A supramolecular double network hydrogel is presented by physical interpenetration of DNA and cucurbit[8]uril networks. In addition to exhibiting an increase in strength and thermal stability, the double network hydrogel possesses excellent properties such as stretchability, ductility, shear-thinning, and thixotropy. Moreover, it is enzymatically responsive to both nuclease and cellulase, as well as small molecules, showing great potential as a new soft material scaffold.
Nonequilibrium oscillation fueled by dissipating chemical energy is ubiquitous in living systems for realizing a broad range of complex functions. The design of synthetic materials that can mimic their biological counterparts in the production of dissipative structures and autonomous oscillations is of great interest but remains challenging. Here, a series of environmentally adaptable hydrogels functionalized with photoswitchable spiropyran derivatives that display a tunable equilibrium‐shifting capability, thus endowing those hydrogels with a high degree of freedom and flexibility is reported. Such nonequilibrium hydrogels are able to responsively adapt their shapes under constant light illumination due to asymmetric deswelling, which in turn generates self‐shadowing and consequently creates autonomous self‐oscillating behaviors through a negative feedback process. Diverse oscillation modes including bending, twisting, and snap‐through buckling with tunable frequency and amplitude are widely observed in three different molecular systems. Density functional theory calculations and finite element simulations further demonstrated the robustness of such a photoadaptable self‐oscillation mechanism. This study provides a useful molecular design strategy for construction of highly adaptable hydrogels with potential applications in self‐sustained soft robots and autonomous devices.
Autonomous robotic functions in materials beyond simple stimulus-response actuation require the development of functional soft matter that can complete well-organized tasks without step-by-step control. We report the design of photo- and electroactivated hydrogels that can capture and deliver cargo, avoid obstacles, and return without external, stepwise control. By incorporating two spiropyran monomers with different chemical substituents in the hydrogel, we created chemically random networks that enabled photoregulated charge reversal and autonomous behaviors under a constant electric field. In addition, using perturbations in the electric field induced by a dielectric inhomogeneity, the hydrogel could be attracted to high dielectric constant materials and autonomously bypasses the low dielectric constant materials under the guidance of the electric field vector. The photo- and electroactive hydrogels investigated here can autonomously perform tasks using constant external stimuli, an encouraging observation for the potential development of molecularly designed intelligent robotic materials.
Living organisms use the amplification
of molecular motions over
orders of magnitude to produce deformation, motion, and function on
the macroscale. The design of artificial molecular machines that can
mimic their biological counterparts in the production of such macroscopic
actuation is of great interest. Here, we designed a polymerizable
bisazobenzene-based molecular photoswitch that displays a highly directional
geometrical transformation upon photoisomerization. When this photoswitch
is incorporated into polymer networks as a cross-linker, its directional
contraction and expansion drive the movement and rearrangement of
polymer chains and amplifies these motions to the macroscale, resulting
into a direct volume change and deformation of the bulk polymeric
hydrogels. These photoswitchable hydrogels therefore mimic macroscopic
biological motions such as muscular contraction and light-driven bending
similar to phototropism. Furthermore, the use of this photoswitch
to tune the macroscopic properties of hydrogels is in principle transferable
to a variety of polymeric systems. This work develops a clear connection
between molecular motion and macroscopic actuation, providing a platform
to investigate this relationship further.
Supramolecular-covalent hybrid polymers have been shown to be interesting systems to generate robotic functions in soft materials in response to external stimuli. In recent work supramolecular components were found to...
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