Tiny, implantable medical device can propel itself through bloodstream

Feb 22, 2012
Engineers at Stanford have developed a wirelessly powered, self-propelled medical device that can propel itself through the blood stream to deliver drugs, perform diagnostics or microsurgeries. Credit: Illustration by Carlos Suarez, StrongBox3d

Someday, your doctor may turn to you and say, "Take two surgeons and call me in the morning." If that day arrives, you may just have Ada Poon to thank.

Yesterday, at the International Solid-State Circuits Conference (ISSCC) before an of her , electrical engineer Poon demonstrated a tiny, wirelessly powered, self-propelled capable of controlled motion through a fluid—blood more specifically. The era of swallow-the-surgeon medical care may no longer be the stuff of science fiction.

Poon is an assistant professor at the Stanford School of Engineering. She is developing a new class of medical devices that can be implanted or injected into the human body and powered wirelessly using electromagnetic radio waves. No batteries to wear out. No cables to provide power.

"Such devices could revolutionize medical technology," said Poon. "Applications include everything from diagnostics to minimally invasive surgeries."

Certain of these new devices, like heart probes, chemical and pressure sensors, cochlear implants, pacemakers, and drug pumps, would be stationary within the body. Others, like Poon's most recent creations, could travel through the bloodstream to deliver drugs, perform analyses, and perhaps even zap blood clots or removing plaque from sclerotic arteries.

Challenged by power

The idea of implantable medical devices is not new, but most of today's implements are challenged by power, namely the size of their batteries, which are large, heavy and must be replaced periodically. Fully half the volume of most of these devices is consumed by battery.

"While we have gotten very good at shrinking electronic and mechanical components of implants, energy storage has lagged in the move to miniaturize," said co-author Teresa Meng, a professor of electrical engineering and of computer science at Stanford. "This hinders us in where we can place implants within the body, but also creates the risk of corrosion or broken wires, not to mention replacing aging batteries."

This image shows the scale of the wirelessly powered, self-propelled medical device developed by electrical engineer Ada Poon at Stanford. Credit: Ada Poon, Stanford School of Engineering

Poon's devices are different. They consist of a radio transmitter outside the body sending signals to an independent device inside the body that picks up the signal with an antenna of coiled wire. The transmitter and the antenna are magnetically coupled such that any change in current flow in the transmitter produces a voltage in the coiled wire — or, more accurately, it induces a voltage. The power is transferred wirelessly. The electricity runs electronics on the device and propels it through the bloodstream, if so desired.

Upending convention

It sounds easy, but it is not. Poon had to first upend some long-held assumptions about the delivery of wireless power inside the human body.

For fifty years, scientists have been working on wireless electromagnetic powering of implantable devices, but they ran up against mathematics. According to the models, high-frequency radio waves dissipate quickly in human tissue, fading exponentially the deeper they go.

Low-frequency signals, on the other hand, penetrate well, but require antennae a few centimeters in diameter to generate enough power for the device, far too large to fit through all but the biggest arteries. In essence, because the math said it could not be done, the engineers never tried.

Then a curious thing happened. Poon started to look more closely at the models. She realized that scientists were approaching the problem incorrectly. In their models, they assumed that human muscle, fat and bone were generally good conductors of electricity, and therefore governed by a specific subset of the mathematical principles known as Maxwell's equations — the "quasi-static approximation" to be exact.

Poon took a different tack, choosing instead to model tissue as a dielectric — a type of insulator. As it turns out human tissue is a poor conductor of electricity. But, radio waves can still move through them. In a dielectric, the signal is conveyed as waves of shifting polarization of atoms within cells. Even better, Poon also discovered that human tissue is a "low-loss" dielectric — that is to say little of the signal gets lost along the way.

She recalculated and made a surprising find: Using new equations she learned high-frequency travel much farther in than originally thought.

Revelation

"When we extended things to higher frequencies using a simple model of tissue we realized that the optimal frequency for wireless powering is actually around one gigahertz," said Poon, "about 100 times higher than previously thought."

More significantly, however, her revelation meant that antennae inside the body could be 100 times smaller and yet deliver the same power.

Poon was not so much in search of a new technology; she was in search of a new math. The antenna on the device Poon demonstrated at the conference yesterday is just two millimeters square; small enough to travel through the bloodstream.

She has developed two types of self-propelled devices. One drives electrical current directly through the fluid to create a directional force that pushes the device forward. This type of device is capable of moving at just over half-a-centimeter per second. The second type switches current back-and-forth in a wire loop to produce swishing motion similar to the motion a kayaker makes to paddle upstream.

"There is considerable room for improvement and much work remains before these devices are ready for medical applications," said Poon. "But for the first time in decades the possibility seems closer than ever."

Explore further: Researchers propose network-based evaluation tool to assess relief operations feasibility

Provided by Stanford School of Engineering

5 /5 (10 votes)

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User comments : 15

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NotAsleep
5 / 5 (1) Feb 22, 2012
I feel like better, smaller versions of this have already been developed... there was a device that was controlled externally like a magnet in a beaker. It was unpowered and designed to deliver a single shot of medicine internally

Perhaps this new device adds more functionality but it's a heck of a lot bigger than previous attempts I've seen
antialias_physorg
3.7 / 5 (6) Feb 22, 2012
Hmm. If I remember my studies on the circulatory system correctly then eventually the bloodstream will carry this to capillaries which are down to 60nanometers wide.

At some point during the intervention you are done. No more power is supplied from the outside and the 'microscopic surgeon' is carried away with the flow of blood. What happens when your 'surgeon' gets to a capillary? 2mm square (for the antenna alone) is far too big to pass through.
Does it just block the passage forever (with the ancilary risk of that capillary being in the brain and you just having made an artificial blood clot - read: stroke)?

