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      Bio-Inspired Functional Surface Fabricated by Electrically Assisted Micro-Embossing of AZ31 Magnesium Alloy

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          Abstract

          Developing bio-inspired functional surfaces on engineering metals is of extreme importance, involving different industrial sectors, like automotive or aeronautics. In particular, micro-embossing is one of the efficient and large-scale processes for manufacturing bio-inspired textures on metallic surfaces. However, this process faces some problems, such as filling defects and die breakage due to size effect, which restrict this technology for some components. Electrically assisted micro-forming has demonstrated the ability of reducing size effects, improving formability and decreasing flow stress, making it a promising hybrid process to control the filling quality of micro-scale features. This research focuses on the use of different current densities to perform embossed micro-channels of 7 μm and sharklet patterns of 10 μm in textured bulk metallic glass dies. These dies are prepared by thermoplastic forming based on the compression of photolithographic silicon molds. The results show that large areas of bio-inspired textures could be fabricated on magnesium alloy when current densities higher than 6 A/mm 2 (threshold) are used. The optimal surface quality scenario is obtained for a current density of 13 A/mm 2. Additionally, filling depth and depth–width ratio nonlinearly increases when higher current densities are used, where the temperature is a key parameter to control, keeping it below the temperature of the glass transition to avoid melting or an early breakage of the die.

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          Most cited references23

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          Processing of bulk metallic glass.

          Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made.
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            Engineered antifouling microtopographies--correlating wettability with cell attachment.

            Bioadhesion and surface wettability are influenced by microscale topography. In the present study, engineered pillars, ridges and biomimetic topography inspired by the skin of fast moving sharks (Sharklet AF) were replicated in polydimethylsiloxane elastomer. Sessile drop contact angle changes on the surfaces correlated well (R2 = 0.89) with Wenzel and Cassie and Baxter's relationships for wettability. Two separate biological responses, i.e. settlement of Ulva linza zoospores and alignment of porcine cardiovascular endothelial cells, were inversely proportional to the width (between 5 and 20 microm) of the engineered channels. Zoospore settlement was reduced by approximately 85% on the finer (ca 2 microm) and more complex Sharklet AF topographies. The response of both cell types suggests their responses are governed by the same underlying thermodynamic principles as wettability.
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              Bioinspired Photocatalytic Shark-Skin Surfaces with Antibacterial and Antifouling Activity via Nanoimprint Lithography

              By combining antifouling shark-skin patterns with antibacterial titanium dioxide (TiO 2 ) nanoparticles (NPs), we present a simple route toward producing durable multifunctional surfaces that decrease microbial attachment and inactivate attached microorganisms. Norland Optical Adhesive, a UV-crosslinkable adhesive material, was loaded with 0, 10, or 50 wt % TiO 2 NPs from which shark-skin microstructures were imprinted using solvent-assisted soft nanoimprint lithography on a poly(ethylene terephthalate) (PET) substrate. To obtain coatings with an exceptional durability and an even higher concentration of TiO 2 NPs, a solution containing 90 wt % TiO 2 NPs and 10 wt % tetraethyl orthosilicate was prepared. These ceramic shark-skin-patterned surfaces were fabricated on a PET substrate and were quickly cured, requiring only 10 s of near infrared (NIR) irradiation. The water contact angle and the mechanical, antibacterial, and antifouling characteristics of the shark-skin-patterned surfaces were investigated as a function of TiO 2 composition. Introducing TiO 2 NPs increased the contact angle hysteresis from 30 to 100° on shark-skin surfaces. The hardness and modulus of the films were dramatically increased from 0.28 and 4.8 to 0.49 and 16 GPa, respectively, by creating ceramic shark-skin surfaces with 90 wt % TiO 2 NPs. The photocatalytic shark-skin-patterned surfaces reduced the attachment of Escherichia coli by ~70% compared with smooth films with the same chemical composition. By incorporating as low as 10 wt % TiO 2 NPs into the chemical matrix, over 95% E. coli and up to 80% Staphylococcus aureus were inactivated within 1 h UV light exposure because of the photocatalytic properties of TiO 2 . The photocatalytic shark-skin-patterned surfaces presented here were fabricated using a solution-processable and roll-to-roll compatible technique, enabling the production of large-area high-performance coatings that repel and inactivate bacteria.
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                Author and article information

                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                16 January 2020
                January 2020
                : 13
                : 2
                : 412
                Affiliations
                [1 ]Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Ministry of Education, Harbin Institute of Technology, Harbin 150080, China; xinweiwang@ 123456hit.edu.cn (X.W.); xjhit@ 123456hit.edu.cn (J.X.); 13B909069@ 123456hit.edu.cn (J.L.); bguo@ 123456hit.edu.cn (B.G.)
                [2 ]Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin 150001, China
                [3 ]School of Mechanical Engineering, Harbin Institute of Technology, Harbin 150001, China; wangzl@ 123456hit.edu.cn
                [4 ]School of Mechanical and Electrical Engineering, Robotics and Microsystems Center, Soochow University, Suzhou 215131, China
                [5 ]Department of Mechanical Engineering, Universitat Politècnica de Catalunya, Av. Eduard Maristany, 16, 08019 Barcelona, Spain; sanchezegea.antonio@ 123456gmail.com
                [6 ]Beijing Hangxing Machinery Manufacture Limited Corporation, Beijing 100013, China; 7w7z@ 123456sohu.com
                [7 ]Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208, USA; jcao@ 123456northwestern.edu
                Author notes
                Author information
                https://orcid.org/0000-0002-7268-4857
                https://orcid.org/0000-0001-8085-6869
                Article
                materials-13-00412
                10.3390/ma13020412
                7014324
                31963120
                2630b4a2-aaf4-4fc6-9837-d90281132c59
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 23 December 2019
                : 12 January 2020
                Categories
                Article

                electrically assisted,micro-embossing,bio-inspired functional surface,bulk metallic glass,photolithography

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