Photoswitchable Spiropyridine Enabled Photoactuation of Polymeric Hydrogels under Physiological pH Conditions

The incorporation of molecular switches into polymer networks has been a powerful approach for the development of functional polymer materials that display macroscopic actuation and function enabled directly by molecular changes.However,such materials sometimes require harsh conditions to perform their functions,and the design of new molecular photoswitches that can function under physiological conditions is highly needed.Here,we report the design and synthesis of a spiropyridine-based photoswitchable hydrogel that exhibits light-driven actuation at physiological pH.Owing to its high p Ka,spiropyridine maintains its ring-open protonated form at neutral pH,and the resulting hydrogel remains in a swollen state.Upon irradiation with visible light,the ring closure of spiropyridine leads to a decrease in the charge and a reduction in the volume of the hydrogel.The contracted gel could spontaneously recover to its expanding state in the dark,and this process is highly dynamic and reversible when the light is switched on and off.Furthermore,the hydrogel shows switchable fluorescence in response to visible light.Bending deformation is observed in the hydrogel thin films upon irradiation from one side.Importantly,the independence of this spiropyridine hydrogel from the acidic environment makes it biotolerant and shows excellent biocompatibility.This biocompatible spiropyridine hydrogel might have important biorelated applications in the future.

Lanthanide coordinated multicolor fluorescent polymeric hydrogels for bio-inspired shape/color switchable actuation through local diffusion of Tb^(3+)/Eu^(3+)ions

Lanthanide coordinated multicolor fluorescent polymeric hydrogels(MFPHs)are quite promising for various applications because of their sharp fluorescence bands and high color purity.However,few attempts have been carried out to locally regulate their fluorescence switching or shape deforming behaviors,but such studies are very useful for patterned materials with disparate functions.Herein,the picolinate moieties that can sensitize Tb^(3+)/Eu^(3+)luminescence via antenna effect were chemically introduced into interpenetrating double networks to produce a robust kind of lanthanide coordinated MFPHs.Upon varying the doping ratio of Tb^(3+)/Eu^(3+),fluorescence colors of the obtained hydrogels were continuously regulated from green to orange and then red.Importantly,spatial fluorescence color control within the hydrogel matrix could be facilely realized by controlled diffusion of Tb^(3+)/Eu^(3+)ions,producing a number of 2D hydrogel objects with local multicolor fluorescent patterns.Furthermore,the differential swelling capacities between the fluorescent patterned and non-fluorescent parts led to interesting 2D-to-3D shape deformation to give well-defined multicolor fluorescent 3D hydrogel configurations.Based on these results,bio-inspired synergistic color/shape changeable actuators were demonstrated.The present study provided a promising strategy to achieve the local fluorescence and shape control within lanthanide coordinated hydrogels,and is expected to be expanded for fabricating useful patterned materials with disparate functions.

Self-healing Polymeric Hydrogels:Toward Multifunctional Soft Smart Materials

The concept of self-healing that involves a built-in ability to heal in response to damage wherever and whenever it occurs in a material,analogous to the healing process in living organisms,has emerged a couple of decades ago.Driven primarily by the demands for life-like materials and soft smart materials,therefore,the development of self-healing polymeric hydrogels has continually attracted the attention of the scientific community.Here,this review is intended to give an in-depth overview of the state-of-the-art advances in the field of self-healing polymeric hydrogels.Specifically,recently emerging trends in self-healing polymeric hydrogels are summarized,and notably,recommendations to endow these hydrogels with fascinating multi-functionalities including luminescence,conductivity/magnetism and shape memory etc are presented.To close,the current challenges and future opportunities in this field are also discussed.

Progress in aggregation-induced emission-active fluorescent polymeric hydrogels

Aggregation-induced emission(AIE)-active fluorescent polymeric hydrogels(FPHs)are the marriage of AIE-active materials and polymeric hydrogels.Different from the widely studied AIE-active materials that are primarily used in solution or dry solid state,they feature a three-dimensional crosslinked polymer network that can absorb water without dissolving.Consequently,they are known to bear many advantageous properties such as soft wet nature,tissue-like mechanical strength,biocompatibility,biomimetic self-healing feature,facilely tailored structure,as well as responsive fluorescence and volume/shape changes,thus representing a promising category of luminescent materials with many frontier uses.This Review is intended to give a systematic summary of the recent progress in this young but flourishing research area,with particular focus on their design and preparation.Current challenges and future outlooks in this field are also discussed in order to attract new interests and inspire more efforts.

