Roberto Hübler

Wear and corrosion protection of 316-L femoral implants by deposition of thin films

The wear and corrosion attack on mobile components of surgical implants, like femoral prosthesis, are one of the responsible of its short lifetime. Ceramic thin films like TiN, ZrN, NbN, VN and HfN are commonly used as protective coatings because they possess high hardness, electrochemical immunity and biocompatibility. Thin films of transition metals nitrides and multilayers of Ti/TiN and Cr/V were deposited on 316-L stainless steel and silicon using reactive magnetron sputtering. The coatings were characterized with respect to microhardness using an ultra micro hardness tester Fisher HV100P and with respect to the abrasive wear resistance using a mechanical simulator for hip prosthesis developed in our laboratory. The abraded surfaces were investigated with scanning electron microscopy as function of the number of cycles in the simulator (steps). The corrosion resistance of the coated 316 L stainless steel has been carried out in a potentiodynamic polarization in an aqueous solution environment. Elemental composition has been obtained by Rutherford backscattering (RBS), energy dispersive spectroscopy (EDS) and X-ray fluorescence analysis (XRF) and the crystal phases structure has been studied with X-ray diffraction (XRD). The better compromise among stoichiometry, microstructure, wear resistance, hardness and corrosion protection indicate that a multilayer containing transition metal nitrides (Ti/TiN) are a serious candidate to be applied as protective layer on femoral implants.

Plasma and ion-beam-assisted deposition of multilayers for tribological and corrosion protection

Abstract Multilayers of Ti/TiN and Al/AlN were deposited on steel and silicon by magnetron sputtering and ion-beam-assisted deposition. Compositions and film thicknesses were determined by Rutherford backscattering. Hardness was measured with a dynamic ultramicrohardness tester. The corrosion protection potential in an aqueous environment was evaluated by electrochemical techniques. The results are discussed in terms of the structure and composition of the multilayer arrangement. It turns out that the multilayer coatings generally show a better corrosion protection performance than both the pure metal and the pure nitride films, with an optimum ratio of nitride film thickness to metal film thickness for a maximum corrosion protection effect. The hardness values are in between that of nitride single film and those of metal single films. Deposition of multilayers with the possibility of selecting the thickness ratio of metal to nitride film for particular mechanical and chemical requirements allows a controlled adaption of the film features to a given application problem.

Hardness and corrosion protection enhancement behaviour of surgical implant surfaces treated with ceramic thin films

Abstract Covalent thin films like TiN and other hard coatings are widely used for tribological and corrosion protection of surfaces. The use of tools covered in thin films in mechanical and chemical industries have increased strongly in the past few years. However, this surface treatment is not commercially applied to surgical implants such as a femoral prosthesis, which is submitted to strong wear and corrosion attack. Ti–6Al–4V ELI alloy together with stainless steel are still the main materials used for medical applications because of their corrosion resistance and biocompatibility. To improve the poor surface hardness and wear resistance of these implants, titanium nitride and (Ti–6Al–4V)N thin films were deposited on the mobile surface. To obtain a good coating–surface adhesion, the protective films were deposited using magnetron sputtering equipment and all samples were cleaned by means of plasma etching in an argon–nitrogen atmosphere. The layers produced have been characterised in terms of phase formation by X-ray diffraction, the composition and depth profile were studied by means of Rutherford backscattering, X-ray photon spectroscopy and energy dispersive spectroscopy (EDS), the hardness was checked using a nano-hardness tester and corrosion protection enhancement was tested using cyclic voltammetry equipment.

