Fabrication of protein microcapsules by controlled precipitation and cross-linking

Bovine serum albumin (BSA) microcapsules, which have a uniform shape and size and can be well dispersed in water, were fabricated by the controlled precipitation of BSA on the surface of MnCO3 microparticles though desolvation, followed by cross-linking and core removal. The thickness of the capsule walls were controlled by the amount of the added non-solvent (ethanol). The as-prepared microcapsules are permeable to TRITC-dextran with a molecular weight of 70000, but not up to 155000, implying that the pore size in the capsule walls is between 18.5-26.2 nm. Due to the excessive carboxylic groups on the BSA molecules, which can be fully charged at an alkaline condition, the BSA capsules expanded their size at pH > 10. This method is applicable to other proteins and enzymes as well, and the pH-sensitive protein capsules may find potential applications in biomedical field because of their biodegradability and biocompatibility.