Rigidity in mechanical biological networks

Area of Science:

• Biophysics
• Developmental Biology
• Materials Science

Background:

• Multicellular organisms develop complex morphologies crucial for function.
• Tissue rheology, or material properties, are actively tuned by organisms.
• Rigidity transitions, from fluid-like to solid-like states, are key to morphological control.

Purpose of the Study:

• To review recent theoretical work on mechanisms driving tissue rigidity transitions.
• To guide biologists in identifying these mechanisms in experimental systems (in vivo and in vitro).

Main Methods:

• Theoretical analysis of rigidity transitions in biological tissues.
• Classification of transitions based on dependence on small-scale structural parameters.
• Review of experimental examples and methods for distinguishing transition types.

Main Results:

• Identified two primary types of rigidity transitions: first-order and second-order.
• First-order transitions depend on connectivity (e.g., cell contacts, polymer branch points).
• Second-order transitions depend on geometry (e.g., cell shape, crosslink distance).

Conclusions:

• Theoretical frameworks explain how changes in microscopic parameters drive macroscopic tissue rigidity.
• Understanding these transitions is essential for comprehending morphogenesis and tissue engineering.
• Experimental validation and differentiation of transition mechanisms are crucial for future research.