Stable superhydrophobic aluminum surfaces based on laser-fabricated hierarchical textures

Laser-microtextured surfaces have gained an increasing interest due to their enormous spectrum of applications and industrial scalability. Direct laser interference patterning (DLIP) and the well-established direct laser writing (DLW) methods are suitable as a powerful combination for the fabrication of single (DLW or DLIP) and multi-scale (DLW+DLIP) textures. In this work, four-beam DLIP and DLW were used independently and combined to produce functional textures on aluminum. The influence of the laser processing parameters, such as the applied laser fluence and the number of pulses, on the resulting topography was analyzed by confocal microscopy and scanning electron microscopy. The static long-term and dynamic wettability characteristics of the laser-textured surfaces were determined through water contact angle and hysteresis measurements, revealing superhydrophobic properties with static contact angles up to 163° and hysteresis as low as 9°. The classical Cassie-Baxter and Wenzel models were applied, permitting a deeper understanding of the observed wetting behaviors. Finally, mechanical stability tests revealed that the DLW elements in the multi-scale structure protects the smaller DLIP features under tribological conditions.Fil: Milles, Stephan. Technische Universität Dresden; AlemaniaFil: Dahms, Johannes. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Lasagni, Andrés F.. Technische Universität Dresden; Alemani

Tribocorrosion behavior of NiTi biomedical alloy processed by an additive manufacturing laser beam directed energy deposition technique

The purpose of the present study was to experimentally assess the synergistic effects of wear and corrosion on NiTi alloy in comparison with Ti-6Al-4V alloy, the most extensively used titanium alloy in biomedical applications. Both alloys were processed by an additive manufacturing laser beam directed energy deposition (LB-DED) technique, namely laser engineered net shaping (LENS), and analyzed via tribocorrosion tests by using the ball-on-plate configuration. The tests were carried out in phosphate buffered saline solution at 37 °C under open circuit potential (OCP) to simulate the body environment and temperature. The synergistic effect of wear and corrosion was found to result in an improved wear resistance in both materials. It was also observed that, for the process parameters used, the LB-DED NiTi alloy exhibits a lower tendency to corrosion as compared to the LB-DED Ti-6Al-4V alloy. It is expected that, during the service life as an implant, the NiTi alloy is less susceptible to the metallic ions release when compared with the Ti-6Al-4V alloy.This work was partially funded by FCT (Fundação para a Ciência e Tecnologia) through the grant SFRH/BD/112280/2015 and the reference projects UID/EEA/04436/2019, COMPETE 2020 with the code POCI-01-0145-FEDER-006941; NORTE-01-0145-FEDER-000018-HAMaBICo and POCI-01-0145-FEDER-031035_LaserMULTICER. Also, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES-Brazil) and Alexander von Humboldt Foundation are acknowledged for the partial support of this work. This work was also partially supported by the Project “EXPERT”, Contract no. 14PFE/17.10.2018 and Auburn University’s Presidential Award for Interdisciplinary Research (PAIR)

Conditioning of hiPSC-derived cardiomyocytes using surface topography obtained with high throughput technology

Surface functionalization of polymers aims to introduce novel properties that favor bioactive responses. We have investigated the possibility of surface functionalization of polyethylene terephthalate (PET) sheets by the combination of laser ablation with hot embossing and the application of such techniques in the field of stem cell research. We investigated the response of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to topography in the low micrometer range. HiPSC-CMs are expected to offer new therapeutic tools for myocardial replacement or regeneration after an infarct or other causes of cardiac tissue loss. However, hiPSC-CMs are phenotypically immature compared to myocytes in the adult myocardium, hampering their clinical application. We aimed to develop and test a high-throughput technique for surface structuring that would improve hiPSC-CMs structural maturation. We used laser ablation with a ps-laser source in combination with nanoimprint lithography to fabricate large areas of homogeneous micron- to submicron line-like pattern with a spatial period of 3 µm on the PET surface. We evaluated cell morphology, alignment, sarcomeric myofibrils assembly, and calcium transients to evaluate phenotypic changes associated with culturing hiPSC-CMs on functionalized PET. Surface functionalization through hot embossing was able to generate, at low cost, low micrometer features on the PET surface that influenced the hiPSC-CMs phenotype, suggesting improved structural and functional maturation. This technique may be relevant for high-throughput technologies that require conditioning of hiPSC-CMs and may be useful for the production of these cells for drug screening and disease modeling applications with lower costs.Fil: Cortella, Lucas R. X.. Universidade de Sao Paulo; BrasilFil: Cestari, Idágene A.. Universidade de Sao Paulo; BrasilFil: Lahuerta, Ricardo D.. Universidade de Sao Paulo; BrasilFil: Arana, Matheus C.. Universidade de Sao Paulo; BrasilFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Rank, Andreas. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés F.. Technische Universität Dresden; AlemaniaFil: Cestari, Ismar N.. Universidade de Sao Paulo; Brasi

