>> Desney Tan: John Rogers is here from UIUC. He does nano and
molecular scale fabrication materials, patterning and builds some
really crazy electronics as you will see today. He has got a
chemistry/physics background and in fact has a physical chemistry PhD
out of MIT. He spent time at Harvard Bell Laboratories where he was in
the Condensed Matter Physics Department and in fact ran the department
for a number of years. He is now the Swanlund Chair in the Materials
Science and Engineering Department at UIUC with joined appointments
across just about every department you can imagine. I am not going to
list them. His publication patent press awards list is massive and
again you can look at his bio for a small snippet of that. He has also
had multiple startups starting with his PhD work and recently with a
company called MC10, which I don’t know if you are going to talk about.
>> John Rogers: A little bit yeah.
>> Desney Tan: But if you look at this project list as well he has done
everything from stretchable lithium ion batteries and silicon
integrated circuits to flexible silicon [indiscernible], electronics on
balloons for surgical catheters, cellular-scale optoelectronics,
negative index metamaterials, and the list goes on and on. The thing
he is going to talk to us about today is in the bio-integrated
electronics space, specifically epidermal electronics. So rather than
get in the way of a great talk I am going to hand it over to John.
>> John Rogers: Okay, thanks a lot Desney for that introduction and for
the invitation to come here and spend some time at the labs. It is
bringing a lot of good memories back from my time at Bell Labs, sort of
a research lab in a company that makes products. So I think it’s a
great environment to do innovation. I will tell you about some of the
things we have been doing at Illinois recently that may be of interest
to hardware interfaces to the body of relevance to future computing,
health, wellness, sports and other things.
And it’s referred to, this is a term we made up, sort of epidermal in
the sense that the electronics themselves have physical properties
pretty well matched to the epidermis. So they go on in a way that’s
more or less invisible to the person wearing the device, which we think
is important for an intimate high functionality interface to the body
to have that kind of wearability.
So I will start by giving you motivation and what we are trying to do
with perspective on how this kind of electronics kind of relate to more
conventional stuff. I will give you some ideas around requirements in
materials, mechanics and manufacturing in order to do this kind of skin
integration. And then the last half, maybe the last third or so is
just step you through a bunch of examples of things we have built with
the idea that this is still in the early days. And I think there are a
lot of opportunities for new ideas and higher levels of functionality,
but just give you a snapshot of where we are right now in the
development of this kind of technology.
So let me just start by telling you something that’s obvious, you
already know it, but it’s a useful reference point which is the future
of electronics where it’s been in the past, where it is now and where
it’s going into the future. And it’s really all about making things
smaller, faster and cheaper. So in the old days you had giant boxes
that filled desktops or filled rooms and were used primarily for
specialized industrial academic computation, but Moore's Law
miniaturization in the transistor sizes, reduction in their cost and
increasing levels of functionality. Really transformed the hardware
into completely new device formats and that’s an engineering
accomplishment. Maybe the more significant one is that it introduced a
qualitative shift in the way that computing devices are used in our
every day lives. It’s much more ubiquitous, much more personal as
communication tools, productivity enhancement, systems and
entertainment devices.
And if this is where we were, this is where we are and were are we
going in the future? It’s a pretty easy answer: You just go to the
semiconductor map and it tells you exactly where this integrated
circuit technology is going to be 5, 10, and 15 years into the future.
And if you think about folks who are in electronic materials,
electrical engineering and thinking about integrated circuits, doing
research on them, the vast majority are working on scientific problems
around that scaling. And that’s a very valid set of problems to be
thinking about because this is a trillion dollar global industry and
there are a lot of interesting fundamental science problems in the
service of that enormous market and enormous impact.
It’s not the future though that we are thinking about these days. We
are trying to do something a little bit different and complementary,
not competitive with that future, but something that might open up a
range of opportunities that are currently unavailable because one thing
that has not changed over the years is the platform for all of this
electronics. It’s always been silicon wafer, which is a wonderful
class of material in a wafer form. It’s a wonderful type of substrate,
but it has certain geometrical constraints that make it tough to say,
“Take your iPhone and wrap it onto your brain, melt it into your skin,
or envelop your heart with it, because the wafer is rigid, brittle and
planer. That’s fin for lots of applications, but there are some that
require intimate integration with biology that cannot be addressed with
commercial integrated circuits that exist today.
And the idea is that if you could do some of this stuff and bring all
of this power to bear on problems of human health or brain/machine
interfaces that could lead to another qualitative shift in the way that
the technology is used and expand out some opportunities there. So
that’s a 30,000 ft view of what we are trying to do. Let me pound that
message home a little bit further in the context of the brain. And we
have done a lot on the brain, the heart, and I will focus this talk in
the skin, but the brain is a good illustration to further help me make
the point that I am trying to make.
So if you think about the brain it is a very sophisticated electrical
system. And if you want to do therapy on the brain, you want to
diagnose abnormality in the brain, or you want to establish a
brain/machine interface the best way to do that might be to take the
most sophisticated man made electronics system, which is Silicon
[indiscernible] Electronics and interface it with the brain. But
that’s not easy to do for the reasons I have just told you. The wafer
itself it planer, it’s a huge geometry mismatch. What is not quite as
obvious is that there is also an enormous mechanics mismatch because
silicon is a very stiff hard material. It has modules of about 150GPa.
The brain is a soft squishy piece of Jell-O. Its modulus is about
5kPa. So you have geometry and mechanics problems there.
So what do people do today? This is the work horse for the last 20
years. It’s really a pretty nice piece of technology and it’s been
very useful for a variety of neuroscience studies. And it accommodates
that geometry mismatch through a micro-machined array of doped silicon
pins that penetrate down into the tissue on one side and on the other
side terminate on a flat platform where you can mount a chip that you
would dice out of the way and establish the electrical interconnect
that way. And you take that integrated thing and with an air hammer
you mount it onto the surface of the brain. These different pins can
penetrate to different depths in the brain, thereby solving the
geometry mismatch problem, but you damage the brain upon insertion.
Then what’s worse is that over time the interfaces between these hard
shafts of silicon in this soft Jell-O degrade, because the brain is not
static in a mechanical sense. It’s swelling, de-swelling, it’s
rattling around in the skull slightly and now you have a pin in a
moving bowl of Jell-O and that’s a bad mechanics interface to think
about.
So this is great and it will likely remain in wide spread use. But
what we are thinking about is what could you do to enable a future in
which the electronics are configured to match biology? So soft in a
mechanics sense, shape, conformal and then made out of bio-compatible
materials. So that’s a pretty clear example. The heart as well where
you can kind of appreciate the motivation. But the same constraints
and considerations apply to skin as well, because the skin; although
not as soft as the brain and not as reticulated in geometry as the
brain is rough, stretch and flexible.
