Biomedical Engineering Reference
In-Depth Information
droplet routing is negligible, which implies that droplet routing has no influ-
ence on the operation completion time. While generating physical layouts,
the synthesis tool in [15] provides only the layouts of the modules, and it
leaves droplet-routing pathways unspecified. The assumption of negligible
droplet transportation times is valid for small microfluidic arrays. However,
for large arrays and for biochemical protocols that require several concurrent
fluidic operations on-chip, the droplet transportation time is not negligible
and routing complexity is nontrivial.
Moreover, due to advances in microfluidic module design (smaller feature
sizes, improved materials, etc.), the fluidic operation times are decreasing
steadily [49]. However, the droplet transportation times are not decreasing at
the same pace. As a result, routing times must be considered during opera-
tion scheduling and in the calculation of assay completion times. For the
synthesis results derived from the methods proposed in [15], the impact of
droplet routing on assay completion time might be significant, and the upper
limit on assay completion time might be violated. In such scenarios, the bio-
chip design will no longer correctly implement the desired biochemical pro-
cedures. Also, if a synthesized design is not routable, either the chip must be
discarded or time-consuming resynthesis must be carried out. To avoid such
occurrences, we have to anticipate the availability of routing paths during
synthesis. Therefore, droplet routing must be included in the synthesis flow
for digital microfluidics.
The other drawback of the synthesis flow described in Chapter 1 is that it
is defect oblivious. It can neither guarantee that the design is robust, that is,
defect tolerant, nor does it facilitate reconfiguration techniques that can be
used to bypass defects. Therefore, defective chips must be discarded if errors
are observed during testing or assay operation. The lack of defect tolerance
leads to reduced yield and higher chip cost in an extremely cost-sensitive
market. Therefore, defect tolerance needs to be integrated with droplet rout-
ing and biochip synthesis.
2.2 Routing-Aware Synthesis
In this section, we describe how we can incorporate droplet routing in the
synthesis flow. Droplet-routing methods can be viewed as being either
anticipatory—that is, anticipate the routability (defined qualitatively as the
ease of droplet routing) of the synthesized biochip and design the system
to be easily routable—or based on postsynthesis routing to find the efficient
droplet pathways.
We attempt to provide a guaranteed level of routability for every module
pair that needs to be connected to each other. Instead of finding efficient
droplet pathways after synthesis, we attempt to achieve high-routability
