Evaluation of Bone Formation within β-Tricalcium Phosphate (βTCP) Scaffolds in a Sheep Scapular Bioreactor Model Using Micro-Computed Tomography Analysis

Critical-sized bone defects in load-bearing regions remain a major clinical challenge. This study investigated how β-tricalcium phosphate (βTCP) scaffold pore size and stem cell source influence bone regeneration using a laser-sintered, plasma-treated polyether ketone (P-PEK) dual-chamber scapular bioreactor model in sheep. On the left scapula, selectively polymerised βTCP (SP-βTCP) scaffolds with two pore sizes were implanted for 16 weeks: a Large Pore design (1.875-mm unit cell; 0.93-mm pore) and a Small Pore design (1.5-mm unit cell; 0.66-mm pore). Adjacent Large Pore scaffolds were loaded with either gelatin methacryloyl (GelMA) alone or GelMA encapsulating autologous adipose-derived stem cells (ADSCs). On the right scapula, Large Pore scaffolds containing GelMA-encapsulated autologous or allogeneic ADSCs were implanted for 12 weeks. Bone formation was quantified by micro-computed tomography (µCT) and validated by resin-embedded histology. Small Pore scaffolds generated greater bone volume than Large Pore scaffolds. Autologous ADSC-laden scaffolds outperformed GelMA-only controls, particularly in lower bioreactors interfacing with native bone. No significant differences were detected between autologous and allogeneic ADSCs. Histology confirmed bioreactor-dependent variation, with lower bone-contacting chambers consistently producing more mineralised tissue. These findings highlight the interplay between scaffold architecture, cell source, and anatomical niche in optimising translational bone regeneration.