Protective hard coatings are appealing for several technological applications and even for orthopaedic implants and prosthetic devices. For what concerns the application to prosthetic components, coating of the surface of the metallic part with low-friction and low-wear materials has been proposed [1, 2]; at the same time, concerning use of ceramic materials in joint arthroplasty, zirconia-toughned-alumina (ZTA) ceramic material has shown high strength, fracture toughness, elasticity, hardness, and wear resistance [3, 4]. The purpose of this study was to directly deposit ZTA coatings by using a novel sputter-based electron deposition technique, namely Pulsed Plasma Deposition (PPD) [5]. Preliminary characterization of realized coatings from the point of view of morphology, wettability, adhesion and friction coefficients was performed. PPD technique was used to deposit ZTA coatings; this technique is able to maintain the stoichiometry of the starting target. In this study we started from a cylindrical ZTA target (30 mm diameter × 5 mm thickness, 75% alumina / 25% zirconia) and followed the procedure described by Bianchi et al [5]. Characterization of morphology, micro-structure and chemistry of deposited coatings was performed by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) and Atomic Force Microscope (AFM). Coating-substrate interface quality were investigated by micro-scratch tests. Measurement of the contact angle between a drop of 1 ml of ultrapure water and the surface of the sample was performed to estimate the degree of wetting. A ZTA-coated stainless steel ball (AISI 420, 3 mm radius) was coupled against medical grade UHMWPE to evaluate the friction of the proposed coupling in preliminary ball-on-disk tribological tests.Introduction
Materials and methods
Total joint arthroplasty is frequently necessary when a traumatic or degenerative disease leads to develop osteoarthritis (OA). Nowadays, the main reason for long term prosthesis failure is due to osteolysys and aseptic loosening of the implant itself, that are related to UHMWPE wear debris [1–3]. Different solutions to overcome this issue have been proposed, including different couplings like metal-on-metal and ceramic-on-ceramic. Our hypothesis was that a hard ceramic thin film realized on the plastic component (i.e. UHMWPE) could improve the friction and wear performance in a prosthetic coupling. The purpose of the presented study was therefore to characterize from the point of view of structure and mechanical performance of this ceramic-coated plastic component. The thin films were specifically realized by means of the novel Pulsed Plasma Deposition (PPD) technique [4]. PPD technique was used to deposit Yttria-stabilized zirconia (YSZ at 3%) films on medical-grade UHMWPE substrates [4]. The morphology and micro-structure were characterized by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). By means of nanoindentation and scratch tests mechanical properties were investigated. Ball-on-disk tribological tests were carried out in air, deionized water and physiological solution against alumina balls (6 mm diameter, grade 200) used as counterpart; friction evaluation of the proposed approach and the corresponding worn track were analyzed by SEM-EDS.Introduction
Materials and methods
