  Phase separation is as familiar as watching vinegar separating from oil in
vinegrette. The observation that phase separation of proteins and nucleic acids
is widespread in living cells has opened an entire field of research into the
biological significance and the biophysical mechanisms of phase separation and
protein condensation in biology. Recent evidence indicate that certain proteins
and nucleic acids condensates are not simple liquids and instead display both
viscous and elastic behaviours, which in turn may have biological significance.
The aim of this perspective is to review the state-of-the-art of this quickly
emerging field focusing on the material and rheological properties of protein
condensates. Finally, we discuss the different techniques that can be employed
to quantify the viscoelasticity of condensates and highlight potential future
directions and opportunities for interdisciplinary cross-talk between chemists,
physicists and biologists.
