Multifunctional Smart Materials Research Articles

Tailoring Photoweldable Shape Memory Polyurethane with Intrinsic Photothermal / Fluorescence Via Engineering Metal‐Phenolic Systems

AbstractMultifunctional shape memory polymers are significant for next‐generation intelligent systems as smart materials. However, their practical applications are limited by toughness, manufacturability, and functional integration strategies. Besides, while 4D printing is used to construct deformable devices, the limited accessible shapes and difficulty of integrating multiple materials hindered the development of multifunctional devices. Herein, metal‐phenolic coordination is used as crosslinks to tailor tough shape memory polyurethanes with intrinsic photothermal effect and/or tunable fluorescence. The reversible dissociation of metal‐phenolic complexes upon loading provides an efficient energy dissipation for the polymer network. The photothermal/fluorescent properties of target polyurethane can be effortlessly programmed by changing the coordinated metals and functional ligands. The obtained fluorescent polyurethane displays tunable fluorescence through the reversible dissociation‐association of dynamic bonds upon thermal stimulus. Moreover, relying on light‐triggered hybrid exchange reactions among various metal‐phenolic coordination bonds, heterogeneous interfaces can be merged to manufacture exquisite 3D shape‐shifting devices and integrate more advanced functions. As demonstrations, intrinsic photothermal‐responsive shape memory stent, and 3D fluorescent encryption device are produced based on photo‐welding instead of 4D printing. This study not only provides a convenient supramolecular strategy for constructing multifunctional smart materials but also demonstrates a feasible method for making personalized integrated architectures.

Multifunctional coatings on Mg‐based metallic biomaterials and implants

Multifunctional materials are propitious materials with numerous functionalities that make them an ideal option for implants and biomedical applications that should simultaneously fulfill various requirements, including satisfactory mechanical strength, biocompatibility, antibacterial property, hydrophilicity, drug delivery, etc. Magnesium, as a metallic biomaterial, fulfills the required mechanical properties, but unfortunately, in some ways alone, it cannot provide the required biological properties. For instance, Mg alloys suffer from poor corrosion resistance and high biodegradability, which should be carefully controlled. On the other hand, multifunctional materials alone are not able to provide the required properties in biomedical applications because the vast majority of them do not have the necessary strength and stability. Therefore, the use of magnesium together with multifunctional or composite coatings will be a very advantageous choice for meeting the needs of implants and biomedical materials. The current study focuses on the introduction and utilization of various multifunctional coatings and composites on Mg‐based alloys for biomedical applications. Numerous organic and inorganic materials could be utilized as composites or multifunctional materials, such as polymers, hydroxyapatites, hydrogels, calcium phosphates, alginates, hyaluronic acids, chitosan, etc. In this regard, numerous types of coating and composite materials, their production technologies, mechanisms, resultant properties, and the involved parameters are thoroughly discussed to provide a comprehensive guide for those interested in this field. It is hoped that this study will pave the way for the production of advanced and smart multifunctional materials with unique properties and play a role in the design of a new generation of Mg‐based biomedical materials.This article is protected by copyright. All rights reserved.

Hierarchical Self-Assembly Molecular Building Blocks as Intelligent Nanoplatforms for Ovarian Cancer Theranostics.

Hierarchical self-assembly from simple building blocks to complex polymers is a feasible approach to constructing multi-functional smart materials. However, the polymerization process of polymers often involves challenges such as the design of building blocks and the drive of external energy. Here, a hierarchical self-assembly with self-driven and energy conversion capabilities based on p-aminophenol and diethylenetriamine building blocks is reported. Through β-galactosidase (β-Gal) specific activation to the self-assembly, the intelligent assemblies (oligomer and superpolymer) with excellent photothermal and fluorescent properties are dynamically formed in situ, and thus the sensitive multi-mode detection of β-Gal activity is realized. Based on the overexpression of β-Gal in ovarian cancer cells, the self-assembly superpolymer is specifically generated in SKOV-3 cells to achieve fluorescence imaging. The photothermal therapeutic ability of the self-assembly oligomer (synthesized in vitro) is evaluated by a subcutaneous ovarian cancer model, showing satisfactory anti-tumor effects. This work expands the construction of intelligent assemblies through the self-driven cascade assembly of small molecules and provides new methods for the diagnosis and treatment of ovarian cancer.

