Direct 4D printing of functionally graded hydrogel networks for biodegradable, untethered, and multimorphic soft robots

Cho, Soo Young; Ho, Dong Hae; Jo, Sae Byeok; Cho, Jeong Ho

doi:10.1088/2631-7990/ad1574

Cited by 4 publications

(1 citation statement)

References 60 publications

(51 reference statements)

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“…These include light-based methods such as photo-cross-linking and photolithography, − 3D printing, microfluidics, electrospinning, and freeze-drying/lyophilization. , Among these, light-based methods turn out particularly promising due to their robustness and precise control over the fabrication and actuation process. This enables the development of hydrogels with tailored properties for potential applications as soft robots, actuators, and sustainable energy generators. − However, the fabrication of light-based actuators involves a complex fabrication process and consumes a high amount of energy to sustain continuous actuation. Moreover, the photoswitching process leads to detrimental quenching effects, which weakens the hydrogel structure .…”

Section: Introductionmentioning

confidence: 99%

Solvent-Responsive Functionally Graded Hydrogel Thin Films for Programmed Actuation

Debta,

Kumbhar,

Ghosh

et al. 2024

ACS Appl. Eng. Mater.

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Shape-shifting solvent-responsive hydrogels have emerged as a crucial material platform for the design of soft robots, sensors, and actuators. Generally, to achieve actuation under different environments, using a layered structure with heterogeneous properties is a prevalent approach. However, the nonuniform force distribution at the interface between the layers can induce material delamination, thus greatly compromising the system’s stability and applicability. Here, we present the fabrication, design, and analysis of a reversible and structurally stable single-component functionally graded (FG) hydrogel thin film. The gradation is in terms of the modulus and diffusion coefficient. The FG film exhibits a fast actuation rate and is capable of actuating in both immersed and nonimmersed aqueous environments. The fabricated FG film can eliminate the requirement for a layered structure yet retain all its functionalities. A coupled diffusion–deformation framework using the finite element (FE) method is employed to comprehend the mechanism and understand the factors governing the actuation of a FG film. The displacement profiles obtained from the simulations are successfully compared with the experiments for a FG–chitosan–water system. The rate of concentration change in different layers of the FG film is shown to play a pivotal role in steering the direction of actuation as well as the reversibility of folding under different conditions. The differential strain obtained from the length change between the different layers of the FG films is identified as a contributing factor for different actuation rates. Additionally, the simulation curvatures from different scenarios elucidate the influence of cross-linking gradation, water diffusion, and thickness on the folding of a FG film. As a prospective application, we demonstrate the design of different underwater grippers using geometrically engineered symmetric and asymmetric FG films.

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Section: Introductionmentioning

confidence: 99%

Solvent-Responsive Functionally Graded Hydrogel Thin Films for Programmed Actuation

Debta,

Kumbhar,

Ghosh

et al. 2024

ACS Appl. Eng. Mater.

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Structural design and simulation of PDMS/SiC functionally graded substrates for applications in flexible hybrid electronics

Yang,

Song,

et al. 2024

Adv. Manuf.

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Nature-inspired miniaturized magnetic soft robotic swimmers

Pramanik,

Verstappen,

Onck

2024

Applied Physics Reviews

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State-of-the-art biomedical applications such as targeted drug delivery and laparoscopic surgery are extremely challenging because of the small length scales, the requirements of wireless manipulation, operational accuracy, and precise localization. In this regard, miniaturized magnetic soft robotic swimmers (MSRS) are attractive candidates since they offer a contactless mode of operation for precise path maneuvering. Inspired by nature, researchers have designed these small-scale intelligent machines to demonstrate enhanced swimming performance through viscous fluidic media using different modes of propulsion. In this review paper, we identify and classify nature-inspired basic swimming modes that have been optimized over large evolutionary timescales. For example, ciliary swimmers like Paramecium and Coleps are covered with tiny hairlike filaments (cilia) that beat rhythmically using coordinated wave movements for propulsion and to gather food. Undulatory swimmers such as spermatozoa and midge larvae use traveling body waves to push the surrounding fluid for effective propulsion through highly viscous environments. Helical swimmers like bacteria rotate their slender whiskers (flagella) for locomotion through stagnant viscid fluids. Essentially, all the three modes of swimming employ nonreciprocal motion to achieve spatial asymmetry. We provide a mechanistic understanding of magnetic-field-induced spatiotemporal symmetry-breaking principles adopted by MSRS for the effective propulsion at such small length scales. Furthermore, theoretical and computational tools that can precisely predict the magnetically driven large deformation fluid–structure interaction of these MSRS are discussed. Here, we present a holistic descriptive review of the recent developments in these smart material systems covering the wide spectrum of their fabrication techniques, nature-inspired design, biomedical applications, swimming strategies, magnetic actuation, and modeling approaches. Finally, we present the future prospects of these promising material systems. Specifically, synchronous tracking and noninvasive imaging of these external agents during in vivo clinical applications still remains a daunting task. Furthermore, their experimental demonstrations have mostly been limited to in vitro and ex vivo phantom models where the dynamics of the testing conditions are quite different compared the in vivo conditions. Additionally, multi-shape morphing and multi-stimuli-responsive modalities of these active structures demand further advancements in 4D printing avenues. Their multi-state configuration as an active solid-fluid continuum would require the development of multi-scale models. Eventually, adding multiple levels of intelligence would enhance their adaptivity, functionalities, and reliability during critical biomedical applications.

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Direct 4D printing of functionally graded hydrogel networks for biodegradable, untethered, and multimorphic soft robots

Cited by 4 publications

References 60 publications

Solvent-Responsive Functionally Graded Hydrogel Thin Films for Programmed Actuation

Solvent-Responsive Functionally Graded Hydrogel Thin Films for Programmed Actuation

Structural design and simulation of PDMS/SiC functionally graded substrates for applications in flexible hybrid electronics

Nature-inspired miniaturized magnetic soft robotic swimmers

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