Micropatterning of Substrates and Cells - Introduction to BioMEMS - page 76

2.6.1.5 PLL-g-PEG Copolymers
In 2003, Gaudenz Danuser (then at ETH Zürich) and colleagues pioneered the spontaneous molec-
ular assembly of a polycationic PEG-grated copolymer, poly-l-lysine(20 kDa)- g {3.5}-PEG(2 kDa)
(PLL-g-PEG), which physisorbs onto surfaces and can be readily loaded onto stamps from aque-
ous solutions. Here, g expresses the grating ratio ( g = 3.5), which is the average number of PLL
monomer units per PEG side chain. Peptide(RGD)-functionalized PLL-g-PEG is also possible.
Not surprisingly, the approach has become very popular as a cell patterning strategy, and PLL-
g-PEG is now commercially available from Surface Solutions (based in Zürich). A group led by
Matthieu Piel and Michel Bornens at the Institut Curie in Paris have shown that PLL-g-PEG can
be microstamped, leading to high-resolution ECM patterns (that are used to modulate the shape of
single cells) when the samples are exposed to a ibronectin solution ( Figure 2.30 ). his group has
been able to micropattern PLL-g-PEG by selectively degrading it with deep UV light (using a low-
pressure mercury lamp, at 185 and 254 nm wavelengths); ater deep UV light exposure, the PEG
carbons (C-O-C) turn to carboxyl groups and are observed to support protein and cell attachment.

2.6.1.6 Micropatterns of Cell-Repellent Hydrogels
PEG is not the only cell-repellent material out there—most nonprotein hydrogels lack cell
attachment motifs and their sot, highly hydrated surface structure is too mobile to support pro-
tein or cell adhesion. Mehmet Toner's group at Harvard Medical School demonstrated a micro-
luidic approach to create micropatterns of hydrogels such as agarose, which has been known to
deter protein physisorption and cell attachment for decades. he trenches of deep PDMS micro-
channel networks were illed with hot (~80°C) molten agarose and the agarose was allowed to
solidify; next, the PDMS/agarose textured surface was incubated in a ibronectin solution, which
presumably physisorbed only onto the bare PDMS areas. Hepatocytes were observed to attach
only onto the ibronectin-coated PDMS “islands” and to limit their spreading precisely to the

Fibronectin solution Cy3-labeled fibronectin

a

b e

Plasma oxidation

PBS

PS on glass or culture dish

100 µm

100 µm 34 µm

f

c

4 h

or

Cy3-fibronectin

PLL-PEG

34 µm

100 µm 34 µm

PLL-PEG

d g 24 h in 10% FCS

PBS

RPE-1 cells

34 µm

34 µm

100 µm

FIGURE 2.30 Deterring.cell.attachment. and. spreading. with. PLL-PEG. copolymers.. (From. Ammar.
Azioune,. Marko. Storch,. Michel. Bornens,. Manuel. Théry,. and. Matthieu. Piel,. “Simple. and. rapid.
process. for. single.cell. micro-patterning,”. Lab Chip . 9,. 1640-1642,. 2009.. Figure. contributed. by.
Manuel.Théry.and.Matthieu.Piel.)