This article discusses the use and benefits of e-Nanoflex that combines nanostructured sensors, smart phones, and cloud computing and promises a new platform for everyday medical monitoring. At the University of Arkansas, a team of surgeons, engineers, and computer scientists has developed a personal heart monitor based on e-Nanoflex nanostructured sensors. The sensors can be embedded in clothing that can be worn and washed just like any other garment. The e-Nanoflex can also monitor recovery from surgery, medical compliance, and neurological diseases, or help athletes optimize their training routines. The nanostructured sensors developed at the University of Arkansas make true portable, wearable electrocardiograph (EKG) systems possible. They consist of tiny metal nanowires growing outwards from the surface of the electrodes. Sophisticated software can monitor data from e-Nanoflex sensors about heart rate consistency and other factors to ensure that patients comply with their prescriptions. The combination of wearable nanostructured sensors, smart phones, and cloud computing makes wearable EKGs possible.
Six months ago, Jane T., a 48-year-old mother of two, had a heart attack.
Since then, she has lost some weight and has tried to spend 20 to 30 minutes walking daily to build up cardiovascular strength. Like many who have had cardiac problems, she has not fully recovered. Jane may not be aware of the data, but 23 percent of women aged 40 and older die within one year of a heart attack.
One winter morning, after rising early to get her children off to school, Jane paused by the kitchen sink. She did not feel well. She thought she might be coming down with the cold going around her children's school. She took an aspirin.
As she turned to go upstairs, her smart phone rang. It was her doctor's office.
“Jane,” the nurse said, “we just received an alert from your health monitoring system.
“The first thing I want to tell you is, don’t worry: you’re not having another heart attack. But your monitor is detecting some irregular activity, and we would like the hospital to take a look at you now, before anything happens.”
Jane could feel her heart beat faster as the room swam around her. “Jane,” said the nurse, “why don’t you sit down. We’ve already dispatched an ambulance. They should be there in a few minutes. We’ll call your husband to meet you at the hospital. We’re going to catch this problem before it gets going.”
These events have not happened yet, but similar scenarios could play out every day within the next few years. The technology to enable such proactive medical care already exists. It includes smart phones, cloud computing, and intelligent software.
At the University of Arkansas, our team of surgeons, engineers, and computer scientists has developed a personal heart monitor based on our own e-Nanoflex nanostructured sensors. The sensors can be embedded in clothing that can be worn and washed just like any other garment. One implementation is our e-bra, which includes sensors fitted into the bra's snaps and woven into its fabric. Such garments could be worn every day, and provide constant health monitoring for people at risk.
The e-Nanoflex sensor system is not limited to cardiovascular detection. It could also monitor recovery from surgery, medical compliance, and neurological diseases, or help athletes optimize their training routines.
Building on New Technologies
Several emerging technologies make personal monitoring systems possible. The first are smart phones. They are essentially small computers. In the e-Nanoflex sensor system, they act as base stations that receive and transmit information to distant computers for intensive processing.
All smart phones are able to receive short-range, low-powered signals over the Bluetooth protocol. Bluetooth transmitters, commonly used in mobile earphones, have grown smaller, more energy efficient, and less expensive every year. This makes them ideal for transmitting information from a sensor system to a phone.
Researchers are actively pursuing ways to make smart phones part of tomorrow's wireless medical monitoring system. Researchers at Finland's Tampere University of Technology, for example, have demonstrated that smart phone processors can detect such simple anomalies as irregular heartbeats and heart attacks in data from conventional electrocardiogram units. Researchers at Israel's Ben-Gurion University of the Negev have developed a way to use smart phone cameras and red laser pointers to detect malaria noninvasively.
The e-Nanoflex sensor system uses smart phones to filter and transmit data. The sensors collect data while the wearer is sitting, walking, working, and doing other things. These activities create motion artifacts in the data. The e-Nanoflex system uses a small amount of the phone's computing capacity to filter out this noise before transmitting information to cloud computers for further processing.
Cloud computing uses remote servers to process and store data from smart phones, workstations, and also personal computers. It already provides back-end processing for many smart phone applications. For example, while smart phones provide GPS positioning data, the cloud maps their position and generates driving directions. It then sends the information back to the app, which displays it on the smart phone. Cloud-based apps let smart phone users scan restaurant recommendations, book travel, and watch movies.
Continuously operating e-Nanoflex sensor systems will generate an enormous amount of data. The cloud will provide the storage needed to hold the data, and the computing power to automate signal analysis and anomaly detection. Simple machine learning algorithms, such as discriminant analysis, will enable us to extract features from data. The type of features will depend on the disease. While simple features, such as the empirical mean, will suffice for diabetes, more complex features, such as the length of time between heartbeats, are needed for heart disease.
Smart software located in the cloud will do more than determine if there is a problem. It will also detect the patient's location, warn his or her physician and family members, provide analytical data to doctors and hospitals, and dispatch the nearest emergency medical service.
EKG to Go
Hundreds, perhaps even thousands, of researchers and inventors are looking for ways to use smart phones and the cloud for medical applications. What make the e-Nanoflex sensor system unique are its low-cost nanostructured sensors, which users can wear in ordinary clothing. Our initial implementation uses these sensors to emulate the electrodes used in an electrocardiograph, commonly known as an EKG (or ECG) system.
