Determination of urethral catheter surface lubricity

Biocompatible Hydrogel Coating on Silicone Rubber with Improved Antifouling and Durable Lubricious Properties

Silicone rubber is widely used in various medical applications. However, silicone rubber is prone to biofouling due to their affinity for lipids and has a high friction coefficient, which can significantly impact their efficacy and performance used as medical devices. Thus, the development of hydrogels with antifouling and lubricious abilities for the modification of silicone rubber is in high demand. We herein prepared a variety of hydrogel coatings mainly based on polyvinylpyrrolidone (PVP) and poly (ethylene glycol) diacrylate (PEGDA). We modified the silicone rubber using the prepared hydrogel coatings and cured it using a heating method. Then, we characterized its surface and evaluated the antifouling property, lubricious property, cytotoxicity, sensitization, and vaginal irritation. The results of water contact angle (WCA), protein adsorption, and friction coefficient indicated the success of the modification of the silicone rubber, leading to a significant decrease in the corresponding test values. Meanwhile, the results of cytotoxicity, sensitization, and vaginal irritation tests showed that the hydrogel coating-modified silicone rubbers have an excellent biocompatibility. This study describes how the silicone rubber could be modified with a biocompatible hydrogel coating. The hydrogel coating-modified silicone rubbers have improved antifouling and durable lubricious properties.

Spectroscopic and Thermal Characterisation of Interpenetrating Hydrogel Networks (IHNs) Based on Polymethacrylates and Pluronics, and Their Physicochemical Stability under Aqueous Conditions

This study describes the physicochemical characterisation of interpenetrating hydrogel networks (IHNs) composed of either poly(hydroxyethylmethacrylate, p(HEMA)) or poly(methacrylic acid, p(MAA)), and Pluronic block copolymers (grades F127, P123 and L121). IHNs were prepared by mixing the acrylate monomer with Pluronic block copolymers followed by free radical polymerisation. p(HEMA)-Pluronic blends were immiscible, evident from a lack of interaction between the two components (Raman spectroscopy) and the presence of the glass transitions (differential scanning calorimetry, DSC) of the two components. Conversely, IHNs of p(MAA) and each Pluronic were miscible, displaying a single glass transition and secondary bonding between the carbonyl group of p(MAA) and the ether groups in the Pluronic block copolymers (Raman and ATR-FTIR spectroscopy). The effect of storage of the IHNs in Tris buffer on the physical state of each Pluronic and on the loss of Pluronic from the IHNs were studied using DSC and gravimetric analysis, respectively. Pluronic loss from the IHNs was dependent on the grade of Pluronic, time of immersion in Tris buffer, and the nature of the IHN (p(HEMA) or p(MAA)). At equilibrium, the loss was greater from p(HEMA) than from p(MAA) IHNs, whereas increasing ratio of poly(propylene oxide) to poly(ethylene oxide) decreased Pluronic loss. The retention of each Pluronic grade was shown to be primarily due to its micellization; however, hydrogen bonding between Pluronic and p(MAA) (but not p(HEMA)) IHNs contributed to their retention.

Understanding the properties of intermittent catheters to inform future development

Despite the extensive use of intermittent catheters (ICs) in healthcare, various issues persist for long-term IC users, such as pain, discomfort, infection, and tissue damage, including strictures, scarring and micro-abrasions. A lubricous IC surface is considered necessary to reduce patient pain and trauma, and therefore is a primary focus of IC development to improve patient comfort. While an important consideration, other factors should be routinely investigated to inform future IC development. An array of in vitro tests should be employed to assess IC's lubricity, biocompatibility and the risk of urinary tract infection development associated with their use. Herein, we highlight the importance of current in vitro characterisation techniques, the demand for optimisation and an unmet need to develop a universal 'toolkit' to assess IC properties.

