Meinhard Kuntz

On the kinetics and impact of tetragonal to monoclinic transformation in an alumina/zirconia composite for arthroplasty applications

Latest trends in load-bearing materials for arthroplastic applications involve the development of highly fracture resistant alumina/zirconia composites, as an alternative choice to alumina and zirconia monolithic ceramics. Composite materials are designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo, whose shadow yet hampers the full exploitation of ceramic materials in the field of arthroplasty. The aim of this paper is to evaluate the resistance to environmental degradation in an alumina/zirconia composite (Biolox Delta), which represents a primary candidate for hip and knee joint applications. Our approach consists first in the experimental determination of an activation energy value for environmentally driven tetragonal to monoclinic (t-m, henceforth) polymorphic transformation in the zirconia phase of the material; then, based on such an experimental value, a prediction is given for the long-term in vivo environmental resistance of prostheses made of the composite material. The present evaluation clarifies the in vivo performance of this new composite for orthopedic applications.

Evaluation of interface parameters in push-out and pull-out tests

Abstract Push-out and pull-out tests with single-fibre model composites are performed to evaluate the frictional parameters of the interface. Analysis of the experimental data according to models based on the assumption of an ideal cylindrically shaped fibre does not satisfy all observed phenomena. Thus, a model is proposed to include the effects of roughness interaction during fibre sliding. The predictions of the model fit the experimental results very well.

Selective etching of injection molded zirconia-toughened alumina: Towards osseointegrated and antibacterial ceramic implants

Due to their outstanding mechanical properties and excellent biocompatibility, zirconia-toughened alumina (ZTA) ceramics have become the gold standard in orthopedics for the fabrication of ceramic bearing components over the last decade. However, ZTA is bioinert, which hampers its implantation in direct contact with bone. Furthermore, periprosthetic joint infections are now the leading cause of failure for joint arthroplasty prostheses. To address both issues, an improved surface design is required: a controlled micro- and nano-roughness can promote osseointegration and limit bacterial adhesion whereas surface porosity allows loading and delivery of antibacterial compounds. In this work, we developed an integrated strategy aiming to provide both osseointegrative and antibacterial properties to ZTA surfaces. The micro-topography was controlled by injection molding. Meanwhile a novel process involving the selective dissolution of zirconia (selective etching) was used to produce nano-roughness and interconnected nanoporosity. Potential utilization of the porosity for loading and delivery of antibiotic molecules was demonstrated, and the impact of selective etching on mechanical properties and hydrothermal stability was shown to be limited. The combination of injection molding and selective etching thus appears promising for fabricating a new generation of ZTA components implantable in direct contact with bone. STATEMENT OF SIGNIFICANCE Zirconia-toughened alumina (ZTA) is the current gold standard for the fabrication of orthopedic ceramic components. In the present work, we propose an innovative strategy to provide both osseointegrative and antibacterial properties to ZTA surfaces: we demonstrate that injection molding allows a flexible design of surface micro-topography and can be combined with selective etching, a novel process that induces nano-roughness and surface interconnected porosity without the need for coating, avoiding reliability issues. These surface modifications have the potential to improve osseointegration. Furthermore, our results show that the porosity can be used for drug delivery and suggest that the etched surface could reduce bacterial adhesion.