Bacteria-surface interaction in the presence of proteins and surface attached poly(ethylene glycol) methacrylate chains

Biodegradable and Cytocompatible Hydrogel Coating with Antibacterial Activity for the Prevention of Implant-Associated Infection

Implant-associated infection (IAI) caused by pathogens colonizing on the implant surface is a serious issue in the trauma-orthopedic surgery, which often leads to implant failure. The complications of IAI bring a big threat to the clinical practice of implants, accompanied by significant economic cost and long hospitalization time. In this study, we propose an antibiotics-free strategy to address IAI-related challenges by using a biodegradable and cytocompatible hydrogel coating. To achieve this, a novel hydrogel system was developed to combine the synergistic effects of good cell affinity and antibacterial properties. The hydrogel material was prepared by modifying a photocross-linkable gelatin-based polymer (GelMA) with cationic quaternary ammonium salt (QAS) groups via a mild and simple synthesis procedure. By engineering the length of the hydrophobic carbon chain on the QAS group and the degree of functionalization, the resulting GelMA-octylQAS hydrogel exhibited an integration of good mechanical properties, biodegradability, excellent bactericidal activity against various types of bacteria, and high cytocompatibility with mammalian cells. When coated onto the implant via the in situ cross-linking procedure, our hydrogel demonstrated superior antimicrobial ability in the infective model of femoral fracture of rats. Our results suggest that the GelMA-octylQAS hydrogel might provide a promising platform for preventing and treating IAI.

Bio-inspired special wettability in oral antibacterial applications

Most oral diseases originate from biofilms whose formation is originated from the adhesion of salivary proteins and pioneer bacteria. Therefore, antimicrobial materials are mainly based on bactericidal methods, most of which have drug resistance and toxicity. Natural antifouling surfaces inspire new antibacterial strategies. The super wettable surfaces of lotus leaves and fish scales prompt design of biomimetic oral materials covered or mixed with super wettable materials to prevent adhesion. Bioinspired slippery surfaces come from pitcher plants, whose porous surfaces are infiltrated with lubricating liquid to form superhydrophobic surfaces to reduce the contact with liquids. It is believed that these new methods could provide promising directions for oral antimicrobial practice, improving antimicrobial efficacy.

Anti-Periprosthetic Infection Strategies: From Implant Surface Topographical Engineering to Smart Drug-Releasing Coatings

Despite advanced implant sterilization and aseptic surgical techniques, periprosthetic bacterial infection remains a major challenge for orthopedic and dental implants. Bacterial colonization/biofilm formation around implants and their invasion into the dense skeletal tissue matrices are difficult to treat and could lead to implant failure and osteomyelitis. These complications require major revision surgeries and extended antibiotic therapies that are associated with high treatment cost, morbidity, and even mortality. Effective preventative measures mitigating risks for implant-related infections are thus in dire need. This review focuses on recent developments of anti-periprosthetic infection strategies aimed at either reducing bacterial adhesion, colonization, and biofilm formation or killing bacteria directly in contact with and/or in the vicinity of implants. These goals are accomplished through antifouling, quorum-sensing interfering, or bactericidal implant surface topographical engineering or surface coatings through chemical modifications. Surface topographical engineering of lotus leaf mimicking super-hydrophobic antifouling features and cicada wing-mimicking, bacterium-piercing nanopillars are both presented. Conventional physical coating/passive release of bactericidal agents is contrasted with their covalent tethering to implant surfaces through either stable linkages or linkages labile to bacterial enzyme cleavage or environmental perturbations. Pros and cons of these emerging anti-periprosthetic infection approaches are discussed in terms of their safety, efficacy, and translational potentials.

