Biophysics Lecture

Many biological systems are spatially heterogeneous and exhibit nonlinear responses, e.g. switching states in response to small changes of local concentration of diffusible signaling molecules. The local concentration of signals depends on the balance of rates of reaction and mass-transport phenomena (including flow and diffusion, which are in turn affected by spatial distribution and matrix binding). Historically, quantitative descriptions of local switching in response to diffusible signals in biological systems were often incomplete: scientists had better tools for controlling rates of reactions than for manipulating transport phenomena, so the rates of production and consumption of signals were better understood than the rate of mass transport. Yet, when these experiments were performed, they suggested that changes in transport rates alone can be significant enough to perturb local concentration of a signal and control switching. Microfluidic and chemical tools are emerging to control transport phenomena and spatial distribution of diffusible signals. I will describe a phenomenon of patchy switching to illustrate how these tools can aid understanding of the interplay of nonlinearities, transport phenomena, and spatial effects. This talk will describe the conceptual framework necessary for understanding patchy switching and related phenomena, and will also provide experimental examples from my lab in blood coagulation and microbial dynamics.