Preparation And Properties Of Joint Double Network Hydrogels With High Mechanical Strength

Hydrogels,as a type of soft and wet materials,composed of three-dimensional polymer network structure and large amount of water.They have a wide range of applications,such as drug delivery systems,superabsorbent materials,soft electronics,contact lenses and tissue engineering scaffold.Because of its good water absorption and water retention,hydrogels are similar to human tissues.Therefore,hydrogels have been systematic researched as a substitute for tissues and organs.However,most of hydrogels suffered from poor mechanical strength compared with hydrogel-like bio-tissues such as cartilage,tendon,muscle,and blood vessel,which caused by the lack of efficient energy dissipation mechanism in the network.Therefore,the research on hydrogels with excellent mechanical properties has become the emphasis for material scientists.Over the past decades,scientists have developed various toughening mechanisms to reinforce hydrogels,such as topological hydrogels,nanocomposite hydrogels,treta-PEG hydrogels,macromolecular microspheres hydrogels,hydrophobic association hydrogels,semi-IPN hydrogels and double-network hydrogels.In the study of strengthening hydrogels by designing structure,the traditional single-network hydrogels appeared at the beginning,with the development of research,dually cross-linked single network,interpenetrating networks,and double-network hydrogels appeared gradually.These different network structures improved the mechanical properties of hydrogels and developed other excellent properties.DN hydrogels were constructed by taking a rigid molecular chain as the first network and another flexible molecular chain as the second network.The loose cross-linked second network can enhance the toughness by dispersing the stress and stopping the crack.Based on the tough double-network hydrogel,a novel further crosslinked DN network hydrogel was developed and named joint double network?JDN?hydrogel.The JDN hydrogel consisting of ionically cross-linked sodium alginate?SA?as the first network,the chemically cross-linked poly?acrylamide-acrylic acid??PAMAAc?as the second network and both of them combined together by ferric ions.As a result,SA/PAMAAc-Fe³⁺hydrogels exhibited high mechanical strength with tensile stress of 1.26 MPa and tensile strain of 653%under a 10%AAc content.Ultraviolet–visible spectroscopy,rheological and swelling tests also illustrated that the JDN structure greatly improved the mechanical properties of hydrogels because of close integration of internal networks.Moreover,the SA/PAMAAc-Fe³⁺JDN hydrogel also owned high water content of 85%,free-plasticity,load-bearing process,compression,folding,puncture resistant and excellent electrical property,which allowed it to be easily molded various shapes for tough electronic devices,flexible electrodes,and wearable equipment.