Figure 1 Schematic illustration of the fabrication
process of (A) a torque-balanced two-plied hair fiber and(B) heterochiral and homochiral hair artificial muscles and the
solvent-driven actuation.
First, a certain length of human hair was hanged vertically with a load
torsionally tethered, and twisted counter-clockwise with a motor for
some time (Figure 2A ). By adjusting the twisting time,
hair fibers with different twist densities (1000, 1500, 2000, 2500, 2650
turns m-1) were obtained. The morphology of these hair
fibers was examined with a micro lens and shown in Figure2B . It can be seen that the longitudinal elements changed from
straight to helical after twisting and their angular displacement
increased with the increase of the twist density. The helical angles can
be approximated with the following equation:
\begin{equation}
\alpha=\operatorname{}{(2\pi rT)}\nonumber \\
\end{equation}
where r is the radial distance from the center of the hair fiber
(~100 μm), and T is the amount of inserted twist divided
by the length of the hair fiber. In addition to the theoretical value,
image J was also used to measure the actual helical angles of these
fibers. It can be seen from the graph in Figure 2Cthat the measured values of these angles agree well with the calculated
values.