my general interest is in talking about
systems such as this tolerant scheme
that you see consisting of particles
each of which is powered or energized it
could be a swinging my problem is Ammar
macro one like this and groups of the
movie clear the regarded as a kind of
material so my interest really is him
taking collections of such objects it
could be a bunch of knots forming a
cloud like things you see sometimes
above your head in evening when you’re
walking outside it could be an organized
stage of millipedes like these seem
Hyderabad monsoon it could be the cells
in a developing tissue and you could
take these materials and you then as a
material not especially anything but as
some material science scientists sighs
and those questions like a what full
pressure of an insect club is it like a
bunch of gas molecules moving around in
a box you can ask is this object is a
weird kind of liquid crystal I mean it
consists of elongated things they
spontaneously lined up is it a funny
state of matter which I can study with
concepts similar to those that come up
on a crystal physics oh you can ask what
is the role of forces and mechanical
flow in organizing tissue into the macro
organism that you see now whatever size
these are not just sort of funny
problems oh how cute
you can look at the Flies on Macs and
think of them as a gas these are grand
transformers because if we can get a
physical understanding of cells tissues
developing tissues wound healing at the
transition to critical migration in
cancer I think a great evil be done to
solve these vital problems not by the
speaking of biochemistry engine
but by the mechanics and flow and force
and there’s a huge trend in present day
physics and little by little in present
day biology good three good systems in
this way so it’s also given rise to
identity into place in physics which is
look you’re all a stunning collection of
gas molecules in a box system a fixed
energy or systemic almost fixed energy
at extend the chair other words and use
particles and you understand from an
annex now supposing instead each of the
particles that was continuously powered
each one had an onboard fuel time or
each other in hydras sugar in the
surroundings that it converted into
motion you would have a collection of
particles which you would then call
active matter if you can understand it
you can understand some of these systems
if you can understand it the weirdest to
understand these can you make a copy of
it can you make it then you may not like
that matter so these are the kinds of
things I’m very very used in these days
now you want a theory of this stuff the
first question is giving a theory of how
something goes from randomly moving to
moving in an organized way there are
very popularly successful theories of
this starting actually from movies of
sandwich and becoming part of physics
over the past 15 years or so which says
you have a particle
among many particles and each of these
guys tries to line up with its neighbors
as best it can and having lined up moves
so imagine doing this all in Padua you
can do this an impersonation really and
what you will find is that if the error
that HP’s agents makes in aligning he’s
small and if the number of neighbors is
large then this state where everybody is
on average moving in the same direction
is favored what that actually is is
fixed by some interaction if the noise
is high or the density is though you get
a random state so it’s not that
different in some ways from how
something becomes a magnetic
and you know it’s not gonna fail
integers or something is crystalline and
low temperatures and liquidity
conditions those mental ideas have been
used very successfully to understand
phenomena
however this is a satisfactory theory of
this special organization of the pattern
of the picture but I think about the
mechanics few understand tissue as
material you’d understand any Kanaks so
we got into this problem some years ago
and said look go back to particles
assume they have a uniform for short
energy supply and each party is capable
of propelling itself now how does it
compare itself either by pushing on the
medium around they said all that pushing
our other particles around itself mutual
pushing is a propulsion mechanism these
are systems not systems in which you are
exerting the total force in women so the
profile of force around each particle
has two bits winding in opposite
direction what we call it either these
objects such as this Factory in here or
this alga disturb the medium around
themselves in characteristic ways the
back meaning by pushing fluid out along
its long axis the alga but we’ll kind of
breaststroke
pulling through it in along a small axis
if you think about these problems
collectively rather than just a single
particle level that has had already been
done for mechanics you formulate what
amounts to a generalization of something
that main engineering students learn you
can make up the continuum mechanics of
active not
corrections of what would say energized
think of them not as individual
particles continuous medium and fill the
mechanical carriers so this is what
happened initially in our research and
