Stimuli Responsiveness Research Articles

NIR-induced photothermal-responsive shape memory polyurethane for versatile smart material applications.

Stimuli responsiveness has been an attractive feature of smart material design, allowing the chemical and physical properties of the materials to change in response to small environmental variations. The versatile shape memory polyurethane (SMPU) has been advanced into thermally-responsive SMPU, enabling its use in neurovascular stents, smart fibers for compression garments, and thermal-responsive components for aircraft and aerospace structures. While thermally-induced SMPU materials exhibit excellent shape recovery and fixity, they encounter limitations such as long response times, energy-intensive heating processes, and potential damage to heat-sensitive components, hindering their wide application. Thus, SMPU has further advanced into a photothermal-responsive material by incorporating photothermal agents into the polymer matrix, offering faster response times, compatibility with heat-sensitive materials, and enhanced mechanical properties, expanding the versatility and applicability of shape memory technology. This review focuses on the classes of NIR-induced photothermal agent used in SMPU systems, their synthesis methods, and photothermal-responsive mechanism under NIR-light, which offers a dual responsiveness to the host SMPU. The advantages and limitations of NIR-induced photothermal SMPU are reviewed, and challenges in their development are discussed.

Fluorescence lifetime imaging of dynamics of mitochondrial and nucleolar microenvironment during stimuli response in living cells

Nucleolus and mitochondria play an important role in maintaining cell balance, and studying their physiological processes is helpful in understanding the biological functions. In this work, a red fluorescent pyrene rhodamine probe is used to target and label cell mitochondria and nucleolus under different conditions, and the binding mode of probe and RNA is also clarified by bio-computational simulation results. Confocal laser scanning microscopy is used to analyze the morphological changes of apoptosis in HeLa cells under the action of laser light, paclitaxel and colchicine, and the changes of micro-environmental viscosity between mitochondria and nucleolus are quantitatively analyzed by fluorescence lifetime imaging phase map. It is determined that the average fluorescence lifetime of mitochondria labeled by probes in steady-state HeLa cells is about 3.65 ns. The mitochondrial viscosity is about 66×10<sup>–3</sup> Pa·s. After laser irradiation, mitochondrial fracture and fusion occur, the fluorescence lifetime of the probe increases to 3.82 ns and the mitochondrial viscosity increases to about 131×10<sup>–3</sup> Pa·s. The mean fluorescence lifetime of the nucleolus of HeLa cells increases from 4.23 ns to 4.32 ns, indicating that the changes of the nucleolus and mitochondrial microenvironment are induced by prolonging laser irradiation. Apoptosis is induced by paclitaxel and colchicine, and the nucleolus moves out of the nucleus and into the cytoplasm. Meanwhile, the fluorescence lifetime of nucleolus and mitochondria labeled by the probe first increase and then decrease. The treatment time of paclitaxel increases from 0.5 h to 4 h, and the average lifetime of nucleolus of HeLa cells labeled by the probe increases from 4.19 ns to 4.47 ns, and finally decreases to 4.42 ns, reflecting the differences in nucleolar microenvironment of HeLa cells induced by different treatment times of paclitaxel. Comparing with the blank HeLa cell, the average lifetime of the probe increases from 4.10 ns to 4.34 ns after 1 h treatment with colchicine at low concentration (10 nM), and continuously increases to 4.47 ns after 1 h treatment with high concentration (100 nmol/L) colchicine. The microenvironments of nucleolus and mitochondria induced by apoptosis induced by colchicine at different concentrations are shown. The above three ways of inducing apoptosis, i.e. by laser light, paclitaxel and colchicine, prove that the changes of nucleolar and mitochondrial microenvironment and functional changes of HeLa cells under the condition of cell instability provide a new method of studying the dynamic process of apoptosis induced by different pathways and the diseases related to nucleolar and mitochondrial dysfunction as well.

A superporous and pH-sensitive hydrogel from Salvia hispanica (chia) seeds: stimuli responsiveness, on-off switching, and pharmaceutical applications.

