Plant‐Inspired Soft Bistable Structures Based on Hygroscopic Electrospun Nanofibers

Abstract

The tissue composition and microstructures of plants have dynamic morphologies that change according to their environments. Recently, multifunctional responsive materials and smart structures also took inspiration from these plants' features. Dionaea muscipula leaves provide a remarkable example of an optimized structure that, owing to the synergistic integration of bistability, material, and geometrical properties, permits to overcome the performance limits of purely diffusive processes. In this paper, a hygroscopic bistable structure (HBS) inspired by the Venus flytrap leaves is presented, obtained by bonding prestretched poly(dimethylsiloxane) (PDMS) layers prior to depositing electrospun polyethylene oxide (PEO) nanofibers. A hygroresponsive bilayer (HBL) is also obtained by electrospinning of PEO on an unstretched PDMS layer. The hygroscopic material (Young's modulus and hygroscopic expansion) is mechanically characterized so as to predict the response time of a bending HBL in response to a step humidity variation. The HBS response time (≈1 s) is sensibly lower than the one of purely diffusive HBL (≈10 s) thanks to bistability. An illustrative implementation is also presented, exploiting an HBS to trigger the curvature of a PDMS optical focusing system. The developed plant‐inspired soft bistable structure can also be used for sensing (e.g., humidity), energy harvesting, as well as advanced soft robotics applications.

Artificial Venus Flytraps: A Research Review and Outlook on Their Importance for Novel Bioinspired Materials Systems

“…Human input is not the only means that can be used to trigger AVFT systems. Changes of environmental conditions such as humidity or temperature have been employed as input, for example, for hydrogel-based artificial traps ( Figure 3D ) (Fan et al, 2019 ; Lunni et al, 2020 ). These systems are based on composite (Fan et al, 2019 ) or hybrid hydrogels (Athas et al, 2016 ), utilizing various swelling behaviors and coefficients of the building components under variable environmental and triggering conditions for movement.…”

“…This system is able to snap open and close in response to solvent as stimuli. A purely humidity-responsive AVFT leaf based on a hygroscopic bistable sheet (HBS) system has been developed by Lunni et al ( 2020 ) ( Figure 3D ). The system consists of a pre-stretched passive layer of polydimethylsiloxane (PDMS) and a hygroscopic active layer of electrospun polyethylene oxide (PEO) nanofibers.…”

“…(C) IPMC-based systems: (1) IPMC-based AVFT with artificial trigger hairs (Shahinpoor, 2011 ); (2) DEA-based AVFT with a fast gripping motion (Wang et al, 2019 ). (D) Humidity-driven systems: (1) HBS-based humidity change-driven AVFT (Lunni et al, 2020 ); (2) hydrogel-based water- and temperature-triggered AVFT (Fan et al, 2019 ); (3) Hydrogel-based solvent-triggered doubly curved system [adapted from Lee et al ( 2010 )]. (E) Pneumatic systems: (1) 3D-printed pneumatic AVFT (Temirel et al, 2016 ); (2) silicone-based AVFT (Pal et al, 2019 ).…”

“… Sketches of the AVFTs are all originals based on the concepts presented in mentioned references . References: [1] Forterre et al ( 2005 ), [2] Jaffe ( 1973 ), [3] Zhang et al ( 2019 ), [4] Zhang et al ( 2016 ) [5] Kim et al ( 2014 ), [6] Shahinpoor ( 2011 ), [7] Shi et al ( 2012 ), [8] Wang et al ( 2019 ), [9] Lunni et al ( 2020 ), [10] Fan et al ( 2019 ), [11] Lee et al ( 2010 ), [12] Pal et al ( 2019 ), [13] Wani et al ( 2017 ), [14] Lim et al ( 2017 ) . …”

Light-assisted electrospinning monitoring for soft polymeric nanofibers

“…In the last years one-dimensional (1D) nanostructures have gained much interest in research and industry because of their potential application in filtration 1 for air purification, tissue engineering 2 , drug delivery 3 , sensors 4 , electronics 5 and as smart materials for soft robotics 6 – 8 . More recent applications comprehend also Surface-enhanced Raman Scattering (SERS) sensing 9 , energy storage 10 and photocatalysis 11 – 14 .…”