Surface modification strategies for hemodialysis catheters to prevent catheter-related infections: A review

Insertion of a central venous catheter is one of the most common invasive procedures applied in hemodialysis therapy for end-stage renal disease. The most important complication of a central venous catheter is catheter-related infections that increase hospitalization and duration of intensive care unit stay, cost of treatment, mortality, and morbidity rates. Pathogenic microorganisms, such as, bacteria and fungi, enter the body from the catheter insertion site and the surface of the catheter can become colonized. The exopolysaccharide-based biofilms from bacterial colonies on the surface are the main challenge in the treatment of infections. Catheter lock solutions and systemic antibiotic treatment, which are commonly used in the treatment of hemodialysis catheter-related infections, are insufficient to prevent and terminate the infections and eventually the catheter needs to be replaced. The inadequacy of these approaches in termination and prevention of infection revealed the necessity of coating of hemodialysis catheters with bactericidal and/or antiadhesive agents. Silver compounds and nanoparticles, anticoagulants (e.g., heparin), antibiotics (e.g., gentamicin and chlorhexidine) are some of the agents used for this purpose. The effectiveness of few commercial hemodialysis catheters that were coated with antibacterial agents has been tested in clinical trials against catheter-related infections of pathogenic bacteria, such as Staphylococcus aureus and Staphylococcus epidermidis with promising results. Novel biomedical materials and engineering techniques, such as, surface micro/nano patterning and the conjugation of antimicrobial peptides, enzymes, metallic cations, and hydrophilic polymers (e.g., poly [ethylene glycol]) on the surface, has been suggested recently.

Studies of zwitterionic sulfobetaine functionalized polypropylene surface with or without polyethylene glycol spacer: surface characterization, antibacterial adhesion, and platelet compatibility evaluation

Microbial adhesion reduction as well as platelet compatibility improvement have been suggested as the key requirements for developing blood-contacting synthetic biomaterials. Surface grafting of hydrophilic polyethylene glycol chains or alkyl chains with zwitterionic terminal ends has been proposed for reducing microbial or platelet adhesion. Nonetheless, none has been reported to incorporate both polyethylene glycol and zwitterionic terminal functionality on the same surface-grafted alkyl chain. In this investigation, a novel surface modification scheme was reported for grafting zwitterionic alkyl chains with or without polyethylene glycol as the spacer. It was noted the bacterial adhesion reduction capability on the zwitterionic modified surface was dependent upon the use of polyethylene glycol spacer or not and the strain of microbe tested. Besides, the zwitterionic modified ones all showed greater antimicrobial adhesion capability than the surface modified with polyethylene glycol alone. On the other hand, significantly reduced platelet adhesion and activation were found, but with no statistical differences noted among the polyethylene glycol-modified surface and zwitterionic ones, with or without polyethylene glycol spacer. These suggested that the use of polyethylene glycol spacer on the zwitterionic terminated surface could further enhance the antimicrobial adhesion against gram-negative bacterial while still keeping its platelet compatibility.

Studies of polypropylene surface modified with novel beta-thiopropionate-based zwitterionic polymeric brush: synthesis, surface characterization, and significantly reduced fouling characteristics evaluation

Creating a surface with anti- or reduced fouling characteristics can lead to a reduction in nonspecific protein adsorption as well as the bacterial adhesion and platelet adhesion/activation that occur as follows. A zwitterionic polymer that consists of both cationic and anionic functionalities have been reported as an effective material to achieve these goals, likely resulted from the strongly-adsorbed hydration layer after being immersed in the physiological environment. In this investigation, a novel beta-thiopropionate-based zwitterionic monomer, 2-ammonio-3-((3-(2-hydroxy-3-(methacryloyloxy)propoxy)-3-oxopropyl)thio)-3-methylbutanoate (DPAMA), was synthesized through a facial process. And then the hydrophobic polypropylene was surface modified with this novel zwitterionic polymer through the surface-initiated atom transfer radical polymerization technique. Surface characterization analyses have been employed to investigate the modified surface properties in each reaction stage. In vitro protein adsorption, bacterial adhesion, and platelet compatibility evaluations have shown the polyDPAMA-modified polypropylene surface has significantly reduced fouling characteristics and good hemocompatibility. Henceforth, this novel zwitterionic polyDPAMA grafting PP and the associated grafting reaction scheme have great potential for future clinical applications.

