Thermoresponsive Structural Coloration of Hydrogel Fibers

Intelligent fibers with a structural color have wide applications in many cutting-edge fields and have attracted significant attention in recent years. However, most reported optical fibers have a fixed structural color because hard colloids were used as blocks of photonic crystals. Herein, we developed a simple and scalable method to realize hydrogel fibers with a dynamic structural color using soft and thermoresponsive microgels as photonic blocks. A full interpenetrated sodium alginate-polyacrylamide hydrogel fiber was prepared through an exclusion process, which is facile for scaled-up and continuous preparation of hydrogel fibers by controlling the injection speed. Amino group-doped poly(N-Isopropylacrylamide) microgels were attached to the surface of hydrogel fibers by the Schiff-base bonds and resulted in amorphous arrays, exhibiting angle-independent colors. Under temperature stimuli, the tunable structural color could be easily displayed through the shrinkage of the microgels. Moreover, the soft microgels could also be attached to the commercial wood fabrics easily, endowing the fabrics with thermochromic properties. Besides temperature, the microgels are also sensitive to humidity and ionic strength; therefore, the fabrics can simultaneously provide measurements of humidity and sweat amount for wireless monitoring. This versatile tunable structural color coating approach shows great potential for smart fibers and clothing fabrics and tracking for changes in environmental factors

Thermoresponsive Microgel Films for Harvesting Cells and Cell Sheets

This work reports the formation of thermoresponsive poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-styrene) (PNIPAAmSt) microgel films and their use for cell growth and detachment via temperature stimuli. Thermoresponsive surface films can be conveniently produced by spin-coating or drop-coating of PNIPAAmSt microgel dispersions onto substrates such as glass coverslips, cell culture plates, and flasks, making this technique widely accessible. The thickness, stability, and reversibility of the PNIPAAmSt films coated on silicon wafers with respect to temperature switching were examined by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). The results unraveled the direct link between thermoreversibility and changes in film thickness and surface morphology, showing reversible hydration and dehydration. Under different coating conditions, well-packed microgel monolayers could be utilized for effective cell recovery and harvesting. Furthermore, cell adhesion and detachment processes were reversible and there was no sign of loss of cell viability during repeated surface attachment, growth, and detachment, showing a mild interaction between cells and thermoresponsive surface. More importantly, there was little deterioration of the packing of the thermoresponsive films or any major loss of microgel particles during reuse, indicating their robustness. These PNIPAAmSt microgel films thus open up a convenient interfacial platform for cell and cell sheet harvesting while avoiding the damage of enzymatic cleavage

Controllable Stabilization of Poly(<i>N</i>-isopropylacrylamide)-Based Microgel Films through Biomimetic Mineralization of Calcium Carbonate

Two types of thermoresponsive microgels, poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) microgels and poly­(<i>N</i>-isopropylacrylamide-<i>co</i>-acrylic acid) (PNIPAMAC) microgels were synthesized and used as templates for the mineralization of amorphous calcium carbonate (ACC) by diffusion of CO₂ vapor under ambient conditions. Thermosensitive PNIPAM/CaCO₃ hybrid macroscopic hydrogels and micrometer-sized PNIPAMAC/CaCO₃ hybrid microgels were controllably obtained and different mineralization mechanistic processes were proposed. The impact of the loaded CaCO₃ on the size, morphology, stability, and thermosensitivity of the microgels was also analyzed. PNIPAM/CaCO₃ hybrid macrogels had a slight decrease in thermoresponsive phase transition temperature, while PNIPAMAC/CaCO₃ hybrid microgels showed a clear increase in phase transition temperature. The difference reflected different amount and location of ACC in the gel network, causing different interactions with polymer chains. The PNIPAMAC/CaCO₃ microgels formed stable monolayer films on bare silica wafers and glass coverslips upon drying. The microgel films could facilitate the attachment and growth of 3T3 fibroblast cells and their subsequent detachment upon temperature drop from 37 °C to the ambient condition around 20 °C, thus, offering a convenient procedure for cell harvesting

Tough and Transparent Photonic Hydrogel Nanocomposites for Display, Sensing, and Actuation Applications

Thermosensitive hydrogels with periodic dielectric structures displaying tunable structural color by temperature stimuli have attracted much research interest recently. However, reported thermosensitive photonic hydrogels either using the poly(N-isopropylacrylamide) (PNIPAM) bulk hydrogel as the responsive matrix or using PNIPAM microgels as the photonic building blocks have poor mechanical strength. Moreover, the expensive and time-consuming preparation process also limits their further application. In this work, a different strategy for preparing PNIPAM-based photonic hydrogel nanocomposite films with strong mechanical strength is proposed by incorporating a PNIPAM microgel film with the polyacrylamide (PAM) hydrogel. The preparation process is simple but efficient, and the obtained nanocomposite films have tunable mechanical strength by changing the crosslinking degree of the PAM hydrogels. More interestingly, the structural color of the nanocomposite films can be retained up to 80 °C (at least), much higher than those of previously reported PNIPAM-based photonic materials. In addition to being thermochromic, the film is sensitive to humidity, and the structural color-changing process is similar to the molting process of cicadas. Furthermore, the nanocomposite films have synchronous shape deformations and color changes and can be used as color-tunable soft actuators. The microgel film-capped photonic hydrogels provide a new strategy for the preparation of thermoresponsive photonic hydrogels and structural color-tunable actuators

