Progress Toward Robust Polymer Hydrogels

Abstract

In this review we highlight new developments in tough hydrogel materials in terms of their enhanced mechanical performance and their corresponding toughening mechanisms. These mechanically robust hydrogels have been developed over the past 10 years with many now showing mechanical properties comparable with those of natural tissues. By first reviewing the brittleness of conventional synthetic hydrogels, we introduce each new class of tough hydrogel: homogeneous gels, slip-link gels, double-network gels, nanocomposite gels and gels formed using poly-functional crosslinkers. In each case we provide a description of the fracture process that may be occurring. With the exception of double network gels where the enhanced toughness is quite well understood, these descriptions remain to be confirmed. We also introduce material property charts for conventional and tough synthetic hydrogels to illustrate the wide range of mechanical and swelling properties exhibited by these materials and to highlight links between these properties and the network topology. Finally, we provide some suggestions for further work particularly with regard to some unanswered questions and possible avenues for further enhancement of gel toughness.

Improving hydrogels׳ toughness by increasing the dissipative properties of their network

“…The obtained noncovalent cross-linked hydrogels usually present a high degree of toughness. However, the stiffness of noncovalent cross-linked hydrogels is significantly lower than covalent cross-linked ones (Sun et al, 2012;Haque et al, 2011;Naficy et al, 2011). Noncovalent cross-linked hydrogels can then not be used in load bearing biomedical applications, where a high degree of stiffness and toughness are simultaneously needed.…”

A phase diagram of neutral polyampholyte – from solution to tough hydrogel

“…The inventions of several strong and tough hydrogels in the early 2000s have greatly expanded the potential possibility of this material [9][10][11][12][13] and initiated many researches to develop high strength hydrogels. [14][15][16][17][18][19][20][21] These studies have also stimulated the fundamental researches on the fracture mechanics of soft and wet materials. [22][23] Studies on the double-network (DN) gels, one of the toughest hydrogels consisting of interpenetrating brittle and ductile networks, have indicated that the internal rupture of the brittle network, which effectively dissipates energy and prevents catastrophic crack propagation upon loading, gives the extraordinarily high toughness.…”

Effect of First Network Topology on the Toughness of Double Network Hydrogels

“…Until quite recently, synthetically produced hydrogels were notoriously brittle and applications somewhat limited 1 . In the past decade or so, several new tough hydrogels have been introduced that have opened up the possibility of new applications, particularly in biomedicine.…”