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Mechanical Performance and Microstructure of Biomimetic PEG-Agarose Interpenetrating Networks as Determined by Dynamic Mechanical Analysis and AFM

Joseph Lomakin, Chemical and Petroleum Engineering, Kansas University, The University of Kansas, 4132 Learned Hall 1530 W. 15th Street, Lawrence, KS 66045, Michael Detamore, Dept. of Chemical & Petroleum Engineering, University of Kansas, 1530 W. 15th St., 4132 Learned Hall, Lawrence, KS 66045, and Stevin H. Gehrke, Departments of Chemical & Petroleum Engineering and Pharmaceutical Chemistry, University of Kansas, 1530 W 15th Street, Lawrence, KS 66045-7609.

The combination of rigid macromolecules embedded in a ductile matrix is common to a wide variety of biological structural composites such as the mammalian extracellular matrix, insect cuticle and crustacean exoskeleton. Novel synthetic materials that mimic this biological organization have recently been shown to possess exceptional mechanical properties with Young's modulus and toughness values orders of magnitude greater than that of individual composite components.

In keeping with this biological design principle, an interpenetrating network (IPN) of PEG-diacrylate in agarose is synthesized and investigated as a novel composite material mimetic of the insect cuticle. The cuticle is largely composed of chitin fibers interpenetrated with a protein matrix. In this synthetic construct, agarose is selected to mimic the role of chitin and the PEG-diacrylate to mimic the role of the cuticular proteins. These materials were also selected because of their utility in a variety of biomedical applications. The interpenetrating networks are formed by photopolymerization of thermally gelled agarose gels soaked in aqueous solution of PEG-diacrylate (700 Da). The resulting IPN hydrogels as well as single networks of crosslinked PEG-diacrylate and agarose are investigated with respect to their compressive mechanical performance via transient and dynamic mechanical analysis. The toughness of initial formulations of agarose-PEG-DA gels has been determined to be 100 times greater than that of agarose and 5 times greater than that of a crosslinked PEG-diacrylate network. The biological potential of the synthesized networks is further established by demonstrating effective chondrocyte encapsulation with high long term cell viability within the novel biomaterial.

The mechanical properties obtained in macroscopic studies depend on the nanoscale material structure and mechanical properties as probed by submerged AFM. AFM is used to determine pore sizes and microscale organization of agarose and PEG-DA polymers. The heterogeneity of compression modulus on the micron scale is assessed, as this is considered an important parameter underlying the exceptional mechanical properties of interpenetrating networks.