Biocompatibility of silver nitrate and ofloxacine coated bioabsorbable SR-PLLA rods

The purpose of this study was to evaluate the biocompatibility of silver nitrate and ofloxacine coatings of bioresorbable self-reinforced poly-l-lactic acid (SR-PLLA) rods. SR-PLLA rods coated with pure poly(caprolactone-co-l-lactide) or blended with silver nitrate (10, 5 or 2 weight-%) or ofloxacine (5 or 2 weight-%) were implanted in the dorsal muscles of 25 male rabbits. Tissue reactions caused by implantation trauma were seen 1 week after implantation. The positive control and 10 w-% silver nitrate coating showed the most marked reactions 1 month after implantation. Only sparse reactions were seen 6 months after implantation. Tissue reactions were scored semi-quantitatively. As a result of this study, we concluded that silver nitrate or ofloxacine coatings up to five w-% did not alter the good biocompatibility of SR-PLLA essentially. The method may lead to the possibility of preventing bacterial adhesion to urological stents during insertion. Received: 23 August 2000 / Accepted: 6 December 2000     

Bacterial adherence to silver nitrate coated poly-L-lactic acid urological stents in vitro

The purpose of this study was to see whether it is possible to prevent bacterial adherence to bioabsorbable self-reinforced l-lactic acid polymer (SR-PLLA) urological stents. The SR-PLLA stents were coated with silver nitrate blended ɛ-caprolactone/l-lactide copolymer. The adherence of five bacterial strains (Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and two strains of Escherichia coli) to coated and non-coated SR-PLLA wires were tested. It was found that silver nitrate coating prevented the adherence of bacteria (except E. faecalis) to SR-PLLA stents. The preventive effect correlated with the silver nitrate concentration. It was also found that silver nitrate coating reduced the amount of bacteria in ambient urine. In conclusion, silver nitrate coating may reduce stent-associated bacterial infections by preventing the adherence of bacteria. Further studies are needed to confirm its efficacy and safety in clinical practice. Received: 4 January 2000 / Accepted: 20 June 2000     

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.     

Effect of uropathogens on in vitro encrustation of polyurethane double J ureteral stents

Polyurethane stents are used when there is an obstruction to the flow of urine. A majority of the patients with such stents are at the risk of urinary tract infection and salt encrustation. The present study is aimed at analyzing the in vitro encrustation of calcium oxalate and other salts in the presence of common uropathogens (E. coli and P. mirabilis) on films made from Tecoflex^®, a commercial grade polyurethane. In the absence of uropathogens, sodium ions and ammonia favor calcium adsorption whereas magnesium ions greatly depress it, resulting in increased hydrophillicity of the stent. With E. coli, Mg ions enhance the encrustation of calcium, whereas the other salts decrease its deposition. In case of P. mirabilis, irrespective of the type of salt, it enhances calcium encrustation except in the presence of sodium ions. Adhesion of uropathogens to the stent surface was higher in the presence of bovine serum albumin. Understanding the dynamics between various salts and microorganism in the urine, and urine–stent interface would aid in designing stents that are inert, resist encrustation and biofilm formation.     

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.     

Resistance of catheters coated with a modified hydrogel to encrustation during an in vitro test

Summary Mid-shaft specimens were cut from latex catheters coated with a modified hydrogel, latex catheters coated with silicone elastomer, and 100% silicone catheters. These specimens were subjected to controlled in vitro encrustation conditions. During a test period of 11 weeks, there was no significant difference in the quantities of encrusting deposits formed on the three materials.     

The use of poly-L-lactic acid filler in facial aesthetics

The use of poly-L-lactic acid in facial aesthetic surgery has been utilized for over a decade. More recently approved by the Food and Drug Administration as a stimulatory filler for the correction of shallow to deep facial lines, it is gaining popularity in the United States. The advantages of its use include its stimulatory action on collagen formation, the longevity of its effect, and the low side effect profile. Despite these advantages, meticulous preparation practices and injection techniques are paramount to achieving a satisfactory outcome. We review poly-L-lactic acid as a filler, along with its associated side effects, indications of use, and techniques of injection.     

The use of silver nitrate for chemical de-epithelialization and urothelialization of intestine in a rabbit model of augmentation cystoplasty

