>> Dan Morris: So I am welcoming Mike McAlpine to talk to us all. Mike comes to us
from Princeton where he is faculty in mechanical engineering, although you’ll
variously hear him self-described as chemical, electrical, mechanical, and materials.
But rather than reiterate what’s in the talk announcement, which you can read his
bio, I’ll tell you facts that aren’t in the talk announcement.
Mike and I have actually known each other since we were like seven years old. Mike
effectively taught me to play guitar. We played in a, I would say not fantastic, band
together in high school. We had our moments. So I can say without much hesitation
that Mike is not only responsible for my thriving musical career, but Songsmith
would not have happened without Mike McAlpine. I can say that with confidence. I’ll
leave you with that. Don’t judge him.
>> Mike McAlpine: That was going to be my intro. You stole my intro. Okay. Yeah,
so I think it’s kind of interesting that, first of all thanks a lot for having me hear. The
thing I think kind of interesting though is that our paths keep converging because it
sounds like a lot of you guys are working on interfacing certain interface devices
with the body and things like that. And that’s actually what we’ve been working on
too.
And it’s actually come out naturally form the stuff we’ve been doing because a lot of
the materials work these days, actually there are a lot of interesting areas in
materials that have to do with interfacing materials with the body. And I’ll tell you
what the reason for that is, but I think this could be more of like a conversation. So I
have enough slides here to cover the full hour, but if you guys have questions then
I’ll probably skip some things depending on what you guys want to do.
If you want to hammer me with questions I’m happy to do that. If you feel like just
listening I’m fine with that too. But mostly what I want to kind of impress on you is
the fact that you guys are kind of approaching this area from the top, and actually a
lot of materials research these days is approaching this from the bottom because of
the interesting dynamics in term of mechanics and electronics that have to do with
materials as you start to interface them with the body.
So these are the kinds of things that I’ve been interested in. There is, you can
imagine a lot of different areas for this. You guys are working on some really
interesting ones. And I think the stuff that we’re doing interfaces best with the stuff
that you guys are doing, which has to do first with sensing [inaudible] kind of like
the chemical and biological sensing, interfacing sensors with the body, and then also
with mechanical energy harvesting.
And so this is something that we’ve been working on too. So I’m going to talk a little
about these two, these are kind of the two areas of my group that we’ve been
working on. And so these are the things we are going to be focused on here. But
again a lot of the concepts here are actually pretty generic to any different material.
It could be electronic material. It could be silicon. We’re not doing a whole lot of
silicon stuff but there are some people doing that. And so if you have any questions
about the processing or the materials itself or anything, you know, feel free to just
jump out at me and ask. Okay?
And I think the general theme here has to do with the fact that if you look at
something like a silicon wafer, I assume you guys have seen a silicon wafer before, I
don’t know how far -- So basically it looks like this. It kind of is a hard glass-like
substrate. And so it’s hard, it’s brittle, and it needs to be processed at high
temperatures in order to form single-crystal silicon, which is basically what you
need to get the kind of two-gigahertz performance that you see in processors these
days.
And so we’re talking about a thousand degrees C in order to process this silicon into
single-crystal form. You can deposit a [inaudible] silicon at lower temperatures that
are compatible with let’s say the body or with plastics, but then you lose a lot of the
functionality. You won’t be able to get to the high frequencies that you guys are
used to, the two-gigahertz.
So when you think about interfacing with a material like this, like silicon with the
lung, first of all you have this temperature, we call it a dichotomy, you have the
temperature dichotomy, the fact that tissues can only go up to 30-40 C or a little
higher than that, where as this is being processed at a thousand degrees C. But then
you also have the mechanics of it too, which is the fact that tissue is not just flexible
but it’s also stretchable too, where as this is hard and brittle.
It can’t be bent. You can’t bend it very much; you certainly can’t stretch it at all. And
so you have a dichotomy here in terms of the mechanics too. And so what we’re
trying to do is basically use nanoscale engineering in order to overcome this
dichotomy and be able to interface materials that have high performance, not low
performance like amorphous looking, but high performance materials with the
body. And that means tailoring the mechanics, overcoming this temperature issue
too in order to be able to do this.
And so that’s really the general, this is why it’s interesting from a materials
standpoint. Why a lot of people have been interested in this. First it started with
interfacing silicon with biological materials, and then with plastics. And now it’s
really with tissue and things like that. So that’s what we’re trying to accomplish
here. Okay.
So the first part has to do with this, what I’ve shown on the first slide, we’ve been
trying to put sensors directly on the body. This happens to be a tooth here. And the
motivation for this had to do with this story that I read about Michelle Bryant, who
basically suffered an asthma attack in a grocery store recently, and she couldn’t
speak obviously because she has this asthma attack. But fortunately she had this
tattoo on her wrist that said she had asthma.
So the first responders were able to treat her because they knew exactly what was
wrong with her. And actually I have a similar situation because I’m allergic to
penicillin. And so my grandfather actually wore a necklace that said he was allergic.
The necklace didn’t fit me but I have no way of telling people that I’m allergic to
penicillin if I can’t talk. So people have been getting these kinds of medical tattoos in
order to inform first responders.
And I saw this other interesting story at the same time, which had to do with -- this
is purely for cosmetic reasons, people getting tattoos on their teeth. This is William
and Kate here on the teeth. And so they’re getting these tattoos. I have no idea why
you would want them, but these can be permanent or temporary. So this interested
me because teeth basically come in contact with two biological media, he first being
saliva, and the second being breath.
And so both of those can contain indicators of certain disease states in saliva or
breath can be certain indicator of disease. So we thought about going beyond this
kind of passive tattoos, which just contains passive information, to something that’s
more active that could not only give you information but also continuously monitor
your health status and provide some sort of feedback for you.
And so if you look at the properties one would want to accomplish in such a sensor,
the first one is that you need to have compatibility. And so this means two things. It
means that whatever you put on the body has to be compatible with the body,
meaning that your body is not going to reject it or form some sort of irritation to it.
But then also this gets back to this concept about the materials from before, which is
you don’t want the material to degrade.
You want to conserve the high performance of the material whether it’s silicon or
whatever material it is. Conserve it when you transfer it from its native form onto
the body. Second thing is robustness. You want it to be able to be interfaced with
the body and not easily fall off in some way. And also basically be robust in the
sense that the device itself can handle different conditions if you go into different
environments, different temperatures, whatever kind of conditions you’d want the
device to be robust there to.
Also performance, we talk about sensors. The basically performance the two things
we’re interested in, the first one is sensitivity, which means being able to detect at
very low levels, and the second one is selectivity, which means being able to detect
what you want to detect and nothing else.
