A polycationic antimicrobial and biocompatible hydrogel with microbe membrane suctioning ability

Despite advanced sterilization and aseptic techniques, infections associated with medical implants have not been eradicated. Most present coatings cannot simultaneously fulfil the requirements of antibacterial and antifungal activity as well as biocompatibility and reusability. Here, we report an antimicrobial hydrogel based on dimethyldecylammonium chitosan (with high quaternization)-graft-poly(ethylene glycol) methacrylate (DMDC-Q-g-EM) and poly(ethylene glycol) diacrylate, which has excellent antimicrobial efficacy against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Fusarium solani. The proposed mechanism of the antimicrobial activity of the polycationic hydrogel is by attraction of sections of anionic microbial membrane into the internal nanopores of the hydrogel, like an 'anion sponge', leading to microbial membrane disruption and then microbe death. We have also demonstrated a thin uniform adherent coating of the hydrogel by simple ultraviolet immobilization. An animal study shows that DMDC-Q-g-EM hydrogel coating is biocompatible with rabbit conjunctiva and has no toxicity to the epithelial cells or the underlying stroma.     

Green antimicrobial coating based on quaternised chitosan/organic montmorillonite/Ag NPs nanocomposites

This work is aimed at developing a green antimicrobial coating. First, a green antimicrobial agent, quaternised chitosan (QCS)/organic montmorillonite (OMMT)/silver nanoparticles (Ag NPs) (QOMA) nanocomposite was fabricated through an environmental-friendly one-step approach. Morphological and structural characteristics of QOMA were investigated, and good antimicrobial activity was proved. QOMA was then incorporated into powder coating formulations to form a homogeneous coating on steel plates, which was studied by scanning electron images. Besides, the physical and mechanical properties as well as the antimicrobial performances of the coatings were discussed. The results showed that the addition of QOMA imparted good antimicrobial capacity to the powder coating, but did not affect its physical and mechanical properties. The coatings were able to effectively inactivate Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus) and fungi (Aspergillus niger, Penicillium funiculosum, Chaetomium globasum, Paecilomyces varioti, Asp. terreus and Aureobasidium pullulans). Our findings demonstrate the possibilities of green antimicrobial coating containing QOMA for practical applications in medical devices, domestic appliances and other solid surfaces concerning bacterial infection and contamination.     

Oberflächenmodifizierung von Titan zur Verbesserung der Grenzflächenverträglichkeit

Surface Modification of Titanium for Improvement of the Interfacial Biocompatibility We report the CVD‐polymerisation of amino‐functionalized [2,2]‐paracyclophane for polymer coating and functionalization of titanium surfaces. Additionally, the functionalization was carried out by silanization with 3‐aminopropyl‐triethoxysilane. The generated amino‐groups were used for covalent immobilization of bioactive substances to stimulate the adhesion and growth of osteoblasts. As bioactive substances the pentapeptide GRGDS and the growth factor BMP‐2 were chosen. The covalent bonding was achieved by activation with hexamethylene diisocyanate. Each modification step was characterized by X‐ray‐photoelectron‐spectroscopy (XPS), atomic force microscopy (AFM) and contact angle measurements. The covalent bonding of the bioactive substances was proven by radiolabelling and surface‐MALDI‐ToF‐MS. In vitro‐biocompatibility tests with primary, human osteoblasts demonstrated the improved cell adhesion and spreading on the bioactive modified titanium surfaces.     

Nanoporous alkoxy-derived titanium oxide coating: a reactive overlayer for functionalizing titanium surface

Effective immobilization of bioactive substances such as adhesive proteins, synthetic peptides and growth factors on metallic substrates is required for a number of medical applications. In the present work, evidence is presented to show that an alkoxy-derived nano-porous titanium oxide coating, synthesized electrochemically on titanium in methanolic electrolytes, may act as an effective interface for functionalizing a titanium surface. It is demonstrated that nanoporous oxide coatings could facilitate fast diffusion of small organic molecules within the oxide network and form strong chemical bonds with the functional groups of these molecules at room temperature. Fourier transformed–infrared spectroscopy was used to investigate the nature of the interfacial interactions between the oxide network and a range of molecules containing COOH, OH, NH2, C=O and phosphoric acid functional groups. The results indicate that the nanometre-sized oxide clusters within the coating may play an essential role in effective immobilization of organic molecules by providing numerous binding sites for chemisorption of these species. The surface-derivatized oxide coating may provide a solid phase for the subsequent attachment of a broad range of biochemically active molecules on the titanium surface. © 1998 Chapman & Hall     