Multifunctional smart engineering nano magnetic materials with ultrahigh synergetic adsorption-photocatalytic performance

Water contamination by organic dyes is a severe environmental and health issue requiring a sustainable remedial solution. Among different acid dyes, the Acid Violet-19 (AV-19) extensively used for the coloring of fabrics has toxic and carcinogenic effects, which need to be effectively treated with state-of-the-art photocatalysts and techniques. In the present work, a series of nanomagnetic spinel ferrites (MFe2O4: M = Mg, Ca, Mn, Ni, Zn, and Cd) were synthesized for dye remediation through a facile combustion route. The synthesis involved the pioneering use of DL-Glutamic acid as a fuel due to low ignition temperatures (200–250 °C), cost-effectiveness, and environmental compatibility. The nanomagnetic particles with d90 < 200 nm and crystallite sizes lower than 50 nm were synthesized, exhibiting strong superparamagnetic properties and high surface areas. The synthesized nanoparticles exhibited ultrahigh adsorptive elimination and superior photocatalytic degradation of AV-19 under high concentration (250 and 100 mg/L) conditions. High monolayer absorbance capacities of 3905, 1061, and 814 mg/g were achieved for CaFe2O4, MgFe2O4, and CdFe2O4. The AV-19 elimination is well described by the Langmuir isotherm and second-order kinetic model. The dipole-dipole and Yoshida H-bonding interactions are the proposed adsorption mechanisms. The ZnFe2O4 showed exceptionally high photocatalytic dye degradation (∼ 100 % within 1 h), with the first-order kinetic rate constant being 0.063 min−1 at a photocatalyst dose of 0.1 g/L. The synthesized catalyst also showed high removal-degradation efficiency against different cationic and anionic dyes, including Malachite green, crystal violet, and Titan yellow. The solution pH showed an insignificant effect on the synergetic adsorption and photocatalytic degradation efficiency of MFe2O4. The present study shows that synthesized magnetic nanoparticles through the facile combustion route effectively eradicate the dye pollutants from wastewater.

Characteristics and long-term kinetics of an azobenzene derivative and a donor-acceptor Stenhouse adduct as orthogonal photoswitches.

Light-triggered molecular switches are extensively researched for their applications in medicine, chemistry and material science and, if combined, particularly for their use in multifunctional smart materials, for which orthogonally, i.e. individually, addressable photoswitches are needed. In such a multifunctional mixture, the switching properties, efficiencies and the overall performance may be impaired by undesired mutual dependences of the photoswitches on each other. Within this study, we compare the performance of the pure photoswitches, namely an azobenzene derivative (Azo) and a donor-acceptor Stenhouse adduct (DASA), with the switching properties of their mixture using time-resolved temperature-dependent UV/VIS absorption spectroscopy, time-resolved IR absorption spectroscopy at room temperature and quantum mechanical calculations to determine effective cross sections, switching kinetics as well as activation energies of thermally induced steps. We find slightly improved effective cross sections, percentages of switched molecules and no increased activation barriers of the equimolar mixture compared to the single compounds. Thus, the studied mixture Azo + DASA is very promising for future applications in multifunctional smart materials.

Heating Capacity and Biocompatibility of Hybrid Nanoparticles for Magnetic Hyperthermia Treatment.

Cancer is one of the deadliest diseases worldwide and has been responsible for millions of deaths. However, developing a satisfactory smart multifunctional material combining different strategies to kill cancer cells poses a challenge. This work aims at filling this gap by developing a composite material for cancer treatment through hyperthermia and drug release. With this purpose, magnetic nanoparticles were coated with a polymer matrix consisting of poly (L-co-D,L lactic acid-co-trimethylene carbonate) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer. High-resolution transmission electron microscopy and selected area electron diffraction confirmed magnetite to be the only iron oxide in the sample. Cytotoxicity and heat release assays on the hybrid nanoparticles were performed here for the first time. The heat induction results indicate that these new magnetic hybrid nanoparticles are capable of increasing the temperature by more than 5 °C, the minimal temperature rise required for being effectively used in hyperthermia treatments. The biocompatibility assays conducted under different concentrations, in the presence and in the absence of an external alternating current magnetic field, did not reveal any cytotoxicity. Therefore, the overall results indicate that the investigated hybrid nanoparticles have a great potential to be used as carrier systems for cancer treatment by hyperthermia.

