Surfactant polymers designed to suppress bacterial (Staphylococcus epidermidis) adhesion on biomaterials

Profilometer Comparison of the Surface Roughness of Four Denture Base Resins: An In Vitro Study

Background: The roughness of denture base materials is mainly affected by inherent material features, the polishing technique, and the operator’s manual skills. The surface irregularities of the denture base resin’s roughness profile is one of the components characterizing the superficial topography of dental prostheses, and it is a critical parameter for describing surface morphology. Generally, the increment of the surface roughness minimizes cleanability and promotes the rate of bacterial adherence, affecting the expression of bacterial adhesins. The purpose of this in vitro study was to investigate the roughness of four commercially available denture base resins employed for removable prosthodontics. Methods: Twenty-five specimens were realized and submitted to observation for three dimensions (vertically, horizontally, 45°). Average surface roughness (Ra), Rv, Rp, and Rq were measured with a calibrated mechanical roughness tester (Taylor Hobson Surtronic 25; Taylor Hobson, Leicester, UK). Data were analyzed through a Kruskal–Wallis test. Results: Significant differences in Ra between the groups were assessed. Baltic Denture System™ (Merz Dental GmbH; Lütjenburg, Germania) showed a lower surface roughness coefficient and a more homogeneous surface. Conclusions: The functional importance of surface roughness parameters for denture base materials must be explored, not only considering recognized surface features.

Biofilm Formation Reduction by Eugenol and Thymol on Biodegradable Food Packaging Material

Biofilm is a structured community of microorganisms adhering to surfaces of various polymeric materials used in food packaging. Microbes in the biofilm may affect food quality. However, the presence of biofilm can ensure biodegradation of discarded packaging. This work aims to evaluate a biofilm formation on the selected biodegradable polymer films: poly (lactic acid) (PLA), poly (butylene adipate-co-terephthalate) (PBAT), and poly (butylene succinate) (PBS) by selected bacterial strains; collection strains of Escherichiacoli, Staphylococcusaureus; and Bacillus pumilus, Bacillussubtilis, Bacillustequilensis, and Stenotrophomonasmaltophilia isolated from dairy products. Three different methods for biofilm evaluation were performed: the Christensen method, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and fluorescence microscopy. High biofilm formation was confirmed on the control PBS film, whereas low biofilm formation ability was observed on the PLA polymer sample. Furthermore, the films with incorporated antimicrobial compounds (thymol or eugenol) were also prepared. Antimicrobial activity and also reduction in biofilm formation on enriched polymer films were determined. Therefore, they were all proved to be antimicrobial and effective in reducing biofilm formation. These films can be used to prepare novel active food packaging for the dairy industry to prevent biofilm formation and enhance food quality and safety in the future.

Investigating the relationship between the mechanical properties of plasma polymer-like thin films and their glass transition temperature

This work aims at understanding the influence of the substrate temperature (T_s) on the viscoelastic properties of propanethiol plasma polymer films (PPFs). By means of state-of-the-art AFM characterization-based techniques including peak force quantitative nanomechanical mapping (PFQNM), nano dynamic mechanical analysis (nDMA) and "scratch" experiments, it has been demonstrated that the mechanical behaviour of PPFs is dramatically affected by the thermal conditions of the substrate. Indeed, the material behaves from a high viscous liquid (i.e. viscosity ∼ 10⁶ Pa s) to a viscoelastic solid (loss modulus ∼ 1.17 GPa, storage modulus ∼ 1.61 GPa) and finally to an elastic solid (loss modulus ∼ 1.95 GPa, storage modulus ∼ 8.51 GPa) when increasing T_s from 10 to 45 °C. This behaviour is ascribed to an increase in the surface glass transition temperature of the polymeric network. The latter has been correlated with the chemical composition through the presence of unbound molecules acting as plasticizers and the cross-linking density of the layers. In a second step, this knowledge is exploited for the fabrication of a nanopattern by generating surface instabilities in the propanethiol PPF/Al bilayer system.

Gentamicin-Releasing Titania Nanotube Surfaces Inhibit Bacteria and Support Adipose-Derived Stem Cell Growth in Cocultures

Infection is the second leading cause of failure of orthopedic implants following incomplete osseointegration. Materials that increase the antimicrobial properties of surfaces while maintaining the ability for bone cells to attach and proliferate could reduce the failure rates of orthopedic implants. In this study, titania nanotubes (Nts) were modified with chitosan/heparin polyelectrolyte multilayers (PEMs) for gentamicin delivery. The antimicrobial activity of the surfaces was tested by coculturing bacteria with mammalian cells. Over 60% of gentamicin remained on the surface after an initial burst release on the first day. Antimicrobial activity of these surfaces was determined by exposure to Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) for up to 24 h. Gentamicin surfaces had less live E. coli and S. aureus by 6 h and less E. coli by 24 h compared to Nt surfaces. S. aureus and human adipose-derived stem cells (hADSCs) were cocultured on surfaces for up to 7 days to characterize the so-called "race to the surface" between bacteria and mammalian cells, which is hypothesized to ultimately determine the outcome of orthopedic implants. By day 7, there was no significant difference in bacteria between surfaces with gentamicin adsorbed on the surface and surfaces with gentamicin in solution. However, gentamicin delivered in solution is toxic to hADSCs. Alternatively, gentamicin presented from PEMs enhances the antimicrobial properties of the surfaces without inhibiting hADSC attachment and cell growth. Delivering gentamicin from the surfaces is therefore superior to delivering gentamicin in solution and represents a strategy that could improve the antimicrobial activity of orthopedic implants and reduce risk of failure due to infection, without reducing mammalian cell attachment.

