Biology Reference
In-Depth Information
comings, this approach is still a viable one to be used for patterning the adhe-
sion of cells.
Recent advances in the study of SAMs of alkanethiolates on gold surfaces
has provided a more versatile approach to the patterning of cells. These SAMs
are highly ordered molecular assemblies that chemisorb on the surface of gold
with nearly crystalline packing to produce a new interface whose properties
are determined solely by those of the head-group of the alkanethiol
(13)
. This
system makes it possible to control the interfacial properties of surfaces
exposed to cells with greater molecular-level detail than other methods, and it
affords the chance to influence cellular adhesion with greater specificity than
with other methods
(14
,
15)
. The synthetic procedures used to make alka-
nethiols are compatible with complex ligands that interact biospecifically on
the cell
(15
,
16)
. Alkanethiols can be patterned easily on a gold surface using
microcontact printing (
CP), a technique in which a flexible polymeric stamp
is used to print the alkanethiols in a specified pattern; the size of the stamped
regions can be defined arbitrarily with dimensions from 500 nm (or, with
greater experimental difficulty from 200 nm) and up
(17)
. After printing a
hydrophobic alkanethiol, the remaining bare surface of the gold is exposed to
an alkanethiol that presents tri(ethylene glycol) groups (e.g., HS(CH
2
)
11
O
(CH
2
CH
2
O)
2
CH
2
CH
2
OH) that resist the adsorption of proteins. Thus, a pattern
of these two SAMs presented on a substrate defines the pattern of ECM that
adsorbs from solution onto the substrate
(3
,
18)
. The hydrophobic SAMs cre-
ated on flat gold substrates pattern the otherwise nonspecific adsorption of
ECM proteins (fibronectin, fibrinogen, vitronectin, collagen I, and laminin)
that promote the adhesion of different cell types (bovine capillary endothelial
and rat hepatocytes) to the surfaces, whereas the tri(ethylene glycol) SAMs
resist protein adsorption and cell adhesion
(1
,
3
,
18-22)
.
Here, we describe how to use
µ
CP to fabricate substrates that present pat-
terned SAMs with features >500 nm; features as small as 200 nm can be
obtained in special cases, but they are not necessary for most conventional
biological applications
(23)
. This technique uses an elastomeric stamp with
bas-relief to transfer an alkanethiol to the surface of gold in the same pattern
defined by the stamp. The stamps are usually fabricated by pouring a
prepolymer of polydimethylsiloxane (PDMS) onto a master relief pattern,
which is often formed by photolithographic methods. Because
µ
CP relies on
self-assembly of an alkanethiol, it does not require a dust-controlled laboratory
environment, and can produce patterned gold substrates at relatively low cost.
µ
2. Materials for Microcontact Printing
2.1. Glass Substrates Coated with Titanium then Gold
Microscope slides (Fisher, Pittsburgh, PA, no. 2) are loaded on a rotating
carousel in an electron-beam evaporator (most of these are partially home
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