See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/221709145 ChemInform Abstract: Complex Polymer Brush Gradients Based on Nanolithography and Surface-Initiated Polymerization ARTICLE in CHEMICAL SOCIETY REVIEWS · MARCH 2012 Impact Factor: 33.38 · DOI: 10.1039/c2cs15316e · Source: PubMed CITATIONS READS 23 89 3 AUTHORS, INCLUDING: Xiankun Lin Qiang He Harbin Institute of Technology Harbin Institute of Technology 18 PUBLICATIONS 248 CITATIONS 90 PUBLICATIONS 2,752 CITATIONS SEE PROFILE SEE PROFILE Available from: Qiang He Retrieved on: 28 October 2015 View Online / Journal Homepage / Table of Contents for this issue Chem Soc Rev Dynamic Article Links Cite this: Chem. Soc. Rev., 2012, 41, 3584–3593 www.rsc.org/csr TUTORIAL REVIEW Complex polymer brush gradients based on nanolithography and surface-initiated polymerization Xiankun Lin,a Qiang He*a and Junbai Li*b Received 25th November 2011 DOI: 10.1039/c2cs15316e Confined surface gradients consisting of polymer brushes have great potential in various applications such as microfluidic devices, sensors, and biophysical research. Among the available fabrication approaches, nanolithographies combined with self-assembled monolayers and surface- initiated polymerization have became powerful tools to engineer confined gradients or predefined complex gradients on the nanometre size. In this tutorial review, we mainly highlight the research progress of the fabrication of confined polymer brush gradients by using electron beam, laser, and probe-based nanolithographies and the physical base for these approaches. The application of these polymer brush gradients in biomedical research is also addressed. Introduction groups, and responsive behavior under external stimuli. A promising way to render solid surfaces with diverse Accessing surfaces with tailorable properties is very important for functionalities is to integrate functional macromolecules such diverse applications from daily life to advanced technologies. as self-assembled monolayers, polymer brushes, block copolymers, A lot of approaches have been employed to engineer surfaces and layer-by-layer polyelectrolyte multilayers onto various solid with a variety of surface energies, topography, patterns, functional substrates.1–3 Particularly, patterned and/or stimuli-responsive polymer brushes have attracted considerable attention from a Key Laboratory of Microsystems and Microstructures industrial and academic areas for advanced technologies such Manufacturing, Ministry of Education, Micro/Nano Technology as microfluidic devices, biological sensors, tissues engineering, Downloaded by Harbin Institute of Technology on 17 April 2012 Research Centre, Harbin Institute of Technology, Yikuangjie No. 2, 4,5 Harbin 150080, China. E-mail: [email protected]; and anti-biofouling. Published on 16 March 2012 http://pubs.rsc.org | doi:10.1039/C2CS15316E Fax: +86-451-86403605; Tel: +86-451-86403605 Additionally, surface gradients have recently become a hot b Beijing National Laboratory for Molecular Sciences, Institute of research area, especially in material sciences and biophysical Chemistry, Chinese Academy of Sciences, Zhong Guan Cun, Bei Yi Jie No. 2, Beijing 100190, China. E-mail: [email protected]; research. Gradients on surfaces mean that chemical or physical Fax: +86 10 82614087; Tel: +86 10 82614087 properties of components attached on substrates or substrates Xiankun Lin received his PhD Qiang He graduated from the degree from the State Key Inner Mongolia University and Laboratory of Supramolecular received his PhD degree in 2003 Structure and Materials, Jilin from the Institute of Chemistry, University in 2010 under the the Chinese Academy of supervision of Professor Lixin Sciences (ICCAS). He then Wu, when his research mainly joined the ICCAS as an focused on the self-assembly of assistant professor and block molecule–polyoxometalate became an associate professor composites. He currently is an in 2006. He spent four years as assistant professor in Prof. a research fellow of the Qiang He’s group at Micro/ Alexander von Humboldt Nanotechnology Research Foundation in the Max Plank Center, Harbin Institute of Institute of Colloids and Inter- Xiankun Lin Technology, China. Qiang He faces, Germany. Currently he is a full Professor at the Micro/Nanotechnology Research Center, Harbin Institute of Technology, China. His research interests include self-assembled active biomimetic systems, stimuli-responsive surface patterning for biomedical application. 