An Experiment Study On Antibacterial Plastic Stents Coated With Nono-silver In The Management Of Biliary Leakage

Background and objective:Biliary leakage often happened after the injury of thebiliary tract or the organs nearby. Insertion of endoprosthesis into the bilary tract throughthe sphincter of the duodenal papilla can lower the pressure of the biliary tract, and thenreduce leakage of the bile,which aims to treat biliary leakage. But the commoncomplications of the endoprosthesis are occlusion of the stents, and cholangitis. Some paststudies have shown that there are many bacterial colonies in the blocked stents and thestents made of materials usually used now and the attachment have no antibacterial effects.However, some studies have proved that the silver in a low concentration has theantimicrobial efficacy and the decrease of the the silver's size to nano particles can greatlyincrease its antibacterial effectiveness. By now, there are no reports about the applicationof the endoprosthesis coated with nano-silver. Therefore, plastic stents coated withnano-silver are prepared and then investigated their antimicrobial properties andeffectiveness of treating biliary leakage through the animal experiment and in vitro test forthe purpose of providing a new endoprosthesis for the biliary leakage and a base for thefurther clinical experiments.Methods:1) The plastic biliary stents coated with nano-silver were prepared by thechemical redox process with teflon plastic stents as carriers and silver nitrate as material.Then the micromorphology and chemical composition of the coat were dectected by use ofscanning electron microscope(SEM),transmission electron microscopy (TEM)andEnergy Dispersive X-ray analysis(EDXA), and the elastic modulus and the frictionalcoefficient of the stents were measured by scanning tunneling microscope(STM).2) Theantibacterial properties of the plastic biliary stents coated with nano-silver to colibacillus,the dominant flora in the intestines were studied qualitatively and quantitatively.Meantime,their effects of antiadhesion to the colibacillus were observed by SEM.3)8healthy Bama Minipigs were used as the objects and underwent laparoscopic surgery under general anesthesia.The cystic duct was broken at0.5-1.0cm away from its root and thestump was left open. Finally the gallbladder was separated and removed. Then thefeasibility of these models was judged according to the following aspects: blood routineand hepatic function were monitored in24h pre-and post surgery; endoscopic retrogradecholangiography (ERC) was performed at24h after the surgery; the dead pigs in themidway were butchered immediately and the survival pigs at48hours after the surgerywere butchered for observation the stump of the cystic duct.4)40standard Bama minipigswere included in this study. They were established as animal models of biliary leakagethrough laparoscopic surgeries and then divided into3groups randomly. The biliary stentscoated with nano-silver were used in one group(n=15), the common stents in anothergroup(n=15),and the routine anti-inflammatory treatment was given to the control group(n=10). The accidental dead pigs were butchered immediately for the cause of death. Bloodrountine,hepatic function and blood culture were detected regularly preoperation andpostoperation. After the following-up of10days and20days, the survival animals werebutchered half in every group separately. The position of the stents was observed byfluoroscopy. Then the stents were removed out under the sterile condition and the contentswere used to bacterial culture. The bacteria plaques on the suface of the3sections werecompared under SEM. The pathological changes in duodenal papilla,the3segment of thecommon bile ducts were observed and compared by light microscope.Results:1)The teflon stents coated with nano-silver were prepared successfully andthe size of silver particles was from5to80nm. The coat only contained argentum withoutother chemical constituents.With the increasing of thickness of the coat (0.5-5um),theelastic modulus (Young 's modulus) increased and the frictional coefficient decreased in acertain range.2)Qualitative antibacterial tests showed that there were no inhibition zonearound the common biliary stents, while around the stents coated with nano-ailver,therewere inhibition zones with dimatere6.47±0.74mm, which made a significant differencebetween the two group(sp﹤0.05).Quantitive antibacterial tests showed that after the stentswith length0.5cm and diameter8.5Fr were put into two different concentrations ofcolibacillary suspension(106CFU/ml and104CFU/ml), with the increasing of the culture time, the number of bacterial colonies decreased in the experimental group (with stentscoated with nano-silver) and increased in the control group (with common stents); thecolibacillus was killed totally after6hours of culture in the later concentration and theantibacterial rate was100%; the stents coated with nano-silver performed a strongerantiadhesive activity on the colibacillus by SEM.3)The gallbladder, cystic duct,cysticartery and the anatomical relation between the gallbladder and liver together with thecystic duct and commom bile duct could be fully exposed under laparoscopy. Compared topreoperation, the white blood cells,neutrophil and direct bilirubin increased higher afterthe operation(p﹤0.05). Among the8experimental pigs, the cystic ducts of7ones werebroken at0.5-1cm away from the roots of the cystic ducts and one at2cm. ERC wasperformed in8pigs, among which7ones were found obvious leakage of the contrastmedia and one was not.4)Among40minipigs successfully established as the models,30ones underwent the endoprosthesis and the other10ones did not as the control.3pigs inthe stents'group died within20-38hours after the surgery because of the perforation of thecommon bile ducts,which was proved after butchered. All10ones in the control groupdied with5days after surgery because of biliary peritonitis together with infection. Themortality between the stent group and the control group was significantly different(p﹤0.05). Compared to preoperation, the white blood cells in the stent group increasedhigher after the following-up10days(p﹤0.05)and that in the common stent groupincreased higher after the follow-up20day(p﹤0.05),while that in the group with stentscoated with nano-silver were not found obvisous increase. The contents of the stents werecultured and the bacteria were positive in all pigs after the following-up10days and20days without significant difference in two different stent groups(p＞0.05). The two kindsof stents both caused perforation, migrated and slided out,which showed no significantdifferences between them(p＞0.05). On the suface of the stents in the two groups, therewere varying amounts of inflammatory attachments or cystals adhered and bacteria alsodistributed among them. The number of the bacteria in the stents coated with nano-silvewas significantly lower than that in the common stents. The inferior segment of the stentshad more bacteria than the superior and middle part in both two kinds of stents. By light microscope, the pathological changes in duodenal papilla, the equal3segments of thecommon bile ducts were described as follows: mucosal epithelium missed in differentdegrees, the blood vessels in the mucosal layer were dilated and hyperemia, and theinflammatory cells infiltrated in both two stent groups; what' more, in the common stentgroup, the infiltrating of the inflammatory cells within the whole layer was more apparentand abscess could be seen in some pathological sections.Conclusions:1)The plastic biliary stents coated with nano-sliver are prepared by thechemical redox process with teflon plastic stents as carriers and silver nitrate as material.and perform good physical and chemical properties.2)The biliary stents coated withnano-sliver have strong antibacterial and antiadhesive effects on colibacillus.3)Themodels of biliary leakage established under laparoscopy are safe and feasible with a highsuccessful rate;4)Biliary leakage can be treated by inserting plastic stents into biliary tractsof the minipigs. The following up after the endoprosthesis shows that the stents coatedwith nano-silver can interfere with bacterial adhesion and the formation of bacterialbiomembranes and have obvisous inhibitory actions on local cholangitis to promote thehealing of biliary leakage.