Biomedical Engineering Reference
In-Depth Information
FIGURE 4.48
Bottom and top caps. The bottom cap (left) places a magnetic stirrer that stirs
the solution during the electric polarity change.
4.3.13
F
URTHER
PAN A
CTUATOR
S
YSTEM
D
ESIGN
AND
F
ABRICATION
Figure 4.49 shows the revised design of the fabricated PAN actuator system. First,
in order to minimize the bending movement of the membrane boots, a guide set was
added to the system. After inserting the cathode attached to the surface of the
membrane boots, the spring constant was slightly increased to
k
= 0.014 kg/mm due
to the added stiffness.
When the actuation occurs, the displacement of the membrane boots is measured.
Subsequently, the force induced by the PAN muscle can be calculated. At high pH
conditions, the PAN muscle usually turns into a gel, which exhibits an elastic
behavior. Compared to raw PAN fibers, the mechanical properties of PAN fibers are
weak (a modulus of 4-5 MPa and an ultimate stress of 1.5-2.0 MPa at elongated
states; Schreyer et al., 2000). Therefore, it requires careful operation not to cause
material damages or breakups.
We have gained a significant amount of experience for safe operation. In par-
ticular, any localized stress buildups should be eliminated. Much attention should
be given to the connection between the cap and the PAN fibers. Both ends were tied
up and fixed by epoxy in order to prevent loose bending.
Some difficulties have been found. The PAN fiber loop was broken several times
during the initial shake-up testing of the system and caused the delay of the perfor-
mance testing. Figure 4.50 depicts a loop of PAN fibers in a raw form and in an
activated state.
The PAN fibers were surrounded by a Cu-Zn spring-type anode coated by gold
and immersed in a 0.1-
M
sodium-chloride solution. We applied a typical operating
voltage of 10 V to the system to operate it. Initially, we applied a DC current. A 2-
mm displacement (equivalent to 28
gf
) was maintained until 15 min had passed. When
the time passed about 20 min, suddenly a large amount of current passed through
the system, possibly due to the impurity buildups. The solution temperature was
increased from 24
°
C (room temperature) to 35
°
C. After 20 min, the anode and the
