Bioartificial materials in urology

The scope of our research is the development of polymer-based bioabsorbable stents for urologic applications and in vitro testing of tissue reactions of cultured ureteral and urethral segments induced by implanted polymer stent prototypes. For these purposes a tissue cultivation model was developed using selected techniques of tissue engineering.Essential advantages of degradable over nondegradable urethral stents are elimination of the adverse extraction of epithelialized stents and the potential for recovery of organ-specific functionality. Moreover, the biocompatibility of a degradable urethral stent could potentially reduce the risk of restenosis due to hyperplasia and could be used, even repeatedly, for the treatment of a number of subvesical obstructions. For the treatment of tumor-induced strictures, application of degradable polymer stents coated with cytostatic drugs may be possible. The mechanical effect of the drug-loaded stent as a "place holder" could be complemented by adjuvant or palliative approaches such as local chemotherapy. We have developed and tested in vitro a degradable urethral stent incorporated with the model drug methotrexate for local drug delivery (LDD) by diffusion and during stent degradation.     

A model to quantify encrustation on ureteric stents, urethral catheters and polymers intended for urological use

OBJECTIVE: To validate an encrustation model and to quantify encrustation on currently used urological devices and polymers intended for urological use. Materials and methods An encrustation model was validated: (i) to measure the amount of calcium leaching from the glass model and from the polymer used; (ii) to determine whether the use of a single-source or pooled urine produced similar results; (iii) to determine in vitro encrustation; and (iv) to compare the results of in vivo implantation of the same materials into the bladders of rodents with the in vitro results. A test polymer (a ureteric stent, a urethral catheter or a biomaterial) and a control silicone polymer were housed separately but received human urine from the same reservoir and under the same conditions (pH 6.0 and 37 degrees C) for 5 days. The amount of calcium encrustation on each polymer was measured using atomic absorption spectroscopy. Each experiment was repeated at least four times and the results expressed as an encrustation index, defined as the ratio of encrustation of the test and reference polymers. RESULTS: The amount of calcium leaching from the glass model and polymers tested was insignificant. The use of a single-source or pooled urine gave the same results in the encrustation model. The in vitro results correlated with in vivo implantation of disks into the bladders of rats. Among the commonly used ureteric stents tested, the Cook C-Flex ureteric stents encrusted least. Hydrogel-coated ureteric stents encrusted more than uncoated stents. The Bard polytetrafluoroethylene short-term urethral catheter encrusted more than the Bard hydrogel-coated long-term catheter. A plasma-activated surface modification of a synthetic biomaterial with hyaluronic acid encrusted less than silicone, a long-term biomaterial widely regarded as the 'gold standard'. CONCLUSION: This validated encrustation model is the first to quantify encrustation on currently available ureteric stents and urethral catheters. A novel coating for a biomaterial was identified using the encrustation model, and which encrusted less than silicone.     

BIOCOMPATIBILITY TESTING OF A NEW BIOABSORBABLE X-RAY POSITIVE SR-PLA 96/4 URETHRAL STENT

PURPOSE: Recently a first X-ray-positive bioabsorbable urethral stent was developed by our group. The stent is made from self-reinforced poly-L,D-lactic acid (SR-PLA 96/4) blended with barium sulfate. The aim of this study was to evaluate the biocompatibility properties of the new stent materials. MATERIALS AND METHODS: Rods made from pure SR-PLA 96/4 and SR-PLA 96/4 blended with barium sulfate were inserted into the dorsal muscles of a rabbit. Rods made from latex and silicone were used as positive and negative controls. To evaluate the long-term effect of BASO4 after the bioabsorption of the polymer, fast degrading SR-PGA (self-reinforced polyglycolic acid) and SR-PLA + BASO4 rods were used as controls. Urethral stents made from SR-PLA 96/4 and X-ray-positive SR-PLA 96/4 stents were inserted cystoscopically into the rabbit urethra. Metal stents were used as controls. The animals were sacrificed after 1 week, 1 month or 6 months. RESULTS: In the muscle implantation samples acute tissue reactions due to operative trauma were seen in all specimens at 1 week. After 6 months chronic inflammatory changes and foreign body reaction were seen only in the positive controls. The stent worked well in the rabbit urethra, its biocompatibility was good and there was less encrustation than in the metal stents. CONCLUSIONS: This first X-ray-positive bioabsorbable urethral stent showed no toxic tissue effects.     