In vitro evaluation of microbial adhesion on the different surface roughness of acrylic resin specific for ocular prosthesis

OBJECTIVE

The purpose of this study was to evaluate the influence of surface roughness in biofilm formation of four microorganisms (Staphylococcus epidermidis, Staphylococcus aureus, Enterococcus faecalis, and Candida albicans) on acrylic resin surface of ocular prostheses.

MATERIALS AND METHODS

Acrylic resin samples were divided into six groups according to polishing: Group 1200S (1200 grit + silica solution); Group 1200; Group 800; Group 400; Group 120 and Group unpolished. Surface roughness was measured using a profilometer and surface images obtained with atomic force microscopy. Microbial growth was evaluated after 4, 24, and 48 hours of incubation by counting colony-forming units.

STATISTICAL ANALYSIS USED

For roughness, it was performed 1-way ANOVA and parametric Tukey test α5% (P ≤ 0.05). For CFU data found, it was applied Kruskal-Wallis and Mann-Whitney tests.

RESULTS

Group 120 and 400 presented the highest roughness values. For S. epidermidis and S. aureus, Group 1200S presented the lowest values of microbial growth. For E. faecalis at 4 hour, microbial growth was not observed. C. albicans did not adhere to the acrylic resin. Except for Group 1200S, different surface roughnesses did not statistically interfere with microbial adhesion and growth on acrylic surfaces of ocular prostheses.

CONCLUSIONS

The roughness did not interfere with the microbial adhesion of the microorganisms evaluated. The use of silica decreases significantly microbial growth.

Molecular Genetics of Staphylococcus Epidermidis Biofilms on Indwelling Medical Devices

Staphylococcus epidermidis is an opportunistic pathogen associated with foreign body infections and nosocomial sepsis. The pathogenicity of S. epidermidis is mostly due to its ability to colonize indwelling polymeric devices and form a thick, multilayered biofilm. Biofilm formation is a major problem in treating S. epidermidis infection as biofilms provide significant resistance to antibiotics and to components of the innate host defenses. Various cell surface associated bacterial factors play a role in adherence and accumulation of the biofilm such as the polysaccharide intercellular adhesin and the autolysin AtlE. Furthermore, recent studies have shown that global regulators such as the agr quorum sensing system, the transcriptional regulator sarA and the alternative sigma factor sigB have an important function in the regulation of biofilm formation. Understanding the many complex mechanisms involved in biofilm formation is a key factor in the search for new anti-staphylococcal therapeutics.

Microbiological analysis of conjunctival secretion in anophthalmic cavity, contralateral eye and ocular prosthesis of patients with maxillofacial abnormalities

The purpose of this study was to identify and analyse the micro-organisms present in the conjunctival secretion in anophthalmic cavities of wearers of ocular prostheses, as well as on the prostheses used by them, correlating them with the microbiota of the contralateral eye. Nine patients with maxillofacial abnormalities, wearers of an acrylic resin ocular prosthesis participated in the study. Collections of conjunctival secretions and biofilm were performed on the prosthesis, anophthalmic cavity and contralateral eye for the mycological and bacterial analyses. The data were submitted to statistical analysis, performing a Kendall correlation test to identify the correlation between the collection site and the identified micro-organism (P < 0·05). It was verified that the most prevalent micro-organisms were the Staphylococcus aureus and Staphylococcus epidermidis, independent of the collection site, and that negative cultures for fungi were encountered in 85·2% of collections, independent of the region. It was not possible to establish a correlation among the types of micro-organisms and the collection sites.

SIGNIFICANCE AND IMPACT OF THE STUDY

Some evidence suggests that the surface roughness of ocular prostheses can influence interactions with micro-organisms, with greater prejudicial consequences, such as the establishment of biofilms, which could lead to infections. Thus, it becomes extremely important to identify the micro-organisms present on the acrylic surfaces of ocular prostheses, as well as the microbiota of the anophthalmic cavity and contralateral eye of wearers of the same, so that subsequent control measures promote the homeostatic maintenance of the ocular region.

Bioactive Titanium Implant Surfaces with Bacterial Inhibition and Osteoblast Function Enhancement Properties

Infection in orthopedic implant surgery is a serious complication and a major cause of implant failure. Upon implant insertion, a contest between microbial colonization and tissue integration of the implant surface ensues. This race for the surface determines the probability of tissue integration or infection, and the surface properties of the substrate have an important role to play in determining the outcome. A number of strategies have been developed for the modification of implant surfaces to promote bone cell (osteoblast) functions and inhibit bacterial adhesion and growth. In this article, a review is given of these surface modification strategies, in particular those which can achieve the dual aim of bacterial inhibition and simultaneous enhancement of osteoblast functions. Surfaces of these types can be expected to have excellent potential for orthopedic applications. (Int J Artif Organs 2008; 31: 777–85)

Biomaterial Strategies to Reduce Implant-Associated Infections

Although the prophylaxis in controlling sterility within the operating room environment has been greatly improved, implant-associated infection is still one of the most serious complications in implant surgeries due to the existence of immune depression in the peri-implant area. The antibacterial ability of materials themselves logically becomes an important factor in preventing implant-associated infections. With the understanding of the pathogenesis of implant-associated infections, many approaches have been developed through providing an anti-adhesive surface, delivering antibacterial agents to disrupt cell-cell communication and preventing bacteria aggregation or biofilm formation, or killing bacteria directly (lysing the cell membrane). In this article, we review the current strategies in improving the antibacterial ability of materials to prevent implant infection and further present promising tactics in materials design and applications.

