Biopolymer Based Tough and Self-Recovering Ionic-Covalent Entanglement Hydrogels
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Biopolymer Based Tough and Self-Recovering Ionic-Covalent Entanglement Hydrogels Damian M. Kirchmajer1 and Marc in het Panhuis1 1
Soft Materials Group, School of Chemistry and Intelligent Polymer Research Institute, ARC Centre of Excellence for Electromaterials Science, AIIM Facility, University of Wollongong, Wollongong, NSW 2522, Australia ABSTRACT Emerging applications for hydrogels such as soft robotics and tissue engineering require hydrogels with enhanced mechanical performance. We report the mechanical characteristics of two types of hydrogels: i) ionic-covalent entanglement (ICE) network hydrogels based on calcium cross-linked gellan gum and genipin cross-linked gelatin and ii) ICE microsphere reinforced gelatin hydrogels. This investigation showed that ICE gels can recover up 80% of their mechanical behavior during 5 repeated compressions. In addition, the optimum mechanical performance of gelatin reinforced gels was achieved with inclusion of 40% of ICE microspheres. INTRODUCTION Hydrogels are a class of polymeric materials whose composition comprises a small fraction of hydrophilic polymer network with water or aqueous solution as the major fraction. New and emerging applications of hydrogels such as soft robotics [1] and tissue engineering [2] require hydrogels with enhanced mechanical performance which has stimulated an investigation into how hydrogels may be made tougher and more enduring. The well-known double network approach has been recently adapted for the formation of tough, IPN hydrogels in a “one-pot” synthetic approach [3-5]. These new hydrogels referred to as ionic-covalent entanglement (ICE) network hydrogels consist of a tough and self-recovering, interpenetrating network of an ionotropic polymer and a chemically cross-linkable polymer. Gellan gum is an anionic polysaccharide biopolymer derived from the bacteria Pseudomonas elodea [6]. It comprises a tetrasaccharide repeating unit structure of β-D-glucose, β-D-glucuronic acid and α-L-rhamnose with varying degrees of acetylation. Gelatin is a denatured and partially hydrolysed protein produced from collagen – a biopolymer present in almost all connective tissue in the human body [7]. Gelatin is a highly versatile biopolymer which can be obtained from a variety of animal sources, is cheap, and can be produced at a range of isoelectric points, molecular weights and gel strengths. In this paper, we report on the mechanical characteristics of ICE network hydrogel based on the biopolymers gellan gum (calcium cross-linked) and gelatin (genipin cross-linked) as well as gelatin hydrogels reinforced with ICE microspheres. EXPERIMENT ICE hydrogels were prepared as follows: gellan gum (low acyl form, lot #1/1443A, Gelzan-CM, CP Kelco, Singapore) was added to 80˚C DI water (resistivity 18.2 MΩ cm) with rapid stirring until dissolved on a hot plate/stirrer. Type A, porcine gelatin (Bloom number 300,
molecular weight 87.5 kDa, Sigma Aldrich, USA)was then added and stirred until dissolved. Subsequently, 1 M CaCl2 solution and 20.3% (w/v) genipin was add
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