Stage 1
For this project was selected the original composition Ti-15Ta-5Zr that contains only non-toxic alloying elements, by high Ta content (one of the most resistant element from nature) realises high corrosion resistance and Zr contributes to the formation of a fine microstructure and to the improvement of the mechanical properties.
The alloy presented a homogeneous, bi-phase microstructure alpha + beta as fine lamella.
The native passive film existing on Ti-15Ta-5Zr alloy surface is formed by protective Ti2O3, TiO2 and very protective Ta2O5 and ZrO2 oxides (XPS analysis). The passive native film thickness is 8.5 1.0 nm, a thicker film than that on Ti surface of 1.5 - 5.4 nm.
The corrosion behaviour of the new alloy in Ringer solutions of different pH values (3.54; 7.49; 8.98) showed that the corrosion rates for alloy have values of about 70 times lower and the polarisation resistances of about 10 times lower than those of Ti, proving a more protective passive film, as result of the beneficial effect of the Ta and Zr alloying elements which stabilise, enforce the passive film on the alloy surface.
The corrosion and passivation potentials have more electropositive values, passive current densities and tendencies to passivation have lower values than those of Ti due to Ta and Zr alloying elements which have a better tendency to passivation than that of Ti.
Impedance spectra describe a capacitive passive film with superior properties for alloy in comparison with Ti, conferred by the alloying elements that improve the insulating properties of the passive film. The passive film is formed by two layers: an interior, barrier, electronic conducting layer and an outer, porous layer favouring the absorption of species.
The electrochemical method for the architecturing of the alloy surface was elaborated. The primary layer was electrodeposited by anodic galvanostatic oxidation at high currents and potentials. From AFM (topography and roughness), SEM (morphology and porosity) studies resulted that the most favourable characteristics presented the nanocoating electrodeposited in 1M H3PO4 solution at a current density of 10 mA/cm2, for 45 min. These parameters were selected for the primary architecturing of the new alloy surface and the behaviour of the nanolayer obtained by this method will be studied further.
XPS spectra indicate the existence of TiO2, ZrO2 oxides and PO43- ion in the electrodeposited layer; its thickness is 15.5 1.0 nm; it is a good thickness that assures a very good adherence to the metallic substrate and does not presents risk of exfoliation that can be produced only on the thicker coatings.
SEM images evince a nanolayer that covers the whole surface, with a porous structure, with fine porosity, with pore diameter in the domain of nanometers. This porous structure favours the very good adherence of the subsequent deposition, which will be applied on the new alloy surface.
The electrochemical measurements showed the nobler behaviour of the anodic oxidized alloy in comparison with non-oxidized one, due to the thick oxide layer formed on the surface; the most favourable electrochemical parameters for the anodic oxidized alloy were obtained in neutral Ringer solution, the normal functional conditions of one implant.
The potentiodynamic linear polarisation curves (Tafel representations) permitted the obtaining of the main corrosion parameters. It resulted the accentuate decrease (of about 7 times) of the corrosion current densities and rates; also, the total quantity of ions released in the simulated physiological fluids reduced very much, namely the toxicity of the anodic oxidized alloy is lower than that of the non-oxidized one.
The electrochemical processes that take place at the interface between oxidized alloy and simulated human biofluids were studied by electrochemical impedance spectroscopy (EIS) method. A passive film formed from two layers was determined: a compact, barrier layer resistant to the diffusion of ions through it; a little more permissive layer, more porous that permits the absorption of different compounds and species from human biofluid; this property favours a better adherence of the further layers, which will be deposited over this primary layer.
Dissemination
Scientific paper published in Proceedings
1. P. Drob, E. Vasilescu, C. Vasilescu, S. I. Drob, M. V. Popa, S. Ivanescu, Anticorrosive properties of new titanium based alloy in corrosive environments, Proceeding of "6th International Multi-Conference on Engineering and Technological Innovation: IMETI 2013", Edited by: N. Callaos, H.-W. Chu, B. Sanchez, M.J. Savoie, A. Tremante, Pub.: International Institute of Informatics and Systemics, ISBN-978-1-936338-90-0, pp. 20-25, 2013.
Scientific paper submitted to ISI journal
1. C. Vasilescu, S. I. Drob, P. Drob, P. Osiceanu, J. M. Calderon Moreno, S. Preda, E. Vasilescu, Surface analysis of passive film and electrochemical properties of interface between new Ti-15Ta-5Zr alloy and simulated bioelectrolyte, manuscript submitted to ISI journal.
Scientific paper under preparation for ISI journal
1. Characterization and stability of new Ti-Ta-Zr alloy with electrochemical oxidized surface, manuscript under preparation.
Scientific communication at International Meetings
1. P. Drob, E. Vasilescu, C. Vasilescu, S. I. Drob, M. V. Popa, S. Ivanescu, Anticorrosive properties of new titanium based alloy in corrosive environments, "6th International Multi-Conference on Engineering and Technological Innovation: IMETI 2013", 9 - 12 July, Orlando, SUA, 2013.
Stage 2
Chemical deposition of the hydroxyapatite (HA), Ca10(PO4)6(OH)2 secondary layer was realised by green chemical method using a solution supersaturated in Ca2+ calcium and PO43- phosphate ions. The method comprises the following stages: the preparing of the alloy surface; the application of the HA coating by green chemical method; sample conditioning.
The selection of the best parameters which conducted to the obtaining of the most favourable secondary coating, certified by SEM micrographs and EDX spectra.
The characterization of the nanocoating included the determination of the secondary layer adherence, elemental analysis, and composition by the X-ray photoelectron spectroscopy (XPS).
The HA coating has a very good adherence of 20 MPa that is considered very proper for the bone cell proliferation.
The survey XPS spectrum of the chemical deposited coating shows the peaks for the calcium Ca 2p and phosphorous P 2p, constituent elements of HA.
The examination of the morphology, texture, nano-particle size, pores, and defects, crystallinity of the obtained layer reveals sub-micron morphology of spherical particles with a texture of the parallel chains formed by elongated crystals; also, pores can be observed. The crystalline structure and pores favour the bone cell adherence on this coating surface, conferring it bioactivity properties.
The passivation-dissolution-repassivation mechanisms were studied by the cyclic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods in Ringer solutions of neutral (7.49) and alkaline (8.98) pH values which simulate the real functional conditions of an implant.
The voltammograms revealed a passive, nobler behaviour for the HA covered alloy, namely, the HA layer confers supplementary protection to the alloy, due to the action of compactness, reinforcing of the passive layer pre-existed on the alloy surface.
Electrochemical impedance spectra evinced a capacitive, nobler behaviour, a very resistant, insulating passive film for the covered alloy in comparison with the bare one.
The electric equivalent circuit was modelled with three time constants: the first time constant for the inner, barrier layer described by its resistance and capacitance; the second time constant for the next inner, slightly porous layer, at the limit between passive film and HA coating, represented by the its resistance and capacitance; the third time constant shows the HA porous layer illustrated by the resistance and capacitance of this layer.
The impedance results evinced the dual character of the new alloy surface covered with HA: corrosion resistance due to the inner, compact, barrier layer and bioactivity due to the outer, porous HA layer that stimulates the bone cell growth, favouring the alloy osseointegration.
Protective properties of the bi-layered coating were appreciated from the values of the corrosion current densities, corrosion rates, polarization resistances, ion release, protection efficiency and porosity.
All corrosion parameters have more favourable values for the covered alloy that those for the un-covered one: corrosion rates and ion release decreased about 10 times, showing that the bi-layered coating has protection effect against the corrosion; polarization resistance increased about 3 times, namely, this coating is a barrier against the ion crossing through it. The coating has an efficiency of over 80% and a porosity of about 42%, namely, it is both protective but it permits the interactions with the surrounding environment, human biofluid.
Original results
- Green chemical method adapted to the properties of the new Ti-15Ta-5Zr alloy.
- The determination for the first time of the composition of the hydroxyapatite (HA) coating, by XPS method.
- Scientific novelties regarding the morphology, crystallinity, texture, pores of the HA coating (SEM).
- Original contributions concerning the electrochemical characterization of the bi-layered coating.
- The elaboration of the original electric equivalent circuits for the layers formed on the new Ti-15Ta-5Zr alloy surface.
- Innovative scientific results evincing the improvement of the corrosion resistance of the bi-layered coating.
Dissemination
Article published in ISI journal
1. C. Vasilescu, S. I. Drob, P. Osiceanu, M. Anastasescu, J. M. Calderon Moreno, P. Drob, E. Vasilescu, The morphostructural, compositional, and electrochemical characterization of electrodeposited nanolayers on a new Ti-15Ta-5Zr alloy, J. Nanomater. Volume 2014, Article ID 369034, 12 pages, 2014, impact factor 1,611 (2013).
Article accepted in ISI journal
1. C. Vasilescu, S. I. Drob, P. Drob, P. Osiceanu, J. M. Calderon Moreno, S. Preda, E. Vasilescu, Surface analysis, microstructural, mechanical and electrochemical properties of new Ti-15Ta-5Zr alloy, accepted la Met. Mater. Int. impact factor 1,223 (2013).
Articles published in Proccedings
1. C. Vasilescu, S. I. Drob, J. M. Calderon Moreno, P. Drob, M. Popa, E. Vasilescu, Surface protection obtained by anodic oxidation of new Ti-Ta-Zr alloy, Proceedings of 19th International Corrosion Congress, 2014, Ed. International Corrosion Council, USA, P-89, 1-10.
2. C. Vasilescu, S. I. Drob, M. Popa, J. M. Calderon Moreno, J. C. Mirza Rosca, Corrosion behavior of novel Ti-15Ta-5Zr alloy in simulated physiological solution, Proceedings of 226th Electrochemical Society Meeting, Ed. The Electrochemical Society, Pennington, NJ, USA, 2012, ISSN 1091-8213.
Scientific communication at International Meetings
1. C. Vasilescu, S. I. Drob, J. M. Calderon Moreno, P. Drob, M. Popa, E. Vasilescu, Surface protection obtained by anodic oxidation of new Ti-Ta-Zr alloy, 19th International Corrosion Congress, 2-6 Nov. 2014, Jeju, Korea , P-89.
Stage 3
Characterization of the bioactive nanocoating with two layers (the first layer of oxide containing phosphate ion, the second layer of hydroxyapatite) was made with AFM method. The roughness of the covered Ti-15Ta-5Zr alloy surface is about 6 times higher than that of the un-covered surface, showing a proper surface for the adhesion of the active biological molecules.
The investigation of the Ti-15Ta-5Zr alloy passivation-dissolution-repassivation mechanism for long term (till 1500 immersion hours) in Ringer solutions of different pH values (3.23; 7.41; 9.01) was carried out from the cyclic potentiodynamic and linear polarization curves.
All electrochemical parameters have improved values in time, due to the prolonged interactions with the phosphor and calcium ions from Ringer solutions; these ions favourably influence the protective properties of the surface film.
Corrosion currents and corrosion rates have very low values, typical for a protective passive film. In time, a decrease of these parameter values and an increase of the polarization resistances resulted, that signify the passive film thickening and the improvement of its anticorrosive resistance due to the new depositions from solutions.
XPS analysis and SEM micrographs illustrated that these depositions take place independently of the pH values, namely, Ti-15Ta-5Zr alloy favours the incorporation of ions and species from the bio-electrolyte.
From the XPS depth profiling measurements was determined the thickness of the new depositions: 9.0 nm ± 0.5 nm in Ringer solution of pH = 3.23; 10.5 nm ± 0.5 nm in Ringer solution of pH = 7.41 and pH = 9.01.
In Ringer solution of pH = 3.23, after 1500 immersion hours were deposited nano-particles of brushite; in Ringer solution of pH = 7.41 and pH = 9.01, the depositions are denser, as bigger aggregates of hydroxyapatite (XPS and SEM results).
The study of the electrochemical processes from the interface bi-layered coating / biofluid was realised from the electrochemical impedance Nyquist and Bode spectra.
EIS spectra were modelled with a duplex passive film formed from the inner, compact, resistant, stable, insulating layer and from the outer, porous, less resistant layer. The depth profiling XPS spactra evinced that the inner layer is formed from TiO2, ZrO2 oxides and Ta suboxides and the outer layer is formed Ti2O3, ZrO2 and Ta2O5 oxides.
