  Active in-plane remodelling is an important mechanism of tissue
morphogenesis, yet its underlying physics is not understood. We study a
nonlinear mechanical model of active cell-junction instability, which predicts
universal critical collapse kinetics of its length during cell intercalation.
At the onset of fluidity, where the energy landscape flattens, this collapse
can get stabilized by a limit cycle. This type of junction-length oscillations
is different from quasioscillations, which appear around a stable fixed point
even in the linear-elastic regime. Interestingly, in cuspy regions of the
energy landscape, the instability often causes junctions to "condense" around
the cusps.