Antibacterial coatings on haemodialysis catheters by photochemical deposition of silver nanoparticles

Antibacterial coatings on catheters for acute dialysis were obtained by an innovative and patented silver deposition technique based on the photo-reduction of the silver solution on the surface of catheter, with consequent formation of antibacterial silver nanoparticles. Aim of this work is the structural and morphological characterization of these medical devices in order to analyze the distribution and the size of clusters on the polymeric surface, and to verify the antibacterial capability of the devices treated by this technique against bacterial proliferation. The structure and morphology of the silver nanoparticles were investigated by using scanning and transmission electron microscopy. The antimicrobial capability of the catheters after silver deposition was confirmed by antibacterial tests with Escherichia coli. Both scanning electron microscopy analysis and antibacterial tests were performed also after washing catheters for 30 days in deionized water at 37°C, relating these data to thermogravimetric analysis and to energy dispersive spectroscopy, in order to check the resistance of coating and its antimicrobial capability after the maximum time of life of these devices.     

Microfluidic bacterial traps for simultaneous fluorescence and atomic force microscopy

The atomic force microscope has become an established research tool for imaging microorganisms with unprecedented resolution.However,its use in microbiology has been limited by the difficulty of proper bacterial immobilization.Here,we have developed a microfluidic device that solves the issue of bacterial immobilization for atomic force microscopy under physiological conditions.Our device is able to rapidly immobilize bacteria in well-defined positions and subsequently release the cells for quick sample exchange.The developed device also allows simultaneous fluorescence analysis to assess the bacterial viability during atomic force microscope imaging.We demonstrated the potential of our approach for the immobilization of rod-shaped Escherichia coli and Bacillus subtilis.Using our device,we observed buffer-dependent morphological changes of the bacterial envelope mediated by the antimicrobial peptide CM15.Our approach to bacterial immobilization makes sample preparation much simpler and more reliable,thereby accelerating atomic force microscopy studies at the single-cell level.     

Huge increase of therapeutic window at a bioactive silver/titania nanocomposite coating surface compared to solution

A silver containing coating used in the human body, e.g., on an implant should be both effectively antimicrobial and non-cytotoxic to human cells. It is generally believed that the biologic effect originates from silver ions released from the coating. Nanocomposites with well controlled Ag filling factor were prepared by co-sputtering, and the silver surface concentration and the silver release were determined by XPS and ICP-MS, respectively. Here we show that only a small therapeutic window exists for dissolved silver but the therapeutic window is largely increased at the surface. While the toxicity observed for mammalian cells in contact with the bioactive Ag/TiO₂ nanocomposite surface and for silver ions in solution is rather similar the antimicrobial activity is drastically enhanced at the surface. A model is proposed to explain the strong increase of the antimicrobial activity at the surface. The present results not only question well-established tests for antimicrobial activity but they are also important for the design of antimicrobial coatings, e.g., for biomedical devices.     

Silicon-substituted hydroxyapatite composite coating by using vacuum-plasma spraying and its interaction with human serum albumin

The incorporation of silicon can improve the bioactivity of hydroxyapatite (HA). Silicon-substituted HA (Ca₁₀(PO₄)_6−x (SiO₄) _x (OH)_2−x , Si-HA) composite coatings on a bioactive titanium substrate were prepared by using a vacuum-plasma spraying method. The surface structure was characterized by using XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated and XRD patterns showed that Ti/Si-HA coatings were similar to patterns seen for HA. The only different XRD pattern was a slight trend toward a smaller angle direction with an increase in the molar ratio of silicon. FTIR spectra showed that the most notable effect of silicon substitution was that –OH group decreased as the silicon content increased. XRD and EDS elemental analysis indicated that the content of silicon in the coating was consistent with the silicon-substituted hydroxyapatite used in spraying. A bioactive TiO₂ coating was formed on an etched surface of Ti, and the etching might improve the bond strength of the coatings. The interaction of the Ti/Si-HA coating with human serum albumin (HSA) was much greater than that of the Ti/HA coating. This might suggest that the incorporation of silicon in HA can lead to significant improvements in the bioactive performance of HA.     

