Ultra elastic, stretchable, self-healing conductive hydrogels with tunable optical properties for highly sensitive soft electronic sensors

Author(s): Meng Wu ¹ ^, ² ^, ³ ^, ⁴ , Jingsi Chen ¹ ^, ² ^, ³ ^, ⁴ , Yuhao Ma ⁵ ^, ² ^, ³ ^, ⁴ , Bin Yan ⁶ ^, ⁷ ^, ⁸ ^, ⁹ , Mingfei Pan ¹ ^, ² ^, ³ ^, ⁴ , Qiongyao Peng ¹ ^, ² ^, ³ ^, ⁴ , Wenda Wang ¹ ^, ² ^, ³ ^, ⁴ , Linbo Han ¹⁰ ^, ¹¹ ^, ¹² ^, ⁹ , Jifang Liu ¹³ ^, ¹⁴ ^, ¹⁵ ^, ⁹ , Hongbo Zeng ¹ ^, ² ^, ³ ^, ⁴

Publication date (Electronic): 2020

Journal: Journal of Materials Chemistry A

Publisher: Royal Society of Chemistry (RSC)

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Abstract

A self-healing hydrogel ionic conductor has been developed by combining dynamic covalent chemistry with nanofiller reinforcement and micelle crosslinking, and used for sensing of diverse human activities.

Abstract

Conductive hydrogels are of great significance for soft electronic devices. However, the intrinsically weak nature, lack of fatigue resistance and self-healing capability, and the absence of stimuli-responsiveness of traditional conductive hydrogels hinder their application as durable, reliable and smart conductors to fulfill the increasing demands of modern electronics. Herein, we have developed a novel hydrogel ionic conductor by integrating nanofiller reinforcement with micelle cross-linking. The hydrogel was facilely prepared via one-pot polymerization of acrylamide and an amino-functionalized monomer in the presence of multiwall carbon nanotubes, aldehyde-modified F127 and LiCl. The dynamic chemical and physical interactions of the cross-linked network provide the hydrogel with a wide spectrum of properties, including excellent stretchability (1200%), skin-mimetic modulus, toughness, exceptional elasticity (recovery from 1000% strain), resistance to damage by sharp materials, self-healing properties (636% stretchability after self-healing) and high conductivity (3.96 S m ⁻¹). Besides, the rational design of the hydrogel endows it with multiple sensory capabilities toward temperature, strain and pressure. The hydrogel demonstrated cooling-induced whitening optical behavior. When exploited as a strain and pressure sensor to monitor diverse human motions, the prepared hydrogel sensor showed excellent sensitivity and reliability even for the acquisition of detailed waveform changes of radial artery pulses before and after exercise, suggesting its superior sensitivity compared to previously reported hydrogel sensors. The hydrogel was further integrated with an eye mask to monitor human sleep and showed high reliability for the detection of rapid eye movement (REM) sleep. This work provides new insights into the fabrication of multifunctional, smart and conductive materials, showing great promise for a broad range of applications like wearable sensors, artificial skins, and soft robotics.

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Structural absorption by barbule microstructures of super black bird of paradise feathers

Dakota E. McCoy, Teresa J. Feo, Todd Alan Harvey … (2018)

Many studies have shown how pigments and internal nanostructures generate color in nature. External surface structures can also influence appearance, such as by causing multiple scattering of light (structural absorption) to produce a velvety, super black appearance. Here we show that feathers from five species of birds of paradise (Aves: Paradisaeidae) structurally absorb incident light to produce extremely low-reflectance, super black plumages. Directional reflectance of these feathers (0.05–0.31%) approaches that of man-made ultra-absorbent materials. SEM, nano-CT, and ray-tracing simulations show that super black feathers have titled arrays of highly modified barbules, which cause more multiple scattering, resulting in more structural absorption, than normal black feathers. Super black feathers have an extreme directional reflectance bias and appear darkest when viewed from the distal direction. We hypothesize that structurally absorbing, super black plumage evolved through sensory bias to enhance the perceived brilliance of adjacent color patches during courtship display.

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Highly stretchable and tough hydrogels.

Jeong-Yun Sun, Xuanhe Zhao, Widusha R K Illeperuma … (2012)

Hydrogels are used as scaffolds for tissue engineering, vehicles for drug delivery, actuators for optics and fluidics, and model extracellular matrices for biological studies. The scope of hydrogel applications, however, is often severely limited by their mechanical behaviour. Most hydrogels do not exhibit high stretchability; for example, an alginate hydrogel ruptures when stretched to about 1.2 times its original length. Some synthetic elastic hydrogels have achieved stretches in the range 10-20, but these values are markedly reduced in samples containing notches. Most hydrogels are brittle, with fracture energies of about 10 J m(-2) (ref. 8), as compared with ∼1,000 J m(-2) for cartilage and ∼10,000 J m(-2) for natural rubbers. Intense efforts are devoted to synthesizing hydrogels with improved mechanical properties; certain synthetic gels have reached fracture energies of 100-1,000 J m(-2) (refs 11, 14, 17). Here we report the synthesis of hydrogels from polymers forming ionically and covalently crosslinked networks. Although such gels contain ∼90% water, they can be stretched beyond 20 times their initial length, and have fracture energies of ∼9,000 J m(-2). Even for samples containing notches, a stretch of 17 is demonstrated. We attribute the gels' toughness to the synergy of two mechanisms: crack bridging by the network of covalent crosslinks, and hysteresis by unzipping the network of ionic crosslinks. Furthermore, the network of covalent crosslinks preserves the memory of the initial state, so that much of the large deformation is removed on unloading. The unzipped ionic crosslinks cause internal damage, which heals by re-zipping. These gels may serve as model systems to explore mechanisms of deformation and energy dissipation, and expand the scope of hydrogel applications.

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Antibacterial adhesive injectable hydrogels with rapid self-healing, extensibility and compressibility as wound dressing for joints skin wound healing

Tianlong Zhang, Jin Qu, Xin Zhao … (2018)

Designing wound dressing materials with outstanding therapeutic effects, self-healing, adhesiveness and suitable mechanical property has great practical significance in healthcare, especially for joints skin wound healing. Here, we designed a kind of self-healing injectable micelle/hydrogel composites with multi-functions as wound dressing for joint skin damage. By combining the dynamic Schiff base and copolymer micelle cross-linking in one system, a series of hydrogels were prepared by mixing quaternized chitosan (QCS) and benzaldehyde-terminated Pluronic®F127 (PF127-CHO) under physiological conditions. The inherent antibacterial property, pH-dependent biodegradation and release behavior were investigated to confirm multi-functions of wound dressing. The hydrogel dressings showed suitable stretchable and compressive property, comparable modulus with human skin, good adhesiveness and fast self-healing ability to bear deformation. The hydrogels exhibited efficient hemostatic performance and biocompatibility. Moreover, the curcumin loaded hydrogel showed good antioxidant ability and pH responsive release profiles. In vivo experiments indicated that curcumin loaded hydrogels significantly accelerated wound healing rate with higher granulation tissue thickness and collagen disposition and upregulated vascular endothelial growth factor (VEGF) in a full-thickness skin defect model. Taken together, the antibacterial adhesive hydrogels with self-healing and good mechanical property offer significant promise as dressing materials for joints skin wound healing.