Development of a novel self-healing dental nanocomposite containing PUF nanocapsules and nanoclay

The aims of this research were to develop the first self-healing dental nanocomposite and to evaluate mechanical properties (compressive and flexural strength), crack-healing, and self-healing longevity after 90 days of water aging. The principal reasons for failure are microcracks formed by polymerization shrinkage, recurrent dynamic mechanical stress, water sorption, and thermal fatigue. N, N-dihydroxyethyl p-toluidine and triethylene glycol dimethacrylate (DEPT-TEGDMA) nanocapsules were synthesized as they have been proven previously to be biocompatible for dental materials. Nanoclay was used as a filler to improve the mechanical properties of self-healing tooth nanocomposites. Nanocapsules were prepared by in situ emulsion polymerization of poly urea-formaldehyde (PUF) shells. The synthesized PUF shells were characterized by FTIR, SEM, and DLS analyses. The results showed that incorporating nanocapsules at a 7.5% mass fraction into the nanocomposite increased the mechanical properties. A good self-healing efficiency ranging from 54.06 to 58% recovery was obtained. The 90 days of water-aging compared to 1 day did not reduce the self-healing efficiency (p > 0.1), showing water-aging did not damage the nanocapsules.     

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag⁺ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal–ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal–ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

New supramolecular hybrid liquid-crystalline networks exhibiting self-healing and shape memory properties are developed by self-assembly of small components through hydrogen bonding interactions and coordination bonding.     

Self-healing mineralized hydrogel scaffolds for stretch-triggered dye release

Hydrogels, with self-healing properties that can self-repair spontaneously when subjected to mechanical stress, are gaining popularity in the biomedical field. Numerous attempts have been made to create distinctive hydrogels with self-healing properties, along with stimuli-responsiveness and biocompatibility. Several techniques exist for fabricating hydrogels, including physical and chemical crosslinking via the creation of covalent bonds, and so on. Here, we prepared self-healing, stimuli-responsive, mineralized hydrogel by simply dissolving Kollidon 90-F, sodium chloride (NaCl), and potassium carbonate (K₂CO₃) in an aqueous solution. The dissociated CO₃²⁻ replaces the water molecules from the Kollidon 90-F polymer backbone and facilitates the cross-linking of the polymer chain, resulting in hydrogel formation. In addition, the in-situ produced sodium carbonate (Na₂CO₃) strengthens the hydrogel network. We optimized the mineralized hydrogels by taking various metal salts and different concentrations of K₂CO₃. The optimized hydrogel showed good stability over a period of time, was able to maintain viscoelastic properties, possessed good self-healing ability, and showed a shape retention ability. The shear-thinning property demonstrated by the optimized hydrogel could open a ray of hope in the bioprinting or 3D printing industry. Further, the stretch-responsive release of dye from the Self-healing mineralized hydrogel (SHMH) matrix confirms the mechanoresponsive behavior of the hydrogel. Overall, the findings could be utilized in the future to fabricate a stable drug delivery system that can autonomously release the drug molecules when stretched by daily processes such as joint movements.     

Self-healing characteristic of praseodymium conversion coating on AZNd Mg alloy studied by scanning electrochemical microscopy

Application of rare earth conversion coatings as a surface treatment for magnesium has been the subject of several studies revealing the potential to act as an effective passivating layer. Herein a mechanistic study is presented on the formation of a rare earth conversion layer based on Pr(NO₃)₃ on AZ80X magnesium alloy in simulated biological (buffered) solution. Scanning electrochemical microscopy (SECM) was used to investigate the insulating properties and degradation behaviour of the Pr conversion layer. The self-healing properties of the conversion layer in the presence of Pr^3 + were also studied using SECM. Results revealed the self-healing characteristic of the Pr conversion film in the presence of active, Pr^3 +, species. The Pr conversion layer provided passivation in the short term by producing an electrochemically inert and insulating layer. SECM results in potentiometric mode elucidated the role of near surface pH in the formation of the conversion coating.     

