High Throughput Techniques for the Investigation of Cell–Material Interactions - Biointerfaces: Where Material Meets Biology - page 295

surface-bound RGD concentrations (Figure 10.16C). 76 These studies high-
light an important conceptual advantage of the gradient format in that it
allows for rapid screening of a large number of surface properties that are
important in the bio-interface context, whilst determining effective limits of
immobilised biomolecules required for the observation of a given cellular
phenomena, thereby enabling optimisation. Earlier studies of peptide gra-
dient surfaces have been limited to the linear form of RGD. However, the
cyclic form of RGD has demonstrated significantly enhanced bioactivity
compared to the linear version. 226-228

d n 3 r 4 n g | 7

10.2.4 Two-dimensional Chemical Gradients
The preparation of 2D chemical gradients has been pursued by several Re-
search Groups in recent years, with applications ranging from surface
dewetting and nanoparticle attachment to protein adsorption and opti-
misation of cellular response. 23,101,144,152,167,176,229-234 Orthogonal polymer
brush gradients displaying variations in grafting density and molecular
weight have been reported by Bhat et al. (Figure 10.17A). 23,144,152 Firstly, a
concentration gradient of initiator molecules was deposited onto the sub-
strate through vapour deposition. Secondly, the substrate was placed into a
polymerisation chamber with the initiator gradient running in the 10 dir-
ection. The monomer, poly(dimethyl aminoethyl methacrylate) (PDMAEMA)
solution was slowly drained from the polymerisation chamber which in turn
lead to the formation of a molecular weight gradient in the y-direction.
PHEMA orthogonal gradients were also prepared using this procedure

.

Figure 10.17 (A) Thickness of PHEMA in MW/grafting density (s) orthogonal

PHEMA gradient; (B) thickness of PHEMA MW/s orthogonal gradient
(z-scale in nm); (C) Fn density in MW/s orthogonal gradient (z-scale in
nm). Scales for position on the substrate in parts (B) and (C) are in cm,
(D) images of MC3T3-E1 cells cultured on the PHEMA/Fn gradient
substrates. Images 1 to 3 refer to different regions of the gradient as
shown in (C).
Figure adapted from Bhat et al. 23