Superwetting comonomers reduce adhesion of E. coli BL21

The adhesion of Escherichia coli to copolymers of methacrylates and a trisiloxane-polyether acrylate surfactant was found to be at a minimum with copolymers containing a low (20%) fraction of the surfactant monomer. Rather than wettability, hardness, or water uptake, adhesion was found to be limited by the presence of low concentrations of bound surfactant that can interact with hydrophobic domains on the bacterium inhibiting anchoring to the polymer surface.

Flexible Coils with a Drug-Releasing Hydrophilic Coating: A New Platform for Controlled Delivery of Drugs to the Eye?

Delivery of drugs to the front-side of the eye is routinely done through eye drops. It is known that approximately 80% of each eye-drop is lost, as a result of rapid clearance of the tear fluid via the naso-lacrymal canal. Consequently, repeated administration through several droplets is usually necessary to achieve a desired effect, such as widening of the pupil prior to corneal surgery. A new ocular drug delivery device was studied. The new device is believed to provide a basis for a more convenient and efficient method for ocular drug delivery. The device is a metallic coil with a hydrophilic, drug-containing polymeric coating. The coil is placed in the conjuctival fornix (under the lower eye-lid) and the drug is slowly released by diffusion into the tear fluid. The capacity of the device could be increased by using the lumen of the coils as a depot for the drug to be released. Preliminary experiments with the new device were performed largely in vitro and in vivo. The latter experiments involved the release of a fluorescent dye and atropine (a potent mydriatic agent) in the eye of several healthy volunteers. The first results obtained with the new device indicate its potential utility. More research and development work is required to define the optimal design of the coil in order to minimize the risk of irritation. Furthermore, the parameters that define the kinetics of the intraocular drug release must be defined and optimized with respect to the exact application.

Molecular self assembly of mixed comb-like dextran surfactant polymers for SPR virus detection

The synthesis of two comb-like dextran surfactant polymers, that are different in their dextran molecular weight (MW) distribution and the presence of carboxylic groups, and their characterization are reported. A bimodal carboxylic dextran surfactant polymer consists of poly(vinyl amine) (PVAm) backbone with carboxyl higher MW dextran, non-functionalized lower MW dextran and hydrophobic hexyl branches; while a monomodal dextran surfactant polymer is PVAm grafted with non-functionalized lower MW dextran and hexyl branches. Layer formation of non-covalently attached dextran chains with bimodal MW distributions on a surface plasmon resonance (SPR) chip was investigated from the perspective of mixed physisorption of the bimodal and monomodal surfactant polymers. Separation distances between the carboxylic longer dextran side chains within the bimodal surfactant polymer and between the whole bimodal surfactant molecules on the chip surface could be well-controlled. SPR analysis of shrimp yellow head virus using our mixed surfactant chips showed dependence on synergetic adjustment of these separation distances.

Poly(ethylene oxide) surfactant polymers

We report on a series of structurally well-defined surfactant polymers that undergo surface-induced self-assembly on hydrophobic biomaterial surfaces. The surfactant polymers consist of a poly(vinyl amine) backbone with poly(ethylene oxide) and hexanal pendant groups. The poly(vinyl amine) (PVAm) was synthesized by hydrolysis of poly(N-vinyl formamide) following free radical polymerization of N-vinyl formamide. Hexanal and aldehyde-terminated poly(ethylene oxide) (PEO) were simultaneously attached to PVAm via reductive amination. Surfactant polymers with different PEO:hexanal ratios and hydrophilic/hydrophobic balances were prepared, and characterized by FT-IR, 1H-NMR and XPS spectroscopies. Surface active properties at the air/water interface were determined by surface tension measurements. Surface activity at a solid surface/water interface was demonstrated by atomic force microscopy, showing epitaxially molecular alignment for surfactant polymers adsorbed on highly oriented pyrolytic graphite. The surfactant polymers described in this report can be adapted for simple non-covalent surface modification of biomaterials and hydrophobic surfaces to provide highly hydrated interfaces.

Non-invasive vibrational SFG spectroscopy reveals that bacterial adhesion can alter the conformation of grafted "brush" chains on SAM

Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.

Enhancing the antibacterial activity of biomimetic HA coatings by incorporation of norvancomycin

BACKGROUND

Bacterial infections associated with the use of biomaterials remain a great challenge for orthopedic surgery. The main purpose of the work discussed in this paper was to improve the antibacterial activity of a biomimetic calcium phosphate (CP) coating widely used in orthopedic biomaterials by incorporation of norvancomycin in the biomimetic process.

METHODS

CP coating and CP coating containing norvancomycin were produced on a titanium alloy (Ti6Al4V) surface by a biomimetic process. The morphology, surface crystal structure, and concentrations of elements in the coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), respectively. The amount of norvancomycin and its release were investigated by UV-visible spectroscopy. MTT was used to investigate cell behavior. The morphology of adhered bacteria was observed by SEM. Antibacterial activity was expressed as inhibition zone by using Staphylococcus aureus (ATCC 25923) as model bacteria.