So what’s done today usually involves point contact with conductive
coupling gels, tapes, individual wires that run to a separate box of
electronics. So electronics really not integrated with the skin. It’s
electrodes and this is great for a hospital or research environment,
but nobody is going to wear that long-term because you have got wires
running all over the place. And then also this tape interface to the
skin is irritating over time for reasons I will get into in a few
moments.
So, it’s not great for long-term wearability and also not great for
improving the sophistication of the interface. Because as you add
electrodes you add wires and pretty soon you are swamped with wires.
And it becomes a difficult scaling, which is a shame because the
electronics themselves are racing ahead according to Moore’s law, but
then your interface to the body is stuck in this kind of old approach.
You can get better and there are commercial devices and are more
sophisticated then this obviously. And this is kind of one example
where you have bare dye or individual chips mounted onto flex PCB. So
a tape of [indiscernible], you have adhesive on that and you can put it
on the forehead in this example, but still it’s not great for the same
reasons I just mentioned. You eliminate some of the wires, but you
don’t eliminate the mechanics problems at the interface which are
driven by the fact that the skin is soft and stretch and even a tape is
only flexible, it does not stretch. So it’s constraining the natural
motions of the skin and that’s kind of a problem.
So if you think about that set of circumstances you might conclude, “I
have got to use something other than silicon if I want to do better”.
And we have been working in this space almost 20 years by now and we
spent a lot of time looking at alternatives. And the semi-conductor is
probably the most challenging materials component of an integrated
circuit. So you can think about organics like polymers, small
molecules, single crystals, maybe carbon nanotubes. I don’t think
graphene is interesting tubes. Let’s say these classes of materials
and you might say, “Okay, polymer might be a good choice for a
semiconductor because it’s already kind of soft, bendable, whatnot”.
We have spent a lot of time on this. We have built flexible displays
like this one in the early days. The problems with polymers are that
their electrical properties are lousy. So you can do a slow nonemissive display like this. If you want to do a liquid crystal display
that’s a lot tougher and if you want to make a high-functional
interface to the brain that’s out of the question. So the topic might
be then, “I need a synthesized new polymer so I can move this metric
for transistor performance in terms of the mobility and centimeter
square per volt second from this regime up to something more comparable
to state of the art in organic electronics”. But that’s a large number
of, you know, that’s orders of magnitude is the point. So you have got
a huge gap and how you are going to span that gap becomes a topic of
research.
A lot of folks are still working on that. We sort of moved away
because that just seemed a little bit too daunting. And instead we
come back and ask the question: Is silicon really ill-suited for this
kind of thing? Certainly in the wafer format it is and certainly the
intrinsic material properties are not well matched, but could you do
some simple things to effectively bypass those apparent limitations?
And that’s where we focused and that’s what I will talk to you about
today, but not at a super deep level. I will just give you a sense of
it so I can skip over to what kinds of devices are enabled.
So if you think about the wafer as I already mentioned and as you know
you can’t bend it. And if you try to bend it, it will crack very
quickly. Why is that? That’s because partly the material property.
So you think about the bending stiffness and the degree of bendability
as defined by the peak strains associated with bending given radius of
curvature. It depends on the intrinsic elastic properties of the
material. That’s the Young’s module and you are stuck with that if you
want to go with silicon, but it scales with thickness in a pretty
straightforward, easy to understand way. It is a really strong
scaling. So the bending rigidity or the flex rigidity bending
stiffness is the product of these two things.
So what that means is that if you think about plotting the bending
stiffness as a function of thickness in a [indiscernible] plot you have
a power law behavior. So for a wafer that might be a millimeter thick
the bending stiffness is maybe 10 Newton-meters, but if you take that
wafer, you shave it down to something that’s sort of nanoscale in
thickness, so this is 20 nanometers in thickness, you have reduced the
bending stiffness by up to 15 orders of magnitude. So now it’s 10
[indiscernible] Newton-meters.
And although that’s just linear elasticity Newtonian mechanics, there
is nothing quantum about that, whenever you change a material property
by 15 orders of magnitude that changes qualitatively the way you sort
of think about it. And in fact silicon with that thickness is floppy,
very, very flexible as illustrated with the SEN [indiscernible] image,
in the sense of a low bending stiffness and also in sense of degree of
bendability. So the peak strains associated with bending are going to
define how far you can bend it before you crack it, because silicon can
only withstand about a one percent tensile strain. And what you see is
for a given bend radius R that bending strain goes down linearly with
thickness. So not quite as strong as scaling as the bending stiffness,
but nevertheless thinner is better, so very flexible, very floppy.
Now, if you think about silicon sheet with that type of thickness it’s
great, it’s bendable, but it’s incredible fragile. If you touch it, it
will shatter. It’s just not a sensible platform for an integrated
circuit in the same way that a silicon wafer is. In fact that’s why
people use wafers that are this thick. It gives it some robustness so
robots can move it around and you can put it on a PCD for example. So
the next question is that maybe you think about this as a building
block material for an integrated circuit that you would build on a
sheet of plastic or a piece of rubber.
So that brings up the next challenge then which is: How do you go about
gluing a piece of silicon to a piece of silicone rubber? And that’s a
hard problem because the material properties are so different. The
thermal expansion coefficients in particular are very different, a
hundred or thousand times different. As a result it’s hard to come up
with an adhesive that would keep a silicon chip bonded to a piece of
rubber in kind of a realistic way. But there again thickness comes to
your rescue, because if you think about what drives interface cracks
it’s this parameter, which is the energy release rate. And you can see
how it depends on the differences in thermal expansion coefficients of
the two materials.
Also the change in temperature is driving interface stresses, but here
again it’s scaling in a nice way with thickness. Which means that as I
decrease the thickness of my silicon the energy release rate goes down
the propensity for a crack to open up is diminished. So it relaxes a
lot of constraints on what kind of adhesive you need to think about in
order to keep these dissimilar materials bonded together. Here’s an
example: So this is a very thin plate of silicon. We have printed it
down onto a micro-machined ridge on a plastic sheet. There is no
adhesive at all right here. This is just van der Waals forces keeping
it in this cantilevered state partly because of that scaling. So think
silicon is what we like, its floppy, it’s very flexible and it’s sticky
in some sense. So you can do this kind of heterogeneous integration.
