Fully physically cross-linked hydrogel as highly stretchable, tough, self-healing and sensitive strain sensors


Recent technological advances in the field of wearable technology have led to the development of flexible and stretchable materials. These materials are of high stretchability, excellent toughness, conductivity and have the capability to self-heal. As such, they are highly preferred in the development of flexible wearable electronic devices, whose demand has astronomically increased in recent times. A review of existing literature reveals that available materials for development of such devices tend to fail due to low ductility. Fortunately, recent reports have shown that, soft materials such as hydrogels, possess the capability to achieve both larger deformation capacity and excellent conductivity. This can be attributed to the fact that they incorporate polymer networks and also possess uniformly distributed conductive ions. Technically, hydrogels are constructed with three-dimensional (3D) network of hydrophilic polymers that can swell in water and hold a large amount of water while maintaining the structure due to their stretchability and toughness. In this regard, they are considered as good candidate for new generation of wearable electronics.

Previous publications have also revealed that conductive hydrogel possess excellent mechanical performance that is highly suitable for developing flexible electronics like soft sensors, supercapacitors and electronic skin. Unfortunately, the conductivity of such hydrogels changes significantly under tension making them highly sensitive. In this regard, it remains a priority to develop a novel/alternative conductor material that meets all the requirements for use in the next generation of wearable devices. On this account, CAS Key Laboratory of Mechanical Behavior and Design of Materials researchers: Dr.Yongzhi Liang, Dr. Xingyue Sun, Ms Qiong Lv, Mr. Yuexin Shen and Professor Haiyi Liang developed a new and novel, fully physically cross-linked hydrogel that could potentially overcome the aforementioned shortfalls. Their work is currently published in the research journal Polymer.

Their goal was to develop a hydrogel with excellent self-healing property for wearable electronics. To realize this, the new type of fully physically crossed-linked PVA/PAA/Fe³⁺ hydrogel with stretchable tough conductive and self-healing property was fabricated by using “one-pot” method under room temperature via free radical polymerization. Interestingly, the analysis undertaken revealed that the novel hydrogel exhibited unique features, such as: high tensile strength, high stretchability, high toughness and excellent self-healing property.

In summary, the study presented a novel type of fully physically cross-linked PVA/PAA/Fe³⁺ hydrogels with stretchable, tough, conductive and self-healing properties. To prove its resilience, the conductive hydrogel was used as a resistivity type strain sensor. Overwhelmingly, the hydrogel sensors were able to monitor speaking and the motion of knuckle. In a statement to Advances in Engineering, Professor Haiyi Liang explained that through their study, an in-depth comprehension of fully physically cross-linked hydrogel was achieved marking a significant milestone in this field. He further added that the developed hydrogel was applicable in the field of flexible electronics such as artificial muscles, soft robotic and voice recognition.


Yongzhi Liang, Xingyne Sun, Qiong Lv, Yuexin Shen, Haiyi Liang. Fully physically cross-linked hydrogel as highly stretchable, tough, self-healing and sensitive strain sensors. Polymer, volume 210: 123039.

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