Biomaterials for MEMS

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-

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