Osteogenic differentiation: von Kossa staining. Von Kossa staining revealed that cells of ovariectomized rats ((b) OVX + Diet, (c) OVX + Steroid) showed more matrix mineralization compared to the control group ((a) Sham), whereas no staining for mineralized matrix could be seen in cells treated with the control medium (NC2) ((d) Sham, (e) OVX + Diet, and (f) OVX + Steroid).