• Nanoparticle Transport in Complex Media

Biological hydrogels are known to fulfill a number of important physiological functions. Besides regulating the mechanical properties of cells and lubricating joints, biogels act as barriers against pathogens, thus playing a vital role in protecting human and animal health. Various biogels like mucus and the extracellular matrix (ECM) are a crowded, interacting environment of biomacromolecules and serve as selective filters for nutrients, proteins, ions, pathogens and drugs. Growing evidence suggests additional filtering modes than simple size exclusion must be present in biological gels that act as selective barriers. One can easily imagine the difficulties in interpreting diffusion data through systems which could have many specific and nonspecific interactions such as electrostatics, chemical binding, immobile barriers, and binding sites. Understanding the selective barrier properties of biogels is an ongoing topic of investigation where research from different scientific branches; such as physics, chemistry, biology and medicine merges. Our group is involved in the study of fundamental questions to gain insight into the transport and interactions of particles in complex biological systems. Early work focused on the role of electrostatics on basic mechanisms governing diffusion of charged molecules inside polymer networks. We showed that particle transport in the charged hydrogels is highly asymmetric and that the filtering capability of the gel is sensitive to the solution ionic strength. Simulations done in collaboration with Dr. Roland Netz (FU Berlin) showed this filtering mechanism proceeds primarily through vertices trapping as shown in the figure. We are currently also focused on the creation and application of synthetic mucin-like materials through a collaborative effort.

Simulation unit cells including particle-position snapshots obtained during simulations run for attractive (left) and repulsive (right) interaction potentials. These different trapping mechanisms lead to highly asymmetric filtering capacities resulting from electrostatic interactions.