选相原位法合成立方氮化硼的关键影响因素

利用选相原位法在水溶液中成功制备出了立方氮化硼晶体，对反应条件进行了优化。结果表明，利用选相原位法合成立方氮化硼的最佳实验条件是：反应压力为10.0 MPa，在氯离子加入下利用混合氮源进行反应。在该条件下得到了纯相的立方氮化硼晶体。     

Functioning via host–guest interactions

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host–guest interactions are an effective tool to introduce switching and functional properties into materials. This review focuses on the achievement of selective molecular adhesion, self-healing, toughness, and actuation properties. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). Self-healing materials with host–guest interactions involving CDs have been used to achieve redox-responsive healing properties and healing efficiency. Furthermore, the materials, which undergo self-healing by chemical and physical mechanisms, exhibit rapid and efficient self-healing properties under semi-dry conditions. To prepare a supramolecular actuator using host–guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing distances between the cross-linking points. Both actuators exhibit contractive bending behavior. This review summarizes advancements within the past ten years in supramolecular materials that function via the chemical mechanism of host–guest interactions and the physical mechanism of the sliding motion of ring molecules.     

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core

A phase-selective,bis-urea organogelator with a curved bis-naphthalene core was synthesized and characterized.This gelator is capable of gelating a variety of hydrocarbons and oils.The resulting gels have been characterized by rheology,SEM,and molecular modelling.The gelator can be applied in the powder form for the recovery of a thin layer of petrol oil spill in water.     

Polar-Functionalized,Crosslinkable, Self-Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar-functionalized, crosslinkable, self-healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium-catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self-healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur-induced vulcanization.     

Maleimide Self-Reaction in Furan/Maleimide-Based Reversibly Crosslinked Polyketones: Processing Limitation or Potential Advantage?

Polymers crosslinked via furan/maleimide thermo-reversible chemistry have been extensively explored as reprocessable and self-healing thermosets and elastomers. For such applications, it is important that the thermo-reversible features are reproducible after many reprocessing and healing cycles. Therefore, side reactions are undesirable. However, we have noticed irreversible changes in the mechanical properties of such materials when exposing them to temperatures around 150 °C. In this work, we study whether these changes are due to the self-reaction of maleimide moieties that may take place at this rather low temperature. In order to do so, we prepared a furan-grafted polyketone crosslinked with the commonly used aromatic bismaleimide (1,1′-(methylenedi-4,1-phenylene)bismaleimide), and exposed it to isothermal treatments at 150 °C. The changes in the chemistry and thermo-mechanical properties were mainly studied by infrared spectroscopy, ¹H-NMR, and rheology. Our results indicate that maleimide self-reaction does take place in the studied polymer system. This finding comes along with limitations over the reprocessing and self-healing procedures for furan/maleimide-based reversibly crosslinked polymers that present their softening (decrosslinking) point at relatively high temperatures. On the other hand, the side reaction can also be used to tune the properties of such polymer products via in situ thermal treatments.     

Stimuli-responsive polymeric materials functioning via host–guest interactions

Molecular recognition is essential for realizing functional supramolecular materials. Non-covalent host–guest interactions are an effective tool to introduce switching and functional properties into materials. This review focuses on the achievement of selective molecular adhesion, self-healing, toughness, and actuation properties. These functions have been achieved by reversible bond formation with cyclodextrins (CDs). Self-healing materials with host–guest interactions involving CDs have been used to achieve redox-responsive healing properties and healing efficiency. Furthermore, the materials, which undergo self-healing by chemical and physical mechanisms, exhibit rapid and efficient self-healing properties under semi-dry conditions. To prepare a supramolecular actuator using host–guest complexes, two approaches have been introduced. The first is the functionalization of a supramolecular gel actuator by changing the cross-linking density, and the second is the functionalization of a topological gel actuator by changing distances between the cross-linking points. Both actuators exhibit contractive bending behavior. This review summarizes advancements within the past 10 years in supramolecular materials that function via the chemical mechanism of host–guest interactions and the physical mechanism of the sliding motion of ring molecules.     

Sustainable metal-free polyurethane elastomers from bile acids: self-healing properties and biocompatibility

Currently, self-healing polymers with superior elasticity have made great progress in healthcare devices and flexible electronics. Benefiting from rigid skeletons and hydroxyl groups of bile acids, herein sustainable self-healing polyurethanes have been developed via an alternative metal-free strategy in which bile acid units and oligo(ethylene glycol)s serve as hard and soft segments, respectively. The bile acid based polyurethane could achieve a similar mechanical performance (7.96 MPa of Young's modulus) to certain soft tissues and maximum self-healing efficiency of 90% in tensile strength for 3 h. Multiple hydrogen bonds originated from hydroxyl groups of bile acids and urethane bonds synergistically attribute to self-healing ability, which represents the first example that quadruple hydrogen bonds of sustainable molecules driven elastomers have been reported. Moreover, taking into account the desirable biocompatibility both in vitro and in vivo, it is highly anticipated that these sustainable metal-free self-healing polyurethane elastomers would be explored for practical applications, such as soft tissue repairing.     

