Biomedical Engineering Reference
(Fig. 5) in the samples that gave homogeneous size distribution in the dynamic
light scattering experiment. Those samples that were polydispersed tended to
give irregular membranous layers. The nanotubes that formed had an average
diameter of around 30 nanometers as examined by TEM, consistent with results
obtained from the dynamic light scattering.
These nanotubes have the potential to act as templates for metallization
and formation of nanowires. Furthermore, the nanovesicles may be useful
as an encapsulating system for drug delivery. Chemical modification of the
peptide monomer may expand the function of these structures. For example,
a specific cell-surface ligand can be directly incorporated into a vesicle for
targeted delivery of insoluble drugs to particular cells.
Molecular assembly can be targeted to alter the chemical and physical proper-
ties of a material's surface. Surface coatings instantly alter a material's texture,
color, compatibility with and responsiveness to the environment. Conven-
tional coatings are typically applied by painting or electroplating. Erosion
is common mostly because the coatings are usually in the ten- and hun-
dred micron size ranges and the interface is often not complementary at
the molecular level [47, 73]. Peptides and proteins have also been printed
onto surfaces which have now been modified with a vast family of chem-
ical compounds; Mirkin and colleagues [74-76] have also developed dip-pen
nanolithography to directly print micro- and nano-features onto surfaces.
These developments have spurred new research into the control of molecular
and cellular patterning, cell morphology, and cellular interactions [73, 77-79]
and fueled new technology development.
Work in our laboratory has focused on designing a variety of peptides to
self-assemble into a monolayer on surfaces and to allow adhesion molecules
to interact with cells and adhere to the surface. Using proteins or peptides
as ink, we have directly microprinted specific features onto the non-adhesive
surface of polyethylene glycol to write any arbitrary patterns rapidly without
preparing the mask or stamps (Fig. 6). This simple and rapid printing tech-
nology allowed us to design arbitrary patterns to address questions in neuro-
biology that would not have been possible before. Because understanding of
correct complex neuronal connections is absolutely central to comprehension
of our own consciousness, human beings are always interested in finding ways
to further investigate this. However, the neuronal connections are exceed-
ingly complex, and we must dissect the complex neuronal connections into
smaller and more-manageable units to study them in a well-controlled man-
ner through systematic biomedical engineering approaches. Therefore, nerve
fiber guidance and connections can now be studied on special engineered
pattern surfaces that are printed with protein and peptide materials .