Histological analysis of in vivo bone formation after 7 weeks of ectopic implantation into immunodeficient mice. Scaffolds (a, b) without pig bone marrow mesenchymal stromal cells (pBMSCs) (a) Magnifications: 4×, (b) Magnifications: 20×. (c, d) with 300,000 pBMSCs directly loaded onto the bone scaffold during the surgery. Cells from three different pigs were tested. (c) Magnifications: 4×, (d) Magnifications: 20×. Decalcified implants (n = 6 per condition) were embedded in paraffin and stained with Masson’s Tri-chrome (blue/green = collagen and non-mineralized bone; red = mineralized bone scaffold; purple = nuclei; and pink = cytoplasm). Dotted lines correspond to the areas of new bone formation. NB, new bone; Sc, scaffold ; FT, fibrous tissue.