Organic solvents-free and ambient-pressure drying melamine formaldehyde resin aerogels with homogeneous structures, outstanding mechanical strength and flame retardancy.

Atmospheric drying method for fabricating aerogels is considered the most promising way for casting aerogels on a large scale. However, the organic solvent exchange, remaining environmental pollution risk, is a crucial step in mitigating the impact of surface tension during the atmospheric drying process, especially for wet gel formed through the alkoxy-derived sol-gel process, such as melamine-formaldehyde resin (MF) aerogel. Herein, a tough polymer-assisted in situ polymerization was proposed to fabricate MF resin aerogel with a combination of mechanical toughness and strength, enabling it to withstand the capillary force during water evaporation. The monolithic MF resin aerogel through the sol-gel method can be directly prepared without additional network strengthening or organic solvent exchange. The resulting MF resin aerogel exhibits a homogeneous as well as hierarchical structure with macropores and mesopores (~6 µm and ~5 nm), high compressive modulus of 31.8 MPa, self-extinguishing property, and high-temperature thermal insulation with 97 % heat decrease for butane flame combustion. This work presents a straightforward and environmentally friendly method for fabricating MF resin aerogels with nanostructures and excellent performance in open conditions, exhibiting various applications.

Oxidative Upcycling of Polyethylene to Long Chain Diacid over Co-MCM-41 Catalyst.

Plastic pollution is an emerging global threat due to lack of effective methods for transforming waste plastics into useful resources. Here, we demonstrate a direct oxidative upcycling of polyethylene into high-value and high-volume long chain (C10-C20) saturated dicarboxylic acids in high carbon yield of 85.9% over cobalt-doped MCM-41 molecular sieves, in the absence of any solvent or precious metal catalyst. The distribution of the dicarboxylic acids can be controllably adjusted from short-chain (C4-C10) to long-chain ones (C10-C20) through changing cobalt loading of MCM-41 under nanoconfinement. Highly and sparsely dispersed cobalt along with confined space of mesoporous structure enables complete degradation of polyethylene and high selectivity of dicarboxylic acid in mild condition. So far, this is the first report on highly selective one-step preparation of long chain dicarboxylic acids. The approach provides an attractive solution to tackle plastic pollution and a promising alternative route to long chain diacids.

Water-solvent regulation on complete hydrolysis of thermosetting polyester and complete separation of degradation products.

As one of the largest productions of thermosetting plastics, unsaturated polyester resin (UPR) is difficult to be effectively chemcycled after it is discarded due to its dense network structure. Herein, we demonstrate a mild method for efficient alkaline hydrolysis of UPR into useful feedstocks in mixed solvents of polar aprotic solvent and a small amount of H2O by utilizing the fragmentation effect of the solvent on the UPR and the swelling effect of H2O on the subsequent partially hydrolyzed UPR respectively. The mixed solvents also play a key role in the aggregation and solubility of the degradation products. It is worth noting that the tetrahydrofuran (THF)-H2O system achieved 100 % separation of degradation products in an energy-efficient way taking advantage of the insolubility of the carboxylate-containing products in THF and the low boiling point of THF. The participation of non-reactive mixed solvents greatly promotes both the degradation and the separation process of thermosetting polymers.

Amphibious Nastic Hydrogel Based on the Tropic Movement of Gelatin and Its Opposite Phase Transition to PNIPAm.

