Biomaterial-associated Infections Research Articles

Surface modification of silicone elastomer with rosin acid-based quaternary ammonium salt for antimicrobial and biocompatible properties

Despite advanced sterilized and aseptic techniques, biomaterial-associated infections are still posing a great threat to human life. Therefore, constructing antimicrobial coating that exerts potent antimicrobial activity combined with low cytotoxicity is of great significance. Herein, an antimicrobial coating on the surface of silicone elastomer (PDMS) has been successful constructed, which based on maleopimaric acid quaternary ammonium cation (MPA-N+). The surface morphology and chemical composition of modified PDMS (PDMS-g-MPA-N+) were confirmed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The PDMS-g-MPA-N+ possess excellent antimicrobial activity against both Gram-positive bacterial (Staphylococcus aureus) and Gram-negative bacterial (Escherichia coli, Pseudomonas aeruginosa) strains. In addition, confocal laser scanning microscopy imaging demonstrated that it also can effectively inhibit bacterial biofilm formation over 5 days. Most importantly, PDMS-g-MPA-N+ exhibited excellent biocompatibility, which induced no significant hemolysis and cytotoxicity toward mammalian cells. The study demonstrated that the silicone elastomer surface grafted with MPA-N+ enabled the incorporation of a renewable biomass to effectively combat bacteria and biofilm formation for biomedical applications.

Polarization of Macrophages, Cellular Adhesion, and Spreading on Bacterially Contaminated Gold Nanoparticle-Coatings in Vitro.

Biomaterial-associated infections often arise from contaminating bacteria adhering to an implant surface that are introduced during surgical implantation and not effectively eradicated by antibiotic treatment. Whether or not infection develops from contaminating bacteria depends on an interplay between bacteria contaminating the biomaterial surface and tissue cells trying to integrate the surface with the aid of immune cells. The biomaterial surface plays a crucial role in defining the outcome of this race for the surface. Tissue integration is considered the best protection of a biomaterial implant against infectious bacteria. This paper aims to determine whether and how macrophages aid osteoblasts and human mesenchymal stem cells to adhere and spread over gold nanoparticle (GNP)-coatings with different hydrophilicity and roughness in the absence or presence of contaminating, adhering bacteria. All GNP-coatings had identical chemical surface composition, and water contact angles decreased with increasing roughness. Upon increasing the roughness of the GNP-coatings, the presence of contaminating Staphylococcus epidermidis in biculture with cells gradually decreased surface coverage by adhering and spreading cells, as in the absence of staphylococci. More virulent Staphylococcus aureus fully impeded cellular adhesion and spreading on smooth gold- or GNP-coatings, while Escherichia coli allowed minor cellular interaction. Murine macrophages in monoculture tended toward their pro-inflammatory "fighting" M1-phenotype on all coatings to combat the biomaterial, but in bicultures with contaminating, adhering bacteria, macrophages demonstrated Ym1 expression, indicative of polarization toward their anti-inflammatory "fix-and-repair" M2-phenotype. Damage repair of cells by macrophages improved cellular interactions on intermediately hydrophilic/rough (water contact angle 30 deg/surface roughness 118 nm) GNP-coatings in the presence of contaminating, adhering Gram-positive staphylococci but provided little aid in the presence of Gram-negative E. coli. Thus, the merits on GNP-coatings to influence the race for the surface and prevent biomaterial-associated infection critically depend on their hydrophilicity/roughness and the bacterial strain involved in contaminating the biomaterial surface.

Insect Cecropins, Antimicrobial Peptides with Potential Therapeutic Applications.

The alarming escalation of infectious diseases resistant to conventional antibiotics requires urgent global actions, including the development of new therapeutics. Antimicrobial peptides (AMPs) represent potential alternatives in the treatment of multi-drug resistant (MDR) infections. Here, we focus on Cecropins (Cecs), a group of naturally occurring AMPs in insects, and on synthetic Cec-analogs. We describe their action mechanisms and antimicrobial activity against MDR bacteria and other pathogens. We report several data suggesting that Cec and Cec-analog peptides are promising antibacterial therapeutic candidates, including their low toxicity against mammalian cells, and anti-inflammatory activity. We highlight limitations linked to the use of peptides as therapeutics and discuss methods overcoming these constraints, particularly regarding the introduction of nanotechnologies. New formulations based on natural Cecs would allow the development of drugs active against Gram-negative bacteria, and those based on Cec-analogs would give rise to therapeutics effective against both Gram-positive and Gram-negative pathogens. Cecs and Cec-analogs might be also employed to coat biomaterials for medical devices as an approach to prevent biomaterial-associated infections. The cost of large-scale production is discussed in comparison with the economic and social burden resulting from the progressive diffusion of MDR infectious diseases.