Peripherally Modified Poly(amido amine) Nanocomposite Hydrogel with Stimuli‐Responsive Self‐Healing, High Tensile Strength, and Selective Superadsorption Poperties

AbstractSmart materials with dual functionalities demonstrate considerable potential in various applications. Designing and synthesizing hydrogels with excellent stimuli‐responsive self‐healing and high mechanical strength is extremely challenging. The present study initiates the development of a new generation of smart materials with selective superadsorption capacity. Here, we introduce a novel anthracene‐modified poly (amido amine) (PAMAM)‐N‐isopropyl acrylamide hydrogel (PAMNG). The hydrogel becomes hybrid as we incorporate the silica nanoparticle. PAMAM dendrimer‐based organic/inorganic hybrid silica nanoparticles (PAMAGN) have been characterized using nuclear magnetic resonance (NMR), Fourier‐transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), transmission electrone microscopy (TEM) and rheology. The developed hybrid gel exhibited excellent near‐infrared (IR) responsive self‐healing character. The hybrid gel had excellent mechanical strength, which was as high as 106 Pa. Further, the gel was used for superadsorption studies and showed selective adsorption of methyl orange from water. The adsorption was 96 %, which is remarkable. The results taken together suggest that the PMNG gel can be a promising candidate for developing multifunctional smart materials. In the future, we aim to explore how this self‐healing mechanism applies to biological applications.

Construction of Multi-Stimuli Responsive Highly Porous Switchable Frameworks by In Situ Solid-State Generation of Spiropyran Switches.

Stimuli-responsive molecular systems support within permanently porous materials offer the opportunity to host dynamic functions in multifunctional smart materials. However, the construction of highly porous frameworks featuring external-stimuli responsiveness, for example by light excitation, is still in its infancy. Here a general strategy is presented to construct spiropyran-functionalized highly porous switchable aromatic frameworks by modular and high-precision anchoring of molecular hooks and an innovative in situ solid-state grafting approach. Three spiropyran-grafted frameworks bearing distinct functional groups exhibiting various stimuli-responsiveness are generated by two-step post-solid-state synthesis of a parent indole-based material. The quantitative transformation and preservation of high porosity are demonstrated by spectroscopic and gas adsorption techniques. For the first time, a highly efficient strategy is provided to construct multi-stimuli-responsive, yet structurally robust, spiropyran materials with high pore capacity which is proved essential for the reversible and quantitative isomerization in the bulk as demonstrated by solid-state NMR spectroscopy. The overall strategy allows to construct dynamic materials that undergoes reversible transformation of spiropyran to zwitterionic merocyanine, by chemical and physical stimulation, showing potential for pH active control, responsive gas uptake and release, contaminant removal, and water harvesting.

A viologen-derived luminescent material exhibiting photochromism, photocontrolled luminescence and selective detection of Cr2O72− in aqueous solution

Stable viologen-derived multifunctional smart materials exhibit widespread practical applications in many areas. In this study, a viologen-derived material with 4-fold interpenetrating diamondoid network, {[Cd(1,4-ndc)(cpbpy)]·2H2O}n, was successfully constructed based on asymmetrical N-(3-carboxyphenyl)-4,4′-bipyridinium (cpbpy) and 1,4-naphthalenedicarboxylic acid (1,4-H2ndc). The compound shows reversible photochromic behavior under a xenon lamp, which are proved by UV–vis spectra and EPR characterizations. Moreover, the compound with good photoluminescence properties displays photocontrolled luminescence quenching behaviors. Owing to its good water stability, the compound is then applied in luminescence sensing for the detection of Cr2O72− in aqueous solution. The corresponding luminescence quenching constant for Cr2O72− is KSV = 4.33 × 104 M−1, and the detection limit is 3.66 μM. Systematic investigations on the luminescence quenching mechanism suggest that the inner filter effect resulted in the selective detection of Cr2O72−. This study provides inspiration for the design and synthesis of target luminescent crystalline materials with rigid and asymmetric viologen-derived ligands.