The use of plant seed-based hydrogels to design drug delivery systems (DDSs) has increased due to their swellable, pH-responsive, biocompatible, biodegradable, and non-toxic nature. Herein, the chia seeds hydrogel (CSH) was extracted through an aqueous extraction method to explore its pH and salt-responsive swelling behavior and sustained release potential. The CSH was characterized using Fourier transform infrared (FT-IR) and solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance (solid/state CP-MAS 13C/NMR) spectra. Thermal analysis indicated that the CSH is a thermally stable material and decomposes in two steps. The scanning electron microscope (SEM) images of CSH witnessed the existence of microscopic channeling and a superporous nature with average pore sizes of 18 ± 11 μm (transverse cross-sections) and 23 ± 15 μm (longitudinal cross-sections). The CSH is a haemocompatible material. The CSH revealed pH and saline-responsive swelling in powder and compressed form (tablet) in the following order; distilled water (DW) > pH 7.4 > pH 6.8 > pH 1.2. Moreover, the swelling of CSH followed second-order kinetics. The swelling of CSH powder and tablets was decreased with increasing salt concentration. The pH, solvent, and saline responsive on/off switching (swelling/deswelling) results of the CSH and tablets disclosed its stimuli-responsive nature. The CSH prolonged the release of valsartan for 5 h at pH 7.4, whereas, negligible release (19.3%) was noted at pH 1.2. The valsartan release followed first-order kinetics and the non-Fickian diffusion. In conclusion, the CSH is a stimuli-responsive smart material with great potential to develop pH-sensitive and targeted DDSs.

Hypoxia and Singlet Oxygen Dual-Responsive Micelles for Photodynamic and Chemotherapy Therapy Featured with Enhanced Cellular Uptake and Triggered Cargo Delivery.

Combination therapy provides better outcomes than a single therapy and becomes an efficient strategy for cancer treatment. In this study, we designed a hypoxia- and singlet oxygen-responsive polymeric micelles which contain azo and nitroimidazole groups for enhanced cellular uptake, repaid cargo release, and codelivery of photosensitizer Ce6 and hypoxia-activated prodrug tirapazamine TPZ (DHM-Ce6@TPZ), which could be used for combining Ce6-mediated photodynamic therapy (PDT) and PDT-activated chemotherapy to enhance the therapy effect of cancer. The hypoxia- and singlet oxygen-responsive polymeric micelles DHM-Ce6@TPZ were prepared by film hydration method. The morphology, physicochemical properties, stimuli responsiveness, in vitro singlet oxygen production, cellular uptake, and cell viability were evaluated. In addition, the in vivo therapeutic effects of the micelles were verified using a tumor xenograft mice model. The resulting dual-responsive micelles not only increased the concentration of intracellular photosensitizer and TPZ, but also facilitated photosensitizer and TPZ release for enhanced integration of photodynamic and chemotherapy therapy. As a photosensitizer, Ce6 induced PDT by generating toxic singlet reactive oxygen species (ROS), resulting in a hypoxic tumor environment to activate the prodrug TPZ to achieve efficient chemotherapy, thereby evoking a synergistic photodynamic and chemotherapy therapeutic effect. The cascade synergistic therapeutic effect of DHM-Ce6@TPZ was effectively evaluated both in vitro and in vivo to inhibit tumor growth in a breast cancer mice model. The designed multifunctional micellar nano platform could be a convenient and powerful vehicle for the efficient co-delivery of photosensitizers and chemical drugs for enhanced synergistic photodynamic and chemotherapy therapeutic effect of cancer.

Smart membranes for separation and sensing.

Self-assembled membranes are extensively applied across various fields due to their non-thermal and low-carbon footprint characteristics. Recently, smart membranes with stimuli responsiveness have garnered significant attention for their ability to alter physical and chemical properties in response to different stimuli, leading to enhanced performance and a wider range of applications compared to traditional membranes. This review highlights the recent advancements in self-assembled smart membranes, beginning with widely used membrane preparation strategies such as interfacial polymerization and blending. Then it delves into the primary types of stimuli-responses, including light, pH, and temperature, illustrated in detail with relevant examples. Additionally, the review explores the latest progress in the use of smart membranes for separation and sensing, addressing the challenges and opportunities in both fields. This review offers new insights into the design of novel smart membrane platforms for sustainable development and provides a broader perspective on their commercial potential.

Protein-polymer bioconjugation, immobilization, and encapsulation: a comparative review towards applicability, functionality, activity, and stability.