Study of the Relationship Between Chlorhexidine-Grafted Amount and Biological Performances of Micro/Nanoporous Titanium Surfaces.

Biomaterial-associated infection and lack of sufficient osseointegration contribute to a large proportion of implant failures. Therefore, antibacterial and osseointegration-accelerating properties are important in implant surface design. In this study, a micro/nanoporous titanium surface was prepared through alkaline and heat treatments, covalently conjugated with aminosilane. Then, varying amounts of chlorhexidine (CHX) were covalently grafted onto the aminosilane-modified surface via glutaraldehyde to obtain different CHX-grafted surfaces. These as-prepared surfaces were evaluated in terms of their surface chemical composition, surface topography, CHX grafting amount, antibacterial activity, and osteoblast compatibility. The results showed that the CHX grafting amount increased with increasing CHX concentrations, leading to better antibacterial activity. CHX (1 mg/mL) resulted in the best antibacterial surface, which still retained good osteoblast compatibility. Meanwhile, competitive bacterial-cell adhesion analysis demonstrated that this surface has great value for osteoblast adhesion at the implant–bone interface even in the presence of bacteria. This effortless, easily performed, and eco-friendly technique holds huge promise for clinical applications.

Application of Non-Thermal Plasma on Biofilm: A Review

The formation of bacterial biofilm on implanted devices or damaged tissues leads to biomaterial-associated infections often resulting in life-threatening diseases and implant failure. It is a challenging process to eradicate biofilms as they are resistant to antimicrobial treatments. Conventional techniques, such as high heat and chemicals exposure, may not be suitable for biofilm removal in nosocomial settings. These techniques create surface degradation on the treated materials and lead to environmental pollution due to the use of toxic chemicals. A novel technique known as non-thermal plasma has a great potential to decontaminate or sterilize those nosocomial biofilms. This article aims to provide readers with an extensive review of non-thermal plasma and biofilms to facilitate further investigations. A brief introduction summarizes the problem caused by biofilms in hospital settings with current techniques used for biofilm inactivation followed by the literature review strategy. The remainder of the review discusses plasma and its generation, the role played by plasma reactive species, various factors affecting the antimicrobial efficacy of non-thermal plasma and summarizes many studies published in the field.

Preparation and characterization of a gallium-loaded antimicrobial artificial dermal scaffold.

Artificial dermal scaffolds, which are made of natural or synthetic materials, can improve new blood vessel formation, cell migration and cell proliferation after being implanted into wounds, and they degrade slowly, playing an important role in dermal reconstruction and scar inhibition, finally achieving the goal of wound healing and functional reconstruction. Although these scaffolds have been widely used in clinical applications, biomaterial-associated infection is a deficiency or even a life-threatening problem that must be addressed, as it greatly affects the survival of the scaffolds. The gallium ion (Ga3+) is a novel metallic antimicrobial whose broad-spectrum antimicrobial properties against most bacteria encountered in burn wound infections have been confirmed, and it has been proposed as a promising candidate to prevent implant-associated infections. In this study, a gallium-loaded antimicrobial artificial dermal scaffold was successfully prepared by gallium ions and a collagen solution. The characterization results showed a porous structure with pore sizes ranging from 50 to 150 μm and a large porosity value of 97.4%. The enzymatic degradation rate in vitro was 19 and 28% after 12 and 24 h, respectively. In vitro antimicrobial testing revealed that the 1 h antibacterial rate against Staphylococcus aureus and Pseudomonas aeruginosa was close to 90%, which indicated its great antimicrobial activity. The results of the cytological evaluation showed slight effect on cell proliferation, with a relative growth rate (RGR) value of 80% and great cytocompatibility with cultured cells according to laser scanning confocal microscopy (LSCM) and scanning electron microscope (SEM). Furthermore, the successful prevention of wound infections in SD rats was confirmed with an in vivo antimicrobial evaluation, and the artificial dermal scaffolds also demonstrated great biocompatibility. This gallium-loaded antimicrobial artificial dermal scaffold exerted excellent antimicrobial activity and great biosafety, warranting further research for future clinical applications.

Antimicrobial PHAs coatings for solid and porous tantalum implants

Biomaterial-associated infections (BAI) are the major cause of failure of indwelling medical devices. The risk of BAI can end dramatically in the surgical removal of the affected device. Therefore, a major effort must be undertaken to guarantee the permanence of the implant. In this regard, we have developed antimicrobial coatings for tantalum (Ta) implants, using polyhydroxyalkanoates (PHAs) as matrices for carrying an active principle. The dip-coating technique was successfully used for covering solid Ta discs. An original PHA emulsion flow process was developed for the coating of porous Ta structures, specially for the inner surfaces. The complete characterization of the biopolymer coatings, their antibacterial properties, toxicity and biointegration were analyzed. Thus, non-toxic, well-biointegrated homogeneous biopolymer coatings were attained, which showed antibacterial properties. By using biodegradable PHAs, the resulting drug delivery system assured the protection of Ta against bacterial infections for a period of time.

Bioactive Silk Coatings Reduce the Adhesion of Staphylococcus aureus while Supporting Growth of Osteoblast-like Cells.

Orthopedic and dental implants are associated with a substantial risk of failure due to biomaterial-associated infections and poor osseointegration. To prevent such outcomes, a coating can be applied on the implant to ideally both reduce the risk of bacterial adhesion and support establishment of osteoblasts. We present a strategy to construct dual-functional silk coatings with such properties. Silk coatings were made from a recombinant partial spider silk protein either alone (silkwt) or fused with a cell-binding motif derived from fibronectin (FN-silk). The biofilm-dispersal enzyme Dispersin B (DspB) and two peptidoglycan degrading endolysins, PlySs2 and SAL-1, were produced recombinantly. A sortase recognition tag (SrtTag) was included to allow site-specific conjugation of each enzyme onto silkwt and FN-silk coatings using an engineered variant of the transpeptidase Sortase A (SrtA*). To evaluate bacterial adhesion on the samples, Staphylococcus aureus was incubated on the coatings and subsequently subjected to live/dead staining. Fluorescence microscopy revealed a reduced number of bacteria on all silk coatings containing enzymes. Moreover, the bacteria were mobile to a higher degree, indicating a negative influence on the bacterial adhesion. The capability to support mammalian cell interactions was assessed by cultivation of the osteosarcoma cell line U-2 OS on dual-functional surfaces, prepared by conjugating the enzymes onto FN-silk coatings. U-2 OS cells could adhere to silk coatings with enzymes and showed high spreading and viability, demonstrating good cell compatibility.

Design of an Antifungal Surface Embedding Liposomal Amphotericin B Through a Mussel Adhesive-Inspired Coating Strategy.

Microbial colonization of urinary catheters remains a serious problem for medicine as it often leads to biofilm formation and infection. Among the approaches reported to deal with this problem, surfaces functionalization to render them with antimicrobial characteristics, comprises the most promising one. Most of these strategies, however, are designed to target bacterial biofilms, while fungal biofilms are much less taken into account. In real-life settings, fungi will be inevitably found in consortium with bacteria, especially in the field of biomaterials. The development of antifungal coating strategies to be combined with antibacterial approaches will be pivotal for the fight of biomaterial-associated infections. The main goal of the present study was, therefore, to engineer an effective strategy for the immobilization of liposomal amphotericin B (LAmB) on polydimethylsiloxane (PDMS) surfaces to prevent Candida albicans colonization. Immobilization was performed using a two-step mussel-inspired coating strategy, in which PDMS is first immersed in dopamine solution. Its polymerization results in the deposition of a thin adherent film, called polydopamine (pDA), which allowed the incorporation of LAmB, afterwards. Different concentrations of LAmB were screened in order to obtain a contact-killing surface with no release of LAmB. Surface characterization confirmed the polymerization of dopamine and further functionalization with LAmB yielded surfaces with less roughness and more hydrophilic features. The proposed coating strategy rendered the surfaces of PDMS with the ability to prevent the attachment of C. albicans and kill the adherent cells, without toxicity toward mammalian cells. Overall results showed that LAmB immobilization on a surface retained its antifungal activity and reduced toxicity, holding therefore a great potential to be applied for the design of urinary catheters. Since the sessile communities commonly found associated to these devices exhibit a polymicrobial nature, the next challenge will be to co-immobilize LAmB with antibacterial agents to prevent the establishment of catheter-associated urinary tract infections (CAUTI).