Ion-induced white-light-emitting polymeric hydrogels with high mechanical strength and reversible stimuli-responsive properties

We have developed a facile strategy to fabricate model multicolor hydrogels via a straightforward mixing process of poly acrylonitrile-grafted methacrylamide(PANMAM),polymethacrylic acid(PMAA)and doped lanthanide(Eu/Tb)and zinc ions to form the interpenetrating dual-polymer gel networks.The hydrogels exhibit excellent tunability of multi-spectrum emission colors(including white light)by simply varying the stoichiometry of metal ions.Furthermore,taking the advantage of different metal ion response mechanisms,we have demonstrated the reversible acidity/alkalinity stimuli-responsive behaviors of white-light-emitting hydrogel(WLE gel).Meanwhile,the unique cross-linked network formed through hydrogen-bonding,metal-ligand coordination and ionic interaction is introduced to achieve favorable mechanical strength of hydrogels.These properties enable the possibility in obtaining fluorescent patterns on hydrogels,which are promising candidate for encrypted information with improved security.

Polymer Hydrogel Electrolytes for Flexible and Multifunctional Zinc-Ion Batteries and Capacitors

Flexibility and multifunctionality are now becoming inevitable worldwide tendencies for electronic devices to meet modern life's convenience,efficiency,and quality demand.To that end,developing flexible and wearable energy storage devices is a must.Recently,aqueous zinc-ion batteries(ZIBs)and zinc-ion capacitors(ZICs)stand out as two of the most potent candidates for wearable electronics due to their excellent electrochemical performance,intrinsic safety,low cost,and functional controllability.Simultaneously,polymer electrolytes'introduction and rational design,especially various hydrogels,have endowed conventional ZIBs and ZICs with colorful functions,which has been regarded as a perfect answer for energy suppliers integrated into those advanced wearable electronic devices.This review focuses on the functional hydrogel electrolytes(HEs)and their application for ZIBs and ZICs.Previously reported HEs for ZIBs and ZICs were classified and analyzed,from the flexibility to mechanical endurance,temperature adaptability,electrochemical stability,and finally cell-level ZIBs and ZICs based on multifunctional HEs.Besides introducing the diverse and exciting functions of HEs,working principles were also analyzed.Ultimately,all the details of these examples were summarized,and the related challenges,constructive solutions,and futural prospects of functional ZIBs and ZICs were also dedicatedly evaluated.

Recent advances and innovations in the design and fabrication of wearable flexible biosensors and human health monitoring systems based on conjugated polymers

Wearable biosensors have received great interest as patient-friendly diagnostic technologies because of their high flexibility and conformability.The growing research and utilization of novel materials in designing wearable biosensors have accelerated the development of point-of-care sensing platforms and implantable biomedical devices in human health care.Among numerous potential materials,conjugated polymers(CPs)are emerging as ideal choices for constructing high-performance wearable biosensors because of their outstanding conductive and mechanical properties.Recently,CPs have been extensively incorporated into various wearable biosensors to monitor a range of target biomolecules.However,fabricating highly reliable CP-based wearable biosensors for practical applications remains a significant challenge,necessitating novel developmental strategies for enhancing the viability of such biosensors.Accordingly,this review aims to provide consolidated scientific evidence by summarizing and evaluating recent studies focused on designing and fabricating CP-based wearable biosensors,thereby facilitating future research.Emphasizing the superior properties and benefits of CPs,this review aims to clarify their potential applicability within this field.Furthermore,the fundamentals and main components of CP-based wearable biosensors and their sensing mechanisms are discussed in detail.The recent advancements in CP nanostructures and hybridizations for improved sensing performance,along with recent innovations in next-generation wearable biosensors are highlighted.CPbased wearable biosensors have been—and will continue to be—an ideal platform for developing effective and user-friendly diagnostic technologies for human health monitoring.

Nanocomposite Polymer Hydrogels Reinforced by Carbon Dots and Hectorite Clay

Herein, two nanoparticles with different dimensions, spherical carbon dots (C-dots) and sheetlike hectorite clay, were used as physical crosslinkers to fabricate C-dots-clay-poly(N-isopropylacrylamide)nanocompositehydrogels (coded as C-dots-clay-PNIPAm hydrogels). The mechanical properties, fluorescence features and thermal-responsive properties of the C-dots-clay-PNIPAm hydrogels were evaluated. The experimental results indicate that synergistic effects of C-dots and hectorite clay nanoparticles are able to significantly enhance mechanical properties of the hydrogels. The hydrogels can be stretched up to 1730%with strength as high as 250 kPa when the C-dots concentration is 0.1wt%and the clay concentration is 6wt%. The hydrogels exhibit complete self-healing through autonomic reconstruction of crosslinked network a damaged interface. The hydrogels show favorable thermal-responsive properties with the volume phase transition around 34℃. In addition, the hydrogels are endowed with fluorescence features that are associated with C-dots in the hydrogels. It can be expected that the as-fabricated C-dots-clay-PNIPAm hydrogels are promising for applications in sensors, biomedical carriers and tissue engineering.

