BACKGROUND & AIMS:The major drawback of plastic stents for biliary drainage is the occlusion by sludge. Sludge is accrued because the stent surface allows for the adherence of proteins, glycoproteins, or bacteria and the bile flow is insufficient to clean the surface. In this study, experience from nanotechnology to achieve a clean surface by improved soil-release characteristics is used to optimize biliary stent surface. The aim of this study was to examine sludge accumulation in relation to surface characteristics designed by nanotechnology. METHODS:A variety of inorganic-organic sol-gel-coated stents were incubated in sterilized human bile and enzyme-active Escherichia coli for 35 days. Materials were Teflon (DuPont, Wilmington, DE) coated with hydrophobic Clearcoat (NTC, Tholey, Germany), Teflon with sol-gel coating synthesized of organic epoxides of 190 g/mol or 500 g/mol, and propylaminosilane without or with fluorsilanes for increased hydrophobicity. Scanning electron microscopy and semiquantitative analysis, blinded to the type of coating, were used to determine the amount of sludge accumulated on the surface. RESULTS:Sludge deposition was reduced on the designed surfaces as compared with uncoated Teflon and Clearcoat. The performance of high molecular (500 g/mol) was superior to that of low molecular (190 g/mol) epoxide ligand. However, increasing hydrophobicity by adding fluoraminosilanes resulted in increased adherence of sludge. Less than a micrometer-thin sol-gel coating is inexpensive because very little coating material is required. This is the first published data comparing systematically modified surfaces of biliary stents using nanotechnology. CONCLUSIONS:Optimized soil release by sol-gel nanocoating of plastic stents may prevent biliary plastic stents from clogging.

Background: The major drawback of plastic stents for biliary drainage is the occlusion by sludge. Sludge is accrued due to adherent factors for glycoproteins and bacteria, such that the rate of bile flow is insufficient to remove the sludge. Neither antibiotic measures nor modification of plastic stent design (caliber >10 Fr; hydrophilic coating) reduce the rate of stent occlusion. In this study, the experience from nanotechnology to achieve clean surfaces based on soil-release characteristics is used to optimize the internal surface of plastic biliary stents. Aim: To examine sludge accumulation in relation to plastic surface characteristics (reduction of adherent factors) designed by nanotechnology. Methods: A variety of anorganic-organic sol-gel coated stents were incubated in sterilized human bile for 40 days after addition of enzyme active E.coli. The stent materials were uncoated Teflon and Teflon coated with high and low molecular epoxy resin hydrophobized by 3 different amino-fluoro-silanes. During incubation cell culture plates (each hole filled with an impacted piece of plastic stent material and 3 ml of infected bile) were inclined up and down 10x/minute to simulate bile flow. After every 48 hours 1 ml of bile was removed from each hole and replaced. Scanning electron microscopy (SEM) was performed blinded to the type of coating. The amount of sludge accumulated on the surface was determined semi-quantitatively. Results: Partially hydrophilic-hydrophobic surfaces accumulated less sludge than the hydrophobic surface of Teflon. High-molecular weight (500 M) epoxy resin performed better than low-molecular weight (190 M) epoxy resin. The lowest sludge accumulation was found on 75% hydrophobic surface using “hydrophobic modification type VI” epoxy resin. This corroborated the results of our earlier study. Discussion and Conclusion: Nanometer thin sol-gel coating is inexpensive, because very little coating material is necessary. The coating with the lowest sludge accumulation has been shown to have a superior soil-release characteristic on other surfaces (e.g. cars). Optimized soil release may be the key to prevent biliary plastic stents from clogging. More detailed studies to determine the optimal surface are warranted.

The thermal behaviours of alternating styrene-maleic anhydride copolymer (St/MAn), styrene-methyl maleimide copolymer (St/MMI) and copolymers with different contents of MMI were studied by means of a simultaneous thermal analyser and quadrupole mass spectrometer system (STA/QMS). In addition, special measurements were carried out by a pyrolysis-gas chromatography-mass spectrometer (Py-GC-MS) and a differential scanning calorimeter (DSC). The glass transition of the copolymers in influenced by the degree of imidization, The decomposition behaviour of pure styrene-maleic anhydride copolymer differs from that of styrene-methyl maleimide copolymer. The favoured process of degradation of maleic anhydride-rich structures is reaction in the chains, and that of methyl maleimide-rich structures is the random chain break.