Non-specific adhesion on biomaterial surfaces driven by small amounts of protein adsorption

This work explores how long-range non-specific interactions, resulting from small amounts of adsorbed fibrinogen, potentially influence bioadhesion. Such non-specific interactions between protein adsorbed on a biomaterial and approaching cells or bacteria may complement or even dominate ligand–receptor mating. This work considers situations where the biomaterial surface and the approaching model cells (micron-scale silica particles) exhibit strong electrostatic repulsion, as may be the case in diagnostics and lab-on-chip applications. We report that adsorbed fibrinogen levels near 0.5 mg/m² produce non-specific fouling. For underlying surfaces that are less fundamentally repulsive, smaller amounts of adsorbed fibrinogen would have a similar effect. Additionally, it was observed that particle adhesion engages sharply and only above a threshold loading of fibrinogen on the collector. Also, in the range of ionic strength, I, below about 0.05 M, increases in I reduce the fibrinogen needed for microparticle capture, due to screening of electrostatic repulsions. Surprisingly, however, ionic strengths of 0.15 M reduce fibrinogen adsorption altogether. This observation opposes expectations based on DLVO arguments, pointing to localized electrostatic attractions and hydration effects to drive silica–fibrinogen adhesion. These behaviors are benchmarked against microparticle binding on silica surfaces carrying small amounts of a polycation, to provide insight into the role of electrostatics in fibrinogen-driven non-specific adhesion.     

An adaptive channel equalizer using self-adaptation bacterial foraging optimization

In this paper we propose a self-adaptation bacterial foraging optimization (SA-BFO) approach for an adaptive channel equalizer in which the weights of the equalizer are optimized to minimize the mean square error (MSE) and bit error rate (BER). The adaptive channel equalizer at the receiver removes or reduces the effects of inter symbol interference (ISI) and noise. Tests demonstrate that the proposed adaptive channel equalizer provides better convergence speed and minimal MSE and BER compared to a BFO and a normalized least mean square (NLMS) based equalizer.     

Extraction and partial characterisation of antioxidant pigment produced by Chryseobacterium sp. kr6

Pigments synthesised by Chryseobacterium sp. kr6 growing on feather waste were extracted and characterised. The pigment extract was characterised by KOH test, UV–vis, CIELAB colour system, HPLC-DAD-MS, FTIR and its antioxidant capacity was evaluated. A positive bathochromic shift was observed when kr6 colonies or pigment extracts were subjected to alkaline solution (20% KOH) and a λ_max at 450 nm was detected for acetone extracts, although no typical fine structure of carotenoids was detected in the electomagnetic spectra. The HPLC profile of the extracted pigment showed that the compound has three different peaks with λ_max near 450 nm. The FTIR analysis shows some principal functional groups from a flexirubin-like molecule. The pigmented compound also presents antioxidant activity evaluated by the scavenging of the ABTS radical.     

Steady-state fluorescence and phosphorescence spectroscopic studies of bacterial luciferase tryptophan mutants

Bacterial luciferase, which catalyzes the bioluminescence reaction in luminous bacteria, consists of two nonidentical polypeptides, and . Eight mutants of luciferase with each of the tryptophans replaced by tyrosine were generated by site-directed mutagenesis and purified to homogeneity. The steady-state tryptophan fluorescence and low-temperature phosphorescence spectroscopic properties of these mutants were characterized. In some instances, mutation of only a single tryptophan residue resulted in large spectral changes. The tryptophan residues conserved in both the and the subunits exhibited distinct fluorescence emission properties, suggesting that these tryptophans have different local enviroments. The low-temperature phosphorescence data suggest that the tryptophans conserved in bot the and the subunits are not located at the subunit interface and/or involved in subunit interactions. The differences in the spectral properties of the mutants have provided useful information on the local environment of the individual tryptophan residues as well as on the quaternary structure of the protein.     

Structural Features and Properties of Bacterial Cellulose Produced in Agitated Culture

The structure and some properties of bacterial cellulose produced in agitated culture were studied. Scanning electron microscopy revealed that there was almost no difference between reticulated structures of bacterial cellulose fibrils produced in agitated culture and in static culture. Nevertheless, bacterial cellulose produced in agitated culture exhibited microstuctural changes, namely, a low degree of polymerization and a low crystallinity index. A CP/MAS ¹³C NMR analysis revealed that the cellulose I content of the cellulose produced in agitated culture was lower than that of the cellulose produced in static culture. The bacterial cellulose produced in agitated culture had a lower Young's modulus of sheet, a higher water holding capacity and a higher suspension viscosity in the disintegrated form than that produced in static culture.     

