Tough fully physically crosslinked double network hydrogel for tissue engineering

Abstract

formed from hydrophilic polymers swollen in large amounts of water (more 70 %). Their structure provides them with physical characteristics similar to soft tissues. Nevertheless, conventional single network hydrogels typically exhibit poor mechanical properties. For hydrogels to be able to be applied as scaffold material, they must mimic the mechanical properties of structural soft tissues. Double network (DN) hydrogels, composed of two independent networks exhibiting different mechanical properties, were developed as a strategy to improve the toughness. However, chemically crosslinked DN hydrogels often exhibit poor self-healing properties and low fatigue resistance due to the irreversible chain rupture in covalently crosslinked networks upon deformation. To overcome this problem, we propose a fully physically crosslinked DN hydrogel formed by ionic coordination and hydrogen bonding. Herein, we successfully synthesized a new Ca-Alg/PNAGA DN hydrogels consisting of ionically crosslinked alginate and hydrogen-bonded poly(N-acryloyl glycinamide). We demonstrated the stability of the hydrogen bond among the amide motifs of the PNAGA SN hydrogels and the impact of the incorporations of alginate on the mechanical properties. Also, we demonstrated that photo-polymerized hydrogels exhibited better mechanical properties than thermally polymerized hydrogels. Additionally, we demonstrated that mechanical properties higher than the PNAGA SN hydrogels can be obtained after the incorporation of alginate monomers.