Mimicking the anisotropic structure and environmental adaptation of organisms in nature remains a key objective in the field of hydrogels. However, it has been very challenging due to complex fabrication and confined application only in water. Here, we demonstrate a new strategy of spontaneous fabrication of an anisotropic hydrogel based on our finding in the tropic movement of gelatin toward the Teflon template. The obtained hydrogel exhibits fast response and recovery under temperature stimuli both in aqueous and non-aqueous environments, making use of the approximate transition temperature and opposite phase transition behavior of gelatin and poly(N-isopropylacrylamide) (PNIPAm). Its recovery performance in water is more than 50 times faster than that of the PNIPAm hydrogel. Furthermore, the PNIPAm/gelatin hydrogel can achieve 3D complex deformations, stealth deformation, erasable and reprogrammed surface patterning, and multistage encryption by simply modulating the location and shape of gelatin to achieve an anisotropic structure. The work provides a simple and versatile way to obtain an anisotropic hydrogel with a definite and predictable structure, which is demonstrated across a range of different monomers. It improves the responsive performance and broadens the hydrogel application to the non-aqueous environment. Additionally, this tropic movement of gelatin can be extended for the design of new types of anisotropic materials and thus endows the materials with diverse functionality.

Exploiting valuable supramolecular materials from waste plastics.

A new family of supramolecular materials is exploited from waste thermosets via a one-step retrosynthetic approach, which exhibits distinguished adhesion properties in dry/wet environments, good corrosion resistance and dynamic reversibility. This work opens up a wide design space for supramolecular materials with excellent performances and proposes a new strategy for efficient utilization of hybrid degraded products.

Multifunctional Materials from Aerobic Degradation of Epoxy Thermoset via Phosphotungstic Acid-Involved Activation and Bonding.

The growing scale of production of wind turbines represents a big challenge for chemical recycling of amine-cured epoxy resin (EP) to achieve high-efficiency degradation and high-value utilization of degradation products. Here, H2 O2 /phosphotungstic acid (HPW) catalytic oxidation system is demonstrated to completely degrade EP thermoset with the solid recovery rate of 96% at a reaction temperature of 80 °C for 4 h. Owing to protonation and bonding effect of HPW to the amine groups, the degradation products had a weight-average molecular weight of 4285 with narrow molecular weight distribution. They were used as dye adsorption blend films and supramolecular adhesives based on hydrogen bonding and coordination bonding respectively. The work demonstrates a feasible and promising method to recover the EP thermoset into high-performance materials.

Comprehensive analysis of complete chloroplast genome and phylogenetic aspects of ten Ficus species.

BACKGROUND: The large genus Ficus comprises approximately 800 species, most of which possess high ornamental and ecological values. However, its evolutionary history remains largely unknown. Plastome (chloroplast genome) analysis had become an essential tool for species identification and for unveiling evolutionary relationships between species, genus and other rank groups. In this work we present the plastomes of ten Ficus species. RESULTS: The complete chloroplast (CP) genomes of eleven Ficus specimens belonging to ten species were determined and analysed. The full length of the Ficus plastome was nearly 160 kbp with a similar overall GC content, ranging from 35.88 to 36.02%. A total of 114 unique genes, distributed in 80 protein-coding genes, 30 tRNAs, and 4 rRNAs, were annotated in each of the Ficus CP genome. In addition, these CP genomes showed variation in their inverted repeat regions (IR). Tandem repeats and mononucleotide simple sequence repeat (SSR) are widely distributed across the Ficus CP genome. Comparative genome analysis showed low sequence variability. In addition, eight variable regions to be used as potential molecular markers were proposed for future Ficus species identification. According to the phylogenetic analysis, these ten Ficus species were clustered together and further divided into three clades based on different subgenera. Simultaneously, it also showed the relatedness between Ficus and Morus. CONCLUSION: The chloroplast genome structure of 10 Ficus species was similar to that of other angiosperms, with a typical four-part structure. Chloroplast genome sizes vary slightly due to expansion and contraction of the IR region. And the variation of noncoding regions of the chloroplast genome is larger than that of coding regions. Phylogenetic analysis showed that these eleven sampled CP genomes were divided into three clades, clustered with species from subgenus Urostigma, Sycomorus, and Ficus, respectively. These results support the Berg classification system, in which the subgenus Ficus was further decomposed into the subgenus Sycomorus. In general, the sequencing and analysis of Ficus plastomes, especially the ones of species with no or limited sequences available yet, contribute to the study of genetic diversity and species evolution of Ficus, while providing useful information for taxonomic and phylogenetic studies of Ficus.

