Biomedical Engineering Reference
In-Depth Information
Agarose
a
Agarose
Hydoxyapatite
scaffold
c
1 mm
2.5 mm
2 mm
20-30 mm
Agarose stamp
b
1 mm
2 mm
500 µm
500 µm
d
e
FIGURE 2.49
Direct. transfer. of. mammalian.cells. with. agarose. stamps.. (From.Molly. M.. Stevens,.
Michael.Mayer,.Daniel.G..Anderson,.Douglas.B..Weibel,.George.M..Whitesides,.and.Robert.Langer,.
“Direct. patterning. of. mammalian. cells. onto. porous. tissue. engineering. substrates. using. agarose.
stamps,”.
Biomaterials
.26,.7636-7641,.2005..Reprinted.with.permission.from.Elsevier.)
and form colonies only on the areas contacted by the stamp (
Figure 2.48
), and they can even
replicate on the stamp—a sort of “ink” that regenerates itself.
his idea has also been demonstrated for patterning osteoblasts (mammalian cells) onto
hydroxyapatite (
Figure 2.49
), a highly porous substrate, so it can presumably be extended to
other mammalian cell types and a variety of porous substrates used in biotechnology (e.g., il-
ters) and tissue engineering (e.g., biodegradable polymers).
Importantly, the gel can be loaded with a gradient of biomolecules—for example, by contact-
ing it only partially or with an uneven volume of the loading solution—which has implications
in studies of chemotaxis.
2.6.4.4 Electroactive Substrates
George Whitesides at Harvard University and his former postdoctoral researcher Milan Mrksich,
now a professor at the University of Chicago, developed a powerful method that allows for
changing
the adhesiveness of the cell-adherent substrate using electroactive SAMs. he method
is based on the observation that cell-repellent triethylene-glycol-terminated thiol SAMs (EG
3
-
C
11
) desorb when a voltage pulse of approximately 1.2 V is applied to the gold substrate with
respect to the cell culture medium. Before application of the voltage pulse, cells were conined to
micropatterns in normal growth media for 24 hours, but ater the voltage pulse, they started to
migrate across the “bare” gold (presumably already covered with proteins secreted by the cells
or deposited from the medium) and underwent normal growth and cytokinesis (
Figure 2.50
).
his principle is very versatile. Stripes (or any pattern) of ECM protein can be fabricated
alternating with initially inert electroactive monolayers, so that a population of cells can be
seeded to attach to the protein stripes but not the monolayer; next, on electrical activation of
the monolayer, the spaces between stripes become adhesive and a second cell population can be
