Tumors in low-oxygen environments tend to be more resistant to therapy and spread more aggressively to other parts of the body.
Measuring tumors oxygen levels could help doctors make decisions about treatments but there s currently no reliable noninvasive way to make such measurements.
However a new sensor developed at MIT could change that: A research team led by professor Michael Cima has invented an injectable device that reveals oxygen levels over several weeks
and can be read with magnetic resonance imaging (MRI). Using this kind of sensor doctors may be able to better determine radiation doses
and to monitor whether treatments are having the desired effect according to the researchers who describe the device in the Proceedings of the National Academy of Sciences the week of April 21.
In cases where you are trying to make therapeutic decisions you want to have some numbers that you can fall back on says Vincent Liu a graduate student in Cima s lab at MIT s Koch Institute for Integrative Cancer Research
and lead author of the paper. The injectable device is made of two types of silicone one that provides the MRI signal and one that offers structural support.
This is the first MRI sensor of any kind that can be left in the body for extended periods of time so far up to four weeks in testing with rats.
Cima the David H. Koch Professor of Engineering is the paper s senior author. Other authors are recent MIT Phd recipient Christophoros Vassiliou and recent master s degree recipient Syed Imaad.
Long-term MRIMRI uses magnetic fields and radio waves that interact with protons in the body to produce detailed images of the body s interior.
Injecting magnetic materials known as contrast agents can help boost the visibility of certain tissues but these agents are designed typically to break down soon after the MRI is performed.
Doctors often use MRI to diagnose tumors but currently MRI can only reveal the size and location of a tumor.
With the new MIT sensor doctors could track the state of the tumor and predict how it might respond to radiation treatment according to the researchers.
Radiation kills tumors by initiating DNA damage but oxygen is required to help finish the job.
An accurate reading of how much oxygen is present would help doctors calculate how much radiation might be necessary.
Measuring oxygen levels could also reveal the metastatic potential of a tumor: Those with lower oxygen levels tend to spread more aggressively.
The new MRI sensor combines two forms of silicone a solid called PDMS and a substance known as DDMPS which has an oily consistency.
The oily DDMPS can be dissolved in PDMS creating what s called a swollen polymer. The researchers shaped this polymer into a 1. 5-millimeter sensor that could be implanted in tissue during a biopsy;
they also created smaller particles (tens of microns long) that can be injected through a needle.
After injection these particles clump together to form a solid sensor. DDMPS absorbs molecular oxygen
which alters the proton spins inside the silicone a phenomenon that can be detected with MRI.
Measuring this shift in the MRI signal reveals how much oxygen is present. To test the sensors the researchers implanted them in the hind legs of rats
and then measured how the signal changed as the rats breathed pure oxygen regular air and pure oxygen again.
The sensors detected changes in oxygen pressure as small as 15 millimeters of mercury and it took less than 10 minutes to see the effects of a change in inhaled gas.
When the experiment was repeated four weeks later the sensors yielded the same results. Ralph Weissleder a professor at Harvard Medical school and director of the Massachusetts General Hospital Center for Molecular Imaging Research says this type of sensor is a novel way to potentially track how cancer patients
respond to treatment. The cancer field certainly needs something like this says Weissleder who was not part of the research team.
The ways we currently have to measure oxygen tension are fairly cumbersome and not quantitative so no one really uses them.
What s happening in a tumor This type of sensor could also be useful for monitoring blood flow in diabetic patients who often experience restricted circulation in their extremities
or people who have suffered traumatic injuries. The researchers also anticipate that it could help scientists learn more about tumor biology.
As opposed to just studying the genetic profile of tumor cells this could also reveal how they re interacting with the stroma that surrounds the tumor.
Oxygen tension as simple as it sounds is a good measure of what s happening in a tumor Cima says.
The researchers are now working on sensors that could be used to monitor other biological properties such as ph. We hope this is the first of many types of solid-state contrast agents where the material responds to its chemical environment in such a way that we can detect it by MRI Cima says.
The research was funded by the National Cancer Institute Centers of Cancer Nanotechnology Excellence and the U s army Research Office e
#Bionic ankle'emulates nature'These days Hugh Herr an associate professor of media arts and sciences at MIT gets about 100 emails daily from people across the world interested in his bionic limbs.
Messages pour in from amputees seeking prostheses and from media outlets pursuing interviews. Then there are students looking to join Herr s research group.
The technology inspires young people to get into the field which is wonderful Herr says. It s a mark of the groundbreaking work Herr has done at the MIT Media Lab over the past two decades.
