6.3 Biomimetic Skin

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Figure 6.12: “Smart materials” react to a variety of stimuli with several different responses (adapted from

[32]).

made from biological polymers for medical applications to make them more biocompat-

ible ([33] and references therein).

A lot of smart materials were developed for drug delivery ([34] and references

therein) (Figure 6.13). Generally, these are polymeric capsules that rupture upon a spe-

cific signal. Therefore, they release more specifically next to/inside of a target tissue/cell,

and thus reduce the side effects of drugs that are caused by the drug’s distribution into

healthy tissues and cells.

To make drug delivery even more specific, the body’s system of molecular recogni-

tion and specific transport can be used. One such method is to use the cell’s host-guest

interactions to only release in the presence of a specific cell marker or metabolite ([35]

and references therein). This specific recognition is then transduced to either a read-out

(when used in sensors) or is a trigger for release (when used in drug delivery), sometimes

even in self-healing applications.

Another method to use the body’s specificity is to make the action responsive to an

enzyme reaction ([36] and references therein). Here, the trigger includes an enzyme that

only acts in a specific cell or disease state. In enzyme-responsive systems, it is possible to

also diagnose a disease and only act after diagnosis has occurred, if the enzyme happens

to be a marker for a specific disease.

The other important property of skin, self-healing, has also been mimicked; a large

number of different approaches for different materials and applications have been re-

ported (see recent review and references therein [37]). Only a small number of examples

are highlighted here.

The first generation of self-healing materials was designed for structural materials

[38, 39] (Figure 6.14). Basically, the polymeric material contains capsules with monomer

(labeled “healing agent” in the graph) and in its matrix also a small amount of catalyst.

When a crack develops, it opens a capsule with monomer, which is a liquid that will