The investigation of the Ti-15Ta-5Zr alloy passivation-dissolution-repassivation mechanism realised by the complex electrochemical studies completed by XPS spectroscopy method and SEM microscopy method showed a very good corrosion resistance that improved in time, due to the new depositions from the simulated human biofluids.
The deposition of the biomimetic protein on the bi-layered coating was made with the aim to increase very much the alloy bioactivity and specialy its osseointegration capacity. The deposition of the biomimetic coating was applied on the bi-layered coating and were selected the deposition parameters which conducted to the most favourable properties of the coating with the protein, attested by AFM, SEM and EDS studies.
Original results
- Original results concerning the roughness (AFM method) of the bi-layered coating on the new Ti-15Ta-5Zr alloy surface.
- Scientific results relating the long term (1500 immersion hours) electrochemical behaviour of the new Ti-15Ta-5Zr alloy in simulated physiological solutions
- Innovative scientific results which evince the composition and thickness (with XPS method) of the depositions from the biofluids.
- Original scientific contributions revealing the new alloy surface morphology (by SEM method) after soaking (1500 hours) in the simulated human fluids
- Elaboration of the original electric equivalent circuit for different immersion periods in physiological solutions of various pH values, simulating the real functional conditions of an metallic implant.
- Elaboration of deposition method of the biomimetic coating with protein.
- Selection of the deposition parameters which conduct to the most favourable properties of the biomimetic protein coating, attested by AFM, SEM and EDS studies.
Disemination
Articles published in ISI journals
1. C. Vasilescu, S. I. Drob, J. M. Calderon Moreno, P. Osiceanu, M. Popa, E. Vasilescu, M. Marcu, P. Drob, Long-term corrosion resistance of new Ti-Ta-Zr alloy in simulated physiological fluids by electrochemical and surface analysis methods, Corros. Sci. 93, 310-323, 2015, impact factor 4.42 (2014)
2. C. Vasilescu, S. I. Drob, P. Drob, P. Osiceanu, J. M. Calderon Moreno, S. Preda, E. Vasilescu, Surface analysis, microstructural, mechanical and electrochemical properties of new Ti-15Ta-5Zr alloy, Met. Mater. Int. 21(2), 242-250, 2015, impact factor 1.579 (2014)
3. C. Vasillescu, S. I. Drob, P. Osiceanu, J. M. Calderon-Moreno, P. Drob, E. Vasilescu, Characterisation of passive film and electrochemical behaviour of a new Ti-Ta-Zr alloy in artificial oral media: in time influence of pH and fluoride ion content, Mater. Corros. 66(9) 971-981, 2015. impact factor 1,373 (2014).
Scientific communication at International Meetings
1. C. Vasilescu, S. I. Drob, P. Osiceanu, J. M. Calderon Moreno, Corrosion resistance of new ternary Ti-Ta-Zr alloy in artificial saliva simulating severe functional conditions, 17th Topical Meeting of the International Society of Electrochemistry, 2015, Saint-Malo, France, poster s2f-008.
2. C. Vasilescu, S. I. Drob, P. Osiceanu, J. M. Calderon Moreno, Bioactivity increase of novel ternary Ti based alloy by hydroxyapatite nanocoating, XXII International Symposium on Bioelectrochemistry and Bioenergetics, of the Bioelectrochemical Society, 2015, Malmo, Sweden, in Program & Book of Abstracts, pp. 263.
3. C. Vasilescu, S. I. Drob, P. Osiceanu, J. M. Calderon Moreno, Obtaining, characterisation and protective properties of hydroxyapatite coating on new Ti-Ta-Zr alloy surface, EUROCORR 2015, European Corrosion Congress, 6-10 September, 2015, Graz, Austria, p. 85.
4. C. Vasilescu, S. I. Drob, S. Preda, J. M. Calderon Moreno, P. Osiceanu, Passive film characterization on new ternary Ti-Ta-Zr Alloy Surface, 66th ISE Annual Meeting, 2015, Taipei, Taiwan, s08-015.
