BenchMasteryMolecular biology techniques & virtual lab

Rheology

Amplitude sweeps find the linear region; frequency sweeps show how the material responds on different timescales. Together they give the stiffness you quote.

G′ · G″Simulator readyCore simulatorEngine: Materials, mechanics & devices
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Oscillatory sweeps

Amplitude sweeps find the linear region; frequency sweeps show how the material responds on different timescales. Together they give the stiffness you quote.

How it differs from the standard method

  • Always run the amplitude sweep first.
  • Pick a strain well below the yield point, then keep it fixed.
  • Report G′ and G″ with strain, frequency, geometry and temperature.
In this lesson · about 1 min read
  1. Solid, liquid, or both at once
  2. Always find the linear region first
  3. Shear thinning and printing
  4. Key terms
  5. When to use it
  6. Sub-techniques

1Solid, liquid, or both at once

Hydrogels and bioinks are viscoelastic: they store energy like a solid and dissipate it like a liquid. A rheometer applies a known deformation and measures the stress that comes back.

G′ > G″

Gel

Elastic response dominates: the material holds its shape.

G′ = G″

Gel point

The crossover during crosslinking, where a liquid becomes a solid.

G′ < G″

Liquid

Viscous response dominates: the material flows.

2Always find the linear region first

Moduli only describe the material if the deformation is small enough that the network is not being broken. An amplitude sweep increases the strain until G′ falls away; everything below that is the linear viscoelastic region.

3Shear thinning and printing

In a flow test the sample is sheared steadily and viscosity is plotted against shear rate. Many polymer solutions thin as the rate rises, because the chains align with the flow.

Key terms

Practise these as flashcards →
G′ (storage modulus)

Elastic, recoverable part of the response, in pascals.

G″ (loss modulus)

Viscous, dissipated part of the response, in pascals.

tan δ

G″/G′. Below about 0.1 the material is solid-like; above 1 it flows.

Linear viscoelastic region

The range of strain where moduli do not depend on amplitude.

Gel point

The moment during crosslinking when G′ crosses G″.

Shear thinning

Viscosity falling as shear rate rises; the opposite is shear thickening.

Thixotropy

Structure that breaks down under shear and rebuilds over time at rest.

When to use it

  • Matching a scaffold's stiffness to the tissue you are modelling, since cells respond strongly to substrate mechanics.
  • Checking that a bioink extrudes through a nozzle and holds its shape afterwards.
  • Following crosslinking in real time to find the working window before a gel sets.

Compared with alternatives

Tensile & compression testing →

Measures bulk stiffness and strength to failure, rather than the frequency-dependent response of a soft gel.

Hydrogel synthesis →

Where the formulation being measured comes from.

Scaffold fabrication →

Printing and casting, which depend on the flow behaviour measured here.

Material characterization →

Chemistry and structure, complementing the mechanics.

Sub-techniques

Choosing one here switches the whole page, including the protocol and the lab, to it.

Amplitude sweeps find the linear region; frequency sweeps show how the material responds on different timescales. Together they give the stiffness you quote.

  • Always run the amplitude sweep first.
  • Pick a strain well below the yield point, then keep it fixed.
  • Report G′ and G″ with strain, frequency, geometry and temperature.