Readily prepared and processed multifunctional MXene nanocomposite hydrogels for smart electronics

Booming sophisticated robotics and prosthetics put forward high requirements on soft conductive materials that can bridge electronics and biology,those soft conductive materials should imitate the mechanical properties of biological tissues and build information transmission networks.Until now,it remains a great challenge to handle the trade-off among ease of preparation,high conductivity,processability,mechanical adaptability,and external stimuli responsiveness.Herein,a kind of readily prepared and processed multifunctional MXene nanocomposite hydrogel is reported,which is prepared via the fast gelation of cationic monomer initiated by delaminated MXene sheets.The gelation time can be adjusted(several seconds to minutes)based on the MXene loadings.By adjusting the MXene ratio,the resulting nanocomposites are ultrastretchable(>5000%),three-dimensional(3D)printable,and show outstanding mechanical and electrical self-healing.As expected,the integration of multifunctional systems onto various substrates(e.g.,gloves and masks)is further demonstrated via 3D printing and could achieve diverse sensory capabilities toward strain,pressure,and temperature,showing great prospects as smart flexible electronics.

Utilizing synergistic effects of bifunctional polymer hydrogel PAM-PAMPS for selective capture of Pb(Ⅱ)from wastewater

The preparation of hydrogel adsorbents with admirable performance for efficient selective remove Pb(Ⅱ)in complex wastewater still remains a great challenge.Herein,a novel bifunctional modified polymer hydrogel PAM-PAMPS was prepared by crosslinking acrylamide(AM)and 2-acrylamido-2-methylpropanesulfonic acid(AMPS).Compared with PEG,PAA and PAMPS,PAM-PAMPS exhibited both the maximum adsorption capacity of Pb(Ⅱ)(541.90 mg/g)and satisfactory selectivity for Pb(Ⅱ)in multiple heavy metal ions coexistence solutions.Various characterizations indicated that–SO3H and–NH2as active sites on PAM-PAMPS occur the synergistic effects of ion-exchange and coordination with Pb(Ⅱ)during the adsorption process,respectively.The adsorption energy Ead(PAM-PAMPS)obtained from density functional theory(DFT)calculations was lower than the other three hydrogels,manifesting that PAMPAMPS formed the most stable complex with Pb(Ⅱ),which further demonstrated that Pb(Ⅱ)preferred to combine with PAM-PAMPS to selective capture of Pb(Ⅱ).The practice utilization of PAM-PAMPS was assessed by wastewater of electroplate containing Pb(Ⅱ).Meanwhile,the removal ratio of PAM-PAMPS was maintained at about 89%after 4 adsorption-desorption cycles.This study establishes a new and effective idea for the design and fabrication of bifunctionalized modified polymer hydrogels.

A Review of the Development of Properties and Structures Based on Konjac Glucomannan as Functional Materials

In recent years, konjac glucomannan（KGM） has gained considerable attention due to its non-toxic, harmless, excellent biocompatibility, biodegradability, good water imbibition as well as gel properties. KGM and its derivatives have been widely used in food science, chemical, pharmaceutical, and material areas. In this review, we will focus on the most recent advances in the structures and properties of KGM. We will first describe the influence of different modification methods on the structures and properties of KGM. Then we will review the results obtained with KGM as functional materials in different studies in the fields of hydrogels, aerogels, nanoparticles, membrane materials, microspheres and microcapsule to provide theoretical basis for the further study.

Preparation of pH-sensitive Composite Nanofiltration Membrane

Positively charged composite nanofiltration （NF） membranes were prepared through interfacial polymerization of poly[2-（N,N-dimethyl amino）ethyl methacrylate]（PDMAEMA） on porous polysulfone （PSF） substrate membranes. The effects of pH on swelling ratio （SR） of the pure crosslinked PDMAEMA membrane and on separation performances of the composite NF membrane were investigated. The results show that the quaternized amino groups produced through interfacial polymerization technique are soluble in both phases, which accelerate the crosslinking reaction as self-catalysts. The swelling/contracting behavior of the pure crosslinked PDMAEMA exhibited a well reversible pH sensitive property. Importantly, the rejection and flux of the composite NF membrane show pH-sensitive behavior in NF process. Furthermore, with the help of a relatively novel method to measure membrane conduction, the true zeta potentials calculated on the basis of the streaming potential measurements proved the pH-sensitive behavior of the NF membrane.