RESULTS

Results from SEM, EDX, and XRD revealed formation of a hydroxyapatite (HA) coating. The amount of antibiotic in the CP coating increased with increasing concentration of norvancomycin in the coating solution, followed by a plateau when the concentration of norvancomycin in the coating solution reached 600 mg/l. Approximately 2.16 μg norvancomycin per mg coating was co-precipitated with the CP layer onto titanium alloy discs when 600 mg/l norvancomycin coating solution was applied. The norvancomycin had a fast release profile followed by slow release. The MTT test of osteoblast cell cultures suggested that coatings containing norvancomycin did not cause any cytotoxicity compared with the CP coating and control titanium plate. The antibacterial activity test showed that the norvancomycin released from the coatings inhibited the growth of Staphylococcus aureus; more bacteria were found on the CP coating than on the norvancomycin-loaded coating.

CONCLUSIONS

A norvancomycin-loaded HA-like coating was successfully obtained on titanium surfaces. The norvancomycin incorporated had no negative effects on osteoblast cell behavior. The released norvancomycin results in excellent antibacterial activity of Ca-P coatings. Therefore, incorporation of norvancomycin can enhance antibacterial activity and the norvancomycin-loaded CP coating can be used to inhibit post-surgical infections in orthopaedics.

Effect of Superhydrophobic Surface of Titanium onStaphylococcus aureusAdhesion

Despite the systemic antibiotics prophylaxis, orthopedic implants still remain highly susceptible to bacterial adhesion and resulting in device-associated infection. Surface modification is an effective way to decrease bacterial adhesion. In this study, we prepared surfaces with different wettability on titanium surface based on TiO2nanotube to examine the effect of bacterial adhesion. Firstly, titanium plates were calcined to form hydrophilic TiO2nanotube films of anatase phase. Subsequently, the nanotube films and inoxidized titaniums were treated with 1H, 1H, 2H, 2H-perfluorooctyl-triethoxysilane (PTES), forming superhydrophobic and hydrophobic surfaces. Observed by SEM and contact angle measurements, the different surfaces have different characteristics.Staphylococcus aureus(SA) adhesion on different surfaces was evaluated. Our experiment results show that the superhydrophobic surface has contact angles of water greater than 150∘and also shows high resistance to bacterial contamination. It is indicated that superhydrophobic surface may be a factor to reduce device-associated infection and could be used in clinical practice.

The implantable artificial kidney

The confluence of an increasing prevalence of end-stage renal disease (ESRD), clinical trial data suggestive of benefit from quotidian dialysis, and ongoing cost/benefit reanalysis of healthcare spending have stimulated interest in technological improvements in provision of ESRD care. For the last decade, our group has focused on enabling technologies that would permit a paradigm shift in dialysis care similar to that brought by implantable defibrillators to arrhythmia management. Two significant barriers to wearable or implantable dialysis persist: package size of the dialyzer and water requirements for preparation of dialysate. Decades of independent research into highly efficient membranes and cell-based bioreactors culminated in a team effort to develop an implantable version of the University of Michigan Renal Assist Device. In this review, the rationale for the design of the implantable artificial kidney is described.

Polysorbate 80 inhibition of Pseudomonas aeruginosa biofilm formation and its cleavage by the secreted lipase LipA

Surface-associated bacterial communities known as biofilms are an important source of nosocomial infections. Microorganisms such as Pseudomonas aeruginosa can colonize the abiotic surfaces of medical implants, leading to chronic infections that are difficult to eradicate. Our study demonstrates that polysorbate 80 (PS80), a surfactant commonly added to food and medicines, is able to inhibit biofilm formation by P. aeruginosa on a variety of surfaces, including contact lenses. Many clinical isolates of P. aeruginosa, as well as gram-negative and gram-positive clinical isolates, were also inhibited in their ability to form biofilms in the presence of PS80. A P. aeruginosa mutant able to form biofilms in the presence of this surfactant was identified and characterized, and it was revealed that this mutant overexpresses a lipase, LipA. Surfactants such as PS80 can be cleaved by lipases, and we demonstrate that PS80 is cleaved by LipA at its ester bond. Finally, polyethoxylated(20) oleyl alcohol, a chemical with a structure that is similar to that of PS80 but that lacks the ester bond of PS80, can inhibit the biofilm formation of P. aeruginosa strains, including the mutant overexpressing LipA. Our results demonstrate that surfactants such as PS80 can inhibit bacterial biofilm formation on medically relevant materials at concentrations demonstrated to be safe in humans and suggest that the understanding of the mechanisms of bacterial resistance to such surfactants will be important in developing clinically effective derivatives.

