Stimuli-responsive Polymers Research Articles

Colorimetric Fabry-Pérot Sensor with Hetero-Structured Dielectric for Humidity Monitoring.

A full-color colorimetric humidity sensor with high brightness is proposed by using a hetero-structured dielectric film in a metal-insulator-metal (MIM) resonator. A humidity-responsive polymer is designed to graft on top of a metal-organic frameworks (MOFs) thin film (MOFs-Polymer) as insulator layer in the resonator. Programmable tuning of reflected color is achieved by controlling the polymer thicknesses, and finite difference time domain simulation of light-matter interactions at subwavelength scales proves the dependence of the reflected wavelength on dielectric layer thickness of the resonator. Vivid full-color changing is realized during tracking humidity process due to swelling of the stimuli-responsive polymer. Ultrafast response (≈0.75 s) is achieved for tracking trace H2O from H2O/methanol mixture, which is ≈104 faster than that of the pure polymer-based MIM resonator. Meanwhile, the study observes significant spectral redshift because the porous MOFs film facilitates the preconcentration of external stimulus and improves the detection sensitivity of the resonator. Further, double-channel anti-counterfeiting multiplexing imaging is devised on the MIM resonator by photomask technology. Patterned encoding for security label is achieved on the MIM resonator by engineering humidity-tunable pixels of Au/MOFs-Polymer/Au and humidity-invalid pixels of Au/MOFs/Au.

Antagonistic-contracting high-power photo-oscillators for multifunctional actuations.

High-power autonomous soft actuators are in high demand yet face challenges related to tethered power and dedicated control. Light-driven oscillation by stimuli-responsive polymers allows for remote energy input and control autonomy, but generating high output power density is a daunting challenge requiring an advanced material design principle. Here, inspired by the flight muscle structure of insects, we develop a self-oscillator based on two antagonistically contracting photo-active layers sandwiching an inactive layer. The actuator produces an output power density of 33 W kg-1, 275-fold higher than other configurations and comparable to that of insects. Such oscillators allow for broad-wavelength operation and multifunction integration, including proprioceptive actuation and energy harvesting. We demonstrate high-performance flapping motion enabling various locomotion modes, including a wing with a thrust-to-weight ratio of 0.32. This work advances autonomous, sustained and untethered actuators for powerful robotics.

Polymer-Based Optical Guided-Wave Biomedical Sensing: From Principles to Applications

Polymer-based optical sensors represent a transformative advancement in biomedical diagnostics and monitoring due to their unique properties of flexibility, biocompatibility, and selective responsiveness. This review provides a comprehensive overview of polymer-based optical sensors, covering the fundamental operational principles, key insights of various polymer-based optical sensors, and the considerable impact of polymer integration on their functional capabilities. Primary attention is given to all-polymer optical fibers and polymer-coated optical fibers, emphasizing their significant role in “enabling” biomedical sensing applications. Unlike existing reviews focused on specific polymer types and optical sensor methods for biomedical use, this review highlights the substantial impact of polymers as functional materials and transducers in enhancing the performance and applicability of various biomedical optical sensing technologies. Various sensor configurations based on waveguides, luminescence, surface plasmon resonance, and diverse types of polymer optical fibers have been discussed, along with pertinent examples, in biomedical applications. This review highlights the use of biocompatible, hydrophilic, stimuli-responsive polymers and other such functional polymers that impart selectivity, sensitivity, and stability, improving interactions with biological parameters. Various fabrication techniques for polymer coatings are also explored, highlighting their advantages and disadvantages. Special emphasis is given to polymer-coated optical fiber sensors for biomedical catheters and guidewires. By synthesizing the latest research, this review aims to provide insights into polymer-based optical sensors’ current capabilities and future potential in improving diagnostic and therapeutic outcomes in the biomedical field.

Four-Dimensional Printing of Multi-Material Origami and Kirigami-Inspired Hydrogel Self-Folding Structures.

