Encrustation and strength retention properties of the self-expandable, biodegradable, self-reinforced L-lactide-glycolic acid co-polymer 80:20 spiral urethral stent in vitro.

PURPOSE: Encrustation of urological stents is a clinical problem. The chemical composition and surface properties of the devices have a marked effect on its incidence. The ability of the stent to prevent duct collapse depends on its compression strength, which decreases as degradation progresses. We have developed a new self-reinforced, L-lactide-glycolic acid co-polymer with a molar ratio of 80:20 (SR-PLGA 80/20), that is the SpiroFlow (Bionx Implants, Ltd., Tampere, Finland) stent. We compared the resistance to encrustation of the new stent material to that of 2 temporary metallic stents, Prostakath (Doctors and Engineers, Inc., Copenhagen, Denmark) and Memokath 028 (Engineers and Doctors A/S, Ltd., Kvistgård, Denmark). In addition, mechanical compression properties during degradation were investigated. MATERIALS AND METHODS: For encrustation studies 7 mm segments of the test material of the SR-PLGA 80/20, Prostakath and Memokath stents were incubated in vitro in sterile artificial urine for 4 and 8 weeks, and the SR-PLGA 80/20 also for 12 weeks. After incubation the specimens were fixed in glutaraldehyde, critical point dried and coated with gold in sputter for scanning electron microscope analysis. Analysis was done at 100x magnification in 5 randomly selected areas per sample. Results are presented as a median percent of the whole analyzed area covered by encrustation in each tested material. For compression strength studies 20 mm pieces of manufactured SR-PLGA 80/20 spiral stent wire were similarly incubated in sterile artificial urine for 12 weeks. Measurements were made by compressing the specimens between 2 parallel planes at 2, 4, 6, 8 and 12 weeks. All analyses were made in triplicate. RESULTS: The areas covered by encrustation at 4 weeks were 8.01% for the Memokath, 1.49% for the Prostakath and 0% for the SR-PLGA 80/20. At 8 weeks the percent was 28.4%, 4.1% and 0.12%, respectively, remaining steady at 0.12% in the SR-PLGA 80/20 at 12 weeks. Compression strength of the SR-PLGA stent remained stable up to 6 weeks, after which it decreased rapidly. CONCLUSIONS: The new SR-PLGA 80/20 material is markedly more resistant to encrustation than metallic urethral stent materials and it retains compression strength up to 6 weeks, which is long enough for temporary stenting for most clinical indications in urology. Thus, the new stent is well suited to future clinical use.

Interstitial laser coagulation and biodegradable self-expandable, self-reinforced poly-L-lactic and poly-L-glycolic copolymer spiral stent in the treatment of benign prostatic enlargement.

BACKGROUND AND PURPOSE: Interstitial laser coagulation of the prostate (ILCP) induces necrosis, edema, and an increased risk of postoperative urinary retention. The object here was to evaluate the efficacy, safety, and utility of a new self-expandable self-reinforced (SR) PLGA copolymer(lactic:glycolic ratio 80/20) spiral stent inserted after ILCP to promote voiding. The SR-PLGA stent has a degradation time of 2 to 2.5 months. PATIENTS AND METHODS: Fifty men with a mean age of 70.5 years (range 52-85 years), suffering from lower urinary tract symptoms secondary to benign prostatic enlargement underwent ILCP. A suprapubic catheter was inserted, ILCP performed, and an SR-PLGA 80/20 spiral stent inserted on completion of the operation. The suprapubic catheter was removed when voiding commenced. As prophylactic antibiotic, ciprofloxacin was used in a single dose before ILCP, followed by trimethoprim or nitrofurantoin for 2 weeks. RESULTS: All except three patients started to void on the first postoperative day. In two of the three cases, the stent had moved proximally and had to be relocated, whereafter voiding succeeded. The mean maximum and average flow rates increased, while DAN-PSS-1 symptom score and post voiding residual urine volume decreased statistically significantly. At 2 months, the stent was still intact in the urethra in all except three patients. At 4 months, it had been degraded into small fragments, and at 6 months, it had been completely eliminated. The only exceptions were three patients with an uncalcified piece of the stent in the bladder. Half of the patients had irritative symptoms caused at least partly by ILCP itself; 10% had asymptomatic urinary infection postoperatively. CONCLUSIONS: The self-expandable SR-PLGA copolymer stent is safe and highly biocompatible. It ensures voiding in the case of temporary obstruction caused by prostatic edema. The degradation time is long enough in all patients to cover the need for postprocedure urinary drainage.

Rabbit muscle and urethral in situ biocompatibility properties of the self-reinforced L-lactide-glycolic acid copolymer 80: 20 spiral stent.

PURPOSE: A new type of self-reinforced L-lactide-glycolic acid copolymer, molar ratio 80:20, stent was developed. We evaluated the tissue biocompatibility properties of the new material. MATERIALS AND METHODS: Rods made of self-reinforced L-lactide-glycolic acid copolymer were inserted into rabbit dorsal muscles and rods of latex or polyvinylchloride and silicone served as positive and negative controls, respectively. Urethral stents of self-reinforced L-lactide-glycolic acid copolymer and steel were inserted in situ via cystoscopy into the rabbit prostatic urethra. The animals were sacrificed after 2 weeks, 1, 2 and 3 months, respectively. In situ histological analysis was done. Tissue reactions around the implantation types were analyzed histologically and scored semiquantitatively. In addition, macroscopic analysis was done of the urethral in situ stents. RESULTS: In rabbit muscle implantation test tissue reaction to the self-reinforced L-lactide-glycolic acid copolymer stent resembled that of negative control silicone. Less than moderate chronic inflammatory changes gradually subsided after 2 weeks. Foreign materials in the tissue and the reaction to these materials began to disappear after 1 month and at 3 months were completely absent. All rabbits fitted with the stent voided normally postoperatively. Self-reinforced L-lactide-glycolic acid copolymer stents were soft, partially fragmented and easily disintegrated when touched at 2 months, and were almost completely degraded at 3 months. The material did not encroach into the urethral wall macroscopically or microscopically. No calcification on the self-reinforced L-lactide-glycolic acid copolymer stents or bladder stone formation was seen. CONCLUSIONS: The new self-reinforced L-lactide-glycolic acid copolymer 80:20 material is safe, highly biocompatible and suited for future clinical use. It is most appropriate for preventing postoperative urinary retention after most minimally invasive thermal treatments for benign prostatic hyperplasia.