Experience with urethral stent explantation

PURPOSE: We examined the timing, causes and results of the explantation of UroLume (American Medical Systems, Minnetonka, Minnesota) urethral stents. MATERIALS AND METHODS: The North American Study Group enrolled 465 patients in a trial of UroLume stent placement, including 69 (14.8% of the series) who required removal of a total of 73 stents (15.6% of stents) in 7 years. The time of explantation, reason for stent removal and local histological findings were determined from patient charts and reviewed in relation to the indication for stent placement. RESULTS: In patients treated for bladder outlet obstruction secondary to benign prostatic hyperplasia 23% of the stents were removed, as were 5% of those implanted in patients with bulbar urethral stricture and 22% of those in patients with detrusor-sphincter dyssynergia (see figure). Of the explantations 43.8% were done during year 1. Migration and/or inappropriate placement was the cause in 38.4% of cases. The most common stent site tissue finding was focal inflammation with a hyperplastic tissue response. Stent specific malignant changes were not observed. Stent removal was feasible with no sequelae. CONCLUSIONS When used appropriately, the UroLume endoprosthesis has a low incidence of failure. Stent removal is technically feasible and options are available for subsequent therapy. Local tissue reaction is minimal.     

Biodegradable braided poly(lactic-co-glycolic acid) urethral stent combined with dutasteride in the treatment of acute urinary retention due to benign prostatic enlargement: a pilot study

OBJECTIVE

To evaluate, in a pilot study, the efficacy and safety of combining a braided poly(lactic‐co‐glycolic acid) (PLGA, a copolymer of l ‐lactide and glycolide) urethral stent and dutasteride in the treatment of acute urinary retention (AUR) due to benign prostatic enlargement (BPE).

PATIENTS AND METHODS

Ten men with AUR due to BPE were treated as outpatients. A biodegradable braided PLGA urethral stent was inserted into the prostatic urethra, using a specially designed insertion device under visual control. Dutasteride treatment was started and the patients were followed up for 3 months after insertion of the stents.

RESULTS

In all patients the stents were placed successfully with the new insertion device. All men were able to void after inserting the stent. At 1 month five patients voided freely with a low residual urine volume (<150 mL), two voided but had a high residual urine volume and a suprapubic catheter was placed, and three needed a suprapubic or an indwelling catheter before 1 month, due to AUR or comorbidities. At 3 months five patients were voiding with no problems.

CONCLUSIONS

We have developed a new and effective insertion device for biodegradable braided prostatic stents. The new braided‐pattern stent overcomes the earlier problems of migration and sudden breakage into large particles associated with biodegradable spiral stents. However, the mechanical properties of the new stent need to be improved and tested in a longer follow‐up. We consider that this new biodegradable braided‐pattern urethral stent could provide a new option in the future treatment of AUR.     

A bioresorbable urethral stent

Summary The aim of the present study was to examine the suitability of biodegradable polymers as materials for a urethral stent. A new urethral stent made of biodegradable self-reinforced poly-l-lactide (SR-PLLA) was implanted in 16 male rabbits after urethrotomy. Seven stents of stainless steel served as controls. The dimensions of the two types of stents were identical: length 15 mm, diameter 8.2 mm. The mechanical construction was a helical spiral. The SR-PLLA spiral was sustained with three microspirals, and the whole device was coated withdl-lactide to achieve an active initial tissue reaction and better tissue penetration. The SR-PLLA stent showed more favourable implantation properties than the steel one. Within 6 months all PLLA stents had implanted, and the tissue reaction around the stent material was minimal. The helical spiral of stainless steel induced a remarkable inflammatory reaction due to poor implantation properties. We suggest that biodegradable SR-PLLA is a promising material for a urethral stent to prevent re-stenosis of urethral strictures.     

