Effect of Poisson ratio on cellular structure formation
  Mechanically active cells in soft media act as force dipoles. The resulting elastic interactions are long-ranged and favor the formation of strings. We show analytically that due to screening, the effective interaction between strings decays exponentially, with a decay length determined only by geometry. Both for disordered and ordered arrangements of cells, we predict novel phase transitions from paraelastic to ferroelastic and anti-ferroelastic phases as a function of Poisson ratio. 
Ilka B. Bischofs and Ulrich S. Schwarz (Heidelberg University and MPI   Colloids and Interfaces)