The compressive deformation of multicomponent microcapsules: influence of size, membrane thickness, and compression speed.

The clinical application of microcapsules for the immunoisolation of living tissue requires knowledge about the mechanical stability of polymer membranes. Microcapsules of 400-1000 microm in diameter were formed through the gelation of sodium alginate/sodium cellulose sulfate droplets through calcium chloride, with the membrane produced via complex coacervation between polyanions and poly(methylene-co-guanidine) hydrochloride. The deformation behavior of these multicomponent microcapsules was investigated by uniaxial compression experiments. Specifically, the influence of the deformation speed, capsule diameter, and membrane thickness on the mechanical properties was evaluated. The bursting force was found to be dependent on the deformation speed. Therefore, the measurement of the bursting work, a speed-independent value of the resistance to high stresses and deformations, was recommended as the most valid for capsule mechanical resistance. Furthermore, the bursting force was positively correlated with membrane thickness only for membrane-radius ratios up to 20%. For thicker membranes, the bursting event occurred because the opposite membranes touched each other, and not, because of insufficient strength. Indeed, the resistance to smaller deformations was positively correlated to the membrane thickness over the whole range of membrane-radius ratios. Moreover, the forces for constant deformation were linearly correlated to the total membrane volume, independently of capsule size and membrane thickness.