So those are nice features. Thin silicon looks pretty good, but not
good enough because this kind of characteristic is not what you want or
you need if you want to get on the human body. So this is bending,
what you really need is something that both bend and also stretch,
because if you only have bendability you can only wrap cylinders and
cones. You can’t even wrap a sphere, much less a brain or heart and
you can’t accommodate the kind of complex motions that organs are
undergoing all the time either.
So you need stretching and there is no thickness to which you can make
the silicon that will impart stretchability. So that may seem like a
daunting problem, but even that one is really easy to overcome it turns
out. So if you take this thin silicon and you bond it to your
elastomer substrate, you know ultimately you want something that
stretches. You probably need to use a stretchy substrate. So you
stretch out your silicon rubber and then you use surface chemistry such
that upon contact this silicon will bond very well at the interface
with the rubber. Such that when you relax the pre-strain it induces
compressive forces on the silicon.
And what happens is it will cause the silicon to spontaneously buckle
into that type of shape. And that’s pretty nice because it’s an
accordion bellows made out of silicon on silicone. And in particular if
I stretch it out now I am not stretching the silicon itself, but I get
effective end to end stretchability because I am trading out of plane
displacement for in plane deformation. So the amplitude goes down;
wave length goes up if is stretch it out. And then the reverse happens
when I compress it back down. So that’s simple and it works provided
you understand what’s going on with the mechanics because this kind of
thing is a hard soft composite. You have to know where the stresses
and strains are if you want to do real engineering with these kinds of
ideas. And we spent a lot of time on the mechanics, wrote entire
papers just on that type of structures so we understand what’s going
on.
So that’s the idea, thin silicon, buckling physics, off you go. You
can make integrated circuits. This is not an integrated circuit,
obviously. It’s just a test structure and it’s not even a good
starting point for an integrated circuit because you are never going to
do device processing on rubber; it’s just not going to happen. But,
you can make ultra thin circuits fully formed, flexible and then as a
back end packaging step you bond them to this pre-strained rubber. You
create all this buckle wavy shape and now you have a composite that has
the soft mechanics you want.
And this is an example of one of these stretchy integrated surfaces
based on silicon. This is a picture taken at our Beckman Institute.
We have an imaging technologies group and so they made a nice image
here. So this is a glass pipette, they are just pushing down on the
center of our circuit and you can see how it is able to form in a
continuous curve linear way. You can see the different wrinkles and
the interconnect traces. And here you can see that particular trace is
stretched out by this local force.
So all the wavy structure that was originally present has been pulled
out. You have pulled your accordion out all the way out to its full
extension. If you kept pressing you would probably crack that line.
So the key is being able to understand what the range of defamation
that your devices can accommodate and do the design up front so that
your application requirements can be satisfied. So, circuit designed
combined with mechanics designed to allow you to do what you want to
do.
Now the key thing is that you haven’t sacrificed any of the electronic
properties by doing all this stuff. So its thin silicon, its wavy
circuits, but the electronic performance is very much more comparable
to what you see in a wafer based system. So, factor of 1,000 better
than what you can do with the organics, very nice switching
characteristics in both types of transistors and this is just a simple
ring oscillator. So you take in this stuff, you crumpled it up and yet
you have done it in a systematic way with understanding of the
mechanics so you haven’t disrupted the electronic function. And that’s
the key part of this obviously.
>>: I have a question.
>> John Rogers: Yeah?
>>: Do those electrical properties say constant when the material us
under mechanical mode?
>> John Rogers: Yeah, so that’s a good question, in this geometry, no.
So there are actually finite strains at the device positions. So this
is a p-channel/end-channel MOSS fed and it’s a ring oscillator.
Mobility or the switching characteristics of the transistors change
slightly with strain. That has been exploited by the Semiconductor
industry to increase the speed of integrated circuits. At a modest
level I would say that kind of a 20 percent type shift in the output
currents. So in some cases you can live with that. In some cases you
cannot and in cases that you cannot you actually take this circuit and
you can do things to it to strain isolate the active devices. To
eliminate that dependence, but it’s coupled in this very simple
implementation.
But, I won’t step you through. The basic idea is thin materials,
hybrid hard/soft composites and buckling and from there all kind of
elaborations and different things that you can do to accomplish strain
isolations. It’s a very good question, but you know you can side step,
it’s an engineering problem.
So if you can make soft circuits that way then what do you want do with
it? And I outlined at the beginning what we have at mind and that’s
putting things on the body. And it could be inside the body; it could
be on the body. We got interested in skin mounting maybe four years
ago I guess. And we started to think about what’s out there today that
goes on the skin unlike these tape on electrode wires that is
comfortable and works. And we thought about kids temporary tattoos as
maybe a model to think about how to do circuits on the skin because
they look great, you put them on your skin, you move your skin around,
it can kind of wrinkle, stretch, deform with the skin and you don’t
even know it’s there.
So that’s what we set out to do. To think about whether we can make an
integrated circuit and sensor suite that has that kind of mechanics or
something as close as possible to that. And what does that mean? That
means as thin as you can go. We had a target of 5 microns. We got as
close to that regime, as light as possible in an areal mass loading
sense, maybe a milligram per centimeter squared and as low in modulus
you can go. We had targeted something kind of brain modulus level
5kPa, but the skin is actually much stiffer. It’s about 100kPa, so 100
would be good. We went a little aggressive on that, but 5kPa. It
needed to be at least as stretchable as the skin itself. So skin will
stretch to about 30 percent before it starts to tear. So we wanted
something that had that kind of elastic level stretchability.
And then some additional requirements: You need your sensors and your
electronics electrically isolated from the skin. So it needs to be
waterproofed, but at the same time you don’t want to disrupt natural
processes of transepidermal water loss, so you need some level of
permeability as well. So that’s we had hoped to do and there are a lot
of challenges in getting anything on the skin and they relate to issues
in long-term viability in the interface and you have got to have
access. Adhesion is always a challenge, you know, you want something
that’s soft and conformable, like a tattoo. And then cost, power,
weight and size are also relevant considerations.
This one is a big one and has been over the years, you know, how do you
do robust bonding or binding without irritation? And it turns out that
problem is directly related to the mechanics goals as well. So I am
not going to go through all the details. Let me just highlight the key
points. So if you think about modeling the mechanics of a piece of
electronics, just a generic material bonded to the skin you can run
different scenarios in terms of the modulus of the electronics and its
thickness. And you can calculate interface stresses in particular that
tend to drive delamination. This can be sheer stresses or peeling
stresses and you can do it for different scenarios. A silicon chip
glued to the skin, flexible electronics or plastic sheet on the skin,
thinner, lower in modulus or all the way to this kind of tattoo like
construct that I put forward in the previous slide.
