Comparison of in vitro encrustation on silicone and hydrogel-coated latex catheters

Mid-shaft sections of 100% silicone (Bardex) and hydrogel-coated latex (Biocath) catheters were subjected to controlled in vitro encrustation conditions for periods of up to 18 weeks. There was no significant difference in the quantities of encrusting deposits formed on these two materials during the course of the experiment.     

Nonporous silicone polymer coating of expanded polytetrafluoroethylene grafts reduces graft neointimal hyperplasia in dog and baboon models

Purpose: Neointimal hyperplasia frequently develops after placement of prosthetic vascular grafts and is a major cause of graft failure. This study was an attempt to prevent vascular lesion formation by coating the graft luminal surface with a thin layer of nonporous silicone polymer, and subsequently with an ultrathin layer of vapor phase (plasma gas) deposited fluoropolymer, thereby providing a smooth and chemically uniform surface that was postulated to limit pannus tissue ingrowth across the graft anastomoses.Methods: Bilateral femoral arteriovenous (AV) conduits were constructed in four dogs using expanded polytetrafluoroethylene graft materials (ePTFE; 6-mm inside diameter, 2.5-cm long). In each animal, one femoral AV shunt was constructed from a graft whose luminal surface was entirely coated with polymer. On the contralateral side, an uncoated graft served as a control. Bilateral aortoiliac grafts were placed in three baboons using 5-cm segments of ePTFE (4-mm inside diameter). One end (1 cm) of each graft had been coated with polymer. In each animal, the coated end of one graft was placed proximally and the coated end of the second graft was placed distally in the contralateral vessels.Results: All grafts were patent at 30 days. In the dog model, there was a significant reduction in graft neointimal area at the venous anastomoses for the coated grafts compared with the uncoated grafts (0.03 ± 0.02 mm ² and 1.11 ± 0.54 mm ² , respectively; p < 0.05). In the baboon model, the silicone coating significantly reduced the graft neointimal thickness (0.003 ± 0.003 mm vs 0.21 ± 0.05 mm; p < 0.05) and neointimal area (0.05 ± 0.08 mm ² vs 0.82 ± 0.58 mm ² ; p < 0.05).Conclusions: These data demonstrate that healing of ePTFE grafts can be effectively modified by altering the physical properties of the graft surface. Neointimal hyperplasia within ePTFE grafts is significantly reduced by the local application of a fluorocarbon-coated, silicone-based polymer. The resulting graft flow surface effectively prevents tissue ingrowth from the adjacent native vessel, thereby preserving the anastomosis luminal area. This approach could represent a new strategy for limiting graft surface anastomotic neointimal hyperplasia. (J Vasc Surg 1996;24:825-33.)     

Ureteral stent encrustation

Palliative ureteral stent placement is effective in relieving obstructive renal impairment, especially that precedent to malignant spreading, and can take the place of surgical intervention. Furthermore, cutaneous antegrade and/or endoscopic retrograde stenting can be indicated for other pyelo-ureteric operations and prevent their complications, but is has its consequences: We experienced three cases in which stenting had to be repeated because of its obstruction. The stent catheter blockage is discussed.     

Oxalate-degrading enzymes from Oxalobacter formigenes: a novel device coating to reduce urinary tract biomaterial-related encrustation

BACKGROUND AND PURPOSE: The long-term placement of biomaterials within the urinary tract is limited by the development of encrustation. In a noninfected urinary environment, encrustation often results from the deposition of calcium oxalate on the biomaterial surface. There is an association between the absence of Oxalobacter formigenes, a commensal colonic bacterium capable of degrading oxalate, and calcium oxalate stone formation. This pilot study was designed to evaluate several oxalate-degrading enzymes produced by O. formigenes as a potential biomaterial coating to reduce urinary tract encrustation. MATERIALS AND METHODS: Circular silicone disks of 6-mm diameter were incubated for 48 hours in oxalylcoenzyme A decarboxylase (OXC), formyl-coenzyme A transferase (FRC), and coenzyme A, while control disks were incubated in distilled water. The adsorption of OXC and FRC was assessed using enhanced chemiluminescence (ECL) and atomic force microscopy (AFM). Coated and uncoated disks (20 of each) were implanted in the bladders of 40 female New Zealand White rabbits. After 30 days, the disks were recovered, and the degree of encrustation on the polymer surface was evaluated utilizing dry weight measurement, calcium atomic absorption spectroscopy (AAS), and scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDX). RESULTS: Both ECL and AFM demonstrated coating of the silicone disks with OXC and FRC. The mean dry weights of the coated and control disks following explantation were 0.591 +/- 0.438 g and 0.747 +/- 0.428 g, respectively (P = 0.307). The mean weight of calcium on the coated and control disks, as determined by AAS, was 154.1 +/- 96.25 mg and 258 +/- 181.35 mg, respectively (P = 0.008). CONCLUSIONS: The use of oxalate-degrading enzymes from O. formigenes to coat urinary biomaterials represents a novel paradigm to reduce biomaterial-related encrustation. Coating of silicone with oxalate-degrading enzymes from O. formigenes results in a modest reduction in encrustation with no apparent toxicity. Further studies are warranted.     

