Carbohydrate Polymers 151 (2016) 1073–1081 Contents lists available at ScienceDirect Carbohydrate Polymers j ourna l ho me page: www.elsevier.com/locate/carbpol Influence of natural and synthetic crosslinking reagents on the structural and mechanical properties of chitosan-based hybrid hydrogels I.M. Garnica-Palafox a,b , F.M. Sánchez-Arévalo a,∗ a Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apdo. Postal 70-360, Cd. Universitaria, Cd. de México 04530, Mexico b Posgrado en Ciencia e Ingeniería de Materiales, Universidad Nacional Autónoma de México, Apdo, Postal 70-360, Cd. Universitaria, Cd. de México 04530, Mexico a r t i c l e i n f o Article history: Received 26 February 2016 Received in revised form 7 June 2016 Accepted 8 June 2016 Available online 17 June 2016 Chemical compounds studied in this article: Chitosan (PubChem CID: 71853) Polyvinyl alcohol (PubChem CID: 11199) Genipin (PubChem CID: 442424) Glutaraldehyde (PubChem CID: 3485) Keywords: Chitosan Poly(vinyl alcohol) Hybrid hydrogels Genipin Glutaraldehyde a b s t r a c t The objective of this work was to correlate the physical and chemical properties of chitosan/poly(vinyl alcohol)/genipin (CS/PVA/GEN) and chitosan/poly(vinyl alcohol)/glutaraldehyde (CS/PVA/GA) hydrogels with their structural and mechanical responses. In addition, their molecular structures were determined and confirmed using FTIR spectroscopy. The results indicated that the hybrid hydrogels crosslinked with genipin showed similar crystallinity, thermal properties, elongation ratio and structural param- eters as those crosslinked with glutaraldehyde. However, it was found that the elastic moduli of the two hybrid hydrogels were slightly different: 2.82 ± 0.33 MPa and 2.08 ± 0.11 MPa for GA and GEN, respec- tively. Although the hybrid hydrogels crosslinked with GEN presented a lower elastic modulus, the main advantage is that GEN is five to ten thousand times less cytotoxic than GA. This means that the structural and mechanical properties of hybrid hydrogels crosslinked with GEN can easily be tuned and could have potential applications in the tissue engineering, regenerative medicine, food, agriculture and environmental industries. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, natural and synthetic hydrogels have been developed to meet specific human requirements in different fields, such as the agricultural, environmental, food and even medi- cal industries (Chawla, Srivastava, Pandey, & Chawla, 2014). The synthetic hydrogels that have frequently been used in the afore- mentioned fields are poly(ethylene glycol) (PEG), poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) (Chawla et al., 2014). PVA has some particular advantages; among them, it has been reported to possess very low toxicity, hydrophilic behavior and a high elastic response. Nevertheless, PVA is soluble in water. This property could be disadvantageous for some applications; however, PVA has been widely used in applications such as articular cartilage and pancreas regeneration (Baker, Walsh, Schwartz, & Boyan, 2011; Paradossi, 2013, Chapter 2), drug-eluting ∗ Corresponding author. E-mail address: fsanchez@iim.unam.mx (F.M. Sánchez-Arévalo). contact lenses (Carreira et al., 2014), sensors for biological vari- ables (Carmona, Martinez, Londo no, Montoya, & Torres, 2015; Tou, Koh, & Chan, 2014) and even for capturing organic dyes and metal- lic ions (Hui, Zhang, & Ye, 2015; Li, She, She, Dai, & Kong, 2014). Natural hydrogels such as collagen, gelatin, alginate, agarose and chitosan (CS) are very attractive and are commonly used for biolog- ical applications. These hydrogels take advantage of their excellent biocompatibility properties (Sionkowska, 2013, Chapter 11); how- ever, natural hydrogels do not meet the load requirements for specific applications due to their poor mechanical properties. Fur- thermore, their mechanical properties have to be tuned. The combination of synthetic and natural hydrogels has pro- duced the so-called hybrid hydrogels; due to their easy preparation and the miscibility of PVA in CS, the CS/PVA blend is now one of the most used hybrid hydrogels (El-Hefian, Nasef, & Yahaya, 2010; Naveen Kumar et al., 2010). This blend benefits from the high elasticity of PVA and the good strength and biocompatibility of CS; therefore, the resulting blend, using the correct propor- tions of synthetic and natural hydrogels, could possess mechanical properties that are similar to those of human tissues. However, http://dx.doi.org/10.1016/j.carbpol.2016.06.036 0144-8617/© 2016 Elsevier Ltd. All rights reserved.