On a related note: How do you get these things out after the surgery? Or do you just simply let them accumulate in the system (whenever you need a new treatment you get a new one injected)?

Such electronics aren't passed via the kindeys or the intestine.

Interesting. But the concept stil needs a little work.
Xbw
2.3 / 5 (9) Feb 22, 2012
She may want to forego slapping her last name onto the device. Check the urban dictionary for "Poon" if you don't understand.
jscroft
3.4 / 5 (5) Feb 22, 2012
What, a "Poon sensor"? Already got one of those.
Xbw
2.3 / 5 (9) Feb 22, 2012
What, a "Poon sensor"? Already got one of those.


I think all males were born with them. Mine frequently activates without my permission.
RitchieGuy
1.6 / 5 (7) Feb 22, 2012
LOL . .me too. I think I'll pass on that gadget. . .antialias is right, it could cause problem
RitchieGuy
2 / 5 (8) Feb 22, 2012
wang dang sweet poontang. . .LOL Ted Nugent is the MAN!!

http://www.youtub...aSLCDxQc

back on topic: maybe they should build one that melts away after some time at body temps.
Deesky
3.7 / 5 (9) Feb 22, 2012
AP, my thoughts exactly.

I feel like better, smaller versions of this have already been developed... there was a device that was controlled externally like a magnet in a beaker. It was unpowered and designed to deliver a single shot of medicine internally

Perhaps this new device adds more functionality but it's a heck of a lot bigger than previous attempts I've seen

I think what you're referring to is a camera pill/capsule that you swallow. That device is primarily for taking pictures in the gut and the airways as it slides down the esophagus. It's also a lot bigger - the size of a very large vitamin pill. The two are very different.
TheGhostofOtto1923
1.4 / 5 (7) Feb 23, 2012
What happens when your 'surgeon' gets to a capillary? 2mm square (for the antenna alone) is far too big to pass through.
Does it just block the passage forever... stroke)?
Perhaps youre right... Wait a minute -

"Poon is an assistant professor at the Stanford School of Engineering."

-Do you think it possible that Prof Poon has overlooked this potential in the hundreds of hours she has spent in design? Or that Stanford would allow tech to be developed which could expose them to millions in liability? Or that these pros hadnt considered that the FDA wouldnt approve tech that would present such a clear danger to the public, and so wouldnt waste their time working on it?

Sorry AA I think this is something they would have considered. Dont you?
LOL . .me too. I think I'll pass on that gadget. . .antialias is right, it could cause problem
Nice empty suckup comment BitchieBoy. How typical.
antialias_physorg
5 / 5 (4) Feb 23, 2012
Sorry AA I think this is something they would have considered. Dont you?

In my experience everything that was expressly considered is part of the paper. I can find no mention of this.

But there certainly are areas where one could directly use this (e.g. by not introducing it into the bloodstream, but for surgeries in the bladder or kidney). There the retrieval would be possible after the operation.
NotAsleep
5 / 5 (2) Feb 24, 2012
Deesky, I was actually thinking more along the lines of this:

http://www.medica...tion.htm

It's significantly smaller, probably because it's entirely controlled by an external electromagnetic force
RitchieGuy
1.4 / 5 (9) Feb 25, 2012
ROFLOL. . .how is it that every time I agree with something that antialias (or anyone else) said, that phuking weirdo TheGhostofOtto1923 gets her black tights in a wad and says something like this:
"Nice empty suckup comment BitchieBoy. How typical." I can only surmise that Ghost is going through pre-menstrual syndrome (PMS) again and has to take it out on somebody. I'm glad we don't know her in person, she might throw a rolling pin or fry pan at us. LOL

back to topic: the gadget may need to be made smaller so as not to lodge in narrowed blood vessels, especially in baby veins.
RitchieGuy
1.5 / 5 (8) Feb 26, 2012
Actually , I was agreeing with jscroft and Xbw and stating as to my having a "poon sensor" also just as they do, thus the "me too". However, antialias is right. The device needs more work to make it much smaller. Apparently, Ms. Poon MAY have thought about the possibility of the device getting jammed inside a very small vein, but her device that is displayed in the picture is still too big. It still needs more engineering for size.
Ghost. Deal with it instead of jumping to the wrong conclusions as usual..
TheGhostofOtto1923
1 / 5 (4) Feb 27, 2012
However, antialias is right. The device needs more work to make it much smaller.
In your worthless opinion that is. Right?
Apparently, Ms. Poon MAY have thought about the possibility of the device getting jammed inside a very small vein,
Because after all she is an expert while you are an expert at making sweat stains on your couch?
but her device that is displayed in the picture is still too big
You do realize that that is an artists fanciful rendition of a generic chip, not the actual thing poon is working on? No of course you don't.
It still needs more engineering for size.
In your worthless opinion that is. Come on bitchie what do you know about microelectronic medical devices? You must know you are not qualified to offer opinions of any worth at all on the subject? So why try? Do you enjoy making yourself look DUMB?
NotAsleep
5 / 5 (1) Feb 28, 2012
You do realize that that is an artists fanciful rendition of a generic chip, not the actual thing poon is working on? No of course you don't

While the picture at the top of this page is clearly an artists rendition, the "scale" image of the device on top of a penny appears to be the genuine thing. My calibrated "penny and ruler" device tells me it's 4mm X 6mm. This means only primary arteries could handle the device at it's current size. Compare it to the average size of the internal carotid artery: 4.66mm in women and 5.11mm in men. That's not a lot of wiggle room for traveling down a pathway critical to life...

Source for the artery diameters:
http://stroke.aha...103.full

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