|
| Method/device | Description | Application variants and aspects | Studies using this method |
|
| Young’s modulus and complex shear modulus assessment |
| Note: different methods can give different results for the same tissue |
|
| Macromicroscale (whole tissue specimen elasticity is measured) |
| Micromechanical testing systems | Measuring applied stress and strain during deformation of the specimen of millimeter size (compression, tension, or indentation test); to measure viscoelastic properties (storage and loss modulus) dynamic mechanical analysis is used; that is, sinusoidal stress of certain frequency is applied and the strain in the material is measured | Compression test
Tensile test
Indentation | [53, 55, 132]
[61, 78]
[56, 58] |
| | | | |
| Indentation method | In indentation experiments, a rigid indenter (e.g., a plane ended cylinder, a cone shaped tip, or a sphere) is pressed against the tissue and shear moduli are calculated from the applied load and extent of tissue deflection | Nano- and macroscopic indentation | [33] |
| | | | |
| Rheometer | Two parallel plates or two coaxial cylinders with a narrow gap in-between are moving relative to each other, imposing shear stress on material squeezed in the gap; displacement and force are measured; thus, shear storage modulus and loss modulus are calculated and usually used to measure viscosity or rheology of fluids | Liquefaction stress of thixotropic gels
Viscoelasticity measurement | [87]
[12] |
| | | | |
| Magnetic resonance elastography | Shear waves inside the sample are induced by sonic mechanical vibrator on the surface of the sample; then, the shear wave propagation is recorded with a magnetic resonance technique and the image is assessed to generate a shear stiffness map | Non-invasive method for measuring stiffness in small samples | [76] |
| | | | |
| Ultrasound elastography | An external force is applied to the studied tissue and the resulting displacement and the generated strain are then mapped by ultrasound imaging; the external force can be static (compression, shear) and dynamic (shear waves propagation, whose speed is directly related to the medium shear modulus) | Non-invasive method for measuring tissues stiffness in patients, for instance, suffering from liver fibrosis | [44] |
|
| Nanoscale (local elasticity is measured) |
| Atomic force microscopy (AFM) | The specimen is subjected to indentation by nanometer size indenter; force-indentation distance profiles are collected and analysed with a Hertz cone model to compute the elastic moduli | Nanoindentation | [10, 49, 52, 68, 89] |
| | | | |
| Micropipette aspiration | The tip of a small micropipette is brought in contact with a sample and a series of equal steps in pressure are applied; the length of the sample aspiration representing an equilibrium deformation is determined for each pressure Young’s modulus is calculated from the experimental length–pressure data (using particular theoretical model) | Used for thin matrix samples to assess local characteristics of pericellular matrix | [37] |
|
| Pore size assessment |
|
| Advanced microscopy methods | The porosity and pore sizes of dried hydrogels are examined by microscopic imaging | Scanning electron microscopy (SEM) | [49, 51] |
| Confocal microscopy | [51] |
| | | | |
| DNA electrophoresis | The radius of gyration of extended DNA may be used to estimate the effective maximum pore size of the hydrogel | | [49] |
| | | | |
| Pore size through permeability measurement | Measuring permeability of the gel, that is, fluid flow velocity through the gel under certain pressure, allows calculating mean pore size | | [89] |
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