And what you see in both cases is peeling and sheer is that the
stresses peak up at the edges. So if I stretch on the skin
delamination will start at the edge, which is sort of intuitive, but
then look at the magnitude. So the magnitude for otherwise similar
level of deformation for the silicon chip is large, smaller for plastic
sheet and smaller still for this skin like and same thing over here.
But the actual magnitudes are what notable here. So if you think about
the ratios of the stress, silicon chip to plastic sheet for skin
tension or under a bending deformation going from silicon chip to
plastic chip helped because it’s reducing interface stresses, but not
by a huge amount, by about a factor of 4 to 5.
Now if you think about the ratios though for silicon chip to this
electronic skin, this skin-like scenario now you are talking about 5
orders of magnitude. And that really changes the way that you think
about adhesives to the skin to the point that you don’t even need
adhesives at all. These things just cling to the skin because they are
so soft and deformable. And so you can see that it’s easy to do that
experiment just to see the consequence of that mechanics.
So this is the same chemistry in an elastomer, a silicon based
material. All we have done is we have changed the density of cross
links between polymers in this material to change its modules, the same
thickness, same interface chemistry, just different modulus. And you
can laminate it onto the skin; it’s sort of near the wrist. And then
you can flex your wrist and you can see what happens. No adhesive,
this is just a tackiness of the material itself keeping it bonded.
So here’s a silicon material with a modulus of about 1MPa. So you flex
your wrist and it delaminates. You stretch the skin and again it
drives the delamination front that begins at the edge. Now if you do
the same exact experiment with --. Let me see, can I get rid of this?
Now with lower modulus here’s what happens. So same thing, same region
of the skin, same interface, chemistry, same adhesive strength, it
doesn’t delaminate. And that’s just because you have minimized the
interface stresses. And it sticks now, just clings and you can move
your wrist around and it stays put. So that’s the basic --.
>>: Sorry, what was the change between the first and the second?
>> John Rogers: Modulus stiffness, just softer.
>>: So what about isolated clusters of microneedle and nanoneedles to
give you a --?
>> John Rogers: You could do that, yeah penetrating pins, those are
options. We were trying to get the thing stuck on the skin without any
straps, pins or tapes. But you could add that to improve the
robustness of the adhesion. You could definitely do that.
So how do you get something that has very low modulus? So I told you
some tricks to get stretching, but now you need stretching and also a
very low effective stiffness and it’s a tricky problem. You want a
device that has a modulus of let’s say 100kPA, but you want silicon in
there and that modulus is 150GPa. So, how do you do this kind of
composite engineering? And this is one way to do it: So illuminated by
full 3D finite element modeling. So you take a circuit, an ultra thin
one like I mentioned before with silicon nanomembranes, but don’t use
it in the form of a continuous sheet. Cut it into an open spider web
mesh like this in terms of these intersecting filamentary, serpentine
wires and devices built into that. And then bond it to a low modulus
silicon substrate. Think, you know, 30 microns in thickness and 50kPa.
If you do that fully optimized with modeling guidance and then you
stretch it along this direction or along this direction you can measure
stress/strain behaviors. And that’s telling you how stiff it is. So
the first thing you see is that the measurements along X and Y are
quantitatively captured by the modeling. The other thing you see is
that the modulus is very much comparable to the epidermis itself, which
has a modulus that’s slope is about 160kPa. And you can see it starts
to go non-linear around 15 to 20 percent strained. So this is actually
a better material in some ways. You can stretch it further, but in
this small strain regime it’s very well aligned with skin itself.
So that’s a framework into which you can drop transistors, integrated
circuit sensors and so on. So this example of a field effect
transistor there is a resistive trace of very thin silicon cut into
that geometry. So here’s what it looks like. The transistor performs
well even though it’s in this funky configuration. You can do sensors,
these are strain gages, and you can do [indiscernible] detectors, other
kinds of things. We have done many, many classes of devices in this
context.
So here is what it looks like when it’s mounted up onto the skin. It’s
very soft, no penetrating pins, no adhesives, you just laminate it on
and it’s good to go. It’s the same kind of experiment. This is
laminated on the skin of the post doc who did the work and then we
poked him with a glass rod. So you can kind of see how that moves
around. If you grab it at an edge you can peel it off. This is what
it looks like. It is so flexible, floppy and soft that it doesn’t even
support its own weight, it just kind of collapses down onto itself to
give you a sense of the mechanics. The practical --.
Yeah?
>>: So a question: are spin coding a assume silicon over [inaudible],
is that the substrate?
>> John Rogers: Yeah, so these filaments are [indiscernible] and then
in certain regions there are silicon, metals and dielectrics to make
the devices.
>>: And then you are taking that substrate and probably doing it on a
wafer, pulling it off and then --.
>> John Rogers:
substrate. And
of processing.
much. It can’t
question.
Exactly, yeah, and then transferring it to the soft
the key there is to keep the elastomer out of any kind
It’s not going to happen because it moves around too
get registration from layer to layer. Yeah, good
So in terms of this mechanics the practical question is: How do you
hold this stuff and manipulate it around? And there we just use water
soluble tape. So PVA, put the circuit on there, flip it over, put it
on the skin, wash away the tape and that constitutes the mounting
procedures. I have a movie to show that. So this is just a
demonstration platform that has a number of different types of active
devices; transistors, diodes, inductors, capacitors, LC oscillator,
temperature gages, strain gages, there is an inductive coil and then an
antenna that runs around the outside.
So what you are seeing is this transparent tape backing allowing the
student to place this circuit directly into contact with the skin. So
its skin circuit, silicon rubber backing and then that PVA tape. And
he is washing away the tape by applying a little bit of water. And
eventually that will disappear and just leave the circuit right here
behind and the circuit substrate which extends a bit further out around
the periphery here and you can kind of see that.
So once it’s gone then it’s just this epidermal electronics on the
skin. And you can see then by pinching the skin you can get a sense of
what the mechanics is all about. So here is just the silicon rubber
backing. Here is the rubber backing plus the circuit demonstrator.
And as you pinch this thing what you see is that the skin wrinkles and
folds into forms in the region where the circuit is located almost
exactly the same as the way it deforms in regions where the circuit is
not located. So that’s sort of validating the design approach. So the
circuit is not constraining the skin or preventing it from behaving in
a natural way.
And as a result you put these things on and you don’t even know they
are there and that’s with no adhesive. So you can squeeze it, move it
around and the interface is strong enough to stay bonded, but not in an
absolute sense, it’s not strong bonding. So you can just grab it at an
edge, you can peel it off and that’s what you are seeing here.
>>: Can you stick it afterwards?
