Shape-memory and self-healing functions of DNA-based carboxymethyl cellulose hydrogels driven by chemical or light triggers

Rapid, Localized, and Athermal Shape Memory Performance Triggered by Photoswitchable Glass Transition Temperature

Shape memory polymers that undergo shape recovery at room temperature (RT) are desirable for their potential in vivo applications, yet challenging. Herein, light-triggered athermal shape memory effect of azopolymer networks is reported by photoswitching the glass transition temperature (T_g) rather than external heating. Thanks to the switchable T_g of azopolymer induced by reversible trans-cis isomerization, the entropic energy is trapped in low T_g state (cis-form T_g < RT) to deform into a temporary shape and fixed in high T_g state (trans-form T_g > RT). Upon exposure to UV light, the reduced low T_g allows release of the entropic energy, realizing athermal shape recovery of the permanent shape. By exploring the shape memory performance, we demonstrate diverse light-induced rapid shape recovery from temporary shape to original shape. Because of the instant, precise, and spatiotemporal manipulation of light, programmable shape recovery of surface topography is further extended. We anticipate that this strategy will provide tremendous opportunities for future precise medicine devices and soft robotics.

Stiffness-switchable DNA-based constitutional dynamic network hydrogels for self-healing and matrix-guided controlled chemical processes

Constitutional dynamic networks (CDNs) attract interest as signal-triggered reconfigurable systems mimicking natural networks. The application of CDNs to control material properties is, however, a major challenge. Here we report on the design of a CDN consisting of four toehold-modified constituents, two of which act as bidentate units for chain-elongating, while the other two form a tetradentate structure acting as a crosslinking unit. Their hybridization yields a hydrogel of medium stiffness controlled by the balance between bidentate and tetradentate units. Stabilization of the tetradentate constituent by an auxiliary effector up-regulates the crosslinking unit, yielding a high-stiffness hydrogel. Conversely, stabilization of one of the bidentate constituents by an orthogonal effector enriches the chain-elongation units leading to a low-stiffness hydrogel. Using appropriate counter effectors, the hydrogels are reversibly switched across low-, medium- and high-stiffness states. The hydrogels are used to develop self-healing and controlled drug-release matrices and functional materials for operating biocatalytic cascades.

Dynamic hydrogels with controllable properties are of interest for a range of applications. Here, the authors report on a DNA hydrogel system which can be tailored to have reversible mechanical changes, reversible shape changes, is self-healing and can be used for controlled release applications.

Bioperspectives for Shape-Memory Polymers as Shape Programmable, Active Materials

Within the natural world, organisms use information stored in their material structure to generate a physical response to a wide variety of environmental changes. The ability to program synthetic materials to intrinsically respond to environmental changes in a similar manner has the potential to revolutionize material science. By designing polymeric devices capable of responsively changing shape or behavior based on information encoded into their structure, we can create functional physical behavior, including a shape-memory and an actuation capability. Here we highlight the stimuli-responsiveness and shape-changing ability of biological materials and biopolymer-based materials, plus their potential biomedical application, providing a bioperspective on shape-memory materials. We address strategies to incorporate a shape-memory (actuation) function in polymeric materials, conceptualized in terms of its relationship with inputs (environmental stimuli) and outputs (shape change). Challenges and opportunities associated with the integration of several functions in a single material body to achieve multifunctionality are discussed. Finally, we describe how elements that sense, convert, and transmit stimuli have been used to create multisensitive materials.

Molecularly Imprinted Sites Translate into Macroscopic Shape-Memory Properties of Hydrogels

The polymerization of acrylamide, dopamine methacrylamide, and bis-acrylamide in the presence of one of the electron acceptors, N,N'-dimethyl-4,4'-bipyridinium, (1), N,N'-dimethylbipyridinium-4,4'-ethylene, (2), or bipyridinium dithienylethene, (3), yields hydrogel matrices of high stiffness that are cooperatively cross-linked by bis-acrylamide and electron donor (dopamine)-acceptor complexes. Washing off the diffusional electron acceptor units yields molecularly imprinted matrices of lower stiffness, stabilized only by the bis-acrylamide bridges that include specific binding sites for the selective association of the electron acceptor (1), (2), or (3). These imprinted hydrogel matrices show selective recovery of the stiff properties upon binding the respective electron acceptor units to the imprinted sites. The control over the stiffness properties enables the development of shape-memory, molecularly imprinted hydrogels and stiffness-based sensors. The results show how molecularly imprinted sites translate into macroscopic shape-memory properties of hydrogels.

High strength hydrogels with multiple shape-memory ability based on hydrophobic and electrostatic interactions

Hydrogels with multiple shape-memory ability have aroused great interest due to their promising applications in various fields. Nevertheless, the weak mechanical performance of most shape-memory hydrogels seriously impedes the practical application in more complex environments. Herein, we reported a novel hydrogel with both high mechanical and multi-shape memory properties composed of stearyl methacrylate (SMA), acrylic acid (AA) and quaternary chitosan (QCH). The electrostatic interactions between AA and QCH together with the hydrophobic interactions of alkyl chains in SMA endowed the hydrogel with great strain-stress and fatigue resistance. Furthermore, due to the reversible destruction and construction of physical cross-links, the prepared hydrogels also exhibited the shape-memory ability in response to different stimuli, such as temperature, pH and NaCl solution. Additionally, the multiple shape-memory effect could be accomplished via programmable combination because of the relatively independent physical interactions in the hydrogels.

