Synthesis and Photopolymerization of Tween 20 Methacrylate/N-vinyl-2-Pyrrolidone Blends Ana C. Borges a , A. Jayakrishnan c , Pierre-Etienne Bourban a, ⁎, Christopher J.G. Plummer a , Dominique P. Pioletti b , Jan-Anders E. Månson a a Laboratoire de Technologie des Composites et Polymères (LTC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland b Laboratoire de Biomécanique Orthopédique (LBO), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland c Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600 036, India abstract article info Article history: Received 2 March 2010 Received in revised form 22 May 2012 Accepted 11 June 2012 Available online 16 June 2012 Keywords: Hydrogel Tissue Engineering Swelling Photopolymerization Poly(oxyethylene 20 sorbitan) monolaurate (Tween® 20) methacrylates were synthesized by coupling methacryloyl chloride (MeOCl) to Tween 20 in the presence of 4-(N,N-dimethylamino) pyridine, using THF as a solvent, in order to investigate their suitability as precursors for photopolymerizable hydrogels in tissue engi- neering applications. The degree of substitution could be controlled by adjusting the molar ratio of MeOCl and Tween 20, giving three different monomers: Tween 20 monomethacrylate, Tween 20 dimethacrylate and Tween 20 trimethacrylate. Combined 1 H NMR and MALDI-TOF MS confirmed these monomers to be of high purity and to have polydispersities less than 1.3. It was shown that aqueous solutions of the monomers were photoactive, all the methacrylate groups reacting within 30 minutes exposure to a UV light intensity of 145 mW/cm 2 . Aqueous Tween 20 trimethacrylate was then combined with N-vinyl-2-pyrrolidone (NVP), giving tough copolymer hydrogels on photopolymerization, whose swelling ratios and swelling rates could be tuned by varying the Tween 20 trimethacrylate content. The use of a flexible spacer with a multifunctional monomer gives a permanent three-dimensional network, whilst maintaining degrees of swelling of between 60 and 85%, with potential for a wide range of biological and non-biological applications. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Hydrogels produced by photopolymerization have been extensively investigated as biomaterials for applications such as drug delivery car- riers, scaffolds, coatings and tissue engineering [1]. Photopolymerization is a method of choice since it involves relatively short reaction times and minimal heating, and it does not require organic solvents [2]. The hydro- gel may be prepared from a low viscosity aqueous solution of a mono- mer, oligomer or macromer via a free radical pathway [3], typically resulting in a highly hydrated structure. A key advantage of photo- polymerized hydrogels over chemically or physically crosslinked hydro- gels is that their mechanical properties and swelling behavior may be tuned relatively easily by varying the molecular mass and/or the concen- tration of the precursors. On the other hand, their development is limited by the availability of such precursors and in many cases a high degree of mechanical stability is not required. Three basic strategies have been adopted: (i) use of existing photoactive, water soluble precursors; (ii) addition of photoactive groups to existing non-photoactive hydro- philic precursors; (iii) combination of water-soluble photoinitiators with hydrophilic precursors with limited photoactivity [4]. The third strategy, based on the use of water-soluble photoinitiators, is the most versatile in terms of the range of potential precursors and may be adapted to suit specific wavelengths of UV light, with clear advantages for biomedical applications. Molecules that have been modified for use as precursors for photopolymerizable hydrogels include poly-(ethylene glycol) (PEG) acrylate derivatives [3], PEG methacrylate derivatives [3], poly-(vinyl alcohol) derivatives [5], modified hyaluronic acid [3] and dextran methacrylates [6]. However, these have typically been used in applications where mechanical properties are not determinant, such as drug delivery, soft contact lenses and scaffolds [7]. The present work, on the other hand, focuses on the modification of Tween 20, a bio-inert trifunctional polyoxyethylene derivative of sorbitan monolaurate [8], as a first step towards developing crosslinked hydrated networks with a tailored mechanical response for load-bearing applications. The specific objective is to replace the nucleus pulposus in damaged intervertebral discs, an application for which adequate mechanical properties are essential, as discussed in more detail at the end of this article. Tween 20 is a hydro-soluble surfactant used as a detergent and emulsifier in a number of domestic, engineering, and pharmacological applications [9,10], and is distinguished from the other members of the Tween family by the lengths of the polyoxyethylene and the fatty acid ester moieties. It is considered to be an attractive choice for the production of hydrogels for tissue engineering, since it may readily be modified to produce multifunctional photoactive Tween 20 methacrylates, as will be dis- cussed in what follows, and crosslinking via dimethacrylates has been Materials Science and Engineering C 32 (2012) 2235–2241 ⁎ Corresponding author. Tel.: +41 21 6935806; fax: + 41 21 6935880. E-mail address: pierre-etienne.bourban@epfl.ch (P.-E. Bourban). 0928-4931/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2012.06.009 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec