis with automatic image technique, gamma-ray transmission and x-ray microtomography. These techniques can be used for titanium foams analysis, though their results can not be simply compared, because they use quite different methodologies and take different measurement assumptions.

Abstract: Porous structures are applied as coatings in order to improve surgical implants bone fixation by allowing the mechanical interlocking of the pores and bone. Sintered titanium porous coatings have been used for surgical implants because they have a strong attachment of the coating to the substrate. This works reports the processing and characterization of titanium porous coatings and foam samples, for surgical implants applications. Pure titanium powders mixed with urea as a binder was used for the porous coatings and foam samples. A rod shape of Ti-6Al-7Nb alloy P/M sample was used as substrate. Coatings surfaces were analyzed via scanning electron microscopy and the porosity characterization was made by quantitative metallografic analysis. It was found that coating porosity can be controlled by adjusting the binder percent addition and powder sizes. Sintered samples exhibited a microstructure with micropores and inteconnected macropores which is suitable to be used in surgical implants.