Direct Laser Interference Patterning of Diffraction Gratings in Safrofilcon-A Hydrogel: Fabrication and Hydration Assessment

Refractive index modification by laser micro-structuration of diffractive optical devices in ophthalmic polymers has recently been applied for refractive correction in the fields of optics and ophthalmology. In this work, Safrofilcon-A hydrogel, used as soft contact lenses, was processed by direct laser interference patterning (DLIP) to fabricate linear periodic patterns on the surface of the samples. Periodic modulation of the surface was attained under two-beam interference by using a Q-switched laser source with emission at 263 nm and 4 ns pulse duration. Features of processed areas were studied as a function of both the interference spatial period and the laser fluence. Optical confocal microscopy used to evaluate the topography of the processed samples showed that both structured height and surface roughness increased with laser fluence. Static water contact angle (WCA) measurements were carried out with deionized water droplets on the structured areas to evaluate the hydration properties of DLIP structures. It was observed that the laser structured areas induced a delay in the hydration process. Finally, microstructural changes induced in the structured areas were assessed by confocal micro-Raman spectroscopy showing that at low laser fluences the polymer structure remained almost unaltered. In addition, Raman spectra of hydrated samples recovered the original shape of areas structured at low laser fluence

Effect of pH on wettability properties on aluminium alloy surfaces treated with direct laser writing

Nowadays, lightweight materials become more important in diverse industrial applications, such as automotive and aeronautics. Innovative surface features like superhydrophobicity enable further fields of applications. In this context, aluminium Al 2024-T351 alloy is structured using direct laser writing (DLW) to achieve a superhydrophobic surface. To address the effect of pH on the superhydrophobic behaviour, the static contact angle (SCA) is measured at different pH values (pH 1, 2, 4, 7, 9, 11 and 14), in comparison to a non-structured reference sample. The results show that superhydrophobic state in DLW samples is preserved in the pH range 2 – 9 with SCA between 151.1 ± 1.5° and 157.0 ± 0.5°. While stable hydrophobicity is still observed at pH 1, the samples exposed to pH 11 and 14 solutions exhibit collapse in the droplet and a fast chemical reaction, respectively. Concerning the non-structured samples, SCA is lower at pH 4, 11 and 14 than at neutral pH 7. This effect can be rationalized considering dealloying of Al2CuMg precipitates present in the surface of Al 2024-T351 alloy. Differences between non-structured and laser structured samples can be explained taking into account the change in present phases after laser ablation.Fil: Dib, Josefina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Zschach, Lis G.. Technische Universität Dresden.; AlemaniaFil: Baumann, Robert. Technische Universität Dresden.; AlemaniaFil: Spitz, Franziska. Technische Universität Dresden.; AlemaniaFil: Lasagni, Andrés F.. Technische Universität Dresden.; Alemani

Macro- and microstructuring of deep drawing tools for dry forming processes

AbschlussberichtIn forming processes, lubrication is needed to reduce friction and wear occurring at the contact areas between the work-piece and the tool. This is provided by separating these surfaces as well as transporting abrasive wear out of the sliding interface. With high interest in waste avoidance and efficient use of resources, today’s industry aims for substituting these lubricants. Thereby, deposition of coatings or local surface structuring offer a different way to reduce friction in forming processes. For instance, this can be reached by using different hard coatings as well as by utilizing manufacturing methods capable to control and reduce the contact area in the tribological system. In this project, the flange area of a deep drawing tool was macro-structured by turning-process (rotational symmetric geometry) and by milling-process (non rotational-symmetric part) to decrease the contact area of the work-piece up to 94% during the forming process. Also, the drawing edge radius of the tools was coated with different types of hydrogen-free tetrahedral amorphous carbon layers, e.g. with a sp³-ratios between 60% and 70%. Together with the subsequently introduced micro-features on the ta-C layer, employing the innovative method of Direct Laser Interference Patterning (DLIP), a further reduction of the contact areas was possible as well as to produce local rehybridization of the ta-C material. Also, high-throughput surface texturing of semi-finished sheet metals by DLIP process was performed, for reducing friction by minimizing also the contact area with the deep drawing tool. Forming of test strips showed the influence of the macro-structured flange area by reducing the friction force down to 75%. In addition, different modelling tools were developed for calculating both the process window and to determine the generation of wrinkles during deep drawing with macro-structured tools. The macro-structured deep drawing tools could also enlarge the process limits by increasing the stability against wrinkling of the sheet metal during the drawing process. The ta-C coating on the die radius without application of lubrication was capable to reduce the friction coefficient up to 20% compared to uncoated lubricated conditions. Performed tensile-bend tests on micro-structured ta-C coated cylinders also demonstrated the potential to reduce friction, as well as an excellent capability to reduce wear compared to the standard conditions.03006

