Lyophilization to improve drug delivery for chitosan-calcium phosphate bone scaffold construct: a preliminary...

Lyophilization was evaluated in chitosan-calcium phosphate microspheres and scaffolds to improve drug delivery of growth factors and antibiotics for orthopedic applications. The dual delivery of an antibiotic and a growth factor from a composite scaffold would be beneficial for treatment of complex fracture sites, such as comminuted fractures and segmental bone defects. The aim of this investigation was to increase the loading capacity of the composite by taking advantage of the increased porosity, due to lyophilization, and to produce an extended elution profile using a secondary chitosan-bead coating. The physiochemical properties of the composite were investigated, and loading and elution studies were performed with alkaline phosphatase (ALP), bone morphogenetic protein-2 (BMP-2), and amikacin. Lyophilization was found to increase the surface area of scaffolds by over 400% and the porosity of scaffolds by 50%. Using ALP as a model protein, the loading capacity was increased by lyophilization from 4.3 +/- 2.5 to 24.6 +/- 3.6 microg ALP/mg microspheres, and the elution profile was extended by a supplemental chitosan coating. The loading capacity of BMP-2 for composite microspheres was increased from 74.4 +/- 3.7 to 102.1 +/- 8.0 microg BMP-2/g microspheres with lyophilization compared with nonlyophilized microspheres. The elution profiles of BMP-2 and the antibiotic amikacin were not extended with the supplemental coating. Additional investigations are planned to improve these elution characteristics for growth factors and antibiotics.