Biomaterials for MEMS

16 J. Bai et al.

2.3.2 TEM

Magnetic spider silk film was investigated using TEM, where the size and contour

of the spheres could be much more defined. The spherical particles varied in

diameter, approximately between 150 to 650 nm. A select few were as large

as 1.4 μm. The particles were not dispersed in any orderly fashion. They did

however appear to connect and form chains or clusters (see Figs. 2.4(a) and 2.4(b)).

Note that, particularly in Fig. 2.4(b), the spheres appear to blend in with each

other forming fibrous structures, with the more transparent materials between the

spheres appearing to join them together. It is possible, then, that the spheres not

only exist on the surface, but also within the fiber-like material. However, in areas

that are more concentrated with spider silk material (see Fig. 2.4(c)) spheres exist

in fewer numbers and smaller sizes. These smaller particles could be a result of Fe

particles not being able to bind with oxygen as easily, making diffusion within a

higher concentrated spider silk region more difficult.

2.3.3 FTIR

Fourier Transformed Infrared Spectroscopy (FTIR) was used to characterize the

molecular structure of the spin-on spider silk film. Previously, FTIR measurements

a

b

c

Figure 2.4. TEM images of spheres (a)× 6k (b)×3k (c)×15k magnification.

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Spider Silk as a MEMS Material 17

of native spider silk fibers have shown peaks corresponding to Amide I, II and

III vibration modes. These peaks correspond to the arrangement of polypeptides

present in the silk’s secondary structure. The material properties of spider silk

have been shown to be strongly linked to its secondary structures.

10,33

FTIR Peaks

at wave numbers 1652 and 1669 cm

−1

in the Amide I region have been assigned to

α-helical and β-sheet backbone conformations respectively.

31

A peak at 1540 cm

−1

in the Amide II band corresponds to disordered conformations,

6

while peaks at

1230 and 1240 cm

−1

in Amide III are associated with β-sheets and disordered

conformations.

45

The FTIR spectra are shown in Fig. 2.5. The top spectrum

represents the iron spider silk sample and the bottom spectrum represents the pure

regenerated spider silk sample.

As shown in Fig. 2.5, the FTIR spectrum of the regenerated spider silk thin film

obtained from a spin-on process shows peaks at 1660, 1542 and 1242 cm

−1

.The

pattern of the three peaks, ranging in intensity from moderate to strong, is similar

to that reported to indicate the presence of α-helical and random conformation

components. The β-sheet conformation, which is suggested to be responsible for

the high stiffness and strength of the material

29

was not found to be present in this

work. This indicates a change in the material’s secondary structure in comparison

to the native fiber state.

Peaks below 1450 were not resolved and lacked distinctiveness, thus they are

not addressed here. The Amide I and Amide II peaks are shown at wave numbers

1657 and 1537. The vibration mode in the spectral region between 1600–1700 cm

−1

predominantly originated from the C = O stretching of Amide I group.

21

Based

on the position within this spectral region, 1657 cm

−1

represents a 20% presence

of α-helix in the sample’s secondary structure.

46,47

1537 falls within the Amide II

1660

1542

1242

2014

1823

1657

1537

Wavenumber (cm

-1

)

Transmittance %

Figure 2.5. FTIR of iron spider silk sample. Top spectrum is iron spider silk; bottom

spectrum is the pure regenerated spider silk.

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