SOFT-STIFF HYBRID HYDROGELS

Abstract

Many structures in nature, such as the squid beak, have a combination of stiff and soft parts with very different mechanical properties – for example, the elastic modulus of the stiff part can be about 100 times that of the soft part. Researchers are interested in mimicking these types of structures using hydrogels, but have not succeeded in synthesizing gels with such dramatic variations in mechanical properties. In this work, we describe the synthesis of hybrid hydrogels in which one portion of the gel is very stiff while the other portion is soft. The stiff portion is a nanocomposite made by copolymerizing conventional acrylate monomers and silica precursors. The soft portion is a conventional polymeric gel made from acrylates. We use a technique developed in our lab to form hybrid gels in which the stiff and soft parts are integrated together into a whole while keeping strong interfaces between the parts. Rheological measurements show that the elastic modulus of the stiff part is more than 100 times that of the soft part. This ratio of moduli is the highest reported to date and is three times the ratio in the squid beak. Such soft-stiff gels could have applications in bioengineering, e.g., in interfacing stiff medical implants with soft tissues.