An improved model for bacterial encrustation studies

Biodegradation and Antimicrobial Properties of Zinc Oxide–Polymer Composite Materials for Urinary Stent Applications

Research advancements in the field of urinary stents have mainly been in the selection of materials and coatings to address commonly faced problems of encrustation and bacterial adhesion. In this study, polylactic acid (PLA) and polypropylene (PP) were evaluated with zinc oxide (ZnO) coating to assess its ability to reduce or eliminate the problems of encrustation and bacteria adhesion. PLA and PP films were prepared via twin screw extrusion. ZnO microparticles were prepared using sol-gel hydrothermal synthesis. The as-prepared ZnO microparticles were combined in the form of a functional coating and deposited on both polymer substrates using a doctor blade technique. The ZnO-coated PP and PLA samples as well as their uncoated counterparts were characterized from the physicochemical standpoints, antibacterial and biodegradation properties. The results demonstrated that both the polymers preserved their mechanical and thermal properties after coating with ZnO, which showed a better adhesion on PLA than on PP. Moreover, the ZnO coating successfully enhanced the antibacterial properties with respect to bare PP/PLA substrates. All the samples were investigated after immersion in simulated body fluid and artificial urine. The ZnO layer was completely degraded following 21 days immersion in artificial urine irrespective of the substrate, with encrustations more evident in PP and ZnO-coated PP films than PLA and ZnO-coated PLA films. Overall, the addition of ZnO coating on PLA displayed better adhesion, antibacterial activity and delayed the deposition of encrustations in comparison to PP substrates.

Validation of the CDC biofilm reactor as a dynamic model for assessment of encrustation formation on urological device materials

Contemporary medical science is reliant upon the rational selection and utilization of devices, and therefore, an increasing need has developed for in vitro systems aimed at replicating the conditions to which urological devices will be subjected to during their use in vivo. We report the development and validation of a novel continuous flow encrustation model based on the commercially available CDC biofilm reactor. Proteus mirabilis-induced encrustation formation on test biomaterial sections under varying experimental parameters was analyzed by X-ray diffraction, infrared- and Raman spectroscopy and by scanning electron microscopy. The model system produced encrusted deposits similar to those observed in archived clinical samples. Results obtained for the system are highly reproducible with encrustation being rapidly deposited on test biomaterial sections. This model will have utility in the rapid screening of encrustation behavior of biomaterials for use in urological applications.

Characterization and optimization of experimental variables within a reproducible bladder encrustation model and in vitro evaluation of the efficacy of urease inhibitors for the prevention of medical device-related encrustation

This study presents a reproducible, cost-effective in vitro encrustation model and, furthermore, describes the effects of components of the artificial urine and the presence of agents that modify the action of urease on encrustation on commercially available ureteral stents. The encrustation model involved the use of small-volume reactors (700 mL) containing artificial urine and employing an orbital incubator (at 37 degrees C) to ensure controlled stirring. The artificial urine contained sources of calcium and magnesium (both as chlorides), albumin and urease. Alteration of the ratio (% w/w) of calcium salt to magnesium salt affected the mass of encrustation, with the greatest encrustation noted whenever magnesium was excluded from the artificial urine. Increasing the concentration of albumin, designed to mimic the presence of protein in urine, significantly decreased the mass of both calcium and magnesium encrustation until a plateau was observed. Finally, exclusion of urease from the artificial urine significantly reduced encrustation due to the indirect effects of this enzyme on pH. Inclusion of the urease inhibitor, acetohydroxamic acid, or urease substrates (methylurea or ethylurea) into the artificial medium markedly reduced encrustation on ureteral stents. In conclusion, this study has described the design of a reproducible, cost-effective in vitro encrustation model. Encrustation was markedly reduced on biomaterials by the inclusion of agents that modify the action of urease. These agents may, therefore, offer a novel clinical approach to the control of encrustation on urological medical devices.

