  Tardigrades are microscopic animals widely known for their survival
capabilities under extreme conditions. They are the focus of current research
in the fields of taxonomy, biogeography, genomics, proteomics, development,
space biology, evolution, and ecology. Tardigrades, such as Hypsibius
exemplaris, are being advocated as a next-generation model organism for genomic
and developmental studies. The raw culture of H. exemplaris usually contains
tardigrades themselves, their eggs, and algal food and feces. Experimentation
with tardigrades often requires the demanding and laborious separation of
tardigrades from raw samples to prepare pure and contamination-free tardigrade
samples. In this paper, we propose a two-step acousto-microfluidic separation
method to isolate tardigrades from raw samples. In the first step, a passive
microfluidic filter composed of an array of traps is used to remove large algal
clusters in the raw sample. In the second step, a surface acoustic wave-based
active microfluidic separation device is used to continuously deflect
tardigrades from their original streamlines inside the microchannel and thus
selectively isolate them from algae and eggs. The experimental results
demonstrated the efficient tardigrade separation with a recovery rate of 96%
and an algae impurity of 4% on average in a continuous, contactless, automated,
rapid, biocompatible manner.