Biomimetic fluorocarbon surfactant polymers reduce platelet adhesion on PTFE/ePTFE surfaces

We describe a series of fluorocarbon surfactant polymers designed as surface-modifying agents for improving the thrombogenicity of ePTFE vascular graft materials by the reduction of platelet adhesion. The surfactant polymers consist of a poly(vinyl amine) backbone with pendent dextran and perfluoroundecanoyl branches. Surface modification is accomplished by a simple dip-coating process in which surfactant polymers undergo spontaneous surface-induced adsorption and assembly on PTFE/ePTFE surface. The adhesion stability of the surfactant polymer on PTFE was examined under dynamic shear conditions in PBS and human whole blood with a rotating disk system. Fluorocarbon surfactant polymer coatings with three different dextran to perfluorocarbon ratios (1:0.5, 1:1 and 1:2) were compared in the context of platelet adhesion on PTFE/ePTFE surface under dynamic flow conditions. Suppression of platelet adhesion was achieved for all three coated surfaces over the shear-stress range of 0-75 dyn/cm2 in platelet-rich plasma (PRP) or human whole blood. The effectiveness depended on the surfactant polymer composition such that platelet adhesion on coated surfaces decreased significantly with increasing fluorocarbon branch density at 0 dyn/cm2. Our results suggest that fluorocarbon surfactant polymers can effectively suppress platelet adhesion and demonstrate the potential application of the fluorocarbon surfactant polymers as non-thrombogenic coatings for ePTFE vascular grafts.

Skin microbiota: a source of disease or defence?

Microbes found on the skin are usually regarded as pathogens, potential pathogens or innocuous symbiotic organisms. Advances in microbiology and immunology are revising our understanding of the molecular mechanisms of microbial virulence and the specific events involved in the host-microbe interaction. Current data contradict some historical classifications of cutaneous microbiota and suggest that these organisms may protect the host, defining them not as simple symbiotic microbes but rather as mutualistic. This review will summarize current information on bacterial skin flora including Staphylococcus, Corynebacterium, Propionibacterium, Streptococcus and Pseudomonas. Specifically, the review will discuss our current understanding of the cutaneous microbiota as well as shifting paradigms in the interpretation of the roles microbes play in skin health and disease.

Synthesis and characterization of low surface energy fluoropolymers as potential barrier coatings in oral care

A series of low surface energy fluorinated homopolymers and copolymers has been synthesized and characterized using thermal, optical, spectroscopic, and chromatographic techniques. Their utility as barrier technologies in oral care has been considered, and aqueous nanosuspensions of the materials have been deposited as films on model dental hard surfaces in the presence and absence of a salivary pellicle. Calcium hydroxyapatite has been used as a model for enamel, as has PMMA due to its widespread use in denture fabrication. Surface energy determinations, combined with XPS studies, have provided insights into the molecular-level organization at the surface of the film structures. Studies of solubility in supercritical carbon dioxide have identified the polymers that are suitable for processing in this medium.

Advancements in molecular epidemiology of implant infections and future perspectives

Implant infection remains the major and often irreducible complication in clinical use of biomaterials, demanding new therapeutic and preventive strategies. Etio-pathogenesis of biomaterials-related infections is being more and more studied, and various virulence bacterial factors have progressively been identified, but little is still known about the weight of the distinct molecules in the context of specific peri-implant infection sites. Molecular epidemiology has become recently integrated into the research on implant infections. What distinguishes molecular epidemiology from the simple molecular biology is that the use of molecular techniques is applied to the study of the distribution and prevalence of virulence and resistance genes in collections of bacterial clinical isolates from implant infections. Here, the authors comment on the range of molecular techniques available, reviewing the various applications of molecular epidemiology to the study of implant infections and providing some experimental examples related to the field of orthopaedic implant infections. They highlight the new opportunities arising from molecular epidemiology of designing measures useful to prevent and treat implant infections. The knowledge of the relative weight of virulence factors and of their regulatory mechanisms at molecular level can open the way to new strategies also including gene therapies aimed at silencing or knocking out crucial genes responsible for the aggressive tools (adhesins, biofilm production, antibiotic resistance) of the aetiological agents of implant-related infections.

Controlling biofilm formation with an N-halamine-based polymeric additive

An N-halamine-based polymeric additive, poly[(6-morpholino-s-triazine-2,4-diyl)-N-chloro-[2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene[(2,2,6,6-4-piperidyl) imino]] (APA-1), was prepared in this study. The chemical structure of APA-1 was confirmed by iodometric titration, (1)H NMR, and (13)C NMR analysis. APA-1 was incorporated into polyurethane through solvent casting. The resultant materials demonstrated potent antimicrobial functions against Staphylococcus epidermidis. Zone of inhibition studies showed that APA-1 inactivated the bacteria through contact, without leaching out of the polyurethane samples. In vitro studies illustrated that APA-1-containing polyurethane could prevent the colonization and biofilm formation of S. epidermidis for at least 28 days.