Temporarily implanted urethral coil stent for the treatment of recurrent urethral strictures: a preliminary report

A new urethral stent developed for use in recurrent urethral strictures is presented. This metallic coil is self-expanding when released from its introducing catheter. The stent was used in 18 patients with recurrent strictures necessitating frequent dilation or urethrotomy. The stent is introduced under fluoroscopic guidance after internal urethrotomy or simple dilation. Strictures of 5 to 60 mm. were treated successfully with this device. All strictures were distal to the external sphincter. No serious complications attributed to the device were recorded. When necessary, the stent could be repositioned either under fluoroscopic control or endoscopically. This device can hold the stenotic area of the urethra open for long intervals allowing for complete healing. Even after 6 months the stent is not covered with urethral epithelium and does not become incorporated into the urethral wall. It can be removed easily without an operation by simple manipulation. The large internal caliber permits passage of endoscopes up to 17F in patients who require cystoscopy. The device can be removed before transurethral resections and then a new stent can be inserted at the end of the procedure. Mean followup of our patients with the stent indwelling was 8 months (range 4 to 11 months). Followup after removal of the stent (6 patients) was 3 to 8 months (mean 5 months). The patients voided well during followup and were fully continent. No incrustations were noted in the removed stents even after 6 months and no stent became obstructed due to tissue proliferation or incrustation. In 1 patient the stricture recurred after 3 months and a new stent was inserted. Urine sterilization was obtained in 7 patients with infected urine after relatively short courses of antibiotics. This stent seems to be a promising tool for the nonoperative treatment of recurrent urethral strictures.     

Expansion and fixation properties of a new braided biodegradable urethral stent: an experimental study in the rabbit

PURPOSE: Biodegradable spiral urethral stents have been used with favorable results combined with thermal treatments of the prostate and for recurrent urethral strictures but the configuration of the helical spiral is not ideal. We developed a new tubular mesh configuration for the biodegradable urethral stent and evaluated its expansion and locking properties in the rabbit urethra. MATERIALS AND METHODS: The stents were made of self-reinforced polylactic acid polymer (Bionx Implants, Ltd., Tampere, Finland) blended with BaSO (Alfa Chem, New York, New York) to achieve radiopacity. Two braiding patterns, that is 1 over 1 and 2 over 2 + 1, were used to produce a tubular mesh structure. Stainless steel stents (pattern 1 over 1) served as controls. The stents were inserted into the posterior urethra of 27 male rabbits. The animals were sacrificed after 1 week, 1 and 6 months, respectively. X-rays were done immediately after stent insertion and at sacrifice. Longitudinal movement and expansion were assessed on the x-rays.(4) RESULTS: All stents maintained position in the urethra without fixation. Macroscopic disorientation of the structure of the 2 over 2 + 1 braided self-reinforced polylactic acid polymer stents began before 1 month, while 1 over 1 braided stents retained their construction. At 6 months 3 of 6 biodegradable stents were degraded. Average longitudinal movement was 2 mm. (range 1 to 3) in the 1 over 1 self-reinforced polylactic acid polymer group, 2 mm. (range 0 to 7) in the 2 over 2 + 1 polylactic acid group and 3 mm. (range 3 to 3) in controls at 1 month. CONCLUSIONS: Biodegradable polymers are suitable materials for braided urethral stents. The expansion properties of the 2 braiding models tested in this study sufficed to fix the stents in situ in the prostatic urethra. However, the 1 over 1 braiding pattern was superior to the 2 over 2 + 1 pattern, in that it retained its macroscopic construction until the degradation of single self-reinforced polylactic acid polymer fibers.     

Biocompatibility and implantation properties of 2 differently braided, biodegradable, self-reinforced polylactic acid urethral stents: an experimental study in the rabbit

PURPOSE: Biodegradable urethral stents have been in clinical use for more than 10 years. To solve the problems connected with the helical spiral configuration of the stents used to date we developed a new tubular mesh configuration and evaluated the biocompatibility properties and degradation time of 2 differently braided stents in the rabbit urethra. MATERIALS AND METHODS: The biodegradable, self-expanding stents were made of self-reinforced polylactic acid polymer blended with BaSO4 (Alfa Chem, Kings Point, New York). Two braiding patterns, namely a diamond 1/1 and a regular 2/2 + 1 (Prodesco, Perkasie, Pennsylvania), were used to produce a tubular mesh configuration. Stainless steel stents with 1/1 braiding served as controls. The stents were inserted into the posterior urethra of 36 male rabbits. The animals were sacrificed after 1 week, 1 month, 6 months or 12 months. Light microscopy and scanning electron microscopy analyses were done. RESULTS: Tissue reactions to operative trauma were seen in all specimens at week 1. The changes gradually abated in the biodegradable stent groups, whereas chronic inflammatory changes and fibrosis were increasingly seen with metallic stents after 6 months. Epithelial hyperplasia increased with time for all stent types and materials. As expected, stent fragmentation started at 6 months. CONCLUSIONS: Biodegradable polymers are suitable materials for braided urethral stents. However, the braided configuration of the stent with a decreased mass of material does not prevent the development of epithelial hyperplasia. The biodegradable, self-expanding, braided stents functioned well in the rabbit urethra and are suitable for clinical studies.     

