SKIN LIKE DEVICE MONITORS CARDIOVASCULAR AND SKIN HEALTH

A new wearable medical device can quickly alert a person if they are having cardiovascular trouble or if it's simply time to put on some skin moisturizer, reports a Northwestern University and University of Illinois at Urbana-Champaign study

The small device, approximately five centimeters square, can be placed directly on the skin and worn 24/7 for around-the-clock health monitoring. The wireless technology uses thousands of tiny liquid crystals on a flexible substrate to sense heat. When the device turns color, the wearer knows something is awry.

"Our device is mechanically invisible -- it is ultrathin and comfortable -- much like skin itself," said Northwestern's Yonggang Huang, one of the senior researchers. The research team tested the device on people's wrists.

"One can imagine cosmetics companies being interested in the ability to measure skin's dryness in a portable and non-intrusive way," Huang said. "This is the first device of its kind."

Huang led the portion of the research focused on theory, design and modeling. He is the Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern's McCormick School of Engineering and Applied Science.

The technology and its relevance to basic medicine have been demonstrated in this study, although additional testing is needed before the device can be put to use. Details are reported online in the journal Nature Communications.

"The device is very practical -- when your skin is stretched, compressed or twisted, the device stretches, compresses or twists right along with it," said Yihui Zhang, co-first author of the study and research assistant professor of civil and environmental engineering at Northwestern.

The technology uses the transient temperature change at the skin's surface to determine blood flow rate, which is of direct relevance to cardiovascular health, and skin hydration levels. (When skin is dehydrated, the thermal conductivity property changes.)

The device is an array of up to 3,600 liquid crystals, each half a millimeter square, laid out on a thin, soft and stretchable substrate.

When a crystal senses temperature, it changes color, Huang said, and the dense array provides a snapshot of how the temperature is distributed across the area of the device. An algorithm translates the temperature data into an accurate health report, all in less than 30 seconds.

"These results provide the first examples of 'epidermal' photonic sensors," said John A. Rogers, the paper's corresponding author and a Swanlund Chair and professor of materials science and engineering at the University of Illinois. "This technology significantly expands the range of functionality in skin-mounted devices beyond that possible with electronics alone."

Rogers, who also is director of the Seitz Materials Research Laboratory, led the group that worked on the experimental and fabrication work of the device. He is a longtime collaborator of Huang's.

With its 3,600 liquid crystals, the photonic device has 3,600 temperature points, providing sub-millimeter spatial resolution that is comparable to the infrared technology currently used in hospitals.

The infrared technology, however, is expensive and limited to clinical and laboratory settings, while the new device offers low cost and portability.

The device also has a wireless heating system that can be powered by electromagnetic waves present in the air. The heating system is used to determine the thermal properties of the skin.

The National Science Foundation supported the research.

The title of the paper is "Epidermal Photonic Devices for Quantitative Imaging of Temperature and Thermal Transport Characteristics of the Skin." In addition to Zhang, Li Gao and Viktor Malyarchuk of the University of Illinois at Urbana-Champaign are co-first authors.

LASER DEVICE MAY END PINPRICKS FOR DIABETICS

Princeton University researchers have developed a way to use a laser to measure people's blood sugar, and, with more work to shrink the laser system to a portable size, the technique could allow diabetics to check their condition without pricking themselves to draw blood

We are working hard to turn engineering solutions into useful tools for people to use in their daily lives," said Claire Gmachl, the Eugene Higgins Professor of Electrical Engineering and the project's senior researcher. "With this work we hope to improve the lives of many diabetes sufferers who depend on frequent blood glucose monitoring."

In an article published June 23 in the journalBiomedical Optics Express, the researchers describe how they measured blood sugar by directing their specialized laser at a person's palm. The laser passes through the skin cells, without causing damage, and is partially absorbed by the sugar molecules in the patient's body. The researchers use the amount of absorption to measure the level of blood sugar.

Sabbir Liakat, the paper's lead author, said the team was pleasantly surprised at the accuracy of the method. Glucose monitors are required to produce a blood-sugar reading within 20 percent of the patient's actual level; even an early version of the system met that standard. The current version is 84 percent accurate, Liakat said.

"It works now but we are still trying to improve it," said Liakat, a graduate student in electrical engineering.

When the team first started, the laser was an experimental setup that filled up a moderate-sized workbench. It also needed an elaborate cooling system to work. Gmachl said the researchers have solved the cooling problem, so the laser works at room temperature. The next step is to shrink it.

"This summer, we are working to get the system on a mobile platform to take it places such as clinics to get more measurements," Liakat said. "We are looking for a larger dataset of measurements to work with."

The key to the system is the infrared laser's frequency. What our eyes perceive as color is created by light's frequency (the number of light waves that pass a point in a certain time). Red is the lowest frequency of light that humans normally can see, and infrared's frequency is below that level. Current medical devices often use the "near-infrared," which is just beyond what the eye can see. This frequency is not blocked by water, so it can be used in the body, which is largely made up of water. But it does interact with many acids and chemicals in the skin, so it makes it impractical to use for detecting blood sugar.

Mid-infrared light, however, is not as much affected by these other chemicals, so it works well for blood sugar. But mid-infrared light is difficult to harness with standard lasers. It also requires relatively high power and stability to penetrate the skin and scatter off bodily fluid. (The target is not the blood but fluid called dermal interstitial fluid, which has a strong correlation with blood sugar.)

The breakthrough came from the use of a new type of device that is particularly adept at producing mid-infrared frequencies -- a quantum cascade laser.

In many lasers, the frequency of the beam depends on the material that makes up the laser -- a helium-neon laser, for example, produces a certain frequency band of light. But in a quantum cascade laser, in which electrons pass through a "cascade" of semiconductor layers, the beam can be set to one of a number of different frequencies. The ability to specify the frequency allowed the researchers to produce a laser in the mid-infrared region. Recent improvements in quantum cascade lasers also provided for increased power and stability needed to penetrate the skin.

To conduct their experiment, the researchers used the laser to measure the blood sugar of three healthy people before and after they each ate 20 jellybeans, which raise blood sugar levels. The researchers also checked the measurements with a finger-prick test. They conducted the measurements repeatedly over several weeks.

The researchers said their results indicated that the laser measurements readings produced average errors somewhat larger than the standard blood sugar monitors, but remained within the clinical requirement for accuracy.

"Because the quantum cascade laser can be designed to emit light across a very wide wavelength range, its usability is not just for glucose detection, but could conceivably be used for other medical sensing and monitoring applications," Gmachl said.