Temperature-regulated flexibility of polymer chains in rapidly self-healing hydrogels

Rui Chen,Ian Wyman,Chuanghong Xiao,Zhengping Wang,Danfeng Yu,Hui Yang,Xiubin Xu,Xu Wu,Minhuan Liu

doi:10.1038/s41427-019-0123-0

Abstract

Without the introduction of new functional groups, altering the properties of a substance, such as by changing from a non-self-healing to a rapidly self-healing material, is often difficult. In this work, we report that the properties of 2-hydroxyethyl methacrylate and acrylamide (HEMA/AAm) hydrogels can be easily altered from non-self-healing to rapidly self-healing by simply tuning the reaction temperature. Notably, the hydrogels that are prepared at room temperature do not exhibit self-healing behavior, while those treated at an elevated temperature show automatic self-healing performance within ~15 s. Interestingly, in contrast with the previous self-healing HEMA-based polymeric hydrogels, which function only above their glass transition temperatures (Tg), the hydrogels prepared herein exhibit rapid self-healing properties at room temperature, which is below their Tg. In addition, the stretching capabilities of the hydrogels can be greatly enhanced by up to 30-fold. The hydrogels also exhibit good adhesive performance and can adhere strongly onto various substrates, such as wood, glass, fabric, paper, leather, porcelain, and steel. For example, a 10 kg weight could be suspended from a wooden substrate with the aid of these hydrogels. These results may provide valuable insight regarding the design of self-healing hydrogels and their large-scale production.

Highlights

Manmade materials with self-healing capabilities are highly desirable, and their development has become a goal for many scientists and engineers[1,2,3,4]
Hexamethylene diisocyanate-trimer (HT) served as a crosslinker and underwent random reactions with hydroxyethyl methacrylate (HEMA) and AAm to form urethane groups and urea groups, respectively[36], as was Scheme 1 Schematic illustration depicting the preparation of HEMA/AAm hydrogels with self-healing properties, high stretchability, and excellent adhesion performance confirmed by Fourier transform infrared (FTIR) spectroscopy. 1H NMR spectroscopy confirmed that cross-linking had taken place, as indicated by the resonance at 2.14 ppm corresponding to AAm moieties that had reacted with HT
We found that the self-healing behavior of these hydrogels occurred both very rapidly and readily without the need for external input

Summary

Introduction

Manmade materials with self-healing capabilities are highly desirable, and their development has become a goal for many scientists and engineers[1,2,3,4]. The self-healing behavior can be classified into two categories, namely, extrinsic and intrinsic self-healing[8,9,10]. Extrinsic self-healing relies on pre-embedded healing agents to connect the fractured components of a damaged material via covalent bonds. A class of 3D network materials containing a large amount of water, have excellent potential for a wide range of applications, such as biological and medical applications, soft electronics, and sensors and actuators[14,15].

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Discussion

Conclusion