Ultrafast Fabrication of Gradient Nanoporous All‐Polysaccharide Films as Strong, Superfast, and Multiresponsive Actuators

Abstract

The design of smart hydrogel actuators fully constructed from natural polymers for assessing the biomedical applications is important but challenging. Herein, an extremely simple, green, and ultrafast strategy is presented for preparing robust gradient all-polysaccharide polyelectrolyte complex hydrogel actuators. Driven by diffusing of low molecular weight chitosan into high molecular weight sodium alginate solution, a nanoporous, ultrastrong, and gradient chitosan/sodium alginate complex hydrogel film with adjustable thickness can be directly generated on the interface of two solutions within minutes. The as-prepared film can provide superfast temperature, ionic strength, and pH-triggered programmable deformations, and perform a distinct sequential double folding behavior due to the competitive effect between complexed and noncomplexed segments of polyelectrolyte. Besides, patterning Ca 2+ to locally crosslink sodium alginate in the film enables various more complex shape transformations. This green and simple diffusion-driven strategy provides significant guidance for fabricating bio-friendly actuators with applications in drug delivery, tissue engineering, soft robotics, and active implants. drug delivery, [6] tissue engineering, [7] biomimetic actuators, [8] medical devices, [9] etc. [10] The 3D deformation of self-shaping hydrogel actuator stems from their preprogrammed heterogeneous structures, [11] which cause the in-plane and/or out-ofplane mismatches in volume change upon the trigger of external stimuli. [12] Despite the considerable progress that has been made recently in terms of the sophistication of the shapes and the diversity of the function for self-shaping hydrogels, [13] their applications in biomedicine and engineering remain challenging. The major limitations include the unsatisfactory biocompatibility and biodegradation of synthetic polymers involved in existing hydrogel actuators, as well as their poor mechanical properties and long characteristic response time. [14] Currently, there is a growing demand for developing a broadly applicable method toward designing the ultrastrong hydrogel actuators composed entirely of natural polymers to assess the practical applications.Natural polyelectrolytes are the ideal candidate materials for the hydrogel actuators. Besides inherently prominent advantages of renewability, biocompatibility, and biodegradability for nature polymers, [15] they possess the ability of changing their own conformations in response to external stimuli (e.g., pH and IS). [16] To integrate polyelectrolytes into macroscopic materials, layer-by-layer (LBL) assembly is the most commonly used fabrication method, which is carried out by sequential adsorption of oppositely charge polyelectrolytes onto various substrates. [17] However, the time-consuming LBL technique can only generate ultrathin films on a nanometer scale that cannot be used as freestanding material unless by chemical posttreatment, and thus is inapplicable for the fabricating of biocompatible hydrogel actuators. [...

A New Strategy of Discretionarily Reconfigurable Actuators Based on Self‐Healing Elastomers for Diverse Soft Robots

“…[ 12–14 ] The methods that are currently available for the fabrication of anisotropic structures include one‐step method, [ 15,16 ] layer‐by‐layer polymerization, [ 17–19 ] 3D printing, [ 20 ] photolithography, [ 21 ] and ion printing. [ 22,23 ] These actuators contain crosslinking structures, and chemical crosslinking usually fixes the anisotropic structures of soft actuators and stabilizes their actuation performance. However, the stable crosslinked structures restrict the reprocessing ability of the actuators.…”

Anisotropic Magnetism in Gradient Porous Carbon Composite Aerogels

“…For smaller pore sizes, mainly polymeric membranes exhibiting graded porosity have been synthesized. This can be performed either postsynthetically by selective swelling approaches [31] or during synthesis by diffusion-controlled assembly processes [32]. Similar approaches can be transferred to fully inorganic materials, resulting in graded porous carbons after carbonization [27].…”

Actuating Supramolecular Shape Memorized Hydrogel Toward Programmable Shape Deformation

“…By manipulating the temporary shapes via shape memory behavior, various temporary anisotropic structures can be obtained via the bilayer hydrogel, thus producing diverse reversible shape deformation performances, which is expected to promote the development of intelligent polymeric materials. materials in the rising area of intelligent research, [6,7] have aroused increasing interest and shown promising applications in the fields of soft robotics, [8,9] biomedical engineering, [10][11][12] and biomimetic manufacturing. [13] In the past decade, simple bending, folding, and complex shape deformations have been achieved by inducing anisotropic structure such as gradient, [14,15] bilayer, [16,17] patterned, [18][19][20] or orient structure [21,22] in hydrogel.…”

“…Nature is considered as the common source of inspiration in both designing and fabricating of intelligent materials. [ 1–5 ] Smart hydrogel actuators, one of the most anticipated materials in the rising area of intelligent research, [ 6,7 ] have aroused increasing interest and shown promising applications in the fields of soft robotics, [ 8,9 ] biomedical engineering, [ 10–12 ] and biomimetic manufacturing. [ 13 ] In the past decade, simple bending, folding, and complex shape deformations have been achieved by inducing anisotropic structure such as gradient, [ 14,15 ] bilayer, [ 16,17 ] patterned, [ 18–20 ] or orient structure [ 21,22 ] in hydrogel.…”