Paper Number
BL14                         My Program 

Session
Biomaterials, Bio-fluid Dynamics and Biorheology

Title
Emergent stress transmission in active cytoskeleton composites

Presentation Date and Time
October 20, 2025 (Monday) 4:25

Track / Room
Track 6 / Sweeney Ballroom C

Authors (Click on name to view author profile)

  1. Razzaghi, Aysan (University of San Diego, Physics and Biophysics)
  2. Valentine, Megan T. (university of California Santa Barbara, Mechanical Engineering)
  3. McGorty, Ryan J. (University of San Diego, Physics and Biophysics)
  4. Robertson-Anderson, Rae M. (University of San Diego, Physics and Biophysics)

Author and Affiliation Lines (in printed abstract book)
Aysan Razzaghi1, Megan T. Valentine1, Ryan J. McGorty2 and Rae M. Robertson-Anderson1
1Physics and Biophysics, University of San Diego, San Diego, CA 92110; 2Physics and Biophysics, University of San Diego, San Diego, CA 92110

Speaker / Presenter 
Razzaghi, Aysan

Keywords
experimental methods; bio-fluid dynamics; biorheology; techniques

Text of Abstract
The cytoskeleton provides structural integrity to the cell and plays a critical role in regulating essential mechanical processes such as stiffening and softening, intracellular transport, and morphogenesis. To gain an understanding of the mechanical properties of the cytoskeleton, we prepare in vitro reconstituted cytoskeletal composites which consist of co-polymerized actin filaments and tubulin dimers along with motor proteins such as kinesin, which bind to and move along microtubules thereby inducing active contractile behavior. These active cytoskeletal composites (ACCs) have been shown to exhibit pronounced spatiotemporal heterogeneity, not only in their microstructure but also in their mechanical responses due in part to their viscoelasticity and the excess stresses generated by active contractions. To characterize the complex spatiotemporal response of ACCs to applied stress, we combine nonlinear micro-rheology and time-resolved differential dynamic microscopy (DDM). To apply perturbations, we employ holographic optical tweezers to oscillate a single or a pair of particles that can produce well controlled stress fields within the sample that locally approximate pure shear, simple shear, or compressional and extensional stress. Our findings reveal that while increasing the concentration of kinesin motors up to a certain threshold enhances local stress generation, it simultaneously leads to shorter-range stress propagation. Our powerful approach allows for the discovery of emergent rheological properties of ACCs that were found to directly be linked to the transport across cells membrane. Further, our method can be implemented to investigate other active matter with exquisite sensitivity across a broad range of length and time scales.