Urinary tract reconstruction using bowel segments can result in complications such as electrolyte abnormalities, infections, stones and cancer. Intestinal mucosa is the primary site responsible for these complications. De-epithelialization of the mucosa and subsequent urothelialization might alleviate these problems. We recently reported our success in de-epithelialization and subsequent uroepithelialization of intestinal segments using 10 g/100 ml AgNO₃ solution in a rat model of augmentation. In this study, chemical de-epithelialization of a colonic segment was attempted using 10 g/100 ml AgNO₃ solution in a rabbit model of augmentation. Sigmoid cystoplasty was performed in 20 male New Zealand rabbits using a 6 cm patch of sigmoid colon. There were two groups, including one group of five rabbits (control, group 1) that underwent augmentation alone, while another group (15 rabbits, treatment group or group 2) was treated with 10g/100 ml AgNO₃ solution before augmentation. Control rabbits were killed at the week 8 of experimentation. Treatment rabbits were killed at 2-, 4-, 6- and 8-week intervals. Immediately before augmentation and at the end of the 8 week experimental period each rabbit underwent cystometry. De-epithelialization of the bowel epithelium without urothelialization was apparent in the treatment rabbits killed at 2 and 4 weeks. Histological analysis revealed almost complete urothelialization of the augmented sections treated with 10 g/100 ml AgNO₃ solution at the end of the 6 and 8 week of experimental periods. The preoperative and postoperative bladder capacities increased substantially in all groups. There was no obvious histologic difference in the amount of collagen present in the augmented tissues in any of the experimental groups. The present study confirmed that the treatment of intestinal segments with 10g/100 ml AgNO₃ solution led to chemical de-epithelialization and urothelialization of the augmented segments. This procedure could, theoretically, have applications to human surgery.     

Electrically-induced, nerve-mediated relaxation of rabbit urethra involves nitric oxide.

Isolated smooth muscle preparations from the rabbit urethra precontracted with noradrenaline (10(-5) M), endothelin (10(-7) M), or arginine vasopressin (10(-7) M) responded to electrical field stimulation by frequency-dependent non-adrenergic, non-cholinergic relaxations, which could be blocked by tetrodotoxin (10(-6) M). Relaxation was more pronounced in preparations precontracted by endothelin than by noradrenaline or arginine vasopressin. The electrically induced relaxations were reduced in a concentration-dependent manner by pretreatment for 30 minutes with NG-nitro-L-arginine (10(-6) to 10(-4) M) and NG-monomethyl-L-arginine (10(-5) to 10(-4) M). At the highest concentration of NG-nitro-L-arginine used (10(-4) M), relaxation was abolished and/or changed into a contraction. The effect of NG-nitro-L-arginine was reversible. NG-nitro-D-arginine had no effect. Pretreatment for 30 minutes with L-arginine (10(-3) M) slightly, but significantly, enhanced the maximum relaxation to field stimulation in noradrenaline-precontracted preparations. L-arginine pretreatment also prevented the effects of low, but not high, concentrations of NG-nitro-L-arginine. In contrast, D-arginine had no effect. Electrically induced relaxations were not significantly affected by methylene blue (10(-5) M) or superoxide dismutase (20 U/ml). Addition of nitric oxide (present in acidified solution of NaNO2) caused transient and concentration-dependent relaxations in preparations precontracted by noradrenaline. At the maximum concentration used (10(-3) M), the relaxant response averaged 67% of the tension induced by noradrenaline. Nitric-oxide-induced relaxations were not affected by NG-nitro-L-arginine or L-arginine, but were significantly inhibited by methylene blue. In preliminary experiments, effects similar to those found in rabbit urethra were also observed in isolated urethral preparations obtained from three patients. It is suggested that in the urethra, nitric oxide is involved in the mediation of relaxation evoked by electrical stimulation of nerves.     

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.     

Control of prolonged,benign, renal hematuria by silver nitrate instillation

Four patients with protracted benign hematuria underwent silver nitrate instillation of the tipper collecting system. The doses varied from 10 ml. of 0.25 per cent silver nitrate to 14 ml. of 1 per cent silver nitrate. In all 4 cases the hematuria resolved within four days without significant complications. At follow-up extending from three to twenty-four months there have been no recurrences of gross hematuria. Silver nitrate instillation appears to be a safe and effective method of treating benign renal hematuria, thus obviating the need fin- extirpative surgery.     

Emerging concepts in the treatment of intracranial aneurysms: stents, coated coils, and liquid embolic agents

Endovascular techniques for the treatment of intracranial aneurysms are rapidly evolving. Modifications of more traditional coils have been introduced. Such modifications include newer coils coated with various polymers to increase both coil thrombogenicity and degree of aneurysm packing. In addition, newer coil designs aimed at improving the conformability of the coil to the aneurysm have been used with promising preliminary results. The availability of a newer generation of stents specifically designed for intracranial navigation allows for more effective treatment of aneurysms with wide necks, which usually have been considered unsuitable for optimal endovascular treatment. Endovascular alternatives to coil embolization, such as liquid embolic materials, also have been explored for the treatment of intracranial aneurysms, with varying results. We summarize the rationale for use of these newer devices and early clinical experiences. Areas of current research and future directions of endovascular aneurysm treatment also are discussed.     

