Flexible hydrogel sensors for a variety of application scenarios have been introduced

Zhang Xiaoyong, a young teacher from the School of Materials Science and Engineering of Anhui University of Science and Technology, prepared a functional hydrogel material with antifreeze and anti-drying, strong surface adhesion and adjustable mechanical properties in situ in view of the problem that the mechanical properties of conventional hydrogels are single and cannot be realized in multiple scenarios and applications, and the material is assembled into a flexible strain sensor, which can monitor human movement in real time according to specific mechanical property requirements. The research results were recently published in the journal ACS Applied Materials and Interfaces.

Schematic diagram of the inspiration and design strategy of the hydrogel flexible sensor. Courtesy of Anhui University of Science and Technology

Conductive hydrogels have a wide range of applications in the fields of e-skin and flexible wearable sensors. However, conventional hydrogels have a single mechanical performance and cannot be used in multiple scenarios, resulting in a hydrogel that can only be used in a specific environment. Therefore, the development of a class of hydrogels with in-situ tunable mechanical properties to meet their applications in different environments is still a key scientific problem to be solved.

“The mechanical properties of hydrogels largely depend on the relationship between the interaction forces between molecular chains and the cross-linking density, so the in-situ adjustment of their mechanical properties can be achieved through the strategy of regulating their network density, based on the fact that zirconium ions and carboxyl groups can form metal coordination characteristics at room temperature, and zirconium ions can be used as ‘molecular chain switches’ to realize the network density regulation of hydrogels, which can provide theoretical guidance for this project according to the above ideas. Zhang Xiaoyong introduced to China Science News.

In recent years, experts and scholars at home and abroad have carried out a lot of related research on hydrogels, and they have shown wide application potential in the field of wearable technology and personalized medical monitoring. However, due to the fact that hydrogels contain a large amount of water, and at the same time, they will inevitably freeze at sub-zero temperatures, and they are easy to dehydrate at high temperatures, resulting in a short service life, so how to achieve in-situ adjustment of the mechanical properties of hydrogels and environmental tolerance is still a challenge.

In this study, Zhang Xiaoyong et al. proposed to introduce 3,4-dihydroxyphenyl-l-alanine (L-Dopa) grafted polyacrylic acid and zirconium ions into hydrogels, and adjust the in-situ aggregation state of ions on the polymer chain by controlling the coordination effect, thereby changing the mechanical properties of the hydrogels in situ. The catechol group of L-Dopa imparts high adhesion to the skin and device interface, including wet and dry environments.

“We have found that by adding glucose, a functional material with greater binding ability to water molecules, the evaporation of water and crystallization properties at low temperatures can be limited, and the hydrogels produced in a wide temperature range of minus 35 degrees Celsius to minus 65 degrees Celsius show excellent environmental stability for up to 60 days. Zhang Xiaoyong said.

Further, the researchers assembled this functional hydrogel into a flexible strain sensor that can monitor human behavior according to specific mechanical property requirements. “This feature brings new possibilities for the future of wearable technology and personalized medical monitoring. ”

The reviewers believe that the authors have developed and prepared multifunctional flexible hydrogel materials with excellent performance by combining biological inspiration and smart materials, which effectively solves the problems of poor water retention and freezing resistance, single mechanical properties and poor adhesion of traditional hydrogels, which is an interesting and valuable research work, and provides new innovative ideas for a new generation of wearable devices with a wider range of applications. (Source: Wang Min, China Science News)

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