Self-Healing Chameleon Skin Functioning in the Air Environments

Chameleons are famous for their uncommon ability to change skin colors rapidly by tuning the lattice distance of guanine nanocrystals within the dermal iridophores. This mechanism has inspired various artificial photonic crystal (PC) films with tunable structural colors. However, the structural colors of most reported films are facile to be destroyed by external factors such as friction, impact, or water evaporation. Herein, an artificial intelligent skin, which has an elastomer–colloidal photonic crystal–hydrogel sandwich structure, is presented in this work. The outer modified polydimethylsiloxane layer acts as the cuticle to protect the hydrogel layer from water evaporation and endows the skin with self-healing ability. The inner hydrophilic hydrogel layer embedded with the colloidal photonic crystals acts as the dermis layer, and the polystyrene colloids layer plays the role of the guanine nanocrystals. A programmed color change can be easily controlled by varying the elongation of the artificial skin, covering the full visible spectrum range. Moreover, skin with patterned stripes, which is similar to the panther chameleon skin that can manipulate multiple colors, has also been achieved. The present artificial skin will offer fresh perspectives on the preparation of artificial chameleon skin similar to the real dynamic flexible skin, which would promote the application of PCs in optical devices

Self-Healing Chameleon Skin Functioning in the Air Environments

Chameleons are famous for their uncommon ability to change skin colors rapidly by tuning the lattice distance of guanine nanocrystals within the dermal iridophores. This mechanism has inspired various artificial photonic crystal (PC) films with tunable structural colors. However, the structural colors of most reported films are facile to be destroyed by external factors such as friction, impact, or water evaporation. Herein, an artificial intelligent skin, which has an elastomer–colloidal photonic crystal–hydrogel sandwich structure, is presented in this work. The outer modified polydimethylsiloxane layer acts as the cuticle to protect the hydrogel layer from water evaporation and endows the skin with self-healing ability. The inner hydrophilic hydrogel layer embedded with the colloidal photonic crystals acts as the dermis layer, and the polystyrene colloids layer plays the role of the guanine nanocrystals. A programmed color change can be easily controlled by varying the elongation of the artificial skin, covering the full visible spectrum range. Moreover, skin with patterned stripes, which is similar to the panther chameleon skin that can manipulate multiple colors, has also been achieved. The present artificial skin will offer fresh perspectives on the preparation of artificial chameleon skin similar to the real dynamic flexible skin, which would promote the application of PCs in optical devices

Self-Healing Chameleon Skin Functioning in the Air Environments

Chameleons are famous for their uncommon ability to change skin colors rapidly by tuning the lattice distance of guanine nanocrystals within the dermal iridophores. This mechanism has inspired various artificial photonic crystal (PC) films with tunable structural colors. However, the structural colors of most reported films are facile to be destroyed by external factors such as friction, impact, or water evaporation. Herein, an artificial intelligent skin, which has an elastomer–colloidal photonic crystal–hydrogel sandwich structure, is presented in this work. The outer modified polydimethylsiloxane layer acts as the cuticle to protect the hydrogel layer from water evaporation and endows the skin with self-healing ability. The inner hydrophilic hydrogel layer embedded with the colloidal photonic crystals acts as the dermis layer, and the polystyrene colloids layer plays the role of the guanine nanocrystals. A programmed color change can be easily controlled by varying the elongation of the artificial skin, covering the full visible spectrum range. Moreover, skin with patterned stripes, which is similar to the panther chameleon skin that can manipulate multiple colors, has also been achieved. The present artificial skin will offer fresh perspectives on the preparation of artificial chameleon skin similar to the real dynamic flexible skin, which would promote the application of PCs in optical devices

Visible and Near-Infrared Dual-Emission Carbogenic Small Molecular Complex with High RNA Selectivity and Renal Clearance for Nucleolus and Tumor Imaging

Fluorescence imaging requires bioselective, sensitive, nontoxic molecular probes to detect the precise location of lesions for fundamental research and clinical applications. Typical inorganic semiconductor nanomaterials with large sizes (>10 nm) can offer high-quality fluorescence imaging due to their fascinating optical properties but are limited to low selectivity as well as slow clearance pathway. We here report an N- and O-rich carbogenic small molecular complex (SMC, MW < 1000 Da) that exhibits high quantum yield (up to 80%), nucleic acid-binding enhanced excitation-dependent fluorescence (EDF), and a near-infrared (NIR) emission peaked at 850 nm with an ultralarge Stokes shift (∼500 nm). SMCs show strong rRNA affinity, and the resulting EDF enhancement allows multicolor visualization of nucleoli in cells for clear statistics. Furthermore, SMCs can be efficiently accumulated in tumor in vivo after injection into tumor-bearing mice. The NIR emission affords high signal/noise ratio imaging for delineating the true extent of tumor. Importantly, about 80% of injected SMCs can be rapidly excreted from the body in 24 h. No appreciable toxicological responses were observed up to 30 days by hematological, biochemical, and pathological examinations. SMCs have great potential as a promising nucleolus- and tumor-specific agent for medical diagnoses and biomedical research