Carbohydrate Polymers 111 (2014) 348–355 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me pa g e: www.elsevier.com/locate/carbpol Chitosan/agarose hydrogels: Cooperative properties and microfluidic preparation Vanessa Zamora-Mora a,b , Diego Velasco b , Rebeca Hernández b , Carmen Mijangos a,b , Eugenia Kumacheva a,c,d,∗ a Institute of Polymer Science and Technology, The Spanish National Research Council (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain b Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario M5S 3H6, Canada c Institute of Biomaterials & Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada d Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, Toronto, Ontario M5S 3E5, Canada a r t i c l e i n f o Article history: Received 13 February 2014 Received in revised form 14 April 2014 Accepted 22 April 2014 Available online 28 April 2014 Keywords: Chitosan Agarose Composite hydrogels Microfluidics Mechanical properties Drug release a b s t r a c t The preparation of composite biopolymer hydrogels offers the capability to produce biocompatible and biodegradable materials with cooperative properties. In this paper, two natural polymers, namely, chitosan and agarose were employed to prepare composite hydrogels with dual pH and temperature properties. The elastic modulus of the composite hydrogels increased with agarose concentration reach- ing the value of 1 kPa for the chitosan/agarose gel with a 2% (w/v) concentration of agarose. In addition, composite gels exhibited a higher stability in acidic aqueous solutions, in comparison with agarose gels. The drug release properties of the composite hydrogels were tested by loading a model anticancer drug, 5-Fluorouracil, in the hydrogel interior. At pH = 7.4, the cumulative release of 5-FU was ∼50% within 96 h and decreased to ∼33% at pH = 5.2, which was attributed to the different solubility of 5-FU as a function of pH. The preparation of composite microgels with controllable dimensions in the range from 42 to 18 m and with narrow size distribution (polidispersity not exceeding 1.5%) was achieved by the microfluidic emulsification of an aqueous mixture of chitosan and agarose and subsequent gelation of the precursor droplets by cooling. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Hydrogels obtained from natural polymers are currently the focus of considerable scientific research for the development of biomedical applications due to their inherent biocompatibility and biodegradability (Li, Rodrigues, & Tomas, 2012), (Dang & Leong, 2006). In particular, agarose, an alternating copolymer found in some seaweeds consisting of 1,4-linked 3,6-anhydro-- l-galactose and 1,3-linked -d-galactose derivatives is a neutral polysaccharide that forms thermorreversible gels upon cooling agarose aqueous solutions. The mechanical and thermal properties of agarose hydrogels depend on polymer concentration, pH and solvent type (Fernández et al., 2008; Guenet, 1992; Ramzi, Rochas, & Guenet, 1998). The biocompatibility of agarose and the mild conditions of its gelation make agarose suitable for applications ∗ Corresponding author at: Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario M5S3H6 Canada. Tel.: +416 978 3576. E-mail address: ekumache@chem.utoronto.ca (E. Kumacheva). in tissue engineering (Kong & Dumitriu, 2004), however, agarose hydrogels exhibit low cell adhesiveness (Lin et al., 2005) and slow degradation rate (Zhang et al., 2012). To overcome these disadvantages, agarose can be chemically functionalized (Luo & Shoichet, 2004) or blended with others biopolymers, e.g., with gelatin (Imani, Emami, Moshtagh, Baheiraei, & Sharifi, 2012; Tripathi, Kathuria, & Kumar, 2009). In particular, the combination of chitosan and agarose in composite gels has improved the mechanical and cell-adhesive properties of agarose (Cao, Gilbert, & He, 2009; Gómez-Mascaraque, Méndez, Fernández-Gutiérrez, Vázquez, & San Román, 2014). Chitosan, the linear cationic (1-4)- 2-amino-2-deoxy--d-glucan with typical degree of acetylation ca. 0.25, is soluble in certain acidic aqueous solutions, owing to the protonation of the primary amine groups. Due to the pH- responsiveness and inherent biocompatibility, chitosan gels are attractive for biomedical applications (Dash, Chiellini, Ottenbrite, & Chiellini, 2011; Muzzarelli & Muzzarelli, 2005; Muzzarelli et al., 2012) and especially, as materials for controlled drug delivery (Park, Saravanakumar, Kim, & Kwon, 2010; Puga, Lima, Mano, Concheiro, & Alvarez-Lorenzo, 2013; Wei, Cai, Lin, Wang, & Zhang, 2011; Zhang, Mardyani, Chan, & Kumacheva, 2006). http://dx.doi.org/10.1016/j.carbpol.2014.04.087 0144-8617/© 2014 Elsevier Ltd. All rights reserved.