Does heparin coating reduce encrustation of biliary plastic endoprostheses? A prospective randomized trial

Design, safety and efficacy evaluation of gemcitabine-eluting nanoyarn-integrated heparinized self expanding metallic stents for long-term management of malignant biliary obstruction

Malignant biliary obstruction presents a significant therapeutic challenge and has serious consequences including cholangitis and death. Clinically, biliary stenting using self-expanding metallic- stent(SEMS) relieves this obstruction. However, stent occlusion occurs with time due to tumor/epithelial in-growth and bacterial colonization. To achieve sustained palliative benefit of stent-based approaches, both biliary sludge formation and in-growth need to be obviated. In this study, an innovative approach was adopted to inhibit sludge deposition and tissue in-growth by developing a heparinized drug-eluting SEMS. For this, heparinisation was performed on dopamine-functionalised-stents, which averted bile protein adsorption in vitro. Further, Gemcitabine loaded polycaprolactone electrospun-nanoyarns were integrated with heparinized-SEMS to achieve sustained drug release for nearly six months in vitro. Nanoyarn integration with heparinized-SEMS did not hamper its crimping, ease of deployment or functional behaviour. In vivo safety and efficacy were evaluated for five months after implantation in porcine bile duct through Endoscopic Retrograde Cholangiopancreatography. Minimal sludge deposition with no obstruction in bile flow, good stent patency and localized-sustained drug elution were observed for nanoyarn-integrated heparinized-SEMS. No alterations in the biochemical parameters, nor any inflammatory reactions were observed in vivo, all in comparison to control-SEMS. Overall, our research established an efficient multipronged strategy to tackle malignant biliary obstruction. STATEMENT OF SIGNIFICANCE: Bile duct occlusion due to cancer has several life-threatening consequences. This is clinically treated using metallic stents, with simultaneous intravenous use of anti-cancer drugs at high-doses. Nevertheless, tumor-growth along with bile-sludge accumulation happens after stenting, causing re-occlusion. Existing research uses stent modifications that fail to tackle both simultaneously, yielding short-term efficacy. To address this, heparinized-metallic stents were modified using chemo-drug eluting polymeric-nanoyarn integration. The key features of this device are: nanoyarn-integrated, uncovered stent design facilitating easy endoscopic implantation in bile duct; reduced bile-sludge deposition; prolonged, low-dose, localised drug release that can mitigate tumor-growth; and provide long-term stent patency without stent migration. This device proved to be safe, functional and efficacious for a period of five months in pig bile duct.

Biliary stents for active materials and surface modification: Recent advances and future perspectives

Demand for biliary stents has expanded with the increasing incidence of biliary disease. The implantation of plastic or self-expandable metal stents can be an effective treatment for biliary strictures. However, these stents are nondegradable and prone to restenosis. Surgical removal or replacement of the nondegradable stents is necessary in cases of disease resolution or restenosis. To overcome these shortcomings, improvements were made to the materials and surfaces used for the stents. First, this paper reviews the advantages and limitations of nondegradable stents. Second, emphasis is placed on biodegradable polymer and biodegradable metal stents, along with functional coatings. This also encompasses tissue engineering & 3D-printed stents were highlighted. Finally, the future perspectives of biliary stents, including pro-epithelialization coatings, multifunctional coated stents, biodegradable shape memory stents, and 4D bioprinting, were discussed.

Reducing deposition of encrustation in ureteric stents by changing the stent architecture: A microfluidic-based investigation

Ureteric stents are clinically deployed to retain ureteral patency in the presence of an obstruction of the ureter lumen. Despite the fact that multiple stent designs have been researched in recent years, encrustation and biofilm-associated infections remain significant complications of ureteral stenting, potentially leading to the functional failure of the stent. It has been suggested that "inactive" side-holes of stents may act as anchoring sites for encrusting crystals, as they are associated with low wall shear stress (WSS) levels. Obstruction of side-holes due to encrustation is particularly detrimental to the function of the stent, since holes provide a path for urine to by-pass the occlusion. Therefore, there is an unmet need to develop novel stents to reduce deposition of encrusting particles at side-holes. In this study, we employed a stent-on-chip microfluidic model of the stented and occluded ureter to investigate the effect of stent architecture on WSS distribution and encrustation over its surface. Variations in the stent geometry encompassed (i) the wall thickness and (ii) the shape of side-holes. Stent thickness was varied in the range 0.3-0.7 mm, while streamlined side-holes of triangular shape were evaluated (with a vertex angle in the range 45°-120°). Reducing the thickness of the stent increased WSS and thus reduced the encrustation rate at side-holes. A further improvement in performance was achieved by using side-holes with a triangular shape; notably, a 45° vertex angle showed superior performance compared to other angles investigated, resulting in a significant increase in WSS within "inactive" side-holes. In conclusion, combining the optimal stent thickness (0.3 mm) and hole vertex angle (45°) resulted in a ∼90% reduction in encrustation rate within side-holes, compared to a standard design. If translated to a full-scale ureteric stent, this optimised architecture has the potential for significantly increasing the stent lifetime while reducing clinical complications.

Bile Flow Phantom Model and Animal Bile Duct Dilation Model for Evaluating Biliary Plastic Stents with Advanced Hydrophilic Coating

Background/Aims

The efforts to improve biliary plastic stents (PSs) for decreasing biofilm formation and overcome short patency time have been continued. The aim of this study is to evaluate the effect of advanced hydrophilic coating for patency and biodurability of PS.

