Spider Silk as a MEMS Material 27
R
2
= 0.9274
R
2
= 0.9777
R
2
= 0.9112
0
0.2
0.4
0.6
0.8
1
1.2
1.4
00.20.40.60.811.21.41.61.82
Magnetic Induction (kOe)
Vertical displacement (mm)
75 mins
7.5 hrs
24 hrs
Figure 2.16. Bending distance as magnetic induction (field) increases.
spectra of regenerated spider silk in a thin-film form have been measured
12
leading
to the suggestion that the β-sheet conformation, which is responsible for the high
stiffness and strength of spider silk,
29
is missing from thin-film spider silk. This
result indicates a dramatic change in the material’s secondary structure compared
to its native fiber state. Furthermore, the significant decrease in mechanical
property shown in Ni/spider-silk film silk is perhaps due to the porosity of the
material, which would allow stress concentration to occur around the Ni particles.
The material property could be improved if the dilution of Ni/spider silk was
reduced. However, in this work the near maximum dilution was used in order
increase the material’s magnetic properties.
Furthermore, contact with water during the release step also affects the
strength of the microbridge. Previous studies have shown that water causes
changes in the arrangement of the silk fibroins and causes super-contraction of
the silk fibers, which can decrease the UTS and increase the brittleness of the
material.
30,31,40
When regenerated fibers were stretched in water, the UTS was
reduced to 25 MPa.
30
It is unlikely that our silk structures would super-contract
as native fibers do; however, the immersion in water likely does enable some
rearrangement of the protein-polymer backbone. The regenerated Ni/spider silk
studied in this work has a comparable UTS to PDMS (with UTS in the range of
2.4–7 MPa [mit]), a popular material in MEMS.
2.4 CONCLUSIONS AND OUTLOOK
This chapter has presented regenerated Ni/spider silk as a material for MEMS.
Thin-film formation using a spin-on process and a modified surface microma-
chined Ni/spider-silk microbridge were demonstrated. Static and dynamic bend-
SO13997_text.indd 35SO13997_text.indd 35 26/01/2011 3:50 PM26/01/2011 3:50 PM

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