Four-dimensional printing refers to a process through which a 3D printed object transforms from one structure into another through the influence of an external energy input. Self-folding structures have been extensively studied to advance 3D printing technology into 4D using stimuli-responsive polymers. Designing and applying self-folding structures requires an understanding of the material properties so that the structural designs can be tailored to the targeted applications. Poly(N-iso-propylacrylamide) (PNIPAM) was used as the thermo-responsive material in this study to 3D print hydrogel samples that can bend or fold with temperature changes. A double-layer printed structure, with PNIPAM as the self-folding layer and polyethylene glycol (PEG) as the supporting layer, provided the mechanical robustness and overall flexibility to accommodate geometric changes. The mechanical properties of the multi-material 3D printing were tested to confirm the contribution of the PEG support to the double-layer system. The desired folding of the structures, as a response to temperature changes, was obtained by adding kirigami-inspired cuts to the design. An excellent shape-shifting capability was obtained by tuning the design. The experimental observations were supported by COMSOL Multiphysics® software simulations, predicting the control over the folding of the double-layer systems.

Chiral Co-assembly Based on a Stimuli-Responsive Polymer towards Amplified Full-Color Circularly Polarized Luminescence.

Stimuli-responsive circularly polarized luminescence (CPL) materials have been attaching wide attention in the field of optical information storage and encryption, while still facing the challenge of the realization of highluminescence dissymmetryfactors (glum). This work presents a pair of stimuli-responsive chiral co-assemblies P7R3 and P7S3 by combining polymer PFIQ containing iso-quinoline units with chiral inducers. The obtained chiral co-assemblies can reversibly undergo significant modification in CPL behavior under trifluoroacetic acid (TFA) fumigation and annealing treatment, with the |glum| values exhibiting a reversible shift between 0.2 and 0.3. Moreover, the chiral co-assemblies before TFA fumigating can effectively induce achiral emitters to generate intense full-color CPL signals through CPL energy transfer (CPL-ET), with the corresponding |glum| values larger than 0.2. Moreover, information encryption and decryption as well as a multi-level logic gates application are achieved by leveraging the reversible stimuli-responsive CPL activity of the chiral co-assembly. This work provides a new perspective for the construction of stimuli-responsive chiral luminescent materials with large |glum| values and the activation of CPL behavior in achiral emitters.

Water vapor responsiveness of chitosan: An experimental and simulation analysis.

Stimuli-responsive polymers have gained significant research interest in recent years owing to their potential applications in diverse areas. Here, we present a study on the actuation characteristics of chitosan-based free-standing films that exhibit full reversibility and repeatability in response to water vapor exposure. The effect of pH of the water and the degree of cross-linking of the chitosan films on the actuation performance is studied. In the case of free-standing polymer film-based actuators, the primary driving force behind actuation is understood to be the differential strain induced by the gradient in volume changes across the thickness of the film. To understand it further, we conducted full atomistic molecular dynamics simulation studies to explore water absorption and adsorption into the chitosan matrix. Our simulations revealed an accumulation of water molecules in the surface layer that rapidly desorb when shielded from water vapor. Furthermore, estimates of the energy gain resulting from the adsorption of water on the surface suggest that it is adequate to drive the shape change of the actuator when subjected to asymmetric exposure to water vapor. This finding supports the fact that the adsorbed layer of water on the surface of the chitosan film plays a role in actuation.

Stimulus-responsive magnetic enzyme-encapsulated coordination polymer for the potential field monitoring of alkaline phosphatase using personal glucometer

Stimulus-responsive magnetic enzyme-encapsulated coordination polymer for the potential field monitoring of alkaline phosphatase using personal glucometer

Preparation of Gradient HEA-DAC/HPA Hydrogels by Limited Domain Swelling Method.

Hydrogels are widely used in biological dressing, tissue scaffolding, drug delivery, sensors, and other promising applications owing to their water-rich soft structures, biocompatibility, and adjustable mechanical properties. However, most of the conventional hydrogels are isotropic. The anisotropic structures existed widely in the organizational structure of plants and animals, which played a crucial role in biological systems. In this work, a method of limited domain swelling to prepare anisotropic hydrogels is proposed. Through spatially controlled swelling, the extension direction of hydrogels can be limited by a tailored mold, further achieving anisotropic hydrogels with concentration gradients. The external solution serves as a swelling solution to promote swelling and extension of the hydrogel matrix in a mold which can control the extension direction. Due to the diversity of external solutions, the method can be applied to prepare a variety of stimulus-responsive polymers. The limited domain swelling method is promising for the construction of anisotropic hydrogels with different structures and properties.

A New Class of Mechano-Responsive PolyureThane Via Anthracene -TAD Diels-Alder (DA) Click Chemistry.

Smart or stimuli-responsive polymers have garnered significant interest in the scientific community due to their response to different stimuli like pH, temperature, light, mechanical force, etc. Mechanophoric polymer is an intriguing class of smart polymers that respond to external mechanical force by producing fluorescent moieties and can be utilized for damage detection and stress-sensing assessment. In recent reports on mechanophoric polymers, different mechanophoric motifs such as spiropyran, rhodamine, coumarin, etc. are explored. This investigation reports a new kind of mechanophoric polyurethane (PU) adduct based on Diels-Alder (DA) click chemistry. Here, an anthracene(An)-end capped tri-armed urethane system is synthesized, followed by a DA reaction using bis-(1,2,4-triazoline-3,5-dione) (bis-TAD) derivative. The incorporation of bis-TAD in the urethane system renders the anthracene inactive ("turn-off") by dismantling its conjugation as a result of a successful DA reaction. The soft PU translated into a harder material through bis-TAD linkages between polymer chains as evident from nanoindentation (NINT) analysis. The resulting material reverts back to its fluorescent "turned-on" mode owing to a force-accelerated retro-Diels-Alder (r-DA) reaction. Besides the mechanophoric attributes, the material demonstrates self-healing behavior examined by microscopic investigations. This innovative approach can be a potential route to design responsive polymers with dynamic functionalities for advanced material applications.

Competence of Carbonaceous Fibers/Nanofillers (Graphene, Carbon Nanotube) Reinforced Shape Memory Composites/Nanocomposites Towards Aerospace—Existent Status and Expansions

Abstract Shape memory or stimuli responsive polymers have established a unique grouping of smart materials. The technical merit of these polymers has been evaluated in aerospace sector, since last few decades. Particularly, the stimuli responsive polymers render inherent competences to recuperate the structural damages in exterior/interior space architectures. In this context, both the thermoplastics as well as thermosetting polymers depicted essential stimuli responsive behaviour. As interpreted in this state-of the-art review, the carbonaceous reinforcement like carbon fibers and nano-reinforcements including nanocarbons (graphene, carbon nanotube) have been employed in the shape recovering matrices. The performance of ensuing shape retrieving aerospace materials was seemed to be reliant on the polymer chain crosslinking effects, filler/nanofiller dispersal/alignment, microstructural specs, interfacial contour and interactions, and processing techniques used. Consequently, the shape actuations of polymer/carbon fiber composites were found to be instigated and upgraded through the inclusion of nanocarbon nano-additives. The ensuing high-tech shape memory composites/nanocomposites have anomalous significance for various aero-structural units (fuselage, wings, antennas, engines, etc.) due to prevention of possible thermal/shock/impact damages. Future implications of carbonaceous shape memory composites/nanocomposites in aerospace demands minimizing the structure-property-performance challenges and large scale fabrication for industrial scale utilizations. In this way, deployment of carbonaceous nanofiller/filler based composites revealed enormous worth due to low density, anti-fatigue/wear, anti-corrosion, non-flammability, self-healing, and extended durability and long life operations. However, there are certain challenges associated with the use of nanocarbons and ensuing nanocomposites in this field markedly the adoption of appropriate carbon fiber coating technique, aggregation aptitude of nanocarbons, additional processing steps/cost, nanoparticle initiated invisible defects/voids, difficulty in machinability operations due to presence of nanoparticles, and corrosion risk of composite structures in contact with metal surfaces. By overcoming these hinderances, nanoparticles modified carbon fiber based composites can be promising towards a new look of upcoming modernized aerospace industry.