Metabolic stimulation-elicited transcriptional responses and biosynthesis of acylated triterpenoids precursors in the medicinal plant Helicteres angustifolia.

BACKGROUND: Helicteres angustifolia has long been used in Chinese traditional medicine. It has multiple pharmacological benefits, including anti-inflammatory, anti-viral and anti-tumor effects. Its main active chemicals include betulinic acid, oleanolic acid, helicteric acid, helicterilic acid, and other triterpenoid saponins. It is worth noting that some acylated triterpenoids, such as helicteric acid and helicterilic acid, are characteristic components of Helicteres and are relatively rare among other plants. However, reliance on natural plants as the only sources of these is not enough to meet the market requirement. Therefore, the engineering of its metabolic pathway is of high research value for enhancing the production of secondary metabolites. Unfortunately, there are few studies on the biosynthetic pathways of triterpenoids in H. angustifolia, hindering its further investigation. RESULTS: Here, the RNAs of different groups treated by metabolic stimulation were sequenced with an Illumina high-throughput sequencing platform, resulting in 121 gigabases of data. A total of 424,824 unigenes were obtained after the trimming and assembly of the raw data, and 22,430 unigenes were determined to be differentially expressed. In addition, three oxidosqualene cyclases (OSCs) and four Cytochrome P450 (CYP450s) were screened, of which one OSC (HaOSC1) and one CYP450 (HaCYPi3) achieved functional verification, suggesting that they could catalyze the production of lupeol and oleanolic acid, respectively. CONCLUSION: In general, the transcriptomic data of H. angustifolia was first reported and analyzed to study functional genes. Three OSCs, four CYP450s and three acyltransferases were screened out as candidate genes to perform further functional verification, which demonstrated that HaOSC1 and HaCYPi3 encode for lupeol synthase and ß-amyrin oxidase, which produce corresponding products of lupeol and oleanolic acid, respectively. Their successful identification revealed pivotal steps in the biosynthesis of acylated triterpenoids precursors, which laid a foundation for further study on acylated triterpenoids. Overall, these results shed light on the regulation of acylated triterpenoids biosynthesis.

Characterization of the Complete Chloroplast Genome of Buddleja lindleyana.

BACKGROUND: Buddleja lindleyana Fort., which belongs to the Loganiaceae with a distribution throughout the tropics, is widely used as an ornamental plant in China. There are several morphologically similar species in the genus Buddleja, but the lack of comprehensive molecular and phylogenetic studies makes it difficult to distinguish related species, which hinders further studies of this genus. OBJECTIVE: Using molecular biology techniques to sequence and analyze the complete chloroplast (cp) genome of B. lindleyana. METHODS: After sequencing of the genomic DNA using next-generation sequencing, a series of bioinformatics software were used to assemble and analyze the molecular structure of the cp genome of B. lindleyana. RESULTS: The complete cp genome of B. lindleyana is a circular 154 487-bp-long molecule with a GC (Guanine and Cytosine) content of 38.1%. It has a quadripartite structure, including a LSC region (85 489 base pair (bp)), a small single-copy region (17 898 bp), and a pair of inverted repeat regions (25 550 bp). A total of 133 genes were identified in this genome, including 86 protein-coding genes, 37 tRNA (transfer Ribonucleic Acid) genes, eight rRNA (ribosomal Ribonucleic Acid) genes, and two pseudogenes. CONCLUSION: These results suggest that the B. lindelyana cp genome could be used as a potential genomic resource to resolve the phylogenetic positions and relationships of Loganiaceae, and will offer valuable information for future research in the identification of Buddleja species and will conduce to genomic investigations into these species. HIGHLIGHTS: This paper study the B. lindelyana cp genome and it's structural characteristics, and analyze the phylogeny of Loganiaceae.

