Doug Turner wrote:


.... range of tensions with a specific knot and specific material, one
could repeat the "knot-in-a-sponge - warm rinse cycle" and see if
there is a threshold. Similarily, different materials may have a
requirement for a much higher tension when setting a knot to obtain
resistance to unravelling than other materials.

I think this might be a fruitfull avenue to explore. Intuitively I
think that with failure under load the tension when tying the knot might
not matter all that much, where as for unravelling when not loaded (I
still think there needs to be a generally accepted term for this) it
might be a more important factor.


Continuing with the "thought experiment" ...

Another variable to interpret the "knot-in-a-sponge - warm rinse
cycle" would be the "spring" in the thread. By "spring" I mean the
force of the thread to straighten itself when bent. This spring would
act against the frictional force stopping the knot from unravelling.
It would be another force, in addition to the forces created by
shaking, that the tension used to set each part of the knot would have
to overcome. If there is a tension threshold for the resistance to
unravelling when not loaded, then it would nicely mark some complex
relationship between coef. of friction, stretch, spring, environment,
perhaps the thread's diameter and other unidentified variables. If you
do the "rough and tumble method" experiment and there appears to be a
threshold, I would very grateful if you would let us know!

A suggestion for a generally accepted term for unravelling when not
loaded is UNL (Unravelling when Not Loaded). I think UNL trips lightly
from the tongue and acronyms are always fun and popular. :-)

I was interested to see that in some climbing ropes a few meters of
each end of the rope were manufactured to have diffent
characteristics. Those characterists, which were not acceptable for
the rope as a whole, recognised that the ends typically had knots tied
in them.

As a "brain storming" suggestion, perhaps the suture should be
manufactured so that the needle and the first 1/2 of the suture are
friendly to piercing tissue. The second half changes (perhaps with
colour for identification) to have properties to reduce UNL.

If this isn't already the case, and if you mention this to a suture
manufacturer, please let us know their response. If their response to
you is, "when you learn to tie knots properly, you won't have this
problem", I will have to say "Dem's the breaks". If you are Doug
Turner, the "orthopod", I expect, when you read this, to hear your
groan where I live - 1/2 way around the world.

Best wishes - Brian.