Influence of heparin coating on in vitro bacterial adherence to poly(vinyl chloride) segments

Synthesis of novel chitosan-PVC conjugates encompassing Ag nanoparticles as antibacterial polymers for biomedical applications

We herein describe the synthesis of four Cs-PVC conjugates three of them were functionalized with benzothiazole (BTh) derivative as an antibacterial agent. Two of these BTh-functionalized conjugates, namely Cs2 and Cs3, comprise silver nanoparticles (AgNPs) and Ag/TiO₂ NPs, respectively. The structures were characterized via FTIR spectroscopic analysis, morphological investigation such as scanning (SEM) and transmission (TEM) electron microscopy, and thermal gravimetric analysis (TGA). Spectral data confirmed the introduction of the BTh to the Cs backbone as well as the coupling between the two polymers. SEM data showed homogenous polymer surfaces with well-distributed Ag nanoparticles. The Ag contents in the prepared samples Cs2 and Cs3 were, respectively, 0.61 and 0.21%, however, TEM analysis showed that the sizes of AgNPs and Ag/TiO₂ NPs were in the range of 3-7 nm and 15-22 nm for the prepared conjugates, respectively. The antibacterial activity of the synthesized conjugates was investigated against two Gram-negative (E. coli, and S. typhimurium) and two Gram-positive (S. aureus, and L. monocytogenes) bacteria. The antibacterial assay showed that all three Cs-PVC (Cs1, Cs2, and Cs3) conjugates modified with BTh exhibited excellent bacterial inhibition after 30, 60, and 120 min.

Modern Strategies in the Prevention of Implant-Associated Infections

The application of medical devices either for temporary or permanent use has become an indispensible part of almost all fields of medicine. However, foreign bodies are associated with a substantial risk of bacterial and fungal infections. Implant-associated infections significantly contribute to the still increasing problem of nosocomial infections.

To reduce the incidence of such infections, specific guidelines providing evidence-based recommendations and comprising both technological and nontechnological strategies for prevention have been established. Strict adherence to hygienic rules during insertion or implantation of the device are aspects of particular importance. Besides such basic and indispensable aspects, the development of new materials which could withstand microbial adherence and colonization has become a major topic in recent years. Modification of surface by primarily physico-chemical methods may lead to a change in specific and unspecific interactions with microorganisms and, thus, to a reduction in microbial adherence. Medical devices made out of a material that would be ideally antiadhesive or at least colonization-resistant would be the most suitable candidates to avoid colonization and subsequent infection. However, it appears impossible to create a surface with an absolute “zero”-adherence due to thermodynamical reasons and due to the fact that a modified material surface is in vivo rapidly covered by plasma and connective tissue proteins. Therefore, another concept for the prevention of implant-associated infections involves the impregnation of devices with various antimicrobial substances such as antibiotics, antiseptics, and/or metals.

In fact, already commercially available materials for clinical use such as antimicrobial catheters have been introduced, in part with considerable impact on subsequent infections. However, future studies are warranted to translate the knowledge on the pathogenesis of device-associated infections into applicable prevention strategies.

Surface modification of polymeric biomaterials: Utilization of cyclodextrins for blood compatibility improvement

A novel modified polymeric biomaterial surface using cyclodextrins (CDs) for improved blood compatibility was studied. Plasticized poly(vinyl chloride) (PVC-P) was selected for modification and polyethylene was used as a reference material. The modification was achieved by polymer blending. Fibrinogen and albumin adsorption were utilized as indices for the assessment of the blood compatibility. Surface characterization confirmed that CDs were able to accumulate at the PVC surface and alter the surface properties. The combination of other hydrophilic polymers such as poly(ethylene oxide) (PEO) and PEO/poly(propylene oxide) (PPO) copolymers, such as Pluronic F68 (F68), with CDs were also investigated. These modified materials have a remarkable protein-resistant surface. The combination of B-cyclodextrin (B-CD)/PEO and B-CD/F68 in certain feeding ratio are synergistic in producing enhanced blood compatibility.

Surface thiocyanation of plasticized poly(vinyl chloride) and its effect on bacterial adhesion

Thiocyanates, especially bis-alkylthiocyanates are highly effective in killing a number of bacterial strains and are reported to be potent biocides at ppm concentrations. In order to examine whether a covalently bound and immobilized thiocyanate group on a biomaterial surface is still effective as a bactericide, plasticized poly(vinyl chloride) (PVC) was thiocyanated using sodium thiocyanate in the presence of a phase transfer catalyst in aqueous media leading to the nucleophilic substitution of chlorine by thiocyanate on the PVC surface. Thiocyanation imparted hydrophilicity to the surface in comparison with bare PVC. Control and thiocyanated PVC surfaces were exposed to two strains of bacteria commonly implicated in device-associated infections, such as Staphylococcus aureus and Staphylococcus epidermidis. Bacterial adhesion and colonization was quantitated by counting the viable organisms on the adhered surface as well as by optical and scanning electron microscopy. Significantly reduced retention of S. epidermidis and S. aureus was seen on the thiocyanated PVC surface. Immobilized thiocyanate was non-cytotoxic in a preliminary cell culture assay. The study thus showed that even though an immobilized thiocyanate moiety on the polymer surface was not as effective as a bactericide unlike soluble thiocyanates, it prevented the retention and colonization of the bacteria to a considerable extent.

Bacterial adhesion onto azidated poly(vinyl chloride) surfaces

A plasticized poly(vinyl chloride) surface was modified by azidation using sodium azide in the presence of a phase transfer catalyst in aqueous media. Subsequent to azidation, the surface was crosslinked using ultraviolet radiation. Contact angle measurements showed that the surface became hydrophilic on azidation whereas photoirradiation did not have any further effect on the hydrophilicity of the azidated surface. Control, azidated, and photocrosslinked surfaces were exposed to two strains of bacteria commonly implicated in device infection such as Staphylococcus aureus and Escherichia coli. Whereas the control and photocrosslinked surfaces showed no significant difference in bacterial adhesion, the azidated surface showed significantly reduced adhesion to both strains. Data obtained indicate that the presence of an intact azide function on the polymer surface is responsible for the reduced bacterial adherence and the surface hydrophobicity/hydrophilicity did not exert any effect in the present case. Although azides are known to be effective only against Gram-negative species, surprising was the observation that the azidated polymer surface was equally effective against a Gram-positive species such as S. aureus. Because sodium azide is routinely used as a preservative to prevent bacterial and fungal growth in many microbiology reagents and diagnostic kits, covalent binding of the azide onto a polymer surface or synthesizing azide containing polymers may be an interesting method to investigate in tackling the problem of bacterial adhesion and colonization of medical devices.

Efficacy of antiadhesive, antibiotic and antiseptic coatings in preventing catheter-related infections: review

In recent years, central venous catheters (CVCs) are increasingly used in clinical practice. However, complications such as local or systemic infections are frequent for both temporary and indwelling vascular catheters. Annually, in the United States of America there are more than 200,000 cases of nosocomial bloodstream infections (BSIs), of which 90% are related to the use of an intravascular device. These infections are associated with increased morbidity and mortality, prolonged hospitalization and growing medical costs. Technological treatments of polymer surfaces including coating the catheter with antimicrobial substances may be promising tools for prevention of catheter-associated infections. A large number of surface-treated central venous catheters are now commercially available. In this paper the features and the clinical efficacy of different antimicrobial coatings are reviewed.