In vitro antimicrobial properties of silver–polysaccharide coatings on porous fiber-reinforced composites for bone implants

Biostable fiber-reinforced composite (FRC) implants prepared from bisphenol-A-dimethacrylate and triethyleneglycoldimethacrylate resin reinforced with E-glass fibers have been successfully used in cranial reconstructions in 15 patients. Recently, porous FRC structures were suggested as potential implant materials. Compared with smooth surface, porous surface allows implant incorporation via bone ingrowth, but is also a subject to bacterial attachment. Non-cytotoxic silver–polysaccharide nanocomposite coatings may provide a way to decrease the risk of bacterial contamination of porous FRC structures. This study is focused on the in vitro characterization of the effect porosity on the antimicrobial efficiency of the coatings against Staphylococcus aureus and Pseudomonas aeruginosa by a series of microbiological tests (initial adhesion, antimicrobial efficacy, and biofilm formation). Characterization included confocal laser scanning microscopy and scanning electron microscopy. The effect of porosity on the initial attachment of S. aureus was pronounced, but in the case of P. aeruginosa the effect was negligible. There were no significant effects of the coatings on the initial bacterial attachment. In the antimicrobial efficacy test, the coatings were potent against both strains regardless of the sample morphology. In the biofilm tests, there were no clear effects either of morphology or of the coating. Further coating development is foreseen to achieve a longer-term antimicrobial effect to inhibiting bacterial implant colonization.     

Hybrid fibers containing protein-templated nanomaterials and biologically active components as antibacterial materials

The persistent and emerging threat of bacterial infections now extends to many real world scenarios that drive a requirement for antimicrobial fabrics. Such functionalized textiles may find application in protective wear for medical and military personnel and provide functional wound dressings that reduce infection in situ. In this work, biomimetic enzyme entrapment and protein-directed nanomaterials synthesis is combined and applied to the antimicrobial functionalization of fabrics. A multi-faceted approach was adopted to address the fabrication of textiles with Ag nanoparticles, bactericidal proteins and mineral coatings that may contribute (singularly or in unison) to provide antimicrobial activity. Fibroin coordinated silver ions, for example, were chemically reduced to generate silver nanoparticles within the interior of silk fabric fibers. Silk textiles were further functionalized by the surface adsorption of the bactericidal enzyme lysozyme. The exposure of such lysozyme-conjugated fabrics to mineralizing solutions enabled the self-directed immobilization of the enzyme in a subsequent protective matrix of amorphous silica or titania. Silk-immobilized lysozyme was also utilized to adsorb nanocrystalline TiO₂ from solution onto the fabric surface; a subsequent layer of enzyme served to entrap the ceramic particles under a layer of biomimetically mineralized titania. The multiplicity of antimicrobial activities derived from this approach thereby combined; 1) the hydrolytic activity of lysozyme (demonstrated by radial diffusion assays), 2) the bactericidal properties of silver nanoparticles (demonstrated effective against Staphylococcus aureus, Escherichia coli, and silver resistant E. coli) and 3) the photocatalytic bactericidal response of TiO₂ under UV illumination.     

食品抗菌包装及其在鲜肉包装中的应用

重点对食品抗菌包装的5 种类型(在包装中添加含有挥发性抗菌成分的小袋或衬垫;直接合并抗菌剂到聚合物包装材料中;在聚合物表面涂布或吸附抗菌剂;通过离子键或共价键将抗菌剂固定到聚合物中;使用本身具有抗菌作用的包装材料)及其各自的特点进行了综述,最后介绍了抗菌包装在易腐食品鲜肉中的具体应用及实际抗菌保鲜效果,并对抗菌食品包装的发展趋势进行了展望。     

CVD-Beschichtung mit einem funktionalisierten Poly-p-xylylen – ein universell anwendbares Verfahren zur Ausrüstung von Medizinimplantaten mit Wirkstoffen

CVD-polymerization of a functionalized poly( p -xylylene) – a generally applicable method for the immobilization of drugs on medical implants We report a generally applicable polymer coating that allows one-step coating and functionalization of implant materials as stainless steel, platinium or Nitinol alloys. Coating is achieved by CVD-polymerisation of a functionalized [2.2]-paracyclophane. Poly(amino-p-xylylene)-co-poly(p-xylylene) interfaces include free functional groups that were used for immobilization of the thrombin inhibitor r-hirudin. These bio-active surfaces might contribute to the development of stents with reduced restenosis.     