Effect of hydrophilic coating on microorganism colonization in silicone tubing

Summary Background. Shunt infections are one of the major causes of mortality and morbidity of patients with hydrocephalus. The aim of this research is to compare the bacterial colonization characteristics of a regular silicone elastomer shunt material coated with polyvinylpyrrolidone and dimethylpolysiloxane (silicone).Method. Regular coated shunt materials were compared by in-vivo and in-vitro methods. In the in-vitro experiment, silicone and coated material immersed and not immersed in vancomycin solution was treated with a certain concentration of Staphylococcus epidermidis. In the in-vivo study, silicone and coated material specimens were treated with Staphylococcus epidermidis and they were stereotactically placed in the lateral ventricles of the rats. One week after the inoculation, shunt pieces were removed and the colonies were counted by using a scanning electron microscope.Findings. There was a statistically significant difference of colonization in the in-vitro groups in coated material vs. silicone, coated material vs. vancomycin treated silicone, vancomycin treated coated material vs. silicone, vancomycin treated coated material vs. vancomycin treated silicone. There was no statistically significant difference for colonization in in-vitro groups of coated material and vancomycin treated coated material. With in-vivo experiments we can say that, coated material catheters are superior than the silicone catheters in respect to colonization but after the bacterial colonization has occurred, the amount of colonization did not differ.Interpretation. Coated material catheters are superior to silicone catheters and they prevent bacterial colonization in some respect.     

Verapamil‐containing silicone gel reduces scar hypertrophy

A hypertrophic scar is a common dermal fibroproliferative lesion usually treated with topical silicone. Verapamil, a type of calcium channel blocker, is considered a candidate drug for the treatment of hypertrophic scars. Here, we report that the addition of verapamil to topical silicone gel enhances treatment outcomes of hypertrophic scars. Upon creation of hypertrophic scars with the rabbit ear model, varying concentrations of verapamil‐added silicone gel (0.1, 1, and 10 mg/g) were applied daily for 28 days. After the animals were euthanised, microscopic measurement was performed for (a) scar elevation index (SEI), (b) fibroblast count, and (c) capillary count. On gross analysis, features of hypertrophic scars were significantly alleviated in the verapamil‐added groups. On histologic examination, verapamil‐added groups showed (a) reduced SEI (1.93 (1.79‐2.67) for control vs 1.34 (1.21‐1.51) for silicone only and 1.13 (1.01‐1.65) for verapamil‐added silicone), (b) fibroblast count 700.5 (599.5‐838.5) for control, 613.25 (461‐762.5) for silicone only, and 347.33 (182.5‐527) for verapamil‐added silicone), and (c) capillary formation (52 (35.5‐96.5) for control, 46 (28‐64.5) for silicone only, and 39.83(24‐70) for verapamil‐added silicone) (Kruskal‐Wallis test, P < .05). On western blot, expression levels of collagen I protein was lower in the 1 mg/g and 10 mg/g verapamil‐added silicone compared with control. Therefore, we suggest a therapeutic concentration of verapamil‐added silicone gel of at least over 1 mg/g. Further study regarding maximally effective concentration and deeper insight into the mechanism of action should follow.     

