Mechanics of tough hydrogels

• Applicants: Professor Dr.-Ing. Mikhail Itskov; Dr. Alexander Southan
• Subject Area: Mechanics ; Applied Mechanics, Statics and Dynamics ; Polymer Materials ; Preparatory and Physical Chemistry of Polymers
• Term: from 2016 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320336785

The objective of this project is to understand the structure-property relationships of tough hydrogels. To this end, on the one hand new synthetic approaches to the formation of tough hydrogels will be developed and their mechanical properties will be characterized. On the other hand, the micro-structure will be studied and the mechanical behavior of tough hydrogels under large deformations will be modeled.In biomechanics, hydrogels are considered as a revolutionary synthetic material which allows the diffusion of cell nutrients, proteins and enzymes and acts as a substrate for the cell regeneration in damaged organs. However, the application of hydrogels has been limited for decades due to their weak mechanical properties. In comparison to conventional hydrogels, tough hydrogels can keep their high water content intact under deformation and have also significantly (up to 10 times) higher strength and stiffness. The excellent mechanical properties of tough hydrogels make them a perfect choice as an implant for damaged load bearing organs such as ligaments, cartilage and muscles. However, the design procedure of the implants remains a challenging issue, mostly due to the complex mechanical behavior of hydrogels.Similarly to rubbers tough hydrogels can undergo large strains and demonstrate pronounced inelastic effects like, for example, stress softening, yielding and self-healing. However, in rubbers these effects are mostly due to the contribution of fillers and their interaction with the polymer matrix. In hydrogels, there should be, however, another micro-structural source of inelasticity due to the absence of any fillers. Thus, the broad knowledge generated in mechanics of elastomers cannot be fully implemented here to study hydrogels. For this reason, constitutive modeling of tough hydrogels represents an interesting and challenging problem in the field of soft materials and requires interdisciplinary study between polymer science and mechanics of gels.In this project, we are going to develop a multi-scale constitutive model of tough hydrogels based on micro-mechanics of their interpenetrating polymer networks. These networks are assumed to be assembled of different layers of polymers clustered and cross-linked together at different levels. Both theoretical and numerical results will be verified against experimental data obtained from quasi-static cyclic compressive and tensile tests of differently cross-linked tough hydrogels. For the synthesis of such hydrogels, new cross-linking chemistries will be examined which allow for the investigation of the effect of network structure on the mechanical properties. Additionally, self-healing behavior based on strain-induced covalent bond cleavage of mechanophores will be introduced and investigated.

• DFG Programme: Research Grants
• International Connection: Denmark, Israel
• Cooperation Partners: Professor Dr. Aleksey Drozdov, Ph.D.; Professor Dr. Mahmood Jabareen; Professor Dr. Günter Tovar