Immunohistochemical staining of BMP2 and Collagen I of the transplanted scaffold at six weeks post-implantation. (a) BMP2 and (c) Collagen I staining in the normal USCs transplantation group. (b) BMP2 and (d) Collagen I staining in the Lentiviral-BMP2 transplantation group. The arrows indicate the positive staining of BMP2 or Collagen I in the Lentiviral-BMP2 transplantation group. Scale bar for a and c = 50 μm; b and d = 100 μm. BMP2, bone morphogenic proteins 2; USCs, urine-derived stem cells.