An amputee himself Herr has been designing (and wearing) bionic leg prostheses that he says emulate nature mimicking the functions and power of biological knees ankles and calves.
Last month Herr s TED talk made headlines as Adrianne Haslet-Davis a professional dancer
whose leg was amputated partially after the 2013 Boston Marathon bombings used one of his prostheses to rumba on stage.
Most of these prostheses have reached the world through Herr s startup Biom (originally called iwalk.
Since 2010 the company has brought the world s first bionic foot -and-calf system to more than 900 patients worldwide including some 400 war veterans.
It s always good to design something people will use. It s great to do the science yes but it s also great to see humanity using something that one has invented Herr says adding:
Translating technology out of the lab keeps engineers honest. Initially developed by Herr s research group Biom s prosthesis dubbed the Biom T2 System simulates a biological ankle
(and connected calf muscle) delivering a natural ankle function during strides. Using battery-powered bionic propulsion two microprocessors
and six environmental sensors adjust ankle stiffness power position and damping thousands of times per second at two major positions:
First at heel strike the system controls the ankle s stiffness to absorb shock and thrust the tibia forward.
Then algorithms generate fluctuating power depending on terrain to propel a wearer up and forward. When fitting the prosthesis to patients prosthetists can program appropriate stiffness
and power throughout all the stages of a gait using software created by Herr s group a process the company calls Personal Bionic Tuning.
Among other things the system restores natural gait balance and speed; lowers joint stress; and drastically lowers the time required to acclimate to the prosthesis
(which can take weeks or months with conventional models). Often within minutes a patient is walking around even running around says Herr Biom s chief technology officer.
The system Herr says could also help prevent osteoarthritis a joint condition caused by age
and leg strain by providing calf and ankle power and support even in old age. etting from bench to bedside Throughout the 1990s
or hydraulics and don t release more energy than they absorb they walk more slowly consume more metabolic energy
and experience greater musculoskeletal stress which causes joint osteoarthritis. The scientific and engineering research that ultimately led to today s Biom prosthesis was conducted by Herr s research group within the MIT Media Lab
. Since 2003 the group has designed and fabricated many prosthetic prototypes to test hypotheses on human-machine interaction.
Several of these prototype designs with exposed mechanical parts and looping wires are on permanent display at the MIT Media Lab. Still today Herr can remember stepping into the group s first bionic leg prototype and then back
to a traditional prosthesis for the first time. It was as profound as when you re walking through the airport
Herr s experience commercializing a computer-controlled knee joint designed by his group for the Icelandic company Ossur inspired him to launch iwalk in 2006.
and manipulated by an electromagnetic field to either stiffen or relax during a wearer s gait.
and investment to get from bench to bedside Herr says. Starting a company is one way of enhancing that efficiency.
Today s Biom system has undergone more than 20 iterations funded by roughly $50 million of venture capital
Osteoarthritis humanoid design and personal bionics Biom s broader goal is to prevent costly conditions such as osteoarthritis. As we age the loss of fast muscle fibers
and calf muscles to lose power driving painful joint disorders such as knee osteoarthritis and low back pain caused in part by awkward limping gaits.
Across the elderly population joint osteoarthritis is a leading cause of mobility impairment. At least among amputees Herr says Biom could help by fitting elderly populations with leg prostheses equal in biomechanical agility and control to a young adult s legs:
We find ourselves in a position where we can put 18-year-old calf muscles on patients independent of their age mitigating the problem of joint osteoarthritis across all populations Herr says.
By advancing prostheses Herr says the technology could also lead to innovation in a closely related field:
One could just bolt these pieces together to produce a humanoid hardware platform Herr says.
But ultimately the work of both Biom and Herr s group at MIT he says aims to help revolutionize the idea of personal bionics blurring the lines between electromechanics and the human body.
#Excitons observed in action for the first time A quasiparticle called an exciton responsible for the transfer of energy within devices such as solar cells LEDS
and semiconductor circuits has been understood theoretically for decades. But exciton movement within materials has never been observed directly.
This could enable research leading to significant advances in electronics they say as well as a better understanding of natural energy transfer processes such as photosynthesis. The research is described this week in the journal Nature Communications in a paper co-authored by MIT postdocs Gleb
Akselrod and Parag Deotare professors Vladimir Bulovic and Marc Baldo and four others. This is the first direct observation of exciton diffusion processes Bulovic says showing that crystal structure can dramatically affect the diffusion process.
