Protective hard coatings are appealing for several technological applications like solar cells, organic electronics, fuel cells, cutting tools and even for orthopaedic implants and prosthetic devices. At present for what concerns the application to prosthetic components, the coating of the surface of the metallic part with low-friction and low-wear materials has been proposed [1]. Concerning the use of ceramic materials in joint arthroplasty, zirconia-toughned-alumina (ZTA) reported high strength, fracture toughness, elasticity, hardness, and wear resistance [2]. The main goal of this study was to directly deposit ZTA coating by using a novel sputter-based electron deposition technique, namely Pulsed Plasma Deposition (PPD) [3]. The realized coatings have been preliminary characterized from the point of view of morphology, wettability, adhesion and friction coefficients. ZTA coatings were deposited by PPD technique, which is able to maintain the stoichiometry of the starting target. In this case we started from a cylindrical ZTA target (30 mm diameter × 5 mm thickness, 75% alumina / 25% zirconia). The morphology, micro-structure and chemistry of deposited coatings were characterized by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectrosopy (EDS) and Atomic Force Microcscope (AFM). Coating-substrate interface quality were investigated by microscratch tests. The degree of wetting was estimated by measuring the contact angle between a drop of 1 ml of ultrapure water and the surface of the sample. Preliminary ball-on-disk tribological tests were carried out in air and deionized water coupling ZTA-coated stainless steel ball (AISI 420, 3 mm radius, grade 200) against medical grade UHMWPE to evaluate the friction of the proposed coupling.Introduction
Materials and methods
Wear of the ultra-high molecular weight polyethylene (UHMWPE) insert is one of the major issue related to orthopaedic implants. In this study, the tribo-mechanical properties of zirconia-coated UHMWPE deposited by means of Pulsed Plasma Deposition (PPD) technique were analyzed. Specifically, strength to local plastic deformation, indentation work portioning and creep behavior were evaluated through nanoindentation and micro-scratch tests, whereas preliminary wear data were obtained by tribology tests. A strong reduction of plastic deformation and a drop of the creep phenomenon for the zirconia-coated UHMWPE were evidenced, whereas - in spite of similar wear data - different wear mechanism was also detected. This study supported the use of hard ceramic thin films to enhance the mechanical performance of the plastic inserts used in orthopaedics.
When osteoarthritis occurs, joint replacement is the most frequent treatment. Currently, the mean survival rate for total joint arthroplasty is ∼90% after 10 years: the main reason for long-term implant failure, that generally required a revision surgery, are osteolysis and aseptic loosening of the implant, which are strongly correlated with wear debris formation from the UHMWPE insert [Ingham, 2005], as a consequence of the cyclic loading against the metallic or ceramic counterface [Dumbleton, 2002]. Wear debris bring to chronic inflammation of periprosthetic tissues causing an increase of bone reabsorption that finally provoke aseptic loosening, so implant failure[Holt, 2007]. Different solutions were proposed to reduce wear debris production but agreement has not been achieved yet. Our challenging approach prefigures the direct coating of the plastic component with a hard and well-adherent ceramic film, in order to drastically reduce wear debris formation from the plastic substrate while preserving its well-established bulk mechanical properties, especially under high local loads [Bianchi, 2013]. 3%yttria-stabilized zirconia films were deposited by PPD technique. PPD is a new vapour deposition technique based on the ablation of a target material as a consequence of the impact of a high-energy electron beam. The plasma plume of ablated material is directed toward and deposited onto the substrate. Films were characterized by SEM-EDX, X-ray diffraction, nanoindentation, adhesion and tribological tests. Moreover, capability of ZrO2–UHMWPE system of carrying local loads – i.e. an estimation of the resistance to a third-body abrasion – was investigated.Introduction
Methods
