Automated path planning for washing in digital microfluidic biochips

A digital microfluidic biochip is often deployed for multiplexing several assays in space and in time. The residue left by one assay may contaminate the droplets used in the subsequent assays. Many biochemical assays involving cell culture also require sweeping of some residual media from an active droplet on-chip. Thus, fluidic operations like washing or residue removal are needed to be performed routinely either to clean contamination from the droplet pathways or for rinsing off certain droplets on the chip. In this work, we present graph-based algorithms for path planning of wash droplets in both array-based and irregular geometry biochips. The proposed algorithms can be used for total washing i.e., for cleaning the entire biochip or for selective washing of sites or pathways located sparsely on the chip. We address the problem of reducing the path length and washing time with or without capacity constraints of the wash droplets. The contaminated pathways are assumed to be Manhattan or curved, and hence our algorithms are applicable not only to conventional field-actuated biochips, but also to the emerging class of light-actuated biochips. This technique will be useful in automating reliable operation of a wide class of digital microfluidic healthcare devices.