Investigation of the geometries and surface topographies of UHMWPE wear particles

• 3D images of the wear particles were captured using the AFM technique.
• Particle classification was achieved using objective mathematical algorithms.
• Particle topographic features were analysed by numerical analysis techniques.
• Four groups of wear particles had distinct geometrical and topographical properties.

Investigation of the topographical features on the surface of wear particles is important as the surface textures of ultrahigh molecular weight polyethylene (UHMWPE) wear particles potentially impact the biocompatibility of an implanted prosthesis. In this study, atomic force microscopy (AFM) was used to examine the geometry and surface topographies of UHMWPE wear particles at a nanometre-scale. The wear particles were categorised into four distinct groups based on their geometrical features and via the use of objective mathematical algorithms. The four groups were defined as granular, fibrous, platelet and flake-like particles. The particles in each category also had distinct topographical properties. Granular particles were comprised of a large number of valley structures and had a smooth surface. The Sa value of most granule particles fell into a range of 10–20 nm. Fibrous particles had a surface dominated by a peak structure, while the surface of platelet particles had a valley structure. Despite this difference, approximately half of both the fibrous and platelet particles had a similar Sa value, in a range of 20–40 nm. Flake-like particles had a rough surface and Sa value of 80% of them were larger than 70 nm. The results of this study have clearly shown that there were differences in the geometrical and topographical properties of granule, fibrous, platelet and flake-like particles. This quantitative study of the surface topographies of the UHMWPE particles has laid a foundation for quantitatively assessing the influence of particle surface textures on the pathophysiological responses of the particles at the nanometre scale. This information can be used to determine the optimal surface texture of wear particles for an improved control of wear and the adverse particle-tissue reaction process in the future.