Hicham Benhayoune

Pulsed electrodeposition for the synthesis of strontium-substituted calcium phosphate coatings with improved dissolution properties

Strontium-substituted calcium phosphate coatings are synthesized by pulsed electrodeposition on titanium alloy (Ti6Al4V) substrates. Experimental conditions of the process are optimized in order to obtain a coating with a 5% atomic substitution of calcium by strontium which corresponds to the best observations on the osteoblast cells activity and on the osteoclast cells proliferation. The physical and chemical characterizations of the obtained coating are carried out by scanning electron microscopy associated to energy dispersive X-ray spectroscopy (EDXS) for X-ray microanalysis and the structural characterization of the coating is carried out by X-ray diffraction. The in vitro dissolution/precipitation properties of the coated substrates are investigated by immersion into Dulbeccos Modified Eagle Medium (DMEM) from 1h to 14 days. The calcium, phosphorus and strontium concentrations variations in the biological liquid are assessed by Induced Coupled Plasma - Atomic Emission Spectroscopy for each immersion time. The results show that under specific experimental conditions, the electrodeposition process is suitable to synthesize strontium-substituted calcium phosphate coatings. Moreover, the addition of hydrogen peroxide (H2O2) into the electrolytic solution used in the process allows us to observe a control of the strontium release during the immersion of the prosthetic materials into DMEM.

In vitro corrosion behavior of electrodeposited calcium phosphate coatings on Ti6Al4V substrates

Calcium phosphate coatings on titanium alloy substrates are synthesized by pulsed electrodeposition and characterized by scanning electron microscopy associated to energy dispersive X-ray spectroscopy and by X-ray diffraction. The corrosion behavior of CaP/Ti6Al4V systems and uncoated Ti6Al4V are investigated using electrochemical methods in three physiological solutions and simulated with an equivalent circuit. The results reveal that the calcium phosphate coatings act as a protective layer especially when electrodeposition is carried out in the presence of hydrogen peroxide into the electrolyte which is used to control the chemical composition of the coatings and which implies a control of the corrosion behavior of the prosthetic material.

A new sol–gel synthesis of 45S5 bioactive glass using an organic acid as catalyst

In this paper a new sol-gel approach was explored for the synthesis of the 45S5 bioactive glass. We demonstrate that citric acid can be used instead of the usual nitric acid to catalyze the sol-gel reactions. The substitution of nitric acid by citric acid allows to reduce strongly the concentration of the acid solution necessary to catalyze the hydrolysis of silicon and phosphorus alkoxides. Two sol-gel powders with chemical compositions very close to that of the 45S5 were obtained by using either a 2M nitric acid solution or either a 5mM citric acid solution. These powders were characterized and compared to the commercial Bioglass®. The surface properties of the two bioglass powders were assessed by scanning electron microscopy (SEM) and by Brunauer-Emmett-Teller method (BET). The Fourier transformed infrared spectroscopy (FTIR) and the X-ray diffraction (XRD) revealed a partial crystallization associated to the formation of crystalline phases on the two sol-gel powders. The in vitro bioactivity was then studied at the key times during the first hours of immersion into acellular Simulated Body Fluid (SBF). After 4h immersion into SBF we clearly demonstrate that the bioactivity level of the two sol-gel powders is similar and much higher than that of the commercial Bioglass®. This bioactivity improvement is associated to the increase of the porosity and the specific surface area of the powders synthesized by the sol-gel process. Moreover, the nitric acid is efficiently substituted by the citric acid to catalyze the sol-gel reactions without alteration of the bioactivity of the 45S5 bioactive glass.

Electrophoretic Deposition of Bioactive Glass Coatings on Ti12Mo5Ta Alloy

Titanium alloys used in orthopedic surgery are usually coated with hydroxyapatite to improve their biocompatibility and osseointegration. Bioactive glasses (BGs) are an interesting alternative to hydroxyapatite for the production of prosthetic coatings due to their osteoproductive property (Class A bioactivity) and to their resorbability. However the classical techniques used to obtain prosthetic coatings are not suitable in the case of BGs. In this study bioactive glass coatings are obtained by electrophoretic deposition on a Ti12Mo5Ta alloy. These coatings were obtained from ethanol suspensions of two different bioglass powders: a Sol-Gel derived 58S and a Melting-Quenching derived 46S. Scanning electron microscopy observations were used to characterize the coatings (morphology and thickness) and the coating/substrate interfaces. The chemical composition of the coatings was studied by X-ray microanalysis and X-ray maps were performed to characterize the spatial distributions of all elements composing the coatings.