And then the last thing is of course power and readout, which I think is most in the
kind of electrical engineering area that you guys are in, which basically means you
don’t want to have wires coming out of your tooth. You don’t want a battery on your
tooth. You want to have remote power and remote readout too.
So I’ll give you the punch line here which is a strategy we came up with recently,
which is basically to interface some sort of device here, put it on some sort of
temporary tattoo platform that can be dissolved, let’s say on a tooth or on your skin
or something like that, and then basically tailor it in such a way that you can pick out
what exactly you’re interested in and reject everything else.
And this happens to be a graphing sheet here that we’re using as a sensor platform
because that’s what’s providing the sensitivity that I spoke about before. Okay. So
let’s break this down part by part, and again if you have any questions about the
materials feel free to ask.
So basically what we’re graphing is this is kind of a hot material these days. If
you’ve ever used, if anyone ever uses pencils anymore, I’m not sure, but basically the
pencil lead is not lead, of course, it’s graphite. If you’ve taken basic chemistry you
know that graphite is basically alternating layers here, basically stacked layers of
carbon, these kinds of hexagonal carbon sheets here, which are stacked.
So they can basically glide one sheet to the next across and basically glide across
from each other and you can slop off the sheets there. But the thing is, so it sounds
like a kind of weak material, but in the plane actually it’s actually extremely strong
material. It has the [inaudible] of about a terapascal, which is almost the same as
diamond in this individual plane here.
So in 2004, and also in terms of electronics, there’s nothing particularly special
about graphite in terms of electronics. But the individual sheet that this graph,
which is the individual sheet, has amazing electronic properties. It actually has a
mobility that is 100 times higher than silicon. So you can imagine it for kind of next
generation processing and things like that.
But people couldn’t figure out for the longest time exactly how to isolate one of
these single layers of graphene from this graphite composite here. And the way that
in 2004 they figured out how to do it, which is they invested in some scotch tape
from CVS and they basically were able to peel off just the top layer of the graphene
there and you just print it onto a silicon wafer like that.
So this won the Nobel Prize in 2010 after they made the discovery in 2004. Okay.
>>: [inaudible]
>> Mike McAlpine: Yeah, I mean any time even when you write you’re basically
going to have a few here and there like a single layer of ->>: So anywhere there’s graphite there’s some graphene?
>> Mike McAlpine: Yeah, basically. Yeah. So what happens is in the full graphite
structure the electronics are basically being dampened by the fact that you have
poor electronics, poor mechanics in this direction, but incredible mechanics and
electronics in that direction. So by isolating the single sheet that’s where the magic
happens.
Yes?
>>: How do you get just a single sheet and not two sheets and three sheets?
>> Mike McAlpine: You get the whole thing. But the point is that you were able to
go under the microscope, and using nanoscale tools to be able to see where you had
a single sheet jutting out from two and three, you can see that the color changes
actually as you go down. And so you can basically just isolate the single sheet part of
it and do your measurements there.
These days you can grow them over large areas by using a process called CVD, you
can actually grow it over an entire wafer. Okay. So they don’t use the scotch tape
method anymore.
>>: [inaudible] to graphenesupermarket.com the last time we ->> Mike McAlpine: Yeah, we buy ours from graphene supermarket. Right next to
Whole Foods.
>>: [inaudible]
>> Mike McAlpine: Yeah. It’s right next to Whole Foods.
[laughter]
Okay. So what’s the point? Are we just using graphene because it’s a hot material or
is there some reason for it? And this gets back to the original properties we want to
look at before.
So this is a nanoscale material. It’s a single atom thick. So what exactly does that
give you? And the first thing is gives you is it gives you incredible mechanics
because the bond between the carbon here and any one of these carbons and the
substrate is pretty weak. It’s called a Van der Waal’s bond. But the thing is you’re
integrating this over an entire sheet and also the sheet is incredibly flexible so it can
form to any kind of rugged surface here.
So they did these kinds of bubble tests here to see exactly what the adhesion
between the graphene and the substrate is. And it actually turns out to be the same
as a liquid sod adhesion. So it’s incredibly strong adhesion. So when you think
about this in terms of a device that you’re putting on the body this is something that
will be able to adhere pretty well to the body.
And then the second thing is because every atom is a surface atom as a sensor,
anything that binds to this graphene is going to basically, it’s bonding to the entire
structure of the graphene here. So it’s really going to modulate the electronic
properties of the graphene and give you some sort of response. And that’s what
we’ll see as we go along here.
So the next question is what kind of temporary tattoo platform do we use here? And
so this is a silk moth here. And it turns out silk moths, there’s going to be a lot of
animals in this talk, this I just the first of many, and it turns out the silk moth is just
like a dog. It’s not something that developed naturally over time. It was basically, as
it kind of grew, as people trying to produce as much silk as possible form the silk
moth to produce clothes in China for the past 5,000 years.
But what we can do in our lab is get a bunch of undergrads to buy these silk cocoons
here and basically they’ll spend some time in the back of the building cutting these
things open and dumping the worm out. And what you can do is you can dissolve
those cocoons in a solution here. And form this solution of silk they can then
process into it’s kind of like a gummy kind of solution and you can basically process
it out into thin films. And they kind of look like transparency films but they’re
actually a little bit sticky.
And that’s kind of the key thing about this silk, which is that it’s basically soluble in
water. So it’s just like any kind of temporary tattoo substrate where you want to put
your device on this substrate but then you want the substrate itself to dissolve away.
So it turns out silk from a silk moth is actually what we use as this kind of temporary
tattoo platform. It’s nice and water-soluble.
I should have brought some today. I gave a talk once where I wore a few of them on
my wrist here but that’s ->>: Any allergy issues here?
>> Mike McAlpine: Not so much. It’s pretty biocompatible and it doesn’t irritate the
skin at all, at least when I wore it for like 24 hours.
So what you can do, we talked before, you can print graphene from the original
graphite using scotch tape. And what you can do is if you wet the silk a little bit it
gets a little bit sticky. It’s kind of like glue. So you can print graphene on here and it
kind of looks like someone scribbled with pencil onto silk here. You can print
multiple times these kind of graphene sheets on there, and then you can basically
dissolve away that silk and then transfer your graphene to maybe some electrodes.
Here are two gold electrodes and here’s a graphene let’s say onto a tooth. And this
is our collaborator’s tooth here. I have no idea why he had this available. We said
we needed a tooth for this project. He’s in his forties and he said, okay, I’ll send you
one tomorrow. We got it the next day. I have no idea why.
