Dynamic Light Scattering Microrheology Reveals Multiscale Viscoelasticity of Polymer Gels and Precious Biological Materials

Abstract

The development of experimental techniques capable of probing the viscoelasticity of soft materials over a broad range of time scales is essential to uncovering the physics that governs their behavior. In this work, we develop a microrheology technique that requires only 12 μL of sample and is capable of resolving dynamic behavior ranging in time scales from 10–6 to 10 s. Our approach, based on dynamic light scattering in the single-scattering limit, enables the study of polymer gels and other soft materials over a vastly larger hierarchy of time scales than macrorheology measurements. Our technique captures the viscoelastic modulus of polymer hydrogels with a broad range of stiffnesses from 10 to 104 Pa. We harness these capabilities to capture hierarchical molecular relaxations in DNA and to study the rheology of precious biological materials that are impractical for macrorheology measurements, including decellularized extracellular matrices and intestinal mucus. The use of a commercially available benchtop setup that is already available to a variety of soft matter researchers renders microrheology measurements accessible to a broader range of users than existing techniques, with the potential to reveal the physics that underlies complex polymer hydrogels and biological materials.

Spectroscopic photonic force optical coherence elastography

“…We speculate that the discrepancy may be attributed to the microscale forced fluid flow dynamics induced by the oscillation of each bead, compared to the relatively homogeneous fluid flow dynamics resulting from bulk mechanical loading. Nevertheless, the power-scaling law trends in our results are in good agreement with other microrheological measurements in PAAm hydrogels measured with dynamic light scattering or AFM, which have obtained similar frequency-dependent behaviors [4,35], providing a side validation to our spectroscopic PF-OCE.…”

“…For instance, spectroscopic rheological properties of active cytoplasm in cells can provide unique fingerprint-like information for identifying different cell viabilities, providing additional quantitative pathological characteristics [3]. Spectroscopic rheology can also be helpful in revealing dynamics of polymer networks, including DNA hydrogels [4,5].…”

Dynamic Light Scattering Measurements for Soft Materials on Solid Substrates: Employing Evanescent-wave Illumination and Dark-field Collection with a High Numerical Aperture Microscope Objective

“…Dynamic light scattering (DLS) is a useful method for conducting studies of the dynamic properties of soft materials, such as polymer gels, liquid crystals, colloids, and lipid assemblies. [1][2][3][4][5][6][7] Since it probes molecular relaxations that occur in the wide time region ranging from 10 -3 s down to 10 -6 s, DLS enables us to extract information of multi-scale dynamic properties derived from the fluctuations from collective (e.g., entangled polymer networks) to individual (e.g., single polymer chains) motions. 1,3,[5][6][7] Over the last two decades, soft materials supported on solid substrates, such as polymer brushes and supported lipid membranes (SLBs), have become increasingly important in the development of organic transistors, implantable materials such as artificial joints, and sensor devices for the microanalysis of gases, cells, and blood components.…”

“…[1][2][3][4][5][6][7] Since it probes molecular relaxations that occur in the wide time region ranging from 10 -3 s down to 10 -6 s, DLS enables us to extract information of multi-scale dynamic properties derived from the fluctuations from collective (e.g., entangled polymer networks) to individual (e.g., single polymer chains) motions. 1,3,[5][6][7] Over the last two decades, soft materials supported on solid substrates, such as polymer brushes and supported lipid membranes (SLBs), have become increasingly important in the development of organic transistors, implantable materials such as artificial joints, and sensor devices for the microanalysis of gases, cells, and blood components. [8][9][10][11][12] The static properties of soft materials supported on solid substrates, such as domain structure, thickness, and molecular conformations, have been widely investigated using atomic force microscope, sum frequency generation spectroscopy, and X-ray or neutron scattering methods.…”

“…However, few studies on the dynamic properties of soft materials supported on solid substrates with DLS have been reported, 16 although there are many DLS measurements of the dynamic properties of soft materials in bulk, such as hydrogels and free-standing black lipid membranes. [1][2][3][4][5][6][7]17,18 In contrast to soft materials in bulk, in the application of DLS to soft materials supported on solid substrates, the intensity of the reflected light from substrates is extremely high, which hinders the detection of the small changes in the intensity of scattered light derived from the fluctuations of the soft materials at the interfaces. In addition, in the supported soft materials, inhomogeneous domains are expected to be formed on substrates depending on the compositions and concentrations of material components.…”