S. epidermidis biofilm formation: effects of biomaterial surface chemistry and serum proteins

Most infections due to implanted cardiovascular biomaterials are initiated by bacterial adhesion of Staphylococcus epidermidis, followed by colonization and biofilm formation on the surface of the implant. This study examined the role of serum proteins and material surface chemistry in the formation of S. epidermidis biofilm on polyurethanes (Elasthane 80A, hydrophobic) modified with polyethylene oxide (Elasthane 80A-6PEO, hydrophilic) and fluorocarbon (Elasthane 80A-6F, hydrophobic). Initial adhesion, aggregation, biofilm thickness, viability, and slime formation of S. epidermidis strain, RP62A in phosphate buffered saline (PBS), tryptic soy broth (TBS), and 20% pooled human serum was quantified. In the presence of adsorbed serum proteins, initial bacterial adhesion was suppressed significantly to <2% relative to adhesion in TSB or PBS. However, adhesion, aggregation, and proliferation increased dramatically in the 12-24 h period on Elasthane 80A and Elasthane 80A-6F, which resulted in an extensive network of biofilm. A contrasting trend was observed on the hydrophilic Elasthane 80A-6PEO surface, with minimal bacterial adhesion, which decreased steadily over 24 h. In the presence of serum proteins, an increasingly thick ( approximately 20 mum) biofilm formed on the hydrophobic surfaces over 48 h whereas the formation of a mature biofilm on the hydrophilic surface was impeded with few viable bacteria present over 48 h. Furthermore, slime was detected during the initial phase of bacterial adhesion at 2 h and increased over time with the formation of biofilm. These results have shown that while initial S. epidermidis adhesion is suppressed in the presence of adsorbed proteins, inter-bacterial adhesion possibly aided by slime production leads to the formation of a robust mature biofilm. Also, biomaterial surface chemistry affected biofilm formation and, most notably, polyethylene oxide significantly inhibited S. epidermidis biofilm formation over 48 h in vitro.

Effects of biomaterial surface chemistry on the adhesion and biofilm formation of Staphylococcus epidermidis in vitro

The formation of biofilm, a structured community of bacteria enclosed in slime, is a significant virulence factor in medical-device-centered infection. The development of cardiovascular device infection can be separated into two phases: initial bacterial adhesion and aggregation, followed by proliferation and production of slime. It is possible to modulate the adhesion and biofilm formation of Staphylococcus epidermidis, a commensal skin bacterium commonly found on infected medical devices, through biomaterial surface chemistry. This study examines bacterial adhesion and biofilm formation on surface-modified polyethylene terephthalate (PET), including surfaces with varying hydrophilic, hydrophobic, and ionic character. Bacterial adhesion and biofilm formation were observed over 48 hours in phosphate-buffered saline (PBS) and 20% pooled human serum. The hydrophilic surface (PAAm) had significantly less nonspecific adhesion of bacteria than that in the control (PET) and other surfaces, when cultured in PBS (P < 0.0001). Charged surfaces, both anionic and cationic, had increased adhesion and aggregation of bacteria in comparison with the control (PET) in the presence of serum proteins over 24 hours (P < 0.0001). Bacteria cultured in serum on the charged surfaces did not have significantly different amounts of biofilm formation compared with that of the control (PET) surface after 48 hours. This study showed that biomaterial surface chemistry characteristics impact initial adhesion and aggregation of S. epidermidis on biomaterials.

Comblike poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers as anti-infection surface modifying agents

A series of structurally well-defined poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers that undergo surface induced self assembly on hydrophobic biomaterial surfaces were synthesized and characterized. The surfactant polymers consist of low molecular weight (Mw) chitosan backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexyl pendant groups. Chitosan was depolymerized by nitrous acid deaminative cleavage. Hexanal and aldehyde-terminated PEO chains were simultaneously attached to low Mw chitosan hydrochloride via reductive amination. The surfactant polymers were prepared with various ratios of the two side chains. The molecular composition of the surfactant polymers was determined by FT-IR and 1H NMR. Surface active properties at the air-water interface were determined by Langmuir film balance measurements. The surfactant polymers with PEO/hexyl ratios of 1:3.0 and 1:14.4 were used as surface modifying agents to investigate their anti-infection properties. E. coli adhesion on Silastic surface was decreased significantly by the surfactant polymer with PEO/hexyl 1:3.0. Surface growth of adherent E. coli was effectively suppressed by both tested surfactant polymers.

The significance of infection related to orthopedic devices and issues of antibiotic resistance

Over the last 15 years, with the advent of modern standards in the control of sterility within the operating room environment and adequate protocols of peri-operative antibiotic prophylaxis, the incidence of infections associated to orthopedic implants has become very low. Nevertheless, the event of infection still represents one of the most serious and devastating complications which may involve prosthetic devices. It leads to complex revision procedures and, often, to the failure of the implant and the need for its complete removal. In orthopedics, for the enormous number of surgical procedures involving invasive implant materials, even if nowadays rare, infections have a huge impact in terms of morbidity, mortality, and medical costs. The difficult battle to prevent and fight bacterial infections associated to prosthetic materials must be played on different grounds. A winning strategy requires a clear view of the pathogenesis and the epidemiology of implant-related infections, with a special attention on the alarming phenomenon of antibiotic resistance. In this regard staphylococci are the prevalent and most important causative pathogens involved in orthopedic implant-related infections, and, thus, the main enemy to defeat. In this paper, we offer an overview of the complexity of this battleground and of the current and new, in our opinion most promising, strategies in the field of biomaterials to reduce the risks and counteract the establishment of implant infections.

pH-dependence of the properties of hydrophobically modified polyvinylamine

A series of N-alkyl or N-benzyl substituted polyvinylamines (PVAm) were prepared and the properties of aqueous solutions were measured as functions of pH. The polymer solutions showed almost no surface activity under acidic conditions whereas surface tension was reduced to 40-50 mN/m around pH 9. Increasing either the degree of hydrophobic substitution or the hydrophobic chain length lowered the pH at which surface tension lowering was observed. Hydrophobic substitution also shifted plots of the degree of ionization versus pH toward lower pH which means lower pH values were required to achieve a given value of polymer charging. The hydrophobically modified PVAm associated in water giving species whose apparent diameter measured by dynamic light scattering decreased with increasing pH, whereas the electrophoretic mobilities of the associated species increased with decreasing pH. Although many hydrophobically modified and pH sensitive polymers have been described in the literature for applications in biomaterials, drug release and as pH sensitive surfactants, the hydrophobically modified PVAms are particularly attractive because they are easily prepared from commercially available polyvinylamines.

