Injectable, thermo-reversible and complex coacervate combination gels for protein drug delivery

Injectable and thermo-reversible physical combination gels were formed in aqueous solution by preparing complex coacervate with two oppositely charged biomacromolecules that composed of negatively charged chondroitin 6-sulfate and positively charged high molecular weight gelatin type A and co-formulating with a negative, thermo-sensitive polysaccharide, methylcellulose containing a salting-out salt, ammonium sulfate. The combination of complex coacervation and a thermo-reversible gel demonstrated synergistic effects on the complex coacervate formation the release rates of model proteins and in situ gel depot formation. Gels indicated sustained release patterns of the protein over 25 days with minimal initial bursts. Optimized novel in situ gel depot systems containing dual advantages of complex coacervation and temperature responsiveness demonstrated a potential for efficient protein drug delivery in terms of high protein loading, sustained protein release, ease of administration, an aqueous environment without toxic organic solvents, and a simple fabrication method. (C) 2008 Elsevier B.V. All rights reserved.