Solvent control of crack dynamics in a reversible hydrogel

The resistance to fracture of reversible biopolymer hydrogels is an important control factor of the textural characteristics of food gels1 (such as gummy candies and aspic preparations). It is also critical for their use in tissue engineering, for which mechanical protection of encapsulated components is needed2,3. Its dependence on loading rate4 and, recently, on the density and strength of crosslinks3 has been investigated. But, so far, no attention has been paid to solvent or to environment effects. Here we report a systematic study of crack dynamics in gels of gelatin in water/glycerol mixtures. We show in this model system that increasing solvent viscosity slows down cracks; moreover soaking with solvent markedly increases gel fragility; finally tuning the viscosity by adding a miscible liquid affects crack propagation through diffusive invasion of the crack tip vicinity. The results highlight the fact that fracture occurs by viscoplastic chain pull-out. This mechanism, as well as the related phenomenology, should be common to all reversibly crosslinked (physical) gels.

[1]  D. Mooney,et al.  Hydrogels for tissue engineering. , 2001, Chemical reviews.

[2]  P. Janmey,et al.  Dynamic Viscoelastic Properties of Gelatin Gels in Glycerol‐Water Mixtures , 1980 .

[3]  A. Clark,et al.  Large deformation and ultimate properties of biopolymer gels: 1. Single biopolymer component systems , 1985 .

[4]  T. Vliet.  Large deformation and fracture behaviour of gels. , 1996 .

[5]  B. Lawn.  Fracture of Brittle Solids by Brian Lawn , 1993 .

[6]  Toyoichi Tanaka,et al.  Spectrum of light scattered from a viscoelastic gel , 1973 .

[7]  D. Mooney,et al.  Independent Control of Rigidity and Toughness of Polymeric Hydrogels , 2003 .

[8]  Bonn,et al.  Delayed fracture of an inhomogeneous soft solid , 1998, Science.

[9]  R. Rivlin,et al.  Rupture of rubber. I. Characteristic energy for tearing , 1953 .

[10]  K. Nishinari,et al.  On the temperature dependence of elasticity of thermo-reversible gels , 1985 .

[11]  Brian Lawn,et al.  Fracture of brittle solids: References and reading list , 1993 .

[12]  P. Higgs,et al.  Some ideas concerning the elasticity of biopolymer networks , 1989 .

[13]  D. L. Johnson,et al.  Elastodynamics of gels , 1982 .

[14]  A. Thomas,et al.  The strength of highly elastic materials , 1967, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[15]  A. Thomas,et al.  Rupture of rubber , 1960 .

[16]  A. Onuki.  Theory of phase transition in polymer gels , 1993 .

[17]  Self-healing slip pulses and the friction of gelatin gels , 2003, The European physical journal. E, Soft matter.

[18]  A. Jagota,et al.  Crack blunting and the strength of soft elastic solids , 2003, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[19]  P. Higgs,et al.  Creep measurements on gelatin gels. , 1990, International journal of biological macromolecules.

[20]  J. Gornall,et al.  Induced helicity in biopolymer networks under stress. , 2005, Proceedings of the National Academy of Sciences of the United States of America.