Biomedical Engineering Reference
In-Depth Information
instead of photoresist. In particular, his group has focused high-powered pulsed lasers to deposit
biocompatible structures made of photo-cross-linkable albumin
in the presence
of live cells
(
Figure 1.16a
). he non-cross-linked protein is simply rinsed away ater the fabrication pro-
cedure (so there is no development step). In one experiment, “corrals” (which actually have a
roof that is not visible because it is out of focus) were built to trap bacteria (
Figure 1.16b
and
c
);
a microsphere trapped inside a 28-μm-diameter circular microchamber is seen to do a whole
orbital turn in 0.3 to 0.4 seconds (corresponding to a linear velocity of ~150 μm/s) because of the
clockwise swimming of
Escherichia coli
(
Figure 1.16b
). In another experiment, albumin lines
were used to constraint the growth of axons within corrals (
Figure 1.16d
). Other more complex
structures such as two-story “apartment buildings” were also possible.
Serial writing with a laser is limiting because writing 3-D structures is a slow process that
involves scanning the beam in all three dimensions, and programming the beam movements can
be a painstaking procedure. A more eicient way is to reduce arbitrary shapes to slices using imag-
ing sotware and to project the laser beam with a DMD (see Section 1.3.6.1). he Shear lab has,
indeed, coupled multiphoton lithography successfully with a DMD to produce arbitrary micro-
structures of photo-cross-linked bovine serum albumin (BSA) (
Figure 1.17
). A titanium sapphire
Lens Obj
Microstructure
a
Mask
b
X-Y
(Beam scan)
Z
(Specimen scan)
c
t = 0 s
t = 5 s
2 µm
10 µm
t = 0 h
t = 3.5 h
d
FIGURE 1.16
Laser. deposition. of. “corrals”. for. containing. cell. growth. and. motility.. (From. Kaehr,.
B., R.. Allen,. D.J.. Javier,. J.. Currie,. and. J.B.. Shear,. “Guiding. neuronal. development. with. in. situ.
microfabrication,”.
Proc. Natl. Acad. Sci. U. S. A.
,.101,.16104,.2004..Copyright.(2004),.National.
Academy.of.Sciences,.U..S..A.;.Kaehr,.B..and.J.B..Shear,.“High-throughput.design.of.microluidics.
based.on.directed.bacterial.motility,”.
Lab. Chip.
,.9,.2632,.2009..Reproduced.with.permission.from.
The.Royal.Society.of.Chemistry.)