The Fate of Osteoblast-Like MG-63 Cells on Pre-Infected Bactericidal Nanostructured Titanium Surfaces.

Biomaterials that have been newly implanted inside the body are the substratum targets for a “race for the surface”, in which bacterial cells compete against eukaryotic cells for the opportunity to colonize the surface. A victory by the former often results in biomaterial-associated infections, which can be a serious threat to patient health and can undermine the function and performance of the implant. Moreover, bacteria can often have a ‘head start’ if implant contamination has taken place either prior to or during the surgery. Current prevention and treatment strategies often rely on systemic antibiotic therapies, which are becoming increasingly ineffective due to a growing prevalence of antibiotic-resistant bacteria. Nanostructured surfaces that kill bacteria by physically rupturing bacterial cells upon contact have recently emerged as a promising solution for the mitigation of bacterial colonization of implants. Furthermore, these nanoscale features have been shown to enhance the adhesion and proliferation of eukaryotic cells, which is a key to, for example, the successful osseointegration of load-bearing titanium implants. The bactericidal activity and biocompatibility of such nanostructured surfaces are often, however, examined separately, and it is not clear to what extent bacterial cell-surface interactions would affect the subsequent outcomes of host-cell attachment and osseointegration processes. In this study, we investigated the ability of bactericidal nanostructured titanium surfaces to support the attachment and growth of osteoblast-like MG-63 human osteosarcoma cells, despite them having been pre-infected with pathogenic bacteria. MG-63 is a commonly used osteoblastic model to study bone cell viability, adhesion, and proliferation on the surfaces of load-bearing biomaterials, such as titanium. The nanostructured titanium surfaces used here were observed to kill the pathogenic bacteria, whilst simultaneously enhancing the growth of MG-63 cells in vitro when compared to that occurring on sterile, flat titanium surfaces. These results provide further evidence in support of nanostructured bactericidal surfaces being used as a strategy to help eukaryotic cells win the “race for the surface” against bacterial cells on implant materials.

Fabrication of silicon nanopillar arrays by electron beam lithography and reactive ion etching for advanced bacterial adhesion studies

Within this work we demonstrate the fabrication of silicon nanopillar arrays for advanced cell/surface interaction studies and the results of the bacterial interaction of Escherichia coli with such highly ordered nanostructures. By combination of Electron Beam Lithography and Reactive Ion Etching a powerful and highly precise method for the fabrication of nanopillars with different diameters in the sub 100 nm region and high aspect ratios is available. The fabrication method allows building highly ordered nanotopographies which can help to increase the understanding of cell/substrate interaction. The biological results indicate that the adhesion of E. coli correlates to the available discrete adhesion bond points on top of the pillars and additionally that the cells align with the nanostructures to maximize their contact to the surface. The research of such structures will lead to the development of novel materials which might reduce biomaterial associated infections.

A Zebrafish Embryo Model for In Vivo Visualization and Intravital Analysis of Biomaterial-associated Staphylococcus aureus Infection.

Biomaterial-associated infection (BAI) is a major cause of the failure of biomaterials/medical devices. Staphylococcus aureus is one of the major pathogens in BAI. Current experimental BAI mammalian animal models such as mouse models are costly and time-consuming, and therefore not suitable for high throughput analysis. Thus, novel animal models as complementary systems for investigating BAI in vivo are desired. In the present study, we aimed to develop a zebrafish embryo model for in vivo visualization and intravital analysis of bacterial infection in the presence of biomaterials based on fluorescence microscopy. In addition, the provoked macrophage response was studied. To this end, we used fluorescent protein-expressing S. aureus and transgenic zebrafish embryos expressing fluorescent proteins in their macrophages and developed a procedure to inject bacteria alone or together with microspheres into the muscle tissue of embryos. To monitor bacterial infection progression in live embryos over time, we devised a simple but reliable method of microscopic scoring of fluorescent bacteria. The results from microscopic scoring showed that all embryos with more than 20 colony-forming units (CFU) of bacteria yielded a positive fluorescent signal of bacteria. To study the potential effects of biomaterials on infection, we determined the CFU numbers of S. aureus with and without 10 µm polystyrene microspheres (PS10) as model biomaterials in the embryos. Moreover, we used the ObjectJ project file "Zebrafish-Immunotest" operating in ImageJ to quantify the fluorescence intensity of S. aureus infection with and without PS10 over time. Results from both methods showed higher numbers of S. aureus in infected embryos with microspheres than in embryos without microspheres, indicating an increased infection susceptibility in the presence of the biomaterial. Thus, the present study shows the potential of the zebrafish embryo model to study BAI with the methods developed here.

