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Thermo-responsive hydrogel-based circular valve 463

mix was poured into the two sets of molds (one for each wire diameter of the SMA spring).
The molds were then put in the da Vinci UV curing chamber with UV LED
(λ 5 375 405 nm) for 2 hours. The molds are then removed from the chamber, and the
SMAHVs are removed from the molds and tested for their performance.

20.3 Results

20.3.1 Performance of the thermo-responsive hydrogel valve

The TRHV fabricated based on mold 2 (dimensions are 4 mm inner diameter, 10 mm outer
diameter, and 3 mm height) is used to test the response time of the TRHV when it is

exposed to heat. The TRHV is immersed in a water bath, which is maintained at 40 C,
regulated by a hot plate, as shown in Fig. 20.4A.
The process of the contraction of the TRHV is video-recorded, and the displacement of the
TRHV during the heating process is analyzed using Tracker 5.0 (Douglas Brownr). The
data is plotted from the point of exposure to heat until the displacement starts to stabilize.
It required 230 seconds for the mold 2 design of TRHV to stabilize in the displacement.
The time-resolved displacement of the mold 2 TRHV during the heating is shown in

Fig. 20.4B. The heating of TRHV at 40 C for 230 seconds had a displacement of 1 mm.
The displacement increased to 1 mm in the first 100 seconds and then started to stabilize
slowly and completely stabilized at 230 seconds.

The TRHVs fabricated using different dimensions of molds 1 5(Table 20.1) were
subjected to three thermal cycles (heating continued by cooling). In the heating phase, the

hydrogel was heated to 40 C. The heat was provided by a laboratory hot plate, as shown in
Fig. 20.4A. In the cooling phase, the hydrogel was left to cool to 23 C, which was room

temperature. Each phase lasted 20 minutes to ensure that the hydrogel valves achieved the
target temperature. At the end of 20 minutes, the inner diameter of the hydrogel valve
lumen was measured through photo-analysis through images obtained from a DMS1000
optical microscope (Leica Microsystems GmbH, Germany). The TRHV was then
transferred to the corresponding thermal setup. This process was repeated five times over
the three thermal cycles. When the TRHV is heated to 40 C, the area of the lumen expands

to open the lumen, increasing the lumen area. The material of the TRHV that is removed
in the lumen area to open the valve is going to a thickness of the TRHV. Thus as the area
of the lumen is increased, the height of the TRHV is also increased. When TRHV is cooled,
the lumen contracts and returns to its initial position, inducing the TRHV to return to its
initial height. This change in area due to the heating and cooling of the TRHV is shown
schematically in Fig. 20.5A. The time-resolved area of the lumen in the TRHV for all mold

designs for three thermal cycles (varying between 23 C and 40 C) are shown in Fig. 20.5B

and the values of the area of lumen in all molds are shown in Table 20.3. The TRHV from