Micropatterning of Substrates and Cells - Introduction to BioMEMS - page 92

exposure to an oxidizing agent such as HBrO; the agent is produced locally with a microelec-
trode “pen” (a Ag/AgCl electrode positioned 5 μm above the surface biased with 1.7 V for
30 seconds) in the presence of a Br — -containing solution (25 mM KBr), which is compatible
with cells ( Figure 2.47a ). hus, Nishizawa's group was able to “erase” patterns of BSA in the
presence of HeLa cells and observe the growth and migration of new cells in the albumin-free
areas ( Figure 2.47b ).
Nishizawa's technique is highly specialized in that, so far, it has only been demonstrated to
work for albumin. But how about using light, instead of electrical current, to pattern proteins
in situ? We have already seen how the high-energy femtosecond pulsed laser of a multiphoton
microscope can be used for writing protein structures ( Figure 2.12 ). Jason Shear and colleagues
at the University of Texas in Austin have photo-cross-linked nonadherent albumin “corrals” in
the presence of cells (neurons and bacteria; see Figure 1.16 ).

2.6.4.3 Microstamping of Cells
It is possible to locally deposit cells from an agarose stamp, both with bacterial and mammalian
cell types. he hydrogel stamp, instead of being loaded with an etchant (see Section 1.7), can be
loaded with a bacterial suspension using the same simple protocol. he bacteria get “printed”

(a) (f )

Agarose stamp with
positive features

Add suspension of cells

(b)

1 mm

Stamp absorbs excess liquid

(g)

(c)

Cells deposited
on stamp

Invert stamp and print

Media surface

Petri dish

(h)

(d)

Incubate

Bacterial colony

(e)

FIGURE 2.48 Microstamped.bacterial.colonies..(a).Schematic.of.an.agarose.stamp..(b).A.bacterial.
suspension.is.added.to.the.agarose.stamp.(3%.agarose)..(c).The.cells.deposit.on.the.surface.of.the.
stamp.after.excess.liquid.is.removed..(d).Stamp.is.applied.to.an.agar.plate.(a.common.bacterial.
culture.substrate)..(e).Bacterial.colonies.form.on.the.areas.contacted.by.the.stamp..(f-h).Images.
depicting. the. growth. of. the. patterns. of. bacteria. over. time:. (f). bright-ield. image. after. 10. hours.
of. growth. (no. photoluminescence. was. detected);. (g). 20. hours;. (h). 40. hours.. (From. Douglas. B..
Weibel,.Andrew.Lee,.Michael.Mayer,.Sean.F..Brady,.Derek.Bruzewicz,.Jerry.Yang,.Willow.R..DiLuzio,.
Jon.Clardy,.and.George.M..Whitesides,.“Bacterial.printing.press.that.regenerates.its.ink:.Contact-
printing.bacteria.using.hydrogel.stamps,”. Langmuir .21,.6436,.2005..Reprinted.with.permission.of.
the.American.Chemical.Society..Figure.contributed.by.George.Whitesides.)