Browsing by Subject "Biopolymer networks"

Now showing 1 - 2 of 2

Advanced imaging of biopolymer networks and filaments to resolve structure, filament-level mechanics, and cell-matrix interactions
(2018-12) Lissek, Emanuel Norbert; Florin, Ernst-Ludwig; Gordon, Vernita; Marder, Michael; Baker, Aaron; Fink, Manfred
The extracellular matrix (ECM) makes up the environment of many cells in our body and gives tissues their stability. It is comprised of highly non-linear fibrous biopolymer networks which display unique mechanical properties, such as stiffening by several orders of magnitude under strain. Cells interact with individual filaments of these networks, exploiting their properties to communicate and orient themselves, while migrating through the extracellular space. Its mechanical properties in turn profoundly influence the fate of cells. The cell-matrix interaction, however, is not well understood due to a lack of experimental techniques to both study the mechanical interplay between cells and their local environment on the single filament length scale, and quantify the contribution of single filaments to the large-scale network properties. To address this need, two novel microscopy techniques are described. First, quantitative Thermal Noise Imaging (TNI), a three-dimensional scanning probe technique which relies on a trapped nanoparticle as the probe. TNI is capable of imaging soft, optically heterogeneous and porous matter, with submicroscopic spatial resolution in aqueous solution. TNI images of both collagen fibrils in a network and grafted microtubules are shown, and it is demonstrated that structures can be localized with a precision of ~ 10nm. As a direct consequence of the work done with TNI, Activity Microscopy (aMic), a new way to visualize local network mechanics with single filament resolution is also introduced. Fibril positions in large two-dimensional slices through a collagen network with nanometer precision are localized, and fibrils' transverse thermal fluctuations with megahertz bandwidth along their contour are quantified. The fibrils' thermal fluctuations are then used as an indicator for their tension. The network displays a heterogeneous stress distribution, where “cold" fibrils with small thermal fluctuations surround regions of highly fluctuating “hot" fibrils. Finally, HeLa cells are seeded into the collagen network and the anisotropy in the propagation of their forces is quantified. While the data shown is limited to collagen, aMic will be of significant use when studying the mechanics of other fibrous networks and their application to artificial tissue and organ growth
Physical characterization of bacterial biofilm polymer networks to determine the role of mechanics in infection and treatment
(2018-11-29) Kovach, Kristin N.; Gordon, Vernita Diane; Florin, Ernst-Ludwig; Marder, Michael P; Smyth, Hugh D; Lynd, Nathaniel
Biofilms are communities of microorganisms that produce a matrix of extracellular polymers to surround and protect themselves from external forces in their environment. This communal lifestyle is incredibly beneficial for microorganism survival. Characterization of the mechanical properties of biofilms is a vital and understudied component of fully understanding these biological systems. In this dissertation, we break down the mechanical response of the Pseudomonas aeruginosa biofilm by its constituent polymers. These bacteria produce unique polymers to resist a variety of stresses. In the first part of this dissertation, using oscillatory bulk rheology, we characterize the viscoelasticity of biofilm polymer networks. Using genetically manipulated lab strains of P. aeruginosa, we isolate the mechanical response of each polymer by analyzing biofilms comprised primarily of one type of polymer. We find that the polymers have unique mechanical properties: some increase the yield strain and others increase elastic modulus. In strains of P. aeruginosa isolated from chronic infections, we find that the bacteria evolve to increase production of polymers that maximize the energy required to yield the matrix. In the second part of this dissertation, we work to mechanically compromise each of the polymers in the matrix. By attacking different matrix components, we learn more about the structural properties that give rise to mechanical properties as well as identify the most promising therapeutic treatments to break down biofilm infections. We find that specific enzymes are useful for decreasing yield strain of biofilms and increasing the diffusivity of the matrix. Decrease in yield strain means that biofilms will take less deformation before losing mechanical integrity, and the increase in matrix diffusivity means that current treatments such as antibiotics are more effective as the antibiotics can more easily reach the bacteria in the matrix to effectively kill them. This dissertation treats biofilms as polymer networks, divorcing the analysis from biological responses, in an attempt to well-characterize the understudied mechanical properties of biofilms. By approaching these systems from a physical standpoint, we are able to learn more about biofilms by breaking the mechanical response into constituent components, as well as learn about how enzymatic treatments alter biofilm properties.