Biomedical Engineering Reference
In-Depth Information
arbitrarily complex microfluidic systems becomes tractable. The constituent
cells may be reorganized at different hierarchical levels, either through hard-
ware or software, to provide new functionality on demand.
By varying the patterns of control voltage activation, many fluid-handling
operations such as droplet merging, splitting, mixing, and dispensing can
be executed in a similar manner. For example, mixing can be performed
by routing two droplets to the same location and then turning them about
some pivot points. The digital microfluidic platform offers the additional
advantage of flexibility, referred to as reconfigurability, since fluidic
operations can be performed anywhere on the array. Droplet routes and
operation-scheduling results are programmed into a microcontroller that
drives electrodes in the array. In addition to electrodes, optical detectors
such as LEDs and photodiodes are also integrated in digital microfluidic
arrays to monitor colorimetric bioassays [23].
To address the need for low cost, PCB technology has been employed
recently to inexpensively mass-fabricate digital microfluidic biochips. Using
a copper layer for the electrodes, solder mask as the insulator, and a Teflon
AF coating for hydrophobicity, the microfluidic array platform can be fabri-
cated by using an existing PCB-manufacturing process [25]. This inexpensive
manufacturing technique allows us to build disposable PCB-based micro-
fluidic biochips that can be easily plugged into a controller circuit board,
which can be programmed and powered via a standard USB port. Figure 1.2a
shows a typical experimental setup, where a PCB-based microfluidic biochip
is plugged into a controller platform that is connected to a PC. Biochip users
can activate or deactivate the on-chip electrodes to execute fluidic operations
by simply manipulating the control pins using a software interface, as shown
in Figure 1.2b.
However, multiple metal layers for PCB design for large-scale microfluidic
biochips may lead to reliability problems and increase fabrication cost. Thus,
reducing the number of independent control pins is important for successful
commercialization. We can also address individual electrodes separately by
employing a serial-to-parallel interface. However, this requires active circuit
components on the PCB, for example, logic elements such as gates and flip
flops, which will lead to increased cost and power consumption.
1.2 Synthesis, Testing, and Pin-Constrained Design Techniques
Recent years have seen growing interest in the automated design and syn-
thesis of microfluidic biochips [14-18]. One of the first published methods
for biochip synthesis decouples high-level synthesis from physical design
[11]. It is based on rough estimates for placement costs such as the area of
the microfluidic modules. These estimates provide lower bounds on the