An Overview of Injectable Thermo-Responsive Hydrogels and Advances in their Biomedical Applications

BACKGROUND

Injectable hydrogels are a thermo-responsive system based on biomaterials. Injectable hydrogels have been broadly investigated mainly as vehicles or scaffolds of therapeutic agents that include drugs, proteins, cells, and bioactive molecules among others, utilized in the treatment of diseases such as cancers and the repair and regeneration of tissues.

RESULTS

There are several studies that have described the multiple features of hydrogels. However, the main aspect that breaks the paradigm in the application of hydrogels is the thermoresponsiveness that some of them have, which is an abrupt modification in their properties in response to small variations in temperature. For that reason, the thermo-responsive hydrogels with the unique property of sol-gel transition have received special attention over the past decades. These hydrogels show phase transition near physiological human body temperature. This feature is key for being applied in promising areas of human health-related research.

CONCLUSION

The purpose of this study is the overview of injectable hydrogels and their latest advances in medical applications including bioactive compound delivery, tissue engineering, and regenerative medicine.

Photoresponsive Self-Assembled DNA Nanomaterials: Design, Working Principles, and Applications

Photoresponsive DNA nanomaterials represent a new class of remarkable functional materials. By adjusting the irradiation wavelength, light intensity, and exposure time, various photocontrolled DNA-based systems can be reversibly or irreversibly regulated in respect of their size, shape, conformation, movement, and dissociation/association. This Review introduces the most updated progress in the development of photoresponsive DNA-based system and emphasizes their advantages over other stimuli-responsive systems. Their design and mechanisms to trigger the photoresponses are shown and discussed. The potential application of these photon-responsive DNA nanomaterials in biology, biomedicine, materials science, nanophotonic and nanoelectronic are also covered and described. The challenges faced and further directions of the development of photocontrolled DNA-based systems are also highlighted.

Multistimuli-Responsive and Photocontrolled Supramolecular Luminescent Gels Constructed by Anthracene-Bridged Bis(dibenzo-24-crown-8) with Secondary Ammonium Salt Polymer

A novel multistimuli-responsive and photcontrolled supramolecular luminescent gel is fabricated from anthracene-bridged bis(dibenzo-24-crown-8) (1) and secondary ammonium salt-functionalized graft polymer (3). X-ray crystallographic analysis reveals that the dibenzo-24-crown-8 (DB24C8) ring is located at the opposite site of 1, which will greatly hinder the mutual intermolecular π-π stacking between anthracene groups. By taking advantage of the controllable binding of 1 with 3, the unique gel-sol transition could occur under different temperatures, pH, and competitive guest bindings. Benefiting from the photo-oxygenation of anthracene, the luminescence behavior of the supramolecular gel could be switched off and on under UV light (365 nm) and heating treatment, which provides a new approach for constructing photocontrolled supramolecular luminescent gel.

DNA-Based Hydrogels Loaded with Au Nanoparticles or Au Nanorods: Thermoresponsive Plasmonic Matrices for Shape-Memory, Self-Healing, Controlled Release, and Mechanical Applications

Gold nanoparticles (AuNPs) or gold nanorods (AuNRs) are loaded in polyacrylamide hydrogels cooperatively cross-linked by bis-acrylamide and nucleic acid duplexes or boronate ester-glucosamine and nucleic acid duplexes. The thermoplasmonic properties of AuNPs and AuNRs are used to control the stiffness of the hydrogels. The irradiation of the AuNP-loaded (λ = 532 nm) or the AuNR-loaded (λ = 808 nm) hydrogels leads to thermoplasmonic heating of the hydrogels, the dehybridization of the DNA duplexes, and the formation of hydrogels with lower stiffness. By ON/OFF irradiation, the hydrogels are switched between low- and high-stiffness states. The reversible control over the stiffness properties of the hydrogels is used to develop shape-memory hydrogels and self-healing soft materials and to tailor thermoplasmonic switchable drug release. In addition, by designing bilayer composites of AuNP- and AuNR-loaded hydrogels, a reversible thermoplasmonic, light-induced bending is demonstrated, where the bending direction is controlled by the stress generated in the respective bilayer composite.

Shape-changing polymers for biomedical applications

Smart polymers that are capable of controlled shape transformations under external stimuli have attracted significant attention in the recent years due to the resemblance of this behavior to the biological intelligence observed in nature. In this review, we focus on the recent progress in the field of shape-morphing polymers, highlighting their most promising applications in the biomedical field.

Development of improved dual-diazonium reagents for faster crosslinking of tobacco mosaic virus to form hydrogels

New bench-stable reagents with two diazonium sites were designed and synthesized for protein crosslinking. Because of the faster diazonium-tyrosine coupling reaction, hydrogels from the crosslinking of tobacco mosaic virus and the reagent DDA-3 could be prepared within 1 min at room temperature. Furthermore, hydrogels with the introduction of disulfide bonds viaDDA-4 could be chemically degraded by dithiothreitol. Our results provided a facile approach for the direct construction of virus-based hydrogels.

Improved dual-diazonium reagents were developed for more efficient crosslinking of tobacco mosaic virus to form hydrogels.