Tailored wrinkles for tunable sensing performance by stereolithography

Conducting polymer hydrogel can address the challenges of stricken biocompatibility and durability.Nevertheless,conventional conducting polymer hydrogels are often brittle and weak due to the intrinsic quality of the material,which exhibits viscoelasticity.This property may cause a delay in sensor response time due to hysteresis.To overcome these limitations,we have designed a wrinkle morphology three-dimensional(3D)substrate using digital light processing technology and then followed by in situ polymerization to form interpenetrating polymer network hydrogels.This novel design results in a wrinkle morphology conducting polymer hydrogel elastomer with high precision and geometric freedom,as the size of the wrinkles can be controlled by adjusting the treating time.The wrinkle morphology on the conducting polymer hydrogel effectively reduces its viscoelasticity,leading to samples with quick response time,low hysteresis,stable cyclic performance,and remarkable resistance change.Simultaneously,the 3D gradient structure augmented the sensor's sensitivity under minimal stress while exhibiting consistent sensing performance.These properties indicate the potential of the conducting polymer hydrogel as a flexible sensor.

A high strength pH responsive supramolecular copolymer hydrogel

Constructing high strength pH sensitive supramolecular polymer hydrogel remains very challenging due to the unavoidable network swelling caused by ionization of acid or basic groups at a specified pH.In this work,we proposed a simple and very convenient approach to fabricate high strength pH responsive supramolecular polymer(SP) hydrogels by one-pot copolymerization of N-acryloyl glycinamide(NAGA) and 2-vinyl-4,6-diamino-1,3,5-triazine(VDT),two feature hydrogen bonding monomers.In these PNAGA-PVDT SP hydrogels obtained,the hydrogen bonding of NAGA was shown to play a dominant role in reinforcing strength,while the hydrogen bonding of diaminotriazine served as a pH sensitive moiety.At pH 3,the mechanical properties of PNAGA-PVDT hydrogels decreased to a different extent due to the breakup of hydrogen bonding;in contrast,the hydrogel resumed the original strength while pH was raised to 7.4 because of reconstruction of hydrogen bonding.Over the selected pH range,the PNAGA-PVDT hydrogels exhibited up to 1.25 MPa tensile strength,845% breaking strain,69 kPa Young's modulus and 21 MPa compressive strength.This novel high strength pH-responsive SP hydrogels may find applications in biomedical and industrial fields.

Boosting the energy density of aqueous MXene-based supercapacitor by integrating 3D conducting polymer hydrogel cathode

The wide-spread proliferation of aqueous MXene-based supercapacitor has been largely shadowed by the limited cell potential window(typically in the range of 0-0.6 V).To address this baffling issue,designing asymmetric supercapacitor(ASC)is proposed as a rational strategy to enlarge the potential window(thus energy density)of individual cell in aqueous electrolytes.To this date,however,it still remains a great challenge to develop easy fabricating,3D nanostructured,and pseudocapacitive cathode materials that can perfectly match with MXene anodematerials.In this work,we propose a supramolecular strategy to construct conducting polymer hydrogel(CPH)with highly interconnected 3D nanostructures and large pseudocapacitance,which can finely match with 2D Ti_(3)C_(2)T_(x).The as-assembled CPH//Ti_(3)C_(2)T_(x) ASCwith CPH cathode and MXene anode can operate in a broadened potential window of 1.15 V in aqueous PVA/H_(2)SO_(4) gel electrolyte with remarkably improved energy density of 16.6μWh/cm^(2)(nine times higher than that of symmetric MXene supercapacitor).Additionally,this ASC exhibits outstanding cyclic stability with no trackable performance decay over 30,000 galvanostatic charge and discharge cycles.It is demonstrated in this work that employing positive CPH electrode is a feasible yet promising strategy to enhance the potential window and energy density of aqueous MXene supercapacitors.

Multi-bond Network Hydrogels with Robust Mechanical and Self-healable Properties

Multi-bond network（MBN） which contains a single network with hierarchical cross-links is a suggested way to fabricate robust hydrogels. In order to reveal the roles of different cross-links with hierarchical bond energy in the MBN, here we fabricate poly（acrylic acid） physical hydrogels with dual bond network composed of ionic cross-links between carboxylFe3＋ interactions and hydrogen bonds, and compare these dually cross-linked hydrogels with singly and ternarily cross-linked hydrogels. Simple models are employed to predict the tensile property, and the results confirm that the multi-bond network with hierarchical distribution in the bond energy of cross-links endows hydrogel with effective energy-dissipating mechanism. Moreover, the dually cross-linked MBN gels exhibit excellent mechanical properties（tensile strength up to 500 k Pa, elongation at break ~ 2400%） and complete self-healing after being kept at 50 °C for 48 h. The factors on promoting self-healing are deeply explored and the dynamic multi-bonds are regarded to trigger the self-healing along with the mutual diffusion of long polymer chains and ferric ions.

