Abstract
Hip-implants structured with anti-bacterial textures should show a low-friction coefficient and should not leach hazardous substances into the human body. The surface of a typical material used for hip-implants, namely Cobalt–Chrome–Molybdenum (CoCrMo) was textured with different types of laser-induced periodic surface structures (LIPSS)—i.e., low spatial frequency LIPSS (LSFL), hierarchical structures consisting of grooves superimposed with high spatial frequency LIPSS (HSFL) and Triangular shaped Nanopillars (TNP)—using a picosecond pulsed laser source. The effect of LIPSS on the wettability, friction, as well as wear of the structures, when slid against a polyethylene (PE) counter surface and biocompatibility was analyzed. Surfaces covered with LSFL show superhydrophobicity and grooves with superimposed HSFL, as well as TNP, show hydrophobic behavior. The coefficient of friction (CoF) of LIPSS against a polyethylene (PE) counter surface was found to be higher (ranging from 0.40 to 0.66) than the CoF of (polished) CoCrMo, which was found to equal 0.22. It was found that the samples release cobalt within biocompatible limits. Compared to polished reference surfaces, LIPSS cause higher friction of CoCrMo against PE contact. However, the wear of the PE counter surface only increased significantly for the LSFL textures. For these reasons, it is concluded that LIPSS are not suitable for a heavily loaded metal-on-plastic bearing contact.
Highlights
At least 3% of the patients that require primary total hip arthroplasty surgery need a revision due to severe prosthetic joint infections [1]
Besides exposing the material to linear laser polarization, a quarter wave plate was included in the setup to achieve circular polarization, which may lead to triangular shaped laser-induced periodic surface structures (LIPSS) textures
Two types of surface textures were processed using linear polarized laser irradiation, by applying increasing peak fluence levels and various number of overscans during the laser processing. These two types are low spatial frequency LIPSS (LSFL, see Figure 2) and hierarchical structures composed of micro-grooves and superimposed LSFL
Summary
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. 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. The characteristic dimensions of the bacteria are one to three μm in diameter [5,6]
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