Investigation Of A Novel Degradable Ureteral Stent

Objective:To evaluate the biocompatibility of the new biodegradable polyurethane ureteral stent and the biodegradability,drainage effect and safety of the stent in pig model.Methods:1.Cytotoxicity test:uroepithelium cells were used,and gradient degradation polyurethane ureteral stent were cut into small segments of about 2mm,and extracted and made into extracts of different concentrations(original extracts and six concentrations of 1:2,1:4,1:8,1:16 and 1:32),which were added to cultured urine derived epithelial cells for culture.The cell culture medium without extract was used as a negative control,and the cell culture medium with 10%dimethyl sulfoxide was used as a positive control.The absorbance was detected on a microplate,and the relative proliferation rate of cells was calculated as RGR(%).2.Animal assay:gradient degradation polyurethane ureteral stent or biostable stent were randomly placed into the ureter on one side of the pig.Computerized tomography(CT)was performed immediately postoperative.CT and blood studies,liver function tests,renal function tests and urine studies were performed at 1 weeks,2 weeks,3 weeks and 4 weeks postoperative to observe the degradation of stent,kidney seeper and renal damage.Experimental animals were sacrificed at different time points after surgery,and the pathological changes were observed by HE staining.Residual ureteral stents were removed,weighed and the weightlessness rate calculated.Results:The cells in the experimental group grew well at all time points.Results in the experimental group(1:4,1:8,1:16,1;32)were similar to those in the negative control group(P>0.05),and the extractions at different concentrations were significantly higher than those in the positive control group(P<0.001).Gradient degradation polyurethane ureter stents were placed in the ureter and were basically complete within 1 week,followed by degradation and complete degradation within 4 weeks.The degradation started from the distal end of the stents and gradually progressed to the proximal end.There was no residual degradation debris or hydronephrosis during the degradation process.There was no significant increase in serum creatinine in the experimental group and the control group(P>0.05).The white blood cells in the two groups were significantly increased at week 1 after surgery,while the white blood cells in the experimental group were significantly different from those in the control group at week 2 and 3(P<0.05),recovered to the preoperative level at week 4.Urine pH values of the two groups were within the normal range,and there was no statistically significant difference between the two groups(P>0.05).There was no significant difference in body weight between the experimental group and the control group(P>0.05).The pathological results at 4 weeks after placement in the pig ureter showed that the glomeruli in the renal parenchyma of the experimental group and the control group were normal,the epithelial cells of the proximal and distal convoluted tubules were not degenerated,and there was no inflammatory cell infiltration in the interstitium.The renal pelvis,ureter and bladder were infiltrated by submucosal lymphocytes and plasma cells.The weight loss rate of degradable ureteral stents was 7.6%at 1 week,44.23%at 2 weeks,74.42%at 3 weeks,and 100%at 4 weeks.Conclusion:Gradient degradation polyurethane ureteral stents have good biocompatibility.After placed into the ureter of pigs,it was basically complete within 1 week,and then began to degrade.The degradation debris had certain stimulation effect on the renal pelvis and ureteral mucosa,but did not affect the renal function and drainage.The inflammation caused by the degradation debris was mild and reversible,and disappeared after stent was completely degraded.It indicated that the biodegradable stents had good histocompatibility.