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I'm not an engineer but a neuroscientist.

I do research in spinal cord injury whereby a clip is used to clamp the spinal cord to induce a bilateral compression injury model.

My research looks at the differences in the injuries to the neck and lower back spinal cord. The key problem here is that the neck spinal cord is wider in diameter than the lower back cord.

Our clip is 1 mm in width. So my question is, if a 35 gram clip is used to clamp a cord of a smaller diameter, and we wanted to hold the distribution of force equal in a larger cord, would the force increase or decrease?

My logic says that the force must be increased, but when we do a 35 gram injury to the neck cord, all of the animals die so it may be difficult to use force normalization in our particular case.

Thanks!

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Assuming you want to maintain the same pressure on the tissue on the thicker part of the cord of the animal you would need more force.

Say by applying 30 grams pressure to a one millimetre diameter cord you squish it to an oval with a 2 millimetre side, it means it is under 15 grams/mm stress.

If you were to apply the same stress to a two millimetre diameter cord so as to squish it to a four millimetre wide oval but with the same 15 grams per millimeter of pinched area, now you'd need 60 grams clip.

This is purely a mechanical outlook, as to the sensitivity of different areas of a nerve cord or spinal cord, that's your area of expertise.

On a personal note I owe my left thumb to a colleague of you guys, a hand surgeon at UCLA hospital who helped my chain sawed thumb get implanted back to full function by borrowing some nerve from my leg, more than twenty years ago.

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  • $\begingroup$ Thanks so very much, that’s what I expected. It may be like comparing apples and oranges. On the note of your thumb, I’m very happy to hear that you got it restored! $\endgroup$ – James Hong Nov 2 '18 at 14:31

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