Comparison of Antibacterial Adhesion When Salivary Pellicle Is Coated on Both Poly(2-hydroxyethyl-methacrylate)- and Polyethylene-glycol-methacrylate-grafted Poly(methyl methacrylate)

Although poly(2-hydroxyethyl methacrylate) (pHEMA) and polyethylene glycol methacrylate (PEGMA) have been demonstrated to inhibit bacterial adhesion, no study has compared antibacterial adhesion when salivary pellicle is coated on polymethyl methacrylate (PMMA) grafted with pHEMA and on PMMA grafted with PEGMA. In this study, PMMA discs were fabricated from a commercial orthodontic acrylic resin system (Ortho-Jet). Attenuated total reflection-Fourier transform infrared spectra taken before and after grafting confirmed that pHEMA and PEGMA were successfully grafted on PMMA. Contact angle measurements revealed PMMA-pHEMA to be the most hydrophilic, followed by PMMA-PEGMA, and then by PMMA. Zeta potential analysis revealed the most negative surface charges on PMMA-PEGMA, followed by PMMA-pHEMA, and then by PMMA. Confocal laser scanning microscopy showed green fluorescence in the background, indicating images that influenced the accuracy of the quantification of live bacteria. Both the optical density value measured at 600 nm and single plate-serial dilution spotting showed that pHEMA was more effective than PEGMA against Escherichia coli and Streptococcus mutans, although the difference was not significant. Therefore, the grafting of pHEMA and PEGMA separately on PMMA is effective against bacterial adhesion, even after the grafted PMMA were coated with salivary pellicle. Surface hydrophilicity, bactericidality, and Coulomb repulsion between the negatively charged bacteria and the grafted surface contributed to the effectiveness.

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)

Electrochemical impedance spectroscopy reveals a new mechanism based on competitive binding between Tris and protein on a conductive biomimetic polydopamine surface

A novel mechanism was developed to study the interaction of mussel inspired polydopamine surfaces with bovine serum albumin using electrochemical impedance spectroscopy.

Recent Nanotechnology Approaches for Prevention and Treatment of Biofilm-Associated Infections on Medical Devices

Bacterial colonization in the form of biofilms on surfaces causes persistent infections and is an issue of considerable concern to healthcare providers. There is an urgent need for novel antimicrobial or antibiofilm surfaces and biomedical devices that provide protection against biofilm formation and planktonic pathogens, including antibiotic resistant strains. In this context, recent developments in the material science and engineering fields and steady progress in the nanotechnology field have created opportunities to design new biomaterials and surfaces with anti-infective, antifouling, bactericidal, and antibiofilm properties. Here we review a number of the recently developed nanotechnology-based biomaterials and explain underlying strategies used to make antibiofilm surfaces.

Effects of immobilized VEGF on endothelial progenitor cells cultured on silicon substituted and nanocrystalline hydroxyapatites

Immobilized VEGF effects on angiogenic cells cultured on silicon substituted and nanocrystalline hydroxyapatites.

A novel nano-silver coated and hydrogel-impregnated polyurethane nanofibrous mesh for ventral hernia repair

Patches for hernia repair have two existing concerns: antibacterial and tissue adhesion.

Layer-by-layer assembly for biomedical applications in the last decade

In the past two decades, the design and manufacture of nanostructured materials has been of tremendous interest to the scientific community for their application in the biomedical field. Among the available techniques, layer-by-layer (LBL) assembly has attracted considerable attention as a convenient method to fabricate functional coatings. Nowadays, more than 1000 scientific papers are published every year, tens of patents have been deposited and some commercial products based on LBL technology have become commercially available. LBL presents several advantages, such as (1): a precise control of the coating properties; (2) environmentally friendly, mild conditions and low-cost manufacturing; (3) versatility for coating all available surfaces; (4) obtainment of homogeneous film with controlled thickness; and (5) incorporation and controlled release of biomolecules/drugs. This paper critically reviews the scientific challenge of the last 10 years--functionalizing biomaterials by LBL to obtain appropriate properties for biomedical applications, in particular in tissue engineering (TE). The analysis of the state-of-the-art highlights the current techniques and the innovative materials for scaffold and medical device preparation that are opening the way for the preparation of LBL-functionalized substrates capable of modifying their surface properties for modulating cell interaction to improve substitution, repair or enhancement of tissue function.

