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Influence of surface modifications on bioactivity and (tribo) corrosion of beta Ti-Nb-(Zr) alloys with low elastic modulus for application as implant

Grant number: 21/03865-9
Support type:Scholarships in Brazil - Post-Doctorate
Effective date (Start): February 01, 2022
Effective date (End): January 31, 2024
Field of knowledge:Interdisciplinary Subjects
Principal researcher:Conrado Ramos Moreira Afonso
Grantee:Mariana Correa Rossi
Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
Associated research grant:18/18293-8 - Titanium alloys: phase transformations and additive manufacturing applied to obtaining functionally graded materials, AP.TEM

Abstract

The purpose is to compare two routes of surface modification of beta-type Ti alloys (Ti-Nb- (Zr)), in order to improve the electrochemical and biological properties for better acceptance in the biomedical field. The materials were obtained by melting process and will be superficially modified by anodizing and plasma electrolytic oxidation (PEO).The modification by PEO will be carried out by an electrolytic solution with 0.1% sodium fluoride (NaF) and other products at based on Ca and P.The treatment will be carried out at 25A/dm2, while anodization will use an electrolyte based on NH4F + Glycerol + H2O. An electrolytic cell containing two electrodes will be used, containing a platinum wire that will act as the cathode and the alloys will act as an anode. A potential of 20 V for 6 hours will be applied in order to promote the metal oxides formation. To confirm and distinguish the oxides formed by surface treatments and also their elementary composition, an X-ray photoelectron spectroscope will be used. In the microstructural characterization of the surface modifications, SEM will be used, coupled with EDS and MET. The surface wettability will be investigated by contact angle measurements, and its roughness by atomic force microscopy and a profilometer techniques. Corrosion resistance will be studied with the aid of a potentiostat /galvanostat, being investigated in two solutions that simulate the body fluid (Ringer Hartmann and HANK solution), at 37ºC. The tribocorrosive behavior will be investigated, using an alumina sphere of 4 mm in diameter, with an oscillation frequency of 1Hz for 1600 cycles. The electrolytes used will be the same as those tested in the corrosion test. At the end of the experiment, the surfaces will be evaluated by SEM-EDS and the wear volume will be determined by the profilometer. The bioactivity and biocompatibility tests will be carried out on the materials that present better resistance to corrosion and tribocorrosion. In the bioactivity test, an ionic composition solution that simulates the body fluid (SBF) will be used. This solution together with the materials will be kept incubated at 37ºC and the formation of the apatite layer will be studied at 7, 14 and 28 days with the aid of a scanning electron microscope with cryogenic field emission (cryo-FESEM). The biological effect, such as biocompatibility, evaluation of cell adhesion, as well as cell morphology patterns will be investigated, using mesenchymal stem cells (MSCs) deposited on the surface of the alloys and will be maintained for 24 h incubated under ideal culture conditions. Then, the cellular biological characteristics will be studied through SEM-EDS. The process of osteogenic differentiation of MSCs will be carried out by the cell mineralization test, marked formed calcium deposits stained with alizarin red. The MSCs will be place on the surfaces of the alloys and kept in culture for up to 21 days, receiving culture medium with molecules that induce the osteogenic process. After this time and stained, they will be evaluated by SEM-EDS, in order to confirm the calcium deposits, as well as a change in its morphology, which will prove its differentiation in bone cells. These modifications are expected to promote improvements in the face of corrosion and tribocorrosion and to allow better cell adhesion and stimulate their proliferation and osteogenic differentiation.

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