Liposome-coated metal stents: an in vitro evaluation of controlled-release modality in the ureter

PURPOSE: In vitro preparation of liposome-covered metal stents and loading of liposomal drug formulations that will slowly release the drug in the vicinity of the stent. MATERIALS AND METHODS: Polytetrafluoroethylene-coated stents were used. Large multilamellar (MLV) liposomes (phosphatidylcholine:cholesterol 1:1 mol/mol), empty or entrapping the corticosteroid anti-inflammatory drug, dexamethasone, were prepared by the thin-film hydration method and applied to pieces of stent using a simple and mild evaporation technique. Initially, a freeze-drying method for applying liposomes to stents was also evaluated, but it failed to produce stents that efficiently retain liposomal lipid when incubated in an aqueous environment. The presence of liposomes on the stent surface was confirmed by scanning electron microscopy. RESULTS: After analyzing the release of liposomal lipid (using a phospholipid assay) and liposomal drug (by a modified dexamethasone high-pressure liquid chromatography method) in an in vitro system developed to simulate in vivo conditions, it was found that 39.11+/-6.8% of the lipid and 50.84+/-5.48% of the drug was released from the stent pieces during 48 hours of incubation in the presence of artificial urine. The amount of dexamethasone released from stents during their application procedure was found to be negligible in an in vitro dry run. CONCLUSION: The use of stent-associated liposomal drug formulations as slow-release depots could be an efficient method of treating the untoward event of ureteral stent obstruction.     

How to manage acute urethral false passage due to intermittent catheterization in spinal cord injured patients who refused insertion of an indwelling catheter

PURPOSE: Acute urethral false passage is an important complication of clean intermittent catheterization in spinal cord injured patients. Temporary urethral stenting with an indwelling catheter is generally an excellent conventional therapeutic option to treat patients with acute false passage. However, how can acute false passage be managed in a patient who refuses insertion of an indwelling catheter? MATERIALS AND METHODS: For 3 years 5 male patients with acute urethral false passage due to catheterization refused urethral stenting because indwelling catheter insertion would prevent sexual intercourse. We placed a nitinol prostatic stent successfully in the false urethral passage in all 5 patients. The stents were left in place for 3 to 6 months. RESULTS: The stent migrated in 1 patient and it was replaced. During a retention period of 3 to 6 months all patients continued clean intermittent catheterization without any difficulty and achieved sexual intercourse. On urethral cystoscopy we observed that all false passages disappeared without a gross tissue reaction. The stents were then removed without any complications. During a mean followup of 11.8 months (range 4 to 25) none of these patients had another false passage. All continued to perform clean intermittent catheterization without any further difficulty. CONCLUSIONS: Temporary placement of a removable endourethral stent is a safe and effective method for managing acute urethral false passage in patients on clean intermittent catheterization who refuse insertion of an indwelling catheter. This approach makes further clean intermittent catheterization possible and improves patient quality of life.     

Prostatic stents for benign prostatic hyperplasia

Treatment options for benign prostatic hyperplasia (BPH) have developed rapidly over the past several years. These options include surgical intervention, medical therapy, and minimally invasive modalities such as prostatic stents. Prostatectomy remains the treatment of choice for symptoms that are the result of bladder outflow obstruction, with success rates of 85-90%. Medical therapy with selective alpha-1 antagonists, 5 alpha-reductase inhibitors, LHRH antagonists, antiandrogens, and aromatase inhibitors have increased in popularity and are mainly used to treat patients with mild to moderate prostatic obstruction. Prostatic urethral stents have recently emerged as an alternative treatment for BPH throughout Europe and Asia, but few investigators have used prostatic stents in the United States because of strict regulatory forces and a debate concerning the indications for these devices. The possibility of providing a treatment option for BPH to patients who are frail and elderly, as well as to patients with multiple medical problems, has prompted enthusiasm toward prostatic stents in the urologic community. The focus of this review will be an up-to-date discussion of the types of prostatic stent available, including a review of recent clinical trials involving the use of each available stent.     

