Structured surfaces for hemocompatibility

Abstract

The rise of micro- and nano-technologies has brought to light intriguing examples of scale-driven performance in a diverse array of fields. The quest to create highly hydrophobic surfaces is one such field. The application of this new generation of hydrophobic surfaces, however, has not received much research attention in comparison to the development of new methods to create surfaces. The one application of super hydrophobic surfaces that has received significant attention is their ability to resist fouling by dirt and other contaminants. Much of the attention paid to this application is due to the discovery that the Lotus flower and several other plants use nano-structure to keep themselves clean, a property that has an important place in the world of biomedical engineering. Any biomedical device that is implanted in the body has to avoid the body's natural defense system, which can quickly cause device failure. One of these natural defenses specific to blood is the clotting reaction. Any surface, implanted or external, that comes into contact with blood is considered an intruder, and the blood seeks to isolate the object by clotting on the foreign surface.

(cont.) The clotting process involves the identification of a foreign surface, the adsorption of proteins onto that surface, and then the agglomeration of platelets on the proteins to form a clot. Much like the surface tension forces that make structured super hydrophobic surfaces possible, the clotting reactions are surface driven. This research seeks to show that the surface area reduction that results in super hydrophobic surfaces can be used to prevent blood coagulation on artificial surfaces. It is shown that appropriate surface structure, slender posts with a larger period relative to their width, can lead to extremely high apparent contact angles (0'=160°). Additionally, it is shown that the same surfaces scientifically reduce platelet agglomeration in vitro under static blood. In dynamic flow conditions, bacteria are shown to adhere less frequently to similarly structured surfaces with smaller critical dimensions. Computational fluid simulations are used to examine the flow conditions near the structured surfaces that lead to the non-fouling behavior exhibited experimentally.

(cont.) A combination of increased flow velocity near the surface, reduced shear rate in the flow, and the size of the structures relative to the fouling agent (platelet or bacteria) in conjunction with the contact area benefits illustrated in the static case are hypothesized to lead to reduced fouling in dynamic flow.