Biomedical Engineering Reference
In-Depth Information
hologram. Due to its biocompatibility and biodegradability, the patterned silk film
provides a biologically favorable microenvironment that preserves the activity and
functionality of the biological dopants. This being the case, the silk film works as
the optical transducer on a simple bioactive-grating-based spectrometer, which can
monitor the spectra of the embedded biochemical compound in real time.
The process of preparing silk nano- and micro-patterning is always as follows:
remove the sericin of the silk by cutting, cleaning, boiling, and drying the silk
cocoon; dissolve the silk fibers in lithium bromide solution and dialyze to remove
the lithium bromide salt; filter and centrifuge the silk fibroin solution to get rid
of undissolved and recrystallized silk fibroin; dope the silk solution with active
material; deposit the undoped or doped silk solution on an appropriate substrate
and dry under appropriate conditions; detach the silk film from the substrate. The
free-standing silk film with special structure obtained is particularly important
for optical applications that require a periodicity and a size of the order of the
dimensions of the wavelength of incident light.
Fiorenzo
et al
. reported a simple modified soft-lithography process to construct
a nano- and micro-patterned silk fibroin film [9]. They claimed the creation of the
smallest nanopatterns in silk fibroin films. Using this technique, high quality films
containing intricate 2D and 3D nano- and micropatterns were fabricated.
Lithography is very useful for fabricating biomedical devices. However, the silk
fibroin casting process takes 12-36 h, which makes it difficut to rapidly produce
multiple devices, and the resulting silk structures contain artifacts due to drying and
lift-off. Amsden
et al
. [44, 96] demonstrated the application of nanopatterned silk
fibroin films as a self-sensing optofluidic device. To make the device, silk solution
was doped with hemoglobin, and the mixed solution was cast on a glass slide to
form a film. A 600 grooves/mm grating was imprinted on the doped film using
the room temperature nanoimprinting method described above. The obtained film
was annealed with methanol to preserve the imprinted grating and eliminate water
solubility. The doped imprinted silk grating, and polydimethylsiloxane (PDMS)
films coated on glass cover slips were then fabricated into a microfluidic flow cell.
At the top of the flow cell there was a small opening to allow the injection of
water, and on the bottom there was another opening through which gas could pass.
Oxygen and nitrogen were bubbled into the flow cell to test the properties of the
silk microfluidic flow device. The absorption spectra of the doped silk grating were
recorded under different ratios of oxygen and nitrogen. The results show that the
device is sensitive to the ratio of oxygen and nitrogen, and active even after storage
for several months. This technology is related to nanophotonics, biopolymeric,
and biocompatible materials, and provides a new route to the development of
biomedical optical devices.
7.4.5
Construction of Structural Color to Silk Fabrics
Structural color, caused by the interaction of light with the nanoscale periodic
structures of certain materials [97], has attracted extensive attentions for decades
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