Pressure, density, elasticity are classical physical properties, which are required to fully describe the processes in human cell assemblies – for example, to distinguish tumours from healthy tissue or to stimulate the regrowth of nerve cells. These examples illustrate how physics can provide new stimuli for basic medical research.

Today, modern physical methods and physical thinking are being transferred towards physiological application worldwide. In order to promote the exchange between different researchers and working groups, the Max Planck Zentrum für Physik und Medizin is starting a new series of public mini-symposia, in which two to three scientists from North America, Europe or Asia will present their work virtually. The series starts on March 10th, with further symposia planned for March 11th and 19th — and more to follow…

To take part in the symposia, please register for MPL's scientific lectures newsletter (please ensure that you tick the "scientific lecture" checkbox). We will send the Zoom links about one hour before the symposium starts.

The schedule for Thursday, March 11th in detail:

15:00 - 15:05  Welcome

15:05 - 15:50  Knut Drescher, MPI Marburg: "Principles of bacterial multicellular dynamics"

Abstract:

On surfaces, bacteria grow into multicellular communities termed biofilms, which are the most abundant form of life on Earth. Such biofilms cause many chronic and acute infections, which are difficult to treat because the cells inside these communities display strongly increased tolerance to antibiotics and disinfectants. I will first present imaging and image analysis techniques we recently developed to follow dynamical processes in biofilms at the single-cell level. Using these techniques, combined with physical models, I will show how we can reveal unifying principles for the dynamics of different bacterial multicellular systems, using bacterial biofilms and swarms as model systems.

— 10 min break —

16:00 - 16:45  Gijsje Koenderink, TU Delft: A biophysical perspective on connective tissue mechanics

Abstract:

Connective tissues such as skin and arteries are fascinating materials because they combine a superior mechanical strength with the ability to adapt and self-mend. Our aim is to understand the molecular basis of this paradoxical combination of strength and dynamics. Connective tissues are mechanically supported by an extracellular matrix made up of various polymers with complementary physical properties. Collagen forms a rigid fibrillar network that endows tissues with a high tensile strength, whereas proteoglycans and glycosaminoglycans form a soft hydrogel that confers resistance against compressive loads. To understand the mechanisms by which these polymers control tissue mechanics, we take a bottom-up approach: we reconstitute extracellular matrix networks from purified tissue components and quantitatively measure the mechanical properties from the network down to the molecular scale using rheology, optical tweezers, and atomic force microscopy. In this seminar, I will discuss our recent advances in understanding the role of collagen in controlling tissue strain-stiffening, plasticity, and fracture and the interplay of collagen with other matrix constituents including fibrin and proteoglycans. Our findings provide mechanistic insights that can be used to understand disease and to design biomaterials for tissue (re)generation and animal-free disease models.

— 10 min break —

16:55 - 17:40  Michael Krieg, ICFO Barcelona: "Bent enough or bent too much? - Cells and circuits coordinating body-brain interactions in C elegans"

Abstract:

Limb movement, but also visceral morphodynamics such as lung expansion, is powered by collective cell shape changes that are supervised by mechanosensitive receptor cells. During animal locomotion this leads to muscle contraction under extensive neuronal control, giving rise to periodic contraction/relaxation cycles that are performed with sub-maximal capacity. How the stereotypic contraction amplitudes are maintained and monitored by mechanosensory feedback remains largely unexplored. During this talk, I will highlight recent progress from my lab to understand the interplay between molecular cellular and tissuemechanics and their role in regulating proprioception during animal locomotion. We use C elegans as a model organism and exploit conditional genetic strategies to investigate cell-specific functions of neuronal mechanics in selecting the stereotyped locomotion pattern. With indicators for neuronal activity and mechanical stress, optical tweezers and genome editing we discovered that the spectrin has neuron specific roles in measuring bending stresses. To our surprise, we found that spectrin can sustain compressive stresses during body bending, which are required for activation of mechanosensitive ion channels of the TRPN/NOMPC family. On the contrary, application of mechanical tension caused a rapid and transient decrease in neuronal activity through two-pore potassium ion channels (TREK2). Since mechanical tension and compression co-exist in long axons during body bending, our work provides a framework to understand how a single axon with mechanosensory activity can locally regulate proprioceptive functions through mechanical compartmentalization. These finding provide insights into the mechanical regulation of body-brain interaction for muscle an internal organ sensation in general.