But anyway, I didn’t ask any questions.
>>: [inaudible]
>> Mike McAlpine: Yeah, we put a dollar under his pillow afterward. And so what
was kind of cool, we have a little logo for this now because this was in last weeks
Sunday New York Times magazine. I also didn’t know they were going to do this.
Some emailed me and said hey you’re one the cover this. I thought that was kind of
cool, this kind of smart teeth thing.
So this is just basically a device with two electrodes, but this doesn’t get around our
other issue that we want, which is basically to have remote power and remote
readout here as well. So one of the things we’ve been working on is integrating -this is the device, so you’d have a graphene sheet here and then you’d have
electrodes basically that contact the graphene, and then you have some sort of coil
that you can use for the wireless readout.
But the problem is that coil is kind of big. And so unfortunately we couldn’t use a
human tooth for this part so we had the same undergrads go and get a cow tooth
from a local farm. That’s one of the nice things about being in farm territory. You
can just get some animal parts whenever you need them.
So you can interface this thing onto a cow tooth here. You can also interface
anywhere onto an IV bag. Costco cheese was a recent problem with bacterial
contamination. So we put it on Costco cheese. And you can also, of course, put it
directly on the skin if you’d like.
So this is what the device looks like when you interface it onto the skin. And it
seems to hold pretty well if you do it right. So that’s again to this high adhesion of
the graphene. The fact that these are nanoscale materials so they have very high
surface area, so they’re going to conform pretty well to any substrate there.
So in terms of stability, we took the tooth and we put it in Listerine, which is popular
among cows. So we put this tooth in Listerine and we swirled it around for a while
to see exactly what would happen. And if you take the tooth out of the Listerine,
surprisingly the device stays on there.
And you can go and you do a technique called [inaudible] on the graphene there.
You can see that the graphene itself is not too damaged. If you don’t know much
about Ramen, that’s fine. This peak goes up a little bit, which means the graphene
gets a little bit damaged on the tooth, but is actually not too much. The device, as a
whole, stays in tact even through this pretty harsh chemical and mechanical swirling
here.
Of course if you try to brush it it’s going to brush off. So it’s robust up to a point,
okay? But they’re pretty cheap devices. You can just put another one on after that.
Okay. So we’ve spent -- okay.
So the next question is what do you want to tailor this for? What do you want to use
it for? And in fact this is a platform that can tailored for anything. In our case what
we’ve been interested in is looking at bacterial contamination because this has been
in the news a lot recently because it’s a problem in both developing countries where
they have poor sanitation, and also in developed countries where we consume so
much meat and dairy that we have a lot of e coli contamination in our food.
And so you constantly hear stories in the news about person-to-person, food-toperson bacterial pathogenic issues. And so this is something I thought would be an
interesting problem to look at. And this is kind of more the chemistry end of things.
We’ll get to sort of more electrical engineering stuff a little bit later.
So in terms of sensitivity I mentioned before that graphene is this single sheet. So
every atom is a surface atom. So anything that binds to it should modulate the
conductance. And the thing is in terms of bacteria you want the sensitivity to be as
high as possible because it only takes a few bacteria to make you sick, like on the
order of 10. Very small numbers of bacteria that can go in the body, amplify, and
make you sick.
And so the way you do this now is you take a sample of water. You have to send it
away to the lab and they do something called PCR on it to get down to those levels of
bacteria. But what we want is a real time device that can sense in very low
concentrations. Ideally single-cell level. So in this movie here that I have we’re
actually focused in on the graphene plane.
We’re in the plane here. And then we dye our bacteria red. So this bacteria comes
along here and then boom, it just binds to the graphene right there. So we’re
monitoring this optically. This bacteria comes, single-cell bacteria comes, binds to
the graphene here, sits there for a while, and then basically gets up and leaves.
And if you monitor the conductance of this graphene sheet at the same time as
you’re watching this movie, you can actually see that when that bacteria binds the
conductance increases actually here because this is resistance. So the conductance
increases. Then when the bacteria comes off it actually goes back down to the base
level.
So what’s happening here is this is actually just like a transistor, which I assume
most of you guys know. It’s a three terminal device. One of the terminals is called a
gate, which is like a faucet on the sink, which basically modulates the conductance in
your channel.
The same thing is happening here. The bacteria is actually negatively charged. So it
comes down and binds to that graphene, modulates the conductance, and that’s
basically acting exactly like a field effect transistor here in terms of this device. So
it’s basically modulating the conductance there.
So a single bacteria is enough basically to get a real time, this is less sub second,
response here. Around maybe one-second response here that you can actually
measure down to the single cell level. So it’s pretty impressive device here. Yeah?
>>: [inaudible] conductors that were in my digital world there’s conductive and not
conductive, copper and air. Are we talking about going from really conductive to a
little bit less conductive, or in the [inaudible]?
>> Mike McAlpine: Yeah. So the resistance here is on the order of the kilo ohm
level. So that’s pretty typical for nanoscale devices. In this case this is just a single
cell, so you’re talking about a one percent change in that. But the thing is if you had
multiple cells you’d see a much more significant change like ten percent or things
like that. So on that scale, yeah.
>>: So [inaudible] is one bacteria that touches the device and it can sense it. But I
guess I’m wondering if you’re eating a burger that’s infected with e coli and there’s
some bacteria that [inaudible], what’s the probability that those bacteria will come
in contact with the small region of the one tooth that has it? Are there so many
bacteria in the burger that it, or is it still kind of a low probability that the bacteria
gets to the right part?
>> Mike McAlpine: Well, I guess what you can do is put one of these on each one of
your teeth to maximize the probability. And I guess it depends on the way you chew
too. But there would have to come in contact with it and basically form enough of a
residence time here that you’d basically be able to see this response. So we haven’t
done any real time human studies on this sort of thing.
But I’ll show you one real time movie a little bit later, but nothing where we actually
put it directly on someone’s tooth while he’s chewing and things like that. But that
would be in the next stage. Another thing -- yeah?
>>: [inaudible]
>> Mike McAlpine: What was that?
>>: [inaudible]
>> Mike McAlpine: Yeah. So a lot of people make these sensors that are end-by-end
very large numbers essentially. They come with a fingerprint. What we’re trying to
do here is a little bit different. We want to try to maximize selectivity. That’s just
interesting for us from the material side of things. But you don’t want to put the
burden too much on the processing. You want to have some burden on the sensor
itself.
But this is one of the trade offs that has to be addressed. Any more questions?
Okay.