Urinary encrustation of alloplastic materials

Currently, all alloplastic materials placed within the urinary tract are susceptible to encrustation, and devices made from these biomaterials are prone to the associated complications. Encrustation is affected by such surface properties as roughness and irregularity, hydrophobicity and wetability, charge, polymer chemistry, and coatings. The composition of the surface may also influence reactivity at the interface. A raised urinary pH as a result of infection with urease-producing bacteria is an important mechanism of encrustation, but encrustation can take place in the absence of infection. Individual variations in the risk of encrustation have been identified. Better device designs are required, as are better models for examining biomaterials and biofilm formation. With a coordinated multidisciplinary approach and adequate resources, we may solve the problem of encrustation, which has such an adverse effect on patient quality of life and on healthcare costs.     

Calcium phosphate in catheter encrustation

Encrusted catheters from nine female patients were the source of samples of deposits which were examined by X-ray diffraction, atomic absorption spectroscopy, infra-red spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. In eight samples the only crystalline phase which could be clearly distinguished by X-ray diffraction was ammonium magnesium orthophosphate hexahydrate, NH4MgPO4 X 6H2O, which occurs naturally as the mineral struvite. However, atomic absorption spectroscopy revealed an appreciable concentration of calcium in all samples. Calcium phosphates have previously been detected in catheter deposits. Infra-red and EXAFS spectra were consistent with the calcium phosphate being present as a poorly crystalline hydroxyapatite. Thus the deposits appear to consist of a mixture of crystalline struvite and a form of hydroxyapatite which is not fully crystalline.     

The dissolution of urinary catheter encrustation

OBJECTIVES: To identify the optimum volume of acidic bladder washout solution to dissolve catheter encrustations and to compare the effectiveness of different bladder washout delivery devices. MATERIALS AND METHODS: Urinary catheter encrustation was generated in vitro using a model of the catheterized bladder adapted from previous work. An acidic bladder washout solution (Suby G) was applied via the catheter in the model and retained for 15 min. The amount of encrusting material dissolved was measured by colorimetric analysis of the magnesium and calcium content of the solution returned after the washout procedure. The relative effectiveness of different volumes of washout solution and different washout delivery devices (Optiflow, Bard Ltd, Crawley; UroTainer, B/Braun Medical Ltd, Aylesbury; and a bladder syringe) in dissolving catheter encrustations was compared to the 'standardized' conditions commonly used in practice. RESULTS: There was no statistically significant difference between washouts with 100 mL and washouts with 50 mL for any of the delivery devices tested. Gentle agitation with 50 mL Suby G did not significantly improve the dissolution of encrustation but the total amount of material dissolved when two washouts with 50 mL Suby G were used sequentially was significantly better than a single washout with either 100 mL or 50 mL. CONCLUSIONS: Under controlled laboratory conditions, smaller volumes of acidic bladder washout solution (50 mL) are as effective as the 100 mL commonly used in practice, but two sequential washouts with 50 mL are more effective than a single washout. The newly designed Optiflow delivery device is at least as effective as the other devices tested. This study provides new evidence which may contribute to decision-making by practitioners in relation to catheter care.     

输尿管支架结痂的原因分析以及石痂与原发结石成分的比较

目的探讨输尿管支架结痂的原因，比较石痂和原结石成分的异同，了解成因及预防。 方法回顾性分析我院2020年3月至2021年8月80例输尿管支架结痂泌尿系结石患者，及同期接受治疗的80例输尿管支架未结痂泌尿系结石患者的资料。采用结石红外光谱自动分析系统分析结石及石痂，对比其成分的差异。 结果结痂组与非结痂组患者的性别比例、年龄、肌酐、肾小球滤过率、肾积水情况、术前感染控制情况、尿培养情况、手术方式、结石部分、术后口服抗生素时间等差异均无统计学意义（P>0.05）。结痂组和非结痂组患者相比更容易出现腰痛（P<0.05）。结痂组和非结痂组患者相比患代谢综合征的比例高，结石清除率较低，尿pH值较高，饮食偏荤和喜饮茶者较多（P<0.05）。71.25%（57/80）患者的支架管石痂成分与原结石成分一致，28.75%（23/80）患者的支架管石痂与原发结石成分不一致，可能与感染控制不佳和代谢性疾病有关。 结论输尿管支架结痂这一并发症需要引起足够的重视，大部分的石痂与原发结石成分相同。可通过改变生活习惯，控制带管时间，积极控制尿路感染及治疗代谢性疾病预防。     

