van der Henny C. Mei

Surface roughness, porosity and wettability of gentamicin-loaded bone cements and their antibiotic release.

In this study, the release of gentamicin as a function of time was measured for six different gentamicin-loaded bone cements and related with the surface roughness, porosity and wettability of the cements. Initial release rates varied little between the six bone cements (CMW1, CMW3, CMW Endurance, CMW 2000, Palacos, and Palamed) and ranged from 8.6 to 14.1 microg/cm2/h. The total amounts of gentamicin released after 1 week varied between 4.0 and 5.3% of the total amount of antibiotic incorporated for the CMW cements and was 8.4% for Palacos. Palamed released after 1 week significantly more of the gentamicin incorporated (17.0%). The wettability of all cements was similar (water contact angles between 70 and 80 degrees), but the surface roughness and the porosity of the cements varied markedly. Initial release rates increased with surface roughness, although the correlation coefficient was low (0.64), while total amounts released increased linearly (correlation coefficient 0.97) with the bulk porosity of the cements. Consequently, it can be concluded that the release kinetics of gentamicin from bone cements is controlled by a combination of surface roughness and porosity.

Influence of substratum wettability on the strength of adhesion of human fibroblasts

To determine the strength of adhesion and the detachment mechanisms of fibroblasts from substrata with different wettability, the behaviour of adhered cells was studied in a parallel-plate flow chamber during exposure to shear. Adhered cells were observed in situ, i.e. in the flow chamber, by phase-contrast microscope and images were analysed semiautomatically. Detachment was found to be dependent both on shear stress and time, although a critical shear stress can be found below which no detachment occurs. On all substrata, cells round up before detachment and are approximately spherical immediately before detachment. The strength of adhesion calculated ranged from 0.6-3.5 x 10(-10) N per cell on FEP-Teflon (the least wettable material included) to 9.4 x 10(-9) N per cell for glass (the most wettable). Ease of detachment seemed to decrease with increasing wettability. However, cells reacted more strongly with tissue culture polystyrene (TCPS) than expected on the basis of its wettability, probably due to surface chemistry.

Interference in initial adhesion of uropathogenic bacteria and yeasts to silicone rubber by a Lactobacillus acidophilus biosurfactant

Summary The ability of the Lactobacillus acidophilus RC14 biosurfactant ‘surlactin’ to inhibit the initial adhesion of various uropathogenic bacteria and two yeast strains to silicone rubber was investigated in a parallel-plate flow chamber in filter-sterilised pooled human urine. A parallel-plate flow chamber with a silicone rubber bottom plate was filled with a 1.0 mg/ml biosurfactant solution for adsorption overnight (18 h). Subsequently, the adhesion of the bacterial or yeast cells from a urine suspension under low flow (shear rate 15 s-1) was followed in situ by automated image analysis. Control tests were with untreated silicone rubber. Initial deposition rates and numbers of adhering cells after 4 h of flow were determined. Surlactin layers caused a marked inhibition of the initial deposition rates and adhesion numbers after 4 h for the majority of the bacteria (11 of 15 strains tested) and this inhibition was particularly effective against Enterococcus faecalis, Escherichia coli and Staphylococcus epidermidis. Although the initial deposition rates of the two Candida albicans strains were reduced by c. 50% in comparison with the controls, the numbers of yeast cells adhering after 4 h were similar.

Initial adhesion and surface growth of Staphylococcus epidermidis and Pseudomonas aeruginosa on biomedical polymers

