nature materials | VOL 7 | APRIL 2008 | www.nature.com/naturematerials 277 REVIEW ARTICLE ZHIHONG NIE 1 AND EUGENIA KUMACHEVA 1,2,3 1 Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario M5S 3H6, Canada 2 Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario M5S 3E5, Canada 3 Institute of Biomaterials & Biomedical Engineering University of Toronto, Taddle Creek Road, Toronto, Ontario M5S 3G9, Canada e-mail: ekumache@chem.utoronto.ca he past decade has witnessed the rapid development of a broad range of strategies used to pattern polymers. Intense interest in polymer patterning originated from the diversity of existing synthetic and biological polymers, and the ability to ‘design’ new types of polymers so that various functions of polymer-patterned surfaces can be readily addressed. Polymer patterns typically have high idelity, owing to the suppressed lateral difusion of macromolecules. High-resolution polymer patterns can be produced by patterning reactive precursor molecules and polymerizing them directly on the surface. A truly unique approach to surface patterning has been realized through the self-assembly of block copolymers. Polymers have relatively low cost, good mechanical properties and are compatible with most patterning techniques. he applications of polymer-patterned surfaces can be tentatively organized into several categories: (1) the fabrication of light-emitting displays (LEDs), semiconductor microelectronics and plastic electronics 1–3 ; (2) bio-related and medicinal research including the study of cells and tissue engineering 4–6 ; (3) the generation of masks and templates 7,8 ; (4) the production of optical components such as gratings or photonic crystals 9,10 ; and (5) fundamental research in surface science and combinatorial synthesis 11,12 . In this review, we highlight recent advances in top-down and bottom-up patterning of polymers using photolithography, printing techniques, self-assembly of block copolymers and instability-induced patterning. In each section, we briely describe a particular patterning technique, the application of such a technique to polymer patterning, and the most promising applications of the polymer-patterned surfaces. As some of the patterning methods have similar applications, for each technique we highlight the applications in which the method is superior to others. Patterning of surfaces with non-polymeric or polymer–inorganic materials is beyond the scope of this review. We have not included the discussion of patterning by layer-by-layer polyelectrolyte deposition, or the fabrication of 3D patterns using multiphoton irradiation. hese topics have been covered in depth in several other reviews 13–15 . We also focus on the use of light-based patterning in the fabrication of LEDs, and direct the reader to excellent reviews on the progress in organic electronics and optoelectronics 3,16,17 . PHOTOLITHOGRAPHY Over the past three decades, photolithography has been one of the main methods used for the patterning of polymers. In photolithographic methods, patterns are generated by selectively exposing a monomer-, oligomer- or polymer-coated surface to photoirradiation, and, when needed, by subsequently removing selected areas of the ilm through dissolution in an appropriate solvent (Fig. 1a). Irradiation triggers photopolymerization, photocrosslinking, functionalization and decomposition reactions, or induces phase separation in the exposed areas. Photolithographic patterns can be generated in polymer ilms and in monolayers, for example, in polymer brushes 16 . Site-speciic exposure is achieved by illuminating the ilm through a mask or by using optical interference (holographic) techniques 15 . he interference methods generate periodic patterns such as Bravais lattices 10,15,18 . Photolithography is a cost-efective high-throughput technique that is suitable for large-area surface patterning with good alignment, controlled topography and a broad range of features. he resolution of patterns varies from micrometres to sub-100 nanometres. High-resolution patterning is achieved by using non- conventional masks 7 , new photoactive polymers 19 , irradiation at short wavelengths 20 and advanced lithographic optical techniques and set-ups 20 . Photolithographically patterned surfaces are used in their own right or as templates for subsequent patterning of surfaces with other functional materials. In addition to their traditional use in the semiconductor industry, patterned polymers have found applications in the production of LEDs 21 , polymer-dispersed liquid-crystal displays 22 , photonic crystals 10 , optical components 23 , microarrays of cells and proteins 24,25 , sensors and actuators 26 and devices for data storage 27 . Photolithographic patterning of conductive polymers, such as polyacetylene, poly(p-phenylenevinylene), polyaniline and Patterning surfaces with functional polymers The ability to pattern functional polymers at different length scales is important for research fields including cell biology, tissue engineering and medicinal science and the development of optics and electronics. The interest and capabilities of polymer patterning have originated from the abundance of functionalities of polymers and a wide range of applications of the patterns. This paper reviews recent advances in top-down and bottom-up patterning of polymers using photolithography, printing techniques, self-assembly of block copolymers and instability-induced patterning. Finally, challenges and future directions are discussed from the point of view of both applicability and strategies for the surface patterning of polymers. © 2008 Nature Publishing Group