>> John Rogers: Yeah, so there are a couple of ways to do that. You
can come in with one of these water soluble tapes, stick it there and
then peel it off. It will come with the tape and then you can do the
mounting again. But in this case you could not reuse that.
[laughter]
>> John Rogers: So the absolute strength of the bonding is not great,
but if you want to do better one way is to just use existing temporary
transfer tattoos as substrate. You already have FDA approved glue
mounted on the back and then go through the regular thing. So this is
an [indiscernible] pirate, just somehow pirates in tattoos, but there
is no ocean near Illinois, so this doesn’t make a lot of sense, but in
the context of tattoos maybe. So you flip it off. And now the
additional benefit of this is you can conceal your electronics. So if
you are into covert things, we work with CIA and so on that turns out
to be a relevant capability. So the circuit is kind of right there in
the facial region of the pirate.
So I used to travel around with these circuits mounted on my skin just
so people could see it, but it requires students to make lots of
circuits. So I don’t do that anymore; I have given them a break.
>>: [inaudible].
>> John Rogers: Yeah, so you can. I will come back to that in a
second. There is a finite time over which you can stay over the skin
and remain viable in terms of function. I will describe that in a
second, but instead of wearing them I just carry some representative
examples around. So this one is one of these kinds of circuits, but
embedded in about a millimeter thick sheet of rubber. So this is not
epidermal, but you can handle it, kind of twist it around and get a
sense of what’s going on. The other one is one of these epidermal
constructs on PVA so the mechanics here are dominated by the tape. And
just to give you a sense of what it looks like I will pass these
around.
So to your point: How do you get these things on and how long do they
stay on?
So a tattoo is not bad, just van der Waals force is okay for an office
environment, but if you go swimming it’s coming off. So how do you get
it to say on better is something we started to think about? And what
we found is a very simple way to get very robust integration with the
skin that does not compromise this epidermal construction is to just
use spray on bandage. So I don’t know if you guys have ever used it.
You go to Walgreens, you get a little spray can of this stuff. It’s a
copolymer of an acrylate and a silicone. You can spray it down as an
adhesive and then you can spray it down on top as an encapsulate.
In that case you can print just the circuit, so no silicon backing at
all. It’s just the circuit printed off of a silicon stamp and that’s
what’s shown in this video. It’s a little more advanced way. So
there’s the spray on bandage, so a few squirts. That’s only about a
micron thick sheet of that spray on bandage material, but it’s a nice
adhesive. You print your circuit right on to your skin like that and
then you sprits it up with some more sprays on the bandage on top. You
let that dry and now it’s much thinner than it used to be and it’s also
much more robust from a mechanical standpoint. So here is a video we
have.
So now you can go swimming, you can take showers, you can exercise, you
can do essentially whatever you want and it won’t come off. Typically
after a few days in the morning you add on a little spray on bandage to
maintain the integrity of the encapsulating layer. And just to give
you a sense of a little bit bigger piece of electronics designed to do
something a little bit different then the one I showed you before.
This is actually a functional think and you can wash it and do your
thing.
So time frame: These devices will say on about two weeks. That’s about
it and it fails not because of a deficiency in the adhesive or the
encapsulating layer; it fails because the skin is exfoliating cells
from the stratum corneum all the time. And the timescale for that
exfoliation is about two weeks. The entire surface of your skin is
gone in that time scale. So you are not sitting on a stable platform.
It’s shedding those cells and your circuit with it. So that’s a
fundamental biological process. I don’t see a great way around that.
You can imagine taking the device off maybe for a day and then you
could reapply it or something like that, but that’s just the practical
reality of where these things are.
So this is what it looks like on the skin. This is spider web stuff
and the key thing is that it’s conformal to all of the very challenging
topography of the skin except the most daunting crevices. And that’s
good from the standpoint of adhesion, but it’s also good in terms of
the interface to the skin. So the skin is a window into health,
wellness and physiology of a person wearing the device. So you can
imagine put a cell phone in this format. I think it’s more compelling
to think about applications in wellness, sports and healthcare. So
that’s where our emphasis has been and this kind of contact insures you
can make good measurements.
And you can make those measurements on any place on the skin, like
places where you would not be able in a practical sense to have a wire
and a piece of tape. So like a finger, back of the neck, forearm, and
jaw. So if you come into the group you have to be willing to do this
kind of thing. And then you can make all kinds of measurements. I
will come back to the details of what these measurements are, but there
are a number of different measurement options we have shown. And one
of them involves just measuring electrical activity associated with
muscle contractions, so either the heart, skeletal muscles or muscles
that are controlling your eyes or throat. I will show you speech and I
will show you examples of all of those.
This is the heart, so you can measure EKG with high fidelity and the
detailed waveform there is saying something about health status if you
put it on the chest. If you put it on the leg you can measure EMG,
that’s electrical activity associated with contraction of the skeletal
muscles. So you can measure things related to gait for example. So
the subject is walking and then standing. This is that epidermal
electronics here. Here is the conventional Pace non-electrode with
conductive gel just to do a comparison.
So we are not claiming that the fidelity of the measurement itself is
higher or comparable, but it’s different because you don’t have a piece
of tape. You have something matched to the skin and you don’t have
just an electrode you have full electronics. So it’s really a lot
different, but the fidelity is about the same.
>>: Was there circuitry on the device that was actually filtering
[inaudible]?
>> John Rogers: Not in this particular case. You can do that and we
have done that, but not in this particular example.
>> How did you get the wire off of that non-electrode?
>> John Rogers: I will come back to that in a second; very good
question.
Then if you put them on the forehead you can measure EEG and you can
see all the standard things. You can do Stroop tests and you can look
at alpha rhythms. And so if you put it on the head you might think
about a brain machine interface, but these devices because they can go
on unusual parts of the body you don’t have to think just about brain
machine, but just more generically human machine. And we found that if
you put these devices on the throat area you can pick up complex
patterns in EMG associated with muscle contractions involved in speech.
So if you look at the spectrogram of data that you collect when the
subject is saying different words, either vocally or sub-vocally, you
can see different patterns. And we work with folks in electrical
engineering to do pattern recognition so you can train the system on a
finite vocabulary of words and then use that as a brain machine
interface, maybe for someone who suffers a disease of the trachea or as
a prosthetic control mechanism.
My students wanted to develop like a game interface so this was a very
simple example. This was a couple of years back, but you could just
move a cursor up, down, left or right. I have never played this; it’s
some kind of strategy game, but just with your neck. So if you want to
play a video game with your neck we have the technology for that. So
it may be interesting, but maybe not that compelling, but anyway it’s a
demo.