>>: [inaudible]
>> Mike McAlpine: Yeah, so I don’t want to get into the gory details but it turns out
the gram negative are the ones that are, these are called gram negative, so that’s e
coli, h pylori, which I’ll show you later, and strep, those are gram negative. Those
tend to be the ones that most infect humans. And those tend to be the most
negatively charged.
Gram positive ones, things like staff, actually have a significantly less negative
charge so they won’t have as large of a response here. But they’re not as harmful to
humans.
>>: [inaudible]
>> Mike McAlpine: No, we do because if you have ever looked at something called a
trans-conductance curve of a field effect transistor, we’re right on that curve there.
So we’re right on the modulation part where a very small change in the gate voltage
basically produces a huge change in current.
>>: You don’t have that same response curve in the corresponding graph.
>> Mike McAlpine: We do. We always test our graphene like as a standard
transistor for fusing a wafer back gate before we do these types of experiments.
>>: [inaudible]
>> Mike McAlpine: You can see it, yeah. You can measure the trans-cunductance
and all that. I kind of left out some of the gory stuff here a little bit. Okay. So let’s
see. So I’m going to go through this part a little bit fast because it’s more chemistry
related. This is also related to Mary’s question, which is basically if you want to
isolate a bacteria from a group of different populations of bacteria you need to
basically impart some selectivity onto it.
And one way to do that is to use antibodies, which occur in your body. There are
ways to basically -- they are used by the body to kind of target certain bacteria,
certain viruses, and basically let your body know that they’ve been targeted. Well,
the problem with putting antibodies on device is that they can denature pretty
easily. So they limit the lifetime of the device.
So what we use are something called peptides. I’m not going to get too much into
the details here but peptides are basically small-scale versions of antibodies. They
only have a few amino acids, maybe ten, whereas antibodies could have thousands
of amino acids and they fold intricately, whereas these peptides don’t fold as much.
So they’re not as selective as antibodies but they still provide some degree of
selectivity to the device. And so the question is you need to come up with some sort
of peptide sequence that’s going to bind to the bacteria that you’re interested in.
And so we came up with this idea here when I was watching a special on PBS about
this bird called the Red knot.
And this is a bird. The show was about how this bird is kind of going extinct, this
Red knot. And basically they were trying to figure out why this bird is going extinct.
And it turns out that the bird basically spends the winter in Argentina and then it
flies 10,000 miles to the arctic every year to mate.
And I’m not sure why it can’t mate in Argentina, which seems like a perfectly good
place to mate. But the thing is it’s a very long journey so it needs to stop at some
point and refuel along the journey. So what it does is it stops at the Delaware Bay
near me. This is why the show was on by me. So what it does is it feeds on these
horseshoe crabs here.
So the horseshoe crabs are mating in the Delaware bay and so they’re producing
billions of eggs here and they’re not very monogamous, the horseshoe crabs.
Basically as they’re producing these eggs here the birds just come in and start eating
the eggs. And this is what they use to refuel on the halfway point of their journey
there.
And so what was happening to the bird was that the bird was actually going extinct
because the number of horseshoe crabs was actually decreasing. So they’re trying
to figure out why is the horseshoe crab decreasing? And it turns out that there are
two reasons for it.
The first is that people use the horseshoe crab as bait for capturing fish. The fishing
industry there does. But then second reason, which I they talked about and I didn’t
know but I found fascinating had to do with the fact that they use the horseshoe
crabs in the pharmaceutical industry.
And this was something I didn’t realize but it was amazing. What they do is they
collect the horseshoe crabs in boats and they mount them up in the lab. And then
what they do is they drain the blood from the horseshoe crab. So you can see these
horseshoe crabs this is the state of the art in the pharmaceutical industry.
They drain the blood, it happens to be blue, because they have hemocynin
[phonetic] it’s copper based. So they drain this blood and then they throw the
horseshoe crab back in the water. And of course some of the horseshoe crabs die
because they drain most of their blood during this process.
And so you’re probably wondering well why are they draining the blood form the
horseshoe crab? And it turns out that the horseshoe crab lives in this aquatic
environment so it needs a way to defend itself against bacteria because it’s basically
in this microbial soup in this aquatic environment, surrounded by bacteria.
So the blood is incredibly efficient at basically coagulating around bacteria and then
killing them. So what the pharmaceutical industry used to do is they used to take
their drugs and products and basically inject them into rabbits, but it took too long
to wait to see if the rabbit got sick.
So what they found is they take the horseshoe crab blood and drop it on their drug
or their device and if they see it coagulate under their microscope they’ll know
instantly if it’s contaminated with bacteria.
So I got some inspiration from this because I figured there’s got to be a better way
than the horseshoe crab for doing this. This is what they use now in the
pharmaceutical industry. So as we continue the animal theme here, I read this other
article about these African clawed frogs here, which also live in aquatic
environments.
And they’re called clawed frogs because they have claws on their hind legs, they
don’t have teeth so they use their claws to tear their food apart. So the way that
these guys defend, they don’t have the kind of blood that horseshoe crabs do that
kill the bacteria, but what they do have are these peptides, kind of like the ones that
I showed before, that are on the skin of the frog.
And that’s what basically acts as a first line of defense against bacteria. They’re
called antimicrobial peptides. In fact humans have them, for example, in our eyes
that act as a defense mechanism against bacteria. And the nice thing about it is
unlike, you could not put an antibody, you know antibodies exist in the body.
They’re regulated in the blood. That’s how they can remain folded. You couldn’t put
one of those on your skin because they would basically denature.
But a peptide you can put on the skin. So that’s why the frog has peptides on his
skin. And they can basically defend the frog from bacteria. So what we did is we
didn’t kill any frogs but we took the sequence that occurs on the frog skin and
synthesized that in the lab. And you came up with this peptide sequence here. This
is what it looks like.
This is the antimicrobial peptide component. On this end here they came from the
frog sequence. And you can basically put this on your graphene device and it will
basically just assemble naturally across the sheet of the graphene. So you have your
peptides here, your graphene surface underneath, and then the bacteria will come in
and bond to that and basically it acts as a target for these bacteria.
And this is basically what enabled us to go beyond detecting any kind of bacteria
that bonded that I showed before, and actually doing some more selective
measurements. So we were able to actually find an antimicrobial peptide that binds
to h pylori, which occurs in your saliva. Because again we’re talking about teeth
here so we’re interested in saliva and breath disease detection.
So these occur in your saliva and are indicators of stomach ulcers and stomach
cancers, these h pylori bacteria here. So we were able to put the graphene on this
tooth here, this cow tooth, and then basically put a matching coil on top of it that
matches, that’s tuned to match the coil that’s actually on the tooth there.
