The pore size of polycaprolactone scaffolds has limited influence on bone regeneration in an in vivo model.

Bone tissue engineering scaffolds should be designed to optimize mass transport, cell migration, and mechanical integrity to facilitate and enhance new bone growth. Although many scaffold parameters could be modified to fulfill these requirements, pore size is an important scaffold characteristic that can be rigorously controlled with indirect solid freeform fabrication. We explored the effect of pore size on bone regeneration and scaffold mechanical properties using polycaprolactone (PCL) scaffolds designed with interconnected, cylindrical orthogonal pores. Three scaffold designs with unique microarchitectures were fabricated, having pore sizes of 350, 550, or 800 microm. Bone morphogenetic protein-7 transduced human gingival fibroblasts were suspended in fibrin gel, seeded into scaffolds, and implanted subcutaneously in immuno-compromised mice for 4 or 8 weeks. We found that (1) modulus and peak stress of the scaffold/bone constructs depended on pore size and porosity at 4 weeks but not at 8 weeks, (2) bone growth inside pores depended on pore size at 4 weeks but not at 8 weeks, and (3) the length of implantation time had a limited effect on scaffold/bone construct properties. In conclusion, pore sizes between 350 and 800 microm play a limited role in bone regeneration in this tissue engineering model. Therefore, it may be advantageous to explore the effects of other scaffold structural properties, such as pore shape, pore interconnectivity, or scaffold permeability, on bone regeneration when designing PCL scaffolds for bone tissue engineering.