Tuning Mechanical Properties of Chondroitin Sulfate-Based Hydrogels Using the Double-Network Strategy
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Tuning Mechanical Properties of Chondroitin Sulfate-Based Hydrogels Using the Double-Network Strategy Tiffany C Suekama1, Anahita Khanlari1 and Stevin H Gehrke1 1 Chemical & Petroleum Engineering, University of Kansas, Lawrence, KS, United States ABSTRACT The double-network (DN) hydrogel concept developed by J.P. Gong and Y. Osada builds upon interpenetrating networks by combining brittle and ductile components to have significantly enhanced fracture properties. The generality of the DN effect was tested by creating biopolymer-based hydrogels of methacrylated chondroitin sulfate (MCS) and polyacrylamide (PAAm) and extended upon creating DNs of MCS and poly(N,N dimethyl acrylamide) (PDMAAm), verifying that DNs were not limited to the original combination of poly(2acrylamido-2-methylpropanesulfonic acid) (PAMPS)/polyacrylamide (PAAm). Further, the mechanical properties were varied by changing the monomer concentrations, cross-linker concentrations and the addition of cross-linking groups through copolymerizations of MCS and poly(ethylene glycol) diacrylate (PEGDA). Overall, this work demonstrates that a broad range of mechanical properties achievable through DN effect under tension and compression, generally independent of the swelling degree, which is fundamentally different behavior than possible with single networks. INTRODUCTION Hydrogels are excellent materials for the tissue engineering field due the high water content which is similar to biological tissues. However, hydrogels typically are mechanically weak materials, but by using the double-network (DN) strategy researchers have improved toughness and fracture properties in hydrogels. In fact, the mechanical properties of DN hydrogels are similar to soft load-bearing biotissues and rubbers [1]. DN hydrogels are tough and ductile networks produced from a highly cross-linked (typically polyelectrolyte) first network with a lightly cross-linked (typically neutral) second network. DN’s are recognized from their improved properties relative to either single network alone. The enhanced mechanical properties are linked to the internal microfracturing that results in strain energy dissipation. Furthermore, DN hydrogels can have 3 characteristic regions (preyielding, yielding and hardening) with a clear yielding point (transition between preyielding and yielding) that is particularly unusual behavior for hydrogels. Recently, we have demonstrated the utility of the DN concept to a DN gel based on the biopolymer, chondroitin sulfate (CS). CS is a glycosaminoglycan which is a significant structural component of aggrecan [2,3]. CS is modified by adding methacrylate groups allowing for the biopolymer to form a hydrogel upon photopolymerization. These MCS networks have been used in different matrices for tissue engineering [4-7].
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EXPERIMENTAL METHODS Here the experimental methods are outlined. Further details of materials can be found in our recently published papers [5,8]. The methacrylation of MCS used in this report was determined by NMR to be 34.5% after 15 days of
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