Using an electro-conductive polymer, chemical engineers have created what is being described as a synthetic form of skin that, when injured, heals itself in a matter of seconds. The development is being called a “breakthrough” in the fairly new experimental fields of self-healing compounds and “epidermal electronics”.
Previous work in this latter field involved silicon-based materials which, though electrically conductive — a necessary property of artificial skin — were also quite brittle. No, if artificial tissue was going to substitute for actual skin, then it had to behave like actual skin; it needed to be robust — electrically and mechanically.
Over the past half dozen years or so, significant progress has been made. Chemists have since produced plastics that, when cut, can rejoin themselves. Then, in 2008, a group of French engineers (the ESPCI group) designed a rubber compound that could restore its mechanical properties after repeated structural insults, including breaking.
Despite these achievements, however, the materials had low electrical conductance, making them less than ideal for their intended use as sensor material for prosthetics.
But now, engineers at Standford University (Bao et al) have effectively combined these two desired properties to advance the science substantially. The team was able to increase both the self-healing and electrical conducting properties of their new material by incorporating nickel atoms into the polymer which allows electrons to continuously jump between the metal atoms embedded in the polymer.
However, the new polymer is still quite sensitive to applied forces (i.e., pressure and torsion, or twisting) as these forces change the distance between the metal atoms and thus change the electrical resistance of the polymer. Thus, it was necessary to demonstrate that this newest compound could take punishment, like real skin, and still maintain a high level of conductance.
And they did just that; by severing the nickel-doped polymer with a scalpel and then pressing the cut edges together for about 15 seconds. They subsequently found that the compound retained 98% of its conductivity and, more impressively, it could be cut and healed over and over again…like real skin.
These experiments represent the first time that both mechanical and electrical self-healing has been demonstrated. However, critics observe that using a scalpel allows precise cutting which does not significantly alter or deform the area around the “wound”. Mechanical stresses on the polymer due to tension or torsion would not be so precise; these stresses could stretch the new material to a greater degree, preventing full self-healing.
The task now for Bao and her team is to make the polymer even more skin-like by making it elastic (it is currently flexible, but not really “stretchy”) so as to withstand the “slings and arrows” of mechanical deformation. Says Bao: “That’s definitely something we’re moving towards for our next-generation self-healing skin.”
The experiments were published recently in the on-line version of the journal Nature Nanotechnology.