Multivalent binding of nanocarrier to endothelial cells under shear flow.

We investigate the effects of particle size, shear flow, and resistance due to the glycocalyx on the multivalent binding of functionalized nanocarriers (NC) to endothelial cells (ECs). We address the much- debated issue of shear-enhanced binding by computing the binding free-energy landscapes of NC binding to the EC surface when the system is subjected to shear, using a model and simulation methodology based on the Metropolis Monte Carlo approach. The binding affinities calculated based on the free-energy profiles are found to be in excellent agreement with experimental measurements for different-sized NCs. The model suggests that increasing the size of NCs significantly increases the multivalency but only moderately enhances the binding affinities due to the entropy loss associated with bound receptors on the EC surface. A significant prediction of our model is that under flow conditions, the binding free energies of NCs are a nonmonotonic function of the shear force. They show a well-defined minimum at a critical shear value, and thus quantitatively mimic the shear-enhanced binding behavior observed in various experiments. More significantly, our results indicate that the interplay between multivalent binding and shear force can reproduce the shear-enhanced binding phenomenon, which suggests that under certain conditions, this phenomenon can also occur in systems that do not show a catch-bond behavior. In addition, the model also suggests that the impact of the glycocalyx thickness on NC binding affinity is exponential, implying a highly nonlinear effect of the glycocalyx on binding.