Bacterial interaction forces in adhesion dynamics

Wanneer interactiekrachten tussen bacteriën en oppervlakken bepaald worden, hangen deze erg af van de gebruikte meettechniek. De mechanismen die verantwoordelijk zijn voor deze verschillen zijn echter nog niet duidelijk. Om hier meer inzicht in te krijgen, zijn in dit onderzoek interactiekrachten tussen bacteriën en oppervlakken bepaald met de parallelle plaat flow kamer (PPFC) en met behulp van Atomic Force Microscopy (AFM). In niet geforceerde hechting, zoals in de PPFC, zijn krachten om bacteriën van het oppervlak af te spoelen minder sterk dan bij het hydrofobe oppervlak. Tevens vindt er op het hydrofiele oppervlak veel meer adsorptie en desorptie van bacteriën plaats en kunnen bacteriën over het oppervlak rollen. Op het hydrofobe oppervlak is aanhechting een stuk minder dynamisch en is het rollen van bacteriën over het oppervlak nagenoeg afwezig. De verklaring hiervoor is dat beide testoppervlakken een andere capaciteit hebben tot het vormen van waterstofbruggen met de omringende, waterige, vloeistof waarin hechting plaatsvindt. Het hydrofiele oppervlak is goed in staat tot het vormen van waterstofbruggen met de vloeistof. Hierdoor ontstaat bij dit oppervlak een barrière van watermoleculen, waardoor aanhechting van bacteriën aan het hydrofiele oppervlak minder gunstig is. In experimenten met AFM wordt het contact tussen bacteriën en testoppervlak geforceerd. Hierdoor wordt de eerder genoemde barrière mechanisch weggedrukt en wordt de sterkte van interactie bepaald door de vorming van waterstofbruggen tussen bacteriën en testoppervlak. Omdat deze waterstofbruggen wel met het hydrofiele oppervlak, maar niet met het hydrofobe oppervlak gevormd kunnen worden, geeft AFM als resultaat dat hechting aan het hydrofiele oppervlak gunstiger is. Geconcludeerd kan worden dat waterstofbruggen een belangrijke rol spelen in bacteriële hechting aan oppervlakken. Echter, welke waterstofbruggen (tussen bacteriën en vloeistof, tussen oppervlak en vloeistof en tussen bacteriën en oppervlak) domineren bij het meten van interactiekrachten, is afhankelijk van de gebruikte meettechniek. ENGELSE VERSIE: Several methods are available to measure the interaction forces between bacteria and surfaces. However, each technique provides a separate class of interaction force. The mechanisms responsible for these differences are still not fully understood. The aim of this research was to gain more insight in these mechanisms. To meet this aim, interaction forces were determined using a parallel plate flow chamber (PPFC) and Atomic Force Microscopy (AFM). In the PPFC, adhesion takes place like it would in a natural environment. Using this device, it was found that the hydrodynamic forces to stimulate detachment were less strong on the hydrophilic surface as compared to the hydrophobic one. Furthermore, on the hydrophilic surface many more adsorption and desorption events take place and is it possible that bacteria roll over the surface. On the hydrophobic surface, adhesion is less dynamic and also the rolling mode of adhesion was virtually absent. This is caused by the hydrogen bonding capacity of the substrata. Opposite to the hydrophobic surface, the hydrophilic substratum can easily form hydrogen bonds with the surrounding water, creating a “water barrier” and making this substratum surface less favorable for bacterial adhesion. In AFM experiments, contact between bacteria and surfaces is forced and the aforementioned barrier is mechanically overcome. As a result, the formation of hydrogen bonds between bacteria and surfaces is the dominant adhesion mechanism. On a hydrophilic surface the bonds can be formed easily but on a hydrophobic surface it is not possible. This explains why bacterial interaction forces, measured with AFM, are stronger on a hydrophilic surface as compared to the hydrophobic one. In conclusion, hydrogen bonds are important in bacterial adhesion to substratum surfaces, but the used technique determines which hydrogen bonds dominate (i.e. between liquid and substratum, liquid and bacteria and bacteria and substratum).

Een vergelijking van hydraulische en elektrisch aangedreven spuitgietmachines : wanneer is produceren met een elektrische machine voordeliger?

