**1. Introduction**

Laser surface texturing has been established as an effective method to tailor and control the micro-topographic but also physiochemical properties of surfaces. During the last decades, a wide variety of multi-scale surface textures ranging from nanometer to micrometer feature dimensions have been reported that can be produced using pulsed and ultrashort pulsed lasers in surface processing. There is also an increasing trend for applying such microscopic laser textures for functionalization in advanced surface engineering. This is emphasized in Figure 1 on the basis of the SCOPUS abstract and citation database [1], showing a steadily growing number of peer-reviewed journal articles published per year for the search term "Laser surface texturing" (blue bar).

Inspired by nature, a great number of these basic research activities reveal the potential of multi-scale laser textures mimicking natural concepts to be applied for biomimetic surface functionalities, interfaces and products. In this manner, Figure 2 illustrates a variety of characteristic laser textures produced on stainless steel plates: (a) rippled surface texture, (b) multi-scale surface texture and (c) riblets, which can be used, for example, to control optical, wetting or aerodynamic surface behaviors. Thereby, the specific functionality strongly depends on the individual texture feature geometry.

**Figure 1.** Overview of the number of peer-reviewed journal articles published per year in the SCOPUS abstract and citation database as received for the search term "Laser surface texturing" (blue bar), "Laser surface texturing AND Tribology" (red bar) and "Laser surface texturing AND Tribology AND Friction" (green bar) [1].

Laser surface texturing has also attracted great attention in tribology applications which can be recognized in Figure 1 for the search terms "Laser surface texturing AND Tribology" (red bar) as well as "Laser surface texturing AND Tribology AND Friction" (green bar). The ongoing upward trend of research activities in this field is mainly due to the ability of laser textures to also improve the frictional performance of tribological systems with regard to their efficiency, load capacity, wear resistance and life-time. However, most of these tribological studies report on laser surface texturing for reducing internal torque in the lubricant friction regime and micro-dimpled laser textures were applied to function as micro-hydrodynamic bearings, micro reservoirs for lubricant retention or micro-traps for wear particles of sliding systems, for example, in seals, piston rings and thrust bearings [2–8]. Recent studies also report on the reduction of the coefficient of friction (COF) for ripples tested under lubrication friction conditions [9,10]. However, only little research has been spent so far on the increase of friction forces in dry friction contacts. Therein, it was demonstrated that the static COF of frictional engaged connections (cam, press fittings) can be increased by laser fabricated molten and re-solidified bulged microscopic structures [11,12].

**Figure 2.** Laser made microscopic surface textures for mimicking natural functionalities on stainless steel: (**a**) rippled surface texture for optical effects; (**b**) multi-scale features imitating the hydrophobic and self-cleaning behavior of the lotus leaf and (**c**) riblets for skin friction drag reduction in turbulent flows inspired by shark's skin micro structure.

In another recent approach, laser made dimples were identified being valuable for COF enhancement in dry friction contacts [13–15]. As a specialty, the microscopic dimples produced on the surface were surrounded by prominent molten and re-solidified walls potentially enhancing the mechanical interconnection along with higher adhesive friction forces for the joint frictional contact. However, the limited processing speed and throughput of these basically investigated processes are actually the major drawback to bring this promising technology to industrial production and manufacturing.
