RESEARCH INTERESTS
Gurmessa’s research vision is to design biomimetic materials that mimic the adaptive mechanics of living cells. The lab integrates expertise in cytoskeletal polymer networks and nanoscale buckling to engineer composites of protein filaments (actin, vimentin, microtubules) and phospholipid membranes. These systems are built to replicate essential cellular behaviors like stress sensing, active remodeling, and dynamic structural organization. By studying how filaments, crosslinkers, and motors interact to produce large-scale motion, the lab seeks to connect molecular mechanisms to emergent mechanical responses, bridging the physics of biological polymers and soft matter.
What roles does filament stiffness heterogeneity play in shaping the structure and mechanical behavior of composite networks? How do actin–vimentin composites respond under linear and nonlinear mechanical probing? What are the dynamics of network assembly and disassembly in cytoskeletal composites? Soft Matter, 2024, 20, 9007–9021 .
Microscale mechanics of actin networks
We learn from biology textbooks that animal cells are constantly in motion throughout their lives. While some cells—such as amoebae and cancer cells—travel over long distances, others—like muscle cells and dividing cells—remain largely stationary but undergo shape changes or internal structural rearrangements. How do cells generate such a wide range of movement patterns? This question lies at the heart of research in biophysics.
Previous studies suggest that cells achieve this diversity in motion by regulating several key processes:
The organization, dynamics, and geometric architecture of filamentous actin (F-actin), modulated by a wide array of actin-binding proteins.
The interaction between molecular motors and F-actin, particularly the activity of motor proteins.
The non-equilibrium polymerization and depolymerization of F-actin, driven by chemical energy from ATP hydrolysis.
The Gurmessa Lab investigates these mechanisms by integrating optical tweezers, fluorescence microscopy, and microfluidics. Below is a brief overview of our research interests. For more information, visit here or here.
Actin
Actin is a protein found in eukaryotic cells that plays a crucial role in a variety of cellular processes, including cell movement, muscle contraction, and cell division. Actin exists in two forms, globular (G-actin) and filamentous (F-actin), and the polymerization of G-actin into F-actin is a tightly regulated process that involves several actin-binding proteins. Actin networks are formed by the polymerization and organization of actin filaments, which can interact with each other and other cellular structures to create dynamic networks.
Entangled actin networks
How do physically entangled actin networks (see the images above: low (left) and high (right) concentrations with the same scale.) respond to non-linear deformations? What is the critical actin concentration for the non-linear behavior to emerge? How do dynamics scale with a concentration in the nonlinear regime? We use active optical tweezers microrheology to directly probe the microscale mechanical properties of entangled actin networks over a broad range of concentrations and strain rates. Macromolecules 49, 3948-3955(2016)
Crosslinked actin networks
In a reconstituted actin network, the self-assembly of actin structures is orchestrated by a class of proteins known as actin-binding proteins (ABPs). ABPs are found to organize F-actin into several structures, such as homogeneous and isotropically crosslinked networks, bundled networks, and a composite of isotropic and bundled networks (as shown in the image on the right, which is actin crosslinked by alpha-actinin) that provide mechanical support for the cell and play crucial roles in many cellular processes. How do ABPs assemble F-actin into such complex higher orders? How do chemically crosslinked actin networks respond to nonlinear microscale deformations? Biophys. 2017 Oct 3;113(7):1540-1550
Microfluidics
Actin polymerization and network formation are driven by ATP hydrolysis and vary depending on the concentrations of actin monomers and crosslinking proteins. We are interested in exploring the mechanical properties of these non-equilibrium systems during dynamic assembly and disassembly by using microfluidic devices to induce in situ dissolution and re-polymerization of actin networks by varying ATP concentrations in real-time while measuring the mechanical properties during disassembly and re-assembly. Soft Matter, 2019,15, 1335-1344
Previous work
Mechanics of nanoscale polymer thin films
This work focuses on surface instabilities of nanoscale polymer thin films when subjected to controlled external deformations.
Top row: wrinkling of thin films under 0, 6, and 15 % strains. Phys. Rev. Lett. 110, 074301(2013)
middle row: Response of pre-patterned PDMS under 0, 6, and 15 % strains. Soft Matter, 2017,13, 1764-1772, with a cover page article
Bottom row: response of colloidal monolayer to same strains as before. Granular matter, Granular Matter, 10(2013)