Rapid Fabrication of Periodic Patterns on Poly(styrene-co-acrylonitrile) Surfaces Using Direct Laser Interference Patterning

Periodic microstructures in styrene-acrylonitrile (SAN) copolymers are fabricated by two-beam direct laser interference patterning using a nanosecond pulsed laser operating at a wavelength of 266 nm. The SAN copolymers are synthesized using different molar ratios (styrene to acrylonitrile) by a free radical polymerization process. The chemical composition of the copolymers and their properties are determined using Fourier transformed infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Depending on the composition of the irradiated copolymer films, with weight ratios ranging from 58 to 96.5% of styrene to acrylonitrile, different ablation behaviors are observed. The laser fluence necessary to locally ablate the copolymer is found to be dependent on the copolymer composition. Unlike other dielectric polymers, the laser irradiation produced both direct ablation of the irradiated material and collapse of the surface. It is shown that, by varying the laser fluence and the copolymer composition, the surface structure can be changed from a periodic pattern with a swelled topography to an ablated-like structure. The number of holes does not depend monotonically on the amount of PS or PAN units but shows a more complex behavior which depends on the copolymer composition and the laser fluence

Fabrication of highly ordered arrays of platinum nanoparticles using direct laser interference patterning

Highly ordered electrode arrays composed by lines of platinum nanoparticles deposited onto gold substrates have been made by direct laser interference patterning (DLIP) of polyaniline (PANI) thin films, followed by electrochemical deposition of platinum nanoparticles. Nanostructured arrays of electrocatalytic Pt particles are built in that way.The Alfred Krupp Foundation, Alexander von Humboldt Foundation, BMBF (Germany) FONCYT (Grants PICT R03/453, PICT04/25521, and PAE0422711), CONICET (Grant PIP5221), SECYT-UNRC (Argentina), and MEC (Grant MAT2007-60621) (Spain)

Influence of laser micropatterning on the mechanical strength of dental grade zirconia

Laser surface treatments have been explored to create controlled roughness on ceramic implants, aiming to enhance tissue-implant interaction. Among these techniques, Direct Laser Interference Patterning (DLIP) employs light interference to generate well-defined nano- and micro-scale patterns [1]. However, DLIP can induce detrimental effects on bioceramics, including microcrack nucleation, phase transformation, and potentially compromised mechanical resistance. This study investigated the impact of DLIP on the surface morphology, microstructure, mechanical properties, and biological behavior of dental-grade zirconia (3Y-TZP). An infrared nanosecond laser was employed to create linear structures with 6 µm periodicity on discs fabricated via ceramic powder pressing and sintering. Samples were further subjected to aging and mechanical cycling protocols simulating 10 years of clinical service. Confocal microscopy, scanning electron microscopy, and X-ray diffractometry were used to analyze surface and subsurface features, microstructure, and crystallographic changes, respectively. Cell viability on textured surfaces was assessed through biological tests. The nanosecond DLIP treatment introduced surface defects and heterogeneities, including groove depth variations, a recrystallized layer, microcracks, and porosity. Additionally, DLIP-induced phase transformation in 3Y-TZP was observed, further amplified by aging or mechanical cycling. While the flexural strength of laser-textured 3Y-TZP samples remained similar, a lower standard deviation was noted, suggesting enhanced reliability. Interestingly, neither aging nor mechanical cycling significantly affected flexural strength. These findings demonstrate the potential of DLIP for patterning zirconia surfaces but highlight the need for careful optimization to mitigate its detrimental effects on mechanical performance. Future research should focus on exploring alternative laser sources, pulse parameters, and post-treatment strategies to minimize microcrack formation, stabilize phase transformation, and improve overall biocompatibility

Increasing Heat Transfer from Metal Surfaces through Laser-Interference-Induced Microscopic Heat Sinks

With the increasing processing power of micro-electronic components and increasing spatial limitations, ensuring sufficient heat dissipation has become a crucial task. This work presents a microscopic approach to increasing the surface area through periodic surface structures. Microstructures with a periodic distance of 8.5 µm are fabricated via Direct Laser Interference Patterning (DLIP) on stainless steel plates with a nanosecond-pulsed infrared laser and are characterized by their developed interfacial area ratio. The optimal structuring parameters for increasing the surface area were investigated, reaching peak-to-valley depths up to 12.8 µm and increasing surface area by up to 394%. Heat dissipation in a natural convection environment was estimated by measuring the output voltage of a Peltier element mounted between a hot plate and a textured sample. The resulting increase in output voltage compared to an unstructured sample was correlated to the structure depth and developed interfacial area ratio, finding a maximum increase of 51.4%. Moreover, it was shown that the output voltage correlated well with the structure depth and surface area