The dependence of hardness and corrosion protection power of ion- beam-assisted deposition TiN coatings on the ion beam impact angle

Abstract Hard coatings such as titanium nitride are often porous and therefore not necessarily very corrosion resistant. Possibilities for reducing the film porosity are densification and multilayer structures. These methods are studied in our laboratories at present. Ion-beam-assisted deposition (IBAD) TiN films were deposited changing the angle between the substrate normal and the ion beam incidence direction. The films were characterized by transmission electron microscopy, scanning electron microscopy and X-ray diffraction analyses, the hardness was determined by means of a dynamic Vickers hardness tester and the corrosion behaviour was evaluated using current-potential measurements in a multicycle voltammogram mode. The results are strongly dependent on the changes in the crystal orientation induced by the ion flux under different angles. Careful optimization may lead to coatings with high hardness and excellent corrosion protection potential. These results are compared with Ti/TiN multilayers deposited by IBAD and magnetron sputtering and with a sputtered TiN single layer.

Effect of bismuth oxide on white mineral trioxide aggregate: chemical characterization and physical properties

AIM To assess the effect of bismuth oxide (Bi2 O3 ) on the chemical characterization and physical properties of White mineral trioxide aggregate (MTA) Angelus. METHODOLOGY Commercially available White MTA Angelus and White MTA Angelus without Bi2 O3 provided by the manufacturer especially for this study were subjected to the following tests: Rietveld X-ray diffraction analysis (XRD), energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), compressive strength, Vickers microhardness test and setting time. Chemical analysis data were reported descriptively, and physical properties were expressed as means and standard deviations. Data were analysed using Students t-test and Mann-Whitney U test (P = 0.05). RESULTS Calcium silicate peaks were reduced in the diffractograms of both hydrated materials. Bismuth particles were found on the surface of White MTA Angelus, and a greater amount of particles characterized as calcium hydroxide was observed by visual examination on White MTA without Bi2 O3 . The material without Bi2 O3 had the shortest final setting time (38.33 min, P = 0.002), the highest Vickers microhardness mean value (72.35 MPa, P = 0.000) and similar compressive strength results (P = 0.329) when compared with the commercially available White MTA Angelus containing Bi2 O3 . CONCLUSION The lack of Bi2 O3 was associated with an increase in Vickers microhardness, a reduction in final setting time, absence of Bi2 O3 peaks in diffractograms, as well as a large amount of calcium and a morphology characteristic of calcium hydroxide in EDX/SEM analysis.

Low-Level Laser Therapy for Implants Without Initial Stability

OBJECTIVE This study evaluated the effect of low-level infrared laser on removal torque values of implants with poor initial stability inserted in rabbit tibias. BACKGROUND DATA It is important to analyze the effects of laser radiation on bone repair when low-quality bone and implants with poor initial stability are used. MATERIALS AND METHODS Thirty male white New Zealand rabbits (Oryctolagus Cuniculus) about 2 mo old and weighing 1.5-2.0 kg were used. Machined implants with poor initial stability were inserted in the tibia of each animal. Animals were randomly divided into two groups: laser irradiated and laser nonirradiated. Each group was further divided into three subgroups, according to the day the animals were killed: 15, 30, or 45 d. Torque values were measured with an axial digital torquemeter that applied counter-torque. The Students t-test was used to calculate means and standard deviations for the comparisons between laser and control groups. RESULTS A significant increase (p = 0.050) in removal torque values was found in the group of laser-irradiated implants at 15 and 30 d when compared with the control groups. At 45 d, no significant differences were found. CONCLUSION In this study, low-level laser therapy promoted the osseointegration of implants with poor initial stability, particularly in the initial stages of bone healing.

Characterisation of gradient interfaces in thin film multilayers used to protect orthopaedic implants

Abstract Titanium–titanium nitride multilayers were firstly used to enhance the corrosion protection and mechanical properties of coatings and, for this reason, they are good candidates for protective coatings for orthopaedic implants. These properties are strongly dependent on the thin film deposition method and on the shape of the interface between the titanium and the titanium nitride layers. In this work we use a set of multilayers with a titanium to titanium nitride thickness ratio in the range from 0.25 to 4. The films were deposited by magnetron sputtering and ion beam assisted deposition, and the deposition parameters were changed to obtain an interface in gradient (or not as the case may be). The film composition, the periodic structure of the multilayers and the interface type were characterised by means of Rutherford backscattering, nuclear reaction analysis and cross sectional transmission electron microscopy and the crystal phases and textures were studied with X-ray diffraction. To compare the coatings, the corrosion protection power, obtained by means of cyclic voltammetry, and the coating micro-hardness measured with a Vickers indentor, were used.