Stents in urethral stricture repair

Summary The human urethra seems remarkably tolerant of foreign material within its lumen. Providing that a stricture has been adequately cut by means of urethrotomy, or dilated with bougies, the majority of urethras will tolerate both permanent and temporary stents with few problems. Temporary stents have the obvious advantage over permanent stents that no foreign material is left in the urethra but before these can be recommended it is essential that more clinical experience is gained and that long term results up to ten years after removal of the stent are published. Great care is also needed in the use of any sort of permanent device, either the Urolume stent, or varieties of the Strecker such as the Memotherm device. These should not be used in children and should be probably be avoided in young adults. The majority of strictures in this age group are in any case treated more easily by single stage urethroplasty procedures. The use of permanent epithelial covering stents should be limited to the bulbo-membranous urethra, with the possible exception of carefully selected sphincters strictures used in combination with an artificial urinary sphincter. Better results will be obtained by using these stents in strictures with a short history before multiple urethrotomies and dilatations have been carried out and before extensive urethral and periurethral fibrosis has occurred. This means that urethral rupture strictures are unsuitable, and in any case these are simple to deal with be means of stricture excision and primary end to end anastomosis of the urethra particularly when the stricture is in the bulbar urethra. Care must also be taken in using these devices in post-urethroplasty strictures if extensive periurethral fibrosis exists, although it has to be admitted that these stents may be very successful in some of these patients. The difficulty at the present time is our inability to define exactly which traumatic stricture or post-urethroplasty stricture will succeed and which will fail. Metal urethral stents should not be used for the first treatment of a urethral stricture. Depending on the aetiology, the site and the length of the stricture there is always a 40–50 % chance that the stricture may be cured by means of a simple urethrotomy or dilatation and this should always be tried at least once before resorting to urethral stenting. There is no doubt that permanent urethral stents have an important role to play in the treatment of recurrent urethral strictures. Careful patient selection is essential in order to achieve the best results and we need more long term results before the final role of these devices in the treatment of urethral strictures can be determined. Temporary stenting of the urethra with non-epithelial covering stents is a simpler and safer treatment but at this point in time we cannot be sure how effective this treatment is and for which patients it is most successful. Long term results must be awaited before the place of these temporary devices can be defined.      

Simulated Bench Testing to Evaluate the Mechanical Performance of New Carotid Stents

Our group recently developed a novel covered carotid stent that can prevent emboli while preserving the external carotid artery (ECA) branch blood flow. However, our recent in vitro side‐branch ECA flow preservation tests on the covered stents revealed the need for further stent frame design improvements, including the consideration to crimp the stent to a low profile for the delivery of the stent system and having bigger cells. Hence, the current work aims to design new bare metal stents with bigger cell size to improve the crimpability and to accommodate more slits so that the side‐branch flow could be further increased. Three new stent designs were analyzed using finite element analysis and benchmarked against two commercially available carotid stents in terms of their mechanical performances such as crimpability, radial strength, and flexibility. Results indicated that the new bare metal stent designs matched well against the commercial stents. Hence our new generation covered stents based on these designs can be expected to perform better in side‐branch flow preservation without compromising on their mechanical performances.     

A new biodegradable braided self-expandable PLGA prostatic stent: an experimental study in the rabbit

PURPOSE: The biodegradable PLGA (a copolymer of L-lactide and glycolide) urethral stent with a spiral configuration has been used clinically for the prevention of postoperative urinary retention after different types of thermal therapy for benign prostatic hyperplasia. A new braiding pattern for this stent has recently been developed by our group. The aim here was to investigate the in situ degradation and biocompatibility of the new braided stent in the rabbit urethra. MATERIALS AND METHODS: PLGA stents with a one-over-one braiding pattern and steel stents served as controls that were inserted into the posterior urethras of 24 male rabbits using a special delivery instrument. The animals were sacrificed after 1 week, 1 month, 2 months, or 4 months, and light microscopy and histologic analyses were performed. RESULTS: The delivery instrument worked well and cystoscopy was not needed in the insertion process. The braided PLGA stents degraded smoothly in 1 to 2 months. The metallic stents induced more epithelial hyperplasia and epithelial changes than the biodegradable stents at all time points analyzed. These differences increased during follow-up. CONCLUSION: The degradation process was well controlled and the biodegradable stents were more biocompatible than the metallic stents. The new stent can be inserted into the posterior urethra without cystoscopic aid.     

