Semiflexible biopolymers networks such as actin, fibrin, and collagen display interesting mechanical responses such as strain-stiffening at large shear strain and negative normal stress associated with it. Although polysaccharide networks are common, many aspects of the deformation and failure behavior are unknown. This work investigates the mechanical properties of a model polysaccharide network, ionically crosslinked alginate hydrogel. Rheological investigations were conducted on the samples obtained through in situ gelation in a rheometer using divalent calcium salts. Polymer (alginate) fraction was kept constant (1 wt%) and Ca2+ concentration was varied to obtain hydrogels with different crosslink densities. Similar to many biopolymer networks, in addition to strain-stiffening behavior, we captured negative normal stress for alginate gels, which has never been reported in literature. Failure behavior of these gels was studied using cavitation rheology technique. The critical pressure of fracture scales with the crosslinking density and defect size.

Strain stiffening and negative normal stress in alginate gels

251st National Meeting (2016)

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