Polydopamine Microcapsules with Different Wall Structures Prepared by a Template-Mediated Method for Enzyme Immobilization

Microcapsules with diverse wall structures may exhibit different performance in specific applications. In the present study, three kinds of mussel-inspired polydopamine (PDA) microcapsules with different wall structures have been prepared by a template-mediated method. More specifically, three types of CaCO₃ microspheres (<i>poly­(allylamine hydrochloride), (PAH)-doped CaCO</i>_<i>3</i>; <i>pure-CaCO</i>_<i>3</i>; <i>and poly­(styrene sulfonate sodium), (PSS)-doped CaCO</i>_<i>3</i>) were synthesized as sacrificial templates, which were then treated by dopamine to obtain the corresponding PDA-CaCO₃ microspheres. Through treating these microspheres with disodium ethylene diamine tetraacetic acid (EDTA-2Na) to remove CaCO₃, three types of PDA microcapsules were acquired: that was (1) PAH-PDA microcapsule with a thick (∼600 nm) and highly porous capsule wall composed of interconnected networks, (2) pure-PDA microcapsule with a thick (∼600 nm) and less porous capsule wall, (3) PSS-PDA microcapsule with a thin (∼70 nm) and dense capsule wall. Several characterizations confirmed that a higher degree in porosity and interconnectivity of the capsule wall would lead to a higher mass transfer coefficient. When serving as the carrier for catalase (CAT) immobilization, these enzyme-encapsulated PDA microcapsules showed distinct structure-related activity and stability. In particular, PAH-PDA microcapsules with a wall of highly interconnected networks displayed several significant advantages, including increases in enzyme encapsulation efficiency and enzyme activity/stability and a decrease in enzyme leaching in comparison with other two types of PDA microcapsules. Besides, this hierarchically structured PAH-PDA microcapsule may find other promising applications in biocatalysis, biosensors, drug delivery, etc