Mihaela Dinu

Metallurgical Characterization of some Magnesium Alloys for Medical Applications

The magnesium alloys has been intensively studied for their suitable mechanical properties, excellent biocompatibility and their ability to biodegrade in biological environments. Although magnesium biodegradable implants possess many desirable properties, it is important that the alloy is able to be tolerated by the body- the constitutional elements of magnesium-based alloys should be toxic free. In this study two binary magnesium alloys Mg-Ca0,8 and Mg-Ca1,8 were experimentally obtained by casting and was characterized in order to investigate the microstructure, mechanical properties and how alloying elements influenced the characteristics of this new alloys potentially used for orthopedic implants.

In Vitro Biocompatibility of Si Alloyed Multi-Principal Element Carbide Coatings.

In the current study, we have examined the possibility to improve the biocompatibility of the (TiZrNbTaHf)C through replacement of either Ti or Ta by Si. The coatings were deposited on Si and 316L stainless steel substrates by magnetron sputtering in an Ar+CH4 mixed atmosphere and were examined for elemental composition, chemical bonds, surface topography, surface electrical charge and biocompatible characteristics. The net surface charge was evaluated at nano and macroscopic scale by measuring the electrical potential and work function, respectively. The biocompatible tests comprised determination of cell viability and cell attachment to the coated surface. The deposited coatings had C/(metal+Si) ratios close to unity, while a mixture of metallic carbide, free-carbon and oxidized species formed on the film surface. The coatings’ surfaces were smooth and no influence of surface roughness on electrical charge or biocompatibility was found. The biocompatible characteristics correlated well with the electrical potential/work function, suggesting a significant role of surface charge in improving biocompatibility, particularly cell attachment to coatings surface. Replacement of either Ti or Ta by Si in the (TiZrNbTaHf)C coating led to an enhanced surface electrical charge, as well as to superior biocompatible properties, with best results for the (TiZrNbSiHf)C coating.

Clinical, Biomechanical and Biomaterials Approach in the Case of Fracture Repair Using Different Systems Type Plate-Screw

Many researchers perform different research in the area of ostheosznthesis metallic implants used in orthopedic surgery. The main goal of internal fixation is to achieve full operation until patient recovery. Although implants are intended to withstand until bone consolidation in some cases problems occur due to accelerate wear and corrosion processes. The aim of the present study was to determine the causes leading to adverse reactions of the surrounding tissues in case of three implants for osteosynthesis type plate-screw.

Failure Analysis of some Retrieved Orthopedic Implants Based on Materials Characterization

The aim of this paper is to determine causes of failure of orthopedic implants like intramedullary nail based on explants analysis and materials characterization. The clinical performance, corrosion characteristics and metallurgical properties of some retrieved titanium femoral nails have been examined. The macroscopic and the microscopic investigation of explants help us to describe the breaking mechanism and to identify the potential causes that led to implant failure.

Influence of the electrolyte’s pH on the properties of electrochemically deposited hydroxyapatite coating on additively manufactured Ti64 alloy

Properties of the hydroxyapatite obtained by electrochemical assisted deposition (ED) are dependent on several factors including deposition temperature, electrolyte pH and concentrations, applied potential. All of these factors directly influence the morphology, stoichiometry, crystallinity, electrochemical behaviour, and particularly the coating thickness. Coating structure together with surface micro- and nano-scale topography significantly influence early stages of the implant bio-integration. The aim of this study is to analyse the effect of pH modification on the morphology, corrosion behaviour and in vitro bioactivity and in vivo biocompatibility of hydroxyapatite prepared by ED on the additively manufactured Ti64 samples. The coatings prepared in the electrolytes with pH = 6 have predominantly needle like morphology with the dimensions in the nanometric scale (~30 nm). Samples coated at pH = 6 demonstrated higher protection efficiency against the corrosive attack as compared to the ones coated at pH = 5 (~93% against 89%). The in vitro bioactivity results indicated that both coatings have a greater capacity of biomineralization, compared to the uncoated Ti64. Somehow, the coating deposited at pH = 6 exhibited good corrosion behaviour and high biomineralization ability. In vivo subcutaneous implantation of the coated samples into the white rats for up to 21 days with following histological studies showed no serious inflammatory process.

Influence of Thermal Treatment on the Roughness, Corrosion Resistance and Wettability of Hydroxyapatite Films Deposited by RF Magnetron Sputtering

In this paper we report on the preparation and characterization of hydroxyapatite coatings deposited on Ti6Al4V alloy by magnetron sputtering deposition method. The amorphous deposited coatings were thermal annealed in a flux of dry nitrogen and water vapours at 800 °C for 30 and 120 minutes, in order to investigate the effect of this treatment on surface roughness, corrosion resistance and wettability. The films were characterized by surface profilometry, electrochemical tests and contact angle measurements. After annealing, the hydroxyapatite coatings became crystalline, exhibiting rougher surfaces, higher corrosion resistance and lower contact angles. We have demonstrated that the hydroxyapatite coating annealed at 800°C for 30 minutes represents a good candidate to be used for medical implants, due to its superior corrosion behaviour and good wettability.

Corrosion Behavior of TiSiN Coatings Deposited on Ni-Cr Alloy in Artificial Saliva with and without Fluoride

TiSiN thin films were deposited on NiCr dental alloy in order to enhance the corrosion resistance in artificial saliva with and without fluoride content. The TiSiN films were prepared using reactive cathodic arc method at two different substrate bias voltages (-50 V and-200 V). For the corrosion evaluation, artificial saliva with pH=5.2 was chosen, because this is a critical value for mineral dissolution of dental tissue which can affect the dental alloys. A content of 0.1 % NaF was added to the artificial saliva to simulate the effect of fluoride based hygiene products. The TiSiN coated NiCr alloys exhibited a higher corrosion resistance than the NiCr substrate, irrespective of the testing environment. The best corrosion resistance was found for the TiSiN deposited at-200 V.

TiSiN coatings for improved bond strength of CoCr alloy to dental ceramic

In this work, TiSiN coatings were selected to improve the adhesion between dental ceramic and CoCr substrate. The coatings were prepared by the cathodic arc technique in N2 reactive atmosphere, at different bias voltages, and analyzed for elemental composition, surface roughness, wettability and corrosion resistance in Fusayama Meyer artificial saliva. After the coating deposition, low-fusing dental ceramic film was fired on coated alloy, using a dental furnace. The bond strength of these specimens was tested using a 3-point bending test.