Although stevia is best known as a low-calorie sugar alternative, researchers have recently discovered that it might have far-reaching applications beyond sweetening your morning coffee, like driving some of the coolest new electronic gadgets. A new study published in Advanced Materials suggests that a stevia-based hydrogel triboelectric nanogenerator (S-TENG) can be transparent, stretchable, and durable enough for use in foldable devices, opening the door to wearable devices (like those used in sleep tracking) and other soft electronics that are more durable than their existing counterparts. An S-TENG is a kind of self-powered sensor material that generates electricity when pressed, bent or separated, which can then be used for motion detection or wearable detection.
Flexible electronics are currently in the spotlight, with foldable phones and tablets and skin-like devices designed to move and flex with the body making headlines. The challenge in designing these devices, however, has been on the materials side: many of those considered are too fragile, opaque, or too limited in terms of their ability to stretch before their performance collapses. Stevia, or more specifically a transparent, deformable, and recoverable hydrogel built around stevia and polyvinyl alcohol (PVA), may be the key to simultaneously addressing a number of these limitations.
How stevia could unlock flexible technology
The researchers found that adding stevia to PVA to produce a TENG hydrogel improved its mechanical strength while promoting electrical production, making the material more useful than a simple soft polymer for energy-harvesting electronics. The stevia-based hydrogel appears to offer a TENG (soft, transparent and durable) electricity-generating trio by creating a material capable of flexing and recovering without losing properties important for sensing and energy production. It is important to note that only the TENG layer is affected, not other components of a device, meaning it may not have a universal impact on the overall durability of future flexible electronic devices.
The most immediate use case for deploying these new TENGs is for innovative new wearables. It opens the way to devices capable of powering themselves or recharging their batteries by recovering energy from the movement generated by a moving body. If the strengthening effect of stevia could be applied to all hydrogel materials, we could see a revolution in wearables. Hydrogels are already being studied as a platform for flexible displays and touch sensors. If stevia can be used to make them more sustainable, these technologies will appear in the hands of consumers sooner.
What stevia could do
This type of hardware development is part of the broader framework of creating flexible electronics. Researchers have worked to create better substrates, more durable circuit layers, and improved approaches to combat cracking in a broader spectrum of device materials, because one of the main enemies of flexibility is the type of repetitive stress that bending imposes on conventional materials. Advances in stevia are critical in this pursuit, as they could lead to the development of materials in the TENG layer that can stretch and recover while retaining the type of electrical behavior needed to harvest energy from movement and touch.
The potential applications are vast. Stevia hydrogel enables the development of transparent patches that can monitor joint movements (and obstructions), or small sensors that could be sewn directly into clothing to monitor body temperature, heart rate, blood flow, or any other health-related indicator. As part of the study, the team built a sensor that they attached to different parts of the body and used to detect movements such as finger flexion, throat movements (like speaking), as well as wrist, elbow and knee movements. According to Professor Kyungwho Cho, one of the study’s authors, sensors of this type could help improve rehabilitation monitoring and contribute to IoT-based wearable devices.
