Physicists at LMU Munich have developed a groundbreaking new model that explains the formation of active foams, a complex and dynamic structure with potential applications in nanotechnology and synthetic biology.
Unscrambling Filaments and Motors Dance
The autonomous organization of individual particles into complex structures is a central ingredient to many of the life-sustaining chemical processes, as well as their synthetic equivalents in the realm of nanotechnology.
For many years, LMU physicist Professor Erwin Frey and his team have been investigating the processes that underlie this phenomenon of self-organization. Now they have produced a theoretical model of the phase transition to an “active foam”, a new form of organized matter that arises as motorized protein fibers interact with one another.
This pattern emerges from the competition between microtubules and molecular motors, which are proteins that move along the fibers. These motors ‘zip up’ the filaments, co-aligning them and guiding their sliding motions past each other and thereby, (hopefully) lead to the emergence of complex structures such as asters, micelles or even active foams.
Micelles to foams: phase transition driven by density
At UC Santa Barbara, the researchers started with a model system that was far less complex than living cells and confirmed that under biologically relevant conditions they observed the formation of numerous structures, from aster-like micelles to a novel phase called “active foam.”
The secret to this transition is in the density of microtubules and molecular motors. At low numbers of components the individual particles have much more freedom to move, which leads to distinct micelles. However as the density rises these layers take on a band-like appearance and eventually combine to give the complex, honeycomb-like structure of the active foams.
While honeycombs are rigidly structured, these foams constantly shift shape — the filaments and motors can easily move other elements of the pattern. This response is one of the critical features of active matter, a class of materials that can convert available energy into something else and shares in common an internal dynamic.
Conclusion
Professor Frey and his team’s theoretical model may help advance studies of active matter, bio-nanotechnology applications. This breakthrough could illuminate the basic principles underlying the development of complex, self-assembling structures en route to creating new materials and devices whose design is inspired by dynamic processes in nature.
