Probing and modeling of transport properties of hydrogels

Biological hydrogels such as mucus form natural barriers for infectious agents and play important roles in regulating the exchange of molecules and particles between and within cells. Understanding the barrier properties and role of individual hydrogel components on the function of the barrier requires systematic measurements of the transport of particles (e.g., proteins, viruses, bacteria) into and within biological hydrogels.

In the first funding period, we developed a combined experimental/theoretical approach involving confocal microscopy, fluorescence correlation spectroscopy (FCS) and single particle tracking (SPT) that yields the position-dependent diffusivity and free-energy profiles from the diffusion of dye-labeled molecules and particles through hydrogels. Only the combined knowledge of these two position-dependent material properties allows to quantify the hydrogel’s permeability to particles. In this way, we quantified the transport of nm-sized biomolecules into and within stable (i.e., covalently crosslinked) synthetic hydrogels and investigated the impact of steric, electrostatic, and hydrophobic interactions on the particle transport. In addition, we developed theoretical approaches that enable the unbiased analysis of particle trajectories and the extraction of non-Markovian time-dependent friction from particle trajectories. This extraction method has been applied to equilibrium trajectories of passive particles as well to non-equilibrium trajectories of living organisms.