The role of nutrient presence on the adhesion kinetics of Burkholderia cepacia G4g and ENV435g

The adhesion kinetics of Burkholderia cepacia G4g and ENV435g have been investigated in a radial stagnation point flow (RSPF) system under well-controlled hydrodynamics and solution chemistry. The sensitivity of adhesion behavior to nutrient condition was also examined. Supplementary cell characterization techniques were conducted to evaluate the viability, hydrophobicity, electrophoretic mobility, size, and charge density of cells grown in both nutrient rich Luria broth (LB) and nutrient poor basal salts medium (BSM). Comparable adhesion kinetics were observed for the wild-type (G4g) and mutant (ENV435g) grown in the same medium; however, the attachment efficiency increased with the level of nutrient presence for both cell types by approximately 60%. Nutrient condition altered deposition due to its impact on the surface charge characteristics and size of the cells. Adhesion behavior was consistent with expectations based on classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory for colloidal interactions, as the adhesion efficiency increased with ionic strength. However, the results also suggest the involvement of non-DLVO type interactions that influence cell adhesion. Systematic experimentation with B. cepacia in the RSPF system demonstrated that the ENV435g mutant is not “adhesion deficient”; rather, adhesion for both the G4g and ENV435g was a function of the nutrient condition and resulting cell surface chemistry.     

万古霉素修饰磁性纳米粒子的制备及其细菌分离功能

制备了万古霉素修饰的磁性纳米粒子, 并研究了其对金黄色葡萄球菌(S.aureus)和大肠杆菌(E.coli BL21)的选择性吸附分离特性.     

On demand release of ionic silver from gold-silver alloy nanoparticles: fundamental antibacterial mechanisms study

Synthesis and biomedical research of bimetallic gold-silver nanoparticles (Au–Ag NPs) have gained much attention due to their unique properties. Antibacterial mechanism of gold-silver nanoparticles is a current topic of interest in nanomedicine engineering. We used three routes in the synthesis of Au–Ag NPs alloy: i) Co-reduction of [HOOC-4-C₆H₄NN]AuCl₄/AgNO₃, ii) Seeding of AuNPs-COOH/AgNO₃ and iii) immobilization of AgNPs over the parent AuNPs-COOH. Two mild reducing agents, NaBH₄ and 9-BBN (9-borabicyclo(3.3.1)nonane), were used. Colloidal alloy nanoparticles structure was confirmed using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The particles reduced using NaBH₄ were larger (~20 nm) than those synthesized using 9-BBN (<10 nm). The synthesized nanoparticles showed high stability under notoriously leaching conditions of chloride-containing electrolytes. Moreover, we studied the Au–Ag NPs antibacterial activity against the growth of Gram-negative Escherichia coli ATCC strain 25922 and Gram-positive Staphylococcus aureus ATCC strain 29213. The antibacterial mechanisms were evaluated by studying the time-dependent generation of reactive oxygen species (ROS). A major destruction of the bacterial cell wall and leakage of cell components were observed by scanning electron microscopy (SEM), which is clearly visible towards E. coli more than S. aureus bacterial strain. The destruction of the bacterial cell wall was further confirmed by detecting the DNA leakage using gel electrophoresis. The synergistic effect of gold enhanced the antibacterial properties, however, with low cytotoxicity to human dermal fibroblast cells. This study deals with the important aspects of time-dependent mechanisms of the antibacterial action of Au–Ag NPs since the leaching out of Ag ion is slow compared to AgNPs. The Au–Ag NPs alloy efficiently tackles microbial activity that can be controlled to minimize cytotoxicity and thus opens their future applications as antibacterial agents.     

Synthesis of Erythrocyte Nanodiscs for Bacterial Toxin Neutralization

Nanodiscs are a compelling nanomedicine platform due to their ultrasmall size and distinct disc shape. Current nanodisc formulations are made primarily with synthetic lipid bilayers and proteins. Here, we report a cellular nanodisc made with human red blood cell (RBC) membrane (denoted “RBC-ND”) and show its effective neutralization against bacterial toxins. In vitro, RBC-ND neutralizes the hemolytic activity and cytotoxicity caused by purified α-toxin or complex whole secreted proteins (wSP) from methicillin-resistant Staphylococcus aureus bacteria. In vivo, RBC-ND confers significant survival benefits for mice intoxicated with α-toxin or wSP in both therapeutic and prevention regimens. Moreover, RBC-ND shows good biocompatibility and biosafety in vivo. Overall, RBC-ND distinguishes itself by inheriting the biological functions of the source cell membrane for bioactivity. The design strategy of RBC-ND can be generalized to other types of cell membranes for broad applications.