Bone regeneration using stem cell spheroids within 3D-printed scaffolds in a rabbit radial defect model

Bone tissue is generally resilient and can self-heal, but critical-size defects (CSDs) with complex geometries cannot be repaired without clinical intervention. Customized scaffolds developed using three-dimensional (3D) printing techniques can effectively repair complex-shaped CSDs. Adipose-derived stem cells (ADSCs), a type of mesenchymal stem cell (MSC), can differentiate into osteoblasts and exhibit osteoinductive properties. However, ADSC-single cells fabricated via two-dimensional (2D) monolayer cultures have limitations in maintaining cell survival and function over time. Unlike 2D monolayer cultures, ADSC-spheroids fabricated via 3D spheroid cultures can overcome this limitation by increasing the survival of ADSCs and enhancing their in vivo osteogenic capacity. This study aimed to evaluate the potential of a synergistic strategy of ADSC-spheroids within a 3D-printed scaffold made of polycaprolactone/hydroxyapatite (PCL/HA) in bone regeneration. In vitro experiments demonstrated that ADSC-spheroids promoted mineralization in 3D-printed scaffolds. Radiographs and histological analysis performed at eight weeks post-implantation in in vivo experiments using a rabbit radial defect model showed successful bone regeneration in the group containing ADSC-spheroids within the PCL/HA scaffold. These results suggest that the synergistic strategy of incorporating ADSC-spheroids into 3D-printed PCL/HA scaffolds shows promise for clinical applications in treating complex CSDs.