A microrheological study of hydrogel kinetics and micro-heterogeneity

Aufderhorst-Roberts, Anders; Frith, William J.; Donald, Athene M.

doi:10.1140/epje/i2014-14044-y

Cited by 12 publications

(20 citation statements)

References 50 publications

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“…The remarkable FDT states that the memory spectrum of the microstructure in the linear response regime is revealed from the colored noise of the fluctuations of probe particles. For biological materials, including the internal structure of single cells or lung mucus, there are unknown length scales and heterogeneity of the microstructure, so it is not sufficient to probe with one particle or at one location [13,14]. This is why the techniques of microrheology have been developed and honed on benchmark complex fluids such as colloids or pure homogeneous solutions of naked DNA as explained in Chap.…”

Section: Introductionmentioning

confidence: 99%

Complex Fluids and Soft Structures in the Human Body

Vasquez¹,

Forest²

2014

Complex Fluids in Biological Systems

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The human body is a composite of diverse materials able to perform specific functions. Few of these materials are simple liquids or solids; rather they share both liquid-like and solid-like properties. The material world between liquids and solids is unlimited and exploited by Nature to form complex fluids and soft structures with properties that are tuned to perform highly specialized functions. This chapter will briefly summarize the diversity of materials in the human body, and then drill deeper into one complex fluid (mucus, which coats every organ in the body) and one soft structure (an individual cell), and their remarkable properties. Some progress in characterizing these materials and modeling their functional properties, by others and our research group, will be presented with the take home message that we are in the early stages of interpreting experimental data and building predictive models and simulations of biological materials.

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Section: Introductionmentioning

confidence: 99%

Complex Fluids and Soft Structures in the Human Body

Vasquez¹,

Forest²

2014

Complex Fluids in Biological Systems

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“…Simulations of mechanical properties of simple model gels − support this theory, as do some prior experimental studies that measured only the micron-scale dissolution of the gel without simultaneously quantifying the number of cross-links ( i.e. , without measuring p c ). − The simultaneous measurement of both thus produces more quantitative testing of this theory. From these measurements we find that, for adenosine concentrations ranging from 2 to 14 mM, a plot of the normalized fluorescence (which captures the number of intact bonds) versus mean squared bead displacement is biphasic, with an early power law like phase transitioning into a plateau as the extent of dissolution increases and the hydrogel becomes liquid-like (Figure ).…”

Section: Resultsmentioning

confidence: 66%

“…This is unfortunate because the development of strategies for the rational optimization of responsive hydrogels will likely require quantitative understanding of their physical properties. For example, although theoretical − and simulation-based predictions − and indirect experimental studies − regarding the interplay between molecular scale cross-linker dissociation and larger-scale mechanics exist, direct experimental tests of these relationships are lacking. , In response, we demonstrate here methods for the measurement of the response kinetics of DNA hydrogels at length scales ranging from molecular through nanometer to hundreds of microns. As proof of principle, we have employed these methods to measure the dissolution kinetics of a model aptamer-based hydrogel as functions of effector concentration and the depth (within the hydrogel) and the length scale over which dissolution is observed.…”

mentioning

confidence: 97%

Simultaneous Measurement of the Dissolution Kinetics of Responsive DNA Hydrogels at Multiple Length Scales

Simon¹,

Walls-Smith²,

Freddi

et al. 2017

ACS Nano

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Recent years have seen increasing study of stimulus-responsive hydrogels constructed from aptamer-connected DNA building blocks. Presumably due to a lack of simple, quantitative tools with which to measure gel responsiveness, however, the literature describing these materials is largely qualitative. In response, we demonstrate here simple, time-resolved, multiscale methods for measuring the response kinetics of these materials. Specifically, by employing trace amounts of fluorophore-quencher labeled cross-linkers and the rheology of entrapped fluorescent particles, we simultaneously measure dissolution at molecular, hundred-nanometer, and hundred-micron length-scales. For our test-bed system, an adenine-responsive hydrogel, we find biphasic response kinetics dependent on both effector concentration and depth within the gel and a dissolution pattern uniform at scales longer than a few times the monomer–monomer distance. Likewise, we find that, in agreement with theoretical predictions, dissolution kinetics over the hundred nanometer length scale exhibit a power-law-like dependence on the fraction of disrupted cross-links before a distinct crossover from solid-like to liquid-like behavior.

