Tough Hydrogels: Toughening Mechanisms and Their Utilization in Stretchable Electronics and in Regenerative Medicines

摘要

Synthetic hydrogels, the key material for use in contact lenses, wound dressings, cosmetics, and scaffolds for tissue engineering, have been considered mechanically weak and brittle materials. Inspired by natural hydrogels that are mechanically tough and robust, such as muscles and cartilages, there has been extensive research in improving mechanical strengths of hydrogels during the last decade. Consequently, proof-of-concept devices of many unprecedented applications, such as bioimplantable electronics, sensors/actuators in soft machines, surgical glues, and gel electrolytes for energy storage devices, are rapidly realized in recent years. In this chapter, we intend to review a comprehensive perspective regarding the field of tough hydrogels: from physical and chemical fundamentals to applications in various fields. We review the concept of fracture toughness to explain design criteria for tough hydrogels. Sticky hydrogel, a promising subgroup of tough hydrogels, requires distinctive chemistry and characterization methods, so it is separately reviewed. Incorporating nanoscale hard material can add desirable mechanical and functional properties to tough hydrogels. We review various interface modification techniques for the hard/soft material integration, as well as for electronic device integration. Finally, advances in the applications of tough hydrogels in stretchable electronics and soft robotics and in regenerative medicine are reviewed.