Comparison of nitinol urethral stent infections with indwelling catheter-associated urinary-tract infections

BACKGROUND AND PURPOSE: To determine the efficacy of intraurethral metal stents in preventing or eradicating urinary-tract infections (UTI) during the management of bladder outlet obstruction (BOO) by comparing the frequency and nature of the infections with indwelling-catheter-associated UTI. PATIENTS AND METHODS: The SAS relative-risk test was used to compare the risks of UTI in 76 patients with temporary urethral stents, 60 patients with BOO who had never been catheterized nor stented, and 34 patients with a permanent indwelling urethral catheter (PIUC). Infection was assessed 1 month after placement of the devices. Scanning electron microscopy (SEM) of the proximal and distal pieces of the stents removed from five patients with and five patients without UTI was carried out in a search for predisposing changes on the surfaces. RESULTS: After insertion of the catheter, UTI developed in 79.4% of the patients who originally had sterile urine. However, after insertion of the stent, UTI developed in only 40.9% of the patients with sterile urine. In 21 (44.6%) of the catheterized patients who had infected urine, UTI was eradicated after stent insertion. The SEM analysis of the stents showed that a thick organic layer had formed only on the infected devices but with no sign of erosion. CONCLUSION: Urinary infection is a significant problem in patients with PIUC but is significantly less frequent and less severe in patients with urethral stents. This advantage of stents over the conventional urethral catheter, in addition to their obvious convenience for the patient, make them good alternatives to reduce the risk of UTI.     

Biocompatibility properties of a new braided biodegradable urethral stent: a comparison with a biodegradable spiral and a braided metallic stent in the rabbit urethra

OBJECTIVE: To compare the biocompatibility properties of a new braided biodegradable self-reinforced poly-L-lactic acid (SR-PLLA) urethral stent to the former spiral biodegradable SR-PLLA stent and the stainless steel stent in a rabbit model. MATERIALS AND METHODS: In all, 54 male New Zealand White rabbits were anaesthetized and stents inserted into the prostatic urethra, three of each kind for each sample time. The rabbits were killed after 1, 3, 6, 9, 12 or 15 months and light microscopy and scanning electron microscopy used to analyse the effects. RESULTS: The disintegration of the braided SR-PLLA stent was more closely controlled than that of the spiral SR-PLLA stent. The metallic stent induced epithelial hyperplasia and polyposis earlier than the biodegradable stents, and in these rabbits the polyposis disappeared after the disintegration process. There were no differences in the histological analyses between the biodegradable stents, whereas the metallic stents caused the strongest inflammatory reactions. CONCLUSIONS: The braided SR-PLLA urethral stent functioned well in the rabbit urethra and clinical studies are already planned.     

Outcome analysis of the urethral stent (Memotherm®)

A number of patients with benign prostatic hyperplasia can not undergo surgical therapy because of advanced age, concomitant diseases, and other reasons. Since 1980, various types of urethral stents have been used for high-risk patients with benign prostatic hyperplasia. We report our experience with the use of urethral stents (Memotherm?). Between July 2002 and December 2010, we implanted urethral stents in 36 patients. The average follow-up period was 24.0 months. After stent implantation, 34 of the 36 patients were able to micturate. The average residual urine volume was 24.7 ml (0-250 ml), and the maximal urinary flow rate was 10.7 ml/s (3-24 ml/s). One stent had to be removed due to bladder tamponade, and one had to be exchanged due to dislocation. In 2 patients, a stone formed at the bladder end of the stent, and one of these patients underwent transurethral lithotripsy. Our results suggest that therapy with the Memotherm? urethral stent is a good option for patients suffering from urinary retention due to benign prostatic hyperplasia.     

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.     

A new generation of urethral stents--Allium in the therapy of symptomatic prostatic enlargement of various etiology

A number of urethral stents made of different materials, with different time of indwelling and different designs, primarily based on the vascular stent concept, have been applied in the clinical practice so far. According to the published studies, urethral stents have justified their clinical application, however with certain limitations. Within an attempt to overcome the limitations, a covered, temporary urethral stent was initially designed by Daniel Yachie and Ijko Markovi in Allium corporation from Israel. With its triangular shape, the stent is a replica of the obstructive prostatic urethral lumen. In has been applied in a series of 14 patients with lower urinary tract symptoms caused by the obstruction at the level of the prostatic urethra. The subjects were averagely aged 77.4 +/- 5.1 years. Allium prostatic stent remained in place in the patients for 4.93 +/- 3.17 months, at the average.