124

౪

6 Skin, The Body’s Largest Organ

Figure 6.15: A self-healing hydrogel for medical applications. This is a mimic for skin without the sensing

and other functions of skin [43]. (a) Different healing behaviors of single-charged, nonionic and zwitterionic

materials. (b) Chemical structures of the different materials used. (c) How the different blocks combine to

form the block hydrogel. (d) Individual hydrogel building blocks dyed with different colors. (e) A completed

block hydrogel. (f) The block hydrogel upon stretching. (g) The block hydrogel upon bending.

6.4 Summary and the Bigger Picture

To summarize, skin is the largest and most complex organ with the most different func-

tions and the largest amount of different sensors in the human body. The sensing mech-

anisms have not yet been fully worked out in detail, neither for temperature nor for

pressure. Additionally, these sensors are also part of chemical sensing and part of the

sensation of pain; and all of this sensing is so sensitive that the details of surface prop-

erties can be distinguished in a three-dimensional manner. Additionally, these sensors

are built into a complex structure that also acts to maintain homeostasis and self-heals

when the barrier to the outside environment is breached. Some of these functions have

been mimicked in materials but generally separately. There has been progress of build-

ing sensor arrays on a large scale, including progress of addressing each of the sensors