Application Of PLGA-PEG-PLGA Thermogel Solution In Digestive Endoscopic Procedures As Submucosal Injection Substance

Part OneObjective: Endoscopic submucosal dissection (ESD) is the optimal clinical therapyfor early stage neoplastic lesions in gastrointestinal tract. It is, however, faced with acrucial problem of difficulty in learning and perforation with high frequency. Formation ofa submucosal fluid cushion (SFC) via a fluid injection is the best way to avoid perforation,and thus an appropriate biomaterial is vital for this minimally invasive endoscopictechnique.Methods: In this study, we introduced an injectable thermogel as a novel submucosalinjection substance in ESD. The hydrogel synthesized by us was composed of poly(lacticacid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)(PLGA-PEG-PLGA) triblock copolymers. The polymer/water system was a low viscousfluid at room temperature and thus easily injected, and turned into a no-flowing gel at thebody temperature after injection. The submucosal injection of the thermogel to create SFCswas performed in both resected porcine stomachs and living minipigs.Results: High mucosal elevation with a clear margin was maintained for a longduration. Accurate en bloc resection was achieved with the assistance of thermogel. Themean procedure time was strikingly reduced. Meanwhile, no obvious bleeding, perforationand tissue damage were observed. The application of the thermogel not only facilitated theESD procedure, but also increased the efficacy and safety of ESD.Conclusions: The PLGA-PEG-PLGA thermogel provides an excellent submucosalinjection system, and has great potential to improve the ESD technique significantly. Part TwoObjective: Tunnel endoscopy is an innovative endoscopic technique which plays acrucial role in multiple endoscopic interventions. The creation of a submucosalgastrointestinal tunnel is, however, still technically challenging and time-consuming,which significantly limits its clinical applications. To evaluate the use of a biocompatibleand biodegradable poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid)(PLGA-PEG-PLGA) thermogel (a physical hydrogel formed simplyby body heating after injection) as the submucosal injection agent for facilitating theestablishment of a submucosal tunnel in gastrointestine.Methods：The minipigs were fasted for48h before experiment and anaesthetised byintravenous injection of pentobarbital sodium. SMTs in esophagus, stomach, and colon ofthree minpigs were attempted to creat by submucosal injection of the thermogel solution. Aforward-viewing endoscope was attached to a transparent cap and was used to tunnel. ASengstaken-Blakemore tube was inserted into the colon of minipig to clear up theoperational colon segment. Next, the cap-fitted endoscope was introduced into thedigestive tract through the mouth or anus and reached the target site. The polymer solutionwas injected into submucosa using a22-gague fine-needle aspiration needle through theworking channel. Then, the polymer solution spontaneously transformed into a semi-solidgel due to contacting with the physiological heat, resulting in the formation of a thicksubmucosal cushion. Afterwards, a1.5-cm incision was performed on one side of thesubmucosal cushion using a Dual-knife. The cap-fitted endoscope was introduced into thesubmucosal space and moved forward gradually by suctioning the blue gel until theaccomplishment of tunnel. The whole procedure was recorded and the whole volume ofinjected thermogel solution for each tunnel was calculated. After the procedure, pigs weresacrificed and necropsies were performed immediately. The operational digestive tractsegment and adjacent organs were examined carefully to evaluate tissue injury. Meanwhile,the resected colonic segment subjected to another submucosal injection of the thermogel exvivo. The tissue samples of injected colonic mucosa were obtained, fixed with10%neutralbuffered formalin, and embedded in paraffin. Histological sections were stained withHaematoxylin-Eosin (HE), and observed on a light microscope.Results: Submucosal tunnels were established successfully in all desired sites withthe assist of the thermogel for all three minipigs. The tunnels were located in the esophagussegment ranging20-25cm to the mouth, gastric body, and the colon segment ranging15-20cm to the anus. Each injection of the thermogel formed a thick submucosal cushionin target sites. The gel was sunctioned easily by our endoscope and tunnel was createdquickly. Additional electrocautery or blunt dissection was not required during theprocedure. Neither major bleeding nor perforation occurred. Meanwhile, no obviouslaceration of mucosa and muscularis propria was observed during necropsies. Histologicalexamination further demonstrated that submucosal auto-dissection was conducted in the cushion along the inherent anatomical layer.Conclusions: Our experiments confirmed that PLGA-PEG-PLGA thermogel wassuitable as a submucosal injection substance to establish tunnels safely, conveniently, andrapidly in gastrointestine, and had a significant advantage by conducting submucosalauto-dissection in the cushion along the inherent anatomical layer. Part ThreeObjective: Natural orifice transluminal endoscopic surgery (NOTES) is a newlyemerging kind of procedures and has a unique advantage. It makes “no scar” come true andavoids the compliaction of insicion infection and pain, which greatly acceleratepost-procedure recovery and reduce medical expense. However, it has an obvious inherentdisadvantage for digestive endoscope to perform NOTES: it is flexible and lacks enoughaxial force, thus it is difficult to perform intraabdominal dissection. Therefore, thedevelopment of new methods that simplify the procedure associated with NOTES is thusstrongly desired to proliferate and enlarge its practical applications. The current studyassessed the feasibility and safety of NOTES-celiac plexus neurolysis (CPN) assisted byPLGA-PEG-PLGA thermogel injection in living minipigs.Methods：The minipigs were fasted for48h before experiment and anaesthetised byintravenous injection of pentobarbital sodium. A echoendoscope was inserted into thestomach of the minipigs. The thermogel was injected into the operational site through afine-needle aspiration needle under ulatrsound guidance. Next, an endoscope wasintroduced into the esophagus, created a submusal tunnel, and incised the esophageal wallto enter the abodominal cavity. Then we found the thremogel and incised it at one side withendoscopic kinfe.The endoscope was introduced into the inter-gel space and movedforward gradually by suctioning the blue gel until reach the target operational site. Thewhole procedure was recorded. After the procedure, pigs were sacrificed and necropsieswere performed immediately. The operational sites and adjacent organs were examinedcarefully to evaluate tissue injury.Results: NOTES-CPN were performed successfully in abdominal cavity of all threepigs without complication with the assist of the thermogel. The average volume of injectedthermogel was36ml (range25-28ml). Every submucosal injection formed a hemispherical gel block. The cap-fitted endoscope was inserted into inter-gel space and thegel was suctioned easily. There was no need for additional electrocautery or bluntdissection. Neither bleeding nor perforation occurred. No obvious laceration of mucosaand muscularis propria was observed in necropsies as well as iatrogenic injury to adjacentorgans. The average operating time for the whole procedure was35minutes (range28-41minutes).Conclusions: Our experiments confirmed that PLGA-PEG-PLGA thermogel wassuitable as a abdominal injection substance to assist NOTES prodecures and made themsafe, easy, and rapid.