Bone is the second most commonly transplanted tissue in the United States. Limitations of current bone defect treatment options include morbidity at the autograft harvest site, mechanical failure, and poorly controlled growth factor delivery. Combining synthetic scaffolds with biologies may address these issues and reduce dependency on autografts. The ideal scaffolding system should promote tissue in-growth and nutrient diffusion, control delivery of biologies and maintain mechanical integrity during bone formation. This dissertation evaluates how scaffold permeability, conjugated bone morphogenetic protein-2 (BMP-2) and differentiation medium affect osteogenesis in vitro and bone growth in vivo.

"High" and "low" permeability polycaprolactone (PCL) scaffolds with regular architectures were manufactured using solid free form fabrication. Bone growth in vivo was evaluated in an ectopic mouse model. High permeability scaffolds promoted better 8 week bone growth, supported tissue penetration into the scaffold core, and demonstrated increased mechanical properties due to newly formed bone. Next, the effects of differentiation medium and conjugated BMP-2 on osteogenesis were compared. Conjugation may improve BMP-2 loading efficiency, help localize bone growth and control release. High permeability scaffolds were conjugated with BMP-2 using the crosslinker, sulfo-SMCC. When adipose-derived and bone marrow stromal cells were seeded onto constructs (with or without BMP-2), BMSC expressed more differentiation markers, and differentiation medium affected differentiation more than BMP-2. In vivo, scaffolds with ADSC pre-differentiated in osteogenic medium (with and without BMP-2) and scaffolds with only BMP-2 grew the most bone. Bone volume did not differ among these groups, but constructs with ADSC had evenly distributed, scaffold-guided bone growth.

Analysis of two additional BMP-2 attachment methods (heparin and adsorption) showed highest conjugation efficiency for the sulfo-SMCC method. BMP-2 release from all constructs was minimal, proving that BMP-2 was tightly bound to constructs regardless of the attachment method. However, C2C12 myoblasts did not produce alkaline phosphatase when seeded onto heparin- and sulfo-SMCC-conjugated scaffolds suggesting hindrance of BMP-2 bioactivity.

This thesis demonstrated that high permeability PCL scaffolds promote bone growth better than low permeability scaffolds and that in vitro pre-differentiation of cells affects osteogenesis more than conjugated BMP-2. Future work will optimize BMP-2 conjugation to ensure maintenance of bioactivity.