Polymer-based biomaterials have received a lot of attention due to their biomedical, agricultural, and industrial potential. Soluble protein-polymer bioconjugates, immobilized proteins, and encapsulated proteins have been shown to tune enzymatic activity, improved pharmacokinetic ability, increased chemical and thermal stability, stimuli responsiveness, and introduced protein recovery. Controlled polymerization techniques, increased protein-polymer attachment techniques, improved polymer surface grafting techniques, controlled polymersome self-assembly, and sophisticated characterization methods have been utilized for the development of well-defined polymer-based biomaterials. In this review we aim to provide a brief account of the field, compare these methods for engineering biomaterials, provide future directions for the field, and highlight impacts of these forms of bioconjugation.

Polymer-based nanoparticles in targeted cancer therapy: a review

Tumors are the result of unchecked cell proliferation in the body, which leads to the complicated and widespread illness known as cancer. The formidable issue of providing effective cancer treatment has prompted scientists to investigate novel strategies. Using nanoparticles based on polymers tiny particles made of substances that are harmless for the body is one approach that shows promise. Strong anticancer medications are delivered to cancer cells directly via these nanoparticles, which also increase therapy effectiveness and reduce adverse effects on healthy cells. This study explores the field of targeted cancer treatment using polymer-based nanoparticles, using information from reliable sources such as PubMed, Web of Science, and Scopus. A strict and methodical procedure was followed in the selection of published articles to guarantee the inclusion of relevant and excellent research papers. Numerous production techniques, including self-assembly, emulsion/solvent evaporation, and nanoprecipitation, provide fine control over the size, shape, and properties of nanoparticles. Methods based on ligands, pH response, and stimuli response are used to promote enhanced selectivity and accumulation inside malignancies. Diverse advantages are provided by polymer-based nanoparticles for targeted cancer therapy. Their promise in targeted cancer therapy is highlighted by this comprehensive review, which also provides insights into design concepts, manufacturing techniques, and targeting strategies that open the door to individualized and successful therapies. The benefits of polymer-based nanoparticles are emphasized, including their strong drug-loading ability, prolonged half-life, and active targeting of cancer cells with the least amount of damage to healthy tissues. In order to maximize the usage of polymer-based nanoparticles in customized cancer therapies and eventually improve patient outcomes in the area of oncology, further investigation and clinical trials are necessary.

Advancing piezoelectric 2D nanomaterials for applications in drug delivery systems and therapeutic approaches.

Precision drug delivery and multimodal synergistic therapy are crucial in treating diverse ailments, such as cancer, tissue damage, and degenerative diseases. Electrodes that emit electric pulses have proven effective in enhancing molecule release and permeability in drug delivery systems. Moreover, the physiological electrical microenvironment plays a vital role in regulating biological functions and triggering action potentials in neural and muscular tissues. Due to their unique noncentrosymmetric structures, many 2D materials exhibit outstanding piezoelectric performance, generating positive and negative charges under mechanical forces. This ability facilitates precise drug targeting and ensures high stimulus responsiveness, thereby controlling cellular destinies. Additionally, the abundant active sites within piezoelectric 2D materials facilitate efficient catalysis through piezochemical coupling, offering multimodal synergistic therapeutic strategies. However, the full potential of piezoelectric 2D nanomaterials in drug delivery system design remains underexplored due to research gaps. In this context, the current applications of piezoelectric 2D materials in disease management are summarized in this review, and the development of drug delivery systems influenced by these materials is forecast.

Supramolecular DNA nanogels through host-guest interaction for targeted drug delivery.

DNA hydrogels have been demonstrated with the advantages of good stability, easy modification, and extraordinary biocompatibility, which enables their great application prospects in biosensing, tissue engineering, and biomedicine. Based on the host-guest recognition properties of cucurbit[8]uril (CB[8]), we proposed a general method for constructing functional supramolecular DNA nanogels. Guest molecules have been conjugated into the DNA building units, which could be further crosslinked with CB[8] to construct supramolecular DNA nanogels. At the same time, the aptamer has also been modified into the hydrogel network to achieve cell targeting. These supramolecular DNA nanogels have been demonstrated with a controllable size and multiple stimuli responses, in addition to the excellent biocompatibility, stability and good targeting drug transport ability. Such a host-guest based strategy will provide a molecular library as a "toolbox" for the functionalization of DNA nanogels.

Flexible thermoelectric CMTs/KCl/gelatin composite for a wearable pressure and temperature sensor.

