An electron microscopic study on biliary stent materials

Clogging of biliary stents remains an important clinical problem. In vitro studies have shown less sludge formation on the surface of Teflon stents. Recently, stents of Teflon material were used in clinical trials and have shown contradicting results. In this study we investigated the surface characteristics of unused commercially available biliary endoprostheses by scanning electron microscopy. Materials and methods: A total of 8 different types of unused 10 Fr endoprostheses were examined: Polyethylene Amsterdam type (Olympus, PEN Medicals, Scandimed, Wilson-Cook), Polyurethane Amsterdam type (Biosearch), Teflon Amsterdam type (PBN Medicals), Teflon Tannenbaum type (Wilson Cook), and a Tannenbaum type stent with a thin stainless steel mesh between an inner Teflon coating and an outer polyamide layer (Olympus). The stents were cut longitudinally, dried and sputter coated with approximately 15 nm of gold. Random areas of each section were then examined using an ISI SS 40 electron microscope at an accelerating voltage of 5,10 and 25 kV. Results: All Polyethylene stents showed a surface with small irregularities. Polyethylene stents manufactured by PBN Medicals and Scandimed showed in addition areas with barbs protruding in the lumen. Both Amsterdam and Tannenbaum types of Teflon stents showed multiple shallow pits and ridges along the entire longitudinal axis. The Tannenbaum type stent also showed multiple particles protruding into the stent lumen surrounded by holes. The stent with a stainless steel mesh and an inner Teflon coating showed a rather smooth surface without evident barbs or other protrusions. However, the stainless steel mesh did show up in the inner surface in the form of small bulges. The Polyurethane stent showed a very smooth surface, virtually free of irregularities. Conclusions: Scanning electron microscopy of unused endoprostheses has shown the most irregular inner surface on stents made of Teflon material. Our results indicate that results of clinical trials conducted with new stent material can be confounded by irregularities in the surface produced during the manufacturing process. We suggest that the inner surface of new stent material should be evaluated by scanning electron microscopy before a clinical trial is initiated.