Quantifying bacterial adhesion on antifouling polymer brushes via single-cell force spectroscopy

The adhesion forces between a single bacterial cell and different polymer brushes were measured directly with an atomic force microscope and correlated with their resistance to fouling.

Biofilm formation by clinical isolates and its relevance to clinical infections

Reports of biofilms have increased exponentially in the scientific literature over the past two decades, yet the vast majority of these are basic science investigations with limited clinical relevance. Biofilm studies involving clinical isolates are most often surveys of isolate collections, but suffer from lack of standardization in methodologies for producing and assessing biofilms. In contrast, more informative clinical studies correlating biofilm formation to patient data have infrequently been reported. In this chapter, biofilm surveys of clinical isolates of aerobic and anaerobic bacteria, mycobacteria, and Candida are reviewed, as well as those pertaining to the unique situation of cystic fibrosis. In addition, the influence of host components on in vitro biofilm formation, as well as published studies documenting the clinical impact of biofilms in human infections, are presented.

Nuclease-functionalized poly(styrene-b-isobutylene-b-styrene) surface with anti-infection and tissue integration bifunctions

Hydrophobic thermoplastic elastomers, e.g., poly(styrene-b-isobutylene-b-styrene) (SIBS), have found various in vivo biomedical applications. It has long been recognized that biomaterials can be adversely affected by bacterial contamination and clinical infection. However, inhibiting bacterial colonization while simultaneously preserving or enhancing tissue-cell/material interactions is a great challenge. Herein, SIBS substrates were functionalized with nucleases under mild conditions, through polycarboxylate grafts as intermediate. It was demonstrated that the nuclease-modified SIBS could effectively prevent bacterial adhesion and biofilm formation. Cell adhesion assays confirmed that nuclease coatings generally had no negative effects on L929 cell adhesion, compared with the virgin SIBS reference. Therefore, the as-reported nuclease coating may present a promising approach to inhibit bacterial infection, while preserving tissue-cell integration on polymeric biomaterials.

Surface modification of silicone for biomedical applications requiring long-term antibacterial, antifouling, and hemocompatible properties

Silicone has been used for peritoneal dialysis (PD) catheters for several decades. However, bacteria, platelets, proteins, and other biomolecules tend to adhere to its hydrophobic surface, which may lead to PD outflow failure, serious infection, or even death. In this work, a cross-linked poly(poly(ethylene glycol) dimethacrylate) (P(PEGDMA)) polymer layer was covalently grafted on medical-grade silicone surface to improve its antibacterial and antifouling properties. The P(PEGDMA)-grafted silicone (Silicone-g-P(PEGDMA)) substrate reduced the adhesion of Staphylococcus aureus , Escherichia coli , and Staphylococcus epidermidis , as well as 3T3 fibroblast cells by ≥90%. The antibacterial and antifouling properties were preserved after the modified substrate was aged for 30 days in phosphate buffer saline. Further immobilization of a polysulfobetaine polymer, poly((2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide) (P(DMAPS)), on the Silicone-g-P(PEGDMA) substrate via thiol-ene click reaction leads to enhanced antifouling efficacy and improved hemocompatibility with the preservation of the antibacterial property. Compared to pristine silicone, the so-obtained Silicone-g-P(PEGDMA)-P(DMAPS) substrate reduced the absorption of bovine serum albumin and bovine plasma fibrinogen by ≥80%. It also reduced the number of adherent platelets by ≥90% and significantly prolonged plasma recalcification time. The results indicate that surface grafting with P(PEGDMA) and P(DMAPS) can be potentially useful for the modification of silicone-based PD catheters for long-term applications.

