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A flexible, dual-broadband and polarization insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1-bit coding units “0” and “1” are formed by the Pancharatnam-Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this paper can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26-12.87 and 14.84-19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

A linear polarization conversion coding metasurface (MS) is proposed for the radar cross section (RCS) reduction of an object. The designed MS has both wideband RCS reduction and high efficiency of mirror reflection in different frequency bands. The cells are arranged according to different 1 bit coding sequences, and the characteristics of RCS reduction are verified by emulations and experiments. The simulation results indicate that the 01/10 coding MSs possess RCS reduction of greater than 10 dB in 9.5–13.9 and 15.2–20.4 GHz, and the 01/10 coding MS is less sensitive to polarization under normal incidence. The experiment results show that 10 dB RCS reduction is achieved in 10.2–14.0 and 15.3–20.7 GHz under normal incidence, and the relative bandwidth (BW) is 32% and 30%, while high efficiency of mirror reflection is obtained from 14.0 to 15.3 GHz. The experimental results are in good agreement with the numerical simulations. Additionally, for the 01/10 coding MS, the dual-broadband performance is also well maintained under 0°–45° oblique incidence. It is a new and practical method to suppress the scattering of metal objects by the combination of scattering and reflection, which has significant potential in the applications of antenna designs or stealth technology fields.

Shape-switching behavior, where a transient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus, is critical to building smart structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D-print shape-switching liquid crystalline elastomers (LCEs) functionalized with supramolecular crosslinks, dynamic covalent crosslinks, and azobenzene. The salient property of shape-switching LCEs is that light induces long-lived, deformation that can be recovered on-demand by heating. UV-light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks, resulting in a programmed deformation. After UV, the shape-switching LCEs fix more than 90 % of the deformation over 3 days by the reformed supramolecular crosslinks. Using the shape-switching properties, we print Braille-like actuators that can be photoswitched to display different letters. This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.

A formidable scientific challenge for the development of self-healing polymers is how to rationally design molecular architectures that could integrate both highly efficient healing functions and excellent mechanical performances. Here, we present a novel rigid and tough but more healable polymer network enabled by self-catalytic cooperative multiple dynamic moieties (CMDMs) containing metal–ligand coordinations, multiple hydrogen bonds and reversible urea bonds. The strength and toughness of the materials are improved significantly via strong supramolecular interactions of CMDMs, resulting in a modulus, tensile strength and toughness up to 797.4 MPa, 73.6 MPa and 218.2 MJ m−3, respectively. The metal–ligand coordinations of CMDMs facilitate the dynamic exchange reactions between the urea bonds of CMDMs through a self-catalytic mechanism, providing the material with a much higher healing efficiency of 90% compared with 48% for the control sample without metal–ligand coordinations. CMDMs provide a novel paradigm for designing robust healable materials by integrating dynamic covalent bonds and supramolecular interactions into one single moiety.

Self-healing and recycling of fiber reinforced polymer (FRP) composites are of great significance towards pursuing a sustainable and circular economy, but remain a huge challenge due to the infusible and insoluble properties of thermoset polymers. The newly developed dynamic covalent polymers provide a great opportunity to resolve this issue for FRPs. Here we developed a novel type of dynamic covalently cross-linked polyacylsemicarbazide exhibiting a high modulus and self-healing/recycling capability due to the reversible properties of the dynamic acylsemicarbazide (ASC) moieties. Introducing different ASC moieties composed of different dihydrazides into the polymer can dramatically tune the mechanical, self-healing and reprocessing properties. An optimized polyacylsemicarbazide with a Young's modulus of ∼2.84 GPa, a stress at break of ∼100 MPa and a glass transition temperature of ∼123 °C exhibits a self-healing efficiency of ∼94.4% and great reprocessing properties. Furthermore, using this newly developed PASC material as the matrix resin, the carbon fiber reinforced polymer composite was successfully prepared through solution impregnation and thermal pressing. The composite exhibits an interlaminar shear strength of 40 MPa and a healing efficiency of 76.2%. The great dynamic reversible properties of ASC moieties enables the recycling of the carbon fiber and matrix resin, respectively, from the composites by a solvolysis method.