Flexible sensors have promising applications in the fields of health monitoring and artificial intelligence, which have attracted much attention from researchers. However, the design and manufacture of sensors with multiple sensing functions (like simultaneously having both temperature and pressure sensing capabilities) still present a significant challenge. Here, an ionic thermoelectric sensor for synchronous temperature and pressure sensing was developed on the basis of a carbon microtubes (CMTs)/potassium chloride (KCl)/gelatin composite consisting of gelatin as the polymer matrix, CMTs as the conductive material and KCl as the ion source. The designed CMTs/KCl/gelatin composite with the good ductility (830%) and flexibility can achieve a Seebeck coefficient of 4 mV K-1 and a dual stimulus responsiveness to pressure and temperature. In addition, not only the movement of the human body (e.g., fingers, arms), but also the temperature difference between the human body and the environment, were able to be monitored by the designed CMTs/KCl/gelatin sensors. This study provides a novel strategy for the design and preparation of high-performance flexible sensors by utilizing ion-gel thermoelectric materials and promotes the research of temperature and pressure sensing technologies.

NIR-II emissive donor-acceptor-donor fluorophores for dual fluorescence bioimaging and photothermal therapy applications.

Fluorescence bioimaging with near-infrared II (NIR-II) emissive organic fluorophores has proven to be a viable noninvasive diagnostic technique. However, there is still the need for the development of fluorophores that possess increased stability as well as functionalities that impart stimuli responsiveness. Through strategic design, we can synthesize fluorophores that possess not only NIR-II optical profiles but also pH-sensitivity and the ability to generate heat upon irradiation. In this work, we employ a donor-acceptor-donor (D-A-D) design to synthesize a series of NIR-II fluorophores. Here we use thienothiadiazole (TTD) as the acceptor, 3-hexylthiophene (HexT) as the π-spacer and vary the alkyl amine donor units: N,N-dimethylaniline (DMA), phenylpiperidine (Pip), and phenylmorpholine (Morp). Spectroscopic analysis shows that all three derivatives exhibit emission in the NIR-II region with λemimax ranging from 1030 to 1075 nm. Upon irradiation, the fluorophores exhibited noticeable heat generation through non-radiative processes. The ability to generate heat indicates that these fluorophores will act as theranostic (combination therapeutic and diagnostic) agents in which simultaneous visualization and treatment can be performed. Additionally, biosensing capabilities were supported by changes in the absorbance properties while under acidic conditions as a result of protonation of the alkyl amine donor units. The fluorophores also show minimal toxicity in a human mammary cell line and with murine red blood cells. Overall, initial results indicate viable NIR-II materials for multiple biomedical applications.

Cascading responses of stimuli-responsive materials.

Responsiveness to stimuli is important in daily life: natural biological activity is governed by continuous stimulus responsiveness. The design of stimuli-responsive materials is required for the development of advanced sensing systems. Although fully controlled stimuli-responsive systems have been constructed in nature, artificial systems remain a challenge. Conventional stimuli-responsive materials show direct responsiveness to an applied stimulus (Stimulus 1), with structural changes in their molecules and organized states. This feature article focuses on cascading responses as a new concept for integrating stimuli-responsive material design. In cascading responses, an original stimulus (Stimulus 1) is converted into other stimuli (Stimulus 2, 3, …, N) through successive conversions. Stimulus N provides the eventual output response. Integration of multiple stimuli-responsive materials is required to achieve cascading responses. Although cascade, domino, and tandem chemical reactions have been reported at the molecular level, they are not used for materials with higher organized structures. In this article, we introduce functional carriers and sensors based on cascading responses as model cases. The concept of cascading responses enables the achievement of transscale responsivity and sensitivity, which are not directly induced by the original stimulus or its responsive material, for the development of advanced dynamic functional materials.

Injectable smart stimuli-responsive hydrogels: pioneering advancements in biomedical applications.

Hydrogels have established their significance as prominent biomaterials within the realm of biomedical research. However, injectable hydrogels have garnered greater attention compared with their conventional counterparts due to their excellent minimally invasive nature and adaptive behavior post-injection. With the rapid advancement of emerging chemistry and deepened understanding of biological processes, contemporary injectable hydrogels have been endowed with an "intelligent" capacity to respond to various endogenous/exogenous stimuli (such as temperature, pH, light and magnetic field). This innovation has spearheaded revolutionary transformations across fields such as tissue engineering repair, controlled drug delivery, disease-responsive therapies, and beyond. In this review, we comprehensively expound upon the raw materials (including natural and synthetic materials) and injectable principles of these advanced hydrogels, concurrently providing a detailed discussion of the prevalent strategies for conferring stimulus responsiveness. Finally, we elucidate the latest applications of these injectable "smart" stimuli-responsive hydrogels in the biomedical domain, offering insights into their prospects.

