The Promise of Biopolymers in Smart Home IoT
In the infrastructure of the future, based on intelligent computerized systems and control and monitoring devices, the smart home is part of the Internet of Things (IoT). However, in addition to the need to address energy consumption, the widespread adoption of smart homes may also exacerbate the growing problem of increasing amounts of non-recyclable e-waste from IoT devices.
Compared to synthetic plastics, biopolymers offer many unique advantages such as robust structure, light weight, mechanical flexibility, biocompatibility, biodegradability and renewability. Biopolymers, which are abundant in natural products such as cellulose, silk fibroin, polylactic acid, chitosan, collagen, keratin, alginate, starch and gelatin, have great promise for the production of environmentally friendly Internet of Things devices. They are ideal candidates for the use of low-temperature sol–gel coating and ink-printing processes to facilitate the development of low-cost, large-area flexible electronic devices.
This article presents developments known from the literature, as well as the results of original research on the use of biopolymer materials to create flexible, wearable and textile electronic devices, such as sensors, energy storage devices and nanogenerators, soft hydrogel actuators and wireless communication devices that are promising for the Internet of Things but have not yet been implemented in smart homes.
Biopolymers for Smart Home Sensors
The Internet of Things of a smart home receives information from numerous sensors. Among them, non-wearable sensors are usually installed on stationary objects or places in a house or room, such as the floor or furniture, to monitor the occupants’ daily activities, such as walking, using objects, opening/closing a door, or for fall detection.
Pressure and vibration sensors based on biopolymers and biocomposites can generate electrical signals under certain periodically repeated mechanical pressures. These sensors can be divided into different types: piezoresistive, capacitive, piezoelectric and triboelectric.
Piezoresistive Sensors
A piezoresistive sensor works by inversely increasing or decreasing electrical resistance when pressing on a flexible conductive material. Researchers have presented a material for a piezoresistive type sensor, in which biopolymer fibrillar nanocellulose is used as an elastic matrix of a functional composite filled with conductive silver nanowires. The piezoresistive sensor demonstrated excellent elasticity, a wide detection range, and stable signal repeatability over 500 compression/relaxation cycles.
Capacitive Sensors
A capacitive-type pressure sensor registers an increase in the electrical capacity in the event of an increase in pressure. Researchers have fabricated a pressure sensor using a polyvinyl alcohol/fibrillar nanocellulose (PVA/CNF) composite hydrogel with a self-healing ability. This sensor was able to detect subtle pressure changes, such as water droplets falling on a surface, and monitor various human movements.
Piezoelectric and Triboelectric Sensors
Another innovative strategy for manufacturing a piezoresistive pressure and vibration sensor with a wide working pressure range and ultra-high sensitivity uses carbonized cellulose of cotton fabric to build a three-dimensional conductive network. This sensor had not only ultra-high sensitivity, but also a wide operating range, and was able to detect even tiny pressure changes.
Silk fibroin (SF), a protein biopolymer, can also be used to create wearable motion and healthcare sensors. Researchers have developed a strain sensor based on flexible, inexpensive and available single fibers of SF from the silk of the mulberry silkworm, which are covered with electrically conductive graphite flakes.
Biopolymers for Energy Harvesting
To power these biopolymer-based sensors, they can be connected to solar cells on the roof and windows in a smart home or, especially for wearable sensors, to wearable thermoelectric nanogenerators.
Biopolymer films of nanocellulose and silk fibroin have been successfully used as flexible substrates for flexible organic solar cells due to their ability to enhance the light scattering effect, which improves light absorption and energy conversion efficiency.
Wearable thermoelectric nanogenerators can convert the temperature gradient between the human body and the environment into electricity to power wearable electronics. Researchers have developed a flexible, biodegradable and biocompatible thermoelectric generator based on a nanocomposite of nanocellulose and copper iodide that can generate up to 3.8 nW of power from a temperature gradient of 40K.
Biopolymers for Soft Actuators
Smart home IoT devices and human-machine interfaces can provide more convenient interactions through the use of soft actuators based on smart biopolymers with morphing and motion capacities. These include piezoelectric and other shape-changing biopolymers, as well as smart shape-memory and adhesion-changing biopolymer materials.
Hydrogel Actuators
Stimulus-responsive smart hydrogels made from biopolymers like chitosan, alginate, and gelatin can change their size and shape by reversible swelling/deswelling when exposed to external stimuli such as temperature, humidity, light, electricity or magnetic field. These unique properties make them ideal candidates for the preparation of soft actuators used in IoT smart homes as walkers, smart switches, grippers, and artificial muscles.
For example, an electrically-responsive chitosan hydrogel actuator can bend and move when an electrical stimulus is applied, demonstrating long-term durability and suitability for biomedical applications and muscle repair in smart home healthcare.
Biopolymers for Wireless Communication
Radio Frequency Identification (RFID) devices and near-field communication (NFC) technology play an important role in ensuring IoT identification and wireless communication in smart homes. Flexible substrates made of natural biopolymer materials like cellulose paper and silk fibroin are attractive for creating low-cost, biodegradable RFID tags and NFC devices.
Biopolymer-based wireless communication devices can not only replace existing IoT devices, but also contribute to the development of new surveillance methods in smart homes. For example, silk fibroin-based passive RFID antennas can be used for real-time food spoilage detection by monitoring changes in the dielectric properties of the food product. Graphene-based wireless sensors modified with peptides can also be used to identify infections, including antibiotic-resistant ones, on the body of smart home residents.
Conclusion: Towards a Sustainable Smart Home IoT
The widespread application of biopolymers can significantly contribute to the formation of a sustainable smart home IoT by providing a wide range of biodegradable, biocompatible and renewable materials for sensors, energy harvesters, soft actuators and wireless communication devices. By replacing petrochemical-derived plastics, biopolymers offer a promising path towards reducing e-waste and environmental pollution associated with the rapid growth of the Internet of Things.
As demonstrated in this article, biopolymers like cellulose, silk fibroin, chitosan, and their composites have the potential to enable the development of flexible, wearable and textile electronic devices that are crucial for realizing the full potential of smart home technology while prioritizing sustainability. Through continued research and innovation, biopolymer-based IoT solutions can help create a more eco-friendly and human-centric smart home of the future.
