  Microfluidics-based biochips are soon expected to revolutionize clinical
diagnosis, DNA sequencing, and other laboratory procedures involving molecular
biology. Most microfluidic biochips are based on the principle of continuous
fluid flow and they rely on permanently-etched microchannels, micropumps, and
microvalves. We focus here on the automated design of "digital" droplet-based
microfluidic biochips. In contrast to continuous-flow systems, digital
microfluidics offers dynamic reconfigurability; groups of cells in a
microfluidics array can be reconfigured to change their functionality during
the concurrent execution of a set of bioassays. We present a simulated
annealing-based technique for module placement in such biochips. The placement
procedure not only addresses chip area, but it also considers fault tolerance,
which allows a microfluidic module to be relocated elsewhere in the system when
a single cell is detected to be faulty. Simulation results are presented for a
case study involving the polymerase chain reaction.
