A fascinating aspect of living systems is their ability to self-heal and self-repair, i.e. the material reforms into the same functional structure after suffering damage [1,2]. Biological systems have a fascinating ability to repair themselves – properties that would be highly desirable for material scientists to mimic using synthetic materials. A familiar example is simple skin cuts: after a few days the wound is completely healed – usually without any necessary intervention.  Synthetic self-healing materials, e.g. self-repairing coatings, have been created using systems utilizing microcapsules containing chemical curing agents that will flow and covalently link the damaged areas [3]. However, such approaches are irreversible and rely on external chemical agents that need to be properly stored and effectively released into the material. Moreover, it is also generally limited to non-medical application for which toxicity of the curing agents is not an issue. Nature generally uses a more elegant strategy: after perturbation molecules simply self-assemble back to their original structure after rupture [2]. This demands that the structure is energetically or entropically favored, i.e. the structure corresponds to a minimum in the energy landscape.  Here the dynamics plays a crucial role; the system needs to diffuse back to its original state after perturbation on an appropriate time scale.

Figure: Understanding the microscopic origin of viscoelasticity by combining TR-SANS and rheology.

In this project we are interested in the relation between the microscopic dynamics and the viscoelastic properties of hydrogels formed by well-defined hydrophobically end-capped polymers. Using a combination of time-resolved neutron scattering and rheological measurements, we have found a direct relation between the lifetime of the physical bonds connecting the network and the elasticity. A more thorough quantitative understanding of the dynamics of the non-equilibrium process of reforming the network after rupture is more complicated and requires more studies. In addition, we will investigate the potential for drug-encapsulation within these self-assembled networks for sustained release purposes. We also plan to extend this project from purely polymeric “synthetic” systems to hybrid systems containing peptides with specific interactions.

• Zinn, T., Willner, L. & Lund, R. Telechelic Polymer Hydrogels: Relation between the Microscopic Dynamics and Macroscopic Viscoelastic Response. ACS Macro Letters 5, 1353–1356 (2016).
• Zinn, T., Willner, L., Knudsen, K. D. & Lund, R. Self-Assembly of Mixtures of Telechelic and Monofunctional Amphiphilic Polymers in Water: From Clusters to Flowerlike Micelles. Macromolecules 50, 7321–7332 (2017).