A Simple and Fast Compression‐Based Method to Fabricate Responsive Gold‐pNIPAM Hybrid Materials: From Thin Films to Anisotropic Microgels

AbstractIn recent years, hydrogel‐based soft materials with hybrid properties have found widespread use in various technological fields, including tissue engineering, soft actuators, and flexible electronics. The proper implementation of these smart multifunctional materials into real‐world applications requires the development of simple, cost‐effective, and large‐scale fabrication methods. Herein, a simple compression‐ and colloid‐based method is presented to fabricate responsive Au‐poly(N‐isopropylacrylamide) (pNIPAM) hybrid films using photopolymerizable resin containing Au‐pNIPAM core–shell microgels as building blocks. Uniform Au‐pNIPAM hybrid films of 25 × 25 mm with adjustable thickness in the micron‐size range (2.3–1.2 µm) w ere successfully fabricated on glass substrates and flexible commercial acetate sheets. The resulting flexible Au‐pNIPAM films exhibit robust optical and mechanical properties, even after repeated edge‐to‐edge bending cycle tests. Additionally, using patterned light to polymerize the Au‐pNIPAM films allows synthesizing of anisotropic Au‐pNIPAM microgels with high width‐to‐height aspect ratios, such as square, circular, and rectangular microgels, adding a new dimension to the proposed fabrication method.

A smart material: Multi-stimulus-responsive composite microspheres prepared via RAFT polymerization as recyclable pickering emulsifiers and their application in stabilizing real oil phases

The development of smart composites to sustainably separate and recover oil from oily water had attracted much attention. In this study, tri-block (P(LMA-b-NIPAM-b-AA)) polymer brushes were controllably “grown on” the Fe3O4 surface by three-step surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization to prepare Fe3O4-P(LMA-b-NIPAM-b-AA) (MNPLNA) magnetic nanospheres with interfacial activity. The MNPLNA nanospheres were characterized to demonstrate the triple response of pH, temperature and magnetism. Meanwhile, the comparison experiments showed that the MNPLNA nanospheres with tri-block structure had excellent interfacial activity. Then, the O/W type of Pickering emulsion was prepared by using MNPLNA nanospheres as the particle emulsifier. The size variation pattern of Pickering emulsion was comprehensively investigated by adjusting the concentration of nanospheres, oil-water ratio, electrolyte concentration and polarity of oil phase. Pickering emulsions were controllably separated by the action of an external magnetic field, and could be reversibly switched at least 10 cycles between emulsified and broken states under the trigger of pH and temperature. In addition, MNPLNA nanospheres exhibited excellent emulsification properties for stabilizing variety of real oil phases (e.g., canola oil, kerosene, diesel and crude oil). Based on this, MNPLNA nanospheres were applied as smart multifunctional materials in simulated kerosene-containing wastewater separation. MNPLNA nanospheres could be used to recover kerosene with high recovery rate after 10 separation cycles under the stepwise action of pH, temperature and magnetic field.

Effect of doping ferroelectric BaTiO3 nanoparticles on dielectric, electro-optical, and ionic properties of antiferroelectric bent-core liquid crystal

Nano-doping in polar bent-core liquid crystals is the topic of current interest for designing multifunctional smart materials. Here, we study the effect of doping of two different-sized (5–15 nm and 50–70 nm) ferroelectric BaTiO3 nanoparticles on the dielectric, electro-optical and ionic properties of antiferroelectric smectic A bent-core liquid crystal. Doping with both the sizes of nanoparticles results in lowering of the transition temperature of the liquid crystal mesophases. Both, the pure as well as doped samples show a soft mode in their antiferroelectric smectic A phase. In comparison to pure liquid crystal, the dielectric strength of the soft mode in doped samples is decreased, while their relaxation frequencies show an increasing behavior. Additionally, a decrement has been observed in the spontaneous polarization of the doped samples. A drop in polarization as well as soft mode dielectric strength values in doped samples, simultaneously point to an antiparallel dipole–dipole correlation between the ferroelectric nanoparticles and antiferroelectric liquid crystal molecules. Higher values of molecular mode relaxation frequencies obtained in nano-doped samples indicate a decrement in viscosity and dilution of pure liquid crystal. An important electro-optical parameter, the response time shows a remarkable decrement for the higher size (50–70 nm) nanoparticles doped sample. An enhancement in direct current conductivity and ion diffusion coefficient is observed for both the nano-doped samples. The smaller size (5–15 nm) ferroelectric nanoparticles reduce the mobile ion concentration and act as ion-capturing agents for the liquid crystal. A systematic investigation of the nano-doped bent-core liquid crystal can catalyze the use of the combined media for faster switching electro-optic applications.

