Shear-induced solvent release from gel particles: application to drug-delivery systems

The behaviour of a swollen-in-water hydrogel particle and of a chitosan-alginate micro-capsule immersed in a silicon oil under shear is studied by the rheo-optical method. Both gel and capsule quantitatively behave in a same way. Shear stress leads to a solvent release from a particle and a further increase of shear stress induces the solvent detachment from the released areas. Particle deformation and solvent release are reversible: when stopping the shear, the particle recovers its initial shape and volume. But when some solvent is detached, it flows separately as would do low-viscosity droplets immersed in a high-viscosity matrix.