4D-Mechanics of dynamic DNA hydrogels – MIND

Microscale structural and dynamical effects play a critical role, yet poorly understood, on the macroscale mechanical behaviour of soft materials. Biological tissue illustrate beautifully this complex temporal and structural optimisation. These materials combine strength, flexibility, and healing properties, unique among soft systems, despite consisting solely of water-swollen supramolecular networks. Their exceptional performances emerge from the intricate orchestration of network architecture and reorganization mechanisms. For example the extracellular matrix, which supports cells and controls their development, combines both stress stiffening and stress-dependent relaxation. It is now established that stress stiffening comes from network structure (semiflexiblility). Yet, there is little work on the molecular mechanisms that drive stress dependent relaxation. It is notoriously difficult to extract clear mechanism-behaviour relations from pristine biological materials because of their complex composition and non-equilibrium nature. Synthetic self-assembling systems offer a promising alternative to explore dynamical and structural interplay in model materials.
Our understanding of tissue mechanics ties in with our control of dynamical processes in synthetic materials. On contrary to biological tissues that constantly grow and reshape without losing structural integrity, synthetic hydrogels either form dynamic (supramolecular) or robust (covalent) networks. This hinders the conception of efficient biomimetic materials. Nevertheless, hydrogels find many applications in interaction with living organism, e.g. as cell growth medium. We know that their mechanics play a critical role for cell development. Yet, we ignore the role of most dynamic and non-linear processes due to the difficulties to control and study these phenomenon. Indeed, beyond the linear domain, localized stress inhomogeneities and complex relaxation mechanisms impedes the direct interpretation of macroscale rheology data. The challenge is twofold. On the one hand we lack the molecular concepts to control both exchange dynamics and network architectures in synthetic hydrogels. On the other hand we need tools to visualize stress distribution in 3D at the microscale in order to study them.
MIND will use DNA self-assembly to address both challenges. First we will design a new kind of hydrogel that reorganize without losing its structural integrity. Second we will develop tools to map the transient stress inhomogeneities that appear during failure. Altogether MIND will establish a versatile platform to produce model dynamic hydrogels and to explore their mechanical behaviour from a molecular perspective.