The guest CH3CN molecule triggers solid-state photochromism in a Cu2I2-based MOF for advanced time-dependent encryption and inkless erasable printing

It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times. Herein, a 2D Cu2I2-based MOF with photoresponsive spiropyran (SP) groups orderly installed on its skeleton is developed. The structural isomerization from SP to colored merocyanine (MC) form can be triggered by removing the CH3CN guests. Besides, the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH3CN guests, exhibiting dynamic photochromic behavior with multicolor states and tunable retention time. Based on these advantages, time-dependent information encryption is successfully achieved. Furthermore, the long retention time (>72 h) of the MC form under daylight conditions in the CH3CN-removed Cu2I2-based MOF and good repeatability make it promising in various applications, such as temporary calendars, price-cards, billboards, and reusable identity cards. This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.

Programmable Shape Morphing Metasponge

Smart materials respond to environmental signals by changing their microstructure and physical properties. Programming multiple behaviors and functions into a single material could increase its utility and adaptability to ever‐changing environmental conditions. A swellable and stretchable metamaterial hydrogel or “metasponge” engineered to morph into customized sizes and shapes that dynamically tune its physical properties and functions is reported. Multiple case studies that take advantage of the morphing properties of the metasponge, including robotic actuation, light guidance, optical and sonic invisibility (“cloaking”), adaptation of propulsion mode, sampling, and multiple biomedical applications, are illustrated. Developing multifunctional smart materials in which logic is programmed into the materials rather than electronic components could pave a new path to autonomy and dynamic responses in soft robots, sensors, and actuators.

A new class of transformable kirigami metamaterials for reconfigurable electromagnetic systems

The rapid development of radio frequency (RF) components requires smart multifunctional materials that can adapt their physical shapes and properties according to the environment. While most current reconfigurable systems provide limited flexibility with high manufacturing cost, this research proposes to harness the transformable properties of kirigami-inspired multistable mechanical metasurfaces that can repeatedly deform and lock into different configurations to realize a novel class of low-cost reconfigurable electromagnetic structures with a broad design space. The metasurfaces are formed by designing kinematic-based unit cells with metallised coating that can provide adjustable resonant electromagnetic (EM) properties while rotating with respect to each other. Tailoring the cut length and geometry parameters of the patterns, we demonstrate programming of the topologies and shapes of different configurations. The influence of critical parameters on the structural multistability is illustrated by means of both a simplified energy model and finite element simulations. As examples of the reconfigurable electromagnetic devices that can be realized, we report the development of a tuneable half-wave dipole and two frequency selective surface (FSS) designs featuring isotropic and anisotropic responses. While the kirigami dipole can be tuned by mechanically stretching its arms, the FSSs exhibit distinct transmittance and reflectance spectra in each of the kirigami patterns stable states. The functionality of these kirigami devices is validated both by full-wave EM simulations and experiments. The proposed transformable structures can be mechanically actuated to tune the EM response in frequency or induce anisotropies for wave propagation.

Dynamic behavior of structural beams made of innovative smart concrete

The monitoring of structures and infrastructures is nowadays a pivotal activity for guaranteeing the safety of their users. Environmental conditions and exceptional events could affect their performance and integrity, shorten their service lives and even produce unexpected failures. The development of multifunctional smart structural materials with enhanced or novel properties could help to prevent or reduce damages and collapses. Among other building materials, concrete is particularly suitable for such improvements due to its composite nature. The authors have developed a smart concrete doped with carbon microfibers capable to sense variations of applied strains/stresses. The investigation started from the analysis of the performances of small samples, up to the manufacture of two full-scale RC beams. These applications at realistic scales are crucial for a diffuse use of such smart materials in civil engineering. The paper describes the novel characteristics of full-scale smart concrete beams, investigating their main physical, electrical, and monitoring capabilities. For this purpose, dynamic tests are carried out and discussed.

