Wow! While babies have a natural way to let their parents know they need a diaper change, a new sensor developed by Penn State researchers could help child care workers, hospitals and other institutions providing for those who depend on them.
The new sensor – so cheap and easy to manufacture that it can be used by hand with a pencil and paper treated with sodium chloride – could open the way for wearable, self-contained medical devices to be used not only in “smart diapers” but also to report serious health problems such as heart failure and pneumonia.
“Our team is focused on developing tools that can provide important information for human health,” said Huanyu “Larry” Cheng, James L. Henderson, Jr. Memorial Associate Professor of Engineering Science and Mechanics at Penn State. “The goal is to predict disease and health conditions early, so problems can be diagnosed before it’s too late.”
Cheng is the leader of a new study, published in the journal Nano Letters, which describes the process of designing and manufacturing a reliable electrode sensor. The sensor is created using a pencil, which is drawn on a sheet of paper and fixed in a solution of sodium chloride. The hydration sensor is very sensitive to changes in humidity and provides accurate readings at a wide range of humidity levels, from 5.6% to 90%.
Research on wearable sensors has gained renewed momentum because of their wide applications in medical care, disaster warning and military security, Cheng said. Flexible water sensors have become important in health care, for use such as breathing monitoring and body water effects, and achieve high sensitivity and easy disposal in a simple and cheap production process, he added.
Li Yang, a professor at the School of Artificial Intelligence, said, “We want to create something cheap that people will understand how to do and use – and you can’t get more than a pencil and paper.” Technology in China, “You don’t need to get multi-million dollar equipment to make it. You just have to be able to pull the electrode wire that is drawn on the treated sheet. It can be done quickly and easily.
The device uses the way paper reacts to changes in humidity and uses a graphite pencil to interact with water droplets in a sodium chloride solution. As water molecules concentrate on the paper, the solution becomes ionized and electrons begin to flow to the graphite in the pencil, causing the sensor to appear, which detects these changes in humidity in the environment and sends a signal to the smartphone, which shows and saves the data.
Basically, drawing on a finished piece of paper along the finished lines creates a miniature paper circuit board. The paper can be connected to the computer with copper wires and conductive silver paste to act as an ambient humidity sensor. For wireless applications, such as “smart diapers” and breathing-based monitoring, the design is connected to a small lithium battery that enables the transfer of data and information via Bluetooth.
For the breathing monitor, the team drew electrodes directly onto the solution-fixed face mask. The simple sensor differentiates mouth breathing from nasal breathing and can regulate three breathing modes: deep, regular and fast. Cheng said that the collected data can be used to detect the onset of various diseases, such as respiratory arrest and shortness of breath, and provide access to the smart Internet of Things and telemedicine.
He added that the respiratory rate is the main important sign and research has shown that it is the first indicator of various diseases such as heart disease, cold and hospital damage. It can also indicate emotional stress such as stress, heat, cold, physical exertion, and exercise that cause fatigue.
Compared to breathing, human skin shows little change in moisture, but the researchers were still able to detect changes using their pen-and-paper water sensor, even after the probe had applied lotion or is exercise. The skin is the largest part of the body, Cheng explained, so if it doesn’t handle water properly, it could be evidence that another health problem is going on.
“Different diseases cause different amounts of water from our skin,” he said. “The skin will perform different functions depending on the conditions below, which we can define and then know using sensors.”
The team also placed four moisture sensors in the center of the diaper’s sliding surface to create a “smart diaper”, which can detect moisture and alert when it is changed.
“This app was really born from personal experience,” said Cheng, a father of two young children. “There is no easy way to know how wet it is, and this information can be useful for parents. Sensors can provide short-term data, to let him know that diaper changes, but in the long term, to show the types that can inform parents about their child’s overall health.
Applications for moisture sensors go beyond “smart diapers” and monitoring breath and sweat, Cheng explained. The team developed the sensor as a contactless switch, which can detect changes in humidity and air from the presence of a finger without touching the sensor. The team used non-contact switches to operate the elevator, play the keyboard, and light up the LED matrix.
“The atoms in the finger don’t need to touch the button, they need to be close to the surface to spread the water molecules and trigger the signal,” Cheng said. “When we think about what we have learned from epidemics about the importance of preventing that contact on the balcony, sensors like this can be an important tool in stopping possible pollution.”