Introducing an lsoprenaline Eluting Guidewire: Report on its Design and the Results of the Dose-Determining Pilot Study

Introduction: Retrograde intrarenal surgery (RIRS) is associated with complications, many of which are related to the intrarenal pressure (IRP). We aim to describe the design of a novel isoprenaline-eluting guidewire ("IsoWire") and present the results from the first in vitro release studies and the first animal studies showing its effect on IRP. Materials and Methods: The IsoWire comprises a Nitinol core surrounded by a stainless-steel wire wound into a tight coil. The grooves created by this coil provided a reservoir for adding a hydrogel coating into which isoprenaline, a beta-agonist, was loaded. Animal studies were performed using a porcine model. For the control, IRP, heart rate (HR), and mean arterial pressure (MAP) were measured continuously for 6 minutes with a standard guidewire in place. For the experiment, the standard hydrophilic guidewire was removed, the IsoWire was inserted into the renal pelvis, and the same parameters were measured. Results: In vitro analysis of the isoprenaline release profile showed that most (63.9 ± 5.9%) of the loaded drug mass was released in the 1st minute, and almost all of the drug was released in the first 4 minutes exponentially. Porcine studies showed a 25.1% reduction in IRP in the IsoWire that released 10 μg in the 1st minute; however, there was a marked increase in HR. The average percentage reduction in IRP was 8.95% and 21.3% in the IsoWire that released 5 and 7.5 μg of isoprenaline, respectively, with no changes in HR or MAP. Conclusions: The IsoWire, which releases 5 and 7.5 μg of isoprenaline in the 1st minute, appears to be safe and effective in reducing the IRP. Further studies are needed to establish whether the isoprenaline-induced ureteral relaxation will render easier insertion of a ureteral access sheath, reduce IRP during sheathless RIRS, or even promote the practice of sheathless RIRS.

Comparing an Integrated Amphiphilic Surfactant to Traditional Hydrophilic Coatings for the Reduction of Catheter-Associated Urethral Microtrauma

Hydrophilic-coated intermittent catheters have improved the experience of intermittent urinary catheterization for patients compared to conventional gel-lubricated uncoated catheters. However, the incorporation of polyvinylpyrrolidone (PVP) within hydrophilic coatings can lead to significant issues with coating dry-out. Consequently, increased force on catheter withdrawal may cause complications, including urethral microtrauma and pain. Standard methods of evaluating catheter lubricity lack physiological relevance and an understanding of the surface interaction with the urethra. The tribological performance and urethral interaction of commercially available hydrophilic PVP-coated catheters and a coating-free integrated amphiphilic surfactant (IAS) catheter were evaluated by using a biomimetic urethral model designed from a modified coefficient of friction (CoF) assay. T24 human urothelial cells were cultured on customized silicone sheets as an alternate countersurface for CoF testing. Hydrophilic PVP-coated and coating-free IAS catheters were hydrated and the CoF obtained immediately following hydration, or after 2 min, mimicking in vivo indwell time for urine drainage. The model was observed for urethral epithelial cell damage postcatheterization. The majority of hydrophilic PVP-coated catheters caused significantly greater removal of cells from the monolayer after 2 min indwell time, compared to the IAS catheter. Hydrophilic PVP-coated catheters were shown to cause more cell damage than the coating-free IAS catheter. A biomimetic urethral model provides a more physiologically relevant model for understanding the factors that govern the frictional interface between a catheter surface and urethral tissue. From these findings, the use of coating-free IAS catheters instead of hydrophilic PVP-coated catheters may help reduce urethral microtrauma experienced during catheter withdrawal from the bladder, which may lead to a lower risk of infection.