Recent advances in tunable solid-state emission based on α-cyanodiarylethenes: from molecular packing regulation to functional development.

The design and development of organic solid-state luminescent materials stand as crucial pillars within the realm of contemporary photofunctional materials. Overcoming challenges such as concentration quenching and achieving tailored luminescent properties necessitates a judicious approach to molecular structure design and the strategic utilization of diverse stimuli to modulate molecular packing patterns. Among the myriad candidates, α-cyanodiarylethenes (CAEs) emerge with distinctive solid-state luminescent attributes, capable of forming self-assembled packing structures with varying degrees of π-π stacking. This characteristic endows them with potential in the field of intelligent molecular responsive materials and optoelectronic devices. This tutorial review embarks on an exploration of design strategies geared towards attaining tunable solid-state emission through customized packing of CAEs. It explores the utilization of stimuli responses, including such as mechanical forces, light irradiation, solvent interactions, thermal influences, as well as the utilization of co-assembly methodologies. The overarching aim of this review is to provide a widely applicable platform fostering the flourishing development of modern organic photofunctional materials through integrating principles of molecular engineering, organic optoelectronics, and materials science.

Supramolecular hydrogels for wound repair and hemostasis.

The unique network characteristics and stimuli responsiveness of supramolecular hydrogels have rendered them highly advantageous in the field of wound dressings, showcasing unprecedented potential. However, there are few reports on a comprehensive review of supramolecular hydrogel dressings for wound repair and hemostasis. This review first introduces the major cross-linking methods for supramolecular hydrogels, which includes hydrogen bonding, electrostatic interactions, hydrophobic interactions, host-guest interactions, metal ligand coordination and some other interactions. Then, we review the advanced materials reported in recent years and then summarize the basic principles of each cross-linking method. Next, we classify the network structures of supramolecular hydrogels before outlining their forming process and propose their potential future directions. Furthermore, we also discuss the raw materials, structural design principles, and material characteristics used to achieve the advanced functions of supramolecular hydrogels, such as antibacterial function, tissue adhesion, substance delivery, anti-inflammatory and antioxidant functions, cell behavior regulation, angiogenesis promotion, hemostasis and other innovative functions in recent years. Finally, the existing problems as well as future development directions of the cross-linking strategy, network design, and functions in wound repair and hemostasis of supramolecular hydrogels are discussed. This review is proposed to stimulate further exploration of supramolecular hydrogels on wound repair and hemostasis by researchers in the future.

Stimuli-responsive and self-healing supramolecular Zn(II)-guanosine metal-organic gel for Schottky barrier diode application.

Spontaneous formation of a supramolecular metal-organic hydrogel using unsubstituted guanosine as a ligand and Zn2+ ions is reported. Guanosine, in the presence of NaOH, self-assembled into a stable G-quadruplex structure, which underwent crosslinking through Zn2+ ions to afford a stable hydrogel. The gel has been characterized using several spectroscopic as well as microscopic studies. The hydrogel demonstrated excellent stimuli responsiveness towards various chemicals and pH. Furthermore, the gel exhibited intrinsic thixotropic behavior and showed self-healing and injectable properties. The optical properties of the Zn-guanosine metallo-hydrogel suggested a semiconducting nature of the gel, which has been exploited for fabricating a thin film device based on a Schottky diode interface between metal and a semiconductor. The fabricated device shows excellent charge transport characteristics and linear rectifying behavior. The findings are likely to pave the way for newer research in the area of soft electronic devices fabricated using materials synthesized by employing simple biomolecules.

Blue Light Exposure Caused Large-Scale Transcriptional Changes in the Abdomen and Reduced the Reproductive Fitness of the Fall Armyworm Spodoptera frugiperda.

