Biomedical Engineering Reference
In-Depth Information
operation can be accommodated in its designated time interval due to the
availability of slack or unoccupied time slots in the schedule. In this case, the
schedule can simply rely on the available slack or unused time interval for
droplet routing. In the second scenario, operations are scheduled so tightly
that there is not enough slack available for routing. Here, we deal with this
problem by adding an extra time slot for routing. As a result, the schedule
result is “relaxed,” and the completion time is increased. Note that in relax-
ing the schedule, the ordering of the start times of operations is not changed;
therefore, the change in the schedule has no impact on other aspects of syn-
thesis, namely, resource binding and module placement. The updated assay
completion time includes the routing time cost and reflects the actual time
needed for executing the biochemical protocol on the synthesized biochip.
2.3 Defect-Tolerant Synthesis
In Section 2.2, we addressed the problem of integrating droplet routing in
the synthesis flow. In this section, we focus on enhancing the robustness of
the synthesized design. In order to do this, we incorporate defect tolerance
as an objective for routing-aware synthesis. Defect tolerance methods can be
viewed as being either anticipatory—that is, anticipate defect occurrences
and design the system to be defect resilient—or based on postmanufacture
reconfiguration and resynthesis. Here, we refer to these two types of defect
tolerance as presynthesis and postsynthesis defect tolerance, respectively.
2.3.1 Postsynthesis Defect Tolerance
We first focus on postsynthesis defect tolerance. Digital microfluidic bio-
chips are fabricated using standard microfabrication techniques [9]. Due to
the underlying mixed technology and multiple energy domains, they exhibit
unique failure mechanisms and defects. A manufactured microfluidic array
may contain several defective cells. Defects observed include dielectric break-
down, shorts between adjacent electrodes, and electrode degradation [28].
Reconfiguration techniques can be used to bypass faulty cells or faulty opti-
cal detectors to tolerate manufacturing defects. Bioassay operations bound to
these faulty resources in the original design need to be remapped to other
fault-free resources. Due to the strict resource constraints in the fabricated
biochip, alterations in the resource-binding operation, schedule and place-
ment must be carried out carefully. Our proposed system-level synthesis
tool can be easily modified to deal with this issue. To reconfigure a defec-
tive biochip, a PRSA-based algorithm along the lines of the one described in
Section 2.2 is used. The following additional considerations must be taken
into account.
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