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Auxetics are mechanical metamaterials with the unique properties of expanding their transversal section upon longitudinal positive strain, decoupling the deformations in normal and transversal directions. Such property can be exploited to develop soft sensors that can provide feedback to different mechanical stimuli, e.g. pressure and shear force. In this work, we propose for the first time a mathematical model to analytically simulate and design the auxetic behavior in a capacitive strain gauge, and show that, for a polyurethane (PU) auxetic foam, Poisson Ratio’s values can satisfy the negative gauge factor (GF) condition. We develop an innovative thermo-compressive process to obtain anisotropic auxetic PU sponges both in normal and normal/radial directions, and their mechanical properties are in agreement with the theoretical calculations validating our model. Then, we develop a capacitive strain gauge by integrating a normal auxetic PU foam with polydimethylsiloxane /carbon nanotubes electrodes. Results show that the capacitive change caused by an external force, is proportional to the induced deformation, but importantly it is also dependent on the direction of the applied force. A negative GF of GF = −2.8 is obtained for a longitudinal strain range up to 10%. This auxetic foam structure guarantees flexibility and paves the way for an improved design freedom for multimodal mechanical soft sensors providing new opportunities towards smart wearables and perceptive soft robots.

The life cycle of Hydrozoans typically comprises two phases: the polyp, either solitary or colonial, with generally a benthic habitat, and the medusa which lives in the plankton. In its typical metagenetic cycle, the medusa is budded from the polyp, which is the product of sexual reproduction of medusae. However, several alternative reproduction patterns have also been described. In particular some species are able to perform a regressive transformation of the medusae that transform themselves into polyps bypassing sexual reproduction. In a species with alternative morphs switched by the environment, the more labile is the correlation between environmental factors acting on the genetic switch and the factors to which the resulting form is adapted, the more hazardous will be the development of either body form. However, we can explain the evolutionary advantage offered by reversion between morphs of these plastic species living in shallow water unpredictable environments: should produced medusae be released in the "wrong" environment, they would still have a chance of survival under another form.

A wealth of data are available on the seasonal variation of plankton communities, but few studies take into consideration the circannual cycles of benthic organisms. In fact, the macrobenthos is generally considered as composed by slow-growing organisms showing variations mainly in relation to substrate competition. On the contrary, hydroids are an important group of macrobenthos that, in temperate but also in tropical waters, undergo sharp seasonal cycles. For example, on the Portofino Promontory (Ligurian Sea), about half of the recorded species thrive in winter and 30% in the summer, the rest being constant in presence. Here, we revise the available data about the environmental factors switching the passage from quiescent to active phases. The available data suggest that a mosaic of physical factors, biotic interactions, and internal clues triggers the hydroid cyclic behaviour.

This investigation provides the first detailed description of the growth stages of two Distichopora species showing the formation of a primary cyclosystem and explaining the growth process leading from primary cyclosystem to adult pore organisation. The earliest observed stage is an oval calcareous disc from which, at a later stage, a primary cyclosystem raises up. Then, the addition of new gastropores and dactylopores leads to the pore rows typical of the genus. Using X-ray computed microtomography, we are able to visualise the dense canal network that permeates the coenosteum and envelops the gastropores and the dactylopores in all the observed growth stages. In both species, the thin canals surrounding the gastropores are responsible for the formation of the new gastropores that originate between the old ones, while the thin canals placed on the external side of the dactylopore rows produce the new dactylopores.