Excitons are at the heart of devices that are relevant to modern technology Akselrod explains:
The particles determine how energy moves at the nanoscale. The efficiency of devices such as photovoltaics and LEDS depends on how well excitons move within the material he adds.
An exciton which travels through matter as though it were a particle pairs an electron
but it can carry energy. For example in a solar cell an incoming photon may strike an electron kicking it to a higher energy level.
That higher energy is propagated through the material as an exciton: The particles themselves don t move but the boosted energy gets passed along from one to another.
While it was previously possible to determine how fast on average excitons could move between two points we really didn t have any information about how they got there Akselrod says.
which combines optical microscopy with the use of particular organic compounds that make the energy of excitons visible we can directly say what kind of behavior the excitons were moving around with.
This allows us to see new things Deotare says making it possible to demonstrate that the nanoscale structure of a material determines how quickly excitons get trapped as they move through it.
For some applications such as LEDS Deotare says it is desirable to maximize this trapping so that energy is lost not to leakage;
for other uses such as solar cells it is essential to minimize the trapping. The new technique should allow researchers to determine which factors are most important in increasing
or decreasing this trapping. We showed how energy flow is impeded by disorder which is the defining characteristic of most materials for low-cost solar cells
and LEDS Baldo says. While these experiments were carried out using a material called tetracene a well-studied archetype of a molecular crystal the researchers say that the method should be applicable to almost any crystalline or thin-film material.
They expect it to be adopted widely by researchers in academia and industry. It s a very simple technique once people learn about it Akselrod says
and the equipment required is not that expensive. Exciton diffusion is also a basic mechanism underlying photosynthesis:
Plants absorb energy from photons and this energy is transferred by excitons to areas where it can be stored in chemical form for later use in supporting the plant s metabolism.
The new method might provide an additional tool for studying some aspects of this process the team says.
David Lidzey a professor of physics and astronomy at the University of Sheffield who was involved not in this work calls the research a really impressive demonstration of a direct measurement of the diffusion of triplet excitons and their eventual trapping.
He adds Exciton diffusion and transport are important processes in solar-cell devices so understanding what limits these may well help the design of better materials
The work was supported by the U s. Department of energy and by the National Science Foundation and used facilities of the Eni-MIT Solar Frontiers Center r
and store that energy in chemical form, ready to be released again on demand. This solution is no solar-energy panacea:
While it could produce electricity, it would be inefficient at doing so. But for applications where heat is desired the output whether for heating buildings, cooking,
or powering heat-based industrial processes this could provide an opportunity for the expansion of solar power into new realms. t could change the game,
since it makes the sun energy, in the form of heat, storable and distributable, says Jeffrey Grossman, an associate professor of materials science and engineering,
who is a co-author of a paper describing the new process in the journal Nature Chemistry.
Exposing them to sunlight causes them to absorb energy and jump from one configuration to the other,
or electricity and when they relax, they give off heat. In effect, they behave as rechargeable thermal batteries:
taking in energy from the sun, storing it indefinitely, and then releasing it on demand.
The new work is a follow-up to research by Grossman and his team three years ago,
based on computer analysis. But translating that theoretical work into a practical material proved daunting: In order to reach the desired energy density the amount of energy that can be stored in a given weight
or volume of material it is necessary to pack the molecules very close together, which proved to be more difficult than anticipated.
Grossman team tried attaching the molecules to carbon nanotubes (CNTS), but t incredibly hard to get these molecules packed onto a CNT in that kind of close packing,
Kucharski says. But then they found a big surprise: Even though the best they could achieve was a packing density less than half of
what their computer simulations showed they would need, the material nevertheless seemed to deliver the heat storage they were aiming for.
Seeing a heat flow much greater than expected for the lower energy density prompted further investigation,
called azobenzene, protrude from the sides of the CNTS like the teeth of a comb.
they were interleaved with azobenzene molecules attached to adjacent CNTS. The net result: The molecules were actually much closer to each other than expected.
The interactions between azobenzene molecules on neighboring CNTS make the material work, Kucharski says. While previous modeling showed that the packing of azobenzenes on the same CNT would provide only a 30 percent increase in energy storage,
the experiments observed a 200 percent increase. New simulations confirmed that the effects of the packing between neighboring CNTS,
as opposed to on a single CNT, explain the significantly larger enhancements. This realization, Grossman says,
opens up a wide range of possible materials for optimizing heat storage. Instead of searching for specific photoswitching molecules
not electricity, might be desired the outcome of solar power. For example, in large parts of the world the primary cooking fuel is wood or dung
which produces unhealthy indoor air pollution, and can contribute to deforestation. Solar cooking could alleviate that
and since people often cook while the sun isn out, being able to store heat for later use could be a big benefit.