Stimuli-Responsive Polymers at the Interface with Biology.

There has been growing interest in polymeric systems that break down or undergo property changes in response to stimuli. Such polymers can play important roles in biological systems, where they can be used to control the release of therapeutics, modulate imaging signals, actuate movement, or direct the growth of cells. In this Perspective, after discussing the most important stimuli relevant to biological applications, we will present a selection of recent exciting developments. The growing importance of stimuli-responsive polysaccharides will be discussed, followed by a variety of stimuli-responsive polymeric systems for the delivery of small molecule drugs and nucleic acids. Switchable polymers for the emerging area of therapeutic response measurement in theranostics will be described. Then, the diverse functions that can be achieved using hydrogels cross-linked covalently, as well as by various dynamic approaches will be presented. Finally, we will discuss some of the challenges and future perspectives for the field.

A Comprehensive Review of Stimuli-Responsive Smart Polymer Materials-Recent Advances and Future Perspectives.

Today, smart materials are commonly used in various fields of science and technology, such as medicine, electronics, soft robotics, the chemical industry, the automotive field, and many others. Smart polymeric materials hold good promise for the future due to their endless possibilities. This group of advanced materials can be sensitive to changes or the presence of various chemical, physical, and biological stimuli, e.g., light, temperature, pH, magnetic/electric field, pressure, microorganisms, bacteria, viruses, toxic substances, and many others. This review concerns the newest achievements in the area of smart polymeric materials. The recent advances in the designing of stimuli-responsive polymers are described in this paper.

Mechanochromic Displays Based on Photoswitchable Cholesteric Liquid Crystal Elastomers

Stimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color‐changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photo‐switch. The photo‐switch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain independently. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photo‐switch approach to prepare stimuli responsive optical polymers imprinted with color‐changing pictures of unprecedented complexity.

Mechanochromic Displays Based on Photoswitchable Cholesteric Liquid Crystal Elastomers.

Stimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color-changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photo-switch. The photo-switch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain independently. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photo-switch approach to prepare stimuli responsive optical polymers imprinted with color-changing pictures of unprecedented complexity.

The Role of Surface Energy and Wettability in Polymer-Based Drug Delivery Systems: Enhancing Bioadhesion and Drug Release Efficiency

Polymer-based drug delivery systems are pivotal in advancing the precision and efficacy of modern therapeutics. Among the key factors influencing these systems, surface energy and wettability are crucial in determining their interaction with biological tissues and drug release behavior. Surface energy, which governs the adhesive properties of the polymers, plays a significant role in bioadhesion—a critical aspect for drug delivery routes that require prolonged contact with biological surfaces, such as mucosal membranes. Wettability, the extent to which a polymer surface can be wetted by biological fluids, influences both drug loading efficiency and release kinetics. Hydrophilic polymers, characterized by high wettability, typically facilitate rapid drug release, whereas hydrophobic polymers, with low wettability, offer controlled, prolonged release profiles. Additionally, the balance between hydrophilicity and hydrophobicity is essential for optimizing drug-polymer interactions, particularly in systems designed for sustained or targeted drug delivery. Advances in surface modification techniques have enabled precise control over these parameters, allowing for the customization of polymers to meet specific therapeutic requirements. This review discusses the interplay between surface energy, wettability, and drug delivery performance, highlighting how these properties have been manipulated to enhance bioadhesion, drug retention, and release profiles. The review also addresses the challenges in designing polymer wettability, such as maintaining stability, scalability, and regulatory compliance. Finally, it explores emerging trends, including stimuli-responsive polymers and nanotechnology integration, which hold promise for the next generation of drug delivery systems that are more efficient, targeted, and patient-specific, than current systems.

Stimuli-Responsive Polymers for Advanced 19F Magnetic Resonance Imaging: From Chemical Design to Biomedical Applications.

Fluorine magnetic resonance imaging (19F MRI) is a rapidly evolving research area with a high potential to advance the field of clinical diagnostics. In this review, we provide an overview of the recent progress in the field of fluorinated stimuli-responsive polymers applied as 19F MRI tracers. These polymers respond to internal or external stimuli (e.g., temperature, pH, oxidative stress, and specific molecules) by altering their physicochemical properties, such as self-assembly, drug release, and polymer degradation. Incorporating noninvasive 19F labels enables us to track the biodistribution of such polymers. Furthermore, by triggering polymer transformation, we can induce changes in 19F MRI signals, including attenuation, amplification, and chemical shift changes, to monitor alterations in the environment of the tracer. Ultimately, this review highlights the emerging potential of stimuli-responsive fluoropolymer 19F MRI tracers in the current context of polymer diagnostics research.

A Review of the Current State of Research and Future Prospectives on Stimulus-Responsive Shape Memory Polymer Composite and Its Blends

A Review of the Current State of Research and Future Prospectives on Stimulus-Responsive Shape Memory Polymer Composite and Its Blends

Multiple Stimuli-Responsive Color-Changing Polymer Materials for Reversible Writing and Anti-Counterfeiting.

Polymer materials with multiple stimuli-responsive properties have demonstrated many potential and practical applications. By covalently introducing spiropyran (SP1) and spirothiopyran (STP) into the polyurethane backbone, photochromic, mechanochromic, and thermally discolored polymer materials have been prepared. In this work, we report for the first time that white light (violet, blue, and green light) above a certain intensity can activate STP to green color. Based on the above discovery, the polyurethane with SP1 and STP can exhibit reversible three-color changes (brown, green, and purple) in response to four stimuli: ultraviolet irradiation, white light irradiation, mechanical stress, and heat. The color-changing polymer materials have high color contrast and excellent reversibility, and can be used for reversible writing, anticounterfeiting and information encryption, etc.

Effects of Topology Optimization in Multimaterial 3D Bioprinting of Soft Actuators

Recently, there has been a proliferation of soft robots and actuators that exhibit improved capabilities and adaptability through three-dimensional (3D) bioprinting. Flexibility and shape recovery attributes of stimuli-responsive polymers as the main components in the production of these dynamic structures enable soft manipulations in fragile environments, with potential applications in biomedical and food sectors. Topology optimization (TO), when used in conjunction with 3D bioprinting with optimal design features, offers new capabilities for efficient performance in compliant mechanisms. In this paper, multimaterial TO analysis is used to improve and control the bending performance of a bioprinted soft actuator with electrolytic stimulation. The multimaterial actuator performance is evaluated by the amplitude and rate of bending motion and compared with the single material printed actuator. The results demonstrated the efficacy of multimaterial 3D bioprinting optimization for the rate of actuation and bending.

Beyond Traditional Stimuli: Exploring Salt-Responsive Bottlebrush Polymers-Trends, Applications, and Perspectives.

Bottlebrush polymers represent an important class of high-density side-chain-grafted polymers traditionally with high molecular weights, in which one or more polymeric side chains are tethered to each repeating unit of a linear polymer backbone, such that these macromolecules look like "bottlebrushes". The arrangement of molecular brushes is determined by side chains located at a distance considerably smaller than their unperturbed dimensions, leading to substantial monomer congestion and entropically unfavorable extension of both the backbone and the side chains. Traditionally, the conformation and physical properties of polymers are influenced by external stimuli such as solvent, temperature, pH, and light. However, a unique stimulus, salt, has recently gained attention as a means to induce shape changes in these molecular brushes. While the stimulus has been less researched to date, we see that these systems, when stimulated with salts, have the potential to be used in various engineering applications. This potential stems from the unique properties and behaviors these systems show when exposed to different salts, which could lead to new solutions and improvements in engineering processes, thus serving as the primary motivation for this narrative, as we aim to explore and highlight the various ways these systems can be utilized and the benefits they could bring to the field of engineering. This Review aims to introduce the concept of stimuli-responsive bottlebrush polymers, explore the evolutionary trajectory, delve into current trends in salt-responsive bottlebrush polymers, and elucidate how these polymers are addressing a variety of engineering challenges.