Sand dollar skeleton as templates for bacterial cellulose coating and apatite precipitation

In this work, the skeleton of Sand Dollar (Clypeaster subdepressus) was coated by bacterial cellulose (BC) produced by Gluconacetobacter hansenii and subsequently coated with calcium phosphate (apatite). The skeleton of sand dollar is composed of magnesium calcite ((Ca,Mg)CO₃) and exhibits an hierarchically porous structure with interconnected porosity. After coating, the small-sized pores were partially covered by cellulose microfibrils, where apatite particles were homogeneously deposited. The pore geometry of sand dollar is adequate for bone regeneration, allows cell migration through its large cells and permit vascularization through the small pores. Moreover, BC/apatite coating offers a bioactive surface for cell adhesion.     

Surface characteristics and antibacterial activity of a silver-doped carbon monolith

Abstract

A carbon monolith with a silver coating was prepared and its antimicrobial behaviour in a flow system was examined. The functional groups on the surface of the carbon monolith were determined by temperature-programmed desorption and Boehm's method, and the point of zero charge was determined by mass titration. The specific surface area was examined by N₂ adsorption using the Brunauer, Emmett and Teller (BET) method. As a test for the surface activity, the deposition of silver from an aqueous solution of a silver salt was used. The morphology and structure of the silver coatings were characterized by scanning electron microscopy and x-ray diffraction. The resistance to the attrition of the silver deposited on the carbon monolith was tested. The antimicrobial activity of the carbon monolith with a silver coating was determined using standard microbiological methods. Carbon monolith samples with a silver coating showed good antimicrobial activity against Escherichia coli, Staphylococcus aureus and Candida albicans, and are therefore suitable for water purification, particularly as personal disposable water filters with a limited capacity.     

Safe and Effective Ag Nanoparticles Immobilized Antimicrobial NanoNonwovens

Silver nanoparticles (AgNPs) with large surface‐to‐volume ratio have been widely studied as a valuable material for their strong antimicrobial effect. However, the practical applications of AgNPs in health care and water purification are often hampered by the concern of their toxicity and possibility of introduction of secondary pollution. Here, we present a novel strategy to produce a safe and effective antimicrobial nanononwoven material by immobilizing AgNPs on a rigid polymer nanofibrous matrix through simple co‐electrospinning of pre‐prepaired AgNPs and polystyrene (PS). Distribution of the AgNPs on the surface of PS fibers was achieved by tuning fiber diameters during electrospinning. Atomic force microscopy (AFM) analysis revealed that the AgNPs distributed at the fiber surface were still covered by a layer of polymer, which inhibited their antimicrobial activity. UV/ozone treatment was thus employed to degrade the polymer coating without loosening the AgNPs, resulting in an active antimicrobial nonwoven against Gram‐positive Staphylococcus xylosus. The mechanism based on cellular uptake of silver ions via close contact to the surface of AgNPs is proposed. The novel nanononwoven retains the enhanced antimicrobial activities from nanofeatured AgNPs without detectable AgNPs leaching, which holds great potential for safe and recyclable use.     

Staphylococcus aureus adhesion to different treated titanium surfaces

Staphylococcus aureus is a major pathogen, associated with medical-device related infections. Converting biomaterial surfaces into non-interactive surfaces requires a specific surface/interface design. One approach is to polish the surface, and a second is to coat the surface with an antimicrobial or protein resistant coating. This study showed that polishing a titanium surface or coating titanium with various treatments that decreased the surface's coefficient of friction, had no significant effect on minimising S. aureus adhesion to these surfaces under static conditions in comparison to standard medical grade titanium. The cell promoting coating, TAST, was found to increase the S. aureus density on its surface as expected. The only coating that significantly decreased the density of adhering S. aureus was the titanium surface coated with sodium hyaluronate. Thus such a coating could have potential use as a coating for ostoesynthesis, orthopaedic or dental implants.     

