Modulation of blood and vascular cell compatibility by chemical and topographic cues

Abstract

Cardiovascular disease such as coronary artery disease is the leading cause of death in the modern society. Vascular stents or grafts are the most preferred prosthesis for treating such disease. However, lack of multifunctionality of vascular stents or grafts in terms of inhibiting blood coagulation and smooth muscle cell (SMC) growth while concurrently promoting endothelialization has resulted in higher rates of complications that involve thrombosis and restenosis. A wide variety of environmental cues, particularly surface chemistry and substrate topography, have been shown to regulate blood and vascular cell compatibility. Yet the impacts of these chemical and topographical regulators remain insufficiently characterized, and little is known about the cooperative interplay between chemical and topographic cues in regulating blood and vascular cell compatibility. The objective of this study is to systematically investigate the individual and combined effects of these two types of cues on blood and vascular cell compatibility. Polydopamine (PDA), a mussel adhesive protein inspired coating, was synthesized on TiO₂ surfaces by simple dip-coating method. It was demonstrated that surface characteristics and functionalities of the PDA coating could be readily tuned by varying the initial dopamine concentrations. Moreover, it was provided some new insights into the PDA structure through systematic characterizations. Furthermore, the blood and vascular compatibility of the PDA coating was further explored. The results indicated that the PDA coating significantly promoted endothelial cell (EC) attachment, proliferation, focal adhesion formation, and stress fiber development. In contrast, the PDA coating potently inhibited SMC proliferation. It was proposed that the co-existence of quinone and reactive phenolic hydroxyl groups may be crucial for achieving vascular cell selectivity. These data suggest the promising application of the PDA coating in the vascular stents or grafts. Next, a novel patterned platform featuring two typical geometries (groove and pillar) and six pattern sizes (0.5–50 μm) in a single substrate was developed to evaluate the response of vascular cells and platelets. The results indicated that targeted multifunctionality can be indeed instructed by rationally designed surface topography. The pillars non-selectively inhibited the growth of ECs and SMCs. By contrast, the grooves displayed selective effects: in a size-dependent manner, the grooves enhanced endothelialization but inhibited the growth of SMCs. Moreover, it was suggested that topographic cues can affect response of vascular cells by regulating focal adhesion and stress fiber development, which define cytoskeleton organization and cell shape. Notably, both the grooves and the pillars at 1-μm-size drastically reduced platelet adhesion and activation. Importantly, these findings suggested that the topographic pattern featuring 1-μm grooves might be the optimal design of surface multifunctionality that favors vascular cell selectivity and improves hemocompatibility. To further expand the study, a facile and effective PDA-mediated approach was developed to immobilize heparin onto topographically patterned substrate, and the combined effects of these cues on blood and vascular cell compatibility were systematically investigated. It was observed that immobilized heparin and substrate topography cooperatively modulated anti-coagulation activity, EC attachment, proliferation, focal adhesion formation, and endothelial marker expression. The substrate topography was the primary determinant of cell alignment and elongation, driving in vivo-like endothelial organization. Importantly, combining immobilized heparin with substrate topography empowered substantially stronger competitive ability of ECs over SMCs than each cue itself. Moreover, we clearly elucidated the cooperative interplay between immobilized heparin and substrate topography by a proposed and further testified model. This fundamental and systematic study is expected to further the understanding of vascular cell-substrate interactions, and contribute to the future design of new generation of vascular stent or graft systems.

Date of Award	2014
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology