Response of NIH 3T3 Fibroblast Cells on Laser-Induced Periodic Surface Structures on a 15×(Ti/Zr)/Si Multilayer System.

Ultrafast laser processing with the formation of periodic surface nanostructures on the 15×(Ti/Zr)/Si multilayers is studied in order to the improve cell response. A novel nanocomposite structure in the form of 15x(Ti/Zr)/Si multilayer thin films, with satisfying mechanical properties and moderate biocompatibility, was deposited by ion sputtering on an Si substrate. The multilayer 15×(Ti/Zr)/Si thin films were modified by femtosecond laser pulses in air to induce the following modifications: (i) mixing of components inside of the multilayer structures, (ii) the formation of an ultrathin oxide layer at the surfaces, and (iii) surface nano-texturing with the creation of laser-induced periodic surface structure (LIPSS). The focus of this study was an examination of the novel Ti/Zr multilayer thin films in order to create a surface texture with suitable composition and structure for cell integration. Using the SEM and confocal microscopies of the laser-modified Ti/Zr surfaces with seeded cell culture (NIH 3T3 fibroblasts), it was found that cell adhesion and growth depend on the surface composition and morphological patterns. These results indicated a good proliferation of cells after two and four days with some tendency of the cell orientation along the LIPSSs.

Controlling the wettability of stainless steel from highly-hydrophilic to super-hydrophobic by femtosecond laser-induced ripples and nanospikes.

Results on the manipulation of the wetting properties of stainless steel alloy surface by ultrashort pulse laser texturing are presented. The wide range of water droplet contact angles from highly-hydrophilic to super-hydrophobic was achieved by generation of laser-induced periodic surface structures (LIPSS) and nanospikes. In particular, the wetting state was controlled by accumulated laser fluence, which determines the carbon/oxygen content and nano-texture type of the surface after laser treatment. A super-hydrophobic water-repelling surface was generated. The simple, single-step laser processing technology was demonstrated as a promising tool for the large-scale industrial production of self-cleaning stainless steel.

Femtosecond Laser Fabrication of Stable Hydrophilic and Anti-Corrosive Steel Surfaces.

We report on a novel single-step method to develop steel surfaces with permanent highly hydrophilic and anti-corrosive properties, without employing any chemical coating. It is based on the femtosecond (fs) laser processing in a saturated background gas atmosphere. It is particularly shown that the fs laser microstructuring of steel in the presence of ammonia gas gives rise to pseudoperiodic arrays of microcones exhibiting highly hydrophilic properties, which are stable over time. This is in contrast to the conventional fs laser processing of steel in air, which always provides surfaces with progressively increasing hydrophobicity following irradiation. More importantly, the surfaces subjected to fs laser treatment in ammonia exhibit remarkable anti-corrosion properties, contrary to those processed in air, as well as untreated ones. The combination of two functionalities, namely hydrophilicity and corrosion resistance, together with the facile processing performed directly onto the steel surface, without the need to deposit any coating, opens the way for the laser-based production of high-performance steel components for a variety of applications, including mechanical parts, fluidic components and consumer products.

Biomimetic Omnidirectional Antireflective Glass via Direct Ultrafast Laser Nanostructuring.

Here, a single-step, biomimetic approach for the realization of omnidirectional transparent antireflective glass is reported. In particular, it is shown that circularly polarized ultrashort laser pulses produce self-organized nanopillar structures on fused silica (SiO2 ). The laser-induced nanostructures are selectively textured on the glass surface in order to mimic the spatial randomness, pillar-like morphology, as well as the remarkable antireflection properties found on the wings of the glasswing butterfly, Greta oto, and various Cicada species. The artificial structures exhibit impressive antireflective properties, both in the visible and infrared frequency ranges, which are remarkably stable over time. Accordingly, the laser-processed glass surfaces show reflectivity smaller than 1% for various angles of incidence in the visible spectrum for s-p linearly polarized configurations. However, in the near-infrared spectrum, the laser-textured glass shows higher transmittance compared to the pristine. It is envisaged that the current results will revolutionize the technology of antireflective transparent surfaces and impact numerous applications from glass displays to optoelectronic devices.

Biomimetic surface structures in steel fabricated with femtosecond laser pulses: influence of laser rescanning on morphology and wettability.

The replication of complex structures found in nature represents an enormous challenge even for advanced fabrication techniques, such as laser processing. For certain applications, not only the surface topography needs to be mimicked, but often also a specific function of the structure. An alternative approach to laser direct writing of complex structures is the generation of laser-induced periodic surface structures (LIPSS), which is based on directed self-organization of the material and allows fabrication of specific micro- and nanostructures over extended areas. In this work, we exploit this approach to fabricate complex biomimetic structures on the surface of steel 1.7131 formed upon irradiation with high repetition rate femtosecond laser pulses. In particular, the fabricated structures show similarities to the skin of certain reptiles and integument of insects. Different irradiation parameters are investigated to produce the desired structures, including laser repetition rate and laser fluence, paying special attention to the influence of the number of times the same area is rescanned with the laser. The latter parameter is identified to be crucial for controlling the morphology and size of specific structures. As an example for the functionality of the structures, we have chosen the surface wettability and studied its dependence on the laser processing parameters. Contact angle measurements of water drops placed on the surface reveal that a wide range of angles can be accessed by selecting the appropriate irradiation parameters, highlighting also here the prominent role of the number of scans.

Controlling the Wettability of Steel Surfaces Processed with Femtosecond Laser Pulses.

The wettability of a material surface is an essential property that can define the range of applications it can be used for. In the particular case of steel, industrial applications are countless but sometimes limited because of the lack of control over its surface properties. Although different strategies have been proposed to tune the wetting behavior of metal surfaces, most of them require the use of processes such as coatings with different materials or plasma/chemical etching. In this work, we present two different laser-based direct-write strategies that allow tuning the wetting properties of 1.7131 steel over a wide range of contact angles using a high repetition rate femtosecond laser. The strategy consists in the writing of parallel and crossed lines with variable spacing. A detailed morphological analysis confirmed the formation of microstructures superimposed with nanofeatures, forming a hierarchical surface topography that influences the wetting properties of the material surface. Contact angle measurements with water confirm that this behavior is mostly dependent on the line-to-line spacing and the polarization-dependent orientation of the structures. Moreover, we demonstrate that the structures can be easily replicated in a polymer using a laser-fabricated steel master, which enables low-cost mass production. These findings provide a practical route for developing user-defined wetting control for new applications of steel and other materials functionalized by rapid laser structuring.