  Inspired by how cells pack in dense biological tissues, we design 2D and 3D
amorphous materials which possess a complete photonic band gap. A physical
parameter based on how cells adhere with one another and regulate their shapes
can continuously tune the photonic band gap size as well as the bulk mechanical
properties of the material. The material can be tuned to go through a
solid-fluid phase transition characterized by a vanishing shear modulus.
Remarkably, the photonic band gap persists in the fluid phase, giving rise to a
photonic fluid that is robust to flow and rearrangements. Experimentally this
design should lead to the engineering of self-assembled non-rigid photonic
structures with photonic band gaps that can be controlled in real time via
mechanical and thermal tuning.