Convolutional neural networks have achieved amazing success in many areas in recent years, and VGG is a widely used convolutional neural network model. However, it has some limitations, such as a large number of parameters, which take up significant memory and thus restrict its application in resource-constrained scenarios such as mobile devices and embedded systems. In convolutional neural network models, the different number of convolutional layers can extract different granularity features, which represent the different levels of importance in the image recognition process. Here, we propose a new VGG architecture with different granularity feature combinations that combine different granularity features from block1, block2, block3, block4, and block5 in VGG. Each block is followed by a local fully connected layer to reduce the dimensionality of the coarse and fine features, and five different granularity features are combined as the input of the first global fully connected layer. By combining the features of different blocks, it can increase information flow from a lower layer directly to a fully connected layer and increase feature reuse without adding too many connections. The addition of five local fully connected layers means an increase in parameters, so we reduce the neuron number in two global fully connected layers to reduce the number of parameters. The well-known datasets CIFAR-10 and MNIST were used to evaluate the network's classification performance. The experimental results show that the proposed model achieves better training and testing performance than traditional VGGs and reduces the number of parameters.

Liquid crystal elastomers (LCEs), a class of soft materials capable of a large and reversible change in the shape under the trigger of external stimuli, can be fabricated into diverse architectures with complicated deformation modes through four-dimensional (4D) printing. However, the printable LCE ink is only in the form of monomeric precursors and the deformation mode is limited to contraction/extension deformation. Herein, we report a novel approach to break through these limitations. We achieved 4D printing of a single-component liquid crystal polymer ink in its isotropy state through direct ink writing (DIW) technology. The drawing force imposed by the movement of nozzle in the extruded printing process was able to align the mesogen units along the specific printing path. An orientation gradient perpendicular to the printing direction was obtained due to the existence of a temperature gradient between the two sides of printed samples and could be further fixed by post-photo-cross-linking treatment through the dimerizable groups in the LCE, realizing a new actuation mode in the field of extrusion-based printing of LCE actuators. The printed film was able to change reversibly from a strip to a tightly hollow cylinder and could reversibly lift up an object with roughly 600 times its own weight. The orientation gradient can be patterned through liquid-assistant printing or programmed structure design to integrate both bending and contraction actuation modes on the same printed sample, leading to complex deformation and two-dimensional (2D) planar porous structure to three-dimensional (3D) porous cylinder transition. This study opens up a new prospect to directly print a wide variety of LCE actuators with versatile actuation modes.

Stimuli-responsive structurally dynamic polymers are capable of mimicking the biological systems to adapt themselves to the surrounding environmental changes and subsequently exhibiting a wide range of responses ranging from self-healing to complex shape-morphing. Dynamic self-healing polymers (SHPs), shape-memory polymers (SMPs), and liquid crystal elastomers (LCEs), which are three representative examples of stimuli-responsive structurally dynamic polymers, have been attracting broad and growing interest in recent years because of their potential applications in the fields of electronic skin, sensors, soft robots, artificial muscles, and so on. Recent advances and challenges in the developments toward dynamic SHPs, SMPs, and LCEs are reviewed, focusing on the chemistry strategies and the dynamic reaction mechanisms that enhance the performances of the materials including self-healing, reprocessing, and reprogramming. The different dynamic chemistries and their mechanisms on the enhanced functions of the materials are compared and discussed, where three summary tables are presented: A library of dynamic bonds and the resulting characteristics of the materials. Finally, a critical outline of the unresolved issues and future perspectives on the emerging developments is provided.

