Biomedical Engineering Reference
In-Depth Information
10.2.1 Topography Gradients
Research has shown that surface topography influences cellular response
and hence several methods have been developed for the generation of
physical (topographical and mechanical) gradients.
25,103,113
One example of
topography gradients are pore size gradients. The osteogenic differentiation
of MSCs on porous surfaces has been reported to respond differently to the
feature size of nanopores
114
and even symmetry and disorder of nano-
pores.
70
Zhao et al.
115
showed that etched titania surfaces, with pore sizes
around 100 nm and a pore wall width of 20-50 nm promotes osteogenic
differentiation in rMSCs. In another study, it was shown that the ordering of
nanopits (120 nm in diameter and 100 nm deep) in polymethylmethacrylate
(PMMA) significantly influenced the attachment and differentiation of
MSCs.
70
Interestingly, it was observed that the more disordered topography
arrays allowed for significantly increased osteospecific differentiation.
Porous silicon (pSi) gradients
46,108,116
have been designed for applications
ranging from optical sensors
107
to modulation of cell behaviour
116
and stem
cell differentiation.
117
A decrease in pore size has been shown to increase the
attachment of rat mesenchymal stem cells (rMSCs).
108,118
In another study,
the pore size of 41 mm and
o
50 nm in diameter was shown to be optimal
for the attachment of neuron-like cells.
116
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10.2.1.1 Porous Silicon Gradients
pSiisincreasinglybeingchoseninbiomedical applications due to is bio-
compatibility, degradability and the ease in tailoring its structural properties.
119
pSi is a modified format of the chemical element silicon (Si) whereby micro-
and nanoscale pores are formed in the surface structure. Hence, pSi exhibits a
large surface area to volume ratio and hence is highly desirable as a substrate in
biomaterials applications such as drug delivery.
120,121
pSi is formed through
anodisation with hydrofluoric acid (HF) as the electrolyte. The pore structure
can be accurately controlled through varying the etching conditions. The cur-
rent density and the etching time can be modified to control the pore size and
depth of the pores, respectively. Various forms of pSi, such as films, micro-
particles and membranes, can be formed through adjusting the etching con-
ditions and further processing of the etched structures (Figure 10.5).
.
Figure 10.5 Various forms of pSi including (A) films, (B) membranes, (C) micro-
particles
122
and (D) gradients.
Image B courtesy of Yit-Lung Khung, Voelcker Research Group, Flinders
University.
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