Researchers at Northwestern University in Evanston, Illinois and the University of Sussex in Brighton, England, have prototyped new environmentally sustainable devices that can monitor blood pressure and heart rate or treat stubborn ailments like diabetic ulcers.
The devices are also much more advanced than the proof-of-concept stage; the Northwestern device, a temporary dressing that uses electrotherapy to both monitor and treat diabetic wounds, is resorbed in the body. It could be ready for human trials within a year to 18 months, according to Guillermo Amir, director of the Northwest Center for Advanced Regenerative Engineering. The headband consists of two small molybdenum electrodes connected to a batteryless power harvester and a near field communication module that communicates with control software on a smartphone or tablet.
In a study in diabetic mice published in Scientific achievements, Amir and his collaborators, including absorbable electronics pioneer John Rogers, found that the device healed 30 percent faster than a control group using conventional bandages.
The device works by transmitting a small current from an outer annular electrode around the wound site to an inner flower-shaped electrode about 120 micrometers in diameter located above the wound. (The mouse study used about 1 volt of current, and Amir said this may change in upcoming studies in larger animals.) The current stimulates healthy skin regeneration, the progress of which is measured by the difference in current between the electrodes. As the wound heals and dries, the current differential decreases.
Perhaps the most attractive element of the device is the internal electrode. As the wound heals, the regenerated skin grows over the electrode and completely absorbs it. The outer ring electrode and the associated power and communication unit are separated from the inner electrode. The results of a study in mice showed that the concentration of molybdenum in the body returned to that of the control group within 22 weeks.
Amir said that he and his colleagues would not have promoted the idea if they did not consider it safe.
“It’s a matter of risk versus benefit, just like any other drug or medical device,” he said. “This is not meant for your child who has scratched his leg. It is intended for wounds that have not healed for a month or so and are prone to infection, leading to complications and amputations. As the electrode heals, the remaining electrode will become overgrown with skin, which you would expect to dissolve over time. You can explain this to the patient and he and his doctor can make an informed decision.”
He said the technology could be especially useful for hard-to-reach or hard-to-reach parts of the body, such as the soles of the feet. Given that one of the symptoms of diabetes is peripheral nerve damage, Amir said the patient may be suffering from a wound that is getting worse but cannot see or feel it. A constant stream of data from the device to the connected clinician’s control panel can reduce or eliminate this risk.
Algae biodegradable sensor
While part of the Northwestern device is bioresorbable in the body, the sensor, developed at the University of Sussex, is completely biodegradable. It consists of a food grade algae powder added to a graphene slurry composed of graphite, sodium cholate and deionized water and then dried to form a nanocomposite sheet. When soaked in another food component – a water bath with calcium chloride – the leaf swells and forms a conductive hydrogel.
University of Sussex researchers have developed a fully biodegradable conductive hydrogel made from algae, salt water and graphene derived from an aqueous suspension of graphite.University of Sussex
The device described in ACS Sustainable Chemistry and Engineering, also extremely flexible for a nanocomposite (with a Young’s modulus of only 0.6 pascal) and sensitive enough to measure an object as small as 2 milligrams, which the inventors likened to the pressure exerted by a single raindrop on its surface. The researchers speculate that the inherent repulsion between the highly hydrophobic and conductive graphene and the hydrophilic but insulating algae gel, which they called “poor interfacial adhesion,” makes it more susceptible to mechanical deformation. “In terms of applications as mechanical strain gauges, these low mechanical properties are very advantageous because they result in very low initial strain for the electromechanical response,” they concluded.
For initial applications, they suggest that the gels could be used as environmental sensors in a number of applications, including rainfall detection and airflow leakage detection to heat or cool buildings more efficiently.
The study’s corresponding author, Sussex materials physics lecturer Conor Boland, distinguished his lab’s work, which uses electromechanical sensing, from the Northwest bandage, which uses electrochemical sensing, but said both approaches could have legitimate applications in human healthcare. For example, he says, his team is already working on turning a mixture of algae into a material that mimics the mechanical properties of human skin, but also has electronic capabilities to control blood pressure and respiratory rate.
One particularly interesting future application could be pulse oximetry, the measurement of oxygen saturation in the blood. Health researchers have documented a recurring problem with many commercially available oximeters that use optical sensors—they often inaccurately measure oxygen saturation in people with darker pigment.
“We have a physical measurement, you put it on the skin, and it measures the pressure of an artery against the skin,” Boland said. “There will always be the same signal as long as the material is calibrated.”
Boland acknowledges that the ecosystem of fully biocompatible and biodegradable devices is still in its infancy. While his lab’s device is completely degrading, any protective casing designed to extend its life – he said the lab prototype is stable for five or six hours – will not.
“I hope that our work will demonstrate the feasibility of commercializing such materials and open up a wider range of research,” he said.
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