The use of thermosensitive polymers exhibiting an upper critical solution temperature (UCST) for sensing and detecting the presence of CO2 in aqueous solution was demonstrated. By synthesizing random copolymers of acrylamide (AAm), acrylonitrile (AN) and N,N-diethylaminoethyl methacrylate (DEAEMA), which have different relative contents of AAm and AN but a similar and small amount of CO2-responsive DEAEMA (below 3%), two means for monitoring the concentration of CO2 through the transparency change of a polymer sensor solution were investigated. On the one hand, using a single P(AAm-co-AN-co-DEAEMA) copolymer whose phase transition-induced transmittance change upon cooling is completed within a narrow temperature range and whose cloud point (CP) is sensitively decreased upon increasing the amount of CO2, the polymer solution at a given temperature (25 °C) allows a threshold concentration of CO2 to be detected by showing an abrupt change in transmittance. On the other hand, by mixing two copolymers with largely different CPs (over 30 K), the sharp UCST-type phase transition is suppressed; instead the change in the solution transmittance upon cooling proceeds slowly and gradually over a wide temperature region (>35 K). The mixed polymer solution can be used to monitor the increase in the amount of CO2 through gradual and mostly linear changes in transmittance. Both abrupt and gradual transparency changes can be observed by the naked eye.

Significant advances have been made in the development of self-healing synthetic polymer materials in recent years. This review article discusses the recent progress in preparation, characterization and properties of different kinds of intrinsic self-healing elastomers based on reversible covalent bonds and dynamic supramolecular chemistry. Healing conditions, mechanical property recovery and healing efficiency are the main discussion topics. Potential applications, challenges and future prospects in self-healing elastomer fields are also discussed in the last part of this review.

Although shape-memory polymers (SMPs) can alter their shapes upon stimulation of environmental signals, complex shape transformations are usually realized by using advanced processing technologies (four-dimensional printing) and complicated polymer structure design or localized activation. Herein, we demonstrate that stepwise controlled complex shape transformations can be obtained from a single flat piece of SMP upon uniform heating. The shape-memory blends prepared by solution casting of poly(ethylene oxide) and poly(acrylic acid) (PAA) exhibit excellent mechanical and room-temperature shape-memory behaviors, with fracture strain beyond 800% and both shape memory and shape recovery ratio higher than 90%. After plastic deformation by stretching under ambient conditions, the material is surface-patterned to induce the formation of an Fe3+-coordinated PAA network with gradually altered cross-linking density along the thickness direction at desired areas. Upon subsequent heating for shape recovery, strain r...

Shape memory biomaterials are functional biomaterials that recover their original shape at the presence of the right external stimulus, such as temperature, magnetic field, electric field, light, and even moisture. The shape memory effect and/or superelastic property of shape memory biomaterials is particularly useful in shaping tissue in biomedical engineering. In the past 50 years, there were significant progress from shape memory alloys (SMAs) to shape memory polymers (SMPs) being used for medical applications, such as implantable medical devices in dentistry, orthopedics, interventional therapy, minimally invasive surgery tools and drug carriers, etc. This chapter will mainly introduce the mature SMAs and SMPs for biomedical application and propose the future research direction in the field of shape memory biomaterials.

Improving the adsorption capacity of the adsorbent and realizing rapid separation are quite important for water treatment. Herein, one kind of novel Ni/Co-contained reduced graphene oxide aerogel microspheres (rGOAMs-M) with high surface area and magnetic response are synthesized by a novel process comprised of electrospraying, droplets spherification, crosslinking immobilizing of metal, lyophilization and thermal reduction. The aqueous dispersion mixture of graphene oxide and sodium alginate is electrosprayed under high electric voltages to produce droplets, which are collected in a nickel/cobalt acetate tetrahydrate solution and then crosslinked between alginate and metal ions. The obtained rGOAMs-M have the cabbage-like inner structures, and possess the organic solvent/oil adsorption capacities of 107–270 g.g−1 and also extraordinary oil/water emulsion separation ability. The rGOAMs-M also can be rapidly assembled and separated from the medium under a magnetic field.

Shape-switching behavior, where a transient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus, is critical to building smart structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D-print shape-switching liquid crystalline elastomers (LCEs) functionalized with supramolecular crosslinks, dynamic covalent crosslinks, and azobenzene. The salient property of shape-switching LCEs is that light induces long-lived, deformation that can be recovered on-demand by heating. UV-light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks, resulting in a programmed deformation. After UV, the shape-switching LCEs fix more than 90 % of the deformation over 3 days by the reformed supramolecular crosslinks. Using the shape-switching properties, we print Braille-like actuators that can be photoswitched to display different letters. This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.

