A short biodegradable helical spiral ureteric stent provides better antireflux and drainage properties than a double-J stent.

OBJECTIVE: The use of ureteric stents is a standard treatment for the relief of ureter blockages for benign or malignant reasons. The most common stent design in clinical use is a double-J stent with coiled ends to avoid stent displacement. However, there are a number of complications associated with stent use. A double-J stent design bypasses the ureterovesical junction, enables bladder pressure reflection to the renal pelvis and causes vesicoureteral reflux (VUR). This may result in scarring and renal failure. MATERIAL AND METHODS: An animal model was used to investigate whether VUR can be avoided in stented ureters using a short biodegradable partial helical spiral stent design that leaves the ureterovesical junction intact. MATERIALS AND METHODS: Eight female pigs were used. Ureters on the left side were stented using a short helical spiral SR-PLGA stent (group A) and ureters on the right side using double-J stents (group B). Simulated voiding cystoureterography and standard intravenous urography examinations were performed on all eight animals at 4 weeks and on the remaining four animals at 8 weeks. RESULTS: An SR-PLGA single coiled partial stent demonstrated superior drainage properties to a double-J stent at 4 weeks (p = 0.020). A marked but not statistically significant difference in favour of a SR-PLGA stent was also observed at 8 weeks (p = 0.102). A statistically significant difference was observed in VCUG findings in favour of group A at immediate postoperative control as well as in the 4 and 8 week follow-up studies (p = 0.011, p = 0.010, p = 0.046, respectively). CONCLUSION: A self-expandable, SR-PLGA partial ureteric stent presented with superior drainage and antireflux properties compared to a double-J stent. The reflux commonly related to double-J stent use can be minimized by using a partial ureteric stent design.

Drainage and antireflux characteristics of a biodegradable self-reinforced, self-expanding X-ray-positive poly-L,D-lactide spiral partial ureteral stent: an experimental study.

PURPOSE: To evaluate the drainage and antireflux characteristics of a new self-expandable self-reinforced poly-L,D-lactide partial ureteral stent (SR-PLA 96) in an experimental model. MATERIALS AND METHODS: Twelve dogs were used as experimental animals. A low-midline laparotomy and cystotomy were performed on all animals. In group A (six animals), 50-mm long SR-PLA 96 ureteral stents with a double-helical spiral design were inserted into both ureters, leaving the lower ends 2 cm above the ureterovesical junction. In group B (six animals), both ureters were stented with traditional pigtail stents (C-Flex) Double-J; Cook Urological), which were removed 8 weeks after surgery. Renal function and ureteral patency were evaluated by dynamic kidney imaging and urography examinations at 6 and 12 weeks postoperatively. The degrees of vesicoureteral reflux at two levels of the ureters and at the level of the renal pelvis were evaluated by nuclear voiding cystograms at 6 weeks. RESULTS: The partial SR-PLA 96 stent design showed more favorable antireflux properties that the Double-J stent design. The degree of vesicoureteral reflux, reflected in an increase of nuclear enhancement at 6 weeks, was lower in the distal (7.9% +/- 14.7% v 63.2% +/- 17.3%; P < 0.05) and middle (6.1% +/- 8.1% v. 45.5% +/- 19.5%; P = 0.15) levels of the ureters as well as at the level of the renal pelvis (-3.4% +/- 3.6% v 6.2% +/- 3.9%; P = 0.65) than in the Double-J-stented ureters. No significant differences in renal function or ureteral patency were observed at 12 weeks after the Double-J stents had been removed and the SR-PLA 96 stents had fragmented. CONCLUSION: A self-expandable, self-reinforced SR-PLA 96 partial ureteral stent showed more favorable antireflux properties than a Double-J stent.

Repair of radial fractures in toy breed dogs with self-reinforced biodegradable bone plates, metal screws, and light-weight external coaptation.

