Simple microscopical measurement of contact angles on transparent substrates

Dynamic wettability of pHEMA-based hydrogel contact lenses

Standard methods of contact angle analysis include sessile drop, captive bubble and Wilhelmy plate techniques; however, these methodologies are not particularly well suited for assessing the wettability of the surfaces of formed hydrogel contact lenses. This paper describes two methodologies that are adaptations of previously described techniques. The maximum adherent force method is an adaptation of the dynamic Wilhelmy plate technique that allows the assessment of whole, finished contact lenses. The dynamic photographic method allows the simultaneous assessment of the front and back surfaces of strip samples for the assessment of advancing and receding contact angles. Lenses investigated were made from polyhydroxyethyl methacrylate, hydroxyethyl methacrylate/methacrylic acid and hydroxyethyl methacrylate/glycerol methacrylate. The lenses were manufactured by lathing, spin-casting or cast-moulding techniques. Overall, both techniques demonstrated few differences between the wettability of different lens materials and no differences between materials of the 'same' lens type but manufactured by different methods. These findings are consistent with the results of clinical studies, which have shown little difference between contact lens surface wettability in vivo, which may be due to the apparent natural surface wettability-enhancing properties of the pre-lens tear film.

Determination of binding strength and kinetics of binding initiation. A model study made on the adhesive properties of P388D1 macrophage-like cells

The adhesive properties of the mouse P388D1 macrophage-like line were explored. Cells were deposited in glass capillary tubes, and the kinetics of adhesion and spreading were studied. Binding involved the cell metabolism since it was decreased by cold, azide, or a divalent cation chelator. Glass-adherent cells were subjected to calibrated laminar shear flows with a highly viscous dextran solution. A tangential force of about 5 X 10(-3) dyn/cell was required to achieve substantial detachment. The duration of application of the shearing force strongly influenced cell-substrate separation when this was varied from 1-10 s. Further, this treatment resulted in marked cell deformation, with the appearance of an elongated shape. Hence, cell-substrate separation is a progressive process, and binding strength is expected to be influenced by cell deformability. The minimum time required for adhesion was also investigated by making cells adhere under flow conditions. The maximum flow rate compatible with adhesion was about 1000-fold lower than that required to detach glass-bound cells. A simple model was devised to provide a quantitative interpretation for the experimental results of kinetic studies. It is concluded that cell-to-glass adhesion required a cell-substrate contact longer than a few seconds. This first step of adhesion was rapidly followed by a large (about 1000-fold) increase of adhesion strength. It is therefore emphasized that adhesion is heavily dependent on the duration of cell-to-cell encounter, as well as the force used to remove so-called unbound cells.

T-cell-fibroblast hybridoma deformability and concanavalin A-induced agglutination

Cell adhesion influences many important immunological functions such as phagocytosis or T-cell-mediated cytotoxicity. Previous work suggested that the ease of inducing intercellular bonds (i.e. binding efficiency) and the difficulty to separate bound cells with mechanical forces (i.e. binding strength) might be parameters of different significances. The present report describes a study made on two T-lymphocyte/polyoma virus transformed fibroblast hybrid subclones (3D1c and 3D1n) with markedly different adhesive properties: indeed, 3D1c cells were at the same time more readily agglutinated with concanavalin A and more easily disagglutinated than 3D1n. In order to understand these differences, a systematic comparison of various properties of 3D1c and 3D1n cells was undertaken. The following parameters were studied: surface density of concanavalin A binding sites, surface electrostatic charge, hydrophobicity, fluorescence polarization measured on individual cells, and ability to spread on a flat substrate in response to volume or surface forces. It is concluded that cell deformability and/or spreading ability might be an important determinant of binding strength, but the factors governing binding efficiency remained incompletely understood. It is suggested that the methods described in the present report might help understanding differences between various tumor cell lines with different malignant potential.