Macromolecular Rapid Communications

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Stratified Polymer Brushes from Microcontact Printing of Polydopamine Initiator on Polymer Brush Surfaces Qiangbing Wei, Bo Yu, Xiaolong Wang,* Feng Zhou*

Stratified polymer brushes are fabricated using microcontact printing (μCP) of initiator integrated polydopamine (PDOPBr) on polymer brush surfaces and the following surface initiated atom transfer radical polymerization (SI-ATRP). It is found that the surface energy, chemically active groups, and the antifouling ability of the polymer brushes affect transfer efficiency and adhesive stability of the polydopamine film. The stickiness of the PDOPBr pattern on polymer brush surfaces is stable enough to perform continuous μCP and SI-ATRP to prepare stratified polymer brushes with a 3D topography, which have broad applications in cell and protein patterning, biosensors, and hybrid surfaces.

1. Introduction Mussel-adhesive proteins have attracted intensive scientific research interest over the past few decades, because of their strong adhesive ability on a variety of materials with high binding strength under wet conditions.[1,2] Further studies have discovered that the catechol and its derivates exist widely in adhesive proteins and are believed to contribute to adhesion.[3–5] Among catechol derivates, dopamine has been proposed as a readily accessible and suitable monomer for the design of biomimetic adhesives. Hence, a variety of dopamine-based compounds have been synthesized for surface modification to enhance interface adhesion. For example, monolayers of dopamine-based initiators were assembled on various substrates to grow

Q. Wei, Dr. B. Yu, Dr. X. Wang, Prof. F. Zhou State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China E-mail: [email protected]; [email protected] Q. Wei University of Chinese Academy of Sciences Beijing 100049, P. R. China Macromol. Rapid Commun. 2014, DOI: 10.1002/marc.201400052 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

functional polymer brushes in situ via surface initiated polymerization.[6–9] Furthermore, synthetic peptide-dopamine conjugates and dopamine-based polymers prepared by radical copolymerization were developed to modify surfaces via a “grafting to” method.[10–13] Actually, polydopamine has emerged as an universal bio-inspired coating material and was first reported by Messersmith et al.[14] They described a straightforward method consisting of oxidation polymerization of dopamine in alkaline conditions, and in situ spontaneous deposition of the polydopamine on a wide variety of substrates, including metals, metal oxides, ceramics, and even chemically inert polymers, such as polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE). Furthermore, polydopamine coating offers a versatile platform for postfunctionalization using dopamine mediated chemistry and thus can be used to immobilize biomolecules,[15,16] for in situ assisted synthesis of nanoparticles,[17] and to selectively uptake and release charged molecules by encapsulation.[18–20] Recently, a polydopamine pattern was transferred from a PDMS stamp to various substrates via microcontact printing (μCP), which provides a powerful tool for the development of tunable patterned substrates for cell and protein patterning.[21,22]

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DOI: 10.1002/marc.201400052

Early View Publication; these are NOT the final page numbers, use DOI for citation !!

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Macromolecular Rapid Communications

Q. Wei et al.

www.mrc-journal.de

Some possible adhesive interactions between catechol and substrates have been proposed, such as coordination interactions,[23,24] hydrogen bonding,[22] and π–π interactions or hydrophobic interactions.[25] Despite the various substrates that have been coated with polydopamine, investigation of the adhesive behavior of polydopamine on polymer surfaces with different surface properties (such as surface energy, chemical activity, and antifouling ability) is also of great interest yet has rarely been addressed. Polymer brushes prepared by surface initiated polymerization are well known to tailor the surface properties of bulk materials, which thus made them the right class of substrates for this investigation.[26,27] In this study, a robust and feasible initiator integrated polydopamine ink (PDOPBr) that can be transferred to polymer brush surfaces via the μCP technique is demonstrated. Then the PDOPBr pattern is amplified by surface initiated atom transfer radical polymerization (SI-ATRP) to form patterned polymer brushes. A variety of monomers are used to form polymer brushes via surface initiated polymerization to support the required properties (such as neutral, charged, and zwitterionic).[28] Simultaneously modifying polymer brushes with the polydopamine pattern via microcontact printing (μCP) also delivered a feasible approach for post-functionalization of polymer brushes to fabricate stratified polymer with a 3D topography. Growing polymer brushes from polymer brush surfaces through attachment of a new initiator layer has previously been addressed by Chen et al. They developed an effective method to fabricate patterned polymer brushes using μCP to yield the patterned, hydrogen bond-mediated attachment of hydrolyzed trichlorosilane initiator to the COOH-functionalized polymer brush surface.[29] However, trichlorosilane ink is difficult to manipulate due to easy hydrolysis and is also limited to the COOH-functionalized polymer brush film. Herein, combining the μCP technique and SI-ATRP, PDOPBr realized a feasible approach to fabricate stratified polymer brushes with a 3D topography on various polymer brush surfaces with different surface energy, different functional groups, and antifouling ability. Given the advantages of PDOPBr ink for μCP (such as simple preparation, versatile adhesion, and good stability), this approach is believed to be a practical technique for development of polymer patterns on various polymer brush substrates, which have broad applications in cell and protein patterning, hybrid surfaces, and so on.

2. Experimental Section 2.1. Materials 3-Sulfopropylmethacrylate potassium salt (SPMA, 95%, TCI), 2-(methacryloyloxy)-ethyl-trimethylammonium chloride

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(METAC, 80% in water, TCI), [2-(methacryloyloxy)-ethyl] dimethyl (3-sulfopropyl) ammonium hydroxide (SBMA, 97%, Aldrich), methacrylic acid sodium (MAA, 99%, Aldrich), 2-hydroxyethyl methacrylate (HEMA, 97%, Aldrich), 2-(dimethylamino) ethyl methacrylate (DMAEMA, 98%, J&K), methyl methacrylate (MMA, 98%, Aldrich), and styrene (98%, Aldrich) were purchased and used as received. 2,2′-Bipyridyl (bipy), pentamethyldiethylenetriamine (PMDETA), 3-hydroxytyramine hydrochloride (dopamine·HCl), and sodium azide were purchased from Alfa Aesar. Copper (I) bromide was purified via reflux in acetic acid. Other general reagents and solvents were purchased and used as received. The ultrapure water was prepared with a NANOpure Infinity system from Barnstead/Thermolyne Corporation. The silane initiator 3-(trichlorosilyl) propyl 2-bromo-2-methylpropanoate and the dopamine initiator 2-bromo-2-methyl-N-[2-(3, 4-dihydroxyphenyl) ethyl] propionamide were synthesized according to previous reports.[6,30]

2.2. Preparation of Silane Initiator on Si Substrate Fresh Si wafers washed with acetone and ethanol under ultrasound conditions were activated using oxygen plasma for 10 min, and were then sealed in a vacuum desiccator in a vial containing 5 μ L of silane initiator. The chamber was pumped down to

Stratified polymer brushes from microcontact printing of polydopamine initiator on polymer brush surfaces.

Stratified polymer brushes are fabricated using microcontact printing (μCP) of initiator integrated polydopamine (PDOPBr) on polymer brush surfaces an...
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