Molecular Staples for Tough and Stretchable Adhesion in Integrated Soft Materials

TLDR

Soft materials such as tissues, gels, and elastomers are increasingly integrated, but conventional hard‑polymer adhesives constrain their deformation and are unsuitable for such interfaces. This study proposes a design principle that employs hard polymers to create tough adhesion between soft materials that can withstand repeated large‑strain cycles. The approach forms nanoscale islands of hard polymer at the interface of two stretchable polymer networks, ensuring the islands are strong, topologically entangled with the networks, and smaller than the flaw‑sensitivity length, thereby achieving stretchable yet tough bonding. The principle enables many hard polymers to form tough and stretchable adhesion between soft materials.

Abstract

The integration of soft materials-biological tissues, gels, and elastomers-is a rapidly developing technology of this time. Whereas hard materials are adhered using adhesives of hard polymers since antiquity, these hard polymers are generally unsuited to adhere soft materials, because hard polymers constrain the deformation of soft materials. This paper describes a design principle to use hard polymers to adhere soft materials, such that adhesion remains tough after the adhered soft materials are subject to many cycles of large stretches in the plane of their interface. The two soft materials have stretchable polymer networks, but need not have functional groups for adhesion. The two soft materials are adhered by forming, in situ at their interface, islands of a hard polymer. The adhesion is tough if the islands themselves are strong, and the polymers of the islands are in topological entanglement with the polymer networks of the soft materials. The adhesion is stretchable if the islands are smaller than the flaw sensitivity length. Several methods of forming the hard polymer islands are demonstrated, and the mechanics and chemistry of adhesion are studied. The design principle will enable many hard polymers to form tough and stretchable adhesion between soft materials.