We got a little bit better over the last year and a half or so, so that
things can happen faster in terms of the interface so it doesn’t have
to do be just a strategy game. It can be more of an action game. And
there are companies out there now trying to do things like this. The
hardware is totally different, but let me just show you that you can do
this by EMG control. So this is a helicopter drone. Actually if you
just out the lights momentarily then this movie shows up a little
better and then we can go back to the lights on.
So this is a post doc over here so it’s by manual control. He has
these epidermal electronic patches on both forearms and then there is a
computer system that takes that data and then translates it into a set
of commands for the helicopter. And you can see that go here. So the
helicopter, he will rotate his fists and the drone takes off. And then
he is tilting his fist this way and it rotates in that direction. He
will stop that, it will cease rotating. Then he clinches his fists and
it will fly off in that direction. Rotate the other direction, it will
land and then he will rotate again. It will take off and he will tilt
back the other direction and it will rotate counter clockwise in this
case, stop and then he will clinch his fists. And he is trying to fly
the helicopter back to try and get it to land in that box. And he will
cause it to land and you can see he missed. So he needs a little bit
more practice, but you get the idea. It’s just a demo, academic level
demo.
But we think that these devices could be useful in a more commercial
setting and for that reason two or three years ago we put in place a
startup company in the Cambridge area. And they are trying to push
these kinds of ideas out more into the real world. And they are
interested as one application area of sports, wellness monitoring and
as an example of a sporting event to the extent that you think about
NASCAR as a sporting event. We put devices on this guy. He is a
really interesting guy, an undergrad at Duke. So he is a really young
driver on the circuit, but he is interested in advanced technology. So
we put these things on and he races. He has done it two or three times
now. And it’s a great proving ground for the technology because it’s
incredibly hot in these cars. There is a lot of sweating and it’s an
endurance type of thing. So that’s been a great interaction.
We also have as head of the sports segment at MC10 former NFL guy
Isaiah Kacyvenski. He is the highest draft pick ever out of Harvard.
He played for Seattle Seahawks actually for eight years. He played in
the Super Bowl in 2006 and he is a symbol to sports advisory board.
So, usually in a small company you have a technical advisory board, we
have that and then we have this other cool thing; sports advisory
board. And you have got all these famous guys who are part of that,
providing input on what kind of function you would want. It’s not just
lending their name, but actually really intellectual input to what MC10
is trying to do, which is pretty cool.
So MC10 makes these kinds of patches now, here and here. And they
launched their first product in July; July 3 was the launch date. It’s
a joint offering with Reebok and it’s a piece of flexible electronics
that goes in sort of the brim region of a soft good, a skull cap, that
measures in a very precise way three axises accelerometry and
rotations. So it can quantify the detailed physics associated with an
impact to the head and then it uses advanced algorithms to take that
data and then bend it into three categories, moderate hit, severe hit
and then a hit that could represent a concussive impact to the head.
And the idea is to provide additional information to folks on the field
to determine a path of action after a hit to the head. And Matt
Hasselbeck who used to be a quarterback, starting quarterback for the
Seahawks, then the Titans and now he is a back up for the Indianapolis
Colts has been a real evangelist. So this was kind of publically
announced at CS in January. That’s Matt with the device and then there
is our device right there. So that was pretty cool. We got that on a
throwing arm of a starting NFL quarterback.
milestone.
It was kind of a nice
But this is a CHECKLIGHT, you can go and order them up if you want.
You can go to Reebok website and you can buy these, so order early,
order often, it’s a great piece of technology. This is what it looks
like. It’s about 130 bucks and it keeps a running tab on the total
number of hits in these three categories to the head during the course
of the season. So it does overall dosimetry I guess, so to speak in
terms of impacts. And this is the indicator system in the back piece
of this.
So that’s one example. We have a lot of other things going on at MC10.
Our focus of my own university group is not, I mean we are interested
in sports, but back to sort of health care. And you know the wires,
straps; tapes and so on are problems for adults. It’s a real issue for
premature babies that require a lot of monitoring. So this is just
Photoshop, we have not put a device on a baby yet. But this is our
vision of the way that this stuff could be useful. And to do this you
need wireless, you need a radio, and you need onboard power or a
strategy for that. And you need sophisticated sensors as well.
Let me talk about sensors a little bit and then I will talk about
interface and radios, wireless approaches. So we were doing this work
and we were approached by an expert in skin surface temperature
measurement at NIH. And when were approached I was thinking at the
time that temperature is not that interesting, but it turns out it is.
If you have ability to spatial map temperature and measure it at
millikelvin precision. So instead of saying your temperature is 98.6
you can evaluate temperature to 98.653. And what’s happening in that
last digit tells you a lot about health, wellness and what’s going on
with the body.
But you have to be able to do it with that kind of precision and also
have some spatial mapping capability because the surface temperature at
that level on the skin is extremely heterogeneous. Here is an example
of how they do it now. So these are quarter of a million dollar very
sensitive IR cameras that are imaging temperature profiles in space and
time. And this is a close up image of a thumb. And what you see are
these little dots, so each one of these dots is a black region. That’s
a little bit cooler than the rest of the thumb and if you play this,
this is in real time, and you can see that pattern of dots is
constantly changing. The pattern and timescale, it’s almost periodic
type of thing.
Each one of those black dots corresponds to an individual sweat gland.
It fires, a little bit of seat comes out, it evaporates and it cools
locally. So that seemed pretty cool to me. Like if you could do that
without the expense of hardware of the camera, without all the motion
artifacts, so getting the thumb to stay still enough to do this is a
challenge then that might be interesting. The thumb, you know, that’s
kind of curiosity, but if you look at full body temperature maps during
exercise you see, at least for me, things that are really remarkable.
So this is an IR image of an individual on a treadmill and then the
images are manipulated to keep these four points fixed. This is time
so this is average body temperature varying as this person is jogging,
kind of running and then resting. So, if you look at this variation
and say, “Okay, that’s kind of interesting”, it’s not jumping out at
you as something that’s high in information content.
But if you look at the spatial patterns and again with high precision
and spatial resolutions then you see some really funny things. So he
is walking, he will start to jog very slowly. At this point he begins
to sweat and you will see the overall surface temperature of the skin
decrease because of that sweating. So you will see the body starts to
go dark and then as it get’s darker and darker you begin to see an
amazing level of texture that begins to build up on the body. And
these lightning bolts there, that happens to be associated with
vasculature, blood vessels that are transporting blood from the deep
muscle regions up to the skin. And there is a thermal transport
associated with that. So those are hot regions, it’s not sort of
dripping sweat. That’s really telling you about blood flow and in turn
cardiovascular stress and health associated with exercise. So that
seemed interesting.
