Basic proteins play important roles in biological activities and disease treatment, but their high sensitivity to the body environment and short life time have limited their applications. Encapsulating the proteins into carriers has been demonstrated to be an effective way to prolong the protein half life time and to control the release temporally and spatially. However, fabricating protein carriers with high protein loading efficacy under mild conditions is still a big challenge. By doping heparin, a polysaccharide with multiple interaction modes with various proteins, into porous CaCO3, we developed a highly efficient but very simple method to encapsulate basic proteins (Fig. 1). An efficiency of 99.5% and capacity of 91.6 mg g-1 under very gentle conditions were obtained. Most importantly, the activity of the encapsulated proteins were almost 100% retained. Considering the multi-interaction mode of heparin with various proteins and the ability to retain the function of the loaded protein demonstrated in our study, we believe that the developed approach has great potential for encapsulating various functional proteins with a wide range of applications in catalysis, disease treatment, and tissue engineering. This work was published as the cover story in J. Mater Chem. B 2018, 6, 4025-4215.
Furthermore, we took lysozyme as the basic model protein to investigate the kinetics, driving forces on protein loading and factors controlling loading efficiency into porous Hep/CaCO3 particles (Fig. 2). As revealed, the adsorption process obeyed the pseudo second-order kinetics and Langmuir adsorption model. Doping heparin greatly influenced the detailed texture, pore size, surface area, and maximum loading capacity of lysozyme. Accompanying with pH change, the lysozyme orientation shifted from “side on” at lower pH to “end on” at pH around IEP. At proper concentration of NaCl (CNaCl), the loaded lysozyme could be released from Hep/CaCO3 particles, making them available for lysozyme reloading. Most importantly, such release-reloading cycle didn’t disturb the bioactivity of released lysozyme and following reloading ability. This work was published in Colloids and Surfaces B: Biointerfaces 2019, 175, 184-194.
Fig. 1. Schematic illustration of (a) Hep/CaCO3 particle synthesis, (b) protein loading, (c) protective layers construction, (d) sacrificing the template to generate the polyelectrolyte capsules with encapsulated protein.
Fig. 2. Schematic illustration of driving forces on protein loading and factors on protein loading.