The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Mechanistic insights into hydration-driven shape memory response in keratinous avian feather structures

Keratinous materials found in the feather shafts of flying birds possess impressive mechanical attributes, combining excellent strength-to-weight balance, toughness, and more. In this study, we investigate the shape memory effect in bird feather shafts, examining its underlying design principles as templates for bioinspired shape memory composites. Through analytical and computational analysis, we aim to uncover the underlying rules and design guidelines based on stimulus-induced softening (pertaining to strength and/or stiffness) and swelling (pertaining to expansion in volume). More specifically, we study a one-dimensional case to examine the synergistic relationship between the matrix and fibers inside the feather structure. We propose three distinct micro-mechanical modeling approaches to evaluate the contribution of each hydration-induced effect-softening, swelling, and the combined action of both. In all models, the matrix is considered to be an elastic-perfectly plastic material that is sensitive to hydration, while the fibers are treated as purely elastic and unaffected by hydration. The findings of the study provide informative insights into the nuanced nature of swelling within the material, highlighting that its desirability is dependent on specific conditions and circumstances. Furthermore, we find that the softening component plays a large pivotal role in driving the process of shape recovery. Using the proposed analytical framework and design principles, we develop a conceptual feather shaft-like composite, followed by demonstrating its tunability in degree of shape recovery and its versatility in selecting constituent base material components. This research offers valuable core framework for exploring and designing advanced bioinspired shape memory materials while eliminating the need for traditionally active shape memory components, holding promising potential for actuation, deployment, and morphing purposes. STATEMENT OF SIGNIFICANCE: This study investigates the shape-memory effect in bird feather shafts, offering bioinspired strategies for designing advanced shape-memory composites. Unlike conventional materials, which often rely on external stimuli or active components, our research focuses on hydration-driven mechanisms-specifically, matrix softening and swelling. Through micro-mechanical modeling, we demonstrate that softening is the key driver of shape recovery, while swelling plays a secondary role under specific conditions. These insights provide new, passive design principles for creating tunable shape-memory composites without the need for traditional active components. The findings have broad implications for applications in actuation, morphing, and reconfigurable systems, where material adaptability is crucial.

Construction of magnetic response nanocellulose particles to realize smart antibacterial of Pickering emulsion

Smart antibacterial Pickering emulsion can respond to the stimulation of environmental conditions to control the release of antibacterial agents, protecting the quality and safety of food. In this study, Fe3O4 was grafted on the cellulose nanocrystal (CNC) via ultrasound-assisted in situ co-precipitation to synthesize the magnetic cellulose nanocomposite particles. When the ratio of FeCl3 and FeCl2 was 1.5:1, the prepared particles CNC/Fe1.5 exhibited the maximum saturation magnetization intensity of 54.98 emu/g and good emulsion stability, which was used to emulsify oregano essential oil (OEO) to fabricate smart antibacterial Pickering emulsion with magnetically responsive ability. The emulsion with the oil-water ratio of 3:7 and the particle concentration of 0.3 wt% showed the excellent stability and sensitive responsiveness of magnetic. The OEO released rapidly within 0-8 h followed by the slow release when the emulsion was stimulated by 0.2 T, 0.4 T and 0.6 T magnetic field. The antibacterial rate of the emulsion was close to 100 % against both E. coli and L. monocytogenes at magnetic field with 0.4 T and 0.6 T in 12 h, achieving the smart antimicrobial. The prepared smart antibacterial Pickering emulsion would provide a novel material and have the potential in food packaging.

Photoacids and Photobases: Applications in Functional Dynamic Systems

Brønsted photoacids and photobases are a unique class of molecules that undergo a major change in their pKa values between their ground and excited states, resulting in donating or accepting a proton, respectively, but only after light excitation. This property of photoacids/photobases makes them an attractive tool for light-gating various dynamic processes. Here, we review the use of this property to manipulate functional dynamic systems with light. We discuss how a proton transfer event that can happen upon light excitation from a photoacid to a chemical moiety of a certain system or, vice versa, from the system to a photobase, can result in a shift in the equilibrium of the system, resulting in some dynamicity. We detail various systems, including self-assembly processes of nanostructures, self-propulsion of droplets, catalysis for hydrogen evolution or CO2 capturing, nanotechnological devices based on enzymatic processes, and changes in proton-conducting ionophores and materials. We detail the basic guidelines for using Brønsted photoacids and photobases in a desired system and conclude with the current technological gaps in further using these molecules.

Azobenzene-Functionalized Semicrystalline Liquid Crystal Elastomer Springs for Underwater Soft Robotic Actuators

As actuated devices become smaller and more complex, there is a need for smart materials and structures that directly function as complete mechanical units without an external power supply. The strategy uses light-powered, twisted, and coiled azobenzene-functionalized semicrystalline liquid crystal elastomer (AC-LCE) springs. This twisting and coiling, which has previously been used for only thermally, electrochemically, or absorption-powered muscles, maximizes uniaxial and radial actuation. The specially designed photochemical muscles can undergo about 60% tensile stroke and provide 15 kJ m-3 of work capacity in response to light, thus providing about three times and two times higher performance, respectively, than previous azobenzene actuators. Since this actuation is photochemical, driven by ultraviolet (UV) light and reversed by visible light, isothermal actuation can occur in a range of environmental conditions, including underwater. In addition, photoisomerization of the AC-LCEs enables unique latch-like actuation, eliminating the need for continuous energy application to maintain the stroke. Also, as the light-powered muscles processed to be either homochiral or heterochiral, the direction of actuation can be reversed. The presented approach highlights the novel capabilities of photochemical actuator materials that can be manipulated in untethered, isothermal, and wet environmental conditions, thus suggesting various potential applications, including underwater soft robotics.

Zwitterion Interlocked Diarylethene Molecules Order, Unconnected Diarylethene Molecules Disorder

A diarylethene-based zwitterionic molecule (DZM) is newly synthesized for the development of smart films exhibiting reversible color change and switchable ionic conductivity in response to external light stimuli. This dual molecular building block is constructed through zwitterionic interlocking and strong phase separation between the dendron-shaped aliphatic tails and the diarylethene head. Uniaxial shear coating and molecular self-assembly result in anisotropically oriented nanostructures, which are further solidified through photopolymerization. In the absence of zwitterionic interlocking, DZM fails to form ordered structures and remains disordered. The anisotropically oriented nanostructures of DZM exhibit polarization-dependent photochromic properties despite the inherent low anisotropy of a single diarylethene chromophore. Structural analysis reveals that the zwitterion-interlocked molecular building block self-assemble into nanocolumns that align uniaxially during the shear coating process. Alternating ultraviolet and visible light reversibly switches the ionic conductivity of the DZM thin film and a change in color is observed due to the photoisomerization of the diarylethene chromophore. Utilizing the polarization-dependent photochromic properties, light-sensitive smart thin films are demonstrated with potential applications in anti-counterfeiting labels and sensors.

