Magnetic switchable alginate beads

Calcium alginate beads are enclosed in a wide range of products including food, pharmaceuticals, and cosmetic formulations. The biopolymer matrix is often used to stabilize active ingredients and to provide a controlled release under well-defined conditions. In this context, it is of high interest to study the magnetic-induced attraction, elongation, and rupture of capsules or beads. In this work, we synthesized new types of magnetic switchable alginate beads. The magnetic sensitivity was achieved by incorporation of magnetic nanoparticles (MNPs) within the alginate gel. We measured the mechanical properties of single alginate beads in squeezing experiments, the evaporation of water and the magnetic sensitivity by stimulation of these beads in external fields. In all these measurements, the alginate and the nanoparticle concentration were systematically varied. We could show that the incorporation of MNPs generates a magnetic response of the beads and reduces the evaporation of water but has no influence on the mechanical stability of the beads during compression. Calculations of the shear modulus by means of the squeezing data result in good agreement in comparison to the shear moduli measured by rheological frequency sweep tests. With scanning electron microscopy, we could analyze the molecular structure of such composite systems, and we observed a homogeneous distribution of the MNPs within the gel matrix.