Multicycling of Epoxy Thermoset Through a Two-Step Strategy of Alcoholysis and Hydrolysis using a Self-Separating Catalysis System.

Plastic has now become a contradiction between civilization and pollution that human society has to resolve. The recycling of thermosetting plastics in waste plastics is a huge challenge since they are difficult to remold like thermoplastic plastics due to their high crosslinking density. Here, a new strategy was developed to achieve multicycling of anhydride-cured epoxy thermosets. The process consisted of mild and high-efficiency alcoholysis catalyzed by potassium phosphate/low-boiling alcohol system, and subsequent fast hydrolysis to obtain degradation products rich of carboxyl groups. The degradation products were reused as curing agent to prepare new anhydride-cured epoxy thermosets without sacrifice of high strength and stability. Moreover, the new epoxy thermosets could still be repeatedly recycled using the same protocol. The insolubility of potassium phosphate in ethanol at room temperature made the separation and reuse of the catalyst more convenient. The use of low-boiling alcohol not only allowed high-efficiency degradation but also enabled easy separation from the degradation products. The excellent degradation performance was attributed to the improved swelling of the thermoset and the increased solubility of potassium phosphate induced by small amounts of water in the alcohol. This research provides a recycling method that can reintegrate thermoset waste plastics into remodeling ones under the background of circular economy.

Comparative genomic study on the complete plastomes of four officinal Ardisia species in China.

Ardisia Sw. (Primulaceae) is naturally distributed in tropical and subtropical areas. Most of them possess edible and medicinal values and are popular in clinical and daily use in China. However, ambiguous species delineation and genetic information limit the development and utilization of this genus. In this study, the chloroplast genomes of four Ardisia species, namely A. gigantifolia Stapf, A. crenata Sims, A. villosa Roxb. and A. mamillata Hance, were sequenced, annotated, and analyzed comparatively. All the four chloroplast genomes possess a typical quadripartite structure, and each of the genomes is about 156 Kb in size. The structure and gene content of the Ardisia plastomes were conservative and showed low sequence divergence. Furthermore, we identified five mutation hotspots as candidate DNA barcodes for Ardisia, namely, trnT-psbD, ndhF-rpl32, rpl32-ccsA, ccsA-ndhD and ycf1. Phylogenetic analysis based on the whole-chloroplast genomes data showed that Ardisia was sister to Tapeinosperma Hook. f. In addition, the results revealed a great topological profile of Ardisia's with strong support values, which matches their geographical distribution patterns. Summarily, our results provide useful information for investigations on taxonomic differences, molecular identification, and phylogenetic relationships of Ardisia plants.

Genome-Wide Identification and Functional Characterization of the Trans-Isopentenyl Diphosphate Synthases Gene Family in Cinnamomum camphora.

Trans-isopentenyl diphosphate synthases (TIDSs) genes are known to be important determinants for terpene diversity and the accumulation of terpenoids. The essential oil of Cinnamomum camphora, which is rich in monoterpenes, sesquiterpenes, and other aromatic compounds, has a wide range of pharmacological activities and has therefore attracted considerable interest. However, the TIDS gene family, and its relationship to the camphor tree (C. camphora L. Presl.), has not yet been characterized. In this study, we identified 10 TIDS genes in the genome of the C. camphora borneol chemotype that were unevenly distributed on chromosomes. Synteny analysis revealed that the TIDS gene family in this species likely expanded through segmental duplication events. Furthermore, cis-element analyses demonstrated that C. camphora TIDS (CcTIDS) genes can respond to multiple abiotic stresses. Finally, functional characterization of eight putative short-chain TIDS proteins revealed that CcTIDS3 and CcTIDS9 exhibit farnesyl diphosphate synthase (FPPS) activity, while CcTIDS1 and CcTIDS2 encode geranylgeranyl diphosphate synthases (GGPPS). Although, CcTIDS8 and CcTIDS10 were found to be catalytically inactive alone, they were able to bind to each other to form a heterodimeric functional geranyl diphosphate synthase (GPPS) in vitro, and this interaction was confirmed using a yeast two-hybrid assay. Furthermore, transcriptome analysis revealed that the CcTIDS3, CcTIDS8, CcTIDS9, and CcTIDS10 genes were found to be more active in C. camphora roots as compared to stems and leaves, which were verified by quantitative real-time PCR (qRT-PCR). These novel results provide a foundation for further exploration of the role of the TIDS gene family in camphor trees, and also provide a potential mechanism by which the production of camphor tree essential oil could be increased for pharmacological purposes through metabolic engineering.