Thoughts on the Rational Design of MOF-Guest Interactions for Future Intelligent Materials

The MOF-guest relationship is broken down in elementary phases, descriptors, and parameters. These descriptors and parameters allow precise descriptions of processes, whether they occur at the point when the guest enters the MOF, during the stay, or at the point of exiting. Description of these three phases is possible according to the location of the guest inside the MOF, the activity between MOF and guest, whether stimuli can be used, and whether a selective action can be exercised. The vocabulary provided herein can be useful to better formulate requirements when designing host-guest interactions in, and building new classes of, intelligent materials.

Recent Advances of Stimuli-Responsive Liquid-Liquid Interfaces Stabilized by Nanoparticles

Liquid-liquid interfaces offer highly controlled, flexible, and adaptable platforms for precise molecular assemblies, enabling the construction of sophisticated functional materials. Interfacial assemblies of specific nanoparticles (NPs) and ligands can alter their physicochemical states under external stimuli, leading to macroscopic dynamic transformations at the interface. This Review summarizes and analyzes the recent advances of the assembly and disassembly behaviors of various stimuli-responsive nanoparticle surfactants (NPSs) at liquid-liquid interfaces, focusing on their responsive behaviors when exposed to external stimuli and the interaction forces between interfacial molecules. Additionally, we outline recent advancements in applications such as reconfigurable all-liquid devices, all-liquid 3D printing, and chemical reaction platforms. Finally, we discuss current challenges and future prospects for the development of applications in this rapidly evolving field.

Wearable and Implantable Soft Robots

Soft robotics presents innovative solutions across different scales. The flexibility and mechanical characteristics of soft robots make them particularly appealing for wearable and implantable applications. The scale and level of invasiveness required for soft robots depend on the extent of human interaction. This review provides a comprehensive overview of wearable and implantable soft robots, including applications in rehabilitation, assistance, organ simulation, surgical tools, and therapy. We discuss challenges such as the complexity of fabrication processes, the integration of responsive materials, and the need for robust control strategies, while focusing on advances in materials, actuation and sensing mechanisms, and fabrication techniques. Finally, we discuss the future outlook, highlighting key challenges and proposing potential solutions.

Shape-Regulated Motion and Energy Conversion of Polyelectrolyte Membrane Actuators

Smart actuators hold great potential in soft robotics and sensors, but their movement at the fluid interface is less understood and controlled, hindering their performances and applications in complicated fluids. Here an ethanol-containing polyelectrolyte actuator is prepared that demonstrates excellent actuating performance via the Marangoni effect. These actuators exhibit enduring (17 min), repeatable (50 cycles), and autonomous motion on the water surface. More importantly, the motion of actuators are dependent on their shapes. Polygonal actuators with more edges exhibit round motion attached to walls of containers, while the actuators with few edges move randomly. On the basis of this property, the circular actuators can pass through pipe bends with S-shaped complex geometry. These unique advantages lend the actuators to successful applications in wireless sensing (standard 0-5 V level signals) for locating obstructions inside invisible pipes and continuous energy harvesting (7700 nC per cycle) for micro mechanical energy.

Transcriptional regulation of living materials via extracellular electron transfer

Engineered living materials combine the advantages of biological and synthetic systems by leveraging genetic and metabolic programming to control material-wide properties. Here, we demonstrate that extracellular electron transfer (EET), a microbial respiration process, can serve as a tunable bridge between live cell metabolism and synthetic material properties. In this system, EET flux from Shewanella oneidensis to a copper catalyst controls hydrogel cross-linking via two distinct chemistries to form living synthetic polymer networks. We first demonstrate that synthetic biology-inspired design rules derived from fluorescence parameterization can be applied toward EET-based regulation of polymer network mechanics. We then program transcriptional Boolean logic gates to govern EET gene expression, which enables design of computational polymer networks that mechanically respond to combinations of molecular inputs. Finally, we control fibroblast morphology using EET as a bridge for programmed material properties. Our results demonstrate how rational genetic circuit design can emulate physiological behavior in engineered living materials.

Laser-Printed All-Carbon Responsive Material and Soft Robot

Responsive materials and actuators are the basis for the development of various leading-edge technologies but have so far mostly been designed based on polymers, incurring key limitations related to sensitivity and environmental tolerance. This work reports a new responsive material, laser-printed carbon film (LPCF), produced via direct laser transformation of a liquid organic precursor and consists of graphitic and amorphous carbons. The high activity of amorphous carbon combined with the dual-gradient structure enables the LPCF to have a actuation speed of 9400° s-1 in response to the stimulus of organic vapor. LPCF exhibits a conductivity of 950 S m-1 and excellent resistance to various extreme environmental conditions, which are unachievable for polymer-based materials. Additionally, an LPCF-based all-carbon soft robot that can mimic the complex continuous backward somersaulting motions without manual intervention is constructed. The locomotion velocity of the robot reaches a value of 1.19 BL s-1, which is almost one to two orders of magnitude faster than that of reported soft robots. This work not only offers a new paradigm for highly responsive materials but also provides a great design and engineering example for the next generation of biomimetic robots with life-like performance.

Stimuli-responsive biomaterials: smart avenue toward 4D bioprinting

3D bioprinting is an advanced technology combining cells and bioactive molecules within a single bioscaffold; however, this scaffold cannot change, modify or grow in response to a dynamic implemented environment. Lately, a new era of smart polymers and hydrogels has emerged, which can add another dimension, e.g., time to 3D bioprinting, to address some of the current approaches' limitations. This concept is indicated as 4D bioprinting. This approach may assist in fabricating tissue-like structures with a configuration and function that mimic the natural tissue. These scaffolds can change and reform as the tissue are transformed with the potential of specific drug or biomolecules released for various biomedical applications, such as biosensing, wound healing, soft robotics, drug delivery, and tissue engineering, though 4D bioprinting is still in its early stages and more works are required to advance it. In this review article, the critical challenge in the field of 4D bioprinting and transformations from 3D bioprinting to 4D phases is reviewed. Also, the mechanistic aspects from the chemistry and material science point of view are discussed too.

Fluorescent Enhancement of [AgS4] Microplates by Mechanical Force Induced Crystallinity Breaking

Mechanofluorochromic materials are a type of "smart" material because of their adjustable fluorescent properties under external mechanical force, making them significant members of the materials family. However, as the fluorescent characteristics of these materials highly depend on their microstructures, the still insufficiently in-depth research linking molecular structures to light emission motivates researchers to explore the fluorescent properties of these materials under external stimuli. In this work, based on synthetic [AgS4] microplates, we explore a fascinating mechanical-induced photoluminescent enhancement phenomenon. By applying mechanical force to solid-state [AgS4] to damage the surface morphology, a significant enhancement in photoluminescence is observed. Moreover, the emitted intensity increases with the extent of damage, which can be attributed to alterations in crystallinity. This work provides valuable insights into the relationship among photoluminescence, crystallinity, and mechanical force, offering new strategies for designing luminescent devices.