So can you do that kind of thing with this epidermal patch technology?
It turns out that you can. Let me give you a couple of examples. Here
is one of these devices. Now in this case not only mass loading, but
thermal loading becomes a very important consideration. And that was
not on our list of metrics when we started this project. But if you
want to put a sensor on the skin it can’t load the natural processes of
water loss, sweat and it can’t heat as a result. So that becomes an
important aspect and we spent a lot of time on that. But you can use
the high end cameras at NIH. You can measure this way and you can
measure that way and then you can look at the precision and the
accuracy in this kind of sensor. And it turns out that without a huge
amount of difficulty you can do this.
So here is temperature as a function of time, measured with the IR
camera and one of these epidermal sensors, just offset for clarity. So
what you see is that when the patient is just at rest there are some
periodic variations. This is associated with natural vasoconstriction
and vasodilatation of blood vessels in the near surface region of the
skin. There is characteristic amplitude and frequency associated with
that which itself is interesting, but the purpose of this graph is to
show you what happens and the kind of subtle things you can pick up.
So here at this time the patient was told to do a series of operations
in mental math. So division and subtraction and what you can see is
you can pick that up, the effects of that because now your skin is
sweating a little bit. And so you can see that cooling. So you can
say something about cognitive state. The other thing you can do is you
can really pick up subtle effects of physical activity. So here we are
again, sensor IR camera, rest, now physical stimulus and not rest. So
in principal you see the same kind of trend I showed you with the
treadmill. Temperature goes down then it stabilizes, but this physical
stimulus is very subtle. So you have one device measuring on the left
palm and the physical stimulus corresponds to rubbing two fingers
together on the right hand. So just to give you a sense of the
precision and the kind of coupled response of the body are sort of
interesting to me.
So I am running out of time here so let me just skip through and let me
just get to the last few slides. So there was a question about
interface IO. So what we have done is things in two parallel tracks.
One is let’s use a soft cable like this hard wire connection just so we
can understand how the sensors are behaving. We can do thermal
mapping, we can do EEG, we can do other things and we can also look at
device lifetime. So here’s EMG, we are measuring on the forearm right
after the device is mounted and then a week later where the subject is
doing showers and all the normal stuff. You come back and it’s pretty
good, maybe a little bit of increase in noise, but not too bad.
So here this is a releasable cable, we laminate it on, make the
measurement, peel it back and then off they go. That is not the vision
though of how this technology could best be used. You would like to do
wireless interfaces. One way to do that is a simple passive wireless
coupling, a mutual inductive coupling between an external coil and a
stretchy epidermal coil that coupled electrically to the skin. This is
one way to do it. You can measure thermal conductivity of the skin.
You can measure hydration state, impedance of the skin, you can do
different things in that way and that’s fine for certain applications.
It’s not completely generic however and so I will show you at this
point some things that are still un-published, but it’s the result of
integration of a full active radio on the patch. So I won’t get into
the details, but this is full wireless radio transmission in EEG. The
green traces are traces measured with the epidermal patch. The blue
with a standard wired based system and you can see good correlation
there. There is ECG in a sitting state and again very nice correlation
between epidermal and standard wire approaches. This is EMG, same
thing, wave forms look a little bit different here, but again this is
ongoing work so we are trying to tease out the details here.
This is measuring EOG, so you can put these things near your eye and
you can track eye motions because there is muscle activity associated
with that. So this is moving the eyes up and down. You can see
conventional EEG and then this is horizontal back and forth motions of
the eye. And we have shown, this is not great I am going to input a
movie in here, but you can do game control with that kind of thing; eye
motion, track using an electrical measurement and a wireless link. And
we did PAC-MAN, but I just have a still image here.
So that’s kind of all I wanted to say. I would say what we are trying
to do is still early days. There are still lots of opportunities, as I
was saying before, for new ideas or advanced technology development.
But I feel like we have some ideas in place and some functionality
that’s headed in the right direction I would say. It involves a lot of
collaborators, professor Y. Huang does all the mechanics, professor P.
Ferreira does all the manufacturing systems, T. Coleman we have worked
a lot on EEG, these two guys on brain machine interfaces.
But ultimately the students do all the work. They come up with a lot
of the best ideas and so it’s best to kind of end the talk by
acknowledging them and thanking you for your attention. I will be
happy to answer questions if you have any.
[clapping]
>>: So maybe the power is also inducted in the sense how does it get
powered? So not only for taking the signal out and do you have enough
storage built into it?
>> John Rogers: So those are great questions. So the answer is yes to
everything you said. So you can do inductive, you can do Far Field RF
power transfer. We have done both of those. This is an example of
inductive powering of LED’s. These are for implantable devices, you
can get them subdermal and you can light them up in that way. I don’t
have our Far Field RF transmission data, but you can do that as well.
A fair amount of RF comes out of your phone and so you can harvest even
a small fraction of that. You can begin to do those things, depending
on the power requirements.
>>: What kind of power requirements do you have?
>> John Rogers: Yeah, so for R radios, so we have a multi-functional
system that does EMG, temperature and accelerometry with a voltage
controlled oscillator for the radio frequency communication, about 2mW.
So it’s low duty cycle, but that’s not very sophisticated. I mean
think low power Bluetooth, sub-threshold logic, there are a lot of
opportunities for driving down the power requirements. But if it’s a
couple of milliwatt, you have got a watt coming out of your phone you
are pretty close to something that’s reasonable. I think in the case
of a confined environment like a hospital or a research lab you can
always put an RF source. A patch antenna in one corner of the room and
do it that way.
And in fact we haven’t done that in a continuous mode on humans, but we
have done it for LED’s injected into animals for optogenetics studies
at Washington University. So that’s full wireless power and
controlling when the LED is coming on and off. So, inductive Far Field
RF is two options. And in some of these passive systems you don’t need
power directly on the device.
The other would be storage, right, battery. And I think that batteries
are possible, but with batteries I would just be cautious. I think
batteries are challenging. So we are working on it. I think you can
do it. There are some practical aspects around how do you achieve
robust encapsulation when you are in a soft rubber situation? And I
would say that’s a challenge maybe for the community. It’s not one
that we have solved. We are still thinking about it, but we can do
batteries that are soft and stretchy. And this is an example of one.
So this is a rechargeable Lithium-ion battery. Not a huge capacity,
but you can run an LED. And the way to make it stretchable is
basically to just take conventional Lithium-ion anode and cathode
materials and create very small cells and then connect them with the
deformable wires. And then package a soft elastomer top and bottom and
an electrolyte gel in between and so you can do that. So this offers
extreme wide range of stretchability, maybe up to 400 percent biaxial
as you will see here. And the LED stays on during this defamation.
