Fig 5. Cell geometry.

Cell geometry is determined by the ratio of the tension coefficients. a) when η(i,j) = 0, there is no tension on an inner edge, and it can be regarded as an imaginary cell wall; b) when η(i,j) = 0.5η(i,0), there is a strong adhesion force between the two cells; c) when η(i,j) = η(i,0) = η(j,0), the two cells behave as if physically they have the same wall; d) when η(i,j) = 1.5η(i,0), there is a weak adhesion force between the two cells; e) when η(i,j) ≥ 2η(i,0), The two cells have no adhesion and behave like soccer balls. Adding an inner wall would be more costly, as it is equivalent to adding two outer walls. In this case, the overall energy of the two cells is not reduced.