Transition metal nitrides thin films deposition using a dynamically controlled magnetron sputtering apparatus

Transition metal nitrides thin films are normally used as coatings to protect mechanical tools, e.g., bits and drills, to provide biocompatibility for common materials like steel and as decorative layers. Among these nitrides, TiN is the most usual coating deposited as a single film or multilayered with other materials deposited preferentially by magnetron sputtering. The film properties such as adhesion, intrinsic stress and hardness can be controlled and improved by means of a bias potential applied to the substrates. The problem of stoichiometry oscillation during the deposition process was resolved using the dynamic partial pressure control to maintain the argon to nitrogen ratio and the working pressure constant by means of a computer controlled interface. In this work the argon to nitrogen ratio was changed in order to obtain one stoichiometric nitride for the transition metals of group IV and group V. Film characterization was performed using Rutherford backscattering, nuclear reaction analysis and energy dispersive spectroscopy for elemental composition and stoichiometry; X-ray diffraction to study the crystal phase formation and scanning electron microscopy to determine the thin film thickness and microstructure. The corrosion protection ability and microhardness of the samples are also presented in view of the applicability potential of the coatings. The results shows that formation mechanisms of the studied nitrides are similar showing an optimal argon to nitrogen pressure ratio to obtain the stoichiometric phase.

Microhardness characterization of superlattices formed by reactive magnetron sputtering and ion beam assisted deposition

Abstract At present, the development of indentation techniques permits to perform measurements of hardness and other mechanical properties of a material with good accuracy, reproducibility and at a relatively low cost. Nevertheless, since the mechanical contact between indenter and material at low loads is very complex, it is difficult to attribute a hardness value to a film. Several models have been created to solve this problem and are currently in use. The use of particular deposition techniques permits the formation of multilayered coatings with a few nanometers thickness periodicity, which are namely superlattices and are characterized by extremely high hardness. The aim of this paper is to characterize multilayer coatings using the most important nano and microhardness models. The coatings were deposited by reactive magnetron sputtering and ion beam assisted deposition and consists of Cr/V and Ti/TiN layers. The layer periodicity, superlattices wavelengths and elemental characterization were studied by means of grazing angle X-ray diffraction and Rutherford backscattering spectroscopy. The microhardness tests were performed using a computer controlled dynamic load–unload process. The hardness values are either corrected for the indentation size effect or following Oliver–Pharr model. The results show an increase of the hardness values, confirming the development of a superlattice successfully formed by a magnetron sputtering system. The nano and microhardness models show differences in the hardness values obtained, probably due to the difficulty to estimate the real indented area.

Osseointegration of atmospheric plasma‐sprayed titanium implants: Influence of the native oxide layer

The aim of this study was to evaluate in vivo the influence of the native oxide layer on osseointegration and new bone formation on the surface of atmospheric plasma-sprayed porous titanium coatings. Porous titanium coatings were deposited on all implant surfaces, and half of the samples were subsequently submitted to oxide layer removal treatment. Samples were implanted onto the cortical bone of sheep (tibia) and evaluated at 30 and 60 days. Implants were removed en bloc and the attachment of bone to implants was examined by tensile pull-out test (osseointegration assessment), light microscopy, scanning electron microscopy (histological analysis), and instrumented hardness tests (mechanical properties of mature and newly formed bone tissue). Coatings submitted to oxide layer treatment presented higher osseointegration values at both healing periods and showed more mature and mineralized bone tissue when compared with nontreated coatings. Our findings showed that the use of acid-etching in association with atmospheric plasma spraying techniques improves osseointegration of titanium implants.