OBJECTIVE: To describe a surgical technique for, and outcome after, treatment of radial fractures with biodegradable self-reinforced polylactide plates and metal screws, and external coaptation. STUDY DESIGN: Prospective clinical study. SAMPLE POPULATION: Eleven Toy breed dogs. METHODS: Radial fractures were repaired by application of a single or 2 stacked biodegradable self-reinforced polylactide plates (poly-L/D, L-lactide, stereocopolymer [LL-and DL-lactide ratio 70/30]; SR-PLA (70/30) implants) secured with metal screws, and light-weight external coaptation. Healing was evaluated clinically and by radiography at 2, 4, 6, 8, 9, 12, 24-26 weeks, and at 1 and 2 years. Owners were interviewed 3 years after surgery. RESULTS: Radial fracture lines disappeared within 4-14 weeks in 10 dogs; an implant failed in 1 dog. Ambulation was excellent for healed fractures. Excessive skin tension led to removal of implants in 1 dog and suture repair in another dog. No foreign body reaction from implant degradation was observed and the plate was usually no longer palpable at 2 years. One dog had a fracture through a screw hole at 1 year. CONCLUSION: Healing and complication rates after repair of radial fractures with SR-PLA (70/30) plates were considered similar or better than reported after repair with metallic plates or external fixation in Toy breed dogs. No radiographic signs of osteopenia were identified under the plate during follow-up. CLINICAL RELEVANCE: Biodegradable polylactide plates could be considered as an alternative to metal plates for radial fracture repair in Toy breed dogs, however available plates are likely not strong enough when used as a single plate. Implant removal is usually not needed.

Platelet responses and coagulation activation on polylactide and heparin-polycaprolactone-L-lactide-coated polylactide stent struts.

Despite modern stent technology and effective antiplatelet therapy, metallic stents carry the risk of (sub)acute thrombosis. Our aim was to examine short-term differences in platelet deposition and coagulation activation between biodegradable polylactide (PLA), heparin-polycaprolactone-L-lactide-coated polylactide (hepa-P(CL95/L-LA5)-PLA), and stainless steel (SS) stent struts. Gel-filtered platelets (GFP) and platelet-rich plasma (PRP) were labeled with 10 nM (3)H-serotonin. Platelet deposition was measured after incubation of the stent struts in human serum albumin-coated wells at 37 degrees C in either GFP or PRP. Platelet morphology was studied by scanning electron microscopy (SEM). For coagulation activation, the stent struts were incubated in either PRP or platelet-poor plasma (PPP), anticoagulated with D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK), followed by measurement of fibrinogen, thrombin time (TT), prothrombin fragment 1+2 (F1+2), and thrombin-antithrombin complex (TAT). SS showed adherence of larger amounts of GFPs than did PLA at a platelet density of 300 x 10(6)/mL (p < 0.05). Furthermore, representative SEM studies showed more platelet spreading on SS than on PLA stent struts. Between PLA and SS, coagulation activity did not differ at any assessment. Based on prolonged TT values in plasma, the heparin coating strongly inhibited coagulation (p < 0.05). The values of soluble TAT and F1+2 for PLA were similar to those of controls, i.e., to incubated suspensions without a stent strut. In conclusion, when compared with stainless steel, both PLA and hepa-P(CL95/L-LA5)-PLA appear hemocompatible as intravascular stent materials.

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.

Magnetic resonance evaluation of luminal patency after polylactide stent implantation: an experimental study in a rabbit aorta model.