Magnetic Self-Healing Composites: Synthesis and Applications

Magnetic composites and self-healing materials have been drawing much attention in their respective fields of application. Magnetic fillers enable changes in the material properties of objects, in the shapes and structures of objects, and ultimately in the motion and actuation of objects in response to the application of an external field. Self-healing materials possess the ability to repair incurred damage and consequently recover the functional properties during healing. The combination of these two unique features results in important advances in both fields. First, the self-healing ability enables the recovery of the magnetic properties of magnetic composites and structures to extend their service lifetimes in applications such as robotics and biomedicine. Second, magnetic (nano)particles offer many opportunities to improve the healing performance of the resulting self-healing magnetic composites. Magnetic fillers are used for the remote activation of thermal healing through inductive heating and for the closure of large damage by applying an alternating or constant external magnetic field, respectively. Furthermore, hard magnetic particles can be used to permanently magnetize self-healing composites to autonomously re-join severed parts. This paper reviews the synthesis, processing and manufacturing of magnetic self-healing composites for applications in health, robotic actuation, flexible electronics, and many more.     

Highly branched polyethylene used as sorbents for oil-spill cleanup and separation

Highly branched polyethylene (HBPE) was developed into practical application as highly efficient sorbent material for oil-spill cleanup and oil/water separation. To obtain large-scale production of HBPE, a thermal stable Ni(II)-α-diimine catalyst for ethylene polymerization in our previous work has been employed to prepare the polyolefin material in a 10-liter polymerization reactor with a high activity (>10⁶ g_PE/mol_[Ni] h). The structure, molecular weight and distribution, thermal and mechanical properties were systematically characterized by NMR, ATR-FTIR, GPC, DSC, DMA, and TGA, respectively. Through simple but feasible cross-linking process, the HBPE-based oil-absorption materials with contact angles up to 111.5° were directly applied into absorption test using various oil and pure hydrocarbons. Reusability and recovery of the absorption materials and oil or solvents were probed by drying or using the distillation method. Oil/water separation was made to determine the hydrophobic and oleophilic nature of this material. Flory-Rehner polymer swelling theory is employed to study the structure–property relationship via determining the network structure including cross-linking density ρ_c and average molecular weight M_c between two cross-links. The mixture of sorbent material after absorbing oil was regarded as crude oil component to simulate oil refinery process by thermogravimetric analysis, providing an alternative approach for oil-collection.     

强韧型自愈合水凝胶的研究进展

水凝胶作为一种由大量水和与众不同的三维网状结构构成的智能软材料,已经广泛应用于许多领域,如药物输送、软骨修复、废物处理及电子设备等。然而,水凝胶不良的机械性能及自愈合性极大地限制了它们的潜在应用。目前已报道的韧性水凝胶通常不具有或只有很弱的自修复性,而自修复水凝胶通常机械性能非常弱。因此,研发具有高效自修复性能和优异机械性能的水凝胶材料,无论是从学术角度还是工业角度都是非常重要的。本文总结了近些年来强韧型自愈合水凝胶的最新研究进展,从其制备方法、性能等方面进行了简要介绍,并对未来的发展前景进行了展望。     

Tissue-Sequestered Group III-A Metals: Dilute,High Temperature NH4SCN for Simultaneous Measurement of In And Ga By Phase-Selective Stripping Voltammetry

Abstract

Clinical studies have heavily relied on radioanalytical measurements to monitor ¹¹¹In tissue uptake and its cytotoxicity on malignant neoplasms, with substantially opposite analytical conclusions regarding the effect of this Group ^III-A element compared to the growth inhibiting influence displayed by tissue-sequestered ⁶⁷Ga. Evidence shown here would indicate that both gallium and indium present at trace and ultratrace levels in prepared biological material are susceptible to precise, simultaneous measurement with rapid scan, phase-selective anodic stripping (PSAS) using novel conditions recently developed for producing electrochemically reversible gallium behavior without use of densely concentrated electrolytes.     

