Construction Of Biodegradable Drug-loaded Biliary Stent Based On Polyhydroxyalkanoate And Its Application In Benign Biliary Stricture

Background:The common bile duct of adult is about 6-8mm in diameter and carries bile from the liver to the small intestine to aid in food digestion.Benign biliary stricture(BBS)is a kind of common benign biliary disease.It is usually caused by cholecystectomy,liver transplantation,primary/secondary sclerosing cholangitis,chronic pancreatitis and choledochojejunostomy.The main clinical manifestations are jaundice,abnormal liver function and pruritus.Long-term bile duct obstruction can lead to repeated infection,resulting in bile duct stones,serious liver function damage and even cholestatic cirrhosis,hepatocellular carcinoma or cholangiocarcinoma.The main goal of the treatment of benign biliary stricture is to solve the obstruction of the bile duct,achieve long-term patency of the bile duct,and maintain liver function.Endoscopic bile duct dilatation combined with biliary stent placement is the preferred treatment for benign biliary stricture and requires maintenance therapy for at least 1 year.Current biliary stents include plastic stents and metal stents.Because they are both not degradable,repeated removal and timely replacement are required,which increases the burden of patients and easily leads to secondary bile duct injury.Meanwhile,long-term placement is easy to cause local tissue hyperplasia,leading to stricture recurrence.Emerging biodegradable stents appear to solve the disadvantages of the above non-biodegradable biliary stents.Gallstone deposition in the lumen and colonization of bacterial membranes often lead to scaffold failure.In addition,current biodegradable materials may lead to tissue hyperplasia and therapeutic approaches do not target the cause of stricture.Therefore,the recurrence rate after biodegradable stent implantation remains high.Objective:On account of above,we used biosynthetic Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)[P(3HB-co-4HB)] to fabricate a novel shape memory and drug-loaded biodegradable stent.The feasibility and safety of the stent were investigated by establishing a benign biliary stricture model in minipigs.Methods:1.Study on production and physicochemical properties of P(3HB-co-4HB).The Cupriavidus necator was used to produce P(3HB-co-4HB)and the substrate was adjusted to produce P(3HB-co-4HB)with different properties.The physical and chemical properties of P(3HB-co-4HB)were investigated by nuclear magnetic resonance,infrared spectroscopy,gel permeation chromatography,thermogravimetric analysis and universal material testing machine.P(3HB-co-4HB)with appropriate properties was selected to construct biliary stents.Meanwhile,3T3 cells and rats were used to explore the biocompatibility of the material.2.P(3HB-co-4HB)loaded triamcinolone acetonide and its inhibition of 3T3 cells in vitro.The drug release characteristics of drug-loaded PHA films were detected by liquid chromatography.PEG(Polyethylene glycol)was added to P(3HB-co-4HB)to improve the drug release efficiency.The appropriate PEG content was selected.Poppy ethyl iodide oil was added to P(3HB-co-4HB)to endow the material visuality under x-ray and appropriate content was selected by X-ray,tensile and compression experiments.In vitro degradation experiments were conducted to explore its degradation characteristics in bile,PBS and HCl.3.Construction and mechanical properties of drug-loaded spiral stents.The mechanical properties of helical stents with different pitch,diameter and thickness were investigated by universal material testing machine.The adhesion,shape memory and self-expansion characteristics of biliary sludge were studied.4.Drug-loaded spiral stent for the treatment of benign biliary stricture.The model of benign biliary stricture was established in minipigs by thermal injury.The drug-loaded helical stent was endoscopically inserted into the bile duct.The efficacy and safety of treatment were evaluated by serology,x-ray and histopathology.Results:1.P(93.9%3HB-co-6.1%4HB)had good tensile and compressive properties.Compared with P3 HB,the brittleness of P(93.9% 3HB-co-6.1%4HB)had been greatly improved,which could be used to construct stents.Results show that it has good biocompatibility.2.P(3HB-Co-4HB)could successfully load and release triamcinolone acetonide smoothly.Adding 1% poppy ethyl iodide oil to P(3HB-co-4HB)could obtain good imaging effect and had excellent mechanical properties.3.In three groups divided by different pitch,helical stent with 0 pitch could provide the best support.Stent with outer diameter of 2.8 mm and thickness of 0.4 mm could achieve similar mechanical properties as clinical plastic stents.The mass of plastic stents increased in bile,while the mass of PHA helical stents decreased in bile suggesting that it had self-cleaning function.PHA helical stents had shape memory and self-expansion effect in many solvents,which was most obvious in acetone.4.The model of benign biliary stricture was successfully established by thermal injury.The drug-loaded helical stent was successfully implanted into the bile duct under endoscope and the dilated bile duct could be observed under X-ray.Compared with the group without stent implantation,the lumen in stent group was unobstructed and the tissue hyperplasia was greatly improved.Conclusion: P(3HB-co-4HB)had controllable mechanical properties and good biocompatibility.By adjusting the substrate,we obtained P(3HB-co-4HB)with appropriate mechanical properties.By adding PEG to P(3HB-co-4HB),the drug release speed was improved.The stents showed shape memory and self-expansion effects in a variety of solvents.It had a self-cleaning effect on bile sludge in bile.When drug-loaded helical stents were placed into the bile duct of the modeled minipig under endoscopy,the stents not only provided a good mechanical support,but also effectively inhibited tissue hyperplasia by releasing triamcinolone acetonide.