Geometrical control of interface patterning underlies active matter invasion

Area of Science:

• Active matter physics
• Soft matter physics
• Biophysics

Background:

• The interaction between active materials and confinement boundaries is crucial for emergent phenomena in active systems.
• For living active matter (e.g., bacteria), deformable interfaces are common boundaries, but their role in morphogenesis and pattern formation remains unclear.

Purpose of the Study:

• To investigate the evolution of bacterial active matter confined by a deformable boundary.
• To understand how activity-induced interface dynamics lead to morphogenesis and pattern formation.

Main Methods:

• Experimental study of bacterial active matter confined by a deformable boundary.
• Analysis of emergent morphological patterns and self-organization of bacteria.
• Development and application of a continuum active model.

Main Results:

• Emergence of ordered interfacial patterns with periodically spaced protrusions.
• Self-organization of bacteria into multicellular clusters with +1/2 nematic defects behind protrusions.
• Hierarchical transition from interfacial protrusions to creeping branches, enabling rapid, self-similar invasion.
• Identification of collective curvature sensing, where interface patterning is controlled by local curvature.

Conclusions:

• Collective curvature sensing arises from enhanced active stresses in high-curvature regions.
• The active length scale dictates the spacing of interfacial protrusions.
• A novel protrusion-to-branch transition mechanism for active matter invasion was revealed.
• Findings suggest strategies for engineering pattern formation in active materials.