# Fibre elasticity

1. Jan 23, 2016

### tribaggili

Hello,

Im studying amyloid fibres, which are filamentous proteins that intertwine between them (from 2 to 4 and more) and form fibres (2-20nm thick). I see that when that below a threshold length, the fibre is linear, beyond the threshold length, the fibre bend always with the same, constant angle. My questions are:

-why does this happen?

-can I calculate the elastic modulus from the bending angle?

Im not a physicist, trying to become a biophysicist, so any help will be very welcomed!

Thank you,
Andrea

2. Jan 23, 2016

### Nidum

Please post a picture or clear drawing for us to understand this problem properly .

3. Jan 23, 2016

### tribaggili

Here is a picture...on the right part there is a long fibre, with that constant bending, on the left part few small fibres, straight.

Thank you,
Andrea

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4. Jan 23, 2016

### tribaggili

since the radius of curvature is small, it is possible that the bending can be appreciated only on long fibres, so maybe no different behaviour between short and long fibres...these fibres (short and long) are probably composed of 2-or more entwined filaments...my question is why they bend? and could I obtain physical properties from this bending? such as stiffness?

Andrea

5. Jan 23, 2016

### Nidum

6. Jan 23, 2016

### Andy Resnick

If I understand your question correctly, you are asking about the 'persistence length' of a polymer:

https://en.wikipedia.org/wiki/Persistence_length

For amyloids in paerticular:

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.96.238301
http://pubs.acs.org/doi/abs/10.1021/ja206513r

7. Jan 24, 2016

### tribaggili

Well, Nidum and Andy, Im surprised how much you helped me, with your links I think I got all the theoretical and experimental information to properly interpret my fibres and understand their behaviour....I even found a freeware app, FiberApp, that runs with Matlab and should predict all the properties of amyloid fibrils...currently Im trying to install it and hopefully it will works....so a big thank you for your work and very relevant contributions!

Andrea