Design of new delivery systems for therapeutic proteins based on calcium carbonate microspheres

There exists a constant need for delivery systems that are biocompatible, offer bioactives protection from premature degradation and allow for targeted delivery and controlled release. Calcium carbonate (CaCO3) is one such system that has gained great favour for employment in the biomedical field due to possibilities of controlling size, morphology and crystalline forms of particles by tuning the synthesis conditions. CaCO3 has demonstrated ability to increase safety, stability and overall efficiency of protein therapeutics.
The aim of the present work was to assess the significance of polysaccharide-protein complexes in enhancing the encapsulation of proteins in CaCO3 microspheres. A Chitin Binding Domain (ChBD), reported to have affinity for hyaluronic acid, was inserted on β-lactamase enzyme to develop a chimeric protein. The chimeric protein retained the activity of the enzyme and the binding properties and was encapsulated in CaCO3 microspheres by a super critical CO2 (ScCO2) process using hyaluronic acid as a templating agent. The particles were characterised in terms of size, zeta potential, morphology and protein loading.
The results obtained confirmed the affinity of the ChBD to hyaluronic acid towards the production of stable, vaterite microparticles. Protein assays demonstrated that the ChBD enhanced the encapsulation of protein by up to 10 fold. Confocal images also suggested high encapsulation of the chimeric protein compared to native protein. Thus the production of polysaccharide-protein complexes seems effective in enhancing the encapsulation of proteins in CaCO3 microparticles using the ScCO2 process. Moreover this method will further be used to enhance encapsulation of therapeutic proteins such as growth factors for bone and cartilage regeneration.