And we can monitor in real time the detection of h pylori here from a sample of
saliva. So this is bare saliva. You can see the saliva on its own with no bacteria. It
doesn’t produce a very measurable response in the device. But as you add h pylori
to that saliva you can see you start to get this much more significant conductance
change.
Here the concentration is a lot higher so we’re going to like the 10 percent
conductance change level. To address the question from before, as the h pylori
concentration increases you get up to 25 percent change in the conductance. And
we can go down to the ten to the two levels. This is wireless. You lose a little bit
with the wireless coupling.
So we can’t do single bacteria resolution but we can do 100 bacteria, which is
actually still below the amount that it takes to get you infected with h pylori. Yeah?
Question?
>>: [inaudible]
>> Mike McAlpine: Okay, yeah. So we collaborate an electrical engineer on this
because you’re changing the conductance here. Usually if you have LC circuit you
want to change either the capacitance or the inductance. But what’s happening is
resistance is changing in this device. So what we’re actually measuring is we’re
measuring a change in the bandwidth of the device, rather than a shift in the
resonant frequency. Yeah.
It turns out that that also seems to be less susceptible to bumping and moving of the
coil relative to the device. This is something that my student worked out with an
electrical engineer named Naveen Verma [phonetic] at Princeton.
Okay. So this is bacteria. And the once last thing I want to show you related to this
part here, which we’re at the halfway point, anyway is this is the real time
measurement. So there are no peptides on this device. This is just a bare tooth
there.
But the thing is this graphene is extremely sensitive even to water and other volatile
molecules here. So let’s try that again. Turn the volume down. That’s the
measurement. There’s our cow tooth just sitting there free standing on the table.
You can see there are no wires coming out of the cow tooth.
This is our baseline conductance. He filmed this with a potato. And there’s the coil
there. So my student just breathed on the tooth and you can see the conductance
jumps up quite quickly when he breathes on it in this wireless platform here.
So that’s just water molecules and other molecules form the breath interacting with
the tooth there. And then as they absorb off the tooth it drops back down to the
baseline and it can come back in again and he can breathe on the tooth a second
time and it’ll go back up again to this maximum value here.
So we can do this multiple times here with this tooth and get this breath detected.
So what we’re actually doing now is we have samples of breath form asthma
patients and breath from healthy patients and we’re trying to see if we can
distinguish those two patients using this kind of platform here.
So we can see that -- yeah?
>>: I’m kind of curious what you use to try and detect between asthma and normal.
>> Mike McAlpine: We’re using antibodies so yeah. But this goes back to the point
you were making before, which is people have used less selective things and we
wanted to use something that’s a little more controversial. So we wanted to really
up the selectivity there to the antibody level. But people have used large-scale
signal processing.
>>: I’m sure. [inaudible]
>>: Is it possible to resolve the conductance of [inaudible]. So have you done
experiments with that?
>> Mike McAlpine: So the way that we get around that is to use an array of devices.
Because theses are basically micro fabricated the way you would fabricate any kind
of computer chip. So the only thing that’s limiting the size here is that coil. If the
coil wasn’t there you could make it arbitrarily small.
You can make a coil that loops back on itself that’s much smaller but we couldn’t
figure out how to do that here. So if you make an array of devices you can tailor
each one with a different peptide or different antibody so that it responds to
different bacteria and then you can basically come up with the sum of those to come
up with the net response there. Okay.
So this is the other side of my group, which has to do with interfacing energy
harvesting devices with the body. And the way that this project came about is I was
reading about pace makers. And it turns out of course pace makers run off of
batteries.
So you have this pacemaker. You have to open someone’s chest to install this
pacemaker. It runs off a battery, then after five years the battery dies so you
basically have to have an entire surgery again to replace this entire unit here. They
leave these leads in place here but they have to replace the entire pacemaker there.
So this can lead to infections, it’s extremely uncomfortable, to surgery that’s
required. And this happens every five years.
We thought maybe there’s some way that you could harvest energy from some sort
of source in order to prolong the life of this battery. And of course you couldn’t put a
solar panel on, you had to put it on your chest and then wear shirts with holes in it
all the time. So we had another concept that we thought about, which is we read
this paper here by this guy named Thad Starner who is currently working on this
Google glass thing at Google.
So he used to be a professor at Georgia Tech but basically he did this paper in 1996
where he showed that we eat about 10 mega Jules of energy every day. That’s about
a quarter of a liter of gasoline in terms of energy. So that has to be dissipated
somehow, and it turns out that a lot of it is dissipated by walking.
So that’s about 70 watts of power available. But then some of it can be dissipated by
breathing as well. So if you could harvest some of this mechanical motion of your
lungs or your diaphragm to power a pacemaker I think that would be pretty
significant.
And these values here are actually pretty commensurate. You guys would know
better than I would but they’re commensurate with the kind of powers that portable
electronic devices draw these days, which are kind of at the low-watt to mili-watt
and a pacemaker is microwatt level in terms of power. So if you can convert this
energy as efficiently as possible, you could actually imagine powering this device or
at least prolonging the battery life.
If you can go from five years to ten, you know, that’s a significant health issue for the
patient. So again this becomes a materials problem from my perspective because
the question is what kind of material are we going to interface with the lung tissue
in order to harvest this power? And it turns out that there are materials called
piezoelectrics, which I assume most people know about, which are basically
materials that can convert mechanical energy directly into electrical energy.
And at the molecular level the way that they work is this is a quartz crystal here,
which is kind of a naturally occurring piezoelectric. And it has a tetrahedral shape
to it. But when you compress it the bottom part of the tetrahedron basically
becomes a flattened a little bit. So you have a net dipole in this direction in the
individual molecule.
And of course Windows are made out of silicon dioxide as well. But all these dipoles
are oriented in a window, but in quartz crystal they all basically stack up because
you have a net polarization across the crystal. So this is where the piezoelectric
effect comes from. And it can be used in both directions. It can be used as a sensor,
which means converting mechanical into electrical, it can also be used as an
actuator, which means basically actuating making little resonant [inaudible] devices
and things like that.
So this is the thing we were interested in and I can’t give a talk without giving at
least one equation because I am an engineer, but it’s a really simple equation, which
is how much energy is stored in one of these piezoelectrics? And it turns out it only
depends on three things. The first is the volume of the piezo. The more piezo you
have, the more energy that can be stored in there. It’s basically like a capacitive
storage equation here.