then in Paris in President did the same
thing thinking not of collections of
organisms moving through a fluid but of
what goes on inside oneself each saying
it sell their experiments this is a
polymer scaffold concepts where there
are molecular motors
this combined system again is will you
do l’objet plus Angelica Bachchan so the
same equations emerged syphilis X deadly
and this is why it’s what we got with
Nazi curiosity but the other interesting
because got to see something work
mechanics of cells the mechanics of said
aggregates then you have a chance at
answering some of the questions that I
posed a couple of slides ok now this
wasn’t just a description this is a
pretty little kid he predicted a couple
of pretty direct consequences one it
turns out with collection of these
particles and you measure the viscosity
recollection and you compare it to the
same collection of those particles are
dead but still present then the guys
that swim like this make the suspension
more viscous than when they’re dead and
the guys that swim by cooking make the
suspension less viscous than when they
attack so this is a simple picture which
you can understand by just looking in
this garden will you make a set of a
flow like this you align these filaments
they pull back no flow you set up a flow
like this align the holes they push back
from the same book so this will lower
the sauce seems to increase yourself
this simple ideas we tested now in
various
with very little formulations also over
the past several years and as recently
as last year there’s really been
confirmed stunningly in a set of very
nice experience and the other prediction
is supposing you have an alliance state
of much imagined deadly fire but this is
kind of fact me all lined up
he’s that stage sustainable it was a
bunch of dead molecules
that stated this organisation would stay
stable and four little bit distance what
happens to each of these guys has nice
within specified it turns out if you’ve
got these kinds of things a stage that’s
all lined up on average like that if you
disturb it slightly like this sets up
floors which further make the
disturbance go in the same direction so
you put a bunch of pullers also move
together like this this continously
unstable to this disturbance dance
camera this disturbance they distort and
spontaneous flow get set up specific
video aligned seven German particles is
that here we do just self-starting flows
in it you can see I’m getting all the
time and this interesting idea was
confirmed rather beautifully in several
experiments but in particular in
experiments looking at what wasn’t
inside one cell this is the nucleus of a
cell and you’ve got this vlog here which
is going round and round I definitely
use a minute so you’ve got the cell
based on some polymer pirates sitting
there is boundary is fixed and the cell
is the nucleus actually spinning why is
it happening
it has happening basically because of
the effect that we just talk to a fan if
you look at the surroundings of this
nucleus you find these sites carbon
filaments are all nicely an item kind of
a line but with a slight distortion and
this is circulating flow going on that
the flow has a profile which we can
calculate and she will compare to the
measured value and it keeps
qualitatively looks very similar the
rotation rates also look very similar
and so this is a brutal confirmation
something one part about initially the
level of organisms
he said we discovered inside once said
there will be many other tests of this
idea and antenna is one of very nicely
active alliance
it starts going by itself um now moving
away to organisms and cells one of the
things I talked about earlier was how do
you imitate self-propulsion period
before some units at the park even there
are cars and there are clockwork motors
and things but cattle simply do you
discipline and on wood pulp Angus scale
well one cool way to do it is take an
object like this this is the loop ends a
bit more thick like this would say a
flagman put it in a medium containing
chemical that this catalyst bit makes a
breakdown Ceylan into oxide then what
happened you have an imbalance the
distribution of hydrogen peroxide on the
two sides may be less from the catalytic
side and the other side this will give
rise to a
listen get close to the surface it’s
good our swimmer so our interest was in
saying okay you can you can do this but
can you make even smaller particles
maybe particles are not really propel
themselves but there’s a gradient in
some chemical cubic particles have done
at home the point in the direction of
gradient and then swim towards it or
they run away from something so it turns
out you can I want to spread my
practical details but what you can do
basically is you can design the backer
or catalyst on the particle and the
pattern of how the solid particles
interacting surface and make particles
which will have desired chemo factory
fault if they can sit they can orient
and signal to each other by the
separately using around and you can get
all kinds of interesting patterns this
is interesting ongoing work another even
sillier way to imitate motility now I’m
going to be chemical to be very googley