Friction injury of the central vein caused by catheter for hemodialysis: an in vitro study

Vascular injury such as central venous stenosis (CVS) is a common complication in hemodialysis patients with central venous catheters (CVCs), yet the impact of the microstructure and partial physic characteristics of catheter surface on the chronic injury of central vein has not been elucidated. In this study, the microscopic morphology of tips and bodies of six different brands of polyurethane CVCs was observed and their roughness was assessed. Subsequently, an in vitro model was established to measure the coefficients of friction (COF) between CVCs (tips and bodies) and the vena cava intima of Japanese rabbits under the same condition in a linear reciprocating mode, and changes in the intima of vessels after friction were observed. The study found that there was a significant variation in surface roughness among different brands of CVCs (tips P < 0.001, bodies P = 0.02), and the COF was positively correlated with the catheter surface roughness (tips P = 0.005, R = 0.945, bodies P = 0.01, R = 0.909). Besides, the endovascular roughness increased after friction. These findings suggest that the high roughness surface of CVCs may cause chronic mechanical friction injury to the central venous intima, which is one of the potential factors leading to CVS or occlusion. This provides a breakthrough for reducing complications, improving patient prognosis, and advancing catheter surface lubrication technology.

Simulation and Experimental Investigation of Balloon Folding and Inserting Performance for Angioplasty: A Comparison of Two Materials, Polyamide-12 and Pebax

BACKGROUND

A balloon dilatation catheter is a vital tool in percutaneous transluminal angioplasty. Various factors, including the material used, influence the ability of different types of balloons to navigate through lesions during delivery.

OBJECTIVE

Thus far, numerical simulation studies comparing the impacts of different materials on the trackability of balloon catheters has been limited. This project seeks to unveil the underlying patterns more effectively by utilizing a highly realistic balloon-folding simulation method to compare the trackability of balloons made from different materials.

METHODS

Two materials, nylon-12 and Pebax, were examined for their insertion forces via a bench test and a numerical simulation. The simulation built a model identical to the bench test's groove and simulated the balloon's folding process prior to insertion to better replicate the experimental conditions.

RESULTS

In the bench test, nylon-12 demonstrated the highest insertion force, peaking at 0.866 N, significantly outstripping the 0.156 N force exhibited by the Pebax balloon. In the simulation, nylon-12 experienced a higher level of stress after folding, while Pebax had demonstrated a higher effective strain and surface energy density. In terms of insertion force, nylon-12 was higher than Pebax in specific areas.

CONCLUSION

nylon-12 exerts greater pressure on the vessel wall in curved pathways when compared to Pebax. The simulated insertion forces of nylon-12 align with the experimental results. However, when using the same friction coefficient, the difference in insertion forces between the two materials is minimal. The numerical simulation method used in this study can be used for relevant research. This method can assess the performance of balloons made from diverse materials navigating curved paths and can yield more precise and detailed data feedback compared to benchtop experiments.

Numerical Methodology to Evaluate Trackability and Pushability of PTCA Balloon Catheter

PURPOSE

During percutaneous coronary intervention (PCI), the ability to navigate a catheter without causing injury to the vessel and damage to the device is crucial outcome of the procedure. This study aimed to develop a numerical model to analyse the percutaneous transluminal coronary angioplasty (PTCA) catheter navigation in coronary vessels.

METHODS

Trackability and pushability are two major parameters used to characterize the navigation of PTCA balloon catheters, and they are influenced by vessel tortuosity, contact interactions and catheter design. In the current study, finite element analysis model is presented to evaluate trackability and pushability considering two different vessel geometries. Impact of contact interactions among catheter, guidewire, and vessel were studied to validate the numerical model with in vitro test data. Further, a parametric study was conducted to understand the influence of distal shaft, and proximal shaft outer diameter.

RESULTS

Obtained results suggest that contact interaction and co-efficient of friction between guidewire and catheter are critical parameters to obtain numerical results comparable to experimental data. Results from the parametric study predicted strong positive correlation of distal shaft diameter on pushability, and weak correlation on trackability force. Furthermore, parametric variation in proximal shaft diameter has strong positive correlation on trackability force and strong negative correlation on pushability.

CONCLUSION

Numerical methodology presented in this study is a preliminary attempt to simulate the behavior of PTCA balloon catheter navigation. This methodology will be helpful in the design and optimization of PTCA balloon catheter and similar devices with improved deliverability.

