Wearable health sensors that can continuously monitor bodily changes have significantly advanced health technology in recent years. These devices, which include medical patches and wound dressings, must often stay in contact with the skin for extended periods. However, the hydrogels typically used in these products are water-rich and can trap heat and sweat, leading to irritation and potentially affecting sensor accuracy.
A recent study in Nature describes a breakthrough by engineers from the Massachusetts Institute of Technology (MIT). They developed a hydrogel with a stable, three-dimensional network of tiny, air-filled channels. This new approach differs from a 2024 study in Science Advances, which achieved eight days of skin monitoring with a gas-permeable hydrogel sensor just 10 micrometers thick, reinforced with a polyurethane nanomesh.
In the MIT study, the researchers developed a hydrogel featuring stable air pathways while maintaining a 70 percent water content. Despite its high water content, the material demonstrated an oxygen permeability of up to 185 barrer, a unit for measuring gas permeability, in lab tests—approximately 10 times higher than that of conventional hydrogels.
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Inspired by the lung’s air-carrying architecture, researchers adapted a typical hydrogel recipe by incorporating silica aerogel particles, which act as solid-form air bubbles. These particles repel water, trapping air and preventing the collapse of air spaces within the hydrogel.
During production, the particles formed a thin, interconnected network of air-filled channels inside the hydrogel. This network facilitated the passage of oxygen and water vapor through the material while maintaining its high water content. The hydrogels also transmitted water vapor at rates 10 to 100 times higher than silicone and polyurethane patches, aiding moisture escape from the skin.
The hydrogel proved to be both soft and durable, retaining about 95 percent of its air permeability even after 10,000 stretching cycles.
To test the new product’s wearability, researchers compared the comfort of their patches with common silicone ones. Infrared images taken two minutes after removing the patches showed that skin temperature under a silicone patch rose by 6.5 degrees Celsius after a 20-minute workout. In contrast, skin under the new hydrogel cooled by about 1 degree, likely because it allowed heat to escape more efficiently. Additionally, significant sweat accumulated under the silicone patch, while the breathable hydrogel left the skin similar to uncovered areas.
In another test, 10 volunteers wore the new patches on their chests during an hour of moderate exercise, with none reporting itching, irritation, or other adverse skin reactions.
The researchers also adapted the hydrogel for use as an electrode to record the heart’s electrical activity. During cycling tests, conventional hydrogel electrodes produced less stable electrocardiogram (ECG) signals as sweat accumulated, while those made with the air-permeable hydrogel maintained clearer readings during and after exercise.
In extended monitoring, the hydrogel electrodes were worn continuously for 10 days, consistently recording usable ECG signals during various activities, including sleeping, working, walking, and exercising.
Xuanhe Zhao, the study’s senior author and a mechanical engineer at MIT, told ScienceAlert that the most immediate applications could include wearable medical devices, wound dressings, and skin-mounted health monitors. “These technologies often require prolonged contact with the skin, but conventional hydrogels trap heat and moisture because they do not allow sufficient oxygen and water vapor to pass through,” Zhao said. “Our material overcomes this limitation while maintaining the high water content and softness that make hydrogels comfortable and biocompatible.”
However, the material is not yet ready for clinical use. Zhao indicated that further studies must assess its long-term biocompatibility, performance on large animals, sterilization, manufacturing at scale, shelf life, and regulatory safety. Human tests were small and primarily served to demonstrate the material’s feasibility.
The exercise and comfort assessments included up to 10 volunteers, while the skin physiology measurements involved only two participants, and the exercise ECG comparison involved three. Larger and more diverse studies will be needed to confirm the findings.
The material must also be adapted for specific products, as wound dressings, wearable sensors, and implants each have different requirements. The current material is not inherently adhesive, requiring separate backing or attachment mechanisms to remain on the skin.
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In the long term, the design could potentially be used in tissue engineering and implantable devices, where maintaining oxygen supply to cells is a significant challenge. “Many engineered tissues and implants require efficient oxygen transport to maintain cell viability, and our material offers a way to improve gas exchange while preserving the hydrated environment that cells need,” Zhao said. However, implantable applications will require substantially more testing, making skin-based uses the more realistic first step.
The findings are reported in Nature.