Bio-inspired porous SiC ceramics loaded with vancomycin for preventing MRSA infections

Implant-related infections are a serious complication in orthopaedic and dental surgery resulting in prolonged hospitalization, high medical costs and patient mortality. The development of porous implants loaded with antibiotics may enable a local delivery for preventing surface colonization and biofilm formation. A new generation of bio-derived porous ceramic material that mimics hierarchical structures from Nature was evaluated. Silicon carbide ceramics derived from Sapelli wood (bioSiC) were obtained by pyrolysis of Entandrophragma cylindricum wood followed by infiltration with molten silicon. This process renders disks that keep the bimodal pore size distribution (3 and 85 μm) of the original material and are highly cytocompatible (BALB/3T3 cell line). The ability of the bio-ceramic to load the antimicrobial agent vancomycin was evaluated by immersion of disks in drug solutions covering a wide range of concentrations. The disks released at pH 7.4 an important amount of drug during the first 2 h (up to 11 mg/g bioSiC) followed by a slower release, which is related to the presence of macro- and mesopores. Finally, the anti-biofilm effect against methicillin resistant Staphylococcus aureus was assessed and a considerable reduction (92%) of the bacterial film was observed. Results highlight the bioSiC potential as component of medicated medical devices.     

厚朴提取物抗菌包装纸对奶酪货架寿命的影响

目的以厚朴提取物为抑菌成分研制抗菌包装纸,并研究其对奶酪保鲜效果的影响。方法采用超声辅助提取法提取厚朴中的抑菌成分,利用高效液相色谱仪对其进行定性分析,并通过福林酚比色法测试总酚含量。采用涂布和浸渍这2种方法分别制备涂布抗菌纸和浸渍抗菌纸,并对其物理性能进行测试,将2种抗菌包装纸应用于奶酪保鲜,测试其感官品质、菌落总数和过氧化值。结果厚朴提取物中含有厚朴酚、和厚朴酚,总酚含量为47.4 mg/g。涂布抗菌纸的平滑度、定量、抗张强度、撕裂度均优于原纸,仅吸水性出现降低现象。与原纸相比,浸渍抗菌纸和涂布抗菌纸对于保持奶酪的感官品质以及抑制其菌落总数和过氧化值的上升具有明显作用(P<0.05),其中质量分数为10%的厚朴提取物涂布抗菌纸对奶酪保鲜效果最优,与原纸相比可延长其货架寿命约14 d。结论厚朴提取物涂布抗菌纸对奶酪具有较好的保鲜效果,可以明显延长其货架寿命。     

Antimicrobial activity of UV-irradiated nylon film for packaging applications

Antimicrobial packaging could enhance food storage life and safety. An antimicrobial moiety that is permanently bound to the polymer surface and does not leach has particular appeal. The use of 193 nm UV irradiation to convert amide groups on the surface of nylon to amines having antimicrobial activity has been reported previously. We prepared materials accordingly and explored their mode of action and activity against pathogens. Three food related bacterial strains, Staphylococcus aureus, Pseudomonas fluorescens and Enterococcus faecalis were exposed to antimicrobial film in 0.2 M sodium phosphate buffer (pH 7.0). Samples were held shaken at 100 r.p.m. in a 25°C incubator. The antimicrobial film was effective in reduction of microbial concentration in the bulk fluid for all food-related bacteria tested. The effectiveness was dependent on the bacterial strain. Adsorption of bacterial cells diminished the effectiveness of amine groups. Experimental results indicate that the decrease in concentration of bacterial cells in bulk fluid is more likely to be the bactericidal action than adsorption of live cells. © 1998 John Wiley & Sons, Ltd.     

Fluorapatite-mullite glass sputter coated Ti6Al4V for biomedical applications

A number of bioactive ceramics have been researched since the development of Bioglass in the 1970s. Fluorapatite mullite has been developed from the dental glass-ceramics used for more general hard tissue replacement. Being brittle in nature, glass-ceramics are currently used mainly as coatings. This paper shows that fluorapatite glass LG112 can be used as a sputtered glass coating on roughened surfaces of Ti6Al4V for possible future use for medical implants. An AFM was used to measure the roughness of the surface before and after coating to determine the change in the topography due to the coating process as this greatly affects cell attachment. The sputter coating partially filled in the artificially roughened surface, changing the prepared topography. Osteoblasts have been successfully grown on the surface of these coatings, showing biocompatibility with bone tissue and therefore potential use in hard tissue repair.