Microbubbles, as contrast agents and drug carriers, have been widely used for theranostic applications with ultrasound technology over the past three decades. Research in microbubbles has undergone numerous improvements from a compositional perspective as researchers aim for enhanced targeted drug delivery. Microbubbles shells, which typically encapsulate a gaseous core, are conventionally classified into three type's proteins, lipids, and polymers. Microbubbles will volumetrically oscillate or crack in an ultrasound field, which can be useful in targeted drug delivery applications. Polylactic Acid (PLA) can be used to fabricate microbubbles; drugs of interest can be encapsulated into the polymer shells. They can be released at the site with the application of ultrasound to achieve targeted drug delivery. However, two limitations encountered with this microbubble are a lack of controlled drug release upon triggering and the elasticity of the polymer shell in an ultrasound field. This research is focused on the development of novel Ultraviolet (UV) sensitive shape changeable polylactic acid (PLA) microbubbles to control shell properties by incorporation of a Poly (beta-aminoester) containing Azobenzene (ABP). We propose that the unique contrast agent developed in this study can be tuned to control shell elasticity and shell porosity for imaging and drug release in vivo, as well as other biomedical applications.

Aiming at the development of a controlled redox responsive polymeric micelle system, a series of redox-sensitive ABA triblock degradable copolymers with different amounts of disulfide bonds were synthesized. These multi-disulfide-containing amphiphilic copolymers are able to self-assemble in aqueous solution to form spherical micelles with a hydrophobic polyurethane block forming the hydrophobic core. The presence of dynamic and labile disulfide bonds in the copolymer makes the copolymer and its micelle have responsivity to stimuli such as redox agents and ultrasound. The micellar properties and release kinetics of encapsulated guest molecules in response to stimuli were investigated using hydrophobic pyrene as a fluorescent probe and DTT as a redox agent. The redox-responsive behavior could be adjusted by changing the amount of disulfide bonds within the copolymer backbone. A relatively fast release behavior was observed for micelles formed by the copolymers in which every repeat unit of the hydrophobic block contains a disulfide bond. Furthermore, the release rate could be greatly enhanced and adjusted remotely under HIFU irradiation in the presence of DTT. The HIFU/redox combined stimulus for the specially designed copolymer micelles containing disulfide bonds provides a novel modality for drug delivery systems.

Cancer metastasis arises from magical pathological cell migration. An accurate and rapid evaluation of cell migration can reduce the number of animals used in experiments to develop a new drug to restrain the metastasis. In this work, high-strength double network hydrogels were synthesized to develop the three-dimensional (3D) scaffolds, which were applied to screen drug of anticancer in vitro. Compression strength was examined for Poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/ Polyacrylamide (PAMPS/PAAm) double network hydrogel, Polyethylene glycol-Poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/ Polyacrylamide (PEG-PAMPS/PAAm) double network hydrogel and Poly(vinyl alcohol)-Poly(2-acrylamido-2-methyl-1-propanesulfonic acid)/ Polyacrylamide (PVA-PAMPS/PAAm) double network hydrogel in more than 90% deformation rate. The results showed that PEG-PAMPS/PAAm hydrogel and PVA-PAMPS/PAAm hydrogel could provide high mechanical property to afford the scaffold durability and simulate cell metastasis under a simulated blood pressure. Used as the in vitro scaffold, the PEG-PAMPS/PAAm hydrogel and PVA-PAMPS/PAAm hydrogel were co-cultured with the two cancer cell, NB4 cell and A549 cell, which is the acute promyelocytic leukemia cell line and the human lung cancer cell, respectively. The results showed that the hydrogels had no intrinsic cytotoxicity to the two cells. Furthermore, under adriamycin treatment, the NB4 cell migration in two-dimensional (2D) polycarbonate membranes and PEG-PAMPS/PAAm hydrogel scaffold was investigated. The results indicated that the PEG-PAMPS/PAAm hydrogel had inter-connective porous structures and hole walls with deformability, could provide more practical channels to decrease the damage of the amoeboid migrated cells. This paper provides a 3D scaffold for studying cell migration and thus finds a rapid in vitro evaluation of a new drug to restrain the cancer cell metastasis.

