Preparation and properties of stretchable and tough alginate/polyacrylamide hollow capsules

Encapsulation technology has important applications in drug delivery, catalysis, sensing and photonics. In this paper, a stretchable and tough hollow capsule was synthesized using alginate and polyacrylamide (PAAm) as the shell material. Calcium carbonate (CaCO3) microspheres were first chosen as sacrificial templates for the covalent crosslinking of the PAAm network at their surface. Then, they were decomposed using acid to form a hollow capsule, and the released Ca2+ ions were used for the ionic crosslinking of the alginate network. The influence of the density of CaCO3 microspheres on the internal structure of the capsules was explored and the ball loading ball structure was observed by scanning electron microscopy and fluorescence microscopy. The mechanical strength of the prepared capsules was studied by both tensile/compressive testing and an osmotic pressure method, and the results showed that the volume of capsules could be expanded at least 27 times their original sizes without breakage. The release behaviours of the model drug BSA-FITC for three capsules with different crosslinking densities were studied, and the results showed that drug loading capacity and water absorption ratio were proportional to the number of CaCO3 microspheres used during the preparation.