Exudation of additives to the surface of medical devices: impact on biocompatibility in the case of polyurethane used in implantable catheters

Accelerated In Vitro Oxidative Degradation Testing of Ultra-High Molecular Weight Polyethylene (UHMWPE)

Nonabsorbable polymers used in biomedical applications are assumed to be permanently stable based on short-term testing, but some may be susceptible to oxidative degradation over several years of implantation. Traditional in vitro oxidative degradation screenings employ hydrogen peroxide (H2O2) solutions. However, the inherent instability of H2O2 can compromise the consistency of oxidative conditions, especially over extended periods and at elevated temperatures used for accelerated testing. In this study, an automated reactive accelerated aging (aRAA) system, which integrates an electrochemical detection method and a feedback loop, was utilized to ensure precise control of H2O2 concentrations during polymer oxidative degradation testing. The reproducibility of the aRAA system was evaluated by comparing four identical setups. Its efficacy as an oxidation challenge was demonstrated on (i) medical-grade vitamin E (VE) blended ultra-high molecular weight polyethylene (UHMWPE) and (ii) highly crosslinked (HXL) UHMWPE as model materials. The aRAA-aged VE-UHMWPE and HXL-UHMWPE samples were also compared against samples aged via an existing accelerated aging standard, ASTM F2003-02(2022). Samples were analyzed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to calculate their oxidation index per ASTM F2102-17. We observed that the aRAA system was more effective in oxidizing VE-UHMWPE and HXL-UHMWPE than the traditional ASTM F2003-02(2022) method. By providing a standardized and reliable approach to assess polymer oxidative degradation, the aRAA system could enhance the accuracy of long-term stability predictions for nonresorbable polymers in medical devices.

Surface properties and bacterial adhesion on polyurethane central catheters: Impact of ethanol lock solution

It was shown in the literature that ethanol locks have a positive effect on preventing catheter-related infections in patients with central venous catheters without causing any microbial resistance. However, ethanol is known to interact with polyurethanes. The consequences of this interaction on the catheter surface properties were studied as it can impact the biocompatibility of the material and the adhesion phenomena onto the surface. No physical and chemical degradation was put into evidence, but low molecular weight compounds such as additives were extracted from the catheter bulk or migrated and exudated onto its surface. Nevertheless, as far as bacterial adhesion is concerned, after the catheter was locked and the lock removed, the surface modifications promoted no adhesion.

Biofilm reduction potential of 0.02% polyhexanide irrigation solution in several types of urethral catheters

Background

Long-term use of urethral catheters is associated with high risk of urinary tract infection (UTI) and blockage. Microbial biofilms are a common cause of catheter blockage, reducing their lifetime and significantly increasing morbidity of UTIs. A 0.02% polyhexanide irrigation solution developed for routine mechanical rinsing shows potential for bacterial decolonization of urethral catheters and has the potential to reduce or prevent biofilm formation.

Methods

Using an in vitro assay with standard market-leading types of catheters artificially contaminated with clinically relevant bacteria, assays were carried out to evaluate the biofilm reduction and prevention potential of a 0.02% polyhexanide solution versus no intervention (standard approach) and irrigation with saline solution (NaCl 0.9%). The efficiency of decolonization was measured through microbial plate count and membrane filtration.

Results

Irrigation using a 0.02% polyhexanide solution is suitable for the decolonization of a variety of transurethral catheters. The effect observed is significant compared to irrigation with 0.9% saline solution (p = 0.002) or no treatment (p = 0.011). No significant difference was found between irrigation with 0.9% saline solution and no treatment (p = 0.74).

Conclusions

A 0.02% polyhexanide solution is able to reduce bacterial biofilm from catheters artificially contaminated with clinically relevant bacteria in vitro. The data shows a reduction of the viability of thick bacterial biofilms in a variety of commercially available urinary catheters made from silicone, latex-free silicone, hydrogel-coated silicone and PVC. Further research is required to evaluate the long-term tolerability and efficacy of polyhexanide in clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12894-021-00826-3.

UV-induced photolysis of polyurethanes

Waste production associated with the use of non-degradable materials in packaging is a growing cause of environmental concern, with the polyurethane (PU) class being notorious for their lack of degradability. Herein, we incorporate photosensitive ortho-Nitrobenzyl units into PUs to achieve controllable photodegradability. We performed their photolysis in solution and thin films which can inform the design of degradable adhesives.

