Micropatterning of Substrates and Cells - Introduction to BioMEMS - page 59

10 µm

CH 3 COOH

FIGURE 2.14 Substrate.wettability.determines.eficiency.of.protein.transfer.in.microstamp..(From.
John.L..Tan,.Joe.Tien,.and.Christopher.S..Chen,.“Microcontact.printing.of.proteins.on.mixed.self-
assembled.monolayers,”. Langmuir .18,.519-523,.2002..Reprinted.with.permission.of.the.American.
Chemical.Society..Figure.contributed.by.Chris.Chen.)

for example, if the PDMS is derivatized with a very hydrophobic functionality (-CF 3 ), proteins
are transferred well to moderately hydrophilic surfaces, but if the PDMS is derivatized with a
hydrophilic functionality (-NH 2 ), then the surface must be very hydrophilic to ensure eicient
transfer ( Figure 2.15 ). Unfortunately, PDMS derivatization is still a nonquantitative science
because laboratory-speciic, small changes in the procedures involved (PDMS curing, oxygen
plasma oxidation, and silanization) can have dramatic efects in the wettability of PDMS, which
itself can change with time and curing conditions.
Microstamping proteins with a PDMS poses a secondary problem: the PDMS stamp deforms,
so the features are diicult to align on top of each other when several layers are being patterned.
he most obvious solution is to make the PDMS stamp more rigid—either by cross-linking it
more or by mounting a thin slab of it on a thick glass support. Chris Chen's group has proposed
a more creative solution based on multilayer stamps ( Figure 2.16 ). hus, the stamp has several
(discrete) levels, and the surface (whether for inking or for printing) can be brought into contact
with any of those levels by adjusting the vertical pressure applied with the stamp.
It may well be that PDMS is not that well suited for printing proteins: ater all, the PDMS surface
cannot act as reservoir for the ink (the protein). We need something moist . So why not directly use a

a

Printed from
-CF 3 stamp

0% COOH 10% COOH 20% COOH

b

Printed from
-NH 2 stamp

100 µm

70% COOH 80% COOH 90% COOH

FIGURE 2.15 Hydrophobicity. differential. inluences. protein. microstamping.. (From. John. L.. Tan,.
Joe. Tien,. and. Christopher. S.. Chen,. “Microcontact. printing. of. proteins. on. mixed. self-assembled.
monolayers,”. Langmuir .18,.519-523,.2002..Reprinted.with.permission.of.the.American.Chemical.
Society..Figure.contributed.by.Chris.Chen.)