Improved encapsulation of proteins within calcium carbonate microparticles by means of protein-polysaccharide complexes

The controlled delivery of proteins within calcium carbonate particles is currently widely investigated. The success of these carriers has been driven by the ionic interactions between proteins and particles making the encapsulation of proteins highly dependent on the pH of reaction solutions and the isoelectric point of the protein. This poses a great limitation on the successful loading of proteins into microparticles. In this study we explored the use of polysaccharide-protein complexes to enhance the encapsulation of otherwise poorly encapsulated proteins in CaCO3 microparticles. A chitin binding domain (ChBD) was inserted on the protein β-lactamase to form a chimeric protein. A protein-polysaccharide complex was formed between the protein and hyaluronic acid (HA) owing to the intrinsic affinity of the ChBD to HA. The chimeric protein was then loaded into calcium carbonate (CaCO3) microparticles using super critical CO2 technology aided by the templating effect of HA on CaCO3. The microparticles were characterised for size, surface charge, poly-morphism and protein loading. Biochemical stability of the encapsulated β-lactamase was characterized by kinetic reaction with nitrocefin. The presence of the ChBD on the β-lactamase increased the encapsulation of the protein by 6 fold when complexed with HA. Thrombin mediated release increased the release of the protein from the microparticles within 36 hours from <25% to 87%. The protein-polysaccharide complex proved successful in enhancing the encapsulation of protein while retaining up to 81% activity and allowing controlled release of the protein by proteases.