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.

Purpose: Conventionally fractionated gamma-irradiation results in severe damage of tumor capillaries associated with decreasing oxygen partial pressure within the tumor. The present study was undertaken to assess whether vasculo-connective changes are less pronounced after continuous hyperfractionated irradiation, implying better tumor oxygenation and improved radiosensitivity.Materials and Methods: Twenty rats with an isotransplanted R1H rhabdomyosarcoma were irradiated for 12 days with 2 daily fractions of 2.5 Gy (Delta t = 6 h). After 0, 15, 30, 45, and 60 Gy, tumor tissue of 4 rats each was analyzed histologically and electron-microscopically.Results: Untreated rhabdomyosarcomas were composed of spindle-shaped tumor cells with numerous mitoses. There were many apoptotic nuclei and a large central necrosis. Tumor capillaries showed a continuous lining of flattened endothelial cells with broad overlapping cell contacts overlying a delicate continuous basal lamina. During irradiation, mean tumor volume declined from 1.9 cm(3) to 1.2 cm(3). The number of atypical mitoses and apoptoses increased and numerous giant tumor cells appeared. The proportion occupied by necrotic tumor tissue rose from 30% to 60%. After 15 Gy (3 days), a marked vasodilatation was apparent accompanied by an interstitial edema. Occasionally, endothelial cells were rounded up and showed indented nuclei, with the underlying basal lamina disintegrated. These changes progressed with increasing radiation doses. After 30 Gy (6 days), leukocytes started to adhere to the endothelial wall. Electron-dense fine fibrillar and basal lamina-like deposits appeared in the perivascular space. Endothelial cell edema was only observed after 60 Gy (12 days). Cell contact areas were shortened, however, the endothelial lining was not interrupted. No signs of radiation fibrosis were observed.Conclusion: Continuous hyperfractionated irradiation induces relatively discrete alterations of the vasculo-connective tumor tissue as compared to conventional irradiation. This may be an advantage with respect to tumor blood flow, oxygenation, and thus, radiosensitivity. (C) 1999 Elsevier Science Inc.