Abstract: The invention relates to self-cleaning porous structures, e.g., layers or coatings, fabricated within, applied to, or deposited on a blood contacting surface of a medical device, to prevent activation and aggregation of platelets thereon. In certain embodiments, the layer or coating is composed of multi-layered fibers. The porous structure is applied to or deposited such as to form a permeable wall on the blood contacting surface. The blood travels into the wall and subsequently back out (reversing back into the lumen) during a cardiac cycle. Reversal flow is controlled during the diastole phase such that the backward flow repels the platelets and prevents their activation and aggregation and therefore, minimizes thrombus formation.