OK hi everybody Mamie's parents for
a oppose doc in Princeton and

I'm going to tell you about basically two
stories today one is how that contract and

said this in The Express or the Matrix
interact mechanically where there

is there and violent and how that affects
the stiffness of the surround and

the second store so that's basically
relating experiments to maybe make or

break does that mean grow and
a fantastic buzz document and.

I'm just doing the theory so

I'm just going to tell you about whatever
where they've done the second part of

the story is about how we have
been using with Martin Lance and

chase borders using this data to
infer stress fields in these three D.

expect that our matrix.

So consider this contract and cell here
it's a cancer cell but really what

it's been selected for is just because it
is under surrounding collection matrix so

question is the most abundant protein
in your body it's it's there in cattle

agent tendons It's what gives us to
two to delist it into your skin.

And it's well known to have a strong
one in their mechanical properties and

what the them and

they just have been doing is that they've
put small beads small latex beads inside

this matrix and actively pulled
on it using optical tweezers and

then they've been measuring the skills
of force against displacement and

far from the cell you get is that curve
which has starts pretty pretty stuffed and

then stiffens when you get either you
when you go to stronger forces so

it's not in the early stiffening just as
you would expect from macroscopic which

when you get closer to the cell
along the contraction axis

you see that this curve gets steeper and
steeper and

you actually get a stiffer mechanical
response to these micro probes.

So.

This is generic Actually it's
not specific to could I Jen But

if you do it's two in favor of a more
complex networked called could make major

gel you in all these cases you get strong
stiffening near the said contraction

axis of up to two or the magnitude
of stiffening and that stiffening

range is about once a length in
size which is pretty long relished.

And by doing a lot of clever controls
what they found is that really what

induces the stiffening is the contract and
properties of the Center For

instance if you prevent them from for
contracting the network relaxes and

it becomes homogeneous soft.

And so the first take home message is that
the contract and sense really stiffen

messily and in the extended range
does their excessive matrix so

what will they feel basically what
they did where they feel when

the pulling around is not to the nastiness
of the Matrix it's really the stiffness

that induce themselves because of this
this stress and that's something that's

been predicted there it equally unmeasured
experimentally and so face to face

measurement in the past but it's the first
time that someone has shown it in three D.

expects that I matrix.

Now I've been telling you that it's
stress that is responsible for

this how can we does that how
can we measure of stress in this

in this is that we're all so
it's a complicated problem and

there are many challenges to
measuring stresses in three D.

These ordered none in the are that
are yours at the local skate

do one of these is the best approach
on the markets it's called three D.

direction force microscope and
it's basically uses the difference that

it measures strains by imaging before and
after contraction and

to do we have the better yield and
assumes that.

We know that as soon as
that the micro mechanics

is the same as the macro mechanics and
then you can reconstruct some of the.

Stress field but
it's extremely hard to treat and

in there it is it's it's basically
ignored this order and it's.

It's a it's really hard to apply.

When I think I would like to propose is
to develop a new method in which we use

the known in narrative to measure
stresses the way this works is that

well you can measure this reference curve
in which in which it's the derivative

of the force displacement killed here
including the differential stiffness

as a function of the folks and it's in
the locus of this in that that too is

still in our regime it's still
a nasty business and it increases with

increasing force that's the only nasty
thing that I've told you about before.

Getting close to the close to the cell
you get to that don't becomes higher and

higher and it's because of the increasing
stress that is responsible for

an increase of the nastiness and
so this it does that's interesting

there's increasing step stress and
increasing force we don't know about

stress we don't have access to it but
we know what the force because it is so

our idea is to use force as
a proxy to measure stresses so

take a linear look at point in
the point in your in your material you

can measure the linear stiffness and its
associated to an unknown stress you can

you can read out the effective force
that you would need to apply and stress

to matter you are to get to the same Look
at stiffness so this effective force F.

F.
effective is defined as the force

you would need to apply to
get the same stiffness as

you get in at the in our order from
the space so this is kind of a force.

Stress correspondence and
what you would like to say is OK for

some stressed kind of similar quantities
maybe they're proportional and

it's it turns out that this is
actually not such a simple.

Solution No not so simple as as this first
because force and stress have a difference

to me trees forces a dunce or a forces
effect of stresses at themselves and

if you reverse the force you basically
have a symmetry still there in

the first if the stiffness is what I think
in the force when the linear stiffness.

Has got to have it in that in the stress
because it's a there's no symmetry between

one side stresses of
uncompressed of stresses.

What I've shown is that if you go too
strongly in one in the order in a matter

you'll that stiffens as a power load then
actually you have the proportionality

between these two terms which we
called non-industrial which which is

a correspondence between force and
stress and allows us to infer stress.

Using the measurement of
the effective force and

we called this technique known in
a stress inference microscope.

Just a small simulation to give you
a kind of proof of called of principle.

I've been using the same
kind of networks as

charming presented this morning
that this time in three D.

and there is none in the elements but

it must it's here to mimic to do
experiments so we have a contract and

said here and this all these
beads showed the stress field and

that I measured numerically direct and
now I'm going to infer the pull of these

bones on into the stress using the stress
of the technique that I just described and

this is what I get so in the old these
areas actually do there's no stress and

the network is softer than
planned that then the lid

then the background stiffness so you can't
infer stresses using this method but

in all the parts where
there's strong contraction.

You get.

A very faithful representation
of the stress field.

To a professor of the weather so
I've responded to so so that a bit

difficult but it's really a perfect of
this project that we can get using the.

Micro to calibrate our our of
our technique so it's actually

if you want this is a manual fights
them and that is to use this technique.

What you should do to infer.

To infer stress fields in the media
is first you get the micro you.

Know didn't differential
stiffness against force.

And the macro.

Stress the strain.

Then you measure the stress feel.

So this is the stress as a function of
its weight then you measure the stiffness

field this is the sickness as a function
of the distance to the cell for instance

and then you use the stiffness fields and
and the dictionary between stiffness and

effective force to read out
the effective force and

then you and
this gives you the difficult stress and

to check if your consistently applying the
method you need to get you need to get.

In there stiffness that is
significant it consists.

Larger than the background
stiffness of the stress material

you need to be in the strong
in the one in which you are.

Using this method we've been measuring
stress fins in this system and

what we've observed is that the.

The stress is significantly larger than
previously reported it was in the hundreds

of us scales and
interestingly it decays as it

was inexplicable it made us do with
this but distance to the to the cell and

this menace to is actually
something that was predicted.

A number of groups
including where my Ph D.

work and that's something I think that's
expected in such networks because of

a few individual filaments in the network
so that's that was the conclusion I was

very proud of there's a smaller bet here
because actually this is not a conclusive

proof of this kind of network
physics because the renge of this

this is actually close to
the tip of the said here so

if it didn't minus three the two the gets
from the now order is not valid.

You need to think it about it as a two for
some of the boards instead of a four

as they pull and close to a force of
the pull you get or sort of minus two

which is the same prediction and
there's a that they're not known in our.

Predictions So that's kind of
a confused confusion between

what the political unknown in Advocate
here that makes this to claim it to be and

conclusive about long
range FOS transmission but

in any case we have long range stiffening
in this network just to summarize

we've shown that make you reveal this
strong stiffening of the aesthetic.

Of the United States
matrix surrounding says

we've developed stress
in France method to.

To infer stress is using
this in Asked if this is and

we've shown that the if we can
measure stresses this way and

with that this has been
published last week in T.N.A.

Yes And with that I'd like to
thank you for your attention.