Spatiotemporal Regulation of Hydrogel Actuators by Autocatalytic Reaction Networks

Abstract

stimuli such as temperature, [5] pH, [6] metal ions, [7] or ion strain. [8] Nevertheless, the complexity of motion executed by these actuators is limited by two factors: i) the whole volume of the material responses simultaneously to the stimuli; ii) the response lacks temporal regulation (that is, the response coincides with the stimulus, when the stimulus is ON, the response is ON, and no delays, periodicities, or other complex temporal patterns take place). To overcome these limitations, actuation should be spatially and temporarily regulated.Inspired by biological organisms where responses are controlled by biochemical signaling networks, [9] researchers have been developing hydrogel materials and actuators that are autonomously regulated by synthetic chemical reaction networks. [10] Initially, the research focused on using the Belousov-Zhabotinsky (BZ) reaction-the best-known chemical oscillator-or its close analogs to create periodical swelling/shrinking hydrogels. [11] Lately, however, the focus has moved towards using de novo enzymatic, [12] DNA, [13] and organic [14] reaction networks to regulate hydrogel materials. These reaction networks provide control over individual interactions between the system's components and therefore, they are more desirable than the BZ reaction from a design standpoint. Schulman, Gracias, and co-workers demonstrated the selective actuation of various parts of the hydrogel by specific DNA strands. [13b] Walther and coworkers [14a-c,15] and Huck and co-workers [12a] pioneered temporal control of sol-gel transitions by organic or enzymatic reaction networks. Pojman, Taylor, and co-workers demonstrated spatiotemporal regulation of gelation by an autocatalytic front. [12b,16] Nevertheless, autonomous spatiotemporal regulation of hydrogel actuators by de novo reaction networks remains elusive.In this work, we regulated the actuation of disulfide-containing hydrogel materials by autocatalytic fronts that release thiols. These actuators can perform complex motions (that is, gradual unrolling, wave movement, or sequential actuation) otherwise inaccessible to hydrogel actuators without an external control. Results and DiscussionDesigning hydrogel actuators that can be regulated by the autocatalytic front requires developing two compatible Regulating hydrogel actuators with chemical reaction networks is instrumental for constructing life-inspired smart materials. Herein, hydrogel actuators are engineered that are regulated by the autocatalytic front of thiols. The actuators consist of two layers. The first layer, which is regular polyacrylamide hydrogel, is in a strained conformation. The second layer, which is polyacrylamide hydrogel with disulfide crosslinks, maintains strain in the first layer. When thiols released by the autocatalytic front reduce disulfide crosslinks, the hydrogel actuates by releasing the mechanical strain in the first layer. The autocatalytic front is sustained by the reaction network, which uses thiouronium salts, disulfides of β-aminothiols, and maleimide...

Bioinspired Hydrogels as Platforms for Life-Science Applications: Challenges and Opportunities

“…Since their design, the properties of hydrogels can be tuned to mimic the mechanical, biochemical, and functional characteristics of the soft tissues. The biomimetic materials are applied for controlled drug delivery [4,6,41,58,59,108,122,126,127,178,179], in regenerative medicine (tissue engineering, modulating tissue environment to promote the tissue repair) [3,4,176,180], biosensors and actuators [4,9,[11][12][13]86,176,[180][181][182], bioprinting [4,[10][11][12], 3D cell culture [4,42,46,79,177], imaging for medical diagnostics and therapy [183][184][185], personal healthcare and hygienic products [16,165], etc. A variety of hydrogels responsive to different external stimuli were reported: temperature [4,9,22,35,53,78,…”

“…From a chemical point of view, the hydrogels can be obtained from natural or synthetic water soluble (co)polymers of various structures and architectures, interpenetrated polymer networks (IPNs), proteins, peptides, clays, multicomponent systems, etc., having different morphologies and functions [1][2][3]. In particular, smart networks able to respond to physical, chemical, and biological stimuli gained much attention for a wide range of applications: tissue engineering [4], bone regeneration [5], controlled-release drug delivery vehicles [6], wound healing [7], soft robotics [8], biosensing [9], intelligent electronics and artificial intelligence [10], actuators [11][12][13], stretched electronic devices [14], hygiene products [15,16], contact lens [17], cosmetics [18], food nutrition and health, food safety and food engineering and processing [19], advanced wastewater treatment [20], catalysis [21][22][23], etc.…”

Converse two-way shape memory effect through a dynamic covalent network design

“…5 Their reversible actuation, which features a shape shiing between two predetermined shapes, is particularly attractive. [6][7][8] Among various stimuli-responsive polymers, conventional shape memory polymers typically exhibit a thermal induced one-way shape memory effect. [9][10][11] Thus, a reprogramming procedure is needed to enable the shape shiing aer each shape memory cycle.…”

Perpetuating enzymatically induced spatiotemporal pH and catalytic heterogeneity of a hydrogel by nanoparticles

“…In the last few decades, the question of how information can travel across gradients to instigate spatiotemporal communication and motile behavior among chemically interactive (bio)colloidal entities has been a hot research topic among various scientific communities. 9–19 To this end, recent reports in the literature have highlighted many interesting dynamic modulations of solution pH using light or enzymes. Undoubtedly, this has led to the development of materials with adaptive and spatiotemporally controlled properties.…”