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"Diabetics are reluctant to monitor their blood glucose levels because of the painful blood-gathering process," said study author Hyunjae Lee, from Seoul National University in the Republic of Korea. "We highly focused on a noninvasive monitoring and therapy system for diabetics."
The findings were published online March 21 in the journal Nature Nanotechnology. The study team was led by Dae-Hyeong Kim, at Seoul National University. Funding for the study was provided by the Institute for Basic Science in the Republic of Korea.
Currently, people with diabetes have two options for monitoring blood sugar (glucose) levels, said Richard Guy, who wrote an accompanying editorial in the journal. He's a professor of pharmaceutical sciences at the University of Bath in the United Kingdom.
One option is a blood glucose meter that requires a finger stick to draw out a drop of blood for testing. The other option is continuous glucose monitoring, which requires that a sensor be placed underneath the skin and worn constantly. Both of these options are invasive and can be painful.
Previously, a less invasive product called GlucoWatch pulled fluid through the skin to the device to measure blood sugar levels. However, that device was never commercially successful and was taken off the market, Guy said.
The Korean research team used a substance called graphene to develop a thin, flexible patch. Graphene conducts electricity, and can be transparent, soft and very thin, the researchers explained.
The patch also contains a variety of sensors that detect humidity, sweat glucose levels, pH and temperature, the researchers said. In addition, the patch contains heat-sensitive microneedles.
The patch uses sweat to determine "sweat glucose," which can be used to figure out blood glucose levels. Lee said the accuracy of the sweat glucose sensor is similar to that of home blood glucose meters in the United States.
Guy pointed out that someone who sweats a lot might pose a challenge for the patch.
But the researchers said they've already taken this into consideration. "We integrated a humidity sensor in the diabetes patch to check how much sweat is generated. So the person who perspires heavily wouldn't affect the sensing," said Tae Kyu Choi, another study author from Seoul National University.
Likewise, Choi said, the researchers accounted for someone who perspires very lightly.
The researchers tested the glucose-sensing ability of the patch in two humans and found the device was able to accurately measure blood sugar levels.
In the current version of the patch, the researchers used microneedles to deliver the diabetes drug metformin to mice. Over six hours, the drug -- delivered through the skin -- was able to drop blood sugar levels from 400 milligrams per deciliter to 120 milligrams per deciliter, the researchers said. For someone without diabetes, a normal blood sugar level taken randomly would generally be under 125 milligrams per deciliter, according to the U.S. National Library of Medicine.
Insulin -- the hormone necessary to lower blood sugar for people with type 1 diabetes -- wasn't used because it's a protein that would be difficult to deliver through microneedles because it's large, and it would be vulnerable to the heating process that allows the drug to be delivered through the skin, the study authors explained.
But, Guy said he expects that should this system go forward in development, other drugs that can lower blood sugar more effectively might be considered. "I think metformin was chosen as an example of a drug used in diabetics for the illustration of proof-of-concept," he said.
The researchers said they believe the device could be used by either type 1 or type 2 diabetics.
However, Dr. Joel Zonszein, director of the Clinical Diabetes Center at Montefiore Medical Center in New York City, said the cost of the device might make it very impractical for people with type 2 diabetes. And, he said, people with type 2 diabetes don't have to know what their blood sugar levels are as often as people with type 1 diabetes.
"They have proved the concept -- that a sweat patch can do the monitoring and can deliver a drug transdermally [through the skin]. Trying to do something like this noninvasively really is the holy grail of diabetes. So, there may be a future for this, but there are many barriers to be overcome," Zonszein said.
The researchers said their next step is to improve the long-term stability and accuracy of the blood glucose sensor. Lee and Choi estimated it would be at least five years before they could solve any remaining obstacles and commercialize the device.
"The promise of a transdermal, minimally invasive glucose monitoring device is coming closer to fruition. I'd hope we'd see a new effort to bring a skin-based monitoring device for glucose to the market in the next few years," Guy said. "In contrast, such as system combined with drug delivery is, in my opinion, much further away."
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