Strategically prolonged release of multiple antibacterial components from a thin film coating for synergistic effects against Staphylococcus aureus infections.

Biomaterial-associated infections (BAIs) remain a major challenge in clinical surgery because they can potentially cause serious disabilities in patients. This study investigated the use of a multilayer coating technology that can co-deliver two therapeutic components, gentamicin and OP-145 peptide, to treat Staphylococcus aureus effectively. A biocompatible and biodegradable thin film was produced via layer-by-layer assembly using an antibacterial peptide and gentamicin. The thin film was systematically characterized, showing controllable features such as thickness, transparency, cargo loading, and cargo release. In vitro tests showed that the thin film has fewer toxicity problems than soluble cargos; compared to cargos in a soluble form, the thin film has minor impacts on mammalian cells' metabolism. Additionally, the antibacterial cargos assembled on the thin film can effectively inhibit the formation of biofilms and show effective in vitro antibacterial potency. In vivo studies illustrated that the thin film can inhibit the progression of S. aureus in a mouse model, indicating the effectiveness of the thin film structure in the clinic. This study demonstrates that a thin film composed of gentamicin and OP-145 could be employed to prevent BAIs in clinical surgery.

An antibiofilm coating of 5-aryl-2-aminoimidazole covalently attached to a titanium surface.

Biofilms, especially those formed by Staphylococcus aureus, play a key role in the development of orthopedic implant infections. Eradication of these infections is challenging due to the elevated tolerance of biofilm cells against antimicrobial agents. In this study, we developed an antibiofilm coating consisting of 5-(4-bromophenyl)-N-cyclopentyl-1-octyl-1H-imidazol-2-amine, designated as LC0024, covalently bound to a titanium implant surface (LC0024-Ti). We showed in vitro that the LC0024-Ti surface reduces biofilm formation of S. aureus in a specific manner without reducing the planktonic cells above the biofilm, as evaluated by plate counting and fluorescence microscopy. The advantage of compounds that only inhibit biofilm formation without affecting the viability of the planktonic cells, is that reduced development of bacterial resistance is expected. To determine the antibiofilm activity of LC0024-Ti surfaces in vivo, a biomaterial-associated murine infection model was used. The results indicated a significant reduction in S. aureus biofilm formation (up to 96%) on the LC0024-Ti substrates compared to pristine titanium controls. Additionally, we found that the LC0024-Ti substrates did not affect the attachment and proliferation of human cells involved in osseointegration and bone repair. In summary, our results emphasize the clinical potential of covalent coatings of LC0024 on titanium implant surfaces to reduce the risk of orthopedic implant infections. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1908-1919, 2019.

Intraphagolysosomal conditions predispose to Staphylococcus epidermidis small colony variants persistence in macrophages.

Staphylococcus epidermidis small colony variants can survive inside macrophages and their survival has been proposed as a pivotal process in the pathogenesis of biomaterial associated infections. In the present study the intracellular location of clinical isolates of SCV and parental wild type strains inside macrophages was determined. Furthermore, the effect of IFN-γ and rapamycin on the level of SCV/WT as well as lysosomes colocalisation and iNOS induction in THP-activated macrophages in response to WT and SCV strains of Staphylococcus epidermidis were examined. It was demonstrated that SCV strain of S. epidermidis can survive and persist inside macrophages and its intracellular survival is supported by the induction of phagosomal acidification. The ability to reduce the high proportion of LysoTracker positive SCV containing phagosomes was exclusively found when IFN-γ was used. The findings suggest that IFN-γ mediates SCV killing via two distinct mechanisms, phagosome alkalisation and an increased iNOS synthesis, so the cytokine may control S. epidermidis WT and SCV infection in macrophages. Staphylococcus epidermidis SCV is a less potent stimulus of iNOS than the WT strain and the feature may help SCV to persist in hostile environment of macrophages. Rapamycin treatment did not influence the iNOS synthesis but reduced the percentage of both bacterial strains within acidic organelles. However, the percentage of SCV within LysoTracker positive organelles, even though reduced comparing to non-primed cells, was higher than in the WT strain indicating that Staphylococcus epidermidis possesses unique metabolic features allowing SCV to survive within macrophages.