Infection of orthopedic implants with emphasis on bacterial adhesion process and techniques used in studying bacterial-material interactions

Staphylococcus comprises up to two-thirds of all pathogens in orthopedic implant infections and they are the principal causative agents of two major types of infection affecting bone: septic arthritis and osteomyelitis, which involve the inflammatory destruction of joint and bone. Bacterial adhesion is the first and most important step in implant infection. It is a complex process influenced by environmental factors, bacterial properties, material surface properties and by the presence of serum or tissue proteins. Properties of the substrate, such as chemical composition of the material, surface charge, hydrophobicity, surface roughness and the presence of specific proteins at the surface, are all thought to be important in the initial cell attachment process. The biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. The research for novel therapeutic strategies is incited by the emergence of antibiotic-resistant bacteria. This work will provide an overview of the mechanisms and factors involved in bacterial adhesion, the techniques that are currently being used studying bacterial-material interactions as well as provide insight into future directions in the field.

Antifouling coatings: recent developments in the design of surfaces that prevent fouling by proteins, bacteria, and marine organisms

The major strategies for designing surfaces that prevent fouling due to proteins, bacteria, and marine organisms are reviewed. Biofouling is of great concern in numerous applications ranging from biosensors to biomedical implants and devices, and from food packaging to industrial and marine equipment. The two major approaches to combat surface fouling are based on either preventing biofoulants from attaching or degrading them. One of the key strategies for imparting adhesion resistance involves the functionalization of surfaces with poly(ethylene glycol) (PEG) or oligo(ethylene glycol). Several alternatives to PEG-based coatings have also been designed over the past decade. While protein-resistant coatings may also resist bacterial attachment and subsequent biofilm formation, in order to overcome the fouling-mediated risk of bacterial infection it is highly desirable to design coatings that are bactericidal. Traditional techniques involve the design of coatings that release biocidal agents, including antibiotics, quaternary ammonium salts (QAS), and silver, into the surrounding aqueous environment. However, the emergence of antibiotic- and silver-resistant pathogenic strains has necessitated the development of alternative strategies. Therefore, other techniques based on the use of polycations, enzymes, nanomaterials, and photoactive agents are being investigated. With regard to marine antifouling coatings, restrictions on the use of biocide-releasing coatings have made the generation of nontoxic antifouling surfaces more important. While considerable progress has been made in the design of antifouling coatings, ongoing research in this area should result in the development of even better antifouling materials in the future.

Covalent layer-by-layer assembly of polyethyleneimine multilayer for antibacterial applications

Polyelectrolyte multilayer film (PMF) is conventionally fabricated by the layer-by-layer (LBL) assembly of a pair of oppositely charged polyelectrolytes on a substrate through electrostatic attractions. However, the lack of long-term stability of PMF under physiological conditions limits its application as antimicrobial coating in medical devices. In this study, a stable PMF composed of only polyethyleneimine (PEI) was constructed by covalent LBL deposition. First, the specific buildup of PEI during covalent LBL assembly was validated by UV-Vis absorption spectroscopy and atomic force microscopy. Second, silver (Ag) nanoparticles were incorporated into PEI multilayers through in situ reduction of Ag(+) by the pre-absorption of NaBH(4). It was also shown that the mass of Ag nanoparticle can be controlled by varying multilayer thickness and loading cycles. Bacterial live/dead assay showed that the PEI multilayers effectively killed Staphylococcus aureus and Escherichia coli upon contact formation. The inclusion of Ag nanoparticles in (PEI) film not only enhanced the antimicrobial property against adherent bacteria but also led to the inhibition of the bacteria growth in suspended culture via the long-term release of Ag(+) into the liquid medium.

Study of Antibacterial Efficacy of Hybrid Chitosan-Silver Nanoparticles for Prevention of Specific Biofilm and Water Purification

Antibacterial efficacy of silver nanoparticles (Ag NPs) deposited alternatively layer by layer (LBL) on chitosan polymer in the form of a thin film over a quartz plate and stainless steel strip has been studied. An eight-bilayer chitosan/silver (Cs/Ag)8 hybrid was prepared having a known concentration of silver. Techniques such as UV-visible spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), and atomic force microscopy (AFM) were carried out to understand and elucidate the physical nature of the film. Gram-negative bacteria, Escherichia coli (E. coli), were used as a test sample in saline solution for antibacterial studies. The growth inhibition at different intervals of contact time and, more importantly, the antibacterial properties of the hybrid film on repeated cycling in saline solution have been demonstrated. AFM studies are carried out for the first time on the microbe to know the morphological changes affected by the hybrid film. The hybrid films on aging (3 months) are found to be as bioactive as before. Cytotoxicity experiments indicated good biocompatibility. The hybrid can be a promising bioactive material for the prevention of biofilms specific to E. coli and in purification of water for safe drinking.

