Designing stainless steel surfaces with anti-pitting properties applying laser ablation and organofluorine coatings

Long-lasting and superhydrophobic stainless steel with anti-pitting properties is achieved by modifying conventional AISI 304L through a two-step strategy: 1) application of a femtosecond surface laser ablation treatment to generate micro-nano structures on the surface; and 2) deposition of organofluorine nanometric coating. Samples with two different patterns, namely paraboloid- and cauliflower-like, are approached and investigated by means of contact angle hysteresis, X-ray photoelectron spectroscopy, and electrochemical techniques. Results indicate that the stainless steel surface acquires efficient anticorrosive properties due to the homogenization and refinement of the patterned microstructure into a magnetite rich phase, in combination with the formation of a carbonaceous and sol–gel layer. The adherent semiconducting oxide layer is stable over time in presence of an aggressive chloride environment. The prepared superhydrophobic surfaces prevent the steel substrates from getting wet with water, protecting them from the pitting corrosion caused by the electrolyte intrusion. The corrosion resistance is explained by a mechanism in which, in addition of the silane coating, the air trapped into the micro-nano patterned surfaces plays an important role.Peer ReviewedPostprint (author's final draft

Biomimetic nanostructured surfaces for antifouling in dairy processing

In dairy pasteurization equipment, fouling is an ongoing problem. Indeed, when heated, milk and its derivatives generate mineral and proteinaceous deposits on stainless steel walls. This heat-induced fouling impairs the process through the addition of an increasing thermal resistance to the system. Deposits are also a threat to food safety as they provide micro-organisms with good settlement opportunities. As a consequence, fouling mitigating strategies are needed. Biomimetic surfaces in particular, inspired from the surface morphology of lotus leaf could be considered for their self-cleaning abilities. Its dual-scale roughness (i.e. a micro roughness supporpsed by nanoscale roughness) allows for the composite Cassie-Baxter wetting state due to air remaining trapped between the liquid and the solid surface. As a result, those surfaces possess very high contact angles (typically higher than 150o) and very low contact angle hysteresis (typically less than 10°). However, a major limitation of this type of surface is the difficulty to maintain a stable Cassie-Baxter state over time: depending on the experimental conditions (pressure, vibration, evaporation, surface defect) the liquid penetrates sooner or later into the structures degrading their anti-biofouling properties. To overcome this limitation, it has been proposed to impregnate the textured surface by a liquid of low surface tension (usually an inert oil not miscible with water). This led to SLIPS surfaces (Slippery Liquid-Infused Porous Surfaces). Even if these surfaces present low contact angle, their hysteresis is also almost null whatever the experimental conditions leading to antifouling properties [1].   This work aims at designing Cassie-Baxter and SLIPS surfaces and test them in dairy processing conditions to assess their antifouling properties. To this end, 316L stainless steel surfaces were texturized via femtosecond laser irradiation to generate dual-scale (cauliflower-like) structures [2]. Some of the fabricated surfaces underwent further modifications: (i) silanization with perfluorodecyltrichloro-silane or (ii) silanization followed by impregnation with a fluorinated oil to create Slippery Liquid Infused Porous Surfaces (SLIPS) [3]. All surfaces were tested for their fouling properties in a pilot pasteurization equipement (UMET-PIHM, Institut National de la Recherche Agronomique, Villeneuve d'Ascq) [4] allowing to mimick industrial conditions of the pasteurization process. Thorough characterizations were performed on the surfaces before and after fouling, to (i) establish clearly their surface properties (wettability, surface energy, roughness) and (ii) to investigate the impact of the different surface properties on heat-induced dairy fouling compared to a native stainless steel as reference. A wide range of analytical tools such as Goniometry, cross-section Electron Probe Micro-Analysis X-ray mappings, and Scanning Electron Microscopy were implemented to this end. Outstanding results were obtained regarding antifouling properties of dual-scaled roughness surfaces in dairy processing conditions, with a reduction of fouling by more than 90% in weight. References [1] T.-S. Wong, S. H. Kang, S. K. Y. Tang, E. Smythe, B. D. Hatton, A. Grinthal, and J. Aizenberg, ?Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity,? Nature, vol. 477, pp. 443?447, 2011. [2] A.-M. Kietzig, S. G. Hatzikiriakos, and P. Englezos, ?Patterned Superhydrophobic Metallic Surfaces,? Langmuir, vol. 25, no. 8, pp. 4821?4827, 2009. [3] A. K. Epstein, T.-S. Wong, R. A. Belisle, E. M. Boggs, and J. Aizenberg, ?Liquid-infused structured surfaces with exceptional anti-biofouling performance,? PNAS, vol. 109, no. 33, pp. 13182?13187, 2012. [4] M. Jimenez, G. Delaplace, N. Nuns, S. Bellayer, D. Deresmes, G. Ronse, G. Alogaili, M. Collinet-Fressancourt, and M. Traisnel, ?Toward the understanding of the interfacial dairy fouling deposition and growth mechanisms at a stainless steel surface: A multiscale approach,? J. Colloid an interface Sci., vol. 404, pp. 192?200, 2013

