Hello,

Well, without a bit more information this is difficult to answer. What are your samples and what do you wish to obtain by measuring them in this way?

In general assessing materials in this way can tell you a few things. Elastic solids tend to obey Hooke’s law, whereas, viscous fluids obey Newton’s law.

1. Hooke’s Law: σ = G γ (Where σ is the shear stress, γ is the shear strain and G is the shear modulus)

2. Newton’s Law: σ = η γ (Where σ is the shear stress, η is viscosity, γ is the shear strain.)

When these 2 models are compared, their fundamental difference is in the relationship of shear stress.

In Hooke’s model, the shear stress (σ) is related to the shear strain via the shear modulus (G). This equation, therefore, can be considered to measure the ability of a material to elastically deform. Newton’s model, however, relates the shear stress (σ) to the shear strain (γ) via viscosity. This can be considered a measurement of a fluid to resist shear. Many materials do not exclusively obey one of these laws; there are a range of materials, known as viscoelastic materials, which demonstrate behaviour of both and biological samples are one example of this.

For a solid (tissue, cartilage etc) biological sample, I would expect that G' (storage or elastic modulus) would dominate the behaviour and that G' should be greater than G'' (loss or viscous modulus). Tan delta is simply G''/G'. So the lower the value, the more of a "solid" or elastic material you have. The higher the value of Tan delta, the more viscous the sample.

I hope this helps

Laura

Hello,

Well, without a bit more information this is difficult to answer. What are your samples and what do you wish to obtain by measuring them in this way?

In general assessing materials in this way can tell you a few things. Elastic solids tend to obey Hooke’s law, whereas, viscous fluids obey Newton’s law.

1. Hooke’s Law: σ = G γ (Where σ is the shear stress, γ is the shear strain and G is the shear modulus)

2. Newton’s Law: σ = η γ (Where σ is the shear stress, η is viscosity, γ is the shear strain.)

When these 2 models are compared, their fundamental difference is in the relationship of shear stress.

In Hooke’s model, the shear stress (σ) is related to the shear strain via the shear modulus (G). This equation, therefore, can be considered to measure the ability of a material to elastically deform. Newton’s model, however, relates the shear stress (σ) to the shear strain (γ) via viscosity. This can be considered a measurement of a fluid to resist shear. Many materials do not exclusively obey one of these laws; there are a range of materials, known as viscoelastic materials, which demonstrate behaviour of both and biological samples are one example of this.

For a solid (tissue, cartilage etc) biological sample, I would expect that G' (storage or elastic modulus) would dominate the behaviour and that G' should be greater than G'' (loss or viscous modulus). Tan delta is simply G''/G'. So the lower the value, the more of a "solid" or elastic material you have. The higher the value of Tan delta, the more viscous the sample.

I hope this helps

Laura