Antibiofilm elastin-like polypeptide coatings: functionality, stability, and selectivity

Antimicrobial peptides (AMPs) are currently receiving interest as an alternative to conventional antibiotics to treat biomaterial-associated infection. However, the inherent instability of such peptides often limits their efficacy in intended clinical applications. Covalent immobilization of AMPs to surfaces is one strategy to increase the long-term stability and minimize the toxicity. In this work, an antimicrobial peptide, RRPRPRPRPWWWW-NH2 (RRP9W4N), was used to modify elastin-like polypeptide (ELP) surface coatings containing cell-adhesive peptide domains (RGD) using covalent chemistry. The AMP retained its antibacterial activity against Staphylococcus epidermidis, Staphylococcus aureus, and Pseudomonas aeruginosa when covalently bonded to ELP surfaces. Simultaneously, the AMP functionalization had insignificant effect on the viability, function, and differentiation of human osteosarcoma MG63 cells and human mesenchymal stem cells (hMSCs). Furthermore, stability of the immobilized AMP in human blood serum was investigated, and the results suggested that the AMP preserved its antibacterial activity up to 24 h. Combined, the results show that covalently attached AMPs onto RGD-containing ELP are an excellent candidate as an antimicrobial coating for medical devices. Statement of SignificanceBiomaterial associated infection, caused by adherent biofilm, is usually difficult to treat. There is a high demand for new materials and treatments to decrease the infection rates, especially with increasing threats concerning resistant bacteria. Formation of biofilms on medical devices lowers the bacteria susceptibility towards traditional antibiotics and also circumvent our immune system often resulting in revisional surgery and extensive use of antibiotics. One promising strategy is to develop surfaces having low bacterial attractiveness or bacterial killing properties, but still retaining the main function of the device. In this study, we have developed an implant coating that demonstrates a high antimicrobial effect and at the same time showing no negative affect on human cells.

Antibacterial Surface Coating for Bone Scaffolds Based on the Dark Catalytic Effect of Titanium Dioxide.

Biomaterials which promote tissue integration and resist microbial colonisation are required in bone tissue engineering to prevent biomaterial-associated infections. Surface modification of established materials for bone tissue engineering, such as TiO2, have emerged as promising anti-infective strategies. Interestingly, the antibacterial activity of TiO2 in the form of particles can be enhanced by combining it with H2O2, even in the absence of irradiation. However, it remains unknown whether TiO2 surfaces elicit a similar effect. In this study, the antibacterial effect of porous TiO2 scaffolds generated by the catalytic decomposition of H2O2 in the absence of light (dark catalysis) was investigated. Porous ceramic foams were fabricated and sol-gel coated for high catalytic activity. Degradation of methylene blue in the presence of 3% H2O2 increased by 80% for the sol-gel-coated surfaces. The degradation kinetics indicate that intermediate free radicals that form at the liquid-TiO2 interface are responsible for the oxidative behavior of the surface. TiO2 surfaces were further pretreated with 30% H2O2 for prolonged oxidative behavior. The biological response toward such surfaces was assessed in vitro. S. epidermidis biofilms formed on modified surfaces showed reduced viability compared to nonmodified surfaces. Further, the same surface modification showed no cytotoxic effects on MC3T3 preosteoblasts. However, the results from the conducted genotoxicity assay were inconclusive, and further studies are needed to exclude ROS-mediated DNA damage. To conclude, this study provides evidence that a simple surface modification based on the dark catalytic effect of TiO2 can be used to create antibacterial surface properties for ceramic bone scaffolds.

Monitoring local delivery of vancomycin from gelatin nanospheres in zebrafish larvae.

