Self-healing Feature Research Articles

High energy density and interfacial polarization in poly(vinylidene fluoride-chlorotrifluoroethylene) nanocomposite incorporated with halloysite nanotube architecture

Polymer film is current the primary candidate for dielectric capacitor due to its large electric breakdown and intrinsic self-healing feature. High energy density and charge–discharge efficiency of film capacitors are urgent requirements for the miniaturization of power system with lightweight concern. Here the efficient transport tunnel has been constructed in halloysite nanotubes (HNTs)/poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite, in which the polar response is enhanced due to the tubular architecture serving as interior diffusion under external electric field. The HNTs/P(VDF-CTFE) nanocomposite was prepared by simple solution casting method. The dielectric property and electrical energy capability are improved after the incorporation of HNTs, for which the large free space inside tube facilitates the motions of electron and ion that contribute to the large polarization. The energy density of 1 wt% nanocomposite achieves 6.5 J/cm3 at 350 MV/m, which is ascribed to the high content of electroactive phase and enhanced electric displacement. This work provides an effective strategy for developing flexible polymer nanocomposite with high energy density, and sheds a light on the improvement of mechanism in 1D tubular structure/polymer composite for energy storage applications.

Light-Sheet Fluorescence Microscopy with Scanning Non-diffracting Beams

Light-sheet fluorescence microscopy (LSFM) has now become a unique tool in different fields ranging from three-dimensional (3D) tissue imaging to real-time functional imaging of neuronal activities. Nevertheless, obtaining high-quality artifact-free images from large, dense and inhomogeneous samples is the main challenge of the method that still needs to be adequately addressed. Here, we demonstrate significant enhancement of LSFM image qualities by using scanning non-diffracting illuminating beams, both through experimental and numerical investigations. The effect of static and scanning illumination with several beams are analyzed and compared, and it is shown that scanning 2D Airy light-sheet is minimally affected by the inhomogeneities in the samples, and provides higher contrasts and uniform resolution over a wide field-of-view, due to its reduced spatial coherence, self-healing feature and longer penetration depth. Further, the capabilities of the illumination scheme is utilized for both single-and double-wavelength 3D imaging of large and dense mammospheres of cancer tumor cells as complex inhomogeneous biological samples.

Self-healing microcapsules synergetically modulate immunization microenvironments for potent cancer vaccination.

Therapeutic cancer vaccines that harness the immune system to reject cancer cells have shown great promise for cancer treatment. Although a wave of efforts have spurred to improve the therapeutic effect, unfavorable immunization microenvironment along with a complicated preparation process and frequent vaccinations substantially compromise the performance. Here, we report a novel microcapsule-based formulation for high-performance cancer vaccinations. The special self-healing feature provides a mild and efficient paradigm for antigen microencapsulation. After vaccination, these microcapsules create a favorable immunization microenvironment in situ, wherein antigen release kinetics, recruited cell behavior, and acid surrounding work in a synergetic manner. In this case, we can effectively increase the antigen utilization, improve the antigen presentation, and activate antigen presenting cells. As a result, effective T cell response, potent tumor inhibition, antimetastatic effects, and prevention of postsurgical recurrence are achieved with various types of antigens, while neoantigen was encapsuled and evaluated in different tumor models.

Resistance to Long-Term Bacterial Biofilm Formation Based on Hydrolysis-Induced Zwitterion Material with Biodegradable and Self-Healing Properties.

