Phase-separated droplets swim to their dissolution

Area of Science:

• Biophysics
• Cell Biology
• Materials Science

Background:

• Biological macromolecules can form liquid condensates, crucial for membraneless organelles in cells.
• The physical consequences of chemical activity within these condensates are not well understood.

Purpose of the Study:

• To investigate the movement of biological condensates along chemical gradients.
• To explore the phenomenon of active and passive droplets responding to chemical environments.

Main Methods:

• Utilized model bovine serum albumin (BSA) condensates.
• Incorporated urease enzyme into active droplets.
• Applied external gradients of enzyme substrate and products to passive droplets.

Main Results:

• Active BSA droplets containing urease exhibited self-propulsion towards each other.
• Passive BSA droplets displayed varied responses to chemical gradients.
• All studied droplets moved towards conditions that promoted their dissolution, a phenomenon termed 'dialytaxis'.

Conclusions:

• Dialytaxis is driven by gradients in interfacial tension, a consequence of dissolution-favoring conditions.
• This behavior is expected to be a general physical principle applicable to various condensates.
• Findings suggest novel physical mechanisms for active transport in cells and potential for designing fluid micro-robots.