Floating and Tether-Coupled Adhesion of Bacteria to Hydrophobic and Hydrophilic Surfaces.

Models for bacterial adhesion to substratum surfaces all include uncertainty with respect to the (ir)reversibility of adhesion. In a model, based on vibrations exhibited by adhering bacteria parallel to a surface, adhesion was described as a result of reversible binding of multiple bacterial tethers that detach from and successively reattach to a surface, eventually making bacterial adhesion irreversible. Here, we use total internal reflection microscopy to determine whether adhering bacteria also exhibit variations over time in their perpendicular distance above surfaces. Streptococci with fibrillar surface tethers showed perpendicular vibrations with amplitudes of around 5 nm, regardless of surface hydrophobicity. Adhering, nonfibrillated streptococci vibrated with amplitudes around 20 nm above a hydrophobic surface. Amplitudes did not depend on ionic strength for either strain. Calculations of bacterial energies from their distances above the surfaces using the Boltzman equation showed that bacteria with fibrillar tethers vibrated as a harmonic oscillator. The energy of bacteria without fibrillar tethers varied with distance in a comparable fashion as the DLVO (Derjaguin, Landau, Verwey, and Overbeek)-interaction energy. Distance variations above the surface over time of bacteria with fibrillar tethers are suggested to be governed by the harmonic oscillations, allowed by elasticity of the tethers, piercing through the potential energy barrier. Bacteria without fibrillar tethers "float" above a surface in the secondary energy minimum, with their perpendicular displacement restricted by their thermal energy and the width of the secondary minimum. The distinction between "tether-coupled" and "floating" adhesion is new, and may have implications for bacterial detachment strategies.

Women and Their Microbes: The Unexpected Friendship.

Communities of microbiota have been associated with numerous health outcomes, and while much emphasis has been placed on the gastrointestinal niche, there is growing interest in the microbiome specific for female reproductive health and the health of their offspring. The vaginal microbiome plays an essential role not only in health and dysbiosis, but also potentially in successful fertilization and healthy pregnancies. In addition, microbial communities have been isolated from formerly forbidden sterile niches such as the placenta, breast, uterus, and Fallopian tubes, strongly suggesting an additional microbial role in women's health. A combination of maternally linked prenatal, birth, and postnatal factors, together with environmental and medical interventions, influence early and later life through the microbiome. Here, we review the role of microbes in female health focusing on the vaginal tract and discuss how male and female reproductive microbiomes are intertwined with conception and how mother-child microbial transfer is a key determinant in infant health, and thus the next generation.

Elastic and viscous bond components in the adhesion of colloidal particles and fibrillated streptococci to QCM-D crystal surfaces with different hydrophobicities using Kelvin-Voigt and Maxwell models.

A quartz-crystal-microbalance with dissipation (QCM-D) can measure molecular mass adsorption as well as register adhesion of colloidal particles. However, analysis of the QCM-D output to quantitatively analyze adhesion of (bio)colloids to obtain viscoelastic bond properties is still a subject of debate. Here, we analyze the QCM-D output to analyze the bond between two hydrophilic streptococcal strains 91 nm long and without fibrillar surface appendages and micron-sized hydrophobic polystyrene particles on QCM-D crystal surfaces with different hydrophobicities, using the Kelvin-Voigt model and the Maxwell model. A Poisson distribution was implemented in order to determine the possible virtues of including polydispersity when fitting model parameters to the data. The quality of the fits did not indicate whether the Kelvin-Voigt or the Maxwell model is preferable and only polydispersity in spring-constants improved the fit for polystyrene particles. The Kelvin-Voigt and Maxwell models both yielded higher spring-constants for the bald streptococcus than for the fibrillated one. In both models, the drag coefficients increased for the bald streptococcus with the ratio of electron-donating over electron-accepting parameters of the crystal surface, while for the fibrillated strain the drag coefficient was similar on all crystal surfaces. Combined with the propensity of fibrillated streptococci to bind to the sensor crystal as a coupled-resonator above the crystal surface, this suggests that the drag experienced by resonator-coupled, hydrophilic particles is more influenced by the viscosity of the bulk water than by interfacial water adjacent to the crystal surface. Hydrophilic particles that lack a surface tether are mass-coupled just above the crystal surface and accordingly probe the drag due to the thin layer of interfacial water that is differently structured on hydrophobic and hydrophilic surfaces. Hydrophobic particles without a surface tether are also mass-coupled, but their drag coefficient decreases when the ratio of electron-donating over electron-accepting parameters increases, suggesting that hydrophobic particles experience less drag due to the structured water adjacent to the surface.

Quantification of the viscoelasticity of the bond of biotic and abiotic particles adhering to solid-liquid interfaces using a window-equipped quartz crystal microbalance with dissipation.