Effects of hydrophilic coated catheters on urethral trauma, microtrauma and adverse events with intermittent catheterization in patients with bladder dysfunction: a systematic review and meta-analysis

Background

Hydrophilic coated catheters are recommended to reduce the side effects of intermittent catheterization (IC) in patients with bladder dysfunction. However, there is lack of Level one evidence to support the use of this intervention.

Search methods

Several electronic databases were systematically searched to evaluate complication incidences for hydrophilic coated (HC) and non-hydrophilic catheters (NHC).

Results

Twelve studies were eligible for inclusion in the review. The meta-analyses exploring microscopic hematuria frequencies (RR = 0.69; 95% CI 0.52–0.90) and urethral stricture frequencies (RR = 0.28; 95% CI 0.13–0.60) showed a lower risk ratio associated with HC in comparison to NHC, whereas gross hematuria was no statistically significant difference in two groups. Subgroup analyses of gross hematuria which was grouped according to "catheterization frequency", "single/multiple catheterization" and "self/other catheterization” were performed and the values of combined RR were also no statistically significant difference.

Conclusions

Compared with non-hydrophilic catheters, the hydrophilic coated catheters have positive significance in reducing the incidence of urethral microtrauma and the urethral stricture. However, more studies are warranted for evaluating effects of hydrophilic coated catheters on the incidence of gross hematuria.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11255-022-03172-x.

Contact Stability and Contact Safety of a Magnetic Resonance Imaging-Guided Robotic Catheter Under Heart Surface Motion

Contact force quality is one of the most critical factors for safe and effective lesion formation during catheter based atrial fibrillation ablation procedures. In this paper, the contact stability and contact safety of a novel magnetic resonance imaging (MRI)-actuated robotic cardiac ablation catheter subject to surface motion disturbances are studied. First, a quasi-static contact force optimization algorithm, which calculates the actuation needed to achieve a desired contact force at an instantaneous tissue surface configuration is introduced. This algorithm is then generalized using a least-squares formulation to optimize the contact stability and safety over a prediction horizon for a given estimated heart motion trajectory. Four contact force control schemes are proposed based on these algorithms. The first proposed force control scheme employs instantaneous heart position feedback. The second control scheme applies a constant actuation level using a quasi-periodic heart motion prediction. The third and the last contact force control schemes employ a generalized adaptive filter-based heart motion prediction, where the former uses the predicted instantaneous position feedback, and the latter is a receding horizon controller. The performance of the proposed control schemes is compared and evaluated in a simulation environment.

Coatable and Resistance-Proof Ionic Liquid for Pathogen Eradication

Antibiotic-resistant bacteria infect close to 3 million people, and kill 35,000, each year in the United States. Ionic liquid (IL)-based antimicrobial agents have the potential to diversify our ever-diminishing antibiotic arsenal. Here, we describe an IL with potent submicromolar antimicrobial activity in vitro against clinically relevant Gram-negative and Gram-positive bacterial pathogens as well as anti-infective activity in a mouse model. The IL kills pathogenic bacteria such as Acinetobacter baumannii, Salmonella enterica, and Escherichia coli by disrupting their outer membrane and does not select for bacterial resistance. We show incorporation of our IL into surface coatings to generate a type of antibiofilm material. The IL-loaded ionogel surfaces demonstrate high-antimicrobial and antifouling activity by killing bacteria in both static and dynamic tests. Our IL-based antibiofilm surfaces are low-cost and easy to manufacture, can be formed on glass, latex, plastic, and metal surfaces, such as catheters and other medical devices where high local concentrations of antimicrobials are needed, and may have applications in other clinical and industrial settings.

Preparation and characterisation of bifunctional surface-modified silicone catheter in lumen

OBJECTIVES

The purpose of this study was to evaluate the coating of antimicrobial peptides (AMPs) and polyvinylpyrrolidone (PVP) to the surface of a silicone catheter to reduce bacterial growth and to increase hydrophilicity, respectively.