Metabolism and transcriptome profiling provides insight into the genes and transcription factors involved in monoterpene biosynthesis of borneol chemotype of Cinnamomum camphora induced by mechanical damage.

BACKGROUND: The borneol chemotype of Cinnamomum camphora (BCC), a monoterpene-rich woody plant species, is the sole source prescribed by the Chinese Pharmacopoeia for the production of natural D-borneol, a major monoterpene in BCC used for millennia as a topical analgesic in China. Nevertheless, the possible gene-regulatory roles of transcription factors (TFs) in BCC's monoterpenoid biosynthesis remained unknown. Here, a joint analysis of the transcriptome and terpenoid metabolome of BCC induced by mechanical damage (MD) was used to comprehensively explore the interaction between TFs and terpene synthase (TPS) unigenes that might participate in monoterpene biosynthesis in BCC. RESULTS: Gas chromatography-mass spectrometry analysis detected 14 monoterpenes and seven sesquiterpenes. All but two monoterpenes underwent a significantly increased accumulation after the MD treatment. RNA sequencing data revealed that 10 TPS, 82 MYB, 70 AP2/ERF, 38 BHLH, 31 WRKY, and 29 bZIP unigenes responded to the MD treatment. A correlation analysis revealed that three monoterpene synthase genes (CcTPS1, CcTPS3, CcTPS4) highly correlated with multiple monoterpenes, namely D-borneol, camphor, and bornyl acetate, which could be responsible for monoterpenoid biosynthesis in BCC. Furthermore, five WRKY, 15 MYB, 10 ERF/AP2, five bZIP, and two BHLH genes had strong, positive correlations with CcTPS1 or CcTPS4, judging by their high coefficient values (R2 > 0.8). The bioinformatics results were verified by quantitative real-time PCR. CONCLUSION: This study provides insight into the genes involved in the biosynthesis and regulation of monoterpene in BCC and thus provides a pool of candidate genes for future mechanistic analyses of how monoterpenes accumulate in BCC.

Recycling waste thermosetting unsaturated polyester resins into oligomers for preparing amphiphilic aerogels.

The styrene-maleic acid copolymer (SMC) was obtained by selective and complete cleavage of ester groups from waste thermosetting unsaturated polyester resins (WTUPR). The degradation was performed in glycol at 180 °C for 5 h with potassium carbonate as a catalyst and the resultant potassium salt of SMC (SMC-K) can be very easily separated by precipitation using ethanol with a yield of 63.8%. The SMC-K was integrated with polyvinyl alcohol to form amphiphilic aerogels via freeze-thaw and freeze-drying processes. The aerogel exhibits a low density of 0.024 g·mL-1 due to hierarchical pore structures with a size range from nanometer to micrometer scale. Besides, the good compressibility and resilience of the aerogel are demonstrated. The amphiphilic aerogel displayed high absorption of both water and oily liquids (over 30 g.g-1 and 20 g.g-1 for water and dichloromethane respectively), together with a good recycle adsorption efficiency (>90% after 10 cycles). This work provides a new strategy on upcycling of WTUPR.

Mining of candidate genes involved in the biosynthesis of dextrorotatory borneol in Cinnamomum burmannii by transcriptomic analysis on three chemotypes.

