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Intrinsic Hydrophobic Cairnlike Multilayer Films for Antibacterial Effect with Enhanced Durability Hyejoong Jeong,† Jiwoong Heo,† Boram Son,‡ Daheui Choi,† Tai Hyun Park,‡,§ Minwook Chang,∥ and Jinkee Hong*,† †
School of Chemical Engineering and Material Science, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea ‡ School of Chemical and Biological Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea § Advanced Institutes of Convergence Technology, 145 Gwanggyo-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16229, Republic of Korea ∥ Department of Ophthalmology, Dongguk University Ilsan Hospital, 27 Dongguk-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do 10326, Republic of Korea S Supporting Information *
ABSTRACT: One important aspect of nanotechnology includes thin films capable of being applied to a wide variety of surfaces. Indispensable functions of films include controlled surface energy, stability, and biocompatibility in physiological systems. In this study, we explored the ancient Asian coating material “lacquer” to enhance the physiological and mechanical stability of nanofilms. Lacquer is extracted from the lacquer tree and its main component called urushiol, which is a small molecule that can produce an extremely strong coating. Taking full advantage of layer-by-layer assembly techniques, we successfully fabricated urushiol-based thin films composed of small molecule/polymer multilayers by controlling their molecular interaction. Unique cairnlike nanostructures in this film, produced by urushiol particles, have advantages of intrinsic hydrophobicity and durability against mechanical stimuli at physiological environment. We demonstrated the stability tests as well as the antimicrobial effects of this film. KEYWORDS: antibacteria, urushiol, intrinsic hydrophobicity, mechanical stability, layer-by-layer
1. INTRODUCTION Nanobiomedical thin film techniques are becoming increasingly attractive to extend the limitations of existing biomedical devices, including miniaturized, implantable, wearable, and patch-compatible forms.1−3 One of the basic requirements of surface properties in biomedical device assembly is to possess good antibiofouling behavior including antibacterial, antiadhesive, and anti-inflammatory properties.4−9 To further this goal, hydrophobic (static contact angle, SCA > 90°) or superhydrophobic (SCA > 150°) surfaces have been extensively studied as well as hydrophilic surfaces and can be fabricated by several different approaches:10−12 generally coating a rough surface with low surface energy molecules,13 roughening the surface chemistry by hydrophobic materials,14 and fabricating artificial micro- and nanostructures on the surface minimized the liquid−solid contact interfacial area.15 However, unfortunately existing durable superhydrophobic coatings still have some drawbacks in their enhanced mechanical properties of well-ordered microstructured surfaces containing a large © XXXX American Chemical Society
number of air traps, as well as difficulties in controlling uniformity, thickness, and biocompatibility.16 To apply these concepts to antibacterial and waterproof effects, techniques controlling thickness at the nanoscale and producing uniform surfaces are essential for miniaturized and patchable devices. For this purpose, novel approaches to surface control and materials with special desired wettability are needed. Layer-by-layer (LBL) assembly is a well-developed, versatile nanofilm preparation method for assembling various materials with nanosize control. Basically the process of LBL assembly involves sequential adsorption of oppositely charged polymers through electrostatic interaction, as introduced by G. Decher and co-workers.17 Taking full advantage of LBL assembly, we can control the thickness, structure, uniformity, and functionality of films at the molecular level through complementary Received: August 17, 2015 Accepted: November 11, 2015
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DOI: 10.1021/acsami.5b07613 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces interactions depending on the materials.18−21 Accordingly, LBL assembled films can be more stable than other film fabrication methods due to the interactions between substrate and materials or among materials. In this study, we investigated natural lacquer material, which is the sap of the lacquer tree (Toxicodendron vernicif luum). Lacquer has been used as a wood finish in Eastern Asia since ancient times, and lacquerware still remains intact after hundreds of years, such as the printed woodblocks of the Tripitaka Koreana, which are a UNESCO World Heritage treasure.22 The major component, comprising 98%, of lacquer is urushiol, which is responsible for the desirable properties of the lacquer coating. Urushiol is a small molecule (molecular weight of
