Skin-Inspired Multifunctional Luminescent Hydrogel Containing Layered Rare-Earth Hydroxide with 3D Printability for Human Motion Sensing

Abstract

The development of multifunctional hydrogels is gaining a lot of attention owing to its application in electronic skins, wearable electronics, and soft robotics. In this study, an effective and facile one-step preparation strategy is developed to fabricate a multifunctional nanocomposite hydrogel consisting of sodium alginate/sodium polyacrylate/layered rare-earth hydroxide (LRH), where LRH plays multiple roles as a co-cross-linker and ionic carrier and is also the origin of fluorescence. The obtained LRH-based composite hydrogel exhibits excellent three-dimensional printing performance at room temperature. When exposed to different humidity conditions, the hydrogel exhibits humidity-dependent electromechanical properties. The multiple functions of the resultant hydrogel are easily realized by just relying on the addition of cationic LRH nanoplates. A skinlike motion sensor with transparency is fabricated based on the printed hydrogel and is used to monitor human motion. Owing to the fluorescence characteristics of lanthanide ions (Eu3+ and Tb3+) from LRH, the hydrogel shows highly tunable multicolored photoluminescence by adjusting the LRH constituent. This study reveals that the multifunctional hydrogels have potential for applications in sensing.

3D Printed Flexible Strain Sensors: From Printing to Devices and Signals

“…[ 61 ] Additionally, when constructing cations crosslinked networks, the introduction of trivalent cations could provide the hydrogel with higher crosslink density, owing to that the triple charges of cations can coordinate with functional groups tethered to polymers’ chains, and the polymers could be crosslinked stereoscopically, which can present superior mechanical performance than linear crosslinked hydrogel of divalent ions. [ 76 ] Based on currently published reports, 3D printed self‐healing conductive hydrogels are still the focus of future research in the field of electronic skin.…”

Recent advances in the synthesis of smart hydrogels

“…Hydrogels are an emerging material that has attracted significant fundamental and applied interest for wastewater treatment 411 , tissue engineering 325,412 , drug delivery 413,414 , wearable electronics 415 , and energystorage materials 314 . Apart from the aforementioned synthetic processes, the following recent works of functional hydrogel have been added new horizons in numerous fields of application.…”

Layered Double Hydroxides in Bioinspired Nanotechnology

“…The application of LDH in the field of bioinspired sensors was successfully demonstrated by Ren et al [136], who developed a skin-inspired sensor based on a multifunctional nanocomposite hydrogel consisting of sodium alginate/sodium polyacrylate/layered rare-earth hydroxide (LRH) (SA/PAAS/LRH), fabricated through a 3D printing system (Figure 11a,b). The device showed a promising multifunctional behavior, such as humidity-dependent electromechanical properties, a sensitivity to mechanical deformation, thanks to a strain-dependent conductivity (Figure 11c), and tunable fluorescence (Figure 11d), while maintaining the characteristics of transparency and stretchability indispensable for the realization of a device for human motion detection.…”