Response of mesenchymal stem cells to the biomechanical environment of the endothelium on a flexible tubular silicone substrate Eoin D. O’Cearbhaill a,b , Marie A. Punchard a , Mary Murphy c , Frank P. Barry c , Peter E. McHugh a,b , Valerie Barron a, * a National Centre for Biomedical Engineering Science, National University of Ireland, Galway, Galway, Ireland b Department of Biomedical and Mechanical Engineering, National University of Ireland, Galway, Galway, Ireland c Regenerative Medicine Institute, National Centre for Biomedical Engineering Science, National University of Ireland, Galway, Galway, Ireland Received 30 July 2007; accepted 28 November 2007 Available online 14 January 2008 Abstract Understanding the response of mesenchymal stem cells (MSCs) to forces in the vasculature is very important in the field of cardiovascular intervention for a number of reasons. These include the development of MSC seeded tissue engineered vascular grafts, targeted or systemic delivery of MSCs in the dynamic environment of the coronary artery and understanding the potential pathological calcifying role of mechan- ically conditioned multipotent cells already present in the vessel wall. In vivo, cells present in the coronary artery are exposed to the primary biomechanical forces of shear stress, radial stress and hoop stress. To date, many studies have examined the effect of these stresses in isolation, thereby not presenting the complete picture. Therefore, the main aim of this study is to examine the combined role of these stresses on MSC behaviour. To this end, a bioreactor was configured to expose MSCs seeded on flexible silicone substrates to physiological forces e namely, a pulsatile pressure between 40 and 120 mmHg (5.33e1.6  10 4 Pa), radial distention of 5% and a shear stress of 10 dyn/cm 2 (1 Pa) at frequency of 1 Hz for up to 24 h. Thereafter, the ‘pseudovessel’ was assessed for changes in morphology, orientation and expression of endothelial and smooth muscle cell (SMC) specific markers. Hematoxylin and eosin (H&E) staining revealed that MSCs exhibit a similar mechanosensitive response to that of endothelial cells (ECs); they reorientate parallel with direction of flow and have adapted their morphology to be similar to that of ECs. However, gene expression results show the cells exhibit greater levels of SMC-associated markers a-smooth muscle actin and calponin ( p < 0.05). Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Mesenchymal stem cell; Silicone; Bioreactor; Endothelial cell; Smooth muscle cell; Soft tissue biomechanics 1. Introduction The studies of vascular disease, intervention and post- operative care are evolving as the role of undifferentiated cells in the vasculature is being investigated more intensely. The multipotentiality of these cells can be harnessed if properly di- rected and understood. However, their plasticity must be con- sistently controlled, while guarding against differentiation into inappropriate cell types. The study of the effect of vascular physiological forces on mesenchymal stem cells (MSCs) is of particular interest. MSCs are well characterised and can be successfully propagated in large numbers making them suitable for clinical applications [1]. While the multipotential- ity of these cells has been widely explored under biochemical stimulation [2], the role of biomechanical stimulation is less well understood. Several aspects of cardiovascular research would benefit from a greater understanding of cell response to a vascular mechanical environment. The potential of being able to pro- vide autologous terminally differentiated vascular phenotype cell populations would be a major clinical breakthrough in vascular tissue engineering [3,4]. * Corresponding author. Tel.: þ353 91 492805; fax: þ353 91 494596. E-mail address: valerie.barron@nuigalway.ie (V. Barron). 0142-9612/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2007.11.042 Available online at www.sciencedirect.com Biomaterials 29 (2008) 1610e1619 www.elsevier.com/locate/biomaterials