Effect of void structure on the toughness of double network hydrogels

Abstract

Introduction of soft filler in a hard body, which is one of the common toughening methods of hard polymeric materials, was applied for further toughening of robust double network (DN) hydrogels composed of poly(2-acrylamido-2-methylpropanesulfonic acid) gels (PAMPS gels) as the first component and polyacrylamide (PAAm) as the second component. The fracture energy of the DN gels with the void structure (called void-DN gels) became twice when the volume fraction of void was 1-3 vol % and the void diameter was much larger than the Flory radius of the PAAm chains. Such toughening was induced by wider range of internal fracture of the PAMPS network derived from partial stress concentration near void structure. Considering the mechanical tests and the dynamic light scattering results, it is implied that the absence of the load-bearing PAAm structure inside the void is important for the toughening.

Extremely strong and tough hydrogels as prospective candidates for tissue repair – A review

“…This concept was proved to be general and independent of specific chemical interactions between the two networks. [107,115] To date, several tough hydrogels with different macromolecular designs based on DN methodology have been reported such as void-DN gels, [116] inverse DN gels, [117] liquid crystalline DN gels, [118] microgel-reinforced hydrogels [119] and ultra-thin DN gels. [120] One of these tough hydrogels pairs consists of poly (2-acrylamido-2methylpropanesulfonic acid) (PAMPS) as the first network and PAAm as the second structure.…”

Progress of key strategies in development of electrospun scaffolds: bone tissue

“…PAAm) chains can bridge the void gap and create additional stress on the void. Above the critical void size, the chains are too small to bridge the gap and the void can form a true hollow stress-free structure [38].…”

Toughening hydrogels by immersing with oppositely charged polymers

“…Double network (DN) gels are composed of a highly cross‐linked and hence rigid and brittle first network and a less cross‐linked or even uncross‐linked soft and ductile second network, in which the first network breaks into small clusters under a load and the clusters act as the cross‐linking points . Progress related to these hydrogels focuses on their more convenient preparations, enhancing mechanical properties and more detailed studies on their structure–property relationships …”

“…13 Progress related to these hydrogels focuses on their more convenient preparations, enhancing mechanical properties and more detailed studies on their structure-property relationships. [14][15][16][17][18][19][20][21][22][23] In recent years, more attention has been paid to the preparation of tough hydrogels by utilizing physical interactions, such as hydrophobic force, [24][25][26] hydrogen bonding, 27,28 hostguest interactions, 29 electrostatic interactions, 30 crystallization, 31 and complexation, 30 . Mostly, the physical interactions are combined with covalent chemical cross-links to improve the mechanical properties of the gels, and in some cases, several physical interactions are employed together.…”