OICC Press Progress in Biomaterials 2194-0517 7 2 (June 2018) 2018 05 21 Stress phase angle regulates differentiation of human adipose-derived stem cells toward endothelial phenotype 10.1007/s40204-018-0090-5 EN Shahrokh Shojaei Faculty of Biomedical Engineering, Central Tehran Branch, Islamic Azad University, Tehran, IR Mohammad Tafazzoli-Shadpour Cardiovascular Engineering Lab., Faculty of Biomedical Engineering, Amirkabir University of Technology, Tehran, 158754413, IR Mohammad Ali Shokrgozar National Cell Bank of Iran, Pasteur Institute of Iran, Tehran, 1316943551, IR Nooshin Haghighipour National Cell Bank of Iran, Pasteur Institute of Iran, Tehran, 1316943551, IR Fatemeh Hejazi Jahromi Hard Tissue Engineering Research Center, Tissue Engineering and Regenerative Medicine Institute, Central Tehran Branch, Islamic Azad University, Tehran, IR Journal Article 2018 05 21 Abstract Endothelial cells are subjected to cyclic shear by pulsatile blood flow and pressures due to circumferential stresses. Although most of the researches on this topic have considered the effects of these two biomechanical forces separately or concurrently, few studies have noticed the interaction of these cyclic loadings on endothelial behavior. Negative temporal stress phase angle, defined by the phase lag between cyclic shear and tensile stresses, is an established parameter which is known to have substantial effects on blood vessel remodeling and progression of some serious cardiovascular diseases. In this research, intermittent shear and tensile stresses with different stress phase angle values were applied on human adipose stem cells (ASC). The expression level of three major endothelial-specific genes, elastic modulus of cells and cytoskeleton actin structure of cells were studied and compared among control and three test groups subjected to stress phase angle values at 0°, − 45°, and − 90°. Mechanical properties of ASCs were determined by atomic force microscopy and actin fiber structure was visualized by confocal imaging through Phalloidin staining. Results described a decrease in expression of FLK-1 and VE-cadherin and rise of vWF marker expression in case of higher negative stress phase angles. The Young’s moduli of cells were significantly higher and cytoskeletal actin structure was more organized with higher thickness for all test samples subjected to combined stresses; however, these features were less magnificent for applied stress phase angles with higher negative values. The results confirmed significant effects of SPA on endothelial differentiation of mesenchymal stem cells.