Numerical method to characterise capsule membrane permeability for controlled drug delivery

Design and characterisation of capsules is not an easy task owing to the multiple involved preparation factors and parameters. Here, a novel method to characterise capsule membrane permeability to solute molecules by an inverse approach is proposed. Transport of chemical species between the capsule core and the surrounding medium through the membrane is described by the Fick's second law with a position-dependent diffusion coefficient. Solutions are computed in spherical coordinates using a finite difference scheme developed for diffusion in multilayer configuration. They are validated using semi-analytical solutions and fully three-dimensional lattice Boltzmann simulations. As a proof of concept, the method is applied to experimental data available in the literature on the kinetics of glucose release and absorption to determine the membrane permeability of capsules. The proposed method is easy to use and determines correctly the permeability of capsule membranes for controlled drug release and absorption applications.

Squeezing multiple soft particles into a constriction: Transition to clogging

We study numerically how multiple deformable capsules squeeze into a constriction. This situation is largely encountered in microfluidic chips designed to manipulate living cells, which are soft entities. We use fully three-dimensional simulations based on the lattice Boltzmann method to compute the flow of the suspending fluid and on the immersed boundary method to achieve the two-way fluid-structure interaction. The mechanics of the capsule membrane elasticity is computed with the finite-element method. We obtain two main states: continuous passage of the particles and their blockage that leads to clogging the constriction. The transition from one state to another is dictated by the ratio between the size of the capsules and the constriction width and by the capsule membrane deformability. The latter is found to enhance particle passage through narrower constrictions, where rigid particles with similar diameter are blocked and lead to clogging.