Quorum-sensing control in Staphylococci -- a target for antimicrobial drug therapy?

Today, we find ourselves in an urgent need for novel antibacterial drugs, as many important human pathogens have acquired multiple antibiotic resistance factors. Among those, Staphylococcus aureus and S. epidermidis play a major role as the leading sources of nosocomial infections. Recently, it has been suggested to develop therapeutics that attack bacterial virulence rather than kill bacteria. Such drugs are called "antipathogenic" and are believed to reduce the development of antibiotic resistance. Specifically, cell-density-dependent gene regulation (quorum-sensing) in bacteria has been proposed as a potential target. While promising reports exist about quorum-sensing blockers in gram-negative bacteria, the use of the staphylococcal quorum-sensing system as a drug target is now seen in an increasingly critical way. Inhibition of quorum-sensing in Staphylococcus has been shown to enhance biofilm formation. Furthermore, down-regulation or mutation of the Staphylococcus quorum-sensing system increases bacterial persistence in device-related infection, suggesting that interference with quorum-sensing would enhance rather than suppress this important type of staphylococcal disease. The chemical nature and biological function of another proposed staphylococcal quorum-sensing inhibitor, named "RIP", are insufficiently characterized. Targeting quorum-sensing systems might in principle constitute a reasonable way to find novel antibacterial drugs. However, as outlined here, this approach requires careful investigation in every specific pathogen and type of infection.

Plasma deposition and surface characterization of oligoglyme, dioxane, and crown ether nonfouling films

Plasma-deposited PEG-like films are emerging as promising materials for preventing protein and bacterial attachment to surfaces. To date, there has not been a detailed surface analysis to examine the chemistry and molecular structure of these films as a function of both precursor size and structure. In this paper, we describe radio-frequency plasma deposition of a series of short-chain oligoglymes, dioxane, and crown ethers onto glass cover slips to create poly(ethylene glycol)-like coatings. The resultant films were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), dynamic contact angle goniometry, and radiolabeled fibrinogen adsorption. Detailed analysis of the high-mass (120-300 m/z) TOF-SIMS oligoglyme film spectra revealed six classes of significant fragments. Two new models are proposed to describe how these fragments could be formed by distinct film-building processes: incorporation of intact and fragmented precursor molecules. The models also provide for the incorporation of hydrocarbon--a species that is not present in the precursors but is evidenced in XPS C(1s) spectra of these films. Two additional models describe the effects of incorporating intact and fragmented cyclic precursors.

Microbial adhesion to poly(ethylene oxide) brushes: influence of polymer chain length and temperature

Glass surfaces were modified by end-grafting poly(ethylene oxide) (PEO) chains having molecular weights of 526, 2000, or 9800 Da. Characterization using water contact angles, ellipsometry, and X-ray photoelectron spectroscopy confirmed the presence of the PEO brushes on the surface with estimated lengths in water of 2.8-, 7.5-, and 23.7-nm, respectively. Adhesion of two bacterial (Staphylococcus epidermidis and Pseudomonas aeruginosa) and two yeast (Candida albicans and Candida tropicalis) strains to these brushes was studied and compared to their adhesion to bare glass. For the bacterium P. aeruginosa and the yeast C. tropicalis, adhesion to the 2.8-nm brush was comparable to their adhesion on bare glass, whereas adhesion to the 7.5- and 23.7-nm brushes was greatly reduced. For S. epidermidis, adhesion was only slightly higher to the 2.8-nm brush than that to the longer brushes. Adhesion of the yeast C. albicans to the PEO brushes was lower than that to glass, but no differences in adhesion were found between the three brush lengths. After passage of an air bubble, nearly all microorganisms adhering to a brush were removed, irrespective of brush length, whereas retention of the adhering organisms on glass was much higher. No significant differences were found in adhesion nor retention between experiments conducted at 20 and those conducted at 37 degrees C.

Biometric surfactant polymers designed for shear-stable endothelialization on biomaterials

We have developed a series of extracellular matrix (ECM)-like biomimetic surfactant polymers to improve endothelial cell adhesion and growth on vascular biomaterials. These polymers provide a single-step procedure for modifying the surface of existing biomaterials and consist of a poly(vinyl amine) (PVAm) backbone with varying ratios of cell-binding peptide (RGD) to carbohydrate (maltose), ranging from 100% RGD:0% maltose to 50% RGD:50% maltose. Three biomimetic surfaces, as well as a fibronectin (FN)-coated glass surface were seeded at confluence with human pulmonary artery endothelial cells (HPAECs) and exposed to shear stresses ranging from 0-40.6 dyn/cm2 for periods of 2 h and 6 h. Surfaces were examined for HPAEC coverage and cytoskeletal arrangement as a function of time and shear stress. In general, after 6 h of shear exposure, EC retention on 100% RGD > FN > 75% RGD > 50% RGD. The 100% RGD surface maintained more than 50% of its initial EC monolayer at low to moderate shear stresses whereas all other surfaces dropped to approximately 40% or less in the same shear stress range. The most stable surface, 100% RGD, showed a significant increase in cytoskeletal organization at all shear stresses greater than 2.5 dyn/cm2. In contrast, there was no real change in cytoskeletal organization on the FN surface, and there was a decrease on the 75% RGD surface over time. These results indicate that increasing surface peptide density can control EC shear stability. Furthermore, improved shear stability increases with increasing peptide density and is related to the EC's ability to reorganize its cytoskeleton.