The second one is the stress that you apply. If you have more stress applied to the
piezo it’s going to produce more power. Those are both material independent
properties. The one that depends on the material is this piezoelectric chargecoupling constant here. So that’s material dependent.
And so you want that D value to be as high as possible to get as much energy stored
in the material as possible. And if you look at the list of materials that are available
to you, here’s quartz that we mentioned before. Its D value is pretty small. It turns
out that the bone in your body is very, very weakly piezoelectric, but it’d be difficult
to put, like, wires all over your bone and power your ipod or something.
There’s also polymers called PBDF, which are piezoelectric, but the king of all
piezoelectrics is PZT, which stands for Lead zirconate titanate, which has a massive
d33 value and is basically greater than 80 percent efficient at converting energy.
So if you compare this to the best solar cell, which can basically do 25 percent, this is
significantly higher than that. But the problem with pzt is it gets back to this
problem that I discuss on the first slide. It’s exactly like silicon. It’s a brittle
material. It shatters easily. And also the p stands for lead, yeah, it contains lead. So
people remind me of this every day.
But the thing is, you know, in most pacemaker batteries contain cadmium, which is
also toxic too. So if you encapsulate it properly then you should be able to get
around that problem. So these are the kind of -- but this is an issue that has come up
a lot and so I’ll discuss our strategies for how we get around all of these problems.
Okay. So let’s see here. I want to skip a few things. Okay. Let’s skip to this one. So
if you want some of the nitty-gritty details about how we process these things I’ll tell
you but we can process large-scale arrays of pzt nanowire. So each of these
horizontal lines here, these small horizontal lines, is a little pzt nanoribbon hair,
which we can process over an entire wafer.
So you can do this over a wafer scale and in fact if you take this wafer and hold it up
to the light you can actually see a diffraction. This is just a photograph. You can see
the diffraction pattern of the sunlight off of those nanoscale wires on this wafer
here.
>>: [inaudible]
>> Mike McAlpine: Okay. Yeah, so you want the nitty-gritty. So basically what we
do is we do a process called sputtering. You can also do [inaudible]. That’s one of
the nice things about pzt is you can produce it in liquid form. So you can actually
put a drop of it on a wafer, spin the wafer and have a massive ->>: [inaudible]
>> Mike McAlpine: Oh, okay. Yeah, exactly. So it’s come back now. The reason why
this is, I kind of skipped over this, but the reason why this is interesting from a
material standpoint the reason why I got into it is because people have made
nanowires now of every single possible material. But they usually grow them from
the bottom up. PZT you can’t do that because the lead and the zirconium and
titanium all need to be in exactly the right stoichiometry in order to get the
maximum piezoelectric response.
You can’t just grow it that way. So we start with the film like you’re saying and then
carve that film up into wires like this. Yeah, okay. So the question is again why
nano? Why do you need nanowires here? And it turns out the answer is that if you
take -- the answer can be found in optical fibers.
So of course a window pane is not flexible because it’s kind of a thick material and
you can’t bend it very far before it shatters, but the mechanics of any material are
such that if you scale it down so that it’s extremely thin and extremely long, like and
optical fiber, which is also made of glass, you can bend it very easily as if it was just
like a pasta noodle or something like that.
So this is the motivation from a mechanic standpoint of going to the nanoscale level,
which is basically you can increase that mechanical flexibility quite significantly.
And also there may be some interesting effects too as you scale to nanometer scale.
Like for example improvements in piezoelectric response just from this scaling.
So that’s more of the sciency side of what we do. But then the question is, you know,
again pzt is the same problem as with silicon. You need to process it at 600 degrees
in order to make it piezoelectric. So that’s obviously not compatible with the body.
So the question is how do we get it so -- this helps us get around the mechanics by
doing this nanoscale patterning, but then how do we get around this temperature
problem? And the answer is it’s a very, very simple technique. It’s exactly like
printing newspaper ink onto silly putty, which is we basically have these pzt
nanoribbons here as we call them. They’re basically called ribbons because they’re
a little bit wider than they are thick.
And so they’re kind of like ribbony shaped. And they’re on this substrate here, the
starting substrate. So you can process them at very high temperatures to make it
nice stoichiometry, the highest in terms of piezoelectric response. But you can take
this piece of silicon, this pdms, it’s just like silly putty, which is also silicon, and you
can print it down onto these ribbons and literally peel it off.
And you’ll basically be peeling it off that substrate there and you can basically print
these things directly onto the next substrate here. So again it’s exactly like printing
newspaper ink onto silly putty. That’s all it is because this process here is done at
room temperature. So you can basically process the pzt first at the high
temperature and then do the printing at room temperature.
And you can see here that in the before and after, before printing and after printing,
the ribbons actually don’t’ break at all during this process and they don’t get moved
around or anything. They go perfectly before and perfectly after in terms of this
printing.
And of course just like with a newspaper, if you have a large piece of silly putty you
can print the entire newspaper without any more significant effort. So this was
something that, we did this for Time magazine actually wanted this. Somehow they
decided this was one of the inventions of the year in 2010. There must have not
been too many interesting inventions that year.
But we sent them this chip. So this is actually a large chip that we made about handsized here. This is a photograph. We can see these ribbons have been printed over
this entire substrate here. So these are all nanoscale ribbons but it’s over the entire
substrate so you can see them all by eye in this photograph.
And you can see there’s actually some that are missing here, and the reason for that
is because they took the chip and they put it facedown and some of it peeled off. The
screwed up when they were -- we gave them the chip in perfect form but they
messed it up here. And when they sent it back to us they sent it back facedown
totally so they all came off.
But anyway you can scale this to large areas here is the point. And then it’s
piezoelectric so it’s flexible and can produce power. I’ll show that to you later. But
the question is, you know, I mentioned this before, it’s one thing to be flexible. Your
water bottle is flexible, but even the plastic in your water bottle is not stretchable,
right?
Your skin is actually stretchable. It can stretch maybe 20 percent, okay? So the
question is, you know, even though these are nanoscale ribbons, can you they be
stretched at all or will they break? And I’ll leave it to you. What do you think the
answer is?
Will they break or not? Who says they break when you stretch them?
Who says they don’t? Okay.
So here’s the answer. The answer is they do break. So even as you scale them down
to nanometer scale, just by stretching them a little bit they’re going to crack up. If
you listen closely it kind of sounds like Rice Crispies as they shatter on the surface
here. So these ribbons are basically shattering up this direction because we’re
stretching in this direction.
So we needed a way to kind of get around this problem and make these actually
stretchable. And so it turns out there’s a classic problem in mechanics where if you
take a balloon that’s inflated and you put some rigid paint around the surface of the
balloon, the circumference here, if you deflate the balloon what happens is the pain
will actually basically buckle up on the balloon surface here and form these kind of
corrugated structures here, which depends on how fast you deflate the balloon here.
So this looks like a fun paper to read but you can get past the first page because they
go through every possible equation that you can imagine for paint on a balloon. And
the interesting thing about this, of course, if you then re-inflate the balloon the paint
doesn’t break. It goes from buckled to back to the flat state here, this kind of nice
state here.
If you inflate it from this point on it will start to crack but you can go between here
and there by inflating and reflating, which is a stretching process, and without any
issue. This is something called constrained Euler buckling if you’re interested in
this. Euler buckling is buckling of a beam. And the constraint here is that there’s
adhesion between the paint and the balloon, which is what leads to this buckling
phenomenon.
And so we can do the exact same thing here because we print this thing like we do
onto silly putty but our silicone that we use is actually a little bit stretchable. So if
you stretch it first and then print it down and then release the ribbons and then
release the stretching part of it, what will happen is the ribbons will actually buckle
up off of the substrate there. And you can see this. Here’s a little logo for it.
But you can see that this is a flat part of the ribbon and then it will buckle up off the
substrate and then it goes flat and then buckles up here. And by patterning the
substrate there you can actually control where it’s anchored to the substrate and
where it kind of buckles off in these kind of gaps in between. So you can get these
kind of buckled formations here.
And now when you stretch it, instead of breaking, you start with these buckle pzt
ribbons here, now you stretch it out. What they’ll do is they’ll just flatten down onto
the substrate here. You can stretch up to maybe 10 percent, which is almost where
skin can go here. And it will flatten down, and then as you release that stretch it will
just buckle back up.
And you can cycle this multiple times here with the stretch and release type of
process. So the cool thing about this is that as you stretch this thing out, you’re
basically straining the ribbons here. So you’re creating a piezoelectric response
here as you stretch these things and release them as well.
So you can basically generate, create, little energy harvesting generators that will
work in this kind of stretching mode here and interface them with the tissue. Let’s
see how much time we have. Okay. So there’s one little thing that we’ve been able
to do with these devices, which we’ve shown recently, and it has to do with the act
that we’ve actually started interface cells with them.
And that gets back to this question of are they biocompatible? Can you interface
cells with this kind of lead containing materials? So we found this paper in the
literature we were looking at some of these mechanics of these buckled ribbons and
we found that cells actually have a very similar type of mechanics because they’re
also curved just like a buckle and a pzt ribbon.
And this affects their mechanical properties quite significantly because if you inject
current into a cell, let’s say this is a neuron, so we all know that brains are electrical
tissues, they communicate information electrically. But it turns out that there’s
some mechanics there too because if you inject current into a neuron, what happens
is you get a polarization different across the membrane of the neuron. And that
leads to a tension in the membrane, which basically forces the cell to swell a little
bit.
And people have measured this before called AFM, which is basically just a sharp
nanotip that they puncture into the cell here. And it’s exactly like having clothes on
a clothesline. If you pull on a clothesline, the clothes will go up. And it’s the same
thing here. It’ll push this tip up. So it turns out that our brains are not just
electronics but also they have moving parts too. These cells will deform a little bit
when you electrically spike them.
So this is some work that we found in literature where they were able to spike them.
This is just this experiment in action. They spike them using a patch clamp. Here
they spike the cell electrically and they saw that the AFM probe goes up every time
they spike the cell. So the cell is responding mechanically to this electrical
stimulation, which is an amazing thing.
And this has not been studied very much in literature. This is the only paper we
found, which is about ten years ago. They saw the cell mechanically deform every
time they injected it with current.
>>: Is that like a real mechanical response in a structural response? Or is that
because fluid is moving in and out of it?
>> Mike McAlpine: It’s actually a mechanical response. There’s not fluid moving in
and out. Actually, I take that back. There has to be some fluid moving in and out, but
it’s actually a change in the tension of the membrane. So the membrane has charges
in it. You’re injecting charge does interact with the membrane, and then that’s what
forces the volume to change. Yeah?
>>: [inaudible]
>> Mike McAlpine: No. Yeah, until we did it recently. So this is our next thing that’s
coming out in about two weeks. It just got accepted to nature nano so I’m really
excited about this stuff. Where we thought this probe here is pretty invasive, this
AFM tip. It’s a nanoscale tip and it’s pretty invasive. So we thought well, our stuff is
maybe semi-noninvasive. I mean, it does contain lead and everything, but you can
imagine culturing a neuron let’s say onto one of these pzt ribbons. And let’s say we
suspend the ribbon so there’s nothing underneath so it can easily bend up and
down.
And now if you inject current using this pipette into the neuron here, if that neuron
expands, it’ll push the ribbon down. So it pushes this pzt ribbon down. And if it’s
pushing it down you’re going to see that piezoelectric response using electrical
output.
So you have electrical input, electrical output, but you’re measuring the mechanics
of the cell. Yeah.
>>: So you could, I mean, you could replace the pzt with [inaudible]?
>> Mike McAlpine: Mechanically photosensitive?
>>: Yeah, basically. I’m just making sure I understood this. If you give it the charge
optically, as long as the charge is [inaudible].
>> Mike McAlpine: Can you stimulate a neuron --
>>: You don’t care why it’s charged. Whether it’s charged because you injected it
full of electrons or because you put [inaudible]. You don’t care how charged it gets.
[inaudible]
>> Mike McAlpine: Right. But one advantage of this though is, you know, one of the
questions we had when we first started this project is if you didn’t have -- this is a
soft cell. The pzt, even if it’s nanoscale, is still a little bit hard. So the cell should just
expand upward and not downward. So this [inaudible] is also kind of providing like
a top constraint so the cell will push down a little bit as well.
In that case I don’t know if that would work but maybe it would. So this is the
concept that we came up with and you can see these beautiful results. My student
first of all formed these cantilever ribbons here and then was able to culture these
beautiful neurons with nice dendrites and axons and everything on these ribbons.
You can see the size scale.
This is the cell here. And then these ribbons are kind of wide, but they’re still only a
few hundred nanometers thick so they can deform pretty easily there. And then
each side here we have electrode here and an electrode there to measure the piezo
response output. Okay?
And so first question, of course, pzt contains lead. So neurons like to die. If you’ve
ever tried to culture neurons before, they really like to die. So you can imagine if
you put it on a lead surface that they should really, really want to die. But to our
surprise they didn’t, which was really surprising.
