Interaction with nanoscale topography: The use of nanowelltrapped charged ligand-bearing nanoparticle surfaces to modulate physiological focal adhesions in endothelial cells

Achieving cell adhesion, growth and homeostasis on an underlying biomaterial surface may be a desirable feature in implant device design and tissue engineering. Insight has been gained from numerous cell patterning strategies where spatial cues and physical constraints have been shown to regulate the structure and function of cells. Despite significant advances in modifying substrates for cellular attachment, migration and proliferation, the achievement of confluent and aligned growth of functional endothelial cells on cardiovascular blood-contacting implants under physiologically significant wall shear stress has proven difficult. Recently we have reported on a method that enhances cellular adhesion under flow conditions on synthetic polymer surfaces, without reliance on pro-adhesive protein biomaterials, which are often thrombogenic. In this method we utilize electron beam lithography and size-dependent selfassembly to fabricate line arrays of nanowells allowing entrapment and retention of charged nanoparticles, covalently conjugated with a RGD adhesive ligand, GRGDSPK. This approach is an additive strategy of combining substrata topographic alteration, electrostatic charge and biochemical ligands, all uniquely incorporated as an ensemble of charged, ligand-bearing nanoparticles entrapped in arrays of nanowells. However, the modulation of endothelial cell physiologic mechanisms as a result of ensemble surface exposure remains to be characterized. In this report, we extend our studies and probe cell physiologic mechanisms altered as a result of nanofeatured surface exposure. We first examined the functional intactness or normalcy of endothelial cells adherent to the nanofeatured ensemble surface utilizing standard immunostaining and flow cytometry methods. We found β1-integrin expression dominated quiescent adherent endothelial cells while αVβ3-integrins expression was more common in migratory cells. Endothelial cells were noted to express high levels of PECAM-1 over time when exposed to nanofeatured surface and RGD peptides. For understanding the contribution of the nanofeatured surface (entrapped RGD conjugated nanoparticles) to cell adhesion, cytochalasin B was used to alter cell spreading. Confocal microscopy illustrated the uptake of nanoparticles in endothelial cells on composite surfaces, as well as the inhibition of this endocytosis by cytochalasin B. After prohibiting the cells from engulfing nanoparticles, we found an 80% reduction in cell adhesion; suggesting that an endocytic mechanism might play a role in maintaining cell adhesion. Nanofeatured ensemble surfaces appear to be good substrates for achieving a high level of EC adhesion, with maintained growth and stability.