Surface modification for enhanced cell adhesion under high shear stress conditions

Abstract

The vascular system, one of the bases of life mechanisms, connects tissues and organs by means of blood vessels, supplies nutrient–containing blood throughout the body and removes waste products. Any functional abnormalities in vascular system can cause critical diseases such as tumor, angiogenesis and cancer. Cardiovascular diseases are the leading cause of death globally. Therefore, the vascular science is a field with strong translational focus to develop insight in vascular physiology and disease treatments. Many of the vascular functions, hemodynamic forces, cellular interactions and related diseases are strictly associated to the physical geometry of vasculature. Moreover the endothelial lining of blood vessels is subjected to a continuous hemodynamic shear stress, which is also essential to regulate cell morphology and functions. Replication of cardiovascular system in vitro requires a dynamic 3D microenvironment to modulate the fundamentals of vasculature and diseases models. Meanwhile, the introduction of microfluidics in vascular research enables us to study disease models in particular dimensions and at well-defined shear stress. Polydimethylsiloxane (PDMS) based microfluidic systems, lined with endothelial cells, provide a versatile platform to study the mechanoresponse of cells in vitro. Extracellular matrix proteins are used to coat PDMS surface prior to cell growth to provide cell a natural environment. However, the long-term cell studies are limited due to instability of coated proteins inside PDMS microchannels under physiological shear stress conditions. To increase the stability under flow conditions, various protein-substrate linkages were developed for stable cell growth. PDMS surface was functionalized by using four different methods (i) O2 plasma (ii) (3-Aminopropyl)triethoxysilane (APTES) (iii) APTES-Gluteraldehyde and (iv) protonated APTES, in order to develop a stable bond with collagen–an ECM protein. Moreover, collagen at three different pH values (pH 5, 7 and 9), which attributed to certain charge distribution on molecules, was used to further enhance its bond strength with variety of functionalized surfaces. Different microfluidic device designs were used to evaluate coating efficiency and cell growth under continues shear stress (10-300 dyn/cm2), which is even higher than physiological shear stress. The comparison of all surface modification methods showed that, the electrostatic interaction between APTES mediated surfaces and collagen molecules at higher pH values found to be very stable for subsequent cell growth at high shear stress. Therefore, the surface modification technique based on APTES can also be applied to other ECM proteins, enabling long term in vitro cell studies in PDMS micro-channels to replicate blood vessels and related disease models.