Healing of rat calvarial defects assessed by micro-computed tomography. (A) Micro-computed tomography (micro-CT) images of the calvaria, 0, 2, and 4 weeks after implantation of the indicated materials. Newly regenerated bone in the blank, Matrigel™ alone, monolayer rat mesenchymal stem cells (MSCs)/ Matrigel™, and MSC spheroids/ Matrigel™ groups were evaluated. In the blank group, the defect was left unfilled. (B) Quantitative results for micro-CT analysis. Healing of defects was shown as the fraction of new bone with respect to the total defect area as quantified by micro-CT analysis (n = 5 per group). There were statistical differences between the area of new bone formed in the MSC spheroids group and that in the other groups (p < 0.05). There are no significant difference in groups of gray columns jointed to horizontal bar.