Stage 4
Complete and complex characterization of the final biomimetic coating. The identification of elemental composition and of the constituent compounds of the biomimetic bovine serum albumin, BSA coating was realised by the Raman microspectroscopy (RS). The changes in the Raman spectrum of the secondary structure of deposited BSA in comparison with the Raman spectrum of the solid BSA (witness sample) were studied. No differences were observed, thus, the layer deposited on the Ti-15Ta-5Zr alloy surface is formed by the BSA protein that favour the adhesion and development of the bone cells.
Determination of morphology, porosity, texture, size of the nanoparticles of the final biomimetic coating were performed by SEM technique and the main constituent elements were identified from EDX spectra. The deposition of the BSA protein was confirmed; also, calcium and phosphor ions were deposited from the Ringer solution used as deposition solution. The BSA protein forms a biomimetic surface and calcium and phosphor ions confer bioactivity to the metallic substrate.
Evaluation of the final biomimetic coating roughness was realised by AFM method. Both the topography and the values of the roughness of the coating are favourable to the bone cells fixation, adhesion, etc.
Original data bank concerning the corrosion resistance of the bare and coated alloy. The data bank regarding the corrosion and electrochemical parameters indicate the over time behaviour of the bare alloy and of the layers on the Ti-15Ta-5Zr alloy. The specialists from the biomaterial domain can appreciate and compare the anticorrosive performances of the new alloy in comparison with other implant alloys. The specialists can select the alloy with the most stable coating, with the least corrosion rate.
Morpho-structural monitoring of the bare and coated alloy. SEM and AFM studies suggest that the bare alloy interacts with the simulated physiological environment, favouring the deposition of phosphor and calcium compounds, so, it is bioactive; also, the covered alloy incorporates phosphor and calcium compounds in very high quantity due to its biomimetic character.
Original results
- Scientific novelties that reveal the composition, morphology, porosity, texture, topography and roughness of the biomimetic BSA coating deposited on the new Ti-15Ta-5Zr alloy surface (Results obtained from Raman spectra, SEM micrographs and 3D AFM images).
- Innovative scientific contribution concerning the application of the nanocoating formed by three layers, titanium oxide, hydroxyapatite, bovine serum albumin, BSA.
- Original data bank referring to the long-term behaviour of the main electrochemical and corrosion parameters of the multi-layer, multi-functional nanocoatings.
- Original scientific results regarding the long-term monitoring of the new nanocoatings (SEM, AFM).
- Rezultate stiintifice originale privitoare la monitorizarea morfo-structurala pe termen lung a noii nanoacoperirii (SEM, AFM).
Disemination
Article published in ISI journals
1. C. Vasilescu, S. I. Drob, M. Popa, J. M. Calderon Moreno, M. Anastasescu, M. Marcu, Electrochemical and surface characterization of a new Ti-Ta-Zr alloy covered with biomimetic bovine serum albumin, Int. J. Electrochem. Sci., 11 7076-7088 2016. Factor impact 1,692 (2015)
International scientific communications
1. C. Vasilescu, S. I.Drob, P. Osiceanu, M. Anastasescu, J. M. Calderon Moreno, Modification of the new Ti-Ta-Zr alloy surface by electrodeposition. Electrochemical and structural characterization of obtained nanolayer, 19th Topical Meeting of the International Society of Electrochemistry, 17-20 April 2016, Auckland, New Zealand, s1-08.
2. C. Vasilescu, S. I. Drob, M. Popa, J. M. Calderon Moreno, Characterization of passive film on new ternary Ti-Ta-Zr alloy surface, 6th Baltic electrochemistry Conference, Helsinki, 15th - 17th June 2016, Book of Abstract, p. 137.
3. M. Popa, C. Vasilescu, S.I. Drob, J.M. Calderon Moreno, M. Anastasescu, M. Marcu, Characterization of a biomimetic coating applied on surface of new ternary Ti-Ta-Zr alloy, ROMPHYSCHEM 16, 21-23 Sept. Galati, p. 26, S04-P17.
Patent proposal deposited to OSIM
Patent A/ 00320 / 05.05.2016:
Method of biomimetic protein deposition for the osteointegrative biofunctionalisation of the new Ti-15Ta-5Zr alloy surface,
C. Vasilescu, J. M. Calderon Moreno, S. I. Drob, M. Popa.