The infection risk of biomaterials implants varies between different materials and is determined by an interplay of adhesion and surface growth of the infecting organisms. In this study, we compared initial adhesion and surface growth of Staphylococcus epidermidis HBH(2) 102 and Pseudomonas aeruginosa AK1 on poly(dimethylsiloxane), Teflon, polyethylene, polypropylene, polyurethane, poly(ethylene terephthalate), poly(methyl methacrylate), and glass. Initial adhesion was measured in situ in a parallel plate flow chamber with microorganisms suspended in phosphate-buffered saline, while subsequent surface growth was followed in full and in 20 times diluted growth medium. Initial adhesion of both bacterial strains was similar to all biomaterials. In full growth medium, generation times of surface growing S. epidermidis ranged from 17 to 38 min with no relation to wettability, while in diluted growth medium generation times increased from 44 to 98 min with increasing surface wettability. For P. aeruginosa no influence of surface wettability on generation times was observed, but generation times increased with decreasing desorption rates, maximal generation times being 47 min and minimal values down to 30 min. Generally, generation times of adhering bacteria were shorter than of planktonic bacteria. In conclusion, surface growth of initially adhering bacteria is influenced by biomaterials surface properties to a greater extent than initial adhesion.

Preparation and characterization of chemical gradient surfaces and their application for the study of cellular interaction phenomena

Chemical gradient surfaces are surfaces with a gradually changing chemistry along their length which is responsible for a position bound variation in physical properties, most notably, the wettability. In this review, methods to prepare (palladium deposition, diffusion technique, density gradient method, gas diffusion technique, radio frequency plasma and corona discharge, poly(vinylene carbonate) hydrolysis) and characterize gradient surfaces are summarized. The number of techniques available to characterize gradient surfaces is effectively limited to the Wilhelmy plate method for wettability characterization, because the spatial resolution of more chemically oriented techniques, like infrared spectroscopy or X-ray photoelectron spectroscopy is still too limited, apart from their poor surface sensitivity as compared to contact angles. Gradient surfaces are especially useful to study biological interactions along their lengths, as the influence of the entire wettability spectrum upon protein adsorption or cellular interactions can be obtained in one single experiment, therewith minimizing biological variations. In general, proteins adsorb more extensively on the hydrophobic ends of gradient surfaces, which is accompanied by a lesser spreading and adhesion of tissue cells than on the hydrophilic ends of gradient surfaces. An influence of the specific chemistry constituting the gradient, upon protein adsorption as well as on cellular interactions always remains, indicating that biological interactions at an interface are not solely governed by wettability.

A COMPARISON OF VARIOUS METHODS TO DETERMINE HYDROPHOBIC PROPERTIES OF STREPTOCOCCAL CELL-SURFACES

Abstract In order to determine whether various methods which are commonly applied to determine the hydrophobicity of bacterial cell surfaces yield similar results, the hydrophobicity of a range of oral streptococcal isolates was measured using various methods including adsorption to hexadecane, hydrophobic interaction chromatography, salt-aggregation and contact angle measurements. In addition the zela potential and the adhesion to saliva-coated hydroxyapatite were determined. To compare the results of the different methods, linear and rank correlation coefficients were calculated. The resulting correlations were weak when applied to the whole range of strains even in those cases where the tests are expected to probe the same surface characteristics. However, generally good correlations were obtained when a set of strains was examined which were derived from a single parent strain and which only differed in defined surface structures. Accordingly it must be concluded from the methods applied here, that if is not possible to define the surface ‘hydrophobicity’ of a bacterium other than on a comparative level with closely related strains. No clear correlation was found between any hydrophobicity test and the adhesion to saliva-coated hydroxyapatite.

Microbial cell surface hydrophobicity. The involvement of electrostatic interactions in microbial adhesion to hydrocarbons (MATH)