physical Easter get the surface and
sprinkler what about the wrong side and
object like this little stick in my hand
you place it on that and I can shaking
the surface up and down very fast then
these objects will get tossed up and
come down like this and if the two ends
of the party of these rods are different
the contact mechanics is different when
this end hits or that end hits like this
and so this motor will start hopping
preferably preferentially in one
direction the identity itself changes
because of system being a little noisy
so if you look at one single particle it
make it big so that’s one little partner
talking it’s the surface is my making up
and down you are by simulation the
particles own movie dish is telling in
which vehicle which is all the food this
is an idea that a group in Tokyo had
when we do the idea and said if you have
a collection of such particles will they
form an organized block so initially we
studied this for particles whose two
ends were the same and tested some
apparent violations of our theories of
active matter and turned out right there
after we decided to study mixtures of
these kinds of particles and wrong
particles so Google Iasi study the
correction of little rocks like this
surrounded by a bunch of bees because
experiments the rods worth a brass and
the beach world and we need is a little
big objects fine and I’m wrong when I’m
a fake and they found was initially
nothing can be interesting you’ve got a
bunch of rods bunch of beads they’re
also running around like they want to go
somewhere the beads are sort of coming
the way and looks like boy okay
take the same system and study it
keeping the number not increasing the
number of these pointy motile particles
increasing the concentration only
athletes and before your very eyes you
will see that the rods
organize themselves into a coherent
pattern they all start moving in the
same direction the rod sensors aren’t
completely sure they aren’t dropping
each other but they manage to align each
other and so amazingly so what we were
able to show also is the dismal effect
is not an artifact of having walls you
can repeat this thing in a faithful
mechanically faithful computer
simulation you can see this flocking
phenomenon happen even in a computer
simulation where the system has no
you can understand it favorite devices
by looking closely what’s happening in
this relation here’s one rod moving that
way here is the flow of beads around it
notice that out quite a distance the
beads are moving the same way as destroy
the distance up to which that motion
persists in the same direction gets
longer and longer as you increase the
concentration of the beats the other
part of the story the other part of the
story is that if you have one rod
pointing that way let’s say sitting in a
medium of beads flowing that way I clave
the rod will turn the point in the right
direction
this is also one this you can see the
computer study if nothing else if you
pose a cloak off the screen
this guy will start turning so this is
too far dance leads to positive feedback
between the rod make the beats to on the
beats aligning the rods you can make
this fancier but I figure out the
equation because it’s total quantity and
predictively of what density will this
what are you consistent spontaneously
take this so we will do that all the
nicely so we mean continuing this very
interesting area
given primarily by your curiosity how
these ridiculously simple little systems
all the more complicated cellular
systems or word props and special
spectacular properties
hopefully the hope of this understanding
matter in a strongly driven space but
also in the book that is a deeper
understanding of the fundamentals will
ultimately
one applications you’ll be able
understand cell division battery valence
and tissue better you’ll be able to
understand how in these funny systems a
small number of motile articles he’s
able to climb a large number of normal
hypotheses sphere silence of the beats
that cell just jump up and down in
places one for the odds this’ll be this
really cool physics and there’s the
potential for real application in areas
ranging from engineering
so they slightly different systems if
you look at these local models you’ve
been adding some more realism like that
takes time for one of these guys to
smart with neighbors and reorient and
interaction of one of these guys the one
in front of it might not be same as the
one of this guy the one behind it
these effects the traditional striking
features such as farming graves and the
funny instabilities and this is work
that at present is going on so I’m I
closed with that just in time however
the means to that we have in this active
matter of viewpoint a paradigm for
understanding in mechanical and since
your pop is a very good usually huge
range of scales with implications for
very seriously exactly Hughes
it’s important to get the general
principles right and make robust not
model specific regions first because you
can get those right there other things
will fall and some of those that really
start with turn out right and we have a
lot of fun studying artificial clocks with that I close