Self-assembled interpenetrating networks from synthetic polymers

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Double-network hydrogels as a special type of interpenetrating polymer networks are a group of highly investigated innovative materials, giving a promising chance for future development of artificial tissue research. They consist of two independently cross-linked, water-filled polymer networks that are topologically interlocked. A mechanical synergism between the two networks gives such composite hydrogels unique mechanical properties like high strength and toughness. Covalently cross-linked double networks, however, have the draw-back that they cannot recover from suffered damage and that, once prepared, the materials are fixed and hard to process.

Our aim is to develop and study a new class of double polymer network hydrogels, based on physical rather than chemical cross-links. Because physical bonds can form and break reversibly in response to external triggers, such physically cross-linked networks will be responsive and self-healing, producing materials that are not only tough, but also smart.

As a base of our composites we use terpyridine-modified high-molecular-weight telechelic polymers, which in the presence of transition metal ions form linear supramolecular chains.

Supramolecular Assembly of Self-Healing Nanocomposite Hydrogels

In this work we develop a strategy for the bottom-up assembly of transparent and homogeneous composite hydrogels formed exclusively through non-covalent bonding. 

First, we create colloidal building blocks through spontaneous adsorption of terpyridine end-capped polymers onto silica nanoparticles. Subsequently, these multivalent tectons are  assembled into composite hydrogels by addition of Co(II) ions, creating transient metal-coordination linkages between the particles (Figure 1). We show that the mechanics of the resulting networks can be tuned over many orders of magnitude and that, upon breaking, these networks spontaneously restore their mechanical properties within several minutes.

References

M. Gerth, M. Bohdan, R. Fokkink, J. van der Gucht & J. Sprakel. Supramolecular Assembly of Self-healing nanocomposite hydrogels. Macromolecular Rapid Communications, 2014.