Intravascular metallic stents cause magnetic field distortions, disturbing luminal detection. Our aim was to evaluate the effect of polylactic acid (PLA) stents on magnetic resonance angiography (MRA). Biodegradable double spiral helical PLA stents ( n=12) or stainless steel (SS) ( n=6) stents were implanted into the infrarenal aortas of New Zealand White rabbits. All SS- and 6 PLA-stented animals as well as 6 non-operated control rabbits were imaged with gadolinium-enhanced MRA (1.5 T), and infrarenal aortic diameters (proximal, distal, and narrowest), together with the stent artifact, were measured. Six of the PLA-stented rabbits were followed up, and MRA was assessed at 2, 6, 9, and 12 months after the stent implantation. Image artifacts caused by the SS stents were visualized in all cases. The PLA stents caused no magnetic field distortion, allowing imaging of the underlying vessel including the vessel lumen. In the follow-up group of 6 rabbits with a PLA stent, 5 of 6 were patent at the end of the follow-up of 12 months. These stents allowed luminal detection at all time points, with no significant differences in aortic measurements emerging during the whole follow-up period. When immediately postoperatively scanned SS and PLA rabbits were compared with controls, no differences were observable in proximal diameters. Instead, the percentage of distal luminal loss was greater in the PLA-stented rabbits, as compared with SS stents ( p<0.01). The PLA stenting in small vessels allows evaluation of luminal patency with MRA both immediately after implantation and during follow-up.

Use of new bioabsorbable tacks and a tackshooter in cranial bone osteofixation saves operative time.

A new device (a tackshooter) to apply bioabsorbable tacks in craniofacial surgery has been developed. This new device was used in 15 children who underwent various cranioplasty procedures to demonstrate its reliability and simple technical application in cranial bone osteofixation. Bone segments were fixed together and to the cranial bones using Biosorb plates and tacks. Stable and secure fixation was obtained intraoperatively, with reduced operative time (10-15%) compared with earlier use of plates and screws. However, its use in very thin bone (<1 mm thick) is very limited because of bone fragility. In conclusion, use of tacks and a tackshooter reduces operative time, risk of infection and blood loss, and consequently costs. It is therefore very useful in selected craniofacial cases.

Biocompatibility, encrustation and biodegradation of ofloxacine and silver nitrate coated poly-L-lactic acid stents in rabbit urethra.

The purpose of this study was to evaluate the biocompatibility, encrustation and biodegradation properties of silver nitrate and ofloxacine blended caprolactone-L-lactide copolymer coated self-reinforced poly-L-lactic acid (SR-PLLA) urospirals in situ in the male rabbit urethra. SR-PLLA urospirals coated with 10% by weight silver nitrate or 5% by weight ofloxacine blended copolymer or pure copolymer were inserted into the posterior urethra of 18 male rabbits. No prophylactic antibiotics were given. The animals were sacrificed 1 or 6 months after insertion. Urethral tissue reactions were histologically scored semiquantitavely and the appearence of the stents assessed using scanning electron microscopy. The biodegradation time of SR-PLLA stents was remarkably reduced by the caprolactone coating. Silver nitrate and ofloxacine blended copolymer coated urospirals caused less tissue reaction than urospirals with a pure copolymer coating. Silver nitrate coating effectively prevented biofilm formation and stent encrustation. Silver nitrate and ofloxacine blended copolymer coated SR-PLLA urospirals had good biocompatibility properties in rabbit urethra. In particular, coating with silver nitrate may provide possibilities of preventing bacterial adhesion to bioabsorbable stents.

Bioabsorbable SR-PLGA horn stent after antegrade endopyelotomy: a case report.