The use of an external electric field to enhance and modulate the photoluminescence (PL) of lanthanide-doped upconversion nanoparticles (UCNPs) is challenging. A liquid crystal (LC)-based approach is demonstrated in this study. By loading UCNPs in a polymer-stabilized, homogeneous LC matrix, the upconversion PL intensity can increase or decrease almost linearly upon increase or decrease, respectively, of the applied voltage, reaching an enhancement factor of about 6–8 at an electric field of 4.6 V μm−1 depending on the 980 nm excitation laser power and the applied a.c. field frequency. The origin of the electrical enhancement and modulation is the electric field induced LC texture (orientation state) transition that controls the light scattering of the LC/UCNP mixture. Increased scattering of the near infrared (NIR) excitation light before exciting the material increases its probability to be absorbed by the UCNPs and thus leads to enhanced PL emission. This LC scattering-based approach is facile, versatile and can readily be applied to UCNPs with no need for chemical composition or structural modifications that often require tedious synthesis.

A new kind of ultrafast near-infrared light responsive shape memory assisted self-healing polymer composite was prepared by introducing polydopamine particles (PDAPs) into polyurethane containing Diels–Alder bonds. The mechanical properties of the polyurethane composites are significantly enhanced with the addition of PDAPs due to the strong interface interaction between PDAPs and polyurethane segments. Owing to the outstanding photothermal effect of PDAPs and excellent dynamic properties of Diels–Alder bonds, the composites possess rapid light responsive shape memory and self-healing properties. The shape memory ability of the materials also plays an important role in improving the self-healing efficiency. Due to the excellent dispersion and easy preparation method, PDAPs have great potential to be used as high-efficiency and environmentally friendly fillers to obtain novel photoactive functional polymer composites.

Endowing thermoset polymer materials with self-healing and recyclable properties by incorporating dynamic bonds into the polymer networks is of vital realistic significance. However, such materials are still limited because of the difficult synthetic process and expensive dynamic monomers or environment-unfriendly catalysts. Herein, catalyst-free and colorless transparent healable and recyclable poly(oxime-urethane) elastomers based on dynamic oxime–carbamate bonds were developed with scaling-up capability using low-cost and commercially available compounds. These materials display remarkable comprehensive properties and relatively low relaxation activation energy (∼29.7 kcal mol−1) which results in excellent healable and recyclable performance. The poly(oxime-urethane) with a crosslink density ν of ∼0.2 mmol cm−3 possesses a tensile strength of ∼13.5 MPa, a breaking strain of ∼812%, toughness up to ∼40 MJ m−3, an excellent elastic recovery of ∼90% and an average optical transmittance of ∼86% in the visible range. This material can be completely healed at 110 °C in 0.5 h. In situ structural characterizations revealed that the dynamic properties originate from the reversibility of oxime–carbamate bonds and hydrogen bonds.

Tissue adhesives are commonly used in surgeries and regenerative engineering for the repair and regeneration of topical and internal wounds on tissues and organs such as skin, heart, blood vessels, and bone. However, achieving rapid crosslinking, strong wet adhesion and cohesion strengths, and minimal cytotoxicity remains a critical roadblock for clinical translation. Herein, in contrast to harsh and cytotoxic oxidants, magnesium oxide (MgO) particles were found to facilitate rapid crosslinking for injectable citrate-based mussel-inspired tissue bioadhesives synthesized by reacting citric acid, PEG-PPG-PEG diol and dopamine (iC-EPE). Our results confirmed the role of MgO particles as both crosslinkers and composite fillers to concurrently enhance bioadhesive cohesion and adhesion. iC-EPE crosslinked by MgO with/without sodium periodate (PI) exhibit enhanced mechanical strengths (1.0 Mpa tensile strength ≤ 4.5 MPa) compared to that of iC-EPE crosslinked only by PI (~0.75 MPa), high adhesion strength (up to 125 kPa, 8 fold that of fibrin glue (~15 kPa)), tunable degradability (full degradation from1 week to 1 month), excellent in vitro and in vivo biocompatibility, encouraging anti-bacterial performance, and favorable wound closure efficacy. Thus, MgO crosslinked bioadhesives possess great potential for a wide range of applications in surgery and regenerative engineering.