Bulk Modification of Thermoplastic Polyurethanes for Self-Sterilization of Trachea Intubation

Implantable medical devices are widely used, but biomaterial-associated infections (BAIs) impose a huge economic burden and increase the mortality of patients. Therefore, BAIs are a serious concern that must be urgently resolved. Materials with antibacterial properties have become hotspots of current research and development. In the present work, quaternized chitosan (QCS) is used as an antibacterial agent and blended with thermoplastic polyurethane (TPU) to create an antibacterial material for tracheal intubation tubes. The modified TPU material (QCS-TPU) exhibited good mechanical properties and excellent long-term antibacterial performance. Under in vitro hydrodynamic conditions, QCS-TPU retained its strong antibacterial properties. QCS-TPU also possessed a low hemolysis rate and cytotoxicity. The current work is expected to provide a facile and feasible strategy for the preparation of antibacterial catheters and aid in the discovery of promising clinical applications to prevent BAIs.

Surface-Modifying Polymers for Blood-Contacting Polymeric Biomaterials

Bulk blending is considered as one of the most effective and straightforward ways to improve the hemo-compatibility of blood-contacting polymeric biomaterials among many surface modification methods. Zwitterionic structure-, glycocalyx-like structure-, and heparin-like structure-based oligomers have been synthesized as additives and blended with base polymers to improve the blood compatibility of base polymers. Fluorinated end- and side-functionalized oligomers could promote the migration of functionalized groups to the surface of biomedical polymers without changing their bulk properties, and it highly depends on the number and concentration of functional groups. Moreover, oligomers having both zwitterion and fluorine are receiving considerable attention due to their desirable phase separation, which can avoid undesired protein adsorption and platelet adhesion. The surface analysis of the surface-modified materials is usually investigated by analytical tools such as contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Blood compatibility is mainly evaluated via platelet adhesion and protein adsorption test, and the result showed a significant decrease in the amount of undesirable adsorption. These analyses indicated that surface modification using bulk blending technique effectively improves blood compatibility of polymeric biomaterials.

Do bevacizumab solutions interact with silicone or polyurethane catheters during an infusion through implantable venous access ports?

This work aims to evaluate the possible impact of interactions between bevacizumab solutions and an implantable port equipped with a silicone or a polyurethane catheter after infusion through a complete infusion set-up in simulated use conditions. Physico-chemical and structural stability of bevacizumab solution was assessed by visual examination, subvisible particles counting, dynamic light scattering, size exclusion chromatography and ion exchange chromatography. Mechanical properties of the catheters were evaluated by measuring Shore A hardness, strain at break, strain at stress and Young's modulus. The physico-chemical surface state of the catheters was assessed by FTIR-ATR spectroscopy, scanning electron microscopy (SEM) and by water contact angle measurement. The analysis of the bevacizumab solution did not highlight any signs of instability or loss of active substance. Mechanical properties of both materials remained unchanged after the infusion. During material analysis, a decrease in water contact angle observed after infusion and was more pronounced for polyurethane catheters than for silicone, possibly due to bevacizumab adsorption or possible leachable extraction from the materials. Surface modifications were also noted at SEM. This study did not highlight any modifications that could alter the quality of the bevacizumab infusion, nor of the infusion catheter in polyurethane or silicone, despite a modification of surface hydrophilicity. Even if after a single infusion, implantable ports remained safe to use, they aim to be used for several infusion of various drugs during their lifetime, and further studies are needed to assess the impact of repeated infusions.

Impact of simulated biological aging on physicochemical and biocompatibility properties of cyclic olefin copolymers