PURPOSE: To evaluate the suitability of a bioabsorbable stent as a partial internal catheter after percutaneous endopyelotomy in ureteropelvic junction (UPJ) obstruction therapy. PATIENT AND METHODS: The material for the helical spiral stents was a copolymer of polylactide and glycolide (PLGA; L:G ratio 80/20). The self-reinforcement (SR) was accomplished by heating and drawing by Bionx Implants Ltd, Tampere, Finland. The stents were horn shaped, with an initial outside diameter 6 to 3.0 mm +/- 0.2 mm and a length of 90 mm. The stent was partially degraded before insertion so it would degrade faster from the distal end, proceeding gradually to the proximal end. According to in vitro estimation, the degradation time of the material was 2 to 2.5 months. The railroaded cold-knife technique was used for antegrade endopyelotomy. After relief of the UPJ obstruction, the stent was pushed to the upper ureter. RESULTS: The 37-year-old male patient had under open pyeloplasty 5 years previously. He had a pelvic stone 32 mm in diameter and tight restenosis of the UPJ. Percutaneous lithotripsy, incision of the stenosis, and application of the SR-PLGA helical horn-shaped spiral stent was without early or late complications. Eighteen months after the operation, retrograde pyelography showed the UPJ to be totally unobstructed. CONCLUSIONS: The bioabsorbable horn-shaped SR-PLGA helical spiral stent proved a suitable alternative for stenting of the UPJ after antegrade endopyelotomy, bringing a reduced need for postoperative percutaneous kidney drainage and no need for subsequent stent removal. The bioabsorbable helical stent works as a partial catheter, which prevents vesicoureteral reflux and reduces the risk of postoperative renal infection.

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.

Evaluation of the use of a biodegradable ureteral stent after retrograde endopyelotomy in a porcine model.

PURPOSE: We evaluated the use of a poly-L-lactide-co-glycolide (PLGA) bioabsorbable ureteral stent after Acucise balloon incision (Applied Medical Resources, Rancho Santa Magarita, California) endopyelotomy in a porcine model. MATERIALS AND METHODS: After unilateral Acucise endopyelotomy in 9 female Yucatan minipigs a self-reinforced PLGA stent was placed in 5 (group 1) and a 7Fr double pigtail Percuflex stent (Boston Scientific, Natick, Massachusetts) was placed in 4 (group 2). Preoperatively, and 6 and 12 weeks postoperatively plain x-ray of the kidneys, ureters and bladder, cystography, side specific creatinine clearance and retrograde ureterography were done. The contralateral ureters served as untreated controls. The 7Fr stents were removed at 6 weeks. All animals were sacrificed at 12 weeks after bilateral flow studies. Histological specimens from 4 sites along the urinary tract were graded on a healing score of 0-normal, to 3-severe changes. RESULTS: Side specific creatinine clearance was similar to preoperative values at 6 and 12 weeks. At the 2 time points plain x-ray of the kidneys, ureters and bladder in group 1 showed retroperitoneal stent fragments in 3 of the 5 animals, which was confirmed at autopsy. Retrograde ureterography in group 1 showed mild hydronephrosis in all 5 ureters and saccular diverticula in 4, which was similar in 2 and 3 animals, respectively, in group 2. Cystography demonstrated grades 1 to 2 reflux in 2 animals at 6 weeks but none at 12 weeks in group 1 and no reflux at either time point in group 2. Flow rates and healing scores were statistically similar in the 2 groups but the latter trended toward less favorable healing of ureteral musculature with application of the absorbable stent. CONCLUSIONS: In this pilot study the use of self-reinforced PLGA biodegradable ureteral stents was feasible after Acucise endopyelotomy in a porcine model with radiographic and fluid flow results that were relatively similar to those of standard 7Fr stents but with less favorable biocompatibility.

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.

Mechanical properties and in vitro degradation of bioresorbable knitted stents.

The aim of this study was to characterize the mechanical properties and in vitro degradation of bioresorbable knitted stents. Each stent was knitted using a single self-reinforced fibre made out of either PLLA or 96L/4D PLA or 80L/20G PLGA. The mechanical and physical properties of the fibres and stents were measured before and after gamma sterilization, as well as during in vitro degradation. The mechanical properties of the knitted stents made out of bioresorbable fibres were similar to those of commercially available metallic stents. The knitting geometry (loop height) had a marked effect on the mechanical properties of the stents. The rate of in vitro degradation in mechanical and physical properties for the PLLA and 96L/4D PLA stents was similar and significantly lower than that of the 80L/20G PLGA stents. The 80L/20G PLGA stents lost about 35% of their initial weight at 11 weeks. At this time, they had lost all their compression resistance strength. These data can be used as a guideline in planning further studies in vivo.