Soft Robots with Plant-Inspired Gravitropism Based on Fluidic Liquid Metal

Plants can autonomously adjust their growth direction based on the gravitropic response to maximize energy acquisition, despite lacking nerves and muscles. Endowing soft robots with gravitropism may facilitate the development of self-regulating systems free of electronics, but remains elusive. Herein, acceleration-regulated soft actuators are described that can respond to the gravitational field by leveraging the unique fluidity of liquid metal in its self-limiting oxide skin. The soft actuator is obtained by magnetic printing of the fluidic liquid metal heater circuit on a thermoresponsive liquid crystal elastomer. The Joule heat of the liquid metal circuit with gravity-regulated resistance can be programmed by changing the actuator's pose to induce the flow of liquid metal. The actuator can autonomously adjust its bending degree by the dynamic interaction between its thermomechanical response and gravity. A gravity-interactive soft gripper is also created with controllable grasping and releasing by rotating the actuator. Moreover, it is demonstrated that self-regulated oscillation motion can be achieved by interfacing the actuator with a monostable tape spring, allowing the electronics-free control of a bionic walker. This work paves the avenue for the development of liquid metal-based reconfigurable electronics and electronics-free soft robots that can perceive gravity or acceleration.

Shape-memory microfluidic chips for fluid and droplet manipulation

Fluid manipulation is an important foundation of microfluidic technology. Various methods and devices have been developed for fluid control, such as electrowetting-on-dielectric-based digital microfluidic platforms, microfluidic pumps, and pneumatic valves. These devices enable precise manipulation of small volumes of fluids. However, their complexity and high cost limit the commercialization and widespread adoption of microfluidic technology. Shape memory polymers as smart materials can adjust their shape in response to external stimuli. By integrating shape memory polymers into microfluidic chips, new possibilities for expanding the application areas of microfluidic technology emerge. These shape memory polymers can serve as actuators or regulators to drive or control fluid flow in microfluidic systems, offering innovative approaches for fluid manipulation. Due to their unique properties, shape memory polymers provide a new solution for the construction of intelligent and automated microfluidic systems. Shape memory microfluidic chips are expected to be one of the future directions in the development of microfluidic technology. This article offers a summary of recent research achievements in the field of shape memory microfluidic chips for fluid and droplet manipulation and provides insights into the future development direction of shape memory microfluidic devices.

Functional polymeric molecules for performing autonomous synthesis of particles with core-shell structures and customizable shapes

Self-organization by the directed migration of components within a system is an important process in many applications, such as the unidirectional migration of motor proteins for transporting items to specific sites in a cell. This manuscript describes a class of functional polymeric molecules that have a set of instructions written by specific chemical moieties. These instructions allow the functional polymeric molecules to be used for autonomous synthesis of particles: particles with both functional core-shell structure and customizable shapes are fabricated for the first time. The functional polymeric molecules direct the large-scale migration of the liquid molecules to specific sites for forming the required customized structure of the particle, thus overcoming previous challenges of fabricating this class of particles. This first synthesis of this class of particles enables the development of novel applications: the concept of shape specificity for targeting sites. Both the basic structural properties (core-shell structure and customizable shape) are used in the specific applications of targeted drug delivery and imaging. The secure physical fit due to the complementary shapes enables the particles to remain locked in position for the targeting. Polymeric molecules are first shown to be highly capable of being encoded with instructions for autonomous synthesis of structured materials.

Chemically Fueled Logic AND Gate with Double Encoding in the Time Domain

To increase information density and security in communication, Nature at times encodes signals in the time domain, for instance, Ca2+ ion signals. Double encoding in the time domain operates beyond this level of security because the data are encoded in two time-dependent output signals showing distinct periods, frequencies, and full duration half-maxima. To illustrate such a protocol, a three-component ensemble consisting of a double ion-selective luminophore with two distinct receptor sites, hexacyclen, and diaza-18-crown-6 ether is demonstrated to act as a logic AND gate with Ag+ and Ca2+ ions as inputs. The gate shows an unprecedented 2-fold time-encoded fluorescence output at 590 and 488 nm based on metal ion pulses with distinct periods when trichloroacetic acid is applied as chemical fuel.

Smart antibacterial nanocellulose packaging film based on pH-stimulate responsive microcapsules synthesized by Pickering emulsion template

Spoilage results in food waste and endangers consumer health, and the smart antibacterial packaging can effectively inhibit bacterial growth and reduce food spoilage. In this study, the smart antibacterial nanocellulose packaging films were developed by adding the pH-stimulated responsive microcapsules into cellulose nanofibril (CNF) film-forming. The microcapsules were synthesized by interfacial polymerization of Pickering emulsion. Carboxylated cellulose nanocrystals as solid particles stabilized the composited oil phase to prepare the oil-in-water Pickering emulsion. The emulsion with the particle concentration of 1.25 wt% and the oil phase mass fraction of 7.5 % processes excellent stability and uniform particle size, was chosen to synthesize microcapsules. The cinnamaldehyde in the film with the addition amount of microcapsules 0.6 g burst released in the first 1 h and then slowly, and the cumulative release at pH 2.0, 4.0, 5.5 and 7.2 was 28.43 μg/cm2, 18.84 μg/cm2, 16.52 μg/cm2 and 12.89 μg/cm2, respectively. The inhibitory rate of film against both E. coli and L. monocytogenes reached 99 % at pH 4.0. The shelf life of pork packed by the film prolonged to nearly 9 d at room temperature. The developed films have the potential to be used in food packaging.

Programming Deformations of 3D Microstructures: Opportunities Enabled by Magnetic Alignment of Liquid Crystalline Elastomers

Synthetic structures that undergo controlled movement are crucial building blocks for developing new technologies applicable to robotics, healthcare, and sustainable self-regulated materials. Yet, programming motion is nontrivial, and particularly at the microscale it remains a fundamental challenge. At the macroscale, movement can be controlled by conventional electric, pneumatic, or combustion-based machinery. At the nanoscale, chemistry has taken strides in enabling molecularly fueled movement. Yet in between, at the microscale, top-down fabrication becomes cumbersome and expensive, while bottom-up chemical self-assembly and amplified molecular motion does not reach the necessary sophistication. Hence, new approaches that converge top-down and bottom-up methods and enable motional complexity at the microscale are urgently needed. Synthetic anisotropic materials (e.g., liquid crystalline elastomers, LCEs) with encoded molecular anisotropy that are shaped into arbitrary geometries by top-down fabrication promise new opportunities to implement controlled actuation at the microscale. In such materials, motional complexity is directly linked to the built-in molecular anisotropy that can be "activated" by external stimuli. So far, encoding the desired patterns of molecular directionality has relied mostly on either mechanical or surface alignment techniques, which do not allow the decoupling of molecular and geometric features, severely restricting achievable material shapes and thus limiting attainable actuation patterns, unless complex multimaterial constructs are fabricated. Electromagnetic fields have recently emerged as possible alternatives to provide 3D control over local anisotropy, independent of the geometry of a given 3D object. The combination of magnetic alignment and soft lithography, in particular, provides a powerful platform for the rapid, practical, and facile production of microscale soft actuators with field-defined local anisotropy. Recent work has established the feasibility of this approach with low magnetic field strengths (in the lower mT range) and comparably simple setups used for the fabrication of the microactuators, in which magnetic fields can be engineered through arrangement of permanent magnets. This workflow gives access to microstructures with unusual spatial patterning of molecular alignment and has enabled a multitude of nontrivial deformation types that would not be possible to program by any other means at the micron scale. A range of "activating" stimuli can be used to put these structures in motion, and the type of the trigger plays a key role too: directional and dynamic stimuli (such as light) make it possible to activate the patterned anisotropic material locally and transiently, which enables one to achieve and further program motional complexity and communication in microactuators. In this Account, we will discuss recent advances in magnetic alignment of molecular anisotropy and its use in soft lithography and related fabrication approaches to create LCE microactuators. We will examine how design choices-from the molecular to the fabrication and the operational levels-control and define the achievable LCE deformations. We then address the role of stimuli in realizing the motional complexity and how one can engineer feedback within and communication between microactuator arrays fabricated by soft lithography. Overall, we outline emerging strategies that make possible a completely new approach to designing for desired sets of motions of active, microscale objects.

