Crack patterns of drying dense bacterial suspensions

Area of Science:

• Microbiology
• Soft Matter Physics
• Materials Science

Background:

• Drying of bacterial suspensions is common in nature and engineering.
• Evaporation-driven instabilities in dense bacterial suspensions remain understudied.
• Understanding these processes is crucial for various biological and material applications.

Purpose of the Study:

• To investigate the mechanical instabilities and crack pattern formation during the drying of bacterial suspensions.
• To explore the influence of bacterial motility on macroscopic crack structures.
• To link microscopic bacterial behavior to macroscopic pattern formation in drying films.

Main Methods:

• Drying experiments with suspensions of motile and immotile Escherichia coli (E. coli).
• Analysis of crack patterns using principles of elastic fracture mechanics.
• Application of poroelastic theory to model drying-induced stresses.
• Correlation of bacterial collective swimming behavior with crack initiation and propagation.

Main Results:

• Two distinct crack patterns were observed: circular cracks for motile E. coli and spiral cracks for immotile bacteria.
• Circular crack formation is driven by radial drying stress, initiated by the ordered structure of swimming bacteria.
• Bacterial motility significantly influences the macroscopic mechanical instabilities and resulting patterns.

Conclusions:

• Microscopic bacterial swimming behavior directly impacts macroscopic crack formation in drying films.
• The study establishes a connection between active matter dynamics and pattern formation in drying processes.
• Findings offer insights into biological processes involving drying bacterial suspensions and potential applications in material design.