Micro- and Nanopatterned Star Poly(ethylene glycol) (PEG) Materials Prepared by UV-Based Imprint Lithography Marga C. Lensen,* ,² Petra Mela, ² Ahmed Mourran, ² Ju ¨rgen Groll, ²,‡ Jean Heuts, ² Haitao Rong, ‡ and Martin Mo ¨ller* ,² DWI e.V. and Institute of Technical and Macromolecular Chemistry, RWTH Aachen, Pauwelsstrasse 8, D-52056 Aachen, Germany, and SusTech GmbH & Co. KG Darmstadt, Petersenstr. 20, D-64287 Darmstadt, Germany ReceiVed March 15, 2007. In Final Form: April 18, 2007 A UV-based imprint lithography method is used for the direct surface structuring of hydrogel-based biomaterials, which are prepared from a family of tailor-made star poly(ethylene glycol) formulations. Bulk star poly(ethylene glycol) (PEG) hydrogels are fabricated by cross-linking acrylate-functionalized star PEG macromolecules. Cross- linking is achieved by radical reactions initiated by UV irradiation. This UV-curable star PEG formulation allows templating of mold structures to yield a stable, stand-alone, elastomeric replica of the mold. In particular, when a secondary, soft mold is used that consists of a perfluorinated elastomer with inherent excellent release properties, nanometer-sized features (down to 100 nm) can be imprinted without specialized equipment. The applied UV-based imprint lithography is a fast and simple technique to employ for the direct topographic structuring of bulk PEG-based biomaterials. The UV-based imprinting into the star PEG prepolymer by means of a perfluorinated, soft mold can be carried out on the bench top, while nanoscale resolution is demonstrated. Introduction For bioanalytical devices such as biosensors and in biomedical research such as tissue engineering, the detailed structure and physical properties of the surfaces in contact with proteins and living cells are of critical importance in terms of protein adsorption and cellular responses. To control and take advantage of specific and directed protein interaction and cell adhesion, the unspecific binding processes should be suppressed. Correspondingly, several biocompatible and nonadhesive coating materials have been developed, and the methodologies to prepare such coatings have been optimized. 1-7 The most widely used material for this purpose is based on poly(ethylene oxide) (PEO), also called poly(ethylene glycol) (PEG). 8 This polymer is biocompatible and non-cytotoxic, and it meets the requirements to eliminate undesired, unspecific interactions with biological (macro)molecules. 1 To enable specific and directed interaction with cells, usually bioactive molecules, for example, peptides, proteins, or sugars, are tethered to such surfaces so that they can interact specifically with their binding partners. 9,10 This so-called cell patterning is routinely achieved by soft lithography techniques, such as microcontact printing. 11,12 Interestingly, several studies have revealed that not only the chemistry of the substrate but also the topography may influence cell adhesion. 12-16 Decades ago, it was found that fibroblasts adopted their shape and aligned to topographic structures (i.e., micrometer-sized grooves), a process denoted “contact guid- ance”. 17,18 More recent investigations have confirmed the alignment of other cells on topographically patterned surfaces with feature sizes comparable to the dimensions of the cells. 16,19-21 Hence, cells and viruses were confined in, for instance, micrometer-sized wells. 22,23 Other studies demonstrated that protein adsorption and cell adhesion were increased on a nanostructured PEG substrate when compared with bare PEG substrates. 24 This effect was ascribed to the increase in hydrophobicity (due to trapped air) and to the increased surface area. 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J.; Nealey, P. F. J. Vac. Sci. Technol. B 2003, 21, 683-687. 7841 Langmuir 2007, 23, 7841-7846 10.1021/la7007683 CCC: $37.00 © 2007 American Chemical Society Published on Web 06/05/2007