[Seminar] Active contraction of cytoskeletal gels: Energetics & Kinetics

Cytoskeletal gels are engineered prototypes that mimic the contractile behavior of a cell in-vitro. They are composed of an active polymer matrix and a liquid solvent. Their contraction kinetics is governed by two dynamic phenomena: mechanotransduction (molecular motor activation, i.e., a reaction), and solvent diffusion. In our recent paper, presented at this seminar, we solve the transient problem for the simple case of a thin gel slab in uniaxial contraction under two extreme conditions: motor-limited or slow motor activation (SM) regime, and diffusion-limited or fast motor activation (FM) regime. SM occurs when diffusion is much faster than mechanotransduction, where the latter controls the kinetics of this reaction-limited process. FM, on the other hand, occurs in the opposite case, namely when solvent diffusion is the slowest process and thus control the kinetics of such a diffusion-limited process. We finally observe some scaling behavior describing the kinetics of contraction, and discuss the energetic tradeoff of contraction. SM provides contraction at the minimal cost but requiring the longest time, while FM provides the fastest contraction at the maximum energetic cost. Our model, albeit very simple, proposes a novel approach to study the active contraction of cells in the light of a reaction-diffusion phenomenon mediated by chemo-mechanical equilibrium. The energetic analysis will also inspire future studies on the metabolic adaptation of cells.

Mattia Bacca obtained a PhD in Structural Engineering in 2013, at the at the University of Trento, which awarded his thesis as ‘Best PhD Thesis’ that year. Continuing his studies, he joined the University of California, Santa Barbara (USA) as a Postdoctoral Fellow, prior to joining the University of British Columbia (Canada), in 2017, as a faculty member. He is Assistant Professor in Mechanical Engineering, and member of the Biomedical School, and the Institute of Applied Mathematics. During his career as a faculty, he received the Early Career Award from the Human Frontiers in Science Program, who is funding part of his research. His research is devoted to understanding the biological world through the use of mechanics via the development of mathematical and computational models.

(All are welcome to attend.)