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“…Recently, the single particle or multiple particles tracking has been widely used in studying gels and biological systems, such as investigating cell membrane, cell entry mechanics, DNA molecules, and proteins in living cells . Among these applications, the single particle microrheology in a wide frequency range has a good consistency with bulk rheology, but fails in the study of rheological properties when there is some interaction between the probes and the medium, such as the adsorption of polymers onto the probe surface and the electrostatic or hydrodynamic interaction.…”

Section: Passive Microrheologymentioning

confidence: 99%

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

Liu

2017

Macro Chemistry & Physics

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To overcome these shortcomings of macrorheology, a number of novel microrheological methods have emerged during the last few decades, [2] often involving a small tracking or probing particle (micrometer size) dispersed in a softmatter medium. By tracking the fluctuation due to thermal energy or applying an external force, usually in the form of magnetic force or optical trap, one can measure local mechanical responses. The local disturbance in a micrometer scale avoids reconstruction of local viscoelastic response, an inevitable problem in bulk rheology, especially when the probe particle size is smaller than the characteristic length of a soft matter. Depending on whether the probe is manipulated by an external force instead of a random walk due to thermal fluctuation, microrheometers can be generally characterized as active or passive ones. For an equilibrium system, the fluctuationdissipation theorem (FDT) guarantees that these two methods are equivalent. [3] In this review, we will detail these two classes of microrheometers, including their basic principles and typical setups as well as some recently developed hybrid microrheometers, [4][5][6] often used in characterizing polymer solutions and biological materials. Passive MicrorheologyIn a passive microrheometry method, the fluctuation of probes dispersed in a soft-matter medium is detected and analyzed by calculating the mean-square displacement (MSD) often from their video-based trajectories or scattered light intensities. Since the fluctuation of probes in space is driven by an extremely small thermal energy (k B T), the results from a passive method are always fallen inside the linear range of viscoelasticity. Generally, the elastic modulus is estimated within an upper limit of hundreds of Pa, which means that passive microrheometers are more suitable for measuring "soft" materials with a low viscosity and elasticity. Otherwise, the probes would be trapped without a measurable movement. Even newly developed super-resolution microscopes can provide a sub-nanometer resolution, [7] they are still not widely available methods and have a limited frequency range (up to 100 Hz). Mechanical properties of a soft matter can be obtained from MSD by using the generalized Stokes-Einstein relation (GSER). [8,9] In two extreme cases, (1) the probe is dispersed in a Newtonian viscous fluid and undergoes a Brownian motion with an MSD of 〈Δr 2 (t)〉. The viscosity η is related to the translational diffusion coefficient D as Microrheological TechniquesRheological properties of soft matter like polymer solutions/gels, colloidal dispersions, and biological materials have been extensively studied by macroscopic methods. Recently, a set of microrheometers has emerged as powerful tools to investigate the dynamics and structures of homogeneous or heterogeneous soft matter at the micro-or nanoscale. In this review, these microrheometers, including some novel hybrid microrheometers are summarized and compared.

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A microrheological study of hydrogel kinetics and micro-heterogeneity

Cited by 12 publications

References 50 publications

Complex Fluids and Soft Structures in the Human Body

Complex Fluids and Soft Structures in the Human Body

Simultaneous Measurement of the Dissolution Kinetics of Responsive DNA Hydrogels at Multiple Length Scales

Rheological Study of Soft Matters: A Review of Microrheology and Microrheometers

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