Engineering Dental Tissues Using Biomaterials with Piezoelectric Effect: Current Progress and Future Perspectives

Dental caries and traumatic injuries to teeth may cause irreversible inflammation and eventual death of the dental pulp. Nevertheless, predictably, repair and regeneration of the dentin-pulp complex remain a formidable challenge. In recent years, smart multifunctional materials with antimicrobial, anti-inflammatory, and pro-regenerative properties have emerged as promising approaches to meet this critical clinical need. As a unique class of smart materials, piezoelectric materials have an unprecedented advantage over other stimuli-responsive materials due to their inherent capability to generate electric charges, which have been shown to facilitate both antimicrobial action and tissue regeneration. Nonetheless, studies on piezoelectric biomaterials in the repair and regeneration of the dentin-pulp complex remain limited. In this review, we summarize the biomedical applications of piezoelectric biomaterials in dental applications and elucidate the underlying molecular mechanisms contributing to the biological effect of piezoelectricity. Moreover, we highlight how this state-of-the-art can be further exploited in the future for dental tissue engineering.

In Situ Activation of Superhydrophobic Surfaces with Triple Icephobicity at Low Temperatures.

Superhydrophobic surfaces have been widely studied due to their potential applications in aerospace fields. However, superhydrophobic surfaces with excellent water-repellent, anti-icing, and icephobic performances at low temperatures have rarely been reported. Herein, superhydrophobic surfaces with heating capability were prepared by etching square micropillar arrays on the surface of multiwalled carbon nanotube (MWCNT)/poly(dimethylsiloxane) (PDMS) films. The fabricated superhydrophobic surface has triple icephobicity, which can be activated even at low temperatures. The triple icephobicity is triggered by an applied voltage to achieve excellent water-repellent and icephobic capabilities, even at -40 °C. Additionally, theoretical calculations reveal that a droplet on a superhydrophobic surface loses heat at a rate of 8.91 × 10-5 J/s, which is 2 orders of magnitude slower than a flat surface (2.15 × 10-3 J/s). Also, at -40 °C, the mechanical interlocking force formed between the superhydrophobic surface and ice can be released by the heating property of the superhydrophobic surface. This low-energy, multifunctional superhydrophobic surface opens up new possibilities for bionic smart multifunctional materials in icephobic applications.

Performance tests and design of a series of magnetic fluid shock absorbers with varying stiffness based on optimal stiffness formula

With the rapid development of aerospace technology, the vibration problem of the spacecraft flexible structure urgently needs to be solved. Magnetic fluids are a type of multi-functional smart materials, which can be employed in shock absorbers to eliminate these vibrations. Referring to the calculation methods of stiffness coefficients of other passive dampers, the stiffness coefficient formula of magnetic fluid shock absorbers (MFSAs) was derived and refined. Meanwhile, a series of varying stiffness magnetic fluid shock absorbers (VS-MFSAs) were proposed and fabricated based on the second-order buoyancy principle. The range of stiffness coefficients covered by these VS-MFSAs contains the optimal stiffness coefficient estimated by formulas. The repulsive force measurement and vibration attenuation experiments were conducted on these VS-MFSAs. In the case of small amplitude, the relationship between the repulsive force and the offset distance was linear, which means the stiffness was linear. The simulation and experiment curves of the stiffness were in good agreement. The results of vibration attenuation experiments demonstrated that the rod length and the magnetic fluid mass influence the damping efficiency of VS-MFSAs. In addition, these results verified that the VS-MFSA with the optimal stiffness coefficient performed best. Therefore, the stiffness coefficient formula can guide the design of MFSAs.

Rhodamine-containing double-network hydrogels for smart window materials with tunable light transmittance, low-temperature warning, and deformation sensing

Smart window materials have attracted much attention because of their energy savings ability, light passage control in response to external stimuli, but most studies focus on the tunability of a single property, specifically, optical transmittance. Here, we report a rhodamine (Rh) mechanophore-functionalized PNIPAAm-based double-network (DN) hydrogel with the potential to act as multifunctional smart window materials that have the combination of a transmittance regulation ability, freezing−/compression-induced mechanochromic and mechanofluorescent properties. Benefiting from naturally reversible hydrophilic/hydrophobic phase transitions of PNIPAAm chains, DN hydrogels exhibit an excellent temperature-induced optical transmittance change between transparency and opaqueness. Because of the covalent incorporation of Rh mechanophores into the first network within DN hydrogels, the gels can display visualizable mechanochromism or mechanofluorescence upon freezing or compression. This is attributed to the generation of the colored and fluorescent ring-opened Rh spirolactams via mechanoactivation. This work is the first example of thermochromic smart window materials with a visualized low-temperature warning and damage sensing abilities and provides a new strategy to fabricate multifunctional smart window materials.