METHODS

Surface characterisation was performed on bare silicone, AMP-coated, PVP-coated and AMP + PVP-coated silicone catheters using attenuated total reflectance-infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and water contact angle. Antibacterial activity, antibacterial biofilm growth and XTT assay were performed on bare silicone, AMP-coated, PVP-coated and AMP + PVP-coated silicone catheters. Statistical analysis was performed by one-way ANOVA.

RESULTS

The water contact angle of the AMP + PVP-coated silicone catheter was 21.37 ± 2.17° compared with 107.23 ± 0.96°, 74.40 ± 1.76° and 20.77 ± 0.32° for bare silicone, AMP-coated and PVP-coated silicone catheters. Based on in vitro antimicrobial tests, the AMP + PVP-coated silicone catheter had 6.2, 2.2 and 2.5 greater antibacterial activity than that of the bare silicone catheter against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Moreover, bacterial biofilm growth on the surface of the AMP + PVP-coated silicone catheter was minimal as characterised by scanning electron microscopy. MTT assay showed that bare silicone, AMP-coated, AMP + PVP-coated and PVP-coated silicone catheters were non-cytotoxic to 3T3 and human colon cancer (Caco-2) cells.

CONCLUSIONS

This work demonstrates that AMP + PVP-coated silicone catheters have potential clinical application prospects with improved hydrophilicity, excellent biocompatibility, antibacterial activity and a certain antibacterial biofilm effect.

Measurement of Frictional Properties of Aortic Stent Grafts and Their Delivery Systems

Stent grafts are medical devices used to treat abdominal aortic aneurysms (AAAs) in endovascular aneurysm repair (EVAR). Computational and experimental models have been developed to study stent graft delivery and deployment during EVAR; however, frictional properties have not been taken into account in most previous studies. The objective of this study was to determine the coefficients of friction of three commercially available stent grafts (Cook Zenith, Medtronic Endurant, and Vascutek Anaconda), their delivery sheaths, a porcine aorta, and two mock arterial materials. Stent grafts were obtained and separated into stents, graft fabric, and sheaths. Using a custom-made friction measurement apparatus, the coefficients of friction were measured between five material pairs: (i) the stents and inner surface of the sheath, (ii) the graft fabric and inner surface of the sheath, (iii) the outer surface of the sheath and a porcine aorta, (iv) the outer surface of the sheath and three different polyvinyl alcohol (PVA) cryogels, and (v) the outer surface of the sheath and a polydimethylsiloxane (PDMS) sheet. The results show that the coefficients of friction between the graft fabric and the sheath were higher than those between the stents and the sheath. The PVA cryogels showed more comparable frictional properties to the porcine aorta than did the PDMS sheet, suggesting that PVA cryogels provide a more accurate approximation for the in vivo frictional properties. These results can be used to improve the accuracy of computational models for stent graft delivery and deployment and to select appropriate materials for vascular phantoms.

The influence of the nylon balloon stiffness on the efficiency of the intra-aortic balloon occlusion

In interventional procedures, the balloon inflation is used to occlude the artery and thus reduce bleeding. There is no practically accepted measure of the procedure efficiency. A finite element method model with state-of-the-art modelling techniques was built in order to predict the occlusion levels under the influence of different balloon inflation and its material stiffness. The geometries of a healthy human thoracic aorta and an occlusion balloon were idealized. The non-linear constitutive material of Gasser-Ogden-Holzapfel model was employed for the thoracic aorta; the balloon was model as the hyperelastic model. The realistic physiological blood pressure and the balloon inflation pressures were applied to simulate the different occlusion levels. The final outcome shows an important influence of the material stiffness on the balloon deformation and thus the occlusion efficiency.