Long-term resistance of biomaterials to the bacterial biofilm formation without antibiotic or biocide is highly demanded for biomedical applications. In this work, a novel biodegradable biomaterial with excellent capability to prevent long-term bacterial biofilm formation is prepared by the following two steps. Ethylcarboxybetaine ester analogue methacrylate (ECBEMA), poly(ethylene glycol) monomethacrylate (PEGMA), and 3-methacryloxypropyletris(trimethylsiloxy)silane (TRIS) were copolymerized to obtain p(ECBEMA-PEGMA-TRIS) (PEPT). Then, PEPT was cross-linked by isocyanate-terminated polylactic acid (IPDI-PLA-IPDI) to obtain the final PEPTx-PLAy (x and y are the number-average molecular weights (Mn) of PEPT and PLA, respectively) with optimal mechanical strength and adjustable surface regeneration rate. Static contact angle measurement, protein adsorption measurement, and attenuated total reflectance infrared (ATR-IR) results show that the PEPT19800-PLA800 film surface can generate a zwitterionic layer to resist nonspecific protein adsorption after surface hydrolysis. Quartz crystal microbalance with dissipation (QCM-D) results indicates that the PEPT19800-PLA800 film can undergo gradual degradation of the surface layer at the lowest swelling rate. Particularly, this material can efficiently resist the bacterial biofilm formation of both Gram-positive bacteria and Gram-negative bacteria over 14 and 6 days, respectively. Moreover, the material also shows an ideal self-healing feature to adapt to harsh conditions. Thus, this nonfouling material shows great potential in biomedical applications and marine antifouling coatings without antibiotic or biocide.

Self-assembly of active core corona particles into highly ordered and self-healing structures.

Formation of highly ordered structures usually needs to overcome a high free-energy barrier that is greatly beyond the ability of thermodynamic fluctuation such that the system would be easily trapped into a state with many defects and the annealing process of which often occurs on unreachable long time scales. Here, we report theoretically a fascinating example that active core corona particles can successfully self-assemble into a large-scaled and highly ordered stripe or trimer lattice, which is hardly achieved in a nondriven equilibrium system. Besides, such an activity-induced ordered structure shows an interesting self-healing feature of defects. In addition, there exists an optimal level of activity that most favorably enhances the formation of ordered self-assembly structures. Since core corona particles act as important units for self-assembly in real practice, we believe that our study opens a new design-strategy for highly ordered materials.

Two-Dimensional Ga2O3/C Nanosheets as Durable and High-Rate Anode Material for Lithium Ion Batteries.

The self-healing feature of gallium (Ga) is unique, making Ga-based materials attract attention for their potential to solve the anode pulverization issue of lithium ion batteries. In this work, a hierarchical two-dimensional (2D) Ga2O3/C structure has been synthesized by a facile NaCl template method. Ga2O3 nanoparticles (3.8 nm) are uniformly embedded in 2D carbon nanosheets. The long horizontal length of the carbon nanosheets (10 μm) provides long-range electron conductivity, and the thin vertical thickness (75 nm) shortens the Li ion diffusion path. Benefited from the integrated 2D structure and the high electron conductivity, the obtained 2D Ga2O3/C nanosheets exhibit excellent overall performance, including high lithium storage capacity (1026 mAh g-1 at 0.5 A g-1), high rate capability (378 mAh g-1 at 10.0 A g-1), and high cyclability (500 cycles at 0.5 A g-1). The lithiation/delithiation mechanism of 2D Ga2O3/C has been further studied with combined electrochemical and ex situ X-ray diffraction methods.

Self-Healing Anti-Atomic-Oxygen Phosphorus-Containing Polyimide Film via Molecular Level Incorporation of Nanocage Trisilanolphenyl POSS: Preparation and Characterization.

Protection of polymeric materials from the atomic oxygen erosion in low-earth orbit spacecrafts has become one of the most important research topics in aerospace science. In the current research, a series of novel organic/inorganic nanocomposite films with excellent atomic oxygen (AO) resistance are prepared from the phosphorous-containing polyimide (FPI) matrix and trisilanolphenyl polyhedral oligomeric silsesquioxane (TSP–POSS) additive. The PI matrix derived from 2,2’-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,5-bis[(4-amino- phenoxy)phenyl]diphenylphosphine oxide (BADPO) itself possesses the self-healing feature in AO environment. Incorporation of TSP–POSS further enhances the AO resistance of the FPI/TSP composite films via a Si–P synergic effect. Meanwhile, the thermal stability of the pristine film is maintained. The FPI-25 composite film with a 25 wt % loading of TSP–POSS in the FPI matrix exhibits an AO erosion yield of 3.1 × 10−26 cm3/atom after an AO attack of 4.0 × 1020 atoms/cm2, which is only 5.8% and 1.0% that of pristine FPI-0 film (6FDA-BADPO) and PI-ref (PMDA-ODA) film derived from 1,2,4,5-pyromellitic anhydride (PMDA) and 4,4’-oxydianline (ODA), respectively. Inert phosphorous and silicon-containing passivation layers are observed at the surface of films during AO exposure.