Wanneer is produceren met een elektrische machine voordeliger? Dit artikel beschrijft de resultaten van een onderzoek op het gebied van procesoptimalisatie en duurzaamheid in de kunststofverwerkende industrie

Powdercoating on Plastic : effects of gas plasma on adhesion

Effects of plasma surface treatments on morphology and surface chemistry: Improving adhesion of powder coating systems to polypropylene substrates

Lange-duur eigenschappen van composieten : literatuurstudie

In deze literatuurstudie wordt onderzocht wat er bekend is over het lange-duurgedrag van thermoharde composieten. Omdat voor deze materialen in de meeste gevallen polyester als matrix wordt gebruikt is de studie hierop toegespitst

Forces involved in bacterial adhesion to hydrophilic and hydrophobic surfaces

Using a parallel-plate flow chamber, the hydrodynamic shear forces to prevent bacterial adhesion (F(prev)) and to detach adhering bacteria (F(det)) were evaluated for hydrophilic glass, hydrophobic, dimethyldichlorosilane (DDS)-coated glass and six different bacterial strains, in order to test the following three hypotheses. 1. A strong hydrodynamic shear force to prevent adhesion relates to a strong hydrodynamic shear force to detach an adhering organism. 2. A weak hydrodynamic shear force to detach adhering bacteria implies that more bacteria will be stimulated to detach by passing an air-liquid interface (an air bubble) through the flow chamber. 3. DLVO (Derjaguin, Landau, Verwey, Overbeek) interactions determine the characteristic hydrodynamic shear forces to prevent adhesion and to detach adhering micro-organisms as well as the detachment induced by a passing air-liquid interface. F(prev) varied from 0.03 to 0.70 pN, while F(det) varied from 0.31 to over 19.64 pN, suggesting that after initial contact, strengthening of the bond occurs. Generally, it was more difficult to detach bacteria from DIDS-coated glass than from hydrophilic glass, which was confirmed by air bubble detachment studies. Calculated attractive forces based on the DLVO theory (F(DLVO)) towards the secondary interaction minimum were higher on glass than on DIDS-coated glass. In general, all three hypotheses had to be rejected, showing that it is important to distinguish between forces acting parallel (hydrodynamic shear) and perpendicular (DLVO, air-liquid interface passages) to the substratum surface

Bond-Strengthening in Staphylococcal Adhesion to Hydrophilic and Hydrophobic Surfaces Using Atomic Force Microscopy

Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface hydrophobicity on initial adhesion forces for the four different S. epidermidis strains was observed. Over time, strengthening of the adhesion forces was virtually absent on hydrophobic dimethyldichlorosilane (DDS)-coated glass, although in a few cases multiple adhesion peaks developed in the retract curves. Bond-strengthening on hydrophilic glass occurred within 5-35 s to maximum adhesion forces of -1.9 +/- 0.7 nN and was concurrent with the development of multiple adhesion peaks upon retract. Poisson analysis of the multiple adhesion peaks allowed separation of contributions of hydrogen bonding from other nonspecific interaction forces and revealed a force contribution of -0.8 nN for hydrogen bonding and +0.3 nN for other nonspecific interaction forces. Time-dependent bacterial adhesion forces were comparable for all four staphylococcal strains. It is concluded that, on DDS-coated glass, the hydrophobic effect causes instantaneous adhesion, while strengthening of the bonds on hydrophilic glass is dominated by noninstantaneous hydrogen bond formation

Melt spinning and fibre winding of Trimethylenecarbonate (TMC)-based polymers for tissue engineering small diameter blood vessels

The use of melt spinning and fiber winding of trimethylenecarbonate (TMC)-based polymers for tissue engineering small diameter blood vessels was investigated in order to overcome the problems and poor performance of artificial blood vessels. For the study, porous tubular scaffolds were obtained by heating PTMC to a temperature of 220°C. It was found that it is possible to produce tubular TMC-based scaffolds by means of melt spinning. It was also found that combining the synthetic scaffold with collagen further enhances the structural integrity in time permitting to obtain a scaffold that resembles the mechanical properties of native blood vessels