From a conceptual point of view, natural fibers, woven as it should be, must of necessity be made of a uniform diameter, in a word "smooth" if I passed the word deliberately vague. This is accomplished with a series of treatments, often not sustainable, for example, typically, from what you did with the cotton already from 800, the mercerization with caustic soda. This is also made with fibers rather than "hard" cotton, being extracted from the stem and not from seed, such as with the jute, as shown in the figure. Of course, the fibers "hard" issues that have a number of cotton for example, has, starting from fibrillation, namely the detachment of the fibrils, which makes it difficult in any case spinning "tight", ie to make tissue more dense that the mats. There is also a psychological aspect, as well as functional, in all this: what is smooth as finished product and optimal, is considered the most valuable of what is rough, as raw material, if not crude. The nature, given his approach to design, but has shown enough not to be interested in these our mental categories, associated only with the mode of operation of the sense of touch. One of the first things that actually teach our children, perhaps unconsciously, is the effect of texture, the feel of smooth or rough, which remains under the fingertips in a brief contact.
Where there is a hierarchy, but there is a continuous structure to the smallest level. The gecko's paw is neither smooth nor rough, but is adaptable in the sense that it can take the form that, at the nanometer level, is considered more appropriate to join reversibly to the surface, and then in a flexible way to modulate the contact force. At that point the contact without regard to friction, we can never compare, for example, those wheel-rail systems, where the sliding smoothly (so once again go "straight") is always sought in relation to clutch and then to the roughness, through the adoption of techniques such as grinding or polishing. One might even speculate, although clearly the measurement of the adhesion force to the surface the gecko is not easy, that the system operates with a variable friction depending on the condition of the surface. More or less what we are trying with great difficulty di ottenere in molti sistemi ingegneristici, come per esempio gli ammortizzatori, che hanno lo scopo di ridurre le vibrazioni dovute alle condizioni della superficie stradale. E' chiaro che se potessimo modulare la forza di contatto tra la ruota e l'asfalto, sull'esempio del geco (avremmo certo bisogno di un “pneumatico gerarchizzato”), non ci servirebbero ammortizzatori. Per ora, invece, l'unico modo che abbiamo per ridurre la forza con cui il pneumatico preme sulla strada, è rallentare.