Methods

Using an in vitro bile flow phantom model, we compared patency between prototype PS with hydrophilic coating (PS+HC) and prototype PS without hydrophilic coating (PS−HC). We performed an analysis of the degree of luminal narrowing by microscopic examination. Using an in vivo swine bile duct dilation model made by endoscopic papillary closure and stent insertion, we evaluated biodurability of hydrophilic coating.

Results

In the phantom model, PS+HC showed less biofilm formation and luminal narrowing than PS−HC at 8 weeks (p<0.05). A total of 31 stents were inserted into the dilated bile duct of seven swine models, and 24 stents were successfully retrieved 8 weeks later. There was no statistical difference of stent patency between the polyethylene PS+HC and the polyurethane PS+HC. The biodurability of hydrophilic coating was sustained up to 8 weeks, when assessing the coating layer by scanning electron microscopy examination.

Conclusions

Advanced hydrophilic coating technology may extend the patency of PS compared to uncoated PS.

Drug eluting biliary stents to decrease stent failure rates: A review of the literature

Biliary stenting is clinically effective in relieving both malignant and non-malignant obstructions. However, there are high failure rates associated with tumor ingrowth and epithelial overgrowth as well as internally from biofilm development and subsequent clogging. Within the last decade, the use of prophylactic drug eluting stents as a means to reduce stent failure has been investigated. In this review we provide an overview of the current research on drug eluting biliary stents. While there is limited human trial data regarding the clinical benefit of drug eluting biliary stents in preventing stent obstruction, recent research suggests promise regarding their safety and potential efficacy.

Polysaccharide-based antibiofilm surfaces

Surface treatment by natural or modified polysaccharide polymers is a promising means to fight against implant-associated biofilm infections. The present review focuses on polysaccharide-based coatings that have been proposed over the last ten years to impede biofilm formation on material surfaces exposed to bacterial contamination. Anti-adhesive and bactericidal coatings are considered. Besides classical hydrophilic coatings based on hyaluronic acid and heparin, the promising anti-adhesive properties of the algal polysaccharide ulvan are underlined. Surface functionalization by antimicrobial chitosan and derivatives is extensively surveyed, in particular chitosan association with other polysaccharides in layer-by-layer assemblies to form both anti-adhesive and bactericidal coatings.

STATEMENT OF SIGNIFICANCE

Bacterial contamination of surfaces, leading to biofilm formation, is a major problem in fields as diverse as medicine, first, but also food and cosmetics. Many prophylactic strategies have emerged to try to eliminate or reduce bacterial adhesion and biofilm formation on surfaces of materials exposed to bacterial contamination, in particular implant materials. Polysaccharides are widely distributed in nature. A number of these natural polymers display antibiofilm properties. Hence, surface treatment by natural or modified polysaccharides is a promising means to fight against implant-associated biofilm infections. The present manuscript is an in-depth look at polysaccharide-based antibiofilm surfaces that have been proposed over the last ten years. This review, which is a novelty compared to published literature, will bring well documented and updated information to readers of Acta Biomaterialia.

Novel biliary self-expanding metal stents: indications and applications

Endoscopic insertion of a self-expanding metal stent (SEMS) through a malignant common bile duct stricture is the first line of palliation for malignant jaundice. Patency of these stents remains a major concern. SEMS dysfunction can result from tumor ingrowth, overgrowth and/or clogging. Initial SEMS modifications involved covering the central part of the stent in order to reduce ingrowth and ultimately increase patency. Fully covered stents became available shortly after reports of their use in human patients. The potential removability and radial strength of SEMS have led to evaluation of their use in new indications including benign biliary strictures, post sphincterotomy bleeding and perforation. Other aspects of development include the addition of features such as anti-reflux valves, drug elution and spontaneous biodegradability. These aspects and their clinical implications are reviewed and discussed.

Obstructive component analysis of radioactive stents and common plastic stents in the bile duct

BACKGROUND

Endoscopic placement of a iodine-125 radioactive stent is useful to treat obstructive jaundice with unresectable periampullary tumors. This study aimed to retrospectively evaluate the obstructive component of biliary radioactive stents and discuss the different obstructive mechanism with common plastic stents.

PATIENTS AND METHODS

Twenty consecutive patients with malignant obstruction underwent insertion of stents into the common bile duct, including 10 radioactive stents and 10 polyethylene stents. The radioactive stents were withdrawn after ∼3 months or earlier if clinical signs suggested stent clogging. Polyethylene stents were withdrawn after physical signs suggested stent clogging. Bacteriologic analyses included identification of aerobic and anaerobic bacteria. Stent surfaces were observed by scanning electron microscopy. Stent deposition was identified by Fourier-transformed infrared spectroscopy and pyrolysis derivatization/gas chromatography/mass spectrometry.

RESULTS

Radioactive stent group and polyethylene stent group stents were placed for 86 days (interquartile range 62, 114) and 146 days (interquartile range 105, 181) respectively. The placement duration of the two types of stents was statistically significant. A variety of microorganisms were cultured from the stent deposits. Scanning electron microscope images showed a thicker necrotic layer on the external surface of polyethylene stent than the radioactive stent group. The proportions of obstructive components in each stent were different, but none of them were statistically significant. Necrotic tumor tissue was found in the radioactive stent group.

CONCLUSION

Similar clogging events occurred in both radioactive stents and polyethylene stents. The median duration time of the radioactive stent was shorter, probably because of the smaller inner diameter, and the radioactive seeds exerted no beneficial effect in inhibiting microorganisms.