Directed cell attachment by tropoelastin on masked plasma immersion ion implantation treated PTFE Daniel V. Bax a, b, * , David R. McKenzie a , Marcela M.M. Bilek a , Anthony S. Weiss b a Applied and Plasma Physics, School of Physics, University of Sydney, Building A28, New South Wales 2006, Australia b School of Molecular Bioscience, University of Sydney, Building G08, New South Wales 2006, Australia article info Article history: Received 1 April 2011 Accepted 20 May 2011 Available online 12 June 2011 Keywords: Cell patterning Tropoelastin PTFE Plasma treatment ECM protein abstract The ability to generate cell patterns on polymer surfaces is critical for the detailed study of cellular biology, the fabrication of cell-based biosensors, cell separation techniques and for tissue engineering. In this study contact tape masking and steel shadow masks were used to exclude plasma immersion ion implantation (PIII) treatment from defined areas of polytetrafluoroethylene (PTFE) surfaces. This process enabled patterned covalent binding of the cell adhesive protein, tropoelastin, without employing chemical linking molecules. Tropoelastin coating rendered the untreated regions cell adhesive and the PIII-treated area non-adhesive, allowing very fine patterning of cell adhesion to PTFE surfaces. A blocking step, such as with BSA or PEG, was not required to prevent cell binding to the underlying PIII-treated regions as tropoelastin coating alone performed this blocking function. Although tropoelastin coated the entire PTFE surface, the cell binding C-terminus of tropoelastin was markedly less solvent exposed on the PIII-treated, hydrophilic regions. The differential exposure of the C-terminus correlated with the patterned distribution of tropoelastin-mediated cell adhesion. This new methodology specifically enables directed cell behavior on a polymer surface using a simple one-step treatment process, by modulating the adhesive activity of a single extracellular matrix protein. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Synthetic polymers are used extensively for the fabrication of scientific and diagnostic platforms. For example virtually all assays of cell adhesion and biological activity occur on adhesive polymer surfaces. The polymeric material PTFE is used routinely for the fabrication of medical devices such as vascular prosthesis, max- iofacial surgery and dermal applications [1e3]. Often such polymer surfaces are inherently non-cell adhesive, so ECM protein coating is routinely utilized to endow polymers with their biological activity. Such coating is frequently accomplished through simple protein physisorption [4]. Physisorption is dependent upon the polymer chemistry, wettability, energy and topography resulting in variable degrees of protein adsorption, persistence and stability [4e7]. For example PTFE is very hydrophobic and so binds strongly to many proteins [8,9]. However upon adsorption to PTFE, proteins can undergo structural changes [10e14] with implications for in vivo foreign body response [15] and hemocompatibility [16]. We have previously shown that nitrogen PIII treatment of PTFE modifies the PTFE surface chemistry. Upon PIII treatment the surface is defluorinated and oxidized causing increased surface wettability with water contact angles decreasing from 114.4  to 87.8  [17,18]. This in turn modulates the cell binding activity of bound ECM proteins and of bound enzymes [17e24]. In contrast to simple protein physisorption covalent pro- teinepolymer interactions offer the advantage of increased persistence of attached proteins, thereby overcoming a major difficulty arising from use of transiently resident ECM proteins on synthetic surfaces. We have previously shown that in addition to modifying the surface chemistry of PTFE, PIII treatment offers a methodology to covalently link ECM proteins to PTFE without the need for chemical crosslinkers [17]. Tropoelastin is the major constituent of many elastic tissues such as arteries, lung and skin dermis. Elastin is stable in adult humans with a very low turnover. Tropoelastin can bind to fibro- blasts via integrin a V b 3 and heparan sulfate interactions at the C-terminus [25e27]. Such cell binding activity is sensitive to the surface properties of the underlying polymer substrate. Indeed we * Corresponding author. Applied and Plasma Physics, School of Physics, Univer- sity of Sydney, Building A28, Sydney, New South Wales 2006, Australia. Tel.: þ61 2 9351 7333; fax: þ61 2 9351 5858. E-mail address: daniel.bax@sydney.edu.au (D.V. Bax). Contents lists available at ScienceDirect Biomaterials journal homepage: www.elsevier.com/locate/biomaterials 0142-9612/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2011.05.060 Biomaterials 32 (2011) 6710e6718