Short communication Functionalized superhydrophobic biomimetic chitosan-based films Wenlong Song a,b , Vivek Sambhaji Gaware c , Ögmundur Vidar Rúnarsson c , Már Másson c , João F. Mano a,b, * a 3B’s Research Group-Biomaterials, Biodegradables and Biomimetics, Department of Polymer Engineering, University of Minho, AvePark, Zona Industrial da Gandra, S. Cláudio do Barco, 4806-909 Caldas das Taipas – Guimarães, Portugal b IBB – Institute for Biotechnology and Bioengineering, PT Government Associated Laboratory, Guimarães, Portugal c Faculty of Pharmaceutical Sciences, School of Health Sciences, University of Iceland, Hagi, Hofsvallagata 53, IS-107 Reykjavik, Iceland article info Article history: Received 26 November 2009 Received in revised form 15 January 2010 Accepted 20 January 2010 Available online 25 January 2010 Keywords: Superhydrophobic Polysaccharides Biomaterials Lotus-effect abstract Chitosan has been greatly applied in the fields of biomedicine, biomembranes and food/nutrition because of its nontoxic and biocompatible properties. However, water solubility of chitosan at pH < 5 strongly limits the use of chitosan-based films when pH stability and low water uptake are required in many actual applications. In this work, silyl chitosan, 3,6-O-di-tertbutyldimethyl silyl chitosan, a chitosan derivative, was synthesized and used to prepare extreme water-repellent films in the whole pH range of 1–14 using a phase separation method that exhibit topography with a three-level hierarchical rough- ness organization. The polymer also allows posterior chemical modification specifically through the amine group, permitting to control the surface chemistry and wettability. This work not only improve the stabilization of chitosan-based films but also demonstrates the possibility of manufacturing polysac- charide-based superhydrophobic surfaces with potential to be used in anti-bacterial substrates, tissue engineering, food industry and other biomedical applications. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Inspired by the self-cleaning phenomenon found in nature, superhydrophobic surfaces have attracted significant attention due to their potential applications in biotechnology and water- repellent commodity materials (Blossey, 2003). Different materials and technologies have been employed in the production of super- hydrophobic surfaces that typically exhibit a hierarchical rough- ness, at both the nano and micro scales, mimicking the topography found in the lotus leaf or other self-cleaning natural surfaces (Koch, Bhushan, & Barthlott, 2008; Sun, Feng, Gao, & Jiang, 2005). Polysaccharides are a very important class of macromole- cules but there are just few reports on superhydrophobic surfaces based on such materials, being most of them derived from cellulose (Li, Zhang, & Wang, 2008). Highly water-repellent polysaccharide- based surfaces obtained by some low cost and facile processing route could have direct applications in the biomedical, biotechno- logical, textile or environmental field. In this work a chitosan deriv- ative will be used to demonstrate that a simple processing procedure could be employed to obtain such kind of surfaces. Fur- thermore the developed surface exhibits durable extreme hydro- phobic property in a wide pH range, and is chemically versatile as they process free amine groups that can allow for different chemical modifications. Chitosan, poly-(1–4)-2-amino-2-deoxy-b-D-Glucan, as one of natural biodegradable, nontoxic and biocompatible polysaccha- rides has been proposed to be used in multiple fields, such as in biomedical, biotechnological, functional membranes/fibres, food/ nutrition, and agricultural/environmental applications (Francis Suh & Matthew, 2000; Grini & Badot, 2008; Prabaharan & Mano, 2005; Prashanth & Tharanathan, 2007). Due to the existence of a protonable amine group, chitosan shows not only a pH responsive behaviour but also water solubility at pH < 5. This strongly limits the use of chitosan-based materials when pH stability and low water uptake are required as in many actual applications. Both amino and hydroxyl groups in the structure of chitosan permit variety of chemical modifications, which can be used to improve its stabilization and extend its applicability (Alves & Mano, 2008; Chiu et al., 2009). It is well known that the decrease of surface en- ergy is one important way to improve stabilization (Schmidt et al., 1994; Wang et al., 2006). However, chemical modification in chito- san smooth substrates only allows controlling the wettability within the hydrophilic to the hydrophobic range (Campos, Satsan- gi, Rawls, & Mei, 2009; Tangpasuthadol, Pongchaisirikul, & Hoven, 2003). To our knowledge a clear relationship between topography and superhydrophobic (contact angle, CA > 150 o ) properties of chitosan-based systems has not been reported. In this contribution, first a hydrophobic chitosan derivative, 3,6- O-di-tertbutyldimethyl silyl chitosan (SC), was synthesized using 0144-8617/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2010.01.041 * Corresponding author. Address: 3B’s Research Group-Biomaterials, Biodegrad- ables and Biomimetics, Department of Polymer Engineering, University of Minho, AvePark, Zona Industrial da Gandra, S. Cláudio do Barco, 4806-909 Caldas das Taipas – Guimarães, Portugal. Fax: +351 253510909. E-mail address: jmano@dep.uminho.pt (J.F. Mano). Carbohydrate Polymers 81 (2010) 140–144 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol