Layered Rare-Earth Hydroxide/Polyacrylamide Nanocomposite Hydrogels with Highly Tunable Photoluminescence

A pseudo-Double-Network Hydrogel Built upon Layered Double Hydroxides with Self-Strengthening Properties

While great achievements have been made in the development of mechanically robust nanocomposite hydrogels, incorporating multiple interactions on the bases of two demensional inorganic cross-linkers to construct self-strengthening hydrogels has rarely been investigated. To this end, we propose here a new method for the coupling the dynamic covalent bonds and non-covalent interactions within a pseudo double-network system. The pseudo first network, formed through the Schiff Base reation between Tris-modified layered double hydroxides (Tris-LDHs) and oxidized dextran (ODex), is linked to the second network built upon non-covalent interactions between Tris-LDHs and poly(acrylamide-co-2-acrylamido-2-methyl-propanesulfonate) (p-(AM-co-AMPS). The swelling and mechanical properties of the resulting hydrogels have been investigated as a function of the ODex and AMPS contents. The as-prepared hydrogel can swell to 420 times of its original size and retain more than 99.9 wt.% of water. Mechanical tests show that the hydrogel can bear 90 % of compression and is able to be stretched to near 30 times of its original length. Cyclic tensile tests reveal that the hydrogels are capable of self-strengthening after mechanical training. The unique energy dissipation mechanism based on the dynamic covalent and non-covalent interactions is considered to be responsible for the outstanding swelling and mechanical performances.

Effects of Europium Complex on Thermal and Photoluminescence Properties of Polyurethane-Europium Materials

A europium complex with double bonds was synthesized with crotonic acid as the ligand and a europium ion as the center ion. Then, the obtained europium complex was added to synthesized poly(urethane-acrylate) macromonomers to prepare the bonded polyurethane-europium materials by the polymerization of the double bonds in the complex and the poly(urethane-acrylate) macromonomers. The prepared polyurethane-europium materials had high transparency, good thermal stability and good fluorescence. The storage moduli of polyurethane-europium materials are obviously higher than those of pure polyurethane. Polyurethane-europium materials exhibit bright red light with good monochromaticity. The light transmittance of the material decreases slightly with increases in the europium complex content, but the luminescence intensity gradually increases. In particular, polyurethane-europium materials possess a long luminescence lifetime, which has potential applications for optical display instruments.

Layered Gadolinium-Europium-Terbium Hydroxides Sensitised with 4-Sulfobenzoate as All Solid-State Luminescent Thermometers

Ternary layered gadolinium-europium-terbium basic chlorides were synthesised using a facile hydrothermal-microwave technique. A continuous series of solid solutions was obtained in a full range of rare earth concentrations. To sensitise the luminescence of Eu3+ and Tb3+, a 4-sulfobenzoate anion was intercalated in the ternary layered rare earth hydroxides using one of two methods—a high-temperature ion exchange or a single-stage synthesis. The luminescent colour of the materials was governed by the gadolinium content: at low and medium gadolinium concentrations (0–70%), layered Gd-Eu-Tb basic sulfobenzoate exhibited a bright red europium luminescence; at high gadolinium content (70–90%), a bright green terbium luminescence was observed. The colour coordinates of layered Gd-Eu-Tb basic sulfobenzoate luminescence depended on the temperature in the physiological range (20–50 °C). The relative thermal sensitivity of the obtained materials was up to 2.9%·K−1.

Synthesis and Processing of Dynamic Covalently Crosslinked Polydextran/Carbon Dot Nanocomposite Hydrogels with Tailorable Microstructures and Properties

Using functionalized nanoparticles to crosslink hydrophilic polymers is a growing theme of directly constructing nanocomposite (NC) hydrogels. Employing dynamic covalent chemistry at the nanoparticle-polymer interface is particularly attractive due to the spontaneous formation and reversible manner of dynamic covalent bonds. However, the structure and property modulation of the dynamic covalently crosslinked NC hydrogels has not been thoroughly discussed. Here, we fabricated NC hydrogels by using amine-functionalized carbon dots (CDs) to crosslink polydextran aldehyde (PDA) polymers through imine bond formation. The role of PDA with different oxidation degrees (i.e., PDA10, PDA30, and PDA50) in affecting the microstructures and properties of PDA@CD hydrogels was systematically investigated, showing that the PDA50@CD hydrogel presented the densest structure and the highest mechanical strength among the three PDA@CD hydrogels. The pH-responsiveness, 3D printing, electrospinning, and biocompatibility of PDA@CD hydrogels were also demonstrated, showing the great promise of using PDA@CD hydrogels for applications in biomedicine and biofabrication.

Fabrication of Multiresponsive Magnetic Nanocomposite Double-Network Hydrogels for Controlled Release Applications

Nanocomposite double-network hydrogels (ncDN hydrogels) have been demonstrated as promising biomaterials to present several desired properties (e.g., high mechanical strength, stimuli-responsiveness, and local therapy) for biomedicine. Here, a new type of ncDN hydrogels featuring definable microstructures and properties as well as multistimuli responsiveness for controlled release applications is developed. Amine-functionalized iron oxide nanoparticles (IOPs_NH₂ ) are used as nanoparticle cross-linkers to simultaneously connect the dual networks of gelatin (Gel) and polydextran aldehyde (PDA) through hydrogen bonding, electrostatic interactions, and dynamic imine bonds. The pH- and temperature-responsive Gel/PDA/IOP_NH₂ ncDN hydrogels present a fast release profile of proteins at acidic pH and high temperature. Besides, IOP_NH₂ also contributes the magnetic-responsiveness to the ncDN hydrogels, allowing the use of magnetic field to generate heat to facilitate the structural change of hydrogels and the subsequent applications. Taken together, a versatile ncDN hydrogel platform capable of multistimuli responsiveness and local heating for controlled release is developed for advanced biomedical applications.

Layered terbium hydroxides for simultaneous drug delivery and imaging

Layered rare-earth hydroxides have begun to gather increasing attention as potential theranostic platforms owing to their extensive intercalation chemistry combined with magnetic and fluorescent properties. In this work, the potential of layered terbium hydroxide (LTbH) as a platform for simultaneous drug delivery and fluorescence imaging was evaluated. LTbH-Cl ([Tb2(OH)5]Cl·yH2O) was loaded with three nonsteroidal anti-inflammatory drugs (diclofenac, ibuprofen, and naproxen) via ion-exchange. Drug release studies in phosphate buffered saline (pH = 7.4) revealed all three formulations release their drug cargo rapidly over the course of approximately 5 hours. In addition, solid state fluorescence studies indicated that fluorescence intensity is strongly dependent on the identity of the guest anion. It was postulated that this feature may be used to track the extent of drug release from the formulation, which was subsequently successfully demonstrated for the ibuprofen loaded LTbH. Overall, LTbH exhibits good biocompatibility, high drug loading, and a strong, guest-dependent fluorescence signal, all of which are desirable qualities for theranostic applications.

Synthesis of resilient hybrid hydrogels using UiO-66 MOFs and alginate (hydroMOFs) and their effect on mechanical and matter transport properties

Herein, we report the preparation of an organic-inorganic hybrid hydrogel architecture using vinyl alginate and UiO-66 MOFs (metal-organic frameworks) modified with acrylic acid (AA) UiO-66AA. UiO-66 MOFs with different crystal sizes (600, 1500, and 2500 nm) were synthesized and the effect on the mechanical and transport properties of the resulting materials, such as water absorption capacity and drug release, were evaluated. HydroMOF showed higher water absorption capacity than the pure hydrogel and enhanced mechanical properties, which depend on crystal size and the amount of UiO-66AA MOF used. The initial release rate of drug (burst release) from hydroMOFs was lower when small-sized crystals or a small amount of large-sized crystals were used; thus these are essential in changing half-life values of release rates. Finally, the cytotoxicity screening successfully showed that hydroMOFs are promising biocompatible compounds proven to have the advantages of minimized burst release and mechanical robustness.

Multi-Responsive Lanthanide-Based Hydrogel with Encryption, Naked Eye Sensing, Shape Memory, Self-Healing, and Antibacterial Activity

In this work, we reported a multi-responsive luminescent hydrogel with properties of encryption, naked eye sensing of glucose, shape memory, self-healing, and antibacterial activity. The hydrogel (GA/CCS/DNSA/Eu³⁺) was obtained by mixing phenylboronic acid-modified gelatin (GA-DBA), catechol-modified carboxymethyl chitosan (CCS-PCA), 3,5-dinitrosalicylic acid (DNSA), and Eu³⁺ ions through a facile heating-cooling process. The resultant hydrogel exhibits reversible luminescence and color and phase changes in response to temperature, acid/base, salt, and redox stimuli. Based on the multiple responsiveness, information encryption and decryption, naked eye sensing of glucose, remarkable shape memory, and enhanced mechanical properties of the as-prepared hydrogel were realized. In addition, the self-healing capacity was also achieved due to the dynamic bonds in GA/CCS/DNSA/Eu³⁺ hydrogels. Specifically, the GA/CCS/DNSA/Eu³⁺ hydrogels possess antibacterial activity owing to the bacteriostasis of the CCS-PCA and DNSA/Eu³⁺ complex. Thus, GA/CCS/DNSA/Eu³⁺ hydrogels have potential applications in the fields of anticounterfeiting, wearable devices, biomedicine, sensing, etc.

pH-dependent nanodiamonds enhance the mechanical properties of 3D-printed hyaluronic acid nanocomposite hydrogels

Nanocomposite hydrogels capable of undergoing manufacturing process have recently attracted attention in biomedical applications due to their desired mechanical properties and high functionality. 3D printing nanocomposite hydrogels of hyaluronic acid (HA)/nanodiamond (ND) revealed that the addition of ND with the low weight ratio of 0.02 wt% resulted in higher compressive force and gel breaking point, compared with HA only nanocomposites. These HA nanocomposite hydrogels loaded with surface functionalized ND allowed for the enforced compressive stress to be tuned in a pH-dependent manner. HA nanocomposite hydrogels with ND-OH at pH 8 showed an increase of 1.40-fold (0.02%: 236.18 kPa) and 1.37-fold (0.04%: 616.72 kPa) the compressive stress at the composition of 0.02 wt% and 0.04 wt, respectively, compared to those of ND-COOH (0.02%: 168.31 kPa, 0.04%: 449.59 kPa) at the same pH. Moreover, the compressive stress of HA/ND-OH (0.04 wt%) at pH 8 was mechanically enhanced 1.29-fold, compared to that of HA/ND-OH (0.04 wt%) at pH 7. These results indicate that the tunable buffering environment and interaction with the long chains of HA at the molecular level have a critical role in the dependency of the mechanical properties on pH. Due to the pH stability of the ND-OH nanophase, filament-based processing and layer-based deposition at microscale attained enforced mechanical properties of hydrogel. Fine surface tuning of the inorganic ND nanophase and controlled 3D printing leads to improved control over the pH-dependent mechanical properties of the nanocomposite hydrogels reported herein.

Skin-Inspired Multifunctional Luminescent Hydrogel Containing Layered Rare-Earth Hydroxide with 3D Printability for Human Motion Sensing

The development of multifunctional hydrogels is gaining a lot of attention owing to its application in electronic skins, wearable electronics, and soft robotics. In this study, an effective and facile one-step preparation strategy is developed to fabricate a multifunctional nanocomposite hydrogel consisting of sodium alginate/sodium polyacrylate/layered rare-earth hydroxide (LRH), where LRH plays multiple roles as a co-cross-linker and ionic carrier and is also the origin of fluorescence. The obtained LRH-based composite hydrogel exhibits excellent three-dimensional printing performance at room temperature. When exposed to different humidity conditions, the hydrogel exhibits humidity-dependent electromechanical properties. The multiple functions of the resultant hydrogel are easily realized by just relying on the addition of cationic LRH nanoplates. A skinlike motion sensor with transparency is fabricated based on the printed hydrogel and is used to monitor human motion. Owing to the fluorescence characteristics of lanthanide ions (Eu³⁺ and Tb³⁺) from LRH, the hydrogel shows highly tunable multicolored photoluminescence by adjusting the LRH constituent. This study reveals that the multifunctional hydrogels have potential for applications in sensing.

Design and identification of poly(vinyl chloride)/layered double hydroxide@MnO2 nanocomposite films and evaluation of the methyl orange uptake: linear and non-linear isotherm and kinetic adsorption models

In this work, an adsorbent based on poly(vinyl chloride) (PVC) for the removal of methyl orange (MO) dye is proposed.

Effect of Divalent Metals on the UV-Shielding Properties of MII/MgAl Layered Double Hydroxides

Both the particle size and compositions have a strong influence on the UV-shielding performance of layered double hydroxides (LDHs), and they will interact with each other. To investigate the effects of divalent metal ions on the UV-shielding properties of layered double hydroxides (LDHs), M^II/MgAl-CO₃ LDHs (M = Mg, Co, Ni, Cu, or Zn) with the same primary and secondary particle size have been prepared and their UV-shielding performance have been studied in this work. The UV-vis spectra show that the ZnMgAl-LDHs exhibit the highest absorbance under the ultraviolet B and ultraviolet A rays among these LDH samples, but in the ultraviolet C region, the CuMgAl-LDHs show the highest absorbance and this result is in good accordance with the UV-shielding performance, which was examined by protecting the photocatalytic degradation of rhodamine B aqueous solution. Moreover, under UV rays, PP/ZnMgAl-LDH films show excellent resistance to UV aging, which can be attributed to the strong inhibition of ZnMgAl-LDHs during the production of free radicals in polypropene, as has been confirmed by electron spin resonance results.

Luminescence Tuning of Layered Rare-Earth Hydroxides (LRHs, R = Tb, Y) Composites with 3-Hydroxy-2-naphthoic Acid and Application to the Fluorescent Detection of Al3

Tunable luminescence (quenching or blue shift) of HNA/OS-LRH composites (HNA is 3-hydroxy-2-naphthoic acid; OS is the anionic surfactant of 1-octanesulfonic acid sodium; LRHs are layered rare-earth hydroxides, R = Tb³⁺, Y³⁺) in the solid state and delaminated state is reported, which is utilized as an effective fluorescent probe for detecting metal ions. HNA/OS species are intercalated into LRH layers to generate composites of HNA _xOS_{1- x}-LTbH ( x = 0.10, 0.15, 0.20 , 0.25) and HNA _yOS_{1- y}-LYH ( y = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30). In the solid state, LYH composites exhibit green emissions (from 493 to 504 nm) with a large blue shift in comparison to the 542 nm emission of free HNA^- anions, while in the delaminated state in formamide (FM), the composites display blue emission (480 nm) relative to the green emission (512 nm) of an HNA soltuion in FM. However, LTbH composites display coquenched luminescence in both the solid state and delaminated state. Also, HNA_0.25OS_0.75-1:1-LYH, HNA_0.25OS_0.75-1:2-LYH, and HNA_0.05OS_0.95-1:1-LYH (1:1 and 1:2 are HNA:NaOH molar ratios) show significantly elongated fluorescence lifetimes of 15.35, 14.37, and 12.72 ns, respectively, in comparison with free HNA-Na (6.44 ns), and their quantum yields of 23.40%, 21.97%, and 22.31%, respectively, are much larger than that of free HNA-Na (4.86%). The LTbH composite (HNA_0.25OS_0.75-1:1-LTbH) has also a relatively higher quantum yield of 12.46%. The HNA_0.25OS_0.75-1:1-LYH colloid exhibits excellent recognition selectivity for Al³⁺ over other metal ions (Mg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, and Hg²⁺) with distinct fluorescence sensitization. It shows an intense change in its fluorescence emission when it is bound to Al³⁺ ions, giving a lower detection limit of 6.32 × 10^-6 M. This is novel research on the fluorescence chemosensing of LRH composites.

A novel LEuH/PVA luminescent hydrogel with ammonia response and self-recovery luminescence behavior

A dual-use hydrogel for ammonia sensing in gas or liquid exhibits reversibility of luminescence on/off switching.

Synthesis of layered double hydroxide/poly(N-isopropylacrylamide) nanocomposite hydrogels with excellent mechanical and thermoresponsive performances

Nanocomposite (NC) hydrogels of positively charged layered double hydroxide (LDH) single-layer nanosheet (SLNS) cross-linked poly(N-isopropylacrylamide) (PNIPAM) were synthesized. Especially, the LDH SLNSs used here were pre-synthesized via an aqueous synthetic route without using organic solvents and modifiers. The obtained LDH/PNIPAM NC hydrogels were characterized using XRD, SEM, TEM, and DSC. The mechanical and thermoresponsive properties were determined using tensile, compression, and swelling/deswelling tests. Interestingly, different network structures are observed for the NC hydrogels along the horizontal and vertical directions; those along the horizontal direction exhibit a fine and uniform sponge-like network structure while those along the vertical direction exhibit a hierarchical layered architecture. Compared with the conventional N,N'-methylene bisacrylamide cross-linked PNIPAM hydrogel, the NC hydrogels exhibit extraordinary deformability and stretchability and obviously improved thermoresponsive swelling/deswelling characteristics. Furthermore, the fracture elongation observed here is obviously higher than those reported for negatively charged clay/PNIPAM NC hydrogels. With the increase in the LDH content from 0.8 to 2.0 wt%, the fracture strength and the compressive strength at an 85% strain increase from 23.5 to 37.2 kPa and from 0.15 to 0.57 MPa, respectively, while the fracture elongation decreases from 2689 to 2202%. The mechanism for the improved mechanical performances of the NC hydrogels is discussed. To the best of our knowledge, this is the first report on LDH/PNIPAM hydrogels. This work provides a green synthesis route for LDH-containing NC hydrogels. The new NC hydrogels may have great potential applications such as in tissue engineering, drug vehicles, and sorbents.

High strength and anti-fatigue nanocomposite hydrogels prepared via self-initiated free radical polymerization triggered by daylight

A new type of high strength nanocomposite hydrogel was synthesized using TiO₂ nanoparticles as both cross-linkers and photo-initiators under daylight.

Simultaneous superior lubrication and high load bearing by the dynamic weak interaction of a lubricant with mechanically strong bilayer porous hydrogels

Dynamic weak interaction of a lubricant with mechanically strong bilayer porous hydrogels exhibits simultaneous superior lubrication and high load bearing.

Synthesis of magnetic polymeric ionic liquid nanocomposites by the Radziszewski reaction

The application of the Radziszewski reaction is proposed for the first time for the synthesis of magnetic polymeric ionic liquids. After their characterization, the sorption ability of the nanocomposites towards acidic compounds have been evaluated.

Preparation of polyurethane/polyvinyl alcohol hydrogel and its performance enhancement via compositing with silver particles

Polyurethane/polyvinyl alcohol/silver composite hydrogel, showing enhanced mechanical and antibacterial properties, was fabricated.