We study the effect of simulated biological aging on the properties of cyclic olefin copolymers and particularly their biocompatibility. Already reported as biocompatible polymers according to ISO/EN 10993 guidelines, COC are good candidates for medical devices. The influence of two major additives (antioxidants and lubricants) was investigated and comparison with non-aging COC was done. Four in vitro simulated biological conditions were tested: 2 extreme pH (1 and 9) to simulate digestive tract environment; THP-1-derived macrophages contact and pro-oxidant medium with hypochlorite solution simulating the oxidative attack during the foreign body reaction. After one month of incubation with the different media at 37 °C, surface topography was studied by atomic force microscopy (AFM) and IR spectroscopy. Extracts of incubated media were also analysed in chromatography to investigate potential degradation products. Cytotoxicity (MTT and LDH) of the materials was evaluated using cell culture methods with L929 fibroblasts. Oxidative stress (ROS and SOD analysis) and two inflammatory biomarkers (Il-6 and TNF-α secretion) were explored on THP-1-derived macrophages in direct contact with aged COC. Surface topography of COC was modified by aging conditions with an influence of antioxidant presence and under some conditions. HPLC analysis realized on freeze-dried solutions issued from the different incubations showed the presence of traces of low molecular weight compounds issued from polyphenolic antioxidant and from COC degradation. GC-MS analysis carried out directly on the different incubated COC, showed no detectable leachable molecules. No cytotoxicity has been observed with the different aged COC. However, results show that the pH environment had an influence on the cytotoxicity tests with a protecting effect of antioxidant presence; and pro-oxidant incubating conditions decreased cellular viability on COC. pH 1 and pH 9 conditions also induced an increase of ROS production which was partially reduced for COC containing an antioxidant or a lubricant. Il-6 production was globally more important for aged COC compared with basal condition and particularly for oxidative simulated environment. Those results indicate that physiological factors like pH or oxidant conditions have an impact on surface topography and on COC interaction with the biological environment but without compromising their biocompatibility. Antioxidant or lubricant presence could modulate these variations pointing out the necessity of a thoroughly investigation for biocompatibility assessment of COC as a component of implantable devices. COCs show a good biocompatibility even after accelerated aging under extreme biological conditions.

Inhibition of bacterial attachment and biofilm formation by a novel intravenous catheter material using an in vitro percutaneous catheter insertion model

Introduction

Despite sterile barrier precautions and vigorous skin antisepsis, percutaneous insertion of intravenous catheters has been shown to result in attachment to the catheter surface of bacteria residing in the deep structures of the skin. Such attachment poses the risk of biofilm formation and eventual catheter-related bloodstream infection (CRBSI). This study was undertaken to assess whether the non-coated surface treatment of a unique catheter material (ChronoFlex C^® with BioGUARD™) could inhibit bacterial attachment and biofilm formation.

Methods

A novel in vitro model and fluorescence microscopy were used to compare two intravascular catheter materials with respect to bacterial attachment and biofilm formation. The control material was a commonly used polyurethane. The study material was a unique copolymer, treated so as to remove surface additives, alter hydrophobicity and create surface micro-patterning. Outcomes were assessed using both a membrane potential indicator and a cell death reporter with appropriate fluorescent channels. Thus, bacterial cells attached to the catheter surface (living and dead) were imaged without mechanical disruption.

Results

Both bacterial attachment and biofilm formation are significantly inhibited by the study catheter material. In fact, over 5 times more bacteria were able to attach and grow on the control polyurethane material than on the study material (P=0.0020). Moreover, those few bacteria that were able to attach to the study material had a 1.5 times greater likelihood of dying.

Conclusion

Using a novel in vitro percutaneous catheter insertion model, ChronoFlex C with BioGUARD is proven to significantly inhibit bacterial attachment and biofilm formation as compared with a commonly used polyurethane catheter material.

Biocompatibility assessment of cyclic olefin copolymers: Impact of two additives on cytotoxicity, oxidative stress, inflammatory reactions, and hemocompatibility

This work reports the biocompatibility evaluation of cyclic olefin copolymers (COC) as candidates for implantable medical devices. The focus was to establish the influence of two major additives (antioxidant and lubricant) on the overall biocompatibility. The cytotoxicity was evaluated according to ISO 10993-5 guidelines using L929 fibroblasts, HUVEC, and THP-1-derived macrophages. Oxidative stress (ROS, GSH/GSSG, and SOD analysis) and pro-inflammatory cytokines (Il-6 and TNF-α secretion) were quantified using THP-1 cells in direct contact with films. Hemocompatibility was assessed through haemolysis testing, dynamic blood coagulation, platelet adhesion, and activation (membranous P-selectin expression). Results show that the different types of COC have successfully passed the in vitro biocompatibility tests. The presence of antioxidant induces however a slight decrease in ROS production in correlation with a high SOD activity and a modification in blood coagulation profile probably linked to antioxidant recrystallization phenomenon on the surface of COC. The lubricant presence reduced haemolysis, fibrinogen adhesion, and platelet activation. Surface nanotopography of COC highlights different types of needles and globules according to the present additive. Those primary results indicate that COC are promising biomaterial. However, additives influenced some biological parameters pointing out the necessity of a global approach of risk analysis for biocompatibility evaluation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3333-3349, 2017.