Colloids and Surfaces B: Biointerfaces 86 (2011) 409–413 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces journal homepage: www.elsevier.com/locate/colsurfb Short communication Layered hydrogel of poly(-glutamic acid), sodium alginate, and chitosan: Fluorescence observation of structure and cytocompatibility Yen-Hsien Lee a , Jung-Jhih Chang b , Wen-Fu Lai c , Ming-Chien Yang b,∗ , Chiang-Ting Chien d,∗∗ a Graduate Institute of Engineering, National Taiwan University of Science and Technology, Taipei, 106, Taiwan, ROC b Department of Materials Science and Engineering, National Taiwan University of Science and Technology Taipei, 106, Taiwan, ROC c Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, 110, Taiwan, ROC d Department of Medical Research, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, 100, Taiwan, ROC article info Article history: Received 14 February 2011 Received in revised form 29 March 2011 Accepted 1 April 2011 Available online 9 April 2011 Keywords: Alginate Chitosan Poly(-glutamic acid) Fluorescence labeling Hydrogel abstract In this study, a novel layered hydrogel composing of poly(-glutamic acid) (PGA), chitosan (CS), and alginate (AL) were prepared. Furthermore, PGA, CS, and AL were labeled with different fluorescent dyes. The bilayer structure of hydrogel was then revealed using these fluorescent labeled polymers. To mimic the stability of these hydrogels in physiological fluids, the dissolution of PGA and the release of Ca 2+ from these hydrogels in normal saline were also monitored. The results showed that by adding CS to the hydrogel, the dissolution of PGA was decreased by 67%, and the release of Ca 2+ was reduced by 40%. In addition, the hydrogel exhibited no cytotoxicity for L929 fibroblasts. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Hydrogels are polymeric networks that absorb large amount of water while remaining insoluble in aqueous solutions due to chemical or physical crosslinking of individual polymer chains [1]. The physical gels are held together by molecular entanglements, non-covalent bonds, such as hydrophobic interactions, hydrogen bonding, ionic interactions, and van der Waals interactions. In chemical gels polymer chains are connected by covalent bonds [2]. In addition, when a polyelectrolyte is combined with a multivalent ion of the opposite charge, it may form a physical hydrogel known as an ‘ionotropic’ hydrogel [3]. Furthermore, when polyelectrolytes of opposite charges are mixed, the products of such ion-crosslinked systems are known as polyion complexes, or polyelectrolyte com- plexes [3]. Hydrogels can be prepared from natural or synthetic poly- mers [1,4]. Natural polymers, such as polysaccharides and proteins, have also been used as the structural material in hydrogels. Poly(-glutamic acid) (PGA), sodium alginate (AL) and chitosan (CS), have received much attention in biomedical applications of drug delivery and tissue engineering [5–7]. In the literature, ∗ Corresponding author. Tel.: +886 2 2737 6528; fax: +886 2 2737 6544. ∗∗ Corresponding author. Tel.: +886 2 2312 3456x5720; fax: +886 2 2394 7927. E-mail addresses: myang@mail.ntust.edu.tw (M.-C. Yang), ctchien@ntuh.gov.tw (C.-T. Chien). polyanion–polycation complexes formed from alginate and chi- tosan have been investigated and their drug release properties have been studied [5]. Dash et al. used CS/PGA hollow spheres to inves- tigate the effect of size and surface charge on cell viability and cellular internalization behavior and their effect on various blood components [6]. Imoto et al. prepared novel biodegradable hollow nanocapsules composed of CS and PGA [8]. In our laboratory, we successfully prepared AL/PGA hydrogels film as wound dressing and drug release carrier [9]. Fluorescent dyes have been employed to study the structure of polymeric matrices. Ma et al. used confocal laser scanning microscopy (CLSM) to observe the even distribution of rhodamine- labeled collagen (CL) and FITC-labeled CS in the scaffold [10]. Chen et al. visualized individual components with FITC-labeled CS and rhodamine-labeled collagen in the electrospun membranes [11]. Hsieh et al. observed the distribution of two components in a com- posite of rhodamine B-labeled CS and FITC-labeled PGA [6]. Hsu et al. examined the nanofibers comprising of CL and hyaluronic acid (HA) using FITC-labeled CL and rhodamine-labeled HA under a fluorescence microscope [12]. Recent years, numerous studies of wound dressing with layered structure were fabricated to promote wound healing. Bishop et al. prepared a multilayered wound dressing for wounds producing high levels of exudate. Their dressing is comprised of a transmis- sion layer, an absorbent core, and a wound contacting layer, which transmits exudate to the absorbent core, the absorbent core and wound contacting layer limiting the lateral extend of exudate in the 0927-7765/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2011.04.002