Super-hydrophobic nanopatterned interfaces : optimization and manufacturing

This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence, scanning speed and scanning overlap) on the wettability of the resulted micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nanostructures. All of the produced structures were classified according to a newly defined parameter, the Laser Intensity Factor (LIF) that is a function of scanning speed and fluence of laser. By increasing LIF, the ablation rate and the periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluorinated alkylsilane agent. Analysis of the wettability in terms of contact angle (CA) and contact angle hysteresis (CAH) revealed enhanced superhydrophobicity for most of these structures, particularly that possessing triple roughness pattern. This also exhibited a low CAH. The high permanent superhydrophobicity of this pattern is due to the special micro-nano structure of the surface that facilitates the Cassie-Baxter state. A new two-dimensional (2D) thermodynamic model is developed to predict the contact angle (CA) and contact angle hysteresis (CAH) of all types of surface geometries, particularly those with asperities having non-flattened tops. The model is evaluated by micro/nano sinusoidal and parabolic patterns fabricated by laser ablation. These microstructures are analyzed thermodynamically through the use of the Gibbs free energy to obtain the equilibrium CA and CAH. The effects of the geometrical details on maximizing the superhydrophobicity of the nano-patterned surface are also discussed in an attempt to design surfaces with desired and/or optimum wetting characteristics. The analysis of the various surfaces reveals the important geometrical parameters, which may lead to lotus effect (high CA>150° and low CAH150° and high CAH>>10°).Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

Designing stainless steel surfaces with anti-pitting properties applying laser ablation and organofluorine coatings

Long-lasting and superhydrophobic stainless steel with anti-pitting properties is achieved by modifying conventional AISI 304L through a two-step strategy: 1) application of a femtosecond surface laser ablation treatment to generate micro-nano structures on the surface; and 2) deposition of organofluorine nanometric coating. Samples with two different patterns, namely paraboloid- and cauliflower-like, are approached and investigated by means of contact angle hysteresis, X-ray photoelectron spectroscopy, and electrochemical techniques. Results indicate that the stainless steel surface acquires efficient anticorrosive properties due to the homogenization and refinement of the patterned microstructure into a magnetite rich phase, in combination with the formation of a carbonaceous and sol–gel layer. The adherent semiconducting oxide layer is stable over time in presence of an aggressive chloride environment. The prepared superhydrophobic surfaces prevent the steel substrates from getting wet with water, protecting them from the pitting corrosion caused by the electrolyte intrusion. The corrosion resistance is explained by a mechanism in which, in addition of the silane coating, the air trapped into the micro-nano patterned surfaces plays an important role.Peer Reviewe

Effect of Extreme Wettability on Platelet Adhesion on Metallic Implants: From Superhydrophilicity to Superhydrophobicity

In order to design antithrombotic implants, the effect of extreme wettability (superhydrophilicity to superhydrophobicity) on the biocompatibility of the metallic substrates (stainless steel and titanium) was investigated. The wettability of the surface was altered by chemical treatments and laser ablation methods. The chemical treatments generated different functionality groups and chemical composition as evident from XPS analysis. The micro/nanopatterning by laser ablation resulted in three different pattern geometry and different surface roughness and consequently wettability. The patterned surface were further modified with chemical treatments to generate a wide range of surface wettability. The influence of chemical functional groups, pattern geometry, and surface wettability on protein adsorption and platelet adhesion was studied. On chemically treated flat surfaces, the type of hydrophilic treatment was shown to be a contributing factor that determines the platelet adhesion, since the hydrophilic oxidized substrates exhibit less platelet adhesion in comparison to the control untreated or acid treated surfaces. Also, the surface morphology, surface roughness, and superhydrophobic character of the surfaces are contributing factors to platelet adhesion on the surface. Our results show that superhydrophobic cauliflower-like patterns are highly resistant to platelet adhesion possibly due to the stability of Cassie–Baxter state for this pattern compared to others. Our results also show that simple surface treatments on metals offer a novel way to improve the hemocompatibility of metallic substrates

Antifouling biomimetic liquid-infused stainless steel: application to rairy industrial processing

International audienceFouling is a widespread and costly issue, faced by all food-processing industries. Particularly, in the dairy sector, where thermal treatments are mandatory to ensure product safety, heat-induced fouling represents up to 80% of the total production costs. Significant environmental impacts, due the massive consumption of water and energy, are also to deplore. Fouling control solutions are thus desperately needed, as they would lead to substantial financial gains as well as tremendous progress toward eco-responsible processes. This work aims at presenting a novel and very promising dairy fouling-mitigation strategy, inspired by nature, and to test its antifouling performances in real industrial conditions. Slippery liquid-infused surfaces were successfully designed directly on food grade stainless steel, via femtosecond laser ablation, followed by fluorosilanization and impregnation with an inert perfluorinated oil. Resulting hydrophobic surfaces (water contact angle of 112 degrees) exhibited an extremely slippery nature (contact angle hysteresis of 0.6 degrees). Outstanding fouling-release performances were obtained for these liquid-infused surfaces as absolutely no trace of dairy deposit was found after 90 min of pasteurization test in pilot-scale equipment followed by a short water rinse

The investigation of the efficacy and safety of stromal vascular fraction in the treatment of nanofat-treated acne scar: a randomized blinded controlled clinical trial

Abstract Background Acne is the most common skin disorder which is known as a chronic inflammatory disease with psychological burden and reduced quality of life. Adipose tissue-derived stromal vascular fraction (SVF) is recognized as a source of regenerative cells and improves the quality of skin by increasing collagen content. To date, a few studies have been performed on the therapeutic role of SVF in the treatment of acne scars. Methods This randomized, single-blinded clinical trial was performed on 7 patients with acne scars. In all patients, the initial grade of acne (volume, area and depth) was evaluated and ultrasound of the relevant scar was performed to evaluate neocollagenesis. As a spilt face study, for treating the scars, we used nanofat subcutaneously on one side of the face (control group) and combination of nanofat subcutaneously and SVF intradermally on the opposite side (intervention group). The patients were evaluated for severity of acne by visioface after one month, also for thickness of epidermis and dermis by ultrasound after one month and three months. Results All of the apparent findings of scars improved in two groups after one month, but these changes were significant just for the group treated with SVF (p value  0.05). The findings showed that dermal and complete thicknesses of the skin in the first month were different between two groups significantly (p value: 0.042 and 0.040, respectively). Conclusion The use of SVF in the treatment of patients with acne scars accelerates the improvement of volume, area and depth of the scar by increasing collagen content and the dermal thickness, so it can be used as a potentially effective treatment for these patients