When it Just Feels Right
How close are we to synthetic skin that can change all this? A fair way off, if the results of Cabibihan and co's investigations are anything to go by. They compared the properties of two commonly used synthetic skins, silicone and polyurethane, with the human variety and found them sadly wanting.Another interesting material being looked at is smart memory foam. New smart memory foams can actually simulate muscles' "linear actuator" movement.
Human skin, it seems, has some special properties that are difficult to replicate. Cabibihan and co measured three properties: skin compliance, or the degree to which it is deformed by a force; conformance, or the way its shape conforms to an object it touches; and hysteresis, or the energy dissipated under a load--essentially the difference between the way it deforms and reforms.
Synthetic materials require more force to bend them, but they dissipate less energy during this process. So they are unable to match the hysteresis curve of human skin, which looks particularly challenging to reproduce. That's probably because the hysteresis properties are the result of the interaction between the various layers that make up human skin.
The big question for the designers of robotic and prosthetic skin is whether these characteristics can be reproduced by a single layer or whether a more complex (and expensive) skin made of multiple layers will be needed. _ TechnologyReview
The multiple layered approach works well for human skin and tissue. That is what feels natural to us -- not a thick mass of silicone rubber. If humans are ever to accept sex androids and sex dolls on a large scale, the life-sized devices will need to soothe and arouse innate human sexual instincts. To do that, natural is better. It has to feel right.