'Lerarenopleiding moet knop omzetten'

Interview met Lector Beroepsonderwijs Elly de Bruijn Hoogleraar en lector Elly de Bruijn maakt zich sterk voor een andere pedagogische en didactische aanpak in het (v)mbo. Waarom? Tweederde van de jongeren in ons land volgt een opleiding aan een (v)mbo-school, terwijl veel docenten nog traditioneel opgeleid worden in algemeen vormende vakken

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

INTERFACIAL SELF-ASSEMBLY OF A SCHIZOPHYLLUM-COMMUNE HYDROPHOBIN INTO AN INSOLUBLE AMPHIPATHIC PROTEIN MEMBRANE DEPENDS ON SURFACE HYDROPHOBICITY

Hydrophobins are small secreted fungal proteins rich in hydrophobic amino acids with a characteristic hydropathy pattern and conserved location of eight cysteine residues. It was previously shown that purified SC3p hydrophobin of Schizophyllum commune self-assembles at hydrophilic/hydrophobic interfaces into a sodium dodecyl sulphate (SDS)insoluble amphipathic protein membrane typified at the hydrophobic side by a mosaic of parallel rodlets, similar to those seen at the hydrophobic surface of aerial hyphae of this fungus. Here we show the assembly of SC3p at the interface between water and a continuous hydrophobicity gradient surface obtained by coating glass with dichlorodimethylsilane and displaying contact angles of water ranging from 20 degrees up to 107 degrees. The amount of assembled SC3p (defined as SC3p becoming insoluble in hot SDS) sharply increased in the region of the gradient surface displaying advancing water contact angles between 60 degrees and 90 degrees and then more slowly towards the 107 degrees region, i.e. the hydrophobic end. Here, the adsorbed SC3p decreases the advancing water contact angle from 107 degrees on the bare gradient surface to 60 degrees on the protein coated surface (to 39 degrees before extraction with SDS). The SDS-insoluble SC3p was removed by trifluoroacetic acid, which is known to dissociate assembled hydrophobins, hence restoring the wettability characteristics close to those of the original hydrophobicity gradient surface. Since fungal hyphae firmly attach to natural surfaces which are often hydrophobic, these results suggest a role for hydrophobins in fungal pathogenicity and other fungal host interactions

Growth of fibroblasts and endothelial cells on wettability gradient surfaces

The growth, spreading, and shape of human skin fibroblasts (PK 84) and human umbilical cord endothelial cells on dichlorodimethylsilane (DDS) and dimethyloctadecylchlorosilane (DOGS) gradient surfaces were investigated in the presence of serum proteins. Gradient surfaces were prepared on glass using the diffusion technique. Fibroblasts grew well on the hydrophobic and hydrophilic sides of both types of gradient surfaces, but endothelial cells were far more sensitive to changes in wettability. Endothelial cell growth was fully inhibited on the hydrophobic side of the DDS gradient surface, but not on the hydrophobic side of the DOGS gradient surface. In contrast, spreading of both fibroblasts and endothelial cells during growth was approximately uniform over the length of DDS and DOGS gradient surfaces. By comparison with studies involving only adhesion and spreading of cells in the absence of growth, it is suggested that exchange interactions between adsorbed serum proteins and endogeneous adhesive proteins are responsible for cell spreading during growth on the hydrophobic sides of the gradient surfaces. Furthermore, endothelial cells may be able to find hydrophilic footholds through adsorbed DOGS layers needed for their growth, that may occur less on more confluently adsorbed DDS layers. (C) 1997 Academic Press