Seaweed-based Sensor Acts as Second Skin for Health Monitoring

March 08, 2023 by Jake Hertz

Made from seaweed, rock salt, water, and graphene, the sensor is a more sustainable alternative to polymer-based solutions currently used for health-monitoring wearables.

Wearable technology often incorporates flexible and lightweight materials to improve comfort and wearability. Polymer-based materials, in particular, have shown great promise in wearable devices because of their flexibility, durability, and ability to conform to the body. However, as more research emerges on the impact of discarded electronics on the environment, many developers are investigating more sustainable materials.

This week, researchers from the University of Sussex published a new paper describing a seaweed-based alternative for polymer wearable sensors. In addition to breaking down more cleanly in the environment, the new sensor also proved more sensitive and accurate than its plastic or rubber counterparts—proving its value in monitoring a person's vital signs. In this article, we’ll discuss the role of polymers in wearables, the sustainability issues surrounding them, and the new research from Sussex researchers.


The researchers' graphene and seaweed hydrogel

The researchers' ingredients for the graphene and seaweed hydrogel were so simple and biodegradable, the researchers described it as "edible." Image courtesy of the University of Sussex


Polymers and the Search for Sustainability

Polymers play a crucial role in a wide range of electrical engineering applications, including battery electrodes and coatings. One particular research field in which polymer materials have shined is flexible electronic wearable sensors. In this context, polymer-based piezoresistive sensors can detect mechanical strain based on changes in electrical resistance. Used in wearables, this ability can help detect the wearer’s movements to better track their health and fitness.

Researchers have explored different materials to develop these piezoresistive sensors, including mixed-phased nanomaterial-based materials, nanomaterial depositions on elasticated polymer substrates, or electrically-conductive polymers. 


Example of a polymer-based piezoelectric mechanical sensor

Example of a polymer-based piezoelectric mechanical sensor. Image courtesy of ResearchGate


While these materials are considered cost-effective and highly performant, a major concern surrounding them is sustainability. Because they’re polymer-based, these sensors are not biodegradable and end up contributing to e-waste upon their disposal. Furthermore, the manufacturing process for these devices often involves the use of hazardous solvents that contribute to plastic waste. The carbon footprint of these materials could hurt their commercial viability and, with the evolving policies surrounding environmental responsibility, could prevent them from ever reaching the market.

As such, there is a need to identify alternative materials that are environmentally friendly and biodegradable. Rather than relying on non-recyclable, heavily cross-linked rubbers, researchers are exploring other options to create effective devices that will not harm the planet. 


A Seaweed-based Hydrogel Enters the Mix

To solve these issues, researchers from the University of Sussex have developed a new type of sensor that is fully biodegradable and outperforms existing synthetic-based hydrogels and nanomaterials. 

According to the research paper, the new sensors were created by integrating an aqueous solution of pristine graphene into an algae matrix to create a graphene-algae hydrogel. Based on a combination of natural materials such as seaweed, rock salt, and water with graphene, the new sensor is a more sustainable alternative to the polymer-based solutions that currently dominate the market.

While seaweed on its own acts as an insulator, adding a significant amount of graphene to a seaweed mixture yields an electrically-conductive film. When this film was soaked in a salt bath, the researchers observed that the film quickly absorbed the water, creating a "soft, spongy, electrically conductive hydrogel". 


The seaweed-based sensor development process

The seaweed-based sensor development process. Image courtesy of ACS Sustainable Chem. Eng.


The resulting hydrogel was said to have the lowest reported Young’s modulus (approximately 0.6 Pa) for a strain sensor yet and has piezoresistive properties that enable pressure sensing capabilities far exceeding the limits of commercial and literary hydrogel systems. In fact, the sensors are so sensitive that they can measure an object just 2 mg in mass, equivalent to a single rain droplet impacting their surface.

With the new sensor, the researchers believe that they’ve found a way to create greener wearable solutions that doesn't compromise performance. The researchers also see significant value for this hydrogel in the health monitoring industry, opening doors for a clinical-grade wearable sensor that acts as a temporary tattoo or second skin. Made from all-natural ingredients, the solution is a lightweight, comfortable, and safe alternative to invasive hospital instruments containing wires and leads. In addition, the algae-graphene hydrogel is reported to be more sensitive and accurate than existing polymer-based wearables, too.