Biofilm retention on surfaces with variable roughness and hydrophobicity

Biofilms on food processing equipment cause food spoilage and pose a hazard to consumers. The bacterial community on steel surfaces in a butcher's shop was characterized, and bacteria representative of this community enriched from minced pork were used to study biofilm retention. Stainless steel (SS) was compared to two novel nanostructured sol-gel coatings with differing hydrophobicity. Surfaces were characterized with respect to roughness, hydrophobicity, protein adsorption, biofilm retention, and community composition of the retained bacteria. Fewer bacteria were retained on the sol-gel coated surfaces compared to the rougher SS. However, the two sol-gel coatings did not differ in either protein adsorption, biofilm retention, or microbial community composition. When polished to a roughness similar to sol-gel, the SS was colonized by the same amount of bacteria as the sol-gel, but the bacterial community contained fewer Pseudomonas cells. In conclusion, biofilm retention was affected more by surface roughness than chemical composition under the condition described in this study.

Vibrational and electronic characterisation of Staphylococcus aureus wall teichoic acids and relevant components in thin films

This work reports an investigation of S. aureus wall teichoic acid (WTA) and compares this biopolymer with its major occurring components, D: -alanine and glycerol phosphate. Detailed insight into molecular structures and electronic properties is obtained by vibrational and photoemission spectroscopy. Calculations are performed to support the analysis of our experimental vibrational spectra. It is shown that there are contributions of positive and negative charges in WTAs, but the number of negative charges is expected to be higher. The presence of both positive and negative charges on WTA may offer a route for modification of surfaces with the objective of avoiding the formation of biofilms.

In vitro and in vivo comparisons of staphylococcal biofilm formation on a cross-linked poly(ethylene glycol)-based polymer coating

Poly(ethylene glycol) (PEG) coatings are known to reduce microbial adhesion in terms of numbers and binding strength. However, bacterial adhesion remains of the order of 10(4)cm(-2). It is unknown whether this density of bacteria will eventually grow into a biofilm. This study investigates the kinetics of staphylococcal biofilm formation on a commercially produced, robust, cross-linked PEG-based polymer coating (OptiChem) in vitro and in vivo. OptiChem inhibits biofilm formation in vitro, and although adsorption of plasma proteins encourages biofilm formation, microbial growth kinetics are still strongly delayed compared to uncoated glass. In vivo, OptiChem-coated and bare silicone rubber samples were inserted into an infected murine subcutaneous pocket model. In contrast to bare silicone rubber, OptiChem samples did not become colonized upon reimplantation despite the fact that surrounding tissues were always culture-positive. We conclude that the commercial OptiChem coating considerably slows down bacterial biofilm formation both in vitro and in vivo, making it an attractive candidate for biomaterials implant coating.

Reduced bacterial adhesion to fibrinogen-coated substrates via nitric oxide release

The ability of nitric oxide (NO)-releasing xerogels to reduce fibrinogen-mediated adhesion of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli is described. A negative correlation was observed between NO surface flux and bacterial adhesion for each species tested. For S. aureus and E. coli, reduced adhesion correlated directly with NO flux from 0 to 30 pmol cm(-2)s(-1). A similar dependence for S. epidermidis was evident from 18 to 30 pmol cm(-2)s(-1). At a NO flux of 30 pmol cm(-2)s(-1), surface coverage of S. aureus, S. epidermidis, and E. coli was reduced by 96, 48, and 88%, respectively, compared to non-NO-releasing controls. Polymeric NO release was thus demonstrated to be an effective approach for significantly reducing fibrinogen-mediated adhesion of both gram-positive and gram-negative bacteria in vitro, thereby illustrating the advantage of active NO release as a strategy for inhibiting bacterial adhesion in the presence of pre-adsorbed protein.