Assembly and optically triggered disassembly of lipid-DNA origami fibers

The co-assembly of lipids and other compounds has recently gained increasing interest. Here, we report the formation of stimuli-responsive lipid-DNA origami fibers through the electrostatic co-assembly of cationic lipids and 6-helix bundle (6HB) DNA origami. The photosensitive lipid degrades when exposed to UV-A light, which allows a photoinduced, controlled release of the 6HBs from the fibers. The presented complexation strategy may find uses in developing responsive nanomaterials e.g. for therapeutics.

Stimuli-Responsive Hydrogels: The Dynamic Smart Biomaterials of Tomorrow

In the past decade, stimuli-responsive hydrogels are increasingly studied as biomaterials for tissue engineering and regenerative medicine purposes. Smart hydrogels can not only replicate the physicochemical properties of the extracellular matrix but also mimic dynamic processes that are crucial for the regulation of cell behavior. Dynamic changes can be influenced by the hydrogel itself (isotropic vs anisotropic) or guided by applying localized triggers. The resulting swelling-shrinking, shape-morphing, as well as patterns have been shown to influence cell function in a spatiotemporally controlled manner. Furthermore, the use of stimuli-responsive hydrogels as bioinks in 4D bioprinting is very promising as they allow the biofabrication of complex microstructures. This perspective discusses recent cutting-edge advances as well as current challenges in the field of smart biomaterials for tissue engineering. Additionally, emerging trends and potential future directions are addressed.

Multi-responsive Electropolymer Surface Coatings Based on Azo Molecular Switches and Carbazoles: Light, pH, and Electrochemical Control of Z→E Isomerization in Thin Films

Light-responsive surfaces are attracting increasing interest, not least because their physicochemical properties can be selectively and temporally controlled by a non-invasive stimulus. Most existing immobilization strategies involve the chemical attachment of light-responsive moieties to the surface, although this approach often suffers from a low surface concentration of active species or a high inhomogeneity of applied coatings. Herein, electropolymerization of carbazoles as a facile and rapid approach for preparing light-responsive azo-based surface coatings is presented. The electrochemical oxidative polymerization of bis-carbazole containing azo-monomers yields stable films, in which the photochemical properties and specific pH sensitivity of azo molecular switches are retained. Moreover, the molecular design enables electrocatalytic control over Z→E azo double bond isomerization facilitated by the conductive polycarbazole backbone. Ultimately, the high degree of control over macromolecular properties yields conductive surface coatings responsive to a range of stimuli, showing great promise as a strategy for versatile application in organic electronics.

Target-Controlled Redox Reaction and Ru(II) Release of a Smart Metal-Organic Framework Nanomaterial for Highly Sensitive Ratiometric Homogeneous Electroanalysis of Cadmium(II)

In this work, a highly sensitive ratiometric homogeneous electroanalysis (HEA) strategy of cadmium(II) (Cd2+) was proposed via a Cd2+-controlled redox reaction and Ru(bpy)32+ (Ru(II)) release from a smart metal-organic framework (MOF) nanomaterial. For achieving this purpose, Ru(II) was entrapped ingeniously into the pores of an MOF material (UiO-66-NH2) and subsequently gated by the double-strand hybrids of a Cd2+-aptamer (Apt) and its complementary sequences (CP) to form a novel smart nanomaterial (denoted as Ru@UiO-66-NH2); meanwhile, Fe(III) was selected as an additional probe present in electrolyte to facilitate the Ru(II) redox reaction: Fe(III) + Ru(II) → Fe(II) + Ru(III). Owing to the strong binding effect of the Cd2+ target to the specific Apt, the Apt-CP hybridization at Ru@UiO-66-NH2 would be destroyed in the presence of Cd2+, and the related Apt was further induced away from the smart nanomaterial, leading to the opening of the gate and release of Ru(II). Meanwhile, the released Ru(II) was quickly oxidized chemically by Fe(III) to Ru(III). On the basis of the generated Ru(III) and consumed Fe(III), the ratio of the reduction currents between Ru(III) and Fe(III) exhibits an enhancement and it is dependent on the level of Cd2+; thus, a novel HEA strategy of Cd2+ was then designed. Under the optimal conditions, the HEA sensor shows a wide linearity ranging from 10.0 pM to 500.0 nM, and the achieved detection limit of Cd2+ is 3.3 pM. The as-designed ratiometric HEA strategy not only offers a unique idea to realize a simple and sensitive assay for Cd2+ but also possesses significant potential as an effective tool to be introduced for other target analysis just via altering the specific Apt.

Tracing a new path in the field of AI and robotics: mimicking human intelligence through chemistry. Part II: systems chemistry

Inspired by some traits of human intelligence, it is proposed that wetware approaches based on molecular, supramolecular, and systems chemistry can provide valuable models and tools for novel forms of robotics and AI, being constituted by soft matter and fluid states as the human nervous system and, more generally, life, is. Bottom-up mimicries of intelligence range from the molecular world to the multicellular level, i.e., from the Ångström (10 - 10 meters) to the micrometer scales (10 - 6 meters), and allows the development of unconventional chemical robotics. Whereas conventional robotics lets humans explore and colonise otherwise inaccessible environments, such as the deep oceanic abysses and other solar system planets, chemical robots will permit us to inspect and control the microscopic molecular and cellular worlds. This article suggests that systems made of properly chosen molecular compounds can implement all those modules that are the fundamental ingredients of every living being: sensory, processing, actuating, and metabolic networks. Autonomous chemical robotics will be within reach when such modules are compartmentalised and assembled. The design of a strongly intertwined web of chemical robots, with or without the involvement of living matter, will give rise to collective forms of intelligence that will probably reproduce, on a minimal scale, some sophisticated performances of the human intellect and will implement forms of "general AI." These remarkable achievements will require a productive interdisciplinary collaboration among chemists, biotechnologists, computer scientists, engineers, physicists, neuroscientists, cognitive scientists, and philosophers to be achieved. The principal purpose of this paper is to spark this revolutionary collaborative scientific endeavour.

Synchronous Switching of Dielectric Constant and Photoluminescence in Cyanidonitridorhenate-Based Crystals

Switching of multiple physical properties by external stimuli in dynamic materials enables applications in, e.g., smart sensors, biomedical tools, as well as data-storage devices. Among stimuli-responsive materials, inorganic-organic molecular hybrids exhibiting thermal order-disorder phase transitions were tested as promising molecular switches of electrical characteristics, including dielectric constant. We aimed at broadening the multifunctional potential of such hybrid materials towards the switching of not only electrical but also other physical properties, e.g., light emission. We report two ionic salts based on luminescent tetracyanidonitridorhenate(V) anions bearing two different diamine ligands, 1,2-diaminoethane (1) and 1,3-diaminopropane (2), both crystallizing with polar N-methyl-dabconium cations. They exhibit an order-disorder phase transition related to the heating-induced turning-on of the rotation of polar cations. This leads to a unique synchronous switching of the dielectric constant as well as metal-complex-centered photoluminescence, as demonstrated by changes in, e.g., emission lifetime. The roles of organic cations, non-trivial Re(V) complexes, and their interaction in achieving the coupled thermal switching of electrical and optical properties are discussed utilizing experimental and theoretical approaches.

A Role for Bottom-Up Synthetic Cells in the Internet of Bio-Nano Things?

The potential role of bottom-up Synthetic Cells (SCs) in the Internet of Bio-Nano Things (IoBNT) is discussed. In particular, this perspective paper focuses on the growing interest in networks of biological and/or artificial objects at the micro- and nanoscale (cells and subcellular parts, microelectrodes, microvessels, etc.), whereby communication takes place in an unconventional manner, i.e., via chemical signaling. The resulting "molecular communication" (MC) scenario paves the way to the development of innovative technologies that have the potential to impact biotechnology, nanomedicine, and related fields. The scenario that relies on the interconnection of natural and artificial entities is briefly introduced, highlighting how Synthetic Biology (SB) plays a central role. SB allows the construction of various types of SCs that can be designed, tailored, and programmed according to specific predefined requirements. In particular, "bottom-up" SCs are briefly described by commenting on the principles of their design and fabrication and their features (in particular, the capacity to exchange chemicals with other SCs or with natural biological cells). Although bottom-up SCs still have low complexity and thus basic functionalities, here, we introduce their potential role in the IoBNT. This perspective paper aims to stimulate interest in and discussion on the presented topics. The article also includes commentaries on MC, semantic information, minimal cognition, wetware neuromorphic engineering, and chemical social robotics, with the specific potential they can bring to the IoBNT.

One stimulus-induced two-step photophysical response with high contrast and tunable switching time for dynamic displaying

One stimulus-induced two-step photophysical response, especially with tunable switching time, is a great challenge for organic chromophores. Herein, a polymorphic material 2,7-DCF could undergo in situ two sequential dual-channel responses upon dichloromethane fuming. Both the appearance color and the fluorescence change from red to yellow to deep red with high contrast. The first step corresponds to a fast amorphous-to-crystalline transformation, while the second is a slow solid-state cocrystallization process. Based on single crystal structures and theoretical calculations, such distinct color changes are mainly attributed to conformation twisting and the electron coupling with incorporated solvent molecule through C-H⋅⋅⋅O interaction. Importantly, the second slow photophysical response could be drastically sped up by seeding strategy, or be totally inhibited. Such characteristics pave a way for the potential applications in dynamic anti-counterfeiting and data encryption. Based on the two-step transformation, polymorph 2,7-DCF-a could achieve a successive four-level response to external stimuli. In contrast, polymorph 2,7-DCF-d exhibits a stepwise hypsochromic fluorescence shift over 100 nm. This study would significantly promote the development of stimuli-sensitive systems from "one stimulus, one-step response" to "one stimulus, two or multi-step response".

Stimuli-Responsive Langmuir Films Composed of Nanoparticles Decorated with Poly(N-isopropyl acrylamide) (PNIPAM) at the Air/Water Interface

The nanotechnology shift from static toward stimuli-responsive systems is gaining momentum. We study adaptive and responsive Langmuir films at the air/water interface to facilitate the creation of two-dimensional (2D) complex systems. We verify the possibility of controlling the assembly of relatively large entities, i.e., nanoparticles with diameter around 90 nm, by inducing conformational changes within an about 5 nm poly(N-isopropyl acrylamide) (PNIPAM) capping layer. The system performs reversible switching between uniform and nonuniform states. The densely packed and uniform state is observed at a higher temperature, i.e., opposite to most phase transitions, where more ordered phases appear at lower temperatures. The induced nanoparticles' conformational changes result in different properties of the interfacial monolayer, including various types of aggregation. The analysis of surface pressure at different temperatures and upon temperature changes, surface potential measurements, surface rheology experiments, Brewster angle microscopy (BAM), and scanning electron microscopy (SEM) observations are accompanied by calculations to discuss the principles of the nanoparticles' self-assembly. Those findings provide guidelines for designing other adaptive 2D systems, such as programable membranes or optical interfacial devices.

Untethered Soft Microrobots with Adaptive Logic Gates

Integrating adaptative logic computation directly into soft microrobots is imperative for the next generation of intelligent soft microrobots as well as for the smart materials to move beyond stimulus-response relationships and toward the intelligent behaviors seen in biological systems. Acquiring adaptivity is coveted for soft microrobots that can adapt to implement different works and respond to different environments either passively or actively through human intervention like biological systems. Here, a novel and simple strategy for constructing untethered soft microrobots based on stimuli-responsive hydrogels that can switch logic gates according to the surrounding stimuli of environment is introduced. Different basic logic gates and combinational logic gates are integrated into a microrobot via a straightforward method. Importantly, two kinds of soft microrobots with adaptive logic gates are designed and fabricated, which can smartly switch logic operation between AND gate and OR gate under different surrounding environmental stimuli. Furthermore, a same magnetic microrobot with adaptive logic gate is used to capture and release the specified objects through the change of the surrounding environmental stimuli based on AND or OR logic gate. This work contributes an innovative strategy to integrate computation into small-scale untethered soft robots with adaptive logic gates.

Homogeneous voltammetric sensing strategy for lead ions based on aptamer gated methylthionine chloride@UiO-66-NH2 framework as smart target-stimulated responsive nanomaterial

Herein an innovative electrochemical method is proposed for the determination of lead ions (Pb²⁺) based on a homogeneous voltammetric (HVC) sensing strategy using an aptamer gated methylthionine chloride@UiO-66-NH₂ framework as a smart target-stimulated responsive material. The proposed HVC sensor exhibits excellent sensing performance: ultralow detection limit (0.166 pM) and wide linearity (5.0 pM-500.0 nM), simultaneously, it avoids electrodeposition processes and it is simple to modify the electrode compared to previous electrochemical methods for Pb²⁺ detection. Thus our method shows great potential in the highly efficient detection of Pb²⁺ and other heavy metal ions by simply altering the related specific aptamer.

Fast Response and Visual Transparency Switching Hydrochromic Film Based on the Rational Structure of Cellulose/Poloxamer Copolymers Design for Smart Window

The authors are motivated to develop a series of hydrochromic copolymers with fast response, reversibility, repeatability, and visual transparency transition. The hydrochromic block copolymers are based on the rational ratio of hydrophilic segments of poloxamer block and hydrophobic segments of ethyl cellulose according to the preparation method of polyurethane. By tuning the ratio of hydrophilic segments or adding hygroscopic salts, the hydrochromic polymer is endowed with the ability to visualize the transparency in response to the relative humidity. Especially, the response time of the polymer is extremely shortened, up to 1 s for the optimized sample. Within the moisture stimulation, the hygroscopic swelling increases the film thickness, leading to a reversible transparency switching from a highly transparent state (82%) to an opaque white state (20.5%).

Active control of equilibrium, near-equilibrium, and far-from-equilibrium colloidal systems

The development of top-down active control over bottom-up colloidal assembly processes has the potential to produce materials, surfaces, and objects with applications in a wide range of fields spanning from computing to materials science to biomedical engineering. In this review, we summarize recent progress in the field using a taxonomy based on how active control is used to guide assembly. We find there are three distinct scenarios: (1) navigating kinetic pathways to reach a desirable equilibrium state, (2) the creation of a desirable metastable, kinetically trapped, or kinetically arrested state, and (3) the creation of a desirable far-from-equilibrium state through continuous energy input. We review seminal works within this framework, provide a summary of important application areas, and present a brief introduction to the fundamental concepts of control theory that are necessary for the soft materials community to understand this literature. In addition, we outline current and potential future applications of actively-controlled colloidal systems, and we highlight important open questions and future directions.

Perspectives on development of biomedical polymer materials in artificial intelligence age

Polymer materials are widely used in biomedicine, chemistry and material science, whose traditional preparations are mainly based on experience, intuition and conceptual insight, having been applied to the development of many new materials, but facing great challenges due to the vast design space for biomedical polymers. So far, the best way to solve these problems is to accelerate material design through artificial intelligence, especially machine learning. Herein, this paper will introduce several successful cases, and analyze the latest progress of machine learning in the field of biomedical polymers, then discuss the opportunities of this novel method. In particular, this paper summarizes the material database, open-source determination tools, molecular generation methods and machine learning models that have been used for biopolymer synthesis and property prediction. Overall, machine learning could be more effectively deployed on the material design of biomedical polymers, and it is expected to become an extensive driving force to meet the huge demand for customized designs.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

Two-dimensional and pseudo-2D systems come in various forms. Membranes separating protocells from the environment were necessary for life to occur. Later, compartmentalization allowed for the development of more complex cellular structures. Nowadays, 2D materials (e.g., graphene, molybdenum disulfide) are revolutionizing the smart materials industry. Surface engineering allows for novel functionalities, as only a limited number of bulk materials have the desired surface properties. This is realized via physical treatment (e.g., plasma treatment, rubbing), chemical modifications, thin film deposition (using both chemical and physical methods), doping and formulation of composites, or coating. However, artificial systems are usually static. Nature creates dynamic and responsive structures, which facilitates the formation of complex systems. The challenge of nanotechnology, physical chemistry, and materials science is to develop artificial adaptive systems. Dynamic 2D and pseudo-2D designs are needed for future developments of life-like materials and networked chemical systems in which the sequences of the stimuli would control the consecutive stages of the given process. This is crucial to achieving versatility, improved performance, energy efficiency, and sustainability. Here, we review the advancements in studies on adaptive, responsive, dynamic, and out-of-equilibrium 2D and pseudo-2D systems composed of molecules, polymers, and nano/microparticles.

Simple lignin-based, light-driven shape memory polymers with excellent mechanical properties and wide range of glass transition temperatures

Lignin is the most abundant biomass source of aromatic hydrocarbons but, at present, is not effectively utilized. The development of simple and efficient methods for producing lignin-based polymers to replace petroleum-based products is an important strategy for promoting environmentally friendly and sustainable materials and controlling carbon emissions. In this work, lignin-based, light-driven shape memory polymers (ELIDs) with improved mechanical properties have been prepared from enzymatic hydrolysis lignin, itaconic acid and 1,12-dodecanediol, without any chemical modification of the lignin. The polymers contain large proportions of lignin (20-40 wt%, designated ELID20 to ELID40) and their mechanical properties are dependent on the lignin content. Maximum tensile strength (46.9 MPa) was achieved with ELID30, maximum elongation at break (93.7 %) was achieved with ELID20 and highest fracture energy (10.75 J cm^-3) was achieved with ELID25. These excellent mechanical properties are accompanied by good thermal stability and a wide range of glass transition temperatures (21.2-157.3 °C), supporting a broad range of applications. The shape fixation rate (R_f) and shape recovery rate (R_r) were highest for ELID30 (98.7 % and 97.4 %, respectively). Under 1 sun simulated solar irradiation, ELID20 reached a temperature exceeding the glass transition temperature in 15 s and, under 3 sun simulated solar irradiation, ELID30 reached a temperature of 130 °C and shape recovered in 60 s. The excellent mechanical properties and good light-driven shape memory of ELIDs provide inspiration for the development and utilization of lignin-based polymers.

Silk Fibroin Microneedles for Transdermal Drug Delivery: Where Do We Stand and How Far Can We Proceed?

Microneedles are a patient-friendly technique for delivering drugs to the site of action in place of traditional oral and injectable administration. Silk fibroin represents an interesting polymeric biomaterial because of its mechanical properties, thermal stability, biocompatibility and possibility of control via genetic engineering. This review focuses on the critical research progress of silk fibroin microneedles since their inception, analyzes in detail the structure and properties of silk fibroin, the types of silk fibroin microneedles, drug delivery applications and clinical trials, and summarizes the future development trend in this field. It also proposes the future research direction of silk fibroin microneedles, including increasing drug loading doses and enriching drug loading types as well as exploring silk fibroin microneedles with stimulation-responsive drug release functions. The safety and effectiveness of silk fibroin microneedles should be further verified in clinical trials at different stages.

Recent advances in room temperature phosphorescence materials: design strategies, internal mechanisms and intelligent optical applications

Room temperature phosphorescence (RTP) materials comprising organic-inorganic hybrid, pure organic, and polymer RTP materials have been a research focus due to their tunable molecular structures, long emission lifetimes and extensive optical applications. Many design methods including halogen bonding interactions, heavy atom effect, metal-organic frameworks, polymerization, host-guest doping, and H-aggregation have been developed by RTP researchers. Narrowing the energy gap between the S₁ and lowest T_n states, enhancing the intersystem crossing (ISC) rate, increasing the spin-orbit coupling (SOC) value and stabilizing triplet emission states are the core factors to promoting RTP performance. In this review, lots of cases of organic-inorganic hybrid, pure organic, and polymer RTP materials with advanced design strategies, excellent RTP properties and intelligent applications have been classified and sorted. Their molecule structural designability and stimulus responsiveness endow them with RTP adjustability, which makes them excellent phosphors for modern optical applications. This review provides a systematic case elaboration of typical RTP systems in recent years and identifies the future challenges to improving RTP performance and finding novel applications.

Toward Interdisciplinary Synergies in Molecular Communications: Perspectives from Synthetic Biology, Nanotechnology, Communications Engineering and Philosophy of Science

Within many chemical and biological systems, both synthetic and natural, communication via chemical messengers is widely viewed as a key feature. Often known as molecular communication, such communication has been a concern in the fields of synthetic biologists, nanotechnologists, communications engineers, and philosophers of science. However, interactions between these fields are currently limited. Nevertheless, the fact that the same basic phenomenon is studied by all of these fields raises the question of whether there are unexploited interdisciplinary synergies. In this paper, we summarize the perspectives of each field on molecular communications, highlight potential synergies, discuss ongoing challenges to exploit these synergies, and present future perspectives for interdisciplinary efforts in this area.

Emerging Magnetic Fabrication Technologies Provide Controllable Hierarchically-Structured Biomaterials and Stimulus Response for Biomedical Applications

Multifunctional nanocomposites which exhibit well-defined physical properties and encode spatiotemporally-controlled responses are emerging as components for advanced responsive systems. For biomedical applications magnetic nanocomposite materials have attracted significant attention due to their ability to respond to spatially and temporally varying magnetic fields. The current state-of-the-art in development and fabrication of magnetic hydrogels toward biomedical applications is described. There is accelerating progress in the field due to advances in manufacturing capabilities. Three categories can be identified: i) Magnetic hydrogelation, DC magnetic fields are used during solidification/gelation for aligning particles; ii) additive manufacturing of magnetic materials, 3D printing technologies are used to develop spatially-encoded magnetic properties, and more recently; iii) magnetic additive manufacturing, magnetic responses are applied during the printing process to develop increasingly complex structural arrangement that may recapitulate anisotropic tissue structure and function. The magnetic responsiveness of conventionally and additively manufactured magnetic hydrogels are described along with recent advances in soft magnetic robotics, and the categorization is related to final architecture and emergent properties. Future challenges and opportunities, including the anticipated role of combinatorial approaches in developing 4D-responsive functional materials for tackling long-standing problems in biomedicine including production of 3D-specified responsive cell scaffolds are discussed.

Feedback-controlled hydrogels with homeostatic oscillations and dissipative signal transduction

Driving systems out of equilibrium under feedback control is characteristic for living systems, where homeostasis and dissipative signal transduction facilitate complex responses. This feature not only inspires dissipative dynamic functionalities in synthetic systems but also poses great challenges in designing novel pathways. Here we report feedback-controlled systems comprising two coupled hydrogels driven by constant light, where the system can be tuned to undergo stable homeostatic self-oscillations or damped steady states of temperature. We demonstrate that stable temperature oscillations can be utilized for dynamic colours and cargo transport, whereas damped steady states enable signal transduction pathways. Here mechanical triggers cause temperature changes that lead to responses such as bending motions inspired by the single-touch mechanoresponse in Mimosa pudica and the frequency-gated snapping motion inspired by the plant arithmetic in the Venus flytrap. The proposed concepts suggest generalizable feedback pathways for dissipative dynamic materials and interactive soft robotics.

High Throughput Fabrication of Flexible Top-Driven Sensing Probe

In this work, considering the current status of conservative and complicated traditional thrombosis treatment methods, a kind of flexible intelligent probe (FIP) with a top-driven sensing strategy is proposed to realize the expected function of thrombosis accurate localization in a liquid flow environment. After throughput fabrication, we find that the FIP has excellent electrical conductivity and mechanical properties. Notable, our FIP with the principle of piezo-resistive sensing has a quasi-linear sensitivity (approx. 0.325 L per minute) to flow sensing in the low flow velocity range (0-1 L per minute). Via the well-designed magnetically driven method, our FIP has a maximum deflection output force of 443.264 mN, a maximum deflection angle of 43°, and a maximum axial force of 54.176 mN. We demonstrate that the FIP is capable of completing the specified command actions relatively accurately and has a good response to real-time sensing feedback performance, which has broad application prospects in thrombus localization detection.

Magnetic field-driven particle assembly and jamming for bistable memory and response plasticity

Unlike classic synthetic stimulus-responsive and shape-memory materials, which remain limited to fixed responses, the responses of living systems dynamically adapt based on the repetition, intensity, and history of stimuli. Such plasticity is ubiquitous in biology, which is profoundly linked to memory and learning. Concepts thereof are searched for rudimentary forms of "intelligent materials." Here, we show plasticity of electroconductivity in soft ferromagnetic nickel colloidal supraparticles with spiny surfaces, assembling/disassembling to granular conducting micropillars between two electrodes driven by magnetic field B. Colloidal jamming leads to conduction hysteresis and bistable memory upon increasing and subsequently decreasing B. Abrupt B changes induce larger conduction changes than gradual B-changes. Periodic B pulsing drives to frequency-dependent facilitation or suppression of conductivity compared to exposing the same constant field. The concepts allow remotely controlled switching plasticity, illustrated by a rudimentary device. More generally, we foresee adaptive functional materials inspired by response plasticity and learning.

Designable Micro-/Nano-Structured Smart Polymeric Materials

Smart polymeric materials with dynamically tunable physico-chemical characteristics in response to changes of environmental stimuli, have received considerable attention in myriad fields. The diverse combination of their micro-/nano-structural and molecular designs creates promising and exciting opportunities for exploiting advanced smart polymeric materials. Engineering micro-/nano-structures into smart polymeric materials with elaborate molecular design enables intricate coordination between their structures and molecular-level response to cooperatively realize smart functions for practical applications. In this review, recent progresses of smart polymeric materials that combine micro-/nano-structures and molecular design to achieve designed advanced functions are highlighted. Smart hydrogels, gating membranes, gratings, milli-particles, micro-particles and microvalves are employed as typical examples to introduce their design and fabrication strategies. Meanwhile, the key roles of interplay between their micro-/nano-structures and responsive properties to realize the desired functions for their applications are emphasized. Finally, perspectives on the current challenges and opportunities of micro-/nano-structured smart polymeric materials for their future development are presented.

Biomaterials for Tissue Engineering Applications and Current Updates in the Field: A Comprehensive Review

Tissue engineering has emerged as an interesting field nowadays; it focuses on accelerating the auto-healing mechanism of tissues rather than organ transplantation. It involves implanting an In Vitro cultured initiative tissue or a scaffold loaded with tissue regenerating ingredients at the damaged area. Both techniques are based on the use of biodegradable, biocompatible polymers as scaffolding materials which are either derived from natural (e.g. alginates, celluloses, and zein) or synthetic sources (e.g. PLGA, PCL, and PLA). This review discusses in detail the recent applications of different biomaterials in tissue engineering highlighting the targeted tissues besides the in vitro and in vivo key findings. As well, smart biomaterials (e.g. chitosan) are fascinating candidates in the field as they are capable of elucidating a chemical or physical transformation as response to external stimuli (e.g. temperature, pH, magnetic or electric fields). Recent trends in tissue engineering are summarized in this review highlighting the use of stem cells, 3D printing techniques, and the most recent 4D printing approach which relies on the use of smart biomaterials to produce a dynamic scaffold resembling the natural tissue. Furthermore, the application of advanced tissue engineering techniques provides hope for the researchers to recognize COVID-19/host interaction, also, it presents a promising solution to rejuvenate the destroyed lung tissues.

Stimulus responsive microcapsules and their aromatic applications

Fragrances and essential oils are promising for a wide range of applications due to their pleasant odors and diverse effects. However, direct addition to consumer products has the disadvantages of short retention time and easy deterioration of odor. At the same time, releasing a large amount of odor in a short time may be an unpleasant experience, which severely limits the practical application of aromatic substances. Microencapsulation perfectly solves these problems. Stimuli-responsive microcapsules, which combine environmental stimulation with microencapsulation, can not only effectively prevent the rapid decomposition and evaporation of aroma components, but also realize the "on-off" intelligent release of aroma substances to environmental changes, which have great promise in the field of fragrances. In this review, the application of stimuli-responsive microcapsules in fragrances is highlighted. Firstly, various encapsulation materials used to prepare stimuli-responsive aromatic microcapsules are described, mainly including some natural polymers, synthetic polymers, and inorganic materials. Subsequently, there is a detailed description of the common release mechanisms of stimuli-responsive aromatic microcapsules are described in detail. Finally, the application and future research directions are given for stimuli-responsive aromatic microcapsules in new textiles, food, paper, and leather.

Application of Super Photoacids in Controlling Dynamic Processes: Light-Triggering the Self-Propulsion of Oil Droplets

The dynamic control of pH-responsive systems is at the heart of many natural and artificial processes. Here, we use photoacids, molecules that dissociate only in their excited state and transfer their proton to nearby proton acceptors, for the dynamic control of processes. A problem arises when there is a need to protonate highly acidic acceptors. We solve this problem using super photoacids that have an excited-state pK_a of -8, thus enabling them to protonate very weak proton acceptors. The process that we target is the light-triggered self-propulsion of droplets, initiated by an excited-state proton transfer (ESPT) from a super photoacid donor to a surfactant acceptor situated on the surface of the droplet with a pK_a of ∼0. We first confirm using steady-state and time-resolved spectroscopy that a super photoacid can undergo ESPT to the acidic surfactant, whereas a "regular" photoacid cannot. Next, we show self-propulsion of the droplet upon irradiating the solvated super photoacid. We further confirm the protonation of the surfactant on the surface of the droplet using transient surface tension measurements. Our system is the first example of the application of super photoacids to control dynamic processes and opens new possibilities in the field of light-triggered dynamic systems.

Porous organic polymers for drug delivery: hierarchical pore structures, variable morphologies, and biological properties

Porous organic polymers have received considerable attention in recent years because of their applicability as biomaterials. In particular, their hierarchical pore structures, variable morphologies, and tunable biological properties make them suitable as drug-delivery systems. In this review, the synthetic and post forming/control methods including templated methods, template-free methods, mechanical methods, electrospun methods, and 3D printing methods for controlling the hierarchical structures and morphologies of porous organic polymers are discussed, and the different methods affecting their specific surface areas, hierarchical structures, and unique morphologies are highlighted in detail. In addition, we discuss their applications in drug encapsulation and the development of stimuli (pH, heat, light, and dual-stimuli)-responsive materials, focusing on their use for targeted drug release and as therapeutic agents. Finally, we present an outlook concerning the research directions and applications of porous polymer-based drug delivery systems.

Liquid-liquid phase separated microdomains of an amphiphilic graft copolymer in a surfactant-rich medium

The liquid-liquid phase separation (LLPS) of amphiphilic thermoresponsive copolymers can lead to the formation of micron-sized domains, known as simple coacervates. Due to their potential to confine active principles, these copolymer-rich droplets have gained interest as encapsulating agents. Understanding and controlling the conditions inducing this LLPS is therefore essential for applicative purposes and requires thorough fundamental studies on self-coacervation. In this work, we investigate the LLPS of a comb-like graft copolymer (PEG-g-PVAc) consisting of a poly(ethylene glycol) backbone (6 kDa) with ∼2-3 grafted poly(vinyl acetate) chains, and a PEG/PVAc weight ratio of 40/60. Specifically, we report the effect of various water-soluble additives on its phase separation behavior. Kosmotropes and non-ionic surfactants were found to decrease the phase separation temperature of the copolymer, while chaotropes and, above all, ionic surfactants increased it. We then focus on the phase behavior of PEG-g-PVAc in the presence of sodium citrate and a C_14-15 E₇ non-ionic surfactant (N45-7), defining the compositional range for the generation of LLPS microdomains at room temperature and monitoring their formation with fluorescence confocal microscopy. Finally, we determine the composition of the microdomains through confocal Raman microscopy, demonstrating the presence of PEG-g-PVAc, N45-7, and water. These results expand our knowledge on polymeric self-coacervation, clarifying the optimal conditions and composition needed to obtain LLPS microdomains with encapsulation potential at room temperature in surfactant-rich formulations.

Self-assembly of graphene oxide flakes for smart and multifunctional coating with reversible formation of wrinkling patterns

One of the main purposes of smart and multifunctional coatings is to have the versatility to be applied in a wide range of applications. However, the functions of smart materials are often highly limited. In particular, the stimuli-responsive lateral expansion of coatings based on 2D materials has not been reported before. This manuscript describes small two-dimensional graphene oxide (GO) flakes (e.g., thin sheets with a thickness of a few nanometers and much larger lateral dimensions) that act as elementary agents for the formation of smart and multifunctional coatings. The coating can be self-assembled from the GO flakes and disassembled flexibly when required. The coating is stimuli-responsive: upon localized contact with water, it expands and forms wrinkling patterns throughout its whole surface. Evaporating the water allows the wrinkles to disappear; hence, the process is reversible. This stimuli-responsiveness can be controlled to be reduced or completely switched off by temperature or pressure. These features are fundamentally due to the reversible intermolecular interactions among the flakes and favorable packing structure of the coating. The smart coating is shown to be useful for patterned fluidic systems of the desired shapes and the development of channels between fluidic reservoirs via the shortest path. Importantly, these results showed that a simple collection of uniquely 2D elementary agents with small nanoscale thickness can self-assemble into macroscopic materials that perform interactive and multifunctional operations.