Design of Fibrin Matrix Composition to Enhance Endothelial Cell Growth and Extracellular Matrix Deposition for In Vitro Tissue Engineering Divya Pankajakshan and Lissy K. Krishnan Thrombosis Research Unit, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, India Abstract: Tissue-engineered blood vessel substitutes should closely resemble native vessels in terms of structure, composition, mechanical properties, and function. Success- ful cardiovascular tissue engineering requires optimization of in vitro culture environment that would produce func- tional constructs. The extracellular matrix (ECM) protein elastin plays an essential role in the cardiovascular system to render elasticity to blood vessel wall, whereas collagen is responsible for providing mechanical strength. The objec- tive of this study was to understand the significance of various ECM components on endothelial cell (EC) growth and tissue generation. We demonstrate that, even though fibrin is a good matrix for EC growth, fibronectin is the crucial component of the fibrin matrix that enhances EC adhesion, spreading, and proliferation.Vascular EC growth factor is known to influence in vitro growth of EC, but, so far, ECM deposition in in vitro culture has not been reported. In this study, it is shown that incorporation of a mixture of hypothalamus-derived angiogenic growth factors with fibrin matrix enhances synthesis and deposition of insoluble elastin and collagen in the matrix, within 10 days of in vitro culture.The results suggest that a carefully engineered fibrin composite matrix may support EC growth, survival, and remodeling of ECM in vitro and impart optimum properties to the construct for resisting the shear stress at the time of implantation. Key Words: Fibrin—Vascular tissue engineering—Extracellular matrix—Elastin—Collagen IV —Tissue remodeling—Growth factors—Fibronectin. To produce tissue-engineered constructs, organ- specific cells are often seeded onto biodegradable scaffold in vitro and are allowed to remodel prior to transplantation. Ideally, the cells should synthesize tissue-specific extracellular matrix (ECM) eventually to produce a new functional tissue as the scaffold degrades with time.The scaffold constituted with syn- thetic materials is expected to support cell growth and tissue development though, most of the time, cells do not get all the signals required for growth, differentia- tion, and survival on it. Therefore, lack of tissue remodeling on synthetic scaffolds has been a major problem in most of the tissue engineering attempts. Stability of endothelial cells (EC) in the vascular construct is essential to resist the shear stress of blood flow so that cells are not displaced from the lumen when the flow is restored after implantation. To achieve postimplant EC survival and vaso- responsiveness of the construct, remodeling of ECM underlying the EC should be achieved before implantation. The importance of fibrin in the wound-healing response suggests that it can be harnessed to produce improved matrices incorporated with signaling molecules. The advantage is that fibrin can function as a matrix for presentation of other cell-adhesion molecules such as gelatin and fibronectin (FN) and growth factors, whereas fibrin may be readily resorbed to promote remodeling through normal fibrinolysis. Studies have proven that vascular endothelial cell growth factor (VEGF) and fibroblast growth factor-2 (FGF-2) bind with high affinity to fibrin and fibrinogen (1,2). Fibrin has been shown to be an effective substrate for EC adhesion and proliferation on biomaterial surfaces (3). Cylindrical fibrin gel- tissue constructs based on ovine smooth muscle and doi:10.1111/j.1525-1594.2008.00670.x Received May 2007; revised January 2008. Address correspondence and reprint requests to Dr. Lissy K. Krishnan, Thrombosis Research Unit, Biomedical Technology Wing, SCTIMST, Trivandrum-695012, India. E-mail: lissykk@ sctimst.ac.in Artificial Organs 33(1):16–25, Wiley Periodicals, Inc. © 2009, Copyright the Authors Journal compilation © 2009, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc. 16