Biomedical Engineering Reference
In-Depth Information
Remove
template
Cast polymer
Porous Si photonic
crystal template
PSi/polymer composite
Polymer photonic crystal
(a)
~1cm
(c)
5.00
µ
m
(b)
FIGURE 8.11
(a) Schematic illustration of fabrication of polymer photonic materials using porous Si pho-
tonic crystal templates. (b) Cross-sectional SEM micrograph of a porous silicon rugate dielectric mirror tem-
plate showing multi-layers along the
z
direction, prepared via electrochemical etch of a crystalline Si wafer
using a pseudo-sinusoidal current-time waveform. The scale bar is 5 μm. (c) Optical photograph of a polymer
photonic crystal fabricated by templating a porous silicon rugate dielectric mirror.
opaque tissue, if the near-infrared, tissue-penetrating spectral features are encoded into the drug
delivery material, the fi xture conceivably could be probed through the skin or through several mil-
limeters of opaque tissue. This latter concept has been demonstrated with a rugate optical structure
made of biodegradable polylactide, impregnated with a test drug.
118
Drug release correlates to the
decrease in intensity of the spectral features of the drug loaded rugate structure as expected. By
placing the spectral feature of the polylactide imprint within the low-absorbance, near-infrared
window of human tissue, a drug delivery matrix that could be read through the skin was demon-
strated.
118
With the recently demonstrated encoding ability of porous silicon due to the elaborate
optical structure,
94,136
we can design into the material characteristic spectral “bar codes” that enable
the fi xture to be distinguished from tissue, light scattering centers, or highly colored materials in
the body.
117,118
8.3 SUMMARY AND OUTLOOK
In summary, porous nanostructured systems that can take the form of liposomes, nanospheres, nano-
capsules, nanotubes, microspheres, thin fi lms, or other morphologies are intensely studied in labo-
ratories under clinical investigations and some are also commercially available in the market. The
preparation of the porous nanostructured systems can be based on diverse methods or mechanisms,
following for instance, self-assembly, sol-gel, templating, or soft chemistry routes. Precise control of
the nanostructuring and the surface chemistry makes it feasible to achieve functional nanomaterials