Reversibly Assembled Electroconductive Hydrogel via a Host–Guest Interaction for 3D Cell Culture

The study of cells responding to an electroconductive environment is impeded by the lack of a method, which would allow the encapsulation of cells in an extracellular matrix-like 3D electroactive matrix, and more challengingly, permit a simple mechanism to release cells for further characterization. Herein, we report a polysaccharide-based conductive hydrogel system formed via a β-cyclodextrin-adamantane host-guest interaction. Oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of adamantyl-modified sulfated alginate (S-Alg-Ad) results in bio-electroconductive polymer PEDOT:S-Alg-Ad, which can form hydrogel with poly-β-cyclodextrin (Pβ-CD). The PEDOT:S-Alg-Ad/Pβ-CD hydrogels can be tuned on aspects of mechanical and electrical properties, exhibit self-healing feature, and are injectable. Electron microscopy suggested that the difference in stiffness and conductivity is associated with the nacre-like layered nanostructures when different sizes of PEDOT:S-Alg-Ad nanoparticles were used. Myoblast C2C12 cells were encapsulated in the conductive hydrogel and exhibited proliferation rate comparable to that in nonconductive S-Alg-Ad/Pβ-CD hydrogel. The cells could be released from the hydrogels by adding the β-CD monomer. Astonishingly, the conductive hydrogel can dramatically promote myotube-like structure formation, which is not in the non-electroconductive hydrogel. The ability to embed and release cells in an electroconductive environment will open new doors for cell culture and tissue engineering.

NiGa2O4/rGO Composite as Long-Cycle-Life Anode Material for Lithium-Ion Batteries.

This work reports a novel Ga-based material, NiGa2O4, which is typically used as a photocatalyst for water splitting, as an anode for Li-ion battery with a long cycle life. High-surface-area reduced graphene oxide (rGO) has been used as the conductive substrate to avoid the aggregation of NiGa2O4 nanoparticles (NPs). Because the size and shape of NiGa2O4 are very sensitive to the pH of the precursor, ethylene glycol has been employed as the solvent, as well as the reduction agent to reduce GO, to avoid using extra surfactants and also to avoid the variation of pH of the precursor. The obtained NiGa2O4/rGO composite possesses high capacity and long cycle life (2000 cycles, 2 A/g), with NiGa2O4 NPs around 3-4 nm that are uniformly distributed on the rGO surface. Full cell performance with LiCoO2 as cathode has also been studied, with the average loss of 0.04% per cycle after 100 cycles (C/2 of LiCoO2). The long cycle life of the composite was ascribed to the self-healing feature of Ga0 formed during charging.

4D Printing of Smart Stimuli-Responsive Polymers

This paper starts with a short review of smart materials, which can be 4D printed and whose properties can be modified over time through specific stimuli such as heat, light, temperature, electric and magnetic fields. In the second part of the paper, a new polymer material for 4D printing was presented. The material was a thermally activated shape memory polymer (SPM), capable of memorizing a temporary shape and restoring the original one by means of a thermal stimulus. A self-healing behavior was introduced into the polymer, to enhance its durability and make it suitable for application in the fields of soft robotics and actuators. A polycaprolactone (PCL) was selected to provide a shape memory effect, taking into account its molecular weight and the possibility of chemically modifying it in order to make it photo-curable. Self-healing properties were provided by an ureidopyrimidinone (UPy) methacrylate monomer, capable of forming four hydrogen bonds with a self-complementary unit, favored by temperature. This new material was thus 4D printed by a digital liquid processing (DLP) printer. Both the shape memory effect and the self-healing feature were demonstrated, enabling this new material to be used as a raw material for new generation soft robotic actuators.

Self-Healing Supramolecular Hydrogel: Polyrotaxane Cross-Linked By Host-Guest Interactions

Self-healing materials, which can extend the service life of objects, have attracted much attention in efforts to create a sustainable society. One of the most important approaches to obtain self-healing materials is non-covalently bonded systems. Unlike covalently bonds, non-covalent interactions such as hydrogen bonds, π-π stacking interactions, metal-ligand coordination bonds, and host-guest interactions [1] are reversible. It has been recently reported that materials recover their original mechanical property when they are damaged. This self-healing property occurs by introducing a non-covalent interaction site into the end or side chain of a polymer. In this regard, the healing time is affected by the mobility of the polymer chain because self-healing occurs by the formation of non-covalent bonds between the responsible sites via non-covalent interactions in the polymer. To address the expected practical demands and requirements, the development of a self-healing material that recovers in a short time is in high demand. For this purpose, we employ polyrotaxanes (PRxs), which are a class of supramolecular threaded macromolecules in which cyclic molecules are threaded onto linear polymers.[2] The advantage of PRxs is that threaded cyclic compounds are freely mobile along the linear polymer because they are non-covalently assembled between the linear polymer and many cyclic molecules. Thus, compared to functional groups conjugated to a conventional polymer side chain, the functional group conjugated with the cyclic molecules in PRx can effectively bind to the target. Herein we report a self-healing material based on PRx through host-guest interactions. This material was prepared by radical copolymerization of acryl amide (AAm) and the host monomer in the presence of PRx introduced with guest molecules. The resulting material exhibits a self-healing property, and its healing speed is faster than a self-healing material without PRx. [1] (a) T. Kakuta, Y. Takashima, M. Nakahata, M. Otsubo, H. Yamaguchi, A. Harada, Adv. Mater. 2013, 25, 2849-2853. (b) M. Nakahata, Y. Takashima, A. Harada, Macromol. Rapid. Commun. 2016, 37, 86-92. [2] (a) Y. Kobayashi, Y. Nakamitsu, Y. Zheng, Y. Takashima, H. Yamaguchi, A. Harada, Chem. Commun. accepted (b) A. Harada, J. Li, M. Kamachi, Nature 1992, 356, 325-327. Figure 1. (a) Chemical structures of Ad(x)DMEDAPRx–βCD gel, Ad(x)–βCD gel, and AAm(x) gel. (b) Schematic illustration of the self-healing feature of Ad(x)DMEDAPRx–βCD gel. Here, x represents the mol% of the cross-linking unit. Figure 1

Deep imaging in highly scattering media by combining reflection matrix measurement with Bessel-like beam based optical coherence tomography.

Multiple scattering in biomedical tissue limits the imaging depth within a range of 1-2 mm for conventional optical imaging techniques. To extend the imaging depth into the scattering medium, a computational method based on the reflection matrix measurement has been developed to retrieve the singly back-scattered signal light from the dominant detrimental multiple-scattered background. After applying singular value decomposition on the measured matrix in the post-process, the target image underneath the turbid media is clearly recovered. To increase the depth of focus of the incident light by elongating the focal spot along the optical axis, a digital grating pattern is specially designed and displayed on a phase-only spatial light modulator to generate the Bessel-like beam for lateral point scanning. According to the results, the depth of focus is increased up to 2.4 mm which is much longer than the value of ∼50 μm obtained by using the conventional focused Gaussian beam, leading to a deeper penetration depth due to the self-healing feature of the Bessel-like beam. In addition, generation of the Bessel-like beam simplifies the axial scanning process by getting rid of the need to mechanically translate the focal zone along the optical axis of an objective with a high numerical aperture. By combining this method with an optical coherence tomography system with a low coherence light source, a depth-resolved optical image is obtained underneath a highly turbid medium.

A novel design strategy for triple-network structure hydrogels with high-strength, tough and self-healing properties

In this study, we prepared a novel triple-network (TN) structure hydrogel composed of polyacrylic acid (PAA), agar and polyvinyl alcohol (PVA). The obtained TN hydrogel has a superior mechanical property as well as self-healing property feature. In the TN hydrogel system, PAA-Fe3+ polymer mainly providing hydrogel self-healing properties by the ionic coordinates between COO− and Fe3+ as the first network, while, agar and PVA polymers gel mainly providing hydrogel high mechanical properties as the second and third network. The structure of TN the hydrogel can be controlled by adjusting the content of Fe3+ and composition in the three polymers. When 1.5 wt% Fe3+ in the TN hydrogels, the PAA/Agar/PVA TN hydrogels possess high mechanical strength, the fracture strain and fracture stress were 497% and 450 kPa, respectively, and the compression strength reached up to 1337 kPa under the compression deformation of 80%. Besides, the TN hydrogels exhibited excellent self-healing ability, when healed 72% at tensile stress and 84% at tensile strain after 24 h without adding any solvent or additive. The research offers a novel design strategy to improve mechanical strength and self-healing ability of hydrogels by controlling the compositions and interactions in the three networks.

Thermoacoustic focusing lens by symmetric Airy beams with phase manipulations

We report the realization of broadband acoustic focusing lenses based on two symmetric thermoacoustic phased arrays of Airy beams, in which the units of thermoacoustic phase control are designed by employing air with different temperatures surrounded by rigid insulated boundaries and thermal insulation films. The phase delays of the transmitted and reflected units could cover a whole 2π interval, which arises from the change of the sound velocity of air induced by the variation of the temperature. Based on the units of phase control, we design the transmitted and reflected acoustic focusing lenses with two symmetric Airy beams, and verify the high self-healing focusing characteristic and the feasibility of the thermal insulation films. Besides, the influences of the bending angle of the Airy beam on the focusing performance are discussed in detail. The proposed acoustic lens has advantages of broad bandwidth (about 4.8 kHz), high focusing performance, self-healing feature, and simple structure, which enable it to provide more schemes for acoustic focusing. It has excellent potential applications in acoustic devices.

Ionically conducting and environmentally safe gum Arabic as a high-performance gel-like electrolyte for solid-state supercapacitors

The development of innovative gel electrolyte is nowadays considered one of the most important features for the realization of high-safety and high-performance energy storage devices. Consequently, in the past few years, much effort have been dedicated to prepare new gel polymer electrolytes, unfortunately, they suffer from poor wettability with electrode surface which retard them to achieve high ion accessibility. Here, we propose a novel gel-like electrolyte which is prepared by exploiting the emulsifying property of low cost and environmentally safe gum Arabic (GA) as the polymer matrix and ortho-phosphoric acid (H3PO4) as the supporting electrolyte. This prepared gel electrolyte (GA/H3PO4) demonstrates excellent supercapacitive performance in the counterpart of conventional gel electrolyte of polyvinyl alcohol (PVA)/H3PO4 in all-solid-state supercapacitor. Besides the electrolytic performance, as prepared gel also exhibited the self-healing feature, no decay in capacitance was observed upon mechanically separation and restacking of both electrodes of the solid-state assembly. The prepared GA/H3PO4 electrolyte is also capable of maintaining its capacitance over 5000 repeating charge/discharge cycles.

Self-Healing of Wind Turbine Blades Using Microscale Vascular Vessels

Development of high bending stresses due to a sudden gust of wind is a significant cause for the failure of wind turbine blades. Self-healing provides a fool proof safety measure against catastrophic failure by healing the damages autonomously, as they originate. In this study, biomimetic, vascular channel type of self-healing was implemented in glass fiber reinforced polymer matrix composite that is used in wind turbine blades. Microscale borosilicate tubes are used to supply the healing agent to the epoxy type of thermoset polymer matrix, and the healing was very effective. However, 25% decrease in tensile strength and 9% decrease in three-point bending flexural strength were imminent with the inclusion of a single layer of vascular vessels in the composite material. Three-point bending tests were performed before and after self-healing of flat specimens to find the extent of recovery of flexural strength on using vascular channel type of self-healing. An average recovery of flexural strength of 84.52% was obtained using a single layer of vascular vessels on the tensile stress side of three-point bending. Breakage and bleeding of the healing agent within the composite specimens during three-point bending tests were observed in real-time. Based on the encouraging findings, the above self-healing feature was successfully implemented in a prototype wind turbine.

