The research deals with new scanning electron microscopic evaluations of the interface between blood and explanted temporary vena cava filters from patients affected by blood disorders. The biological tissues adherent to the filter and the small thrombi formed in vivo were detached from the metallic structure of the device, fixed, dehydrated and prepared for the histological and the electron microscopy. The analyses showed that both samples (thrombus and newly formed tissue) contained foreign, in some cases nano-sized, bodies. The chemistry of these particles was different and varied, and unusual compounds containing non-biocompatible elements like bismuth, lead, wolfram, tungsten were also detected. The interaction between these debris travelling in the blood stream and the blood itself leads to suspect that the formation of the thrombus can originate from these inorganic and inert foreign bodies that act as triggering agent of the blood coagulation.