(Meeting ID: 827 2887 0880 Passcode: oobleck)
Speaker:
Kalpit Bakal (Eindhoven University of Technology)
Authors:
Kalpit Bakal (Eindhoven University of Technology), Wyss H.M. (Eindhoven University of Technology)
Title:
Extending Capillary Micromechanics for Studying Viscoelastic Behaviour at Microscopic Scales
Abstract:
Capillary Micromechanics measures the elastic modulus of hydrogel particles, biological cells and other soft objects at microscopic length scales. The method uses tapered glass capillaries, with a diameter at the tip that is smaller than the diameter of the particles to be probed. As a suspension of particles is flown through such a capillary, a single particle gets trapped in the tapered section, blocking further fluid flow. The deformation of this particle as a function of the applied pressure difference can then be monitored using microscopic imaging, yielding information on the elastic mechanical properties of the soft particle. Previously, the entire process of regulating the applied pressures and quantifying particle deformations was performed manually, which is a cumbersome process and prone to poor repeatability. Moreover, no efforts have been made to measure the detailed time-dependent response of the soft particles. This would enable us to gain valuable information on the time-dependent, viscoelastic properties of the particles, rather than only the static, elastic behavior. We present a semi-automated implementation of Capillary Micromechanics, where, once a particle is trapped in the tapered capillary, the entire process of pressure regulation and image acquisition is automated. This automation significantly improves the ease of operation and the repeatability of the measurements. Moreover, we have implemented time-dependent measurements such as a creep test, in which the time-dependent deformation of the particle is probed in response to a step-wise increase of the applied pressure. We are also currently working on implementing stress controlled oscillatory tests. These measurements enable us to extract additional information such as or the frequency-dependent viscoelastic moduli of the particles. We validate and test this new approach by performing measurements on microscopic polyacrylamide hydrogels and apply this method to cancer cell spheroids.
Speaker:
Mingyang Tan (Northeastern University)
Title:
Structure and Dynamics of Frictional vs Frictionless Colloidal Gels
Authors:
Mingyang Tan (Northeastern University), Jamali, S. (Northeastern University)
Abstract:
Functional materials of diverse types can be fabricated through dispersions of colloids. The properties of the materials at the macroscopic scale originate from the microscopic features and, ultimately, to the particle level, including the surface functionality and surface topography of the particles. In most studies, the interactions between particles are modeled to be central, where attractive/repulsive forces are aligned with the centerline between two particles. However, in cases where particles having rough surfaces, noncentral forces (e.g., friction) become influential. In this presentation, I will discuss the formation of space-spanning particulate networks of attractive frictional and frictionless colloids, with an emphasis on the structural features of the resulting gels and their network characteristics. This is followed by rheological characterization of the gels and correlating the microscopic features and forces to macroscopic mechanics of the system.