A chemical analysis of the clogging process of polymeric biliary endoprostheses

Insertion of polymeric biliary endoprostheses is widely used as a method of palliation of malignant strictures of the biliary tree. Despite the succes s of this technique, clogging of the stent in a few months is still an exis ting problem. The aim of the present study has been to investigate the caus es of the obstruction, considering both the stent material and the composit ion of the obstructing deposit. 16 ready-to-implant and 33 occluded retriev ed prostheses were analysed by ATR-FTIR spectroscopy. The clogging sludge w as recovered and studied by FTIR spectroscopy and pyrolysis derivatisation/ gas chromatography/mass spectrometry (Py/GC/MS). The results of the analyse s showed that the deposit was mainly formed by proteins, bilirubin, calcium palmitate and bilirubinate, cholesterol and its fatty acids salts. It was found that approximately 50% of the examined ready-to-implant samples were made of ethylene-vinylacetate copolymer (EVA) instead of polyethylene (PE), as was stated in the producer declaration. Moreover, 94% of the retrieved samples were found to be made of EVA indicating that this material is less suitable than PE for this application. All retrieved PE and EVA stents show ed a protein-like black layer strongly absorbed on the surface. (C) 2001 El sevier Science Ltd. All rights reserved.