Microbial adhesion to hydrocarbons (MATH) is the most commonly used method to determine microbial cell surface hydrophobicity. Since, however, the assay is based on adhesion, it is questionable whether the results reflect only the cell surface hydrophobicity or an interplay of hydrophobicity and surface charge properties. In order to demonstrate the involvement of electrostatic interactions in MATH, hydrophobicities by MATH (kinetic mode) were measured in 10 mM potassium phosphate solutions at different pHs and compared with the zeta potentials of the microorganisms and of hexadecane droplets in the same solution. Two oral, microbial strains were involved: Streptococcus salivarius HB (a hydrophobic strain by MATH) and Streptococcus salivarius HB-C12 (a hydrophilic strain by MATH). The initial removal rates of S. salivarius HB-C12 by hexadecane were zero over the entire pH range (pH 2-pH 9) and its zeta potentials were negative in this pH range. S. salivarius HB, however, had an isoelectric point (IEP) at pH 3.2 and accordingly a positive zeta potential below IEP. Correspondingly, the initial removal rates found for this strain were high (2.6 min-1) below and around IEP and much lower (almost-equal-to 0.5 min-1) above IEP. Surprisingly, the hexadecane droplets also had highly negative zeta potentials above pH 4 and appeared uncharged in the pH range 2-3. Taking the product of the bacterial zeta(b) and hexadecane zeta(h) zeta potentials as a measure for electrostatic interactions, it was observed that the measured hydrophobicity of S. salivarius HB, but not of the hydrophilic strain S. salivarius HB-C12, depended on electrostatic interactions as well. The highest removal rates by hexadecane were found in the absence of electrostatic interactions, i.e. in the pH range close to the IEPs of the interacting particles. It is concluded that, in general, MATH does not measure cell surface hydrophobicity but an interplay of hydrophobicity and electrostatic interactions. The involvement of electrostatic interactions in MATH can be reduced by performing the test under ionic conditions in which either the cells or the hydrocarbon droplets (or both) are uncharged.

X-ray photoelectron spectroscopy for the study of microbial cell surfaces

X-ray photoelectron spectroscopy (XPS) is well known for the characterisation of material surfaces, but at first glance, is an unexpected technique to study the composition of microbial cell surfaces. Despite the fact that intimate contact between materials and microbial cell surfaces occurs in many situations, such as on oil-platforms, in water pipelines and bioreactors or on biomedical implants, XPS studies on the composition of microbial cell surfaces are less known, but equally relevant. In this review, microbial sample preparations are discussed, as well as relationships between microbial compositions using XPS. Biochemical and physical properties, such as microbial cell surface charge and hydrophobicity are also discussed. A reference guide, giving the overall cell surface composition of 210 strains determined by XPS, as collected from the literature is given. Hierarchical cluster analysis on these data reveals interesting new insights on staphylococcal cell surfaces, as well as a distinction between staphylococci, yeasts and other microorganisms. It is concluded that XPS on microbial cell surfaces yields useful information, complementing other biochemical and physical cell surface characterisations.

Interference in adhesion of bacteria and yeasts isolated from explanted voice prostheses to silicone rubber by rhamnolipid biosurfactants.

Aims:  The effects and extent of adhesion of four different bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed rhamnolipid biosurfactant layer obtained from Pseudomonasaeruginosa DS10‐129 was studied.

A Comparison of Thermodynamic Approaches To Predict the Adhesion of Dairy Microorganisms To Solid Substrata

AbstractFour different thermodynamic approaches were compared on their usefulness to predict correctly the adhesion of two fouling microorganisms from dairy processing to various solid substrata. The surface free energies of the interacting surfaces were derived from measured contact angles according to:1.The equation of state;2.The geometric-mean equation using dispersion and polar components neglecting spreading pressures;3.The geometric-mean equation using dispersion and polar components while accounting for spreading pressures; and4.The Lifshitz-van der Waals/Acid-Base approach. All approaches yielded similar surface free energies for the low energy surfaces. Application of approach 1 with different liquids did not give consistent values for the high surface free energy substrata. The dispersion or Lifshiftz-van der Waals components were nearly equal for approaches 2, 3, and 4; however, the polar or acid-base components differed greatly according to the approach followed. Approaches 1 and 2 correctly predicted that adhesion should occur, although the trend with respect to the various solid substrata was opposite the one experimentally observed, as was also the trend predicted by approach 4. Only approach 3 correctly predicted the observed bacterial adhesion with respect to the various solid substrata. In approach 3 and 4, adhesion was frequently found, despite a positive free energy of adhesion. This was attributed to either possible local attractive electrostatic interactions, inadequate weighing of surface free energy components in the calculation of free energies of adhesion, or to additional forces arising from structured interfacial water.