Design and validation of a dynamic flow model simulating encrustation of biomaterials in the urinary tract

A number of models exist for assessing encrustation on biomaterials employed as devices in the urinary tract. However, static urine models are suitable only for assessment of biomaterials residing in the bladder and the dynamic models available suffer from a number of disadvantages, notably their complexity and limitation to short-term assessment. The dynamic model described herein is a relatively simple design incorporating the ability to assess a large number of biomaterials in replicate fashion and over long periods of time. The biomaterials tested in the dynamic model conform to the urethral catheter and ureteral stent devices that experience urine flow within the urinary tract. The model was initially validated using Percuflex as a test biomaterial. The mass of calcium and magnesium, representing hydroxyapatite and struvite encrustation, respectively, on Percuflex was detected by atomic absorption spectrometry. No significant differences in encrustation levels were detected either between vessels or between biomaterial positions on any mandrel within the vessels, indicating the suitability of the dynamic model for reproducible determination of biomaterial encrustation. The dynamic model was then used to compare the encrustation of biomaterials commonly employed in urinary-tract devices, namely polyurethane, Percuflex and silicone. Calcium and magnesium levels on polyurethane and Percuflex were shown to be statistically similar, whereas silicone exhibited significantly reduced encrustation. When, subsequently, comparisons were made of biomaterial encrustation between the dynamic model and a static model, calcium and magnesium levels arising from the latter model were significantly higher on each of the biomaterials. However, the same rank order of encrustation resistance was observed for the biomaterials in both models, with silicone performing better than polyurethane or Percuflex. The prediction of in-vivo performance based on in-vitro models of encrustation is often difficult, although the model described provides a more accurate method for assessing the potential of novel and existing biomaterials for use in urinary medical devices requiring flow of urine.

Assessment of PEO/PTMO multiblock copolymer/segmented polyurethane blends as coating materials for urinary catheters: in vitro bacterial adhesion and encrustation behavior

The effective long-term use of indwelling urinary catheters has often been hindered by catheter-associated infection and encrustation. In this study, the suitability of poly(ethylene oxide) (PEO)-based multiblock copolymer/segmented polyurethane (SPU) blends as coating materials for the commercial urinary catheters was assessed by measuring swellability, bacterial adhesion, and encrustation behavior. When exposed to PBS (pH 7.4), the blends absorbed a significant amount of water, which was proportional to the copolymer content. It was demonstrated from bacterial adhesion tests that compared to bare SPU, the blend surfaces could significantly reduce the adhesion of E. coli, P. mirabilis, and S. epidermidis; the number of adherent bacteria correlated with the amount of copolymer additive. indicating that the swellability of the blends affected bacterial adhesion. Of the bacteria studied, the greatest effect of the copolymer additive was observed in S. epidermidis adhesion, in which there was an 85% decrease compared to bare SPU with a small amount of copolymer additive as low as 5% based on a dried blend. By using an artificial bladder model, allowing the catheter to be blocked by encrustation, it was revealed that the blend surfaces could effectively resist encrustation. The duration of patency was extended up to 20 +/- 3.1 h on the blend surface containing 10% of the copolymer additive, whereas the silicone-coated catheter, a control, required the least time for blockage, 7.8 +/- 3.1 h. The superior characteristics of the blends compared to other surfaces might be attributed to their PEO-rich surfaces, produced by the migration of PEO phase in the copolymer chain of the blends in an aqueous environment, and provide promising potential as a coating material on the urinary catheter for long-term catheterization.

Assessment of urinary tract biomaterial encrustation using a modified Robbins device continuous flow model

Encrustation of biomaterials employed in the urinary tract remains a major problem resulting in obstruction or blockage of catheters and stents. Therefore, resistance to encrustation is a desirable feature of biomaterials employed in such devices. The novel assessment of biomaterial encrustation employing a continuous flow model based on a modified Robbins device is described. Artificial urine was used in conjunction with 5% CO2 to simulate the physiological environment within the upper urinary tract. The widely used urinary device biomaterials, silicone and polyurethane, were investigated in the model for hydroxyapatite and struvite encrustation. Scanning electron microscopy, energy dispersive X-ray analysis, and atomic absorption spectroscopy all showed that silicone was less prone to encrustation than polyurethane and that hydroxyapatite deposition was predominant on both surfaces. The model has the advantage that a large number of biomaterials may be investigated simultaneously because several Robbins devices may be placed in parallel. The model is recommended for comparative evaluation of biomaterial candidates for use in urinary tract devices.

Assessment of encrustation behaviour on urinary tract biomaterials

The effective clinical use of biomaterials within the urinary tract is often hindered by the associated problems of bacterial biofilm formation and encrustation which may cause obstruction or blockage of urethral catheters and ureteral stents. Methods for assessing encrustation formation on these devices are reviewed and novel urinary tract biomaterials which may be more effective at resisting encrustation are discussed.