Use of in vitro and haptic assessments in the characterisation of surface lubricity

Lubricity is a key property of hydrophilic-coated urinary catheter surfaces. In vitro tests are commonly employed for evaluation of surface properties in the development of novel catheter coating technologies; however, their value in predicting the more subjective feeling of lubricity requires validation. We herein perform a range of in vitro assessments and human organoleptic studies to characterise surface properties of developmental hydrophilic coating formulations, including water wettability, coefficient of friction, dry-out kinetics and lubricity. Significant reductions of up to 40% in the contact angles and coefficient of friction values of the novel coating formulations in comparison with the control poly(vinylpyrrolidone)-coated surfaces were demonstrated during quantitative laboratory assessments. In contrast, no significant differences in the more subjective feeling of lubricity between the novel formulations and the control-coated surfaces were observed when formulations were haptically assessed by the techniques described herein. This study, importantly, highlights the need for optimisation of in vitro and human haptic assessments to more reliably predict patient preferences.

In vitro hemocompatibility on thin ceramic and hydrogel films deposited on polymer substrate performed in arterial flow conditions

Hydrogel coatings were stabilized by titanium carbonitride a-C:H:Ti:N buffer layers deposited directly onto the polyurethane (PU) substrate beneath a final hydrogel coating. Coatings of a-C:H:Ti:N were deposited using a hybrid method of pulsed laser deposition (PLD) and magnetron sputtering (MS) under high vacuum conditions. The influence of the buffer a-C:H:Ti:N layer on the hydrogel coating was analysed by means of a multi-scale microstructure study. Mechanical tests were performed at an indentation load of 5 mN using Berkovich indenter geometry. Haemocompatible analyses were performed in vitro using a blood flow simulator. The blood-material interaction was analysed under dynamic conditions. The coating fabrication procedure improved the coating stability due to the deposition of the amorphous titanium carbonitride buffer layer.

Ureteral stents should be soaked for several minutes before placement

Purpose

Placement of ureteral stents (DJ-stents) may lead to complications. Inappropriate friction properties of the implant are, inter alia, made responsible for primary injuries, injury-related inflammation and a cascade of consecutive side effects. Hydrophilicity is considered to be related to low friction. The question arises, whether the various products on the market show their respective maximum hydrophilicity directly after unwrapping or a pre-use moistening, as already routinely done with the guide wire, is necessary.

Methods

The surface wettability of commercial and experimental DJ-stents was determined by water contact angle (WCA) measurements using the sessile drop method. One reference surface and 11 different stent surface types were tested. In order to determine the influence of moistening on the stents’ surface wettability, WCAs were measured twice, with dry, and soaked (30 min, 0.9%-NaCl) specimens. Each sample of a surface type was tested at three different positions to avoid effects of surface heterogeneities. Up to six samples of the same surface type were examined.

Results

Mean WCAs on fresh and soaked stent surfaces ranged from 75°–103° and 71°–99°. In every case the WCAs on soaked surfaces were lower. On average the WCAs decrease by 7%, the individual decreases differ considerably, from 2 to 16%. For 7/12 of the examined surface types, the decrease in contact angle is statistically significant with p ≤ 0.01.

Conclusions

DJ-stents freshly unwrapped show less hydrophilic properties compared to DJ-stents soaked in saline. To obtain maximum hydrophilicity at stent placement, DJ-stents should be soaked. The results may advocate a similar approach for other urological equipment.

Surface modification of polymers for biocompatibility via exposure to extreme ultraviolet radiation

Polymeric biomaterials are being widely used for the treatment of various traumata, diseases and defects in human beings due to ease in their synthesis. As biomaterials have direct interaction with the extracellular environment in the biological world, biocompatibility is a topic of great significance. The introduction or enhancement of biocompatibility in certain polymers is still a challenge to overcome. Polymer biocompatibility can be controlled by surface modification. Various physical and chemical methods (e.g., chemical and plasma treatment, ion implantation, and ultraviolet irradiation etc.) are in use or being developed for the modification of polymer surfaces. However an important limitation in their employment is the alteration of bulk material. Different surface and bulk properties of biomaterials are often desirable for biomedical applications. Because extreme ultraviolet (EUV) radiation penetration is quite limited even in low density mediums, it could be possible to use it for surface modification without influencing the bulk material. This article reviews the degree of biocompatibility of different polymeric biomaterials being currently employed in various biomedical applications, the surface properties required to be modified for biocompatibility control, plasma and laser ablation based surface modification techniques, and research studies indicating possible use of EUV for enhancing biocompatibility.