The quartz-crystal-microbalance-with-dissipation (QCM-D) has become a powerful tool for studying the bond viscoelasticity of biotic and abiotic colloidal particles adhering to substratum surfaces. A window-equipped QCM-D allows high-throughput analysis of the average bond viscoelasticity, measuring over 106 particles simultaneously in one single experiment. Other techniques require laborious analyses of individual particles. In this protocol, the quantitative derivation of the spring-constant and drag-coefficient of the bond between adhering colloidal particles and substratum surfaces using QCM-D is explained for bacteria and silica particles, using the particle-mass derived for validation. Bond viscoelasticity is calculated using a coupled resonator model, paying special attention to the protocol for mathematical fitting needed to obtain reliable quantitative output. Knowledge of the viscoelasticity of the bond between colloidal particles and substratum surfaces facilitates development of new strategies to detach adhering particles from or retain them on a surface.

Assembly of poly(dopamine)/poly(N-isopropylacrylamide) mixed films and their temperature-dependent interaction with proteins, liposomes, and cells.

Many biomedical applications benefit from responsive polymer coatings. The properties of poly(dopamine) (PDA) films can be affected by codepositing dopamine (DA) with the temperature-responsive polymer poly(N-isopropylacrylamide) (pNiPAAm). We characterize the film assembly at 24 and 39 °C using DA and aminated or carboxylated pNiPAAm by a quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray photoelectron spectroscopy, UV-vis, ellipsometry, and atomic force microscopy. It was found that pNiPAAm with both types of end groups are incorporated into the films. We then identified a temperature-dependent adsorption behavior of proteins and liposomes to these PDA and pNiPAAm containing coatings by QCM-D and optical microscopy. Finally, a difference in myoblast cell response was found when these cells were allowed to adhere to these coatings. Taken together, these fundamental findings considerably broaden the potential biomedical applications of PDA films due to the added temperature responsiveness.

Cell response to PEGylated poly(dopamine) coated liposomes considering shear stress.

BACKGROUND: Liposomes have gained immerse attention in the field of drug delivery as carriers of therapeutic molecules. Their modification with a polymer either to make them stealth (e.g. using PEG) and/or more stable (e.g. using poly(dopamine) (PDA)) is a crucial aspect to improve their performance e.g. the blood circulation time. Despite their potential, there are only a few commercialized liposome-based formulations for intravenous drug delivery. Hence, there is still considerable need to address the challenges involved in the design and characterization of liposomal therapeutics. In the latter case, it is of paramount importance to consider the dynamic in vivo environment, e.g. the interstitial fluidic pressure in tumors, blood flow, or bile flow in the liver. METHODS: The PEGylation of PDA films was characterized by quartz crystal microbalance with dissipation monitoring, and the optimized protocol was used to assemble PEGylated PDA coated liposomes (LPDA_PEG). Dynamic light scattering, a plate reader, a flow cytometer and a cytotoxicity assay were used to characterize the liposomes and quantify cellular association/uptake and cell viability in the presence and absence of shear stress after 30min and 4h. The immortalized skeletal mouse myoblast (C2C12) cell line was chosen as model cancer cells, and a hepatic cell line (HepG2) was selected due to their importance in nanosized drug carrier clearance from the system in the liver. RESULTS: The presence of hydrophilic cargo did not affect the PDA assembly process. In the absence of shear stress, there was no difference in cellular uptake/association of both PDA coated liposomes (LPDA) and LPDA_PEG for hepatocytes while myoblasts preferentially internalized/associated with LPDA. In the presence of shear stress, hepatocytes preferentially internalized/associated with LPDA after 30min, while there was only a significant difference for myoblasts after 4h. The cell viability remained unaffected in all cases. CONCLUSIONS: LPDA_PEG are a promising platform towards drug delivery. The nature of cells and fluidic flow are important factors to be considered in their characterization using cell cultures. GENERAL SIGNIFICANCE: These findings will contribute in the better understanding of polymer coated liposomes with cells. The importance of microfluidics in cell culture based characterization is demonstrated, and this will eventually affect the way advanced drug delivery vehicles are designed and characterized prior to animal experiments.

Myoblast cell interaction with polydopamine coated liposomes.

Liposomes are widely used, from biosensing to drug delivery. Their coating with polymers for stability and functionalization purposes further broadens their set of relevant properties. Poly(dopamine) (PDA), a eumelanin-like material deposited via the "self"-oxidative polymerization of dopamine at mildly basic pH, has attracted considerable interest in the past few years due to its simplicity, flexibility yet fascinating properties. Herein, we characterize the coating of different types of liposomes with PDA depending on the presence of oleoyldopamine in the lipid bilayer and the dopamine hydrochloride concentration. Further, the interaction of these coated liposomes in comparison to their uncoated counterparts with myoblast cells is assessed. Their uptake/association efficiency with these cells is determined. Further, their dose-dependent cytotoxicity with and without entrapped hydrophobic cargo (thiocoraline) is characterized. Taken together, the reported results demonstrate the potential of PDA coated liposomes as a tool in biomedical applications.

Polydopamine--a nature-inspired polymer coating for biomedical science.

Polymer coatings are of central importance for many biomedical applications. In the past few years, poly(dopamine) (PDA) has attracted considerable interest for various types of biomedical applications. This feature article outlines the basic chemistry and material science regarding PDA and discusses its successful application from coatings for interfacing with cells, to drug delivery and biosensing. Although many questions remain open, the primary aim of this feature article is to illustrate the advent of PDA on its way to become a popular polymer for bioengineering purposes.