Symmetrical dual D-shape photonic crystal fibers (PCFs) for surface plasmon resonance (SPR) sensing are designed and analyzed by the finite element method (FEM). The performance of the sensor is remarkably enhanced by the directional power coupling between the two fibers. We study the influence of the structural parameters on the performance of the sensor as well as the relationship between the resonance wavelengths and analyze refractive indexes between 1.36 and 1.41. An average spectral sensitivity of 14660 nm/RIU can be achieved in this sensing range and the corresponding refractive index resolution is 6.82 × 10-6 RIU. The characteristics of a single D-shape PCF-SPR sensor with the same structural parameters are compared with those of the dual PCFs sensor and the latter has distinct advantages concerning the spectral sensitivity, resolution, amplitude sensitivity, and figure of merits (FOM).

Combining self‐healing functions with damage diagnosing, which can achieve timely healing autonomously, is expected to improve the reliability and reduce life cycle cost of materials. Here, a flexible conductive composite composed of a dynamically crosslinked polyurethane bearing Diels–Alder bonds (PUDA) and carbon nanotubes (CNTs), which possess both crack diagnosing and self‐healing functions, is reported. The introduced dynamic Diels–Alder bonds endow the materials self‐healing function and the powder‐based preparation route based on the specially designed CNTs‐coated PUDA micropowders leads to the formation of segregated CNTs network, which makes the composite possess excellent mechanical properties and high conductivity. Because of the sufficient electrothermal and photothermal effect of CNTs, the composites can be healed rapidly and repeatedly by electricity or near‐infrared light based on the retro‐Diels–Alder reaction. An obvious color difference in the infrared thermograph resulting from the resistance difference between damaged and undamaged area can be observed when applying the voltage, which can be used for crack diagnosing. Using the same electrical circuit, the crack in the PUDA/CNTs composite can be noninvasively detected first and then be autonomously healed. The composites also exhibit a strain‐sensing function with good sensitivity and high reliability, thus will have potential applications in electronic strain sensors.

Tissue adhesives play an important role in surgery to close wounds, seal tissues, and stop bleeding, but existing adhesives are costly, cytotoxic, or bond weakly to tissue. Inspired by the water-resistant adhesion of plant-derived tannins, we herein report a new family of bioadhesives derived from a facile, one-step Michael addition of tannic acid and gelatin under oxidizing conditions and crosslinked by silver nitrate. The oxidized polyphenol groups of tannic acid enable wet tissue adhesion through catecholamine-like chemistry, while both tannic acid and silver nanoparticles reduced from silver nitrate provide antimicrobial sources inherent within the polymeric network. These tannin-inspired gelatin bioadhesives are low-cost and readily scalable and eliminate the concerns of potential neurological effect brought by mussel-inspired strategy due to the inclusion of dopamine; variations in gelatin source (fish, bovine, or porcine) and tannic acid feeding ratios resulted in tunable gelation times (36 s–8 min), controllable degradation (up to 100% degradation within a month), considerable wet tissue adhesion strengths (up to 3.7 times to that of fibrin glue), excellent cytocompatibility, as well as antibacterial and antifungal properties. The innate properties of tannic acid as a natural phenolic crosslinker, molecular glue, and antimicrobial agent warrant a unique and significant approach to bioadhesive design. Statement of Significance This manuscript describes the development of a new family of tannin-inspired antimicrobial bioadhesives derived from a facile, one-step Michael addition of tannic acid and gelatin under oxidizing conditions and crosslinked by silver nitrate. Our strategy is new and can be easily extended to other polymer systems, low-cost and readily scalable, and eliminate the concerns of potential neurological effect brought by mussel-inspired strategy due to the inclusion of dopamine. The tannin-inspired gelatin bioadhesives hold great promise for a number of applications in wound closure, tissue sealant, hemostasis, antimicrobial and cell/drug delivery, and would be interested to the readers from biomaterials, tissue engineering, and drug delivery area.

