Influence of creep phenomenon and surface roughness on the adhesion of Xenopus laevis eggs to different substrates

The adhesion of fertilized and nonfertilized Xenopus laevis eggs to various surfaces differing in texture, roughness, and chemical composition was examined. Techniques regularly used in the fields of coating and adhesives were adopted. The stresses for the disconnection of eggs from different surfaces were evaluated by a custom-made apparatus, which disconnects the eggs by applying a regulated water pressure. The strength of adhesion depends, among others, on the roughness of the surfaces. A commercial roughness tester evaluated this parameter. It was observed that the rougher the surface, the better the adhesion between the egg and the surface. Maximal adhesion between the eggs and rough surfaces was detected 1 h after the first contact. For smooth surfaces (hydrogels), such a maximum was recognized only after 24 h had elapsed. In addition to the character of the surfaces, the creep of the jelly coat with time significantly influenced the strength of adhesion. The creep of the jelly coat was also dependent on the degree of swelling. The swelling of an egg's jelly coat during the first 8.5 h of the process was monitored by weight. Major changes in weight were observed during the first 100 min. After longer periods, the weight reached an asymptotic level. Incorporating polyvinyl pyrrolidone (PVP) into the medium eliminates the adhesion and stickiness of Xenopus eggs in the laboratory. Tensile bond stress and peel techniques were used to estimate the egg's adhesion to several surfaces. These tests revealed that the first contact between the egg and substrate resulted in a stronger adhesion than when the egg was disconnected and re-glued (re-adhered) to the same surface. Adhesion to natural surfaces (pebbles and Nimephea leaves) was better than to synthetic smooth surfaces. The shorter the distance between the female toad and any surface, the better the adhesion of the eggs.