BackgroundInfections such as biomaterial-associated infection and osteomyelitis are often associated with intracellular survival of bacteria (eg, Staphylococcus aureus). Treatment of these infections remains a major challenge due to the low intracellular efficacy of many antibiotics. Therefore, local delivery systems are urgently required to improve the therapeutic efficacy of antibiotics by enabling their intracellular delivery.PurposeTo assess the potential of gelatin nanospheres as carriers for local delivery of vancomycin into macrophages of zebrafish larvae in vivo and into THP-1-derived macrophages in vitro using fluorescence microscopy.Materials and methodsFluorescently labeled gelatin nanospheres were prepared and injected into transgenic zebrafish larvae with fluorescent macrophages. Both the biodistribution of gelatin nanospheres in zebrafish larvae and the co-localization of vancomycin-loaded gelatin nanospheres with zebrafish macrophages in vivo and uptake by THP-1-derived macrophages in vitro were studied. In addition, the effect of treatment with vancomycin-loaded gelatin nanospheres on survival of S. aureus-infected zebrafish larvae was investigated.ResultsInternalization of vancomycin-loaded gelatin nanospheres by macrophages was observed qualitatively both in vivo and in vitro. Systemically delivered vancomycin, on the other hand, was hardly internalized by macrophages without the use of gelatin nanospheres. Treatment with a single dose of vancomycin-loaded gelatin nanospheres delayed the mortality of S. aureus-infected zebrafish larvae, indicating the improved therapeutic efficacy of vancomycin against (intracellular) S. aureus infection in vivo.ConclusionThe present study demonstrates that gelatin nanospheres can be used to facilitate local and intracellular delivery of vancomycin.

Antimicrobial peptide modification of biomaterials using supramolecular additives.

ABSTRACTBiomaterials based on non‐active polymers functionalized with antimicrobial agents by covalent modification or mixing are currently regarded as high potential solutions to prevent biomaterial associated infections that are major causes of biomedical device failure. Herewith a strategy is proposed in which antimicrobial materials are prepared by simply mixing‐and‐matching of ureido‐pyrimidinone (UPy) based supramolecular polymers with antimicrobial peptides (AMPs) modified with the same UPy‐moiety. The N‐terminus of the AMPs was coupled in solution to an UPy‐carboxylic acid synthon resulting in formation of a new amidic bond. The UPy‐functionalization of the AMPs did not affect their secondary structure, as proved by circular dichroism spectroscopy. The antimicrobial activity of the UPy‐AMPs in solution was also retained. In addition, the incorporation of UPy‐AMPs into an UPy‐polymer was stable and the final material was biocompatible. The addition of 4 mol % of UPy‐AMPs in the UPy‐polymer material protected against colonization by Escherichia coli, and methicillin‐sensitive and ‐resistant strains of Staphylococcus aureus. This modular approach enables a stable but dynamic incorporation of the antimicrobial agents, allowing at the same time for the possibility to change the nature of the polymer, as well as the use of AMPs with different activity spectra. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1926–1934

Unveiling the fate of adhering bacteria to antimicrobial surfaces: expression of resistance-associated genes and macrophage-mediated phagocytosis

Since most antibacterial coatings reported to fight biomaterial-associated infections (BAI) fail in completely preventing bacterial colonization, it is crucial to know the impact of that small fraction of adhered bacteria in BAI recrudescence. This study aims to understand the fate of Staphylococcus aureus able to adhere to an antimicrobial coating previously developed, in terms of potential development of bacterial resistance and their macrophage-mediated phagocytosis. Antimicrobial coating comprised the co-immobilization of Palm peptide and DNase I onto polydimethylsiloxane. Expression of genes associated to resistance and virulence mechanisms showed that cells in contact with antimicrobial surfaces for a long period of 30 days, exhibit genes equally or less expressed, as compared to cells recovered from control surfaces. Recovered cells also exhibit the same susceptibility patterns, which strengthens the evidence of no resistance development. Remarkably, cells adhered to modified surfaces shows a reduced metabolic activity upon vancomycin treatment unlike the cells found on control surfaces, which can be identified as a clinical opportunity for prophylactically administration after implant surgery. Furthermore, results highlight that functionalization of PDMS with Palm and DNase I should not compromise the action of host immune cells. The overall results reinforce the potential of this antimicrobial strategy to fight BAI.