Chitosan effects on glass matrices evaluated by biomaterial. MAS-NMR and biological investigations

Bioactive glass 46S6 and biodegradable therapeutic polymer (Chitosan: CH) have been elaborated to form 46S6-CH composite by freeze-drying process. The kinetics of chemical reactivity and bioactivity at the surface were investigated by using physicochemical techniques, particularly solid-state MAS-NMR. Immortalized cell line used to construct multicellular spheroids was employed as three-dimensional (3D) cell cultures for in vitro studies. Obtained results showed a novel structure of the composite; the chemical treatment (ultrasound, magnetic stirring, freeze drying process and lyophilization) led the bioactive glass particles to be loaded in the chitosan-based materials. 29Si and 31P MAS-NMR results showed the emergence of two new species, QSi3(OH) and QSi4, which are characteristic of the vitreous network dissolution in simulated body fluid (SBF). MAS-NMR also confirmed the formation of amorphous calcium phosphate (ACP) at the surface of the initial 46S6-CH. Three-dimensional (3D) cell cultures highlighted the effect of chitosan, where the cell viability reached up to 78% in 46S6-CH composite and up to 67% in 46S6. The association of (CH) and bioactive glass (BG) matrix promotes a highly significant bioactivity, demonstrating surface bone formation and satisfactory behavior in biological environment.

Microstructural characterization of Ti-6Al-4V alloy subjected to the duplex SMAT/plasma nitriding.

In this study, microstructural characterization of Ti‐6Al‐4V alloy, subjected to the duplex surface mechanical attrition treatment (SMAT)/nitriding treatment, leading to improve its mechanical properties, was carried out through novel and original samples preparation methods. Instead of acid etching which is limited for morphological characterization by scanning electron microscopy (SEM), an original ion polishing method was developed. Moreover, for structural characterization by transmission electron microscopy (TEM), an ion milling method based with the use of two ions guns was also carried out for cross‐section preparation. To demonstrate the efficiency of the two developed methods, morphological investigations were done by traditional SEM and field emission gun SEM. This was followed by structural investigations through selected area electron diffraction (SAED) coupled with TEM and X‐ray diffraction techniques. The results demonstrated that ionic polishing allowed to reveal a variation of the microstructure according to the surface treatment that could not be observed by acid etching preparation. TEM associated to SAED and X‐ray diffraction provided information regarding the nanostructure compositional changes induced by the duplex SMAT/nitriding process. Microsc. Res. Tech. 76:897–903, 2013.

Electrophoretic Deposition of Hydroxyapatite and 58S Bioactive Glass Coatings on the Ti6Al4V Alloy Subjected to Surface Mechanical Attrition Treatment

Hydroxyapatite (HAP) and 58S Bioactive Glasses (BG) coatings are successfully synthesized by Electrophoretic Deposition (EPD) on Ti6Al4V alloy subjected to Surface Mechanical Attrition Treatment (SMAT). This process uses steel balls impacts on the Ti6Al4V surface to improve its mechanical properties. However when the Ti6Al4V substrate is treated by SMAT the industrial plasma spray technique is not efficient to obtain adherent HAP coatings. This problem is mainly related to the modifications of the Ti6Al4V surface topography due to the SMAT process. Therefore, in this work we demonstrate that EPD offers an efficient solution to solve this technical problem. Indeed we obtain a homogeneous and adherent HAP coating on the SMATed Ti6Al4V surface from a suspension of nanoparticles in ethanol. Moreover EPD is successfully employed to produce a 58S BG coating on the SMATed Ti6Al4V surface. Scanning Electron Microscopy (SEM) associated to Energy Dispersive X-Ray Spectroscopy (EDXS) reveals that the coatings obtained by EPD are adherent and compact without alteration of their chemical composition.

Influence of the surface mechanical attrition treatment (SMAT) on the corrosion behavior of Co28Cr6Mo alloy in Ringer’s solution

The low carbon Co28Cr6Mo alloy used for artificial joints like hip and knee prostheses is subjected to a surface treatment called SMAT (surface mechanical attrition treatment). The purpose of this treatment is to modify the surface mechanical properties of the treated alloy. Since the SMAT impacts the surface of materials, its influence on the corrosion behavior of the CoCrMo alloy has to be assessed in a physiological solution as Ringer’s solution. Furthermore, a specific biomedical polishing is coupled with the SMAT in order to finalize the production of a hip prosthesis ready for use. The corresponding corrosion behavior is also studied. The corrosion behavior of CoCrMo alloy samples is investigated using electrochemical techniques (potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)) in physiological liquid and simulated by an equivalent circuit. The polarization results show the reduction of the corrosion current density and the increase of the corrosion potential after the SMAT. The EIS analyses also show the benefit of the SMAT on the corrosion resistance of the CoCrMo alloy. The surface morphology modification and the phase’s transformation induced by the SMAT are evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Structural Analysis of Prosthetic Coatings Elaborated by Electrochemical Deposition

In this study, phosphocalcic coatings on titanium alloy Ti6Al4V substrate are elaborated using Electrodeposition (ELD) by adding optimized amount of hydrogen peroxide H2O2 into the electrolyte. Structural analysis is performed by X Rays Diffraction and the data are treated using the RIETVELD method. The characterization of the coatings elaborated by ELD showed that the H2O2 amount variation has an influence on the morphology, the crystal size and the chemical composition (monophasic or biphasic) of the coatings.