Hydroxyapatite scaffold pore architecture effects in large bone defects in vivo

To examine the effect of scaffold pore size on bone regeneration within hydroxyapatite scaffolds in large segmental defects, this study evaluated two porous interconnected architectures having similar porosity and strut thickness but different pore sizes. Using a 10 mm segmental rabbit radius defect model, a bilayer scaffold architecture mimicking the cortical-cancellous organization of bone (pore size 200 µm outer layer, 450 µm inner layer) was compared to a purely trabecular-like architecture (pore size 340 µm) and an untreated defect. Bone regeneration was measured using micro-computed tomography and histology after four and eight weeks of in vivo implantation, and the mechanical strength of the defect site after eight weeks' implantation was assessed using flexural testing. Although both bilayer and trabecular architectures promoted bone growth, the trabecular scaffolds were observed to have more uniform new bone distribution within the scaffold interior at four weeks and greater bone regeneration overall after eight weeks' implantation (149 ± 9 mm³ compared to 121 ± 8 mm³ in the bilayer and 66 ± 14 mm³ in the defect). Additionally, the trabecular scaffolds were observed to exhibit significantly greater flexural strength (124% increase) and toughness (388% increase) when compared to the empty defects after eight weeks' implantation. It was concluded from this study that a larger uniform pore size led to greater functional bone regeneration over a longer implantation period for large segmental defects.