Critical comparison of alternating current and differential pulse voltammetry in the determination of some heavy metals in sea-water

A critical comparison of phase-selective fundamental harmonic a.c. anodic stripping voltammetry and differential pulse anodic stripping voltammetry for the determination of Pb, Cd, Cu and Zn in sea-water is reported. Differential pulse anodic stripping voltammetry was found to be slightly more sensitive than the a.c. technique, but the effect of the charging current could be more effectively eliminated by the latter, especially in the determination of zinc(II) and copper(II). The detection limits for both techniques were found to be about 10^–10-10^–8 M for all four elements. The precision, expressed as relative standard deviation, was of the order of 2–5% for the fundamental harmonic a.c. method and 5–8% for differential pulse voltammetry. The accuracy (expressed as recovery) was 95–105% for the former and 90–110% for the latter.     

Synthesis and characterization of microencapsulated dicyclopentadiene with melamine–formaldehyde resins

Microcapsules containing healing agents have been used to develop the self-healing polymeric composites. These microcapsules must possess special properties such as appropriate strength and stability in surrounding medium. A new series of microcapsules containing dicyclopentadiene (DCPD) with melamine–formaldehyde (MF) resin as shell material were synthesized by in situ polymerization technology. These microcapsules may satisfy the requirements for self-healing polymeric composites. The chemical structure of microcapsule was identified by using Fourier transform infrared (FTIR) spectrometer. The morphology of microcapsule was observed by using optical microscope (OM) and scanning electron microscope. Size distribution and mean diameter of microcapsules were determined with OM. The thermal properties of microcapsules were investigated by using thermogravimetric analysis and differential scanning calorimetry. Additionally, the self-healing efficiency was evaluated. The results indicate that the poly(melamine–formaldehyde) (PMF) microcapsules containing DCPD have been synthesized successfully, and their mean diameters fall in the range of 65.2∼202.0 μm when the adjusting agitation rate varies from 150 to 500 rpm. Increasing the surfactant concentration can decrease the diameters of microcapsules. The prepared microcapsules are thermally stable up to 69 °C. The PMF microcapsules containing DCPD can be applied to polymeric composites to fabricate the self-healing composites.     

Synthesis and Properties of Reversible Disulfide Bond-based Self-healing Polyurethane with Triple Shape Memory Properties

A reversible disulfide bond-based self-healing polyurethane with triple shape memory properties was prepared by chain extending of random copolymer poly(lactide-co-caprolactone)(PCLA),hexamethylene diisocyanate (HDI),polytetrahydrofuran(PTMEG),and 4,4'-aminophenyl disulfide.The chemical structures were characterized using~1H nuclear magnetic resonance (~1H-NMR)spectroscopy,Fourier transform infrared spectroscopy (FTIR),and gel permeation chromatography (GPC).The thermal properties,selfhealing properties,triple-shape memory effect,and quantitative shape memory response were evaluated by differential scanning calorimetry (DSC),tensile tests,two-step programming process thermal mechanical experiments,and subsequent progressive thermal recovery.The self-healing mechanism and procedures were investigated using polarizing optical microscopy (POM) and an optical profiler.It was concluded that self-healing properties (up to 60%) and triple-shape memory properties around 35 and 500C (with shape fixation ratios of 94.3%and 98.3%,shape recovery ratios of 76.6%and 85.1%,respectively) were integrated to the shape memory polyurethane.As-prepared polyurethane is expected to have potential applications in multi-shape coatings,films,and step-by-step deploying structures.     

On the polarographic reduction of nitrate ion in the presence of zirconium(IV)

The polarographic reduction of nitrate ion in the presence of zirconium(IV) is studied by dc and phase-selective ac polarography. The total reduction process was proved by means of controlled-potential electrolysis and chemical analysis to conform to NO⁻₃+8H⁺6e⁻→NH₂OHH⁺=2 H₂O. Using a measurement of differential capacity, a large part of the difference between the reduction transfer to the vicinity of the electrode but to a charge transfer step and/or a chemical reaction step. The zirconium(IV) is concluded to act as an intermediary for the charge transfer from the electrode to the nitrate ion.