Dual Thermal-and p H-responsive Polypeptide-based Hydrogels

Smart hydrogels have received increasing attention for their great potential for the applications in many fields. Herein, we report a facile approach to prepare a class of dual-responsive hydrogels assembled from synthetic statistical/block thermal-responsive copoly（L-glutamate）s copolymerized with poly（ethylene glycol）, which were prepared by ring-opening polymerization（ROP） and post-modification strategy. The incorporation of oligo（ethylene glycol）（OEG） and glutamic acid residues offers the gels with thermal-and p H-responsive properties simultaneously. We have systematically studied the influence of both temperature and p H on the gelation behaviors of these copolymers. It is found that the increase of glutamic acid content and solution p H values can significantly suppress the gelation ability of the samples. Circular dichroism（CD） results show that the α-helix conformation appears to be the dominant secondary conformation. More interestingly, the gelation property of the block copolymer with statistical thermal-responsive copoly（L-glutamate）s shows greater dependence on p H as compared to that with block segments due to the distinct morphology of the self-assemblies. The obtained hydrogels exhibit p H-dependent and thermal-responsive gelation behaviors, which enable them as an ideal smart hydrogel system for biomedical applications.

Hydrogels of Chemically Cross-linked and Organ-metallic Complexed Interpenetrating PEG Networks

The aim of the present work was to prepare a well-defined hydrogel of chemically cross-linked and organ-metallic complexed interpenetrating PEG networks. The hydrogel was synthesized via the reaction of copper（I）- catalyzed 1,3-dipolar azide-alkyne cycloaddition（CuA AC） with poly（ethylene glycol）-dopamine（PEG-DA）（“Click Chemistry”） followed by complexation with Fe-（3＋） ions to crosslink the polymeric network. The chemical composition and morphology of the resulting hydrogels were characterized by Fourier transform infrared spectroscopy（FTIR）, -1H-NMR and scanning electron microscopy（SEM）. Swelling ratio, mechanical strength, conductivity, and degradation behaviors of the hydrogels were also studied. The effect of the polymer chain length on properties of hydrogels was explored. The compressive strength of hydrogels could reach as high as 13.1 MPa with a conductivity of 2.2 × 10^-5 S·cm^-1. The hydrogels also exhibited excellent thermal stability even at a temperature of 300 °C, whereas degradation of the hydrogel after 7 weeks was observed under a physiological condition. In addition, the hydrogel exhibited a good biocompatibility based on its in vivo performance through an in vivo subcutaneous implantation model. No inflammation and no obvious abnormality of the surrounding tissue were observed when the hydrogel was subcutaneously implanted for 2 weeks. This work is a step towards creating a new pathway to synthesize hydrogels of interpenetrating networks which could be of important applications in the future research.

Magnetic poly(acrylic acid)-based hydrogels for rapid ammonium sorption and efficient sorbent separation from sewage

Ammonium sorption and recovery processes typically take place in conventional packed columns,with a configuration that enables maximum sorption by the sorbents.However,batch or semi-continuous operations in packed columns have associated issues such as scaling and frequent backwashing requirements,which are economically prohibitive.As an alternative,ammonium sorption could occur in well-mixed continuously stirred tanks,which would allow for the ammonium sorption process to be retrofitted in existing wastewater treatment plants,provided that efficient sorbent separation can be achieved.This study demonstrates,for the first time,the preparation of magnetic poly(acrylic acid)-based(PAA)ammonium sorbents through the incorporation of magnetic(Fe_(3)O_(4))nanoparticles(MNP)produced via scalable and cost-effective electrochemical synthesis.The MNP and PAA hydrogels were synthesized independently and the MNPs subsequently integrated into the PAA hydrogel network by particle diffusion and physical entrapment.No adverse effects on swelling and ammonium sorption following immersion in either synthetic or real sewage were observed after MNPs were incorporated into the hydrogels.Importantly,PAA-MNP hydrogels demonstrated high ammonium sorption efficiencies(80-93%)in real sewage and achieved rapid ammonium recovery of 73±1.1% within 15 min of mild acid washing(pH 4)15 min at a maximum recovery.