Dual Crosslink Hydrogels with Metal-Ligand Coordination Bonds: Tunable Dynamics and Mechanics Under Large Deformation
Introducing additional physical and reversible crosslinks to a chemically crosslinked hydrogel is an interesting and viable alternative to increase the toughness of a hydrogel. Yet while in general the physical crosslink points provide dissipative mechani
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Dual Crosslink Hydrogels with Metal-Ligand Coordination Bonds: Tunable Dynamics and Mechanics Under Large Deformation Jingwen Zhao, Tetsuharu Narita, and Costantino Creton
Contents 1 Introduction 2 Experimental Section 2.1 Materials 2.2 Sample Preparation 2.3 Linear Viscoelastic Properties 2.4 Uniaxial Tensile Tests 3 Results and Discussion 3.1 Strength of P(AAm-co-VIm)-Ni2+ Dual Crosslink Gel 3.2 Tunable Dynamics: Linear Rheology 3.3 Stress Relaxation 3.4 Intermediate Strain Tensile Cyclic Tests 3.5 Uniaxial Tensile Tests to Fracture 3.6 Step-Cycle Uniaxial Tensile Tests and Energy Dissipation 4 Conclusion References
J. Zhao Laboratoire Sciences et Ingénierie de la Matière Molle, ESPCI Paris, PSL University, Sorbonne Université, CNRS, Paris, France T. Narita (*) and C. Creton (*) Laboratoire Sciences et Ingénierie de la Matière Molle, ESPCI Paris, PSL University, Sorbonne Université, CNRS, Paris, France Global Station for Soft Matter, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan e-mail: [email protected]; [email protected]
J. Zhao et al.
Abstract Introducing additional physical and reversible crosslinks to a chemically crosslinked hydrogel is an interesting and viable alternative to increase the toughness of a hydrogel. Yet while in general the physical crosslink points provide dissipative mechanisms, there are still many details that are unknown in particular on the role that physical crosslinks play on the large strain behavior. We explore the mechanical properties in small and large strain of two dual crosslink gels made from a random copolymer of poly(acrylamide-co-vinylimidazole) with a range of elastic moduli in the tens of kPa. The interaction between vinylimidazole groups and metal ions (Zn2+ and Ni2+) results in physical crosslink points and in a markedly stretch-rate-dependent mechanical behavior. While a main relaxation process is clearly visible in linear rheology and controls the small and intermediate strain properties, we find that the strain hardening behavior at stretches of λ > 4 and the stretch at break λb are controlled by an additional longer-lived physical crosslinking mechanism that could be due to a clustering of physical crosslinks. Keywords Mechanical properties · Metal-ligand coordination bonds · Tough hydrogel · Transient crosslink
1 Introduction Hydrogels are promising candidates for biomedical applications such as artificial organs or tissue engineering thanks to their liquid-like and solid-like properties [1]. However, contrary to biological hydrogels such as cartilage, conventional synthetic hydrogels made by free radical polymerization suffer from mechanical fragility, due to the heterogeneous network structures and the lack of dissipative mechanisms [2]. Mechanical reinforcement has become one of the hottest topics of gel science in the last decades [3–9]. Among the different reinforcement strategies, the introduction of sacrificial bonds inside the gel in order to dissipate energy near the crack tip has proved
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