And so we culture these neurons on these pzt ribbons here. The green means that
they’re still alive. The red means that they’re dead. This is after 72 hours. This is
after 168 hours. And you can see that some of them do die after a longer period of
time, but they also die on a standard culture medium, which is the blue here. So
compared to pzt they actually do -You can grow them on pzt and they are healthy and alive on this pzt sample. This
still doesn’t mean you would necessarily implant it on the body, but the thing is
everything we’ve done to this date has these ribbons the surface. So you can
basically put another thin layer of silicone on top to encapsulate it.
Basically just spin-coat the silicone and then cure it, and then it should be
encapsulated. But studies still need to be done that show that that won’t leak lead
or anything like that. But people have shown that even if you have a buckled system
and you encapsulate it, that you’ll still have the buckling work the way it should.
Yeah.
>>: So you still have some kind of adhesion problem and you haven’t talked about
adhesion at all because you moved into some kind of coating --
>> Mike McAlpine: Yeah, that’s exactly right. So it’s a very weak adhesion between
pzt and the silicone. And we know that because we were doing some other studies
where we saw we could actually push them around, or just like that Time magazine
where if they put it facedown they all come off.
So it’s a pretty weak adhesion. So you would still want to encapsulate them just
strictly for that reason as well because presume you’re going to be tapping on these
things or stressing them, you don’t want that to be the weak point because there’s
lots of other weak points here too.
The cells fire, this is just a standard -- it shows again that they’re healthy, that you
can get an action potential in the neuron on the pzt. And so here’s the response. So
here’s our cell that’s been cultured on the ribbon. Here’s our patch clamp probe that
comes down to inject current. Here are our pzt ribbons here. And so we inject the
current and what do we see?
So here’s the current that’s being injected in green here. And amazingly you can see
this perfectly in phase coherent response from the pzt ribbons to this injected
current. And you can see its AC because all piezoelectrics basically respond AC
because you bend it and then it release. So you get these piezoelectric spikes here
every time you spike the cell.
So pretty remarkably we are actually able to measure the mechanics of these cells
using this electrical simulation here. And the other cool thing is you can go in and
you can actually quantify this by taking just another one of these AFM tips and
pushing down on the ribbon to see it quantify the force versus displacement curve.
So you can translate back form that to see exactly how much quantitative
displacement you’re seeing. So here’s what happens if you zoom in on the plots
here. The green again is injecting the current into the cell and then the blue is your
piezoelectric response. We remove the noise here.
You can see this incredibly beautiful AC response that lines up perfectly, this lower
peak with that upper part and then the upper peak with the other part of the
response there. And if you quantify it we actually see that we got a force being acted
on from the cell on the pzt of the nanonewton scale and a deflection of about a
nanometer.
This actually matches exactly with the results that they got with the AFM tip from
that paper ten years ago. So amazingly this completely different system here was
actually able to quantify the exact same mechanical response from these cells. So
we’re really excited about this.
But then of course we haven’t learned anything new from those AFM studies they
did before. So the question is what’s new here? And the answer is you can’t scale up
this AFM but you can scale up our ribbons to larger areas. So you can scale them up,
you can put inter-digitated electrodes on them. And we’ve gotten good now at
scaling these things.
So here is a wafer. This is a hundred micron scale. The vertical lines here are these
ribbons here and then these are some electrodes that we’re putting on in the
horizontal direction there. And on these ribbons you can scale this up to a full
device here that you can bend and basically generate power.
So you can take this device and do what we’ve been wanting to do from the start,
which was to interface them here with lung tissue. So we got an undergrad to get a
cow lung this time, which is significantly harder than getting a cow tooth because
you have to kind of pull it out. So here’s a cow lung that’s breathing here. And
here’s the device that’s interfaced directly onto this cow lung.
So you can see it stressing every time the lung is breathing there. So we can
measure the piezoelectric charge that’s being generated form this process here. And
so the voltage is actually pretty decent. It’s about a volt peak-to-peak, but the
current is still a little bit on the low side. But of course these are very small strains.
So one of the things we’d like to do is eventually scale this up to a level that’s enough
to generate enough power to power a pacemaker. And I think we can do that cause
this is a very small device. So we have a lot more area we can go here to generate
more power. And so that’s kind of one of the things we’re interested in doing.
And so this is the direct bio interfacing of this device.
>>: [inaudible]
>> Mike McAlpine: Yeah, it goes back to the equation from before. This one. V is the
volume, so usually you’re not going to scale it in a thickness direction because if you
do you’re going to lose the flexibility. So the only way you can go is the surface area.
So if you do that then it is linear.
It’s square with the stress. So this kind of, like, usually pzt crystals are hard so that’s
why people haven’t put them in shoes. If you put one of these crystals in your shoe,
if you step on it you’re not going to be able to compress them.
They basically have the same [inaudible] as steel. So it’s like compressing steel with
the heal of your shoe. You’re not going to be doing very much. But the stress here is
nice because it’s also rod shaped so you can bend it. A lot more stress than you
could with a compression mode type of device here.
So that’s going as a square and then that surface area is going linear, yeah. So that’s
one of the things we’d like to do. Okay. So I’d like to thank my group and then
answer any questions. We’re exactly one hour. So the people that did some of the
work here, Manu [phonetic] did all the tooth stuff, Manu Manoor. He’s been a really
great person to have in the group. And Yong is the guy who’s working on the asthma
samples now, which is a really hard project. So you’re very brave for doing that.
And Fan is the person that did a lot of the piezoelectric ribbon work, especially with
the stuff with the cells with that paper that cam out recently.
And we’ve gotten funding from a number of different places. We’ve worked with
companies before [inaudible] and also with DuPont here and also these government
agencies as well. And some of our collaborators here, particularly Fio Omenetto,
he’s a professor at Tufts, and Naveen was the guy who did a lot of the electrical
engineering of those wireless circuits from before.
So I’d be happy to answer any more questions that you guys have and thanks a lot.
[applause]
>>: [inaudible]
>> Mike McAlpine: Yeah, so you can basically -- you mean the actuator?
>>: I’m just wondering since you’re responding to the curve [inaudible].
>> Mike McAlpine: Yeah, that’s one thing we’ve been interested in and, I mean, I
don’t want to give away any secrets here because this is going on a public website.
But we are interested in doing the inverse and seeing if we can either something like
what you described or maybe even at the cellular level seeing what kind of response
would happen from the cell from actuating it rather then this kind of sensing mode
here.
So that’s the next realm of interest for us so I think it’s a really interesting area so,
yeah.
Any other questions?
Thanks a lot.
[applause]