Effect of tympanostomy tube surface on occlusion

OBJECTIVE

Premature tympanostomy tube (TT) occlusion frequently leads to TT replacement surgery. TT surface preparations have been suggested as a means of reducing TT occlusion. The purpose of this study is to determine if commercial TT compositions or surface preparations impact the rate of TT occlusion using an in vitro model.

METHODS

Commercial TTs composed of titanium, fluoroplastic, and silicone, as well as human serum albumin coated titanium, phosphorylcholine coated fluoroplastic, and polyvinylpyrrolidone coated silicone TTs, were tested for occlusion development in a previously validated in vitro model that simulates middle ear air and mucus flow.

RESULTS

Time to occlusion was longer with all coated TTs relative to all uncoated TTs (p=0.038). Polyvinylpyrrolidone coated silicone TTs had the lowest rate of occlusion and improvement relative to silicone (36% vs. 70%). Time to occlusion was longer in all coated TTs, but individually, none reached statistical significance.

CONCLUSION

TT composition and surface preparations do not dramatically impact the development of TT occlusion. All tested surface coatings seem to delay TT occlusion in this in vitro model. In vivo testing will be necessary to validate these findings.

Candida tropicalis biofilms: artificial urine, urinary catheters and flow model

Adhesion to medical devices and biofilm formation are considered important virulence factors of Candida tropicalis. This work aimed to use artificial urine (AU) and urinary catheters, under flow conditions, for studying C. tropicalis biofilms. Adhesion and biofilm formation on silicone and latex urinary catheters were quantified by crystal violet staining and determination of colony forming units. Candida surface hydrophobicity was also evaluated, as well as the biofilms' matrix content in terms of proteins and carbohydrates. Candida tropicalis was able to adhere and to form biofilms along the entire length of the catheters under flow conditions. It was found that the isolate U69 adhered significantly more to both types of catheters than did the reference strain. However, U69 biofilms contained significantly less cultivable cells and higher biofilm biomass than those of the reference strain. Detachment of cells from biofilms on latex catheter was lower compared to silicone catheter. This model using AU appeared to be suitable for studies mimicking the real body conditions. Additionally, C. tropicalis was in fact able to colonize urinary catheters in the presence of AU and to detach from these catheters, demonstrating their capacity to colonize distal sites.

Prediction of the frictional behavior of mammalian tissues against biomaterials

Frictional and adhesion properties are important characteristics to be assessed in the development of new materials for biological applications, particularly for medical devices such as catheters. In this work a new computational method that predicts frictional and adhesive forces is presented. A multi-asperities adhesion model, based on the JKR theory, coupled with a Monte Carlo method was employed, together with a three components friction model. This takes into account interfacial adhesion, asperities deformation and viscous lubricant film shearing action. We have estimated the frictional coefficients of silicone and polyurethane (common materials in catheters) against aorta and vena cava. In order to do this, we have measured the surface properties of the two blood vessels tissues, such as surface energy components, asperity height distribution and asperity radius of curvature. These data have not been previously reported. The predictions in both the dry and in lubricated (with blood) cases are in very good agreement with our published experimental data of the same materials/tissue combinations.

In vitro multicompartmental bladder model for assessing blockage of urinary catheters: effect of hydrogel coating on dynamics of Proteus mirabilis growth

OBJECTIVES

To investigate the effect of a hydrogel coating on the dynamics of bacterial growth in laboratory models of the catheterized bladder. Infection of the urinary tract by Proteus mirabilis can result in catheter blockage by crystalline biofilm, a common complication in patients undergoing long-term bladder catheterization.

