Functionalization of biomaterials for joint implant application

1 - Articl

Improvement of high-temperature oxidation of titanium alloys by dipping in a phosphoric acid solution

Gamma-TiAl samples were treated by phosphoric acid solutions at different concentrations. With 15 mol/dm3, a viscous deposit was left on the surface leading, after drying and high temperature oxidation, to a very heterogeneous surface aspect. Concentrations below 0.5 mol/dm3 were then used and allowed to greatly ameliorate the homogeneity of the superficial layer. After heating from ambient to oxidation temperature, however, cracks were always observed, due to the departure of gaseous molecules. Isothermal oxidation tests come out at 800°C and 900°C under reconstituted air showed that weight gains were strongly reduced when TiAl had been treated. A compound containing titanium, oxygen and phosphorus was detected at the end of the heating period, identified as titanium pyrophosphate, TiP2O 7. This compound remained the only one detected for 100 h when oxidation was come out at 800°C, but evolved towards TiO2 when oxidation time was increased. In the case of oxidation at 900°C, the evolution from TiP2O7 to TiO2 also happened but appeared to go faster

Formation and evolution of phosphorus-containing species during high-temperature oxidation of TiAl dipped in a low-concentrated phosphoric acid solution

TiAl samples were dipped in a low-concentrated phosphoric acid solution, air dried, then heated to 800 °C under argon gas before oxidation under reconstituted air at this temperature. At the end of the heating ramp, sample surfaces were covered by a titanium pyrophosphate (TiP2O7) layer, well adhered to the substrate. This pyrophosphate was shown to be detectable from 400 °C. Chemical reactions have been proposed for the formation of this compound. TiP2O7 coating strongly increased the oxidation resistance of TiAl at 800 °C for 100 h. After 100 h, a transition period occurred leading to the change of TiP2O7 into TiO2, which was achieved after 230 h, total mass gain always remaining below that of raw substrate. This evolution was demonstrated not resulting from a thermal decomposition of pyrophosphate compound. © 2008 Elsevier B.V. All rights reserved

Effect of a phosphoric acid treatment on the high temperature oxidation behaviour of γ-TiAl: An overall mechanism

TiAl coupons were dipped in a low-concentration phosphoric acid solution, air dried, then heated up to 700 °C or 800 °C before discontinuous oxidation under laboratory air at these temperatures. At the end of the heating ramp, surfaces of TiAl samples were covered by a layer made of a pyrophosphate compound, resulting from reaction between the deposited acid and oxidized titanium. This layer strongly adhered to the substrate surface and allowed to greatly improve the resistance of TiAl to oxidation. After a certain time, a transition period occurred during which pyrophosphate compound disappeared to be changed into TiO2 rutile. For experiments carried on at 800 °C, it was shown that the phosphorus coming from the pyrophosphate group was present in this titanium oxide and that sample mass gain was still lowered. Performed analyses (XRD, SEM, EDS, μ-Raman spectroscopy) allowed to propose an overall mechanism to account for the "phosphorus effect". © 2011 Elsevier Ltd. All rights reserved

The early Stages of the Scale Growth on FeCrAl(+RE)-Type Alumina Formers

International audienc

Microstructure influence on residual stresses in growing chromia oxide films as determined by in situ high temperature Raman spectroscopy

In this work, growth stresses have been investigated in relation with the microstructure in the case of α-Cr2O3 growing oxide films on NiCr30 alloy. The equibiaxial growth stresses have been measured thanks to a technique coupling Raman spectroscopy and in situ high temperature oxidation of the NiCr30 alloy in the temperature range [700°C-900°C]. The low acquisition time necessary to obtain a Raman spectrum allows to follow the chromia growth kinetic with sufficient accuracy. It is demonstrated that the growth stress in such oxide films can attain more than 2 GPa, before additional thermal stress arises on cooling. Moreover, the growth stress kinetic - subsequent establishment and relaxation - are highly microstructure sensitive: in particular, as the oxidation temperature rises, the chromia grain size also increases, and it consequently retards the occurrence of the creep relaxation phenomena which needs an additional stress to start

On dipping of γ-TiAl in low-concentration phosphoric acid solution and consecutive oxidation resistance at 800 °C

The oxidation behaviour of γ-TiAl previously treated in low-concentration phosphoric acid solution has been investigated at 800 °C in air. The chemical treatment promotes, instead of the usual TiO2/Al2O3 mixed phase, the fast formation of a TiP2O7 pyrophosphate layer with a subsequent large reduction in the oxidation rate. © 2006 Acta Materialia Inc

Inhibition of Staphylococcus epidermidis adhesion on titanium surface with bioactive water-soluble copolymers bearing sulfonate, phosphate or carboxylate functions

1 - ArticleImplanted prostheses are sometimes subject to bacterial infections, which can threat their benefit rule on a long-term basis. Various methods are studied to fight against these infections. Among them, the grafting of bioactive polymers onto the prosthesis surface shows up as a promising way to the problem of infections. This work presents the influence of various water-soluble bioactive polymers on the inhibition of the Staphylococcus epidermidis adhesion on the titanium samples surfaces initially preadsorbed with various proteins. Whatever the studied protein is, it is shown that the bioactive polymer containing sulfonate functions generates an inhibition of the adhesion of Staphylococcus epidermidis. For a plasma preadsorption, the inhibition rate rises up to 68% when the concentration of sulfonate function is 2.5 mu mol/L. Titanium surfaces grafted with the bioactive polymer were also tested. We find an inhibitive activity of the adhesion close to that of the previous case. These preliminary results can point up a clinical interest in the fight against the medical devices infection, because they highlight a clear local effect of S. epidermidis adhesion inhibition. Copolymers containing other functional groups (phosphate or carboxylate) were dissolved in a bacterial suspension to monitor the influence of the composition on the adhesion inhibition. Their inhibition rates are not significantly lower than those of pNaSS homopolymers, as much as the sulfonate function proportion remains higher than 50%. Thus, the sulfonate function is the main responsible for the inhibition of the S. epiderrnidis adhesion. (C) 2010 Elsevier Masson SAS. All rights reserved

The early Stages of the Scale Growth on FeCrAl(+RE)-Type Alumina Formers

International audienc