The effect of alginate monomer ratio on protein binding and controlled release: application to albumin loaded in alginate microparticles

Polysaccharide matrices are particularly useful for encapsulation of protein drugs, which is sometimes challenging. The aim of this work was to investigate the impact of the structure of the alginate macromolecule on its affinity with a protein model (bovine serum albumin), and hence protein encapsulation efficiency and release kinetics from the polysaccharide matrix. Indeed, two alginate types, with different monomer ratios were used. Affinity study at physiological pH, with surface plasmon resonance, between alginate and albumin showed that the equilibrium dissociation constant (K_D) is approximately 300 times lower for alginate with higher mannuronic/guluronic monomer ratio. The loading of alginate microparticles with albumin was more important at low pH and for the alginate with the higher mannuronic/guluronic ratio. The release, studied in physiological pH, was faster for alginate with the lower mannuronic/guluronic ratio. In conclusion, this work highlights the affinity implication in the design of polysaccharide-based controlled release matrices for the delivery of protein therapeutics.