We have successfully developed a unique fabrication process to integrate a
gradient-compliant PA gel into a microfluidic system. Most of the characteristics of
the gradient-compliant PA gel have been evaluated. The ability to generate
concentration gradients through our device has also been demonstrated. In theory, this
integrated PA gel-microfluidics device could generate two well-controlled mechanical
cues simultaneously to guide cell migration. The C2C12 cell experiments also provide
important information for further experimental design to test our hypotheses.
To fully demonstrate the potential of our device, there are three important future
works. First of all, establish a protocol or a solid approach to well control the inlet
flow. It is especially important since we need the flow to be slow enough such that the
movement of solutes will be similar with random walk. Passive pump or osmotic
pump (Park, Hwang et al. 2007) are possible solutions and good references to control
very slow speed flow. The challenge would be learning about these two approaches.
Secondly, eliminate the structure defects. These defects will interfere with the
control to the concentration gradients, thus increasing the complexity of quantifying
the relationship between signals and cell migration. Besides the lock and key design
described before, fabricate the master mold of PDMS substrate through
45
photolithography will also be useful. The difficulty would be familiar with multi-layer
SU-8 photoresist processing to construct the spacing in fig 2.7. Another good
approach is to fabricate thin-film PDMS substrate (Jo, Van Lerberghe et al. 2000).
Besides eliminating structure defects, we can replace the groove with a hole, thus
removing the cost of customized Glass_1. It may also enable our device be capable to
be studied with high power objective lens. The difficulty would be establishing an
effective protocol to reproduce the thin-film PDMS substrate.
Finally, use other cell types to evaluate the performance of our device. For
example, VSMC cells, which has been shown that they would respond to stiffness
gradient. Another example, the astrocyte, which has been demonstrated that it prefers
to migrate to the hypotonic region. Although it may increase the cost of the reagents
for cell culture, we can benefit from shortening the time to confirm our device
function well. That will certainly accelerate the optimization of this dual cues device.
For C2C12 cell migration studies, we can evaluate TI value to verify the impacts
of stiffness and osmotic gradients on guiding cell migration. The migration speed
difference between single cue and dual cues (e.g. osmotic and stiffness gradients in
parallel) would be an appropriate approach to test the facilitation between the two
signals.
46
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