Dr. Benjamin Friedrich
Nonlinear dynamics and fluctuations in biological systems
Can we disclose the “patent applications” filed by nature? Can we understand the physical mechanisms used by biological cells and tissues to perform vital functions such as motility, information processing, and self-assembly of functional structures?
In my habilitation thesis in theoretical biological physics, I target these questions at the interface of physics and biology. I could disclose novel mechanisms of flagellar synchronization and cellular navigation, as well as the self-assembly of the contractile machinery in muscle cells. For these results, we combined mathematical modeling, data-driven computer simulations and new algorithms for the analysis of experimental data, while working side-by-side with experimental collaboration partners.
In all three biological system studied, flagella, sperm cells, and myofibrils in muscle cells, there is one theme: simple local interaction rules give rise to complex dynamics in space and time at the scale of cells and tissues. Physical descriptions and quantitative modeling allow to understand this dynamics. Importantly, physics also enables us to unravel the principles that make this dynamics robust with respect to noise and parameter variations, which are ubiquitous at the microscopic scale of biological cells.
My theoretical work was conducted in close collaboration with a network of experimental collaboration partners in Dresden and abroad, and benefited from rapid iteration loops between theory and experiment. Experiments guided the development of the theoretical descriptions developed by my group, while theory predicted new experiments not yet thought of by the experimentalists. Together, we understood examples of self-organized dynamics in selected biological model systems. In the future, we will move step by step to increasingly more complex model organisms such as cilia carpets on airway epithelia, and eventually address alterations of biological processes in models of human diseases such as Duchenne myopathy.
How do single biological cells move, process information, and build regular functional structures? As a theoretical physicist working at the interface of physics and biology, I built mathematical models and data-driven computer simulations with the aim to understand these fundamental questions of life. My habilitation thesis in theoretical biological physics addresses two central dynamical processes in cells and organisms: (i) active motility and motility control and (ii) self-organized pattern formation. The unifying theme is the nonlinear dynamics of biological function and its robustness in the presence of strong fluctuations, structural variations, and external perturbations.
We theoretically investigate motility control at the cellular scale, using cilia and flagella as model system. Cilia and flagella are slender cell appendages, e.g. of sperm cells and ciliated epithelial cells in our airways, which perform regular bending waves that are driven by the collective dynamics of molecular motors. We study the nonlinear dynamics of flagellar swimming, steering, and synchronization, which encompasses shape control of the flagellar beat by chemical signals and mechanical forces. Mechanical forces can synchronize collections of flagella to beat with common frequency. This synchronization occurs in the absence of a central pace maker. We could disclose a novel physical mechanism for flagellar synchronization by mechanical self-stabilization in free-swimming cells. This new mechanism is independent of direct hydrodynamic interactions between flagella, in contrast to a previous consensus in the field. In a theory-experiment collaboration with Prof. Howard (Yale), we confirmed this new mechanism in a simple model organism, the unicellular green alga Chlamydomonas.