Location and concentration of estrogen,progesterone, and androgen receptors in the bladder and urethra of the rabbit

The objective of this study was to determine location and concentration of estrogen, androgen and progesterone receptors in the bladder and urethra of the rabbit. Two urethral and two bladder specimens were obtained from four 12-week-old female New Zealand white rabbits. Rat monoclonal antibody (AN 1–15) to human androgcn receptor and (H222) to human estrogen receptor and mouse monoclonal antibody (PR6) to chicken progesterone receptor were used. Immunocytochemical staining was performed and specimens were evaluated lor presence and location of steroid receptors. Androgen receptors were found in the highest concentrations in urethral and bladder epithelium. Low to low/moderate concentration were found in smooth muscle. Estrogen receptors were found in moderate to moderate/high concentrations in urethral epithelium and bladder and urethral smooth muscle. Progesterone receptors were not found in appreciable concentrations from any location, though the animals were not pretreated with estrogen. The rabbit model suggests a mechanism by which estrogen therapy can be effective in treating postmenopausal lower urinary tract symptoms. Progesterone receptors were not found in appreciable concentrations, suggesting progesterone therapy may not diminish the effectiveness of estrogen therapy by acting on urethral progesterone receptors. The effect of androgcns on the lower urinary tract needs further investigation to determine if androgen therapy can alleviate lower urinary tract symptoms. © 1995 Wiley-Liss, Inc.     

Instillation of silver nitrate in the treatment of chyluria.

A series of 62 patients with chyluria received instillations of 1% silver nitrate in the renal pelvis over an 8-year period; 51 patients responded well but 11 showed no response to treatment. Follow-up ranged from 2 to 7 years. The treatment was found to be safe, effective and minimally invasive.     

Absorbable pins of self-reinforced poly-L-lactic acid for fixation of fractures and osteotomies.

We reviewed 27 patients with small-fragment fractures or osteotomies treated by internal fixation with absorbable self-reinforced poly-L-lactide pins. The follow-up time ranged from eight to 37 months. The two most common indications were chevron osteotomy of the first metatarsal bone for hallux valgus and displaced fracture of the radial head. No redisplacements occurred, and there were no signs of inflammatory foreign-body reaction. Biopsy in two patients 20 and 37 months after implantation showed that no polymeric material remained.     

Comparative autonomic responses of the cat and rabbit bladder and urethra.

The cat and the rabbit have both been utilized extensively in the study of lower urinary tract function. Previous studies have demonstrated that although both the cat and rabbit bladder are approximately the same weight, the in-vitro cat bladder can generate over 6 times the intravesical pressure of the rabbit bladder. The current study was designed to compare the ability of the isolated bladder to generate pressure with the pressures required to maintain flow through the isolated urethra for both the cat and the rabbit. The results can be summarized as follows. 1) The cat bladder is visibly much thicker than the rabbit bladder, and in vitro cystometry demonstrates that it is far less compliant than the rabbit bladder. 2) Over 20 cm.H2O pressure is required to begin flow through the isolated cat urethra preparation, whereas 5 cm.H2O begins flow through the rabbit urethra. 3) Increasing the flow rate (up to 7-fold) through both the isolated cat and rabbit urethra increases intraurethral pressure only slightly. 4) Both the isolated cat and rabbit urethra respond strongly to field stimulation and alpha-adrenergic stimulation (relative to the opening pressure required to begin flow), but not to cholinergic stimulation. 5) Field stimulation following pre-stimulation by methoxamine induces a strong relaxation of the pre-stimulated cat urethra, but an additive contraction in the pre-stimulated rabbit urethra. These studies demonstrate that in order for the cat to empty its bladder, it must generate a comparatively high intravesical pressure, whereas the rabbit is required to generate a relatively low intravesical pressure.     

An in vitro study of the anti-microbial efficacy of a 1% silver sulphadiazine and 0.2% chlorhexidine digluconate cream, 1% silver sulphadiazine cream and a silver coated dressing

Burn sepsis is a leading cause of mortality and morbidity in patients with major burns. The use of topical anti-microbial agents has helped improve the survival in these patients. There are a number of anti-microbials available, one of which, Silvazine (1% silver sulphadiazine (SSD) and 0.2% chlorhexidine digluconate), is used only in Australasia. No study, in vitro or clinical, had compared Silvazine with the new dressing Acticoat. This study compared the anti-microbial activity of Silvazine, Acticoat and 1% silver sulphadiazine (Flamazine) against eight common burn wound pathogens. METHODS: Each organism was prepared as a suspension. A 10 microl inoculum of the chosen bacterial isolate (representing approximately between 10(4) and 10(5) total bacteria) was added to each of four vials, followed by samples of each dressing and a control. The broths were then incubated and 10 microl loops removed at specified intervals and transferred onto Horse Blood Agar. These plates were then incubated for 18 hours and a colony count was performed. RESULTS: The data demonstrates that the combination of 1% SSD and 0.2% chlorhexidine digluconate (Silvazine) results in the most effective killing of all bacteria. SSD and Acticoat had similar efficacies against a number of isolates, but Acticoat seemed only bacteriostatic against E. faecalis and methicillin-resistant Staphylococcus aureus. Viable quantities of Enterobacter cloacae and Proteus mirabilis remained at 24h. CONCLUSION: The combination of 1% SSD and 0.2% chlorhexidine digluconate (Silvazine) is a more effective anti-microbial against a number of burn wound pathogens in this in vitro study. A clinical study of its in vivo anti-microbial efficacy is required.