In Situ Investigation Of New Biodegradable Ureteral Stent

BackgroundThe traditional ureteral stent have been widely used in urologicalsurgery since it was first developed in 1967. The appearance ofdouble-J and double-pigtail stent configuration have greatly decreasedthe incidence of surgical complication, and many urological surgerieshad benefited from this kind of stent drainage. However, there aresome problems to be solved, which have greatly limited theapplication and development of ureteral stent. The problems of thestent includes some aspects: the selection of physical, chemical orbiomaterial type, shape and properties.The traditional indegradable ureteral stent has some shortcomings.First, a second endoscopical procedure of removing the stent at theend of the treatment period was inevitable. Second, after the tentdetains over a long period of time, it's wall formate calculus whichwill be difficult to be taken out, and then it's tenacity decreases at thesame time, it's brittleness increases. when the sent is taken out, it willeasily be cracked, evenly it should be taken out by surgical operationagain. Third, the stent implantation might cause bladder irritation orureteral reflux, which might result in leakage of urine at theanastomosis site and infection. It was reported that the urine leakage atthe anastomosis site would induce local fibrous tissue proliferationand result in stenosis of the anastomosis site in the end.Fouth,migration of stent might cause redrawing difficulties afterimplantation. In some case a second operation would be necessary.Above all the urologists should pay their attention to the investigationof a new biodegradable stent.Both science research and clinical experience have alreadyconfirmed that biodegradable material in the medical science realmcan be applied safely and usefully. The researcher has alreadymanufactured a SR-PLGA and SR-PLA urethra stent, which is appledin the treatment of under urinary obstruction, the treatment has gainedsatisfied curative effect. Currently the researcher try to manufacture akind of new biodegradable urethra stent, which degradates completelyand voides out with the urine flow after heal ureter to drain urine andmake a pedestaled function. This will avoid taking out the stent againby cistoscope woundly. Vesicoureteric reflux and the stimulatelysymptom which will produce when the stent detain for a long time inbladder will be avoided. An ideal biodegradable stent should be designed to maintainexcellent biocompatibility properties as well as the role as a transientinternal support and drainage. It should help decrease the rate ofanastomosis site stenosis. Also, after finishing its mission, the stentshould be degraded and voided out with urine flow immediately. Objective This study was based on a negative direction project: medicalapplication-material properties-physical structure-chemical structure-molecular constitution. PCLGA (block copolymers of lactic acid andglycolic acid 80:20) were manufactured, which will be made into atube for ureteral in situ study. Then we study the law of materialbiodegradation, effectiveness of the stent working as an internaldrainage and the stent's influence on in situ histology and dynamiccharacteristics of the ureter. The feasibility of this kind ofbiodegradable ureteral stent would be demonstrated through the study. Method 1. Intravenous excretory pyelogram (IVP). Observed animalsreceived anesthesia and took IVP 1,3,5 weeks after internal drainagewith PCLGA (1:3:1) ureteral stent. 2. In situ histopathological response to PCLGA (1:3:1) ureteralstent implantation. The animals were sacrificed after 1,3,5 weeks'internal drainage with PCLGA (1:3:1) ureteral stent. Histopathologicalexamination of the kidney and ureter were taken immediately. 3. Dynamic changes of ureter after long-term implantation of thestent (5weeks). Peristalsis was observed when the animals wereanesthetized after 5weeks'internal drainage with PCLGA (1:3:1)ureteral stent. As the animals were sacrificed, the entire urinary tractswere excised. One end of each stented and unstented was ligated andthe other cannulated with a small angiocath and filled with saline at apressure of 60 cm water. The diameters at the stent level of uretersboth sides were measured. Result 1. PCLGA (1:3:1:20) ureteral stent is imaged on X-rayirradiation . 2. Group A: Results of intravenous excretory pyelogram (IVP):Pelvis of normal side were imaged 3 minute after contrast agentinjection. The entire ureter of nnormal side were imaged 10 minutesafter contrast agent injection. The Pelvis of oprational side wereimaged10 minute after contrast agent injection. The ureter wereimaged unsharpnessly 20 minute after contrast agent injection. GroupB: Results of intravenous excretory pyelogram (IVP): Pelvis of bothsides were imaged 3 minute after contrast agent injection. The entireureter of both sides were imaged 10 minutes after contrast agentinjection. Symmetry of both sides were observed in three animalsexcept one animal was observed slight dilatation in the upper segmentof stented ureter which had got right in the followingweekexamination.3. In situ histopathological results. Acute inflammation whichwas observed in the ureters stented with PCLGA 1: 3: 1) ureteral stentwas slight and reversible. Mild changes of epithelial hyperplasia,inflammation of the lamina propria; edema, fibrous degeneration,giant cell reaction of the lamina propria were not observed. 4. Result of dynamic study of ureter after a long-termimplantation of the stent (5wekks). No ureteral dilation was observedin PCLGA group. Peristalsis of ureters was not influened by theimplantation of PCLGA (1:3:1) ureteral stent. Discussion The experiment on the foundation of the PLGA ureteral stentmake a further improvement of the PLGA. For increasing of thePCLGA tenacity and decrease time of the PCLGA degradation, so wemanufactured the PCLGA ureteral stent (CL: LA: GA: is 1: 3: 1; addthe barium to it, barium: PCLGA is 1:9), and we design the funneltype which can be put into the dilated pelvis. The PCLGA (1: 3: 1)ureteral stent is clearly imaged on X-ray irradiation, we can observatethe position, degradated degree of the stent. and whether it broke.Results indicated that the use of biodegradable stents was feasiblewith favorable diographic and fluid flow results. The degraded timewhich is about 5 weeks is fit for the application of clinic. Thehistocompatibility of the tent is better. However the phenomenon ofsent breaking shape still exists, so the festure designand fixing way ofthe stent still are not ideal, are far away with the clinical application,are still problems that is immediately resolved. Conclusion This result indicated that the stent is imaged. the inflammationrelated to PCLGA stent was mildew and recoverable. This studydemonstrated that the PCLGA (1: 3: 1) stent could serve as a scaffold...