BACKGROUND: Dextrorotatory borneol (D-borneol), a cyclic monoterpene, is widely used in traditional Chinese medicine as an efficient topical analgesic drug. Fresh leaves of Cinnamomum trees, e.g., C. burmannii and C. camphor, are the main sources from which D-borneol is extracted by steam distillation, yet with low yields. Insufficient supply of D-borneol has hampered its clinical use and production of patent remedies for a long time. Biological synthesis of D-borneol offers an additional approach; however, mechanisms of D-borneol biosynthesis remain mostly unresolved. Hence, it is important and necessary to elucidate the biosynthetic pathway of D-borneol. RESULTS: Comparative analysis on the gene expression patterns of different D-borneol production C. burmannii samples facilitates elucidation on the underlying biosynthetic pathway of D-borneol. Herein, we collected three different chemotypes of C. burmannii, which harbor different contents of D-borneol.A total of 100,218 unigenes with an N50 of 1,128 bp were assembled de novo using Trinity from a total of 21.21 Gb clean bases. We used BLASTx analysis against several public databases to annotate 45,485 unigenes (45.38%) to at least one database, among which 82 unigenes were assigned to terpenoid biosynthesis pathways by KEGG annotation. In addition, we defined 8,860 unigenes as differentially expressed genes (DEGs), among which 13 DEGs were associated with terpenoid biosynthesis pathways. One 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and two monoterpene synthase, designated as CbDXS9, CbTPS2 and CbTPS3, were up-regulated in the high-borneol group compared to the low-borneol and borneol-free groups, and might be vital to biosynthesis of D-borneol in C. burmannii. In addition, we identified one WRKY, two BHLH, one AP2/ERF and three MYB candidate genes, which exhibited the same expression patterns as CbTPS2 and CbTPS3, suggesting that these transcription factors might potentially regulate D-borneol biosynthesis. Finally, quantitative real-time PCR was conducted to detect the actual expression level of those candidate genes related to the D-borneol biosynthesis pathway, and the result showed that the expression patterns of the candidate genes related to D-borneol biosynthesis were basically consistent with those revealed by transcriptome analysis. CONCLUSIONS: We used transcriptome sequencing to analyze three different chemotypes of C. burmannii, identifying three candidate structural genes (one DXS, two monoterpene synthases) and seven potential transcription factor candidates (one WRKY, two BHLH, one AP2/ERF and three MYB) involved in D-borneol biosynthesis. These results provide new insight into our understanding of the production and accumulation of D-borneol in C. burmannii.

Characteristics analysis of the complete Wurfbainia villosa chloroplast genome.

Wurfbainia villosa, which belongs to the huge family Zingiberaceae, is used in the clinic for the treatment of spleen and stomach diseases in southern China. The complete chloroplast genome of W. villosa was sequenced and analyzed using next-generation sequencing technology in the present work. The results showed that the W. villosa chloroplast genome is a circular molecule with 163,608 bp in length. It harbors a pair of inverted repeat regions (IRa and IRb) of 29,820 bp in length, which separate the large single copy (LSC, 88,680 bp) region and the small single copy (SSC, 15,288 bp) region. After annotation, 134 genes were identified in this plastome in total, comprising of 87 protein-coding genes, 38 transfer RNA genes, 8 ribosomal RNA genes and one pseudogene (ycf1). Codon usage, RNA editing sites and single/long sequence repeats were investigated to understand the structural characteristics of the W. villosa chloroplast genome. Furthermore, IR contraction and expansion were analyzed by comparison of complete chloroplast genomes of W. villosa and four other Zingiberaceae species. Finally, a phylogeny study based on the chloroplast genome of W. villosa, along with that of 15 different species, was conducted to further investigate the relationship among these lineages. Overally, our results represented the first insight into the chloroplast genome of W. villosa, and could serve as a significant reference for species identification, genetic diversity analysis and phylogenetic research between W. villosa and other species within Zingiberaceae.

