Correct use of the contact angle in the evaluation of the protective action induced from polymer coating on the stone.

The control of the protective efficacy obtained on the stone by treatments with polymers is commonly performed through the measure of the static contact angle as it is described by the norm UNI 10921. However this approach does not allow an easy interpretation of the results, because of the porosity and of the heterogeneity of the stone surface, which represent an obstacle to the analysis. Moreover the commonest interpretation of this technique can often bring to important errors. The measure of the static contact angle substantially corresponds to the measure of the so-called "advancing" contact angle and it allows only to verify if on the surface a hydrophobic material is present; unfortunately it cannot determine if the stone is effectively protected. Vice versa, both, the measure of the "true" equilibrium contact angle obtained through a new technique called VIECA, and the measure of the receding contact angle give more coherent parameters which better correlate with the data of absorption of water by capillarity. The equilibrium contact angle corresponds to an "average" description of the surface, the receding angle corresponds, by excess, to the condition of maximum penetration of the liquid by capillarity. From the knowledge of the equilibrium angle of the protective polymer and from the measure of the advancing and receding angles of the protected stone, it is certainly possible to determine what is the minimum polymer quantity to obtain an almost homogeneous stone protection.

Effects on interfacial properties and cell adhesion of surface modification by pectic hairy regions.

Polystyrene Petri dishes, aminated by a plasma deposition process, were surface modified by the covalent linking of two different enzymatically modified hairy regions (HRs) from pectin containing, for example, rhamnogalacturonan-I and xylogalacturonan structural elements. The two polysaccharide preparations share the same structural elements of apple pectin, but the relative amounts and lengths of the neutral side chains present differ. Surface analysis by X-ray photoelectron spectroscopy, contact angle measurement, and atomic force microscope (AFM) force-separation curves was used to characterize the effects on surface chemistry and interfacial forces of the surface modification process. Cell adhesion experiments using continuous L-929 fibroblasts and primary aortic smooth muscle cells were performed to evaluate the effect of the polysaccharide nature on cell adhesion. Results show that immobilization of the HR affects the interfacial field of forces and the cell behavior: "equilibrium" contact angles, obtained by a recently introduced vibrational approach, decrease after HR immobilization reaching a value close to 20 degrees . AFM force-separation curves show a more extended (or softer) interface in the case of the HR bearing longer side chains. Accordingly, depending on the HR preparation, cells shifted from spread morphology and adhesion behavior quantitatively comparable to that observed on conventional tissue culture polystyrene to rounded morphology and significantly lower adhesion. These data show that engineering of plant pectins can be a valuable tool to prepare novel and finely tuned polysaccharides having different chemico-physical and biological properties, to be used in the surface modification of medical devices and materials.