Intraluminal cyclosporine A reduces capsular thickness around silicone implants in rats

One theory of the cause of connective tissue capsule formation around silicone mammary prostheses is based on an immunological interaction. In an in vitro pilot study, it is shown that intraluminal cyclosporine A, a potent T-lymphocyte-specific immunosuppressive agent, can diffuse slowly through the outer shell of a standard double-lumen silicone breast implant. Round silicone tissue expanders containing 50 mg of cyclosporine A were implanted subcutaneously in 10 rats. Ten animals served as controls. Evaluation was performed after three months. A significant decrease in collagen capsular thickness of 21.6 +/- 5.4 microns (mean +/- standard deviation was measured histomorphometrically in the treated group compared with 39.6 +/- 8.6 microns in the control group (p less than 0.001).     

Gentamicin coating of metallic implants reduces implant-related osteomyelitis in rats

Antibiotic prophylaxis is a routine procedure in orthopedic surgery. Various local antibiotic delivery techniques are used to reduce bone- and soft tissue-related infection. The objective of this study was to evaluate the efficacy of a new biodegradable, gentamicin-loaded poly(D,L-lactide) (PDLLA) coating of orthopedic devices in preventing implant-related osteomyelitis. The medullary cavities of tibiae in 30 Sprague Dawley rats were contaminated with Staphylococcus aureus (10(3) colony forming units). Simultaneously titanium Kirschner wires, uncoated (group II), coated with PDLLA (group III), or coated with PDLLA + 10% gentamicin (group IV), were implanted. Ten animals that received phosphate-buffered saline and uncoated Kirschner wires served as controls (group I). Follow-up was 6 weeks. In weekly intervals X-rays of the tibiae were performed, blood counts were taken, and body temperature and weight were determined. After sacrifice infection was evaluated by histological and microbiological analysis. All animals of groups II and III developed microbiological, histological, and radiological signs of infection, including osseous destruction and soft tissue swelling. All animals of the control group remained sterile. Cultures of implants of group IV showed significantly reduced bacterial growth compared to cultures of groups II and III, and three implants of group IV remained sterile. Further radiological and histological signs of infection were significantly reduced in the gentamicin-coated group compared to groups II and III. No significant differences in body weight, body temperature, and blood parameters between all groups were observed. Local application of antibiotic-coated orthopedic devices containing PDLLA and 10% gentamicin significantly reduced implant-related infection in this animal model.     

The physicochemical basis of urinary catheter encrustation.

OBJECTIVES: To determine the relationship between urinary pH and Ca2+ solubility in urine samples from patients who experienced either frequent ('blockers') or infrequent ('nonblockers') catheter blockage by crystalline deposits of divalent cation salts. MATERIALS AND METHODS: Fresh urine samples from 'blockers' and 'nonblockers' were collected and the ionic calcium concentration ([Ca2+ ]) measured using a Ca2+-selective electrode whilst the urinary pH was increased in 0.25 increments between 4.75 and 9.00. The pH at which crystallization occurred (nucleation) was determined and crystal composition analysed. RESULTS: The mean (sd) voided urinary pH of catheter 'blockers' was significantly more alkaline than that from 'nonblockers', at 7.63 (0.64) and 5.97 (0.80), respectively (P=0. 001). The nucleation pH of catheter 'blockers' was significantly more acid than in 'nonblockers', at 7.43 (0.73) and 6.45 (0.65), respectively (P=0.005). Urine from 'blockers' had significantly more Ca phosphate and Mg ammonium phosphate crystals. 'Blockers' were further divided into two subsets with and without urease-based urinary tract infection; both showed a decrease in the nucleation pH. CONCLUSION: In the urine from 'nonblockers' there is a wide safety margin between voided and nucleation pHs; this margin was less in the urine from 'blockers'. This reduction in the safety margin arises partly because the voided pH in those with a urinary tract infection is more alkaline. However, the decrease in the nucleation pH also suggests that a fundamental property of urine is altered, which reduces Ca2+ solubility at more neutral pH values. The long-term goal is to increase the nucleation pH of catheter 'blockers' and increase the margin of safety.