Fabricating Laser-Induced Periodic Surface Structures on Medical Grade Cobalt–Chrome–Molybdenum: Tribological, Wetting and Leaching Properties

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.

Hierarchical Micro-/Nano-Structures on Polycarbonate via UV Pulsed Laser Processing

“…All of these different specific surface properties are the result of so-called functionalized surfaces, which often consist of regular (hierarchical) micro- and nanometer sized surface structures. Functionalized surfaces have received increased scientific attention in recent years, aiming to reproduce them (biomimetics) due to their potential for new applications, such as anti-bacterial hip implants [ 8 , 9 ], increased [ 10 ] or decreased [ 11 ] cell-tissue growth onto implantable materials, liquid motion flow in microfluidics [ 12 ], fluid transport in tribological systems [ 13 ], friction control [ 14 , 15 ], wettability control [ 9 , 16 , 17 ] or colorization of surfaces [ 18 , 19 , 20 , 21 ].…”

“…The direction of the LIPSS depends on the material and the (linear) laser beam polarization. Their periodicity depends on several process parameters, such as the laser wavelength ( ), the angle of incidence ( ), the number of pulses processing effectively impinging one spot ( ) and the laser peak fluence ( ) [ 9 , 25 , 28 ]. Several types of LIPSS can be distinguished, depending on the laser processing parameters and the material, e.g., common Low Spatial Frequency LIPSS (LSFL) with a period of about the laser wavelength ( ), High Spatial Frequency LIPSS (HSFL) with a period well below the laser wavelength ( ), or even hexagonally arranged triangular nanopillars with an overall period close to the laser wavelength ( ) [ 25 , 28 ].…”

“…Several types of LIPSS can be distinguished, depending on the laser processing parameters and the material, e.g., common Low Spatial Frequency LIPSS (LSFL) with a period of about the laser wavelength ( ), High Spatial Frequency LIPSS (HSFL) with a period well below the laser wavelength ( ), or even hexagonally arranged triangular nanopillars with an overall period close to the laser wavelength ( ) [ 25 , 28 ]. LIPSS can be processed on metals [ 8 , 9 , 10 , 18 , 19 , 20 , 29 ], semiconductors [ 12 , 21 , 25 , 28 ], dielectrics [ 30 ], ceramics [ 31 , 32 , 33 ] and polymers [ 34 , 35 , 36 , 37 ]. Large area processing of LIPSS is easily achieved in a one-step approach by scanning the focused laser beam in a meandering way across the sample surface.…”

“…Large area processing of LIPSS is easily achieved in a one-step approach by scanning the focused laser beam in a meandering way across the sample surface. Since the central high fluence part of the Gaussian laser beam profile can generate different types of LIPSS than its low fluence wing, hierarchical micro-/nano-structures are easily feasible [ 9 , 38 ]. Moreover, as the periodicity of HSFL is not constrained by the optical diffraction limit, these extremely fine nanostructures may be even superimposed to sub-micrometric LSFL [ 39 ].…”

Editorial: Special Issue “Laser-Induced Periodic Surface Nano- and Microstructures for Tribological Applications”

“…Van der Poel et al [9] investigated the ps-laser based fabrication of different types of LIPSS on medical grade cobalt-chrome-molybdenum alloy for hip prosthesis applications. Emphasis was laid on their associated tribological, surface wetting, and leaching properties.…”