The adoption of carbon nanotubes to increase materialsenergy storage density is lever, says Yosuke Kanai, an assistant professor of chemistry at the University of North carolina who was involved not in this work.
He adds that the resulting increase in energy storage density s surprising and remarkable. his result provides additional motivation for researchers to design more
and better photochromic compounds and composite materials that optimize the storage of solar energy in chemical bonds, Kanai says.
The team also included MIT research scientist Nicola Ferralis, assistant professor of mechanical engineering Alexie Kolpak, and undergraduate Jennie Zheng,
as well as Harvard professor Daniel Nocera. The work was supported by BP though the MIT Energy Initiative and the U s. Department of energy Advanced Research Projects Agency Energy n
#Tiny particles could help verify goods Some 2 to 5 percent of all international trade involves counterfeit goods, according to a 2013 United nations report.
These illicit products which include electronics, automotive and aircraft parts, pharmaceuticals, and food can pose safety risks and cost governments and private companies hundreds of billions of dollars annually.
Many strategies have been developed to try to label legitimate products and prevent illegal trade but these tags are often too easy to fake,
are unreliable, or cost too much to implement, according to MIT researchers who have developed a new alternative.
Led by MIT chemical engineering professor Patrick Doyle and Lincoln Laboratory technical staff member Albert Swiston the researchers have invented a new type of tiny,
smartphone-readable particle that they believe could be deployed to help authenticate currency, electronic parts, and luxury goods, among other products.
contain colored stripes of nanocrystals that glow brightly when lit up with near-infrared light. These particles can easily be manufactured
They could also be equipped with sensors that can ecordtheir environments noting for example, if a refrigerated vaccine has ever been exposed to temperatures too high or low.
The paper lead authors are MIT postdoc Jiseok Lee and graduate student Paul Bisso. MIT graduate students Rathi Srinivas and Jae Jung Kim also contributed to the research.'
'A massive encoding capacity'The new particles are about 200 microns long and include several stripes of different colored nanocrystals,
known as are earth upconverting nanocrystals. These crystals are doped with elements such as ytterbium, gadolinium, erbium, and thulium,
which emit visible colors when exposed to near-infrared light. By altering the ratios of these elements,
the researchers can tune the crystals to emit any color in the visible spectrum. To manufacture the particles, the researchers used stop-flow lithography,
a technique developed previously by Doyle. This approach allows shapes to be imprinted onto parallel flowing streams of liquid monomers chemical building blocks that can form longer chains called polymers.
Wherever pulses of ultraviolet light strike the streams a reaction is set off that forms a solid polymeric particle.
In this case, each polymer stream contains nanocrystals that emit different colors, allowing the researchers to form striped particles.
So far, the researchers have created nanocrystals in nine different colors, but it should be possible to create many more,
Doyle says. Using this procedure, the researchers can generate vast quantities of unique tags. With particles that contain six stripes,
while on the technical staff at Lincoln Lab. ou can apply different combinations of 10 particles to products from now until long past our time
and youl never get the same combination. he use of these upconverting nanocrystals is quite clever and highly enabling,
a professor of biologically inspired engineering at Harvard university who was involved not in the research. here are several striking features of this work,
or printed onto currency, the researchers say. They could also be incorporated into ink that artists could use to authenticate their artwork.
The researchers demonstrated the versatility of their approach by using two polymers with radically different material properties one hydrophobic and one hydrophilic o make their particles.
without impacting smartphone readout or requiring a complete redesign of the system. Another advantage to these particles is that they can be read without an expensive decoder like those required by most other anti-counterfeiting technologies.
Using a smartphone camera equipped with a lens offering twentyfold magnification anyone could image the particles after shining near-infrared light on them with a laser pointer.
The researchers are also working on a smartphone app that would further process the images and reveal the exact composition of the particles.
The research was funded by the U s. Air force, the Office of the Assistant Secretary of defense for Research and Engineering, the Singapore-MIT Alliance, the National Science Foundation, the U s army Research Office,
#One currency one price? Economics has a aw of one price, which states that identical goods should, in theory,
sell for identical prices or else markets will even out the differences. Empirical work on the topic, however, has produced little evidence in support of this aw,
and many studies showing deviations from it. Now a newly published paper co-authored by two MIT economists,
along with a colleague from the University of Chicago, presents evidence of a strong convergence of prices within the Eurozone, the region of European countries sharing a common currency.