METHODS

Two series of catheters were tested in the infected bladder models: test series 1, silicone catheters impregnated with triclosan (0.5%, 1%, 4%), or silicone catheters with 0% triclosan impregnated with pure solvents and hydrogel coated (based on polyvinylpyrrolidone); and test series 2, silicone catheters, hydrogel-coated with hydrogel plus iodine (polyvinylpyrrolidone plus iodine) or hydrogel plus polyhexamethylene biguanide. Test series 1 was used to detect the influence of triclosan, solvents, impregnation time, and the presence of hydrogel coating on the interval to catheter blockage by P. mirabilis biofilm. The experiments with test series 2 focused on the dynamic interaction of the hydrogel coating and biofilm formation. The division of the catheterized bladder model into 3 sampling zones brought more information about the spatial segregation of the bacterial population.

RESULTS

The bacteriostatic efficiency of the water-soluble polyhexamethylene biguanide and polyvinylpyrrolidone iodine complex was limited to the first hours after catheterization. Only catheters containing triclosan resisted encrustation for significantly longer (up to >7 days). In contrast, the uncoated and hydrogel-coated catheters were occluded by day 2.

CONCLUSIONS

The hydrogel layer can increase aggregation of the planktonic cells and newly nucleated crystals, leading to even faster catheter blockage than in the case of uncoated silicone. However, the addition of active agents were able to suppress this negative effect.

Biocompatible, hyaluronic acid modified silicone elastomers

Although silicones possess many useful properties as biomaterials, their hydrophobicity can be problematic. To a degree, this issue can be addressed by surface modification with hydrophilic polymers such as poly(ethylene glycol), but the resulting structures are usually not conducive to cell growth. In the present work, we describe the synthesis and characterization of covalently linked hyaluronic acid (HA) (35 kDa) to poly(dimethylsiloxane) (PDMS) elastomer surfaces. HA is of interest because of its known biological properties; its presence on a surface was expected to improve the biocompatibility of silicone materials for a wide range of bioapplications. HA was introduced with a coupling agent in two steps from high-density, tosyl-modified, poly(ethylene glycol) tethered silicone surfaces. All materials synthesized were characterized by water contact angle, ATR-FTIR, XPS and (13)C solid state NMR spectroscopy. Biological interactions with these modified silicone surfaces were assessed by examining interactions with fibrinogen as a model protein as well as determining the in vitro response of fibroblast (3T3) and human corneal epithelial cells relative to unmodified poly(dimethylsiloxane) controls. The results suggest that HA modification significantly enhances cell interactions while decreasing protein adsorption and may therefore be effective for improving biocompatibility of PDMS and other materials.

Frictional properties of light-activated antimicrobial polymers in blood vessels

The adhesion of microbes to catheter surfaces is a serious problem and the resulting infections frequently lead to longer hospitalisation and higher risk for the patient. Several approaches have been developed to produce materials that are less susceptible to microbial colonisation. One such approach is the incorporation of photoactivated compounds, such as Toluidine Blue O (TBO), in the polymeric matrix resulting in 'light-activated antimicrobial materials'. The insertion and removal of catheters can cause tissue damage and patient discomfort through frictional forces; hence the lubricity of a catheter material is also very important. In this work the tribological performance of silicone and polyurethane containing TBO and gold nanoparticles were evaluated using two different surfaces, the inner part of the aorta and the superior vena cava of sheep. Static and kinetic friction coefficients of these materials were measured using a tribometric device developed for in vitro applications using dry materials and those lubricated with blood. It was found that neither the preparation process nor the presence of TBO or gold nanoparticles, had an effect on the friction factors in comparison to those of untreated materials. In all cases, static and kinetic friction coefficients on aorta tissue were higher than those on vena cava due to higher surface roughness of the aorta. The presence of blood as a lubricant resulted in lower friction coefficients.