Structural characteristics of thermosensitive chitosan glutamate hydrogels in variety of physiological environments Z. Modrzejewska a,⇑ , K. Nawrotek a , W. Maniukiewicz b , T. Douglas c a Faculty of Process and Environmental Engineering, Lodz University of Technology, Wólczan ´ska 175, 90-924 Lodz, Poland b Institute of General and Ecological Chemistry, Lodz University of Technology, _ Zeromskiego 116, 90-924 Lodz, Poland c Polymer Chemistry and Biomaterials Group, Ghent University, Krijgslaan 281 S4, 9000 Gent, Belgium highlights  Properties of thermosensitive chitosan glutamate are presented (FTIR, WAXS).  Determined changes in hydrogel after conditioning in water, buffer at pH 7 and pH 2.  On the basis of structure changes in water a mechanism formation was proposed. article info Article history: Received 28 January 2014 Received in revised form 20 May 2014 Accepted 11 June 2014 Available online 19 June 2014 Keywords: Hydrogel Chitosan Natural polymer Structural properties abstract In this paper the properties of thermosensitive chitosan hydrogels prepared with the use of chitosan glu- tamate and b-glycerophosphate are presented. The study is focused on the determination of changes in the hydrogel structure in different environments: during conditioning in water and buffer at pH 7 and pH 2 respectively. The structure of gels was observed under the Scanning Electron Microscopy (SEM) and was investigated by infrared (IR) spectroscopy. The crystallinity of gel structure was determined by X- ray diffraction analysis (XRD). On the basis of structural changes during the conditioning in water a mechanism of their formation was proposed. Ó 2014 Elsevier B.V. All rights reserved. Introduction Over the last few years, much attention has been paid to hydro- gels prepared from both natural and synthetic or hybrid polymers [1]. Hydrogels from natural polymers are produced mainly from:  proteins (collagen, gelatin, fibrin, silk, lysozyme, Matrigel™, and genetically engineered proteins such as calmodulin (a calcium- binding protein), elastin-like polypeptides and leucine zipper);  polysaccharides such as hyaluronic acid (HA), agarose, dextran and chitosan;  and hybrid systems: protein/polysaccharide hybrid polymers, such as collagen/HA, laminin/cellulose, gelatin/chitosan and fibrin/alginate;  DNA X-, Y-, T-DNA, linear plasmid DNA. Hydrogels from synthetic polymers are formed from nonbiode- gradable and biodegradable polymers. Nonbiodegradable synthetic hydrogels PHEMA, PHPMA, PNI- PAm, can be prepared by copolymerization of various vinylated monomers or macromers such as 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), acrylamide (AAm), acrylic acid (AAc), N-isopropylacrylamide (NIPAm) and methoxyl poly(ethylene glycol) (PEG) monoacrylate (mPEGMA or PEGMA), with crosslinkers such as N,N 0 -methylenebis(acrylamide) (MBA), ethylene glycol diacrylate (EGDA) and PEG diacrylate (PEG- DA) Ò . Another method to form nonbiodegradable hydrogels is to use nonbiodegradable polymers such as self-assembly of Pluronic Ò polymers with a structure of poly(ethylene oxide) (PEO)–poly(pro- pylene oxide) (PPO)–PEO, chemical cross-linking of modified poly(- vinyl alcohol) (PVA), and radiation cross-linking of linear or branched PEG. Biodegradable synthetic hydrogels are mostly produced from polyesters. These are often hybrid systems containing poly(lactic http://dx.doi.org/10.1016/j.molstruc.2014.06.037 0022-2860/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +48 426313726. E-mail address: zofia.modrzejewska@p.lodz.pl (Z. Modrzejewska). Journal of Molecular Structure 1074 (2014) 629–635 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc