Colloid‐in‐Liquid Crystal Gels that Respond to Biomolecular Interactions

This paper advances the design of stimuli‐responsive materials based on colloidal particles dispersed in liquid crystals (LCs). Specifically, thin films of colloid‐in‐liquid crystal (CLC) gels undergo easily visualized ordering transitions in response to reversible and irreversible (enzymatic) biomolecular interactions occurring at the aqueous interfaces of the gels. In particular, LC ordering transitions can propagate across the entire thickness of the gels. However, confinement of the LC to small domains with lateral sizes of ～10 μm does change the nature of the anchoring transitions, as compared to films of pure LC, due to the effects of confinement on the elastic energy stored in the LC. The effects of confinement are also observed to cause the response of individual domains of the LC within the CLC gel to vary significantly from one to another, indicating that manipulation of LC domain size and shape can provide the basis of a general and facile method to tune the response of these LC‐based physical gels to interfacial phenomena. Overall, the results presented in this paper establish that CLC gels offer a promising approach to the preparation of self‐supporting, LC‐based stimuli‐responsive materials.     

Therapeutic‐Gas‐Responsive Hydrogel

Nitric oxide (NO) is a crucial signaling molecule with various functions in physiological systems. Due to its potent biological effect, the preparation of responsive biomaterials upon NO having temporally transient properties is a challenging task. This study represents the first therapeutic‐gas (i.e., NO)‐responsive hydrogel by incorporating a NO‐cleavable crosslinker. The hydrogel is rapidly swollen in response to NO, and not to other gases. Furthermore, the NO‐responsive gel is converted to enzyme‐responsive gels by cascade reactions from an enzyme to NO production for which the NO precursor is a substrate of the enzyme. The application of the hydrogel as a NO‐responsive drug‐delivery system is proved here by revealing effective protein drug release by NO infusion, and the hydrogel is also shown to be swollen by the NO secreted from the cultured cells. The NO‐responsive hydrogel may prove useful in many applications, for example drug‐delivery vehicles, inflammation modulators, and as a tissue scaffold.     

Stimuli‐Responsive Optical Nanomaterials

Responsive optical nanomaterials that can sense and translate various external stimuli into optical signals, in the forms of observable changes in appearance and variations in spectral line shapes, are among the most active research topics in nanooptics. They are intensively exploited within the regimes of the four classic optical phenomena—diffraction in photonic crystals, absorption of plasmonic nanostructures, as well as color‐switching systems, refraction of assembled birefringent nanostructures, and emission of photoluminescent nanomaterials and molecules. Herein, a comprehensive review of these research activities regarding the fundamental principles and practical strategies is provided. Starting with an overview of their substantial developments during the latest three decades, each subtopic discussion is led with fundamental theories that delineate the correlation between nanostructures and optical properties and the delicate research strategies are elaborated with specific attention focused on working principles and optical performances. The unique advantages and inherent limitations of each responsive optical nanoscale platform are summarized, accompanied by empirical criteria that should be met and perspectives on research opportunities where the developments of next‐generation responsive optical nanomaterials might be directed.     

Mechanochromic Photonic Gels

Polymer gels are remarkable materials with physical structures that can adapt significantly and quite rapidly with changes in the local environment, such as temperature, light intensity, electrochemistry, and mechanical force. An interesting phenomenon observed in certain polymer gel systems is mechanochromism – a change in color due to a mechanical deformation. Mechanochromic photonic gels are periodically structured gels engineered with a photonic stopband that can be tuned by mechanical forces to reflect specific colors. These materials have potential as mechanochromic sensors because both the mechanical and optical properties are highly tailorable via incorporation of diluents, solvents, nanoparticles, or polymers, or the application of stimuli such as temperature, pH, or electric or strain fields. Recent advances in photonic gels that display strain‐dependent optical properties are discussed. In particular, this discussion focuses primarily on polymer‐based photonic gels that are directly or indirectly fabricated via self‐assembly, as these materials are promising soft material platforms for scalable mechanochromic sensors.     

Enzyme‐Responsive Nanoparticle Systems

Inorganic nanoparticles and their accompanying diverse physical properties are now virtually in routine use as imaging tools in cell‐biology. In addition to serving as excellent contrast agents, their size‐ and environment‐dependent optical and magnetic properties can be harnessed to create enzyme biosensor devices of extremely high sensitivity, whilst circumventing the numerous technical limitations associated with traditional enzyme assays. In this Research News article we discuss recent advances in field of enzyme‐responsive nanoparticle systems, where the activity of an enzyme elicits a specific response in the nanoparticle assembly to produce a signal relating to enzyme activity, focusing on three important systems: DNA‐structured nanoparticles, protein kinases and proteases.     

Writing,Self‐Healing,and Self‐Erasing on Conductive Pressure‐Sensitive Adhesives

A simple strategy for enabling conductive pressure sensitive adhesives (PSAs) to work as light‐responsive materials is reported. Direct laser‐writing of PSA substrates was achieved by means of a continuous‐wave He‐Ne laser focused through the objectives of an optical microscope. This approach takes advantage of cooperative interplay between viscoelastic properties of PSAs and enhanced thermal conductivity provided by an extra overlayer of gold. In particular, the thickness of the gold layer is a crucial parameter for tuning the substrate responsiveness. Self‐healing and self‐degradation processes can be exploited for controlling the lifetime of the written information, whereas additional protective coatings can be introduced to achieve permanent storage.     

A Temperature‐Responsive Boronate Core Cross‐Linked Star (CCS) Polymer for Fast and Highly Efficient Enrichment of Glycoproteins

Fast and highly efficient enrichment and separation of glycoproteins is essential in many biological applications, but the lack of materials with high capture capacity, fast, and efficient enrichment/separation makes it a challenge. Here, a temperature‐responsive core cross‐linked star (CCS) polymer with boronate affinity is reported for fast and efficient enriching and separating of glycoproteins from biological samples. The temperature‐responsive CCS polymers containing boronic acid in its polymeric arms and poly(N‐isopropyl acrylamide) in its cross‐linked core are prepared using reversible addition‐fragmentation chain transfer polymerization via an “arm‐first” methodology. The soluble boronate polymeric arms of the CCS polymers provide a homogeneous reaction system and facilitate interactions between boronic acid and glycoproteins, which leads to a fast binding/desorption speed and high capture capacity. Maximum binding capacity of the prepared CCS polymer for horseradish peroxidase is determined to be 210 mg g^?1, which can be achieved within 20 min. More interestingly, the temperature‐responsive CCS polymers exhibit rapid reversible thermal‐induced volume phase transition by increasing the temperature from 15 to 30 °C, resulting in a facile and convenient sample collection and recovery for the target glycoproteins. Finally, the temperature‐responsive CCS polymer is successfully applied to enrichment of low abundant glycoproteins.