High Throughput Techniques for the Investigation of Cell–Material Interactions - Biointerfaces: Where Material Meets Biology - page 296

(Figure 10.17B), and the adsorption of Fn as well as the growth of osteoblast
cells was investigated. Fn was found to bind to the region on the orthogonal
gradient displaying the lowest density and lowest molecular weight of
PHEMA (Figure 10.17C). Osteoblast cell density was also the highest in this
region (Figure 10.17D).
Dual molecular weight polymers have also been prepared using PHEMA
and poly(methyl methacrylate) (PMMA). 23 Firstly, a monolayer of the poly-
merisation initiator was deposited onto the surface. A thickness gradient of
polymer 'A' was prepared through slowly draining the solution from the
beaker so that longer polymer chains would be present in the region im-
mersed in the polymer solution for the longest period of time. Since this
polymer has been grown via ATRP the chains can act as initiators for the
polymerisation of polymer B. The substrate was rotated 901 and placed in the
reaction vessel containing polymer B. following the same solution draining
method, a chain length gradient of polymer B was created orthogonal to that
of polymer A. Polymer thickness was found to be linear along both axes, a
phenomenon that has rarely been seen in gradient preparation before. 7,25,123
This technique has allowed the authors to determine the optimal surface
conditions for both Fn adsorption and cell attachment on PHEMA and
PMMA substrates.
'Click chemistry' has been employed to generate orthogonal peptide con-
centration gradients. 167 In the first of several steps, a silane chemistry gradient
with a terminal chlorine functional group was prepared through a confined
channel vacuum deposition. The sample and a silane reservoir was placed in a
confined chamber and the vacuum was pulled away from the side nearest the
silane reservoir and away from the substrate (Figure 10.18), with a stream of
methanol injected form the opposite end of the chamber to quench the dif-
fusion process. The substrate was then rotated 901 and the vacuum deposition
process was repeated for a vinyl terminated silane. Peptides including RGD
and osteogenic growth peptide (OGP) were immobilised through two orth-
ogonal click reactions (thiolene and copper-free Huisgen cycloaddition).

d n 3 r 4 n g | 7

.

10.2.5 Topography: The Chemistry of Two-dimensional
Gradients
Whilst there are several examples depicting 2D gradient surfaces with
changes in chemical properties along both the x- and y-axis, there are far
fewer examples detailing 2D gradients of topography and chem-
istry 101,102,108,151,235-237 or topography and topography. 238-240 Meredith
et al. 101,102 reported on an orthogonal gradient with variations in polymer
composition (x-axis) and annealing temperature (y-axis). Poly( DL -lactide)
(PDLA) and poly(e-caprolactone) (PCL) co-polymer gradients were prepared
through a syringe pump, as detailed in Figure 10.19A. 101 Although molecular
diffusion will lead to a uniform composition throughout the gradient over
time, the time scale for which the gradient is in the syringe is too short to
reach equilibrium. The polymer gradient was deposited in a strip along the