A nonswellable gradient hydrogel with tunable mechanical properties.

Susceptibility of traditional hydrogels to water leads to the deterioration of their mechanical properties and dimensional instability. Inspired by bone tissues, here, we report a nonswellable gradient hydrogel with adjustable mechanical properties via a simple acid-heat treatment of polyamide-based hydrogels. Both the hydrophilicity/hydrophobicity and crosslinking degree of the gel can be simultaneously regulated by taking advantage of the conversion of amide groups to imide groups in the hydrogel. A gradient imide structure is formed with a dense layer near the surface of the gel. The resultant hydrogel has no size change both in water and 0.9 wt% NaCl solution while it shows high strength with a compressive stress of 70 MPa at 70% strain at a higher imidization degree. At a lower imidization degree, the gel has excellent fatigue resistance and resilience and can return to its original state after 5 cycles of 90% strain.

Fast microwave-assisted hydrolysis of unsaturated polyester resin into column packing for rapid purifying of dye wastewater.

Microwave-assisted selective degradation successfully converts thermosetting unsaturated polyester resins into a low-swelling (below 10 g g-1) gel material (GM) with a high yield (58-65%) in water at 100°C for only 1 h. The obtained GM possesses rough and porous structure while the content of carboxylate group obtained by cleavage of partial ester groups is more than 10%, varying with the concentration of the catalyst. It is suitable for use as packing of adsorption column to rapidly purify sewage. Super high filtering rates of 18582-27002 L h-1 m-3 without external pressure and high removal efficiency of more than 99.8% were achieved, promoting practical application for rapid removal of organic pollutants.

Biomimetic Color-Changing Hierarchical and Gradient Hydrogel Actuators Based on Salt-Induced Microphase Separation.

There have been more challenges for hydrogel actuators to meet the combined requirement of discoloration, complex deformation, and simple preparation. Structural coloration is widely used to fabricate discolored hydrogel via microrearrangement of photonic crystals in the hydrogel framework. However, precise regulation is usually required. Besides, the macro-optical properties are unstable. Herein, we develop a hierarchical and gradient hydrogel actuator with complex deformation and color-changing functions using an electrophoresis method. A simple but effective strategy is presented for fabrication of hierarchical hydrogel composed of homopolymers and copolymers via salt-induced microphase separation during the polymerization of the N-isopropylacrylamide (NIPAm) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (DMC). Meanwhile a gradient distribution of DMC is also formed during the polymerization due to migration of DMC under electric field. The hierarchical and gradient structures are characterized by confocal laser scanning microscope (CLSM), small-angle X-ray scattering measurement (SAXS), temperature-variable Fourier transform infrared (FTIR), etc. The discoloration mechanism is proposed. The as-prepared hydrogel can undergo fast and complex thermo-triggered deformation and discoloration. Bionic movements of discoloration flowering and information encryption are successfully demonstrated, promising great potential in the application of biomimetic materials.

Autofluorescence of hydrogels without a fluorophore.

Fluorescent hydrogels have recently attracted great attention for medical diagnostics, bioimaging and environmental monitoring. However, additional phosphors or fluorophores are always required to label the hydrogels, and they suffer from marker bleaching, signal drifts, or information misrepresentation. Here we report autofluorescence that universally exists in carbonyl-containing hydrogels without any traditional fluorophore. The fluorescence is successfully employed to self-monitor the gelation process since the fluorescence signal is closely related to the internal structural change of the gels. The crosslinked structure is beneficial to the fluorescence efficiency. Specifically, the fluorescence intensity is amplified with decreasing water content of the gels. The system realizes aggregation-induced emission in a water-deficient environment. The fluorescence is quenched by the addition of some specific metal ions, which can realize the successfully erasure and rewriting of information under visible light and ultraviolet light respectively. We believe that the spontaneous fluorescence of a gel provides the most reliable basis for the detection of a gel structure and opens new prospects in the application of hydrogels.