**1. Introduction**

At least 3% of the patients that require primary total hip arthroplasty surgery need a revision due to severe prosthetic joint infections [1]. This leads to additional hospitalizations, costs and compromises the patient's health. Surface textures in the nano- and micrometer scale are observed in nature, that have an antibacterial effect, such as butterfly wings and shark skin [2]. Anti-bacterial surface features must be of the same order or slightly smaller than the bacteria size, in order to influence the adherence behavior of the bacteria [3]. This effect is based on the reduction of the amount of available surface for the bacteria cell to adhere to. Bacteria that most often cause prostheses related infections are *Staphylococcus aureus* and *Escherichia coli* [4]. The characteristic dimensions of the bacteria are one to three μm in diameter [5,6].

Cobalt–Chrome–Molybdenum (CoCrMo) is an alloy that is most often used for the bearing surface of a hip implant, due to its high fatigue, wear and corrosion resistance [7]. In a metal-on-plastic artificial hip joint, the CoCrMo femur head articulates against an polyethylene (PE) acetabulum cup. The surface of the CoCrMo component is traditionally mirror polished [8].

An established method to alter surface properties on the nano- to micrometer scale is laser surface texturing using (ultra-) short laser pulses. Under specific conditions, this can lead to so called laser-induced periodic surface structures (LIPSS). LIPSS are nanometer sized, regular patterned surface textures and can improve tribological performance [9,10], wettability properties [10–15], anti-bacterial properties [15–18] and cell-tissue growth [11].

In order to reduce infections, LIPSS having dimensions (periodicity and amplitude) about the size of the bacterias on the CoCrMo material could improve the antibacterial performance of the CoCrMo femur. However, hip-implants also should show a low-friction coefficient and should not leach hazardous materials into the human body. Therefore, the aim of this study is to not only study the formation of LIPSS on CoCrMo, but also study the tribological properties of CoCrMo on PE as well as the wettability and the leaching properties of the textures. In this study, a picosecond pulsed laser is used to create different types of LIPSS on CoCrMo surfaces. To the best of the authors knowledge, it is the first report of hexagonally packed triangular nanopillar LIPSS produced with a picosecond laser on CoCrMo. The tribological, wetting and leaching properties of different types of LIPSS on CoCrMo are investigated and compared.