The divergence of product prices is 30 to 50 percent lower in Eurozone countries than it is even in neighboring countries
whose currencies are pegged to the Euro. hat is surprising about our paper is that we found the law of one price,
says Roberto Rigobon, the Society of Sloan Fellows Professor of Management at the MIT Sloan School of management,
and a co-author of the paper, nd we found it to be very strongly dependent on the currency in
which the prices are quoted. Indeed, the unity of the currency seems to be a more powerful factor in determining prices than the characteristics of particular countries
or consumers. conomists tend to think what drives international price differences are things like transportation costs, information costs, tariffs, cultural differences, and other factors,
says Alberto Cavallo, a professor at MIT Sloan, and another co-author of the paper. ee finding those things don seem to matter relative to the retailer showing prices in the same currency.
The paper, urrency Unions, Product Introductions, and the Real Exchange rate, is being published by the Quarterly Journal of Economics.
Along with Cavallo and Rigobon, the study was conducted by Brent Neiman, a professor at the University of Chicago Booth School of business.
The study covers prices of thousands of products, drawing on data from four major international firms:
Apple, H&m, Ikea, and Zara. Online pricing data was crapedusing a harvesting technique that Rigobon and Cavallo first developed for the illion Prices Project,
which provides real-time inflation estimates. All told, the researchers examined nearly 120,000 products sold in 85 countries from October 2008 to May 2013.
The researchers checked online and in store prices against each other, finding no significant divergences. Moreover, because the study dealt with international firms that often produce all their goods in a single location
and then use similar logistical systems to distribute the goods, the variation in prices observed in non-Euro countries most likely does not come from variations in production and distribution.
In evaluating the law of one price Rigobon observes, ne question has been, can you find the same item delivered to the consumer in the exact same way with the exact same retailer, with the exact same procedures?
We realized that we had those identical items. More evidence for the idea that the common currency drives identical pricing is that in countries like Denmark,
which do not use the Euro but peg their currencies to it, prices diverge markedly from nearby Eurozone countries.
The same holds for countries that do not use the U s. dollar, but peg their own currencies to it. hen we look at countries that do not use the same currency
but are pegged, we still find an enormous amount of dispersion, Cavallo says. hat points to the fact it not the flexibility
or rigidity of the exchange rate that explains the differences. The research also uncovered nuances in pricing strategies.
For one thing international firms take country-specific taxes into account when setting prices, so that the pretax price in France,
which has a relatively high Value-added tax (VAT), will be lower than in other countries. After taxes,
however, the prices shown to consumers are uniform. One explanation for the price convergence, the researchers suggest,
is shaped consumer psychology by access to prices online: People who can see prices from country to country across the Eurozone would consider it unfair
if those prices diverged. hat possibly driving this, Cavallo says. r it could be that these firms just think about their pricing just in terms of currencies.
Whatever the benefits or flaws of the Eurozone, the research indicates that the common currency is delivering on one of the stated aims of its backers:
a more unified pricing system in Europe. However, as the researchers point out, unified pricing is a double-edged sword:
Relatively well-off consumers in some European countries may gain when prices equalize. But in a place such as Greece, currently suffering a severe recession with deep wage reductions,
unified Eurozone pricing reduces consumerspurchasing power. he companies are pricing Greece and Germany as if they are two neighborhoods of the same city,
Rigobon says, adding: aving one currency means implicitly that in good times, you are buying the price stability of Germany.
But that also means that in bad times, unfortunately, you are buying the price stability of Germany.
The study has attracted already considerable attention among economists. Gita Gopinath, an economics professor at Harvard university, calls the work terrific paperthat adds new information to the field. hat we did not know,
and what this paper shows, is that even when the volatility of the exchange rate is down to zero,
it matters a lot if this zero volatility has to do with countries being in a currency union,
versus if it is fixed because of a exchange rate, Gopinath says. However, she adds, the precise mechanism at work remains unclear:
his striking finding is need something we to understand better. Cavallo, Rigobon, and Neiman take the same view in the paper. uture work should focus on understanding
what determines when prices behave like those documented here and when they do not, they write.
They would also like to collect more data illuminating how companies set prices when new goods are introduced first.
The researchers are already pursuing follow-up studies: For instance, with the entrance of Latvia to the Eurozone, they are now comparing how that change in currency has affected prices in Latvia u
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