Building Self-Healing Alloy Architecture for Stable Sodium-Ion Battery Anodes: A Case Study of Tin Anode Materials

The rational design of anode materials is a challenge in developing sodium ion batteries. Alloy anodes provide high gravimetric and volumetric capacities but suffer the short cycle life as a result of the continuous and accumulated pulverization, resulting from a large volume change during the cycling process. Herein, using pure Sn, an irreversible conversion reaction combined with an alloy reaction (SnO), and a reversible conversion reaction combined with an alloy reaction (Sn4P3) as samples, we demonstrate that the pulverization and aggregation of the alloy anode can be partially recovered and the accumulation of pulverization and aggregation during charge/discharge cycles can be terminated using a reversible conversion reaction combined with an alloy reaction. The cycling stability of three Sn-based anodes increases in order of Sn4P3 > SnO > Sn. The enhancement in Sn4P3 can be attributed to a reversible reaction of Sn4P3 + 9Na ↔ 4Sn + 3Na3P, which repairs the cracks, damage, and aggregation of Sn particles that occurred in the alloy process of 4Sn + 15Na ↔ Na15Sn4 during cycling and, hence, terminates the pulverization. The repair mechanism looks like the self-healing feature in nature, where the damage can be healed by itself. Therefore, the suggested mechanism can be called self-healing, while the repaired anode can be termed as the self-healing anode. The use of self-healing strategies to build an electrode architecture is new and highly desirable because it can increase the cycle life and provide a general approach toward stable electrode materials.

The effect of polyurethane-isophorone microcapsules on self-healing properties of an automotive clearcoat

Purpose – The purpose of this work was to prepare a catalyst-free microcapsules as self-healing agent in an automotive clearcoat to improve the scratch resistance of coatings. Design/methodology/approach – In this research, microcapsule with isophorone diisocyanate (IDPI) core and polyurethane shell were prepared and used in self-healing coatings. Microcapsules synthesised were characterised by thermal gravimeter and infrared spectra. The microcapsules were dispersed in an acrylic-melamine clearcoat, and the scratch resistance was evaluated. Findings – The triplex product and the formed polyurethane bonds were confirmed by thermal gravimeter and infrared spectra. In addition, smooth spherical particles with a diameter of 1.5 to 1.7 micronmeters were observed by a scanning electron microscope. The microcapsules dispersed in an acrylic-melamine clearcoat increased the scratch resistance of coatings. Also, the self-healing feature of those coatings was proved. Research limitations/implications – The size of microcapsules can affect its dispersion in the clearcoat and consequently affect the properties of the cured films. Practical implications – The self-healing coatings are interested for many industries such as building and automotive industries. The reported data can be used by the formulators working in the R & D departments. Social implications – Self-healing systems are considered as one of the smart coatings. Therefore, the developing of its knowledge can help to extend its usage to different applications. Originality/value – The application of microcapsules in the coating as healing agents is a great challenge, which has been hardly investigated so far. In the current research, the effect of polyurethane-IDPI microcapsules in an automotive clearcoat as a self-healing coating was investigated.

Three-dimensional collimated self-accelerating beam through acoustic metascreen.

We report the generation of three-dimensional acoustic collimated self-accelerating beam in non-paraxial region with sourceless metascreen. Acoustic metascreen with deep subwavelength spatial resolution, composed of hybrid structures combining four Helmholtz resonators and a straight pipe, transmitting sound efficiently and shifting fully the local phase is evidenced. With an extra phase profile provided by the metascreen, the transmitted sound can be tuned to propagate along arbitrary caustic curvatures to form a focused spot. Due to the caustic nature, the formed beam possesses the capacities of bypassing obstacles and holding the self-healing feature, paving then a new way for wave manipulations and indicating various potential applications, especially in the fields of ultrasonic imaging, diagnosis and treatment.

Performance Evaluation of Zigbee Routing Protocol under Various Conditions using OPNET Modeler

Zigbee, which has the standard IEEE 802.15.4. It is advisable method to build wireless personal area network (WPAN) which demands a low power consumption that can be produced by Zigbee technique. Our paper gives measuring efficiency of Zigbee involving the Physical Layer (PL) and Media Access Control (MAC) sub-layer , which allow a simple interaction between the sensors. We model and simulate two different scenarios, in the first one, we tested the topological characteristics and performance of the IEEE802.15.4 standard in terms of throughput, node to node delay and figure of routers for three network layouts (Star, Mesh and Cluster Tree) using OPNET simulator. The second scenario investigates the self-healing feature on a mesh topology from earlier design until it supports a large number of end points (>64,000) with dynamic routing. The self-healing is done by removing a router from the network during operation, and seeing the end devices find an alternate path to communicate with the coordinator.