A biodegradable polymer scaffold for delivery of osteotropic factors.

Despite discoveries and developments in osteotropic factors, therapies exploiting these macromolecules have been limited due to a lack of suitable delivery vehicles and three dimensional (3D) scaffolds that promote bone regeneration. To address this limitation, an emulsion freeze-drying process was developed to fabricate biodegradable scaffolds with controlled microarchitecture, and the ability to incorporate and deliver bioactive macromolecules for bone regeneration. The effect of median pore size and protein loading on protein release kinetics was investigated using scaffolds with different protein loading and median pore sizes ranging from 7 to 70 microm. Graphs of protein release from scaffolds showed an initial burst followed by a slower sustained release. Release kinetics were characterized using an unsteady-state, diffusion-controlled model with an effective diffusivity that took tortuosity (tau) and partition coefficient for protein adsorption (Kp) onto the scaffold walls into account. Tortuosity and partition coefficient significantly reduced the protein diffusivity by a factor of 41 +/- 43 and 105 +/- 51 for 60 and 30-microm median pore-sized scaffolds, respectively. The activity of the protein released from these scaffolds was demonstrated by delivering rhBMP 2 and [A-4] (an amelogenin derived polypeptide) proteins from the scaffold and regenerating bone in a rat ectopic bone induction assay [Whang et al. J Biomed Mater Res 1998;42:491-9, Veis et al. J Bone Mineral Res, Submitted].