[Show abstract][Hide abstract] ABSTRACT: A strategy used to reduce wear of the ultra high molecular weight polyethylene (UHMWPE) component of orthopedic joint implants has been to coat the metallic part with a hard ceramic layer. The advantage of this procedure is to reduce both wear and ion release of the metal while keeping a high mechanical resistance. In the present study, the performance of three titanium nitride coatings: TiN, TiNbN, and TiCN for biomedical applications was assessed in terms of their surface properties and cytotoxicity. The morphology, chemical composition, and wettability were determined through atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and contact angle measurement, respectively. The tribological behaviour of the coatings rubbing against UHMWPE in lubricated conditions was investigated using a pin-on-disk apparatus. Albumin adsorption on the three coatings was studied with a quartz crystal microbalance with dissipation (QCM-D) and AFM scratching. Cytotoxicity was determined both in direct or indirect contact of the cells with the coating materials. The results demonstrate that the three coatings have similar surface properties and are not cytotoxic. TiNbN seems to have the best tribological performance in the presence of albumin, although albumin adsorption is slightly higher on TiN.
[Show abstract][Hide abstract] ABSTRACT: The effect of roughness on the tribological behavior of the prosthetic pair ultra high molecular weight polyethylene (UHMWPE)/TiN coated stainless steel was investigated. Standard and polished TiN coated stainless steel pins were tested against either standard or smooth UHMWPE disks. Hanks' Balanced Salt Solution (HBSS) and bovine serum albumin (BSA) solution in HBSS were used as lubricants. Friction and wear were determined using a pin-on-disk apparatus and the wear mechanisms were investigated through optical microscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the decrease in the roughness led to a reduction of the friction coefficient and of the wear rate of UHMWPE. However, the most important effect was achieved through the decrease in the roughness of the hard TiN counterface while keeping the standard UHMWPE surface. If BSA was added to HBSS, a strong decrease of both the friction coefficient and the polymeric wear was observed independently of the roughness of both the TiN and the polyethylene surfaces. Abrasive and fatigue wear mechanisms are proposed to interpret the experimental results.
Journal of Biomedical Materials Research Part B Applied Biomaterials 01/2008; 84(1):98-107. DOI:10.1002/jbm.b.30849 · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work consists of a preliminary evaluation of the performance of TiN, TiNbN and TiCN thin coatings to improve the tribological behaviour of stainless steel (SS) metal-on-metal prostheses. Coatings of TiN, TiNbN and TiCN, with a thickness between 2 and 5 μm, were applied by physical vapour deposition (PVD) on AISI 316L stainless steel substrates. The hardness of TiNbN and TiCN is similar and considerably higher than that of TiN which, in turn, is much higher than that of the SS. Topographical analysis, carried out by atomic force microscopy (AFM), showed that PVD leads to the formation of very smooth coatings, with their average roughness (Ra) between 37 and 44 nm. Ball-on-disk short-term tests were done using Hanks’ balanced salt solution as lubricant. When both rubbing surfaces were coated, the best results were obtained with TiCN and TiN coatings. Tests of the bare SS balls against the coated disks indicated TiN as the most efficient coating. The worn surfaces were observed by scanning electron microscopy (SEM), which enabled for the identification of the wear mechanisms operating in each tribological pair.
[Show abstract][Hide abstract] ABSTRACT: The tribological behaviour of the prosthetic pair TiN coated stainless steel/ultra high molecular weight polyethylene (UHMWPE) may be improved by chlorine-implantation of the TiN surface. Friction and wear were determined using a pin-on-disk apparatus and the wear mechanisms were investigated through scanning electron microscopy (SEM) and atomic force microscopy (AFM). Rutherford backscattering spectrometry (RBS) was used to determine the chlorine distribution profiles in the chlorine-implanted TiN coatings before and after the tribological experiments, while X-ray photoelectron spectroscopy (XPS) was used to characterize chemically the same samples. Chlorine-implantation led to a significant polymeric wear reduction when the lubricant was Hanks’ balanced salt solution (HBSS). If bovine serum albumin (BSA) was added to HBSS, a strong decrease of both friction and polymeric wear was observed for implanted and non-implanted TiN coatings. The former case was explained by the formation of a titanium oxide layer on the TiN surface, while the latter derived from albumin adsorption.
[Show abstract][Hide abstract] ABSTRACT: The influence of sterilization with γ-irradiation in the properties of plasma sprayed hydroxyapatite (HAp) coatings used for medical implants is investigated in this work. HAp coatings were applied on titanium alloy substrates by plasma spraying and then submitted to 1 and 10 cycles of sterilization with y-irradiation. As-applied HAp coatings were used as control samples. Afterwards, the modifications on the samples, induced by the irradiation process, were evaluated by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Water contact angle measurements as well as adhesion tests were also carried out in order to evaluate the influence of the irradiation process on the wettability and mechanical behaviour of the HAp coatings. No microstructural modifications were detected by X-ray diffraction after sterilization. However, the results show that sterilization with γ-irradiation originates modifications of the surface of HAp, as detected by a change of color of the coatings and by the XPS analysis. Nevertheless, these modifications do not result in significant changes in the wettability and mechanical behaviour of the HAp coatings.
Materials Science Forum 01/2006; 514–516(2):1054-1058. DOI:10.4028/www.scientific.net/MSF.514-516.1054