So not out of the question. I personally prefer a Far Field RF because
then you just need an antenna; it’s very simple. It’s constraining a
little bit, but again I keep thinking about the smart phone and that
you might be able to use its battery essentially, right. And
ultimately the phone is going to be part of any kind of monitoring
system anyway. So yeah, power is a good question. We also do
mechanical energy harvesting. So you can do piezoelectric materials.
We have done a lot of things on the heart, the heart is moving. You
can generate enough to power a pacemaker, but for things that are on
the skin you have to think about where you are going to put it to get
enough continuous power to make sense. And it’s not clear to me how
that would work, but we are still tinkering around with that.
Yeah?
>>: All your examples and your answer to that question assume that
everything on that device meets all of your flexibility constraint and
all of your air still get’s to the skin okay constraints. If you are
willing to sacrifice those constraints for a few millimeters here or
there can it [inaudible]?
>> John Rogers: Absolutely, you can think about it. It really depends
on the application requirement. So what I didn’t show you is we have
ways to take unpackaged bare dye and get it into a format, it’s not
full epidermal, like the full academic thing that we kind of strive
for, but in a lot of cases it’s good enough. You talk to our sports
advisory board folks and we hand them the thing that’s made with the
bare dye type approaches. They look at it and think fantastic. It’s
like it doesn’t need to be that simple.
>>: Don’t you think you could put something a little bit rigid there,
because you want that part to not bend. Can you kind of put a little
piece of plastic under that?
>> John Rogers: Yeah, it’s all about mechanical engineering doing
things like that.
>>: Are you putting wire bonded attaching in those cases or how are you
attaching to the bare dye?
>> John Rogers: Yeah, there are a few different ways to do that. Maybe
offline, this is being recorded. We haven’t published that yet. There
are two or three different options. You can imagine what they would
be.
>>: So the temperature work is really interesting.
sort of subsurface blood flow and [inaudible]?
Have you considered
>> John Rogers: Yeah, absolutely. I kind of ran out of time there, but
we are doing a lot around core body. I know you guys are too. You can
do blood flow and that’s interesting because the precision you can pick
up temperature changes. You can see effects of flow on thermal
diffusion. So if you put one of these devices on the arm you constrict
the biceps to prevent flow through and ulnar artery down the arm and
then you release that. You can see a thermal effect, essentially a
pulse type response associated with flow. And again you have to be
able to do mapping, because you don’t know. It’s hard to locate that
artery, it’s deep in the tissue.
But here is one of these devices. This is while the artery is
constricted and then you release it. So, that’s the artery right there
and you can pick it up and some of these channels have very little
response. They are not overlapped and spatially [indiscernible] with
the artery. But some have a very strong response like that. And this
is the IR camera so again an almost perfect match with that quarter
million dollar piece of equipment and the details of how far it
overshoots here, what the time scale of this is can be related to the
flow properties. And that is an important indicator of cardiovascular
health. So you can do this.
What we are finding though is you can also do something that doesn’t
even require the constriction. Like if you put the patches on the arm
the thing that you can do with these patches that you cannot do with an
IR camera is you can operate the temperature sensors as heaters. So
you can light them up. Here we have heated up these four in an array
of 16 and blood flow will cause anisotropy in the resulting thermal
distribution. So if there is an artery running down in this direction
then heat will tend to spread more this way then that way or that way.
And you can map blood flow in that manner.
So this slide doesn’t show that, but this slide is showing that you can
determine thermal conductivity of the skin. So you can pulse the heat
here and depending on how efficient a heat sink you are sitting on that
determines the ultimate temperature of those heaters. And with a
simple model you can back out thermal conductivity. Now why is thermal
conductivity interesting? And it’s because it quantitatively
correlates to hydration of the skin. And so we use a conventional
moisture meter. It’s a handheld thing that makes the measurement
electrically, but we see a very good correlation. So you can do
temperature, hydration and blood flow.
>>: But you can imagine that there [inaudible] that’s being laid over
this [inaudible].
>> John Rogers: Right, so we can do [inaudible] measurements of the
skin and look at Galvanic response, things like that.
>>: [inaudible], can it stick to other things, internal organs?
>> John Rogers: Yeah, so I didn’t put slides, but we have done a lot of
work on the heart and the brain. And I didn’t put it in because it
seemed like it was kind of outside a Microsoft realm of interest. It’s
sort of hardcore clinical medicine is the context there.
Yeah?
>>: Have you guys thought about using these devices for presentation of
information as opposed to gathering information. So gave the little
LED example, but.
>> John Rogers: Yeah, LED’s are not great because they are power hogs
and you are trying to minimize power. So we have thought about
electrophoretic display elements because they are bistable. You have
to think about the mechanics there. We have done some work on
thermochromic materials. I think Coors beer has a thermochromic thing.
So that kind of material and it turns out you can embed those dyes into
rubber. So you can make a fully stretchable little simple indicator.
And it’s being switched by heat and so if you run the numbers it’s more
power efficient than an LED. It’s not bistable like electrophoretic
ink. So we made a little stretchable indicator using leuco dyes.
These heat sensitive dyes. But there may be some other concepts and
that is kind of what we are thinking about. The Reebok device is just
LED’s but I think there is often times value in having the indicator
right on the patch so I think you are asking a great question and we
have thought about it.
>>: Can you play the IR radio again please.
>> John Rogers: Which one, the phone or this one?
>>: And I have a question related to it next.
[laughter]
>> John Rogers: I can send you a copy of the movie. I should really
highlight that this is Alex Gorbatchev and he is our collaborator at
NIH and he is a world’s authority on skin temperature and he is a great
collaborator. And this is his movie. It is not something that we
collected.
>>: In terms of cost I assume that this is low cost, is that true?
there anything that makes it expensive?
Is
>> John Rogers: No, I mean it depends on the devices. Like those
passive devices I have one of this little hydration monitors here.
This is one that uses inductive coupling for the readout. I mean this
is just metal traces, this could be pennies. Some of the things that
involve radios obviously would be more expensive, but I think back to
our initial motivation. We are trying to do things that are aligned
with conventional electronics and then just do a few things on the back
end in terms of rubbers and stuff and mechanics. So our thought is
that it might be incrementally more expensive, but it’s not going to be
qualitatively different in cost structure, but qualitatively different
in mechanics and user interface.
>> Desney Tan: Thank you a lot.
>> John Rogers: Okay, thanks.
[clapping]