Increased release of gentamicin from acrylic bone cements under influence of low-frequency ultrasound

The release profile of antibiotics from antibiotic-loaded bone cement, used to prevent infections in total joint arthroplasty, is neither ideal nor complete. Ultrasound has been used to allow drugs to cross otherwise impermeable barriers. The aim of this study was to establish a possible effect of ultrasound on antibiotic release from bone cements. Samples were made of three commercially available gentamicin-loaded bone cements. Part of the samples was allowed to release gentamicin for 3 weeks before insonation. An insonation device produced an ultrasound field with a time average acoustic intensity of 167 mW/cm2 at a frequency of 46.5 kHz. The samples were exposed to the ultrasound field or not exposed to it as a control. The amount of gentamicin released was measured by fluorescence polarization immunoassay. There was a limited increase of gentamicin release with application of ultrasound in fresh samples but not in the samples that had been allowed to release gentamicin. For fresh samples, a linear regression model showed that this ultrasound effect was statistically significant. The mechanism behind these observations is not clear, but it is suggested that microstreaming or localized temperature rises may be involved.

Fluorocarbon Surfactant Polymers: Effect of Perfluorocarbon Branch Density on Surface Active Properties

We describe a series of fluorocarbon surfactant polymers designed for modifying fluorocarbon surfaces such as poly(tetrafluoroethylene). Novel fluorocarbon surfactant polymers poly(N-vinyldextranaldonamide-co-N-vinylperfluoroundecanamide), in which hydrophilic dextran oligosaccharides and hydrophobic perfluoroundecanoyl groups were incorporated sequentially onto a poly(vinylamine) backbone, were synthesized and characterized by FT-IR, NMR, and XPS spectroscopy. By adjusting the feed ratio of dextran to fluorocarbon branches, surfactant polymers with different hydrophilic/hydrophobic balances were prepared. The surface activity of the surfactants at the air/water interface was demonstrated by significant reductions in water surface tension. Surfactant adsorption and adhesion at the solid PTFE/aqueous interface were examined under well-defined dynamic flow conditions, using a rotating disk system. The surface activity at the air/water interface and adhesion stability on PTFE under an applied shear stress both increase with increasing density of fluorocarbon branches on the polymer backbone. The results show that stable surfactant adhesion on PTFE can be achieved by adjusting the hydrophilic dextran to hydrophobic fluorocarbon branch ratio.

Characterization of poly(ethylene oxide) brushes on glass surfaces and adhesion of Staphylococcus epidermidis

Poly(ethylene oxide) brushes have been covalently bound to glass surfaces and their presence was demonstrated by an increase in water contact angles from fully wettable on glass to advancing contact angles of 54 degrees, with a hysteresis of 32 degrees. In addition, electrophoretic mobilities of glass and brush-coated glass were determined using streaming potential measurements. The dependence of the electrophoretic mobilities on the ionic strength was analyzed in terms of a softlayer model, yielding an electrophoretic softness and fixed charge density of the layer. Brush-coated glass could be distinguished from glass by a 2-3-fold decrease in fixed charge density, while both surfaces were about equally soft. Adhesion of Staphylococcus epidermidis HBH276 to glass in a parallel plate flow chamber was extremely high and after 4 h, 19.0 x 10(6) bacteria were adhering per cm2. In contrast, the organisms did not adhere to brush-coated glass, with numbers below the detection limit, i.e. 0.1 x 10(6) per cm2. These results attest to the great potential of polymer brushes in preventing bacterial adhesion to surfaces.

Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry

Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to < or = 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of < or = 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

Quantitative evaluation of bacteria adherent to polyelectrolyte HEMA-based hydrogels

The use of adhesive poly(HEMA)-based hydrogels is standard practice in dental restorative procedures. Microorganisms, which potentially can cause oral pathologies, may colonize these polymers. In the present work, bacterial adhesion to polymers prepared with 2-hydroxyethyl methacrylate (HEMA) and to different molar ratios of 2-acrylamido-2-methylpropane-sulfonic acid (AMPS) and/or to 2-methacryloyloxyethyl-tri-methyl-ammonium chloride (METAC) co-monomers were tested. A colorimetric assay system that utilizes the Microbo revelation medium (Microbo srl, Rome, Italy) for microbial counts is shown to be capable of counting the number of adherent bacterial cells without removing them from polymer surfaces. In conditions that mimic those present in the oral cavity, similar bacterial adhesion percentages on the same polymer were observed with the different bacteria belonging to both gram-positive and gram-negative genera, such as Streptococcus sobrinus and Streptococcus oralis (resident microorganisms in the oral cavity) and Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa (transient microorganisms in the oral cavity). It is determined that the physico-chemical characteristics of poly(HEMA)-based hydrogels are the major factors promoting bacterial adhesion, which increased with increasing water content in the swollen polymers, reaching maximal values on the cationic polymers.