3584 Chem. Soc. Rev., 2012, 41, 3584–3593 This journal is c The Royal Society of Chemistry 2012 View Online themselves gradually vary along one or more given directions. Gradients play an important role in vivo, they drive a range of biological processes from matter transport across biological membranes to the motion of proteins. Engineering gradients on surfaces could thus provide not only in vivo models for better understanding of biological processes, but also tools to mimic the biological functions. Moreover, gradients are also important characteristics or requirement of advanced materials. As a special type of surface, polymer brush gradients could provide one or more controllable parameters on a substrate, and render a powerful platform for high-throughput analysis to cut down the experimental time and deviation.6–11 Usually, the surface gradient of polymer brushes is divided into a physical gradient and chemical gradient (Fig. 1a). The physical gradient means the variations of physical properties such as topography and surface wettability. As an example for physical gradient, Zhang et al. prepared a topography gradient through applying a temperature field to uniform polystyrene (PS) brushes, due to the difference of the chain mobility under different temperatures.12 Such a topography gradient shows a gradual variation of wettability. In most cases, researchers concentrate more on the chemical gradient of polymer brushes and in particular on the gradual variations of grafting densities and/or molecular weights of polymer chains along one or more directions. They are generally prepared by employing various gradient fields on the initiator densities or polymerization processes for polymer brushes (Fig. 1a). These gradient fields include a temperature gradient,13 a concentration gradient derived from the diffusion in gas14,15 or in solution, and a gradient of the exposure time under UV light, ozone, and monomer solutions. The latter can be realized through a mobile mask,16 pulling the substrates from the reaction solutions,17 or draining the reaction solutions gradually.18,19 They provide Downloaded by Harbin Institute of Technology on 17 April 2012 simple and cheap methods for the primary control to surface Published on 16 March 2012 http://pubs.rsc.org | doi:10.1039/C2CS15316E gradients. For instance, Genzer et al. fabricated orthogonal polymer brush gradients with varied grafting densities and molecular weights in orthogonal directions and have shown the Fig. 1 (a) Possible routes for the fabrication of polymer brush tailored adhesion of cells on such gradient substrates.20,21 These gradients; (b) Atomic force microscopy (AFM) image of a typical approaches for the fabrication of surface-bound gradients patterned polymer brush gradients prepared by nanolithography have been reviewed previously.6–8,11 These gradients are enough combined with surface-initiated living polymerization. for those applications which do not need a precise boundary of polymer brush gradients. However, many other specific studies or applications require elaborate confined gradients or predefined Junbai Li is a full Professor of complex gradients on the nanometre size. Obviously, the above- Chemistry and Director of the mentioned methods cannot satisfy the request and thus, new CAS Key Lab of Colloid and approaches such as various lithographical techniques have to be Interface Science, Institute of introduced. Several lithographical techniques combined with the Chemistry, the Chinese Acad- surface-initiated living polymerization have actually been proved emy of Sciences (ICCAS). He to be powerful tools for tailorable gradient polymer brushes received his BSc and PhD (Fig. 1b). degrees from Jilin University. Regular preparation of polymer brushes uses the ‘‘grafting He then spent two years as a from’’ strategy, but two other methods, self-assembled mono- Postdoctoral fellow at the Max layers (SAMs) and surface-initiated polymerization (SIP), are Planck Institute of Colloids and also crucial in the tool box for fabricating gradient surfaces by Interfaces in Germany and later he had got a collaborative project lithographies. SAMs afford diverse advantages for the preparation for some years. His research of polymer brushes, including simple preparation, well-defined 22 Junbai Li interests involves molecular structures, and easy modification and patterning. After SAMs assembly of biomimetic systems, are modified with initiators, SIP can be performed to synthesize biointerfaces and nanostructures. polymer brushes with controllable structures and polymerization This journal is c The Royal Society of Chemistry 2012 Chem. Soc. Rev., 2012, 41, 3584–3593 3585 View Online degrees. An example of a typical SIP is surface-initiated atom surfaces.28 However, they are not suitable for the fabrication transfer radical polymerization (SI-ATRP). It has been used of gradient surfaces due to their dependence on master widely, because it can provide surface-bound polymers (including patterns. In