EKG electrodes are designed to detect tiny changes in the skin's electrical conductivity as the heart beats. These changes are caused as different chambers of the heart depolarize, or reduce their electrical charges to nearly zero, at the start of each contraction. These changes in electrical charge move through the body, whose cells act like salt water to transmit the current to the surface of the skin.
Depolarization occurs in an orderly progression. It begins in the sinoatrial node and spreads through the heart. As measured on the skin, the cardiac cycle creates the peaks and valleys seen on a typical electrocardiograph. By looking at the size, shape, consistency, and time lapse of the waves, physicians can diagnose many different types of heart conditions.
Traditional EKG systems position as many as 10 electrodes around the heart and on the arms and legs. The electrodes are held in place with a silica adhesive. Because changes in currents running along the skin are so small, the adhesive contains silver particles, which reduce the gel's impedance, allowing the current to move from the skin to the electrode.
As anyone who has ever had an electrocardiogram knows, patients must lie down, relax, and remain still during measurement. If a man has a hairy chest, the nurse may shave off some chest hairs to improve the bond and the electrical connection.
This scheme works well in a hospital or doctor's office, but falls apart when tracking patients during everyday activities. Gels can cause irritation. They may dry out, lose their adhesion, and increase their impedance so signals are lost. While portable, hand-sized machines exist, they cannot be used for continuous monitoring of moving patients.
Nanowired in Case of Emergency
The nanostructured sensors developed at the University of Arkansas make true portable, wearable EKG systems possible. They consist of tiny metal nanowires growing outwards from the surface of the electrodes. The nanowires are approximately 1,000 nanometers (1 micrometer) long and from 20 nanometers to 200 nanometers in diameter.
The nanowires are so small, hundreds of thousands grow on a 0.5-centimeter surface. This is a small enough area to embed in an undergarment or fit on the shoulder snap of a bra. We can also grow them on metallic threads to weave into the fabric of a garment.
The nanowire arrays work very much like conventional electrodes, with one important difference: They push a few nanometers into the skin. This puts hundreds of thousands of nanowires in intimate contact with the skin. In fact, the amount of electrode surface area contacting the skin is thousands of times that of a conventional planar electrode.
As a result, nanostructured electrodes are two orders of magnitude more sensitive to skin currents than planar electrodes. This makes it easier to separate heart signals from motion artifacts when walking, working, or exercising. And nanostructured electrodes do not require any adhesive gel or silver particles.
The sensors are also affordable. We manufacture them by low cost, roll-to-roll electroplating. This involves unwinding a roll of wire or foil and applying a plastic coating. Lasers etch 20-to-200-nanometer-diameter holes into the coating. A current is run through the substrate as it is dipped into an electroplating bath. This attracts the metal ions, which form nanowires inside the holes in the coating. Pyrolyzing, or burning off, the coating, leaves only the metal nanowires behind.
We have grown nanostructures in three different ways. First, we have grown them on planar surfaces. They look like traditional electrodes, but have many times the surface area in contact with skin. These can be used as buttons sewn into clothing, or in shoulder snaps on bras or other tight-fitting garments.
We have also grown nanowires both on conventional metal wires and on small metal segments called nanocapsules that we can attach to conventional metal or conducting polymer wires.
Our conventional metal or conducting polymer wires either attach to nanowire electrodes or contain the nanowires themselves. We can sew all these conventional conducting wires into the garment and use them to carry current from the sensors to an amplifier.
In the lab, we make the nanowires and conducting wires from gold because it withstands oxidation and repeated laundry cycles. Silver is a less expensive alternative, but we have not yet demonstrated that silver will hold up for the 50 wash-and-dry cycles we demand from any e-Nanoflex enabled garment.
The Bluetooth enabled amplifier sends the sensor data to the smart phone, which filters out noise and motion artifacts before sending it to the cloud for further analysis. The amplifier is the only part of the e-Nanoflex sensor system that patients would have to remove from their clothes before washing and drying.
Monitoring in Real Time
Unlike conventional EKG systems, which require doctor visits, the e-Nanoflex system could monitor patients recovering from or at risk for heart disease in real time. At its simplest, it could monitor the heart for coronary problems, and alert physicians and emergency medical services at the first signs of a heart attack or stroke.
More sophisticated analyses may be able to predict when a heart attack or stroke is likely to occur. Many patients take medication following coronary episodes or surgery. Sophisticated software could monitor data from e-Nanoflex sensors about heart rate consistency and other factors to ensure that patients comply with their prescriptions.
Not every sensor needs to monitor the heart. A sensor placed under the chin, for example, could monitor sleep states and provide feedback on sleep disorders. Similarly, monitors in socks would support gait analysis, enabling physicians to track progress as patients rehabilitate after accidents or monitor neurological problems in the elderly.
Nor does every application need to be medical. A tight-fitting e-bra or shirt could provide information to guide cardiovascular training. In fact, there is no need to store this information in the cloud for healthy athletes. They could use their smart phones to analyze, display, and optimize their training routines to achieve maximum strength or stamina. Social networking apps on smart phones can connect virtual “e-workout buddies.” Fitness enthusiasts can use the apps to share information about their workout sessions or motivate each other to work harder.
The combination of wearable nanostructured sensors, smart phones, and cloud computing make wearable EKGs possible. Yet these emerging technologies also promise to create a platform for more comprehensive health monitoring.
For e-Nanoflex, intervening before Jane's heart attack starts to take its toll is only the beginning.