In the present study, we found that blue light stress negatively affected the development periods, body weight, survival and reproduction of Spodoptera frugiperda, and it showed a dose-dependent reaction, as longer irradiation caused severer effects. Further transcriptome analysis found blue light stress induced fast and large-scale transcriptional changes in the head, thorax and, particularly, the abdomen of female S. frugiperda adults. A functional enrichment analysis indicated that shorter durations of blue light irradiation induced the upregulation of more stress response- and defense-related genes or pathways, such as abiotic stimuli detection and response, oxidative stress, ion channels and protein-kinase-based signal pathways. In the abdomen, however, different durations of blue-light-exposure treatments all induced the downregulation of a large number genes and pathways related to cellular processes, metabolism, catalysis and reproduction, which may be a trade-off between antistress defense and other processes or a strategy to escape stressful conditions. These results indicate irradiation duration- and tissue-specific blue light stress responses and consequences, as well as suggest that the stress that results in transcriptional alterations is associated with the stress that causes a fitness reduction in S. frugiperda females.

Optimized DOX Drug Deliveries via Chitosan-Mediated Nanoparticles and Stimuli Responses in Cancer Chemotherapy: A Review.

Chitosan nanoparticles (NPs) serve as useful multidrug delivery carriers in cancer chemotherapy. Chitosan has considerable potential in drug delivery systems (DDSs) for targeting tumor cells. Doxorubicin (DOX) has limited application due to its resistance and lack of specificity. Chitosan NPs have been used for DOX delivery because of their biocompatibility, biodegradability, drug encapsulation efficiency, and target specificity. In this review, various types of chitosan derivatives are discussed in DDSs to enhance the effectiveness of cancer treatments. Modified chitosan-DOX NP drug deliveries with other compounds also increase the penetration and efficiency of DOX against tumor cells. We also highlight the endogenous stimuli (pH, redox, enzyme) and exogenous stimuli (light, magnetic, ultrasound), and their positive effect on DOX drug delivery via chitosan NPs. Our study sheds light on the importance of chitosan NPs for DOX drug delivery in cancer treatment and may inspire the development of more effective approaches for cancer chemotherapy.

Recent progress on solid-state cross-polarization (CP)/magic angle spinning (MAS) NMR measurements: a tool for investigating structural changes in stimuli-responsive organic compounds

Abstract Over the years, cross-polarization/magic angle sample spinning (CP/MAS) NMR has proven to be valuable for obtaining detailed structural information in solid-state materials. A notable advantage of this technique is that it does not require a well-organized arrangement in the sample such as single crystals. Consequently, even materials with low crystallinity such as amorphous substances can be analyzed to obtain structural information. In recent years, research on externally stimuli-responsive molecules utilizing crystal phase transitions has attracted attention. Certain aryl disilane and oligosilane compounds exhibit external stimulus responsiveness even in the crystalline state due to the hindered rotation of the Si–Si σ bond and sparse crystal packing. Understanding the structural alternations linked to changes in physical properties is crucial for investigation of the responsiveness. High-resolution CP/MAS NMR spectra are particularly suitable for analyzing crystalline polymorphs, crystal phase transitions, and solid-state conformations. In this report, we present the results of natural abundance 13C, 29Si, and 15N CP/MAS NMR experiments conducted on externally stimuli-responsive disilane-bridged molecules. These measurements provide information on the structure before and after crystal phase transitions, as well as the amorphous state. A comprehensive analysis of our findings is essential for elucidating alternations in the structure and arrangement of crystalline materials under external stimuli.

Liquid Crystalline Network Microstructures for Stimuli Responsive Labels with Multi-Level Encryption.

Two-photon direct laser writing enables the fabrication of shape-changing microstructures that can be exploited in stimuli responsive micro-robotics and photonics. The use of Liquid Crystalline Networks (LCN) allows to realize 3D micrometric objects that can contract along a specific direction in response to stimuli, such as temperature or light. In this paper, the fabrication of free-standing LCN microstructures is demonstrated as graphical units of a smart tag for simple physical and optical encryption. Using an array of identical pixels, information can be hidden to the observer and revealed only upon application of a specific stimulus. The reading mechanism is based on the shape-change of each pixel under stimuli and their color that combinetogether in a two-level encryption label. Once the stimulus is removed, the pixels recover their original shape and the message remains completely hidden. Therefore, an opto-mechanical equivalent of an "invisible ink" is realized. This new concept paves the way for introducing enhanced functionalities in smart micro-systems within a single lithography step, spanning from storage devices with physical encryption to complex motion actuators.