Alginate/poly-l-lysine capsules: mechanical properties and drug release characteristics

Abstract

In this paper we studied the mechanical stability and the release kinetics of different types of liquid-filled calcium alginate/poly-L-lysine capsules. The aqueous cores of these particles were filled with anthocyanins which have antioxidant abilities and may, as additives in foods, provide several benefits of health. By means of spinning capsule experiments it was possible to measure the deformation of the gel particles at various centrifugal forces. These investigations provided insight into the elastic properties of the capsule membranes. In a series of experiments we measured the capsule deformation as a function of the poly-L-lysine concentration and the adsorption time. From these data we calculated the surface Young moduli. In addition, the use of a pH-dependent UV/VIS-absorption spectroscopy method gained access to the diffusive drug-release performance of the encapsulated anthocyanins. From these kinetic measurements we could evaluate the effective diffusion constants of the encapsulated compounds. The performed experiments showed that the mechanical properties of liquid-filled alginate capsules could be changed and adjusted selectively by the addition of poly-L-lysine. The drug release properties, however, did not change significantly for different compositions of the multi-component capsules. In addition, it could be shown that a high amount of anthocyanin molecules was immobilized in the capsules. This phenomenon could be explained by adsorption or polymerization processes of the colored ingredients.