A near-infrared-light (NIR)- and UV-light-responsive polymer nanocomposite is synthesized by doping polymer-grafted gold nanorods into azobenzene liquid-crystalline dynamic networks (AuNR-ALCNs). The effects of the two different photoresponsive mechanisms, i.e., the photochemical reaction of azobenzene and the photothermal effect from the surface plasmon resonance of the AuNRs, are investigated by monitoring both the NIR- and UV-light-induced contraction forces of the oriented AuNR-ALCNs. By taking advantage of the material's easy processability, bilayer-structured actuators can be fabricated to display photocontrollable bending/unbending directions, as well as localized actuations through programmed alignment of azobenzene mesogens in selected regions. Versatile and complex motions enabled by the enhanced photocontrol of actuation are demonstrated, including plastic "athletes" that can execute light-controlled push-ups or sit-ups, and a light-driven caterpillar-inspired walker that can crawl forward on a ratcheted substrate at a speed of about 13 mm min-1 . Moreover, the photomechanical effects arising from the two types of light-triggered molecular motion, i.e., the trans-cis photoisomerization and a liquid-crystalline-isotropic phase transition of the azobenzene mesogens, are added up to design a polymer "crane" that is capable of performing light-controlled, robot-like, concerted macroscopic motions including grasping, lifting up, lowering down, and releasing an object.

The structure and nanoscale mechanical properties of Ni48.8Mn27.2Ga24 thin film fabricated by DC magnetron sputtering are investigated systematically. The thin film has the austenite state at room temperature with the L21 Hesuler structure. During nanoindentation, stress-induced martensitic transformation occurs on the nanoscale for the film annealed at 823 K for 1 hour and the shape recovery ratio is up to 85.3%. The associated mechanism is discussed.

The concept of using ultrasound to trigger shape memory assisted healing of covalently cross-linked dynamic polymers is demonstrated. The well-designed dynamically crosslinked poly(e-caprolactone)-based polyurethane bearing Diels–Alder bonds not only possesses high mechanical strength and toughness, but also exhibits shape memory assisted crack-closure and healing upon exposure to high-intensity focused ultrasound owing to breaking and reformation of dynamic bonds. The use of focused ultrasound allows the healing process to be activated remotely and to be controlled locally by depositing the acoustic energy only in the damaged region without detriment to the undamaged parts of the material. The healable polyurethane materials have potential applications such as long-term load-bearing engineering components and anti-fatigue medical devices.

A big challenge in developing stimuli-responsive materials is to integrate multiple functionalities such as shape memory property, healable ability, recyclability into a single-component material. With this purpose, we designed a novel poly(n-butyl acrylate-co-methyl methacrylate) bearing a side group 2,6-bis(1′-methylbenzimidazolyl)pyridine ligand, which is dynamically crosslinked by the metal salt zinc trifluoromethanesulfonate to obtain the metallosupramolecular polymer. The shape recovery and healing is achieved upon application of a thermal or light stimulus due to the specific metal–ligand interactions which not only serve as an “inert” crosslink network at low temperature to produce the shape recovery, but also dissociate at high temperature for healing. The healing rate is quick and the healing efficiently is close to ∼90%.

Photoresponsive actuators based on semicrystalline poly(ethylene-co-vinyl acetate) (EVA) loaded with small amounts of gold nanoparticles (AuNPs) are described. Upon absorption of light (532 nm), the heat released by the AuNPs raises the temperature in the irradiated region to Tlight to melt crystallites with lower melting temperatures (Tm Tlight . Once the light is turned off, the recrystallization of oriented chains in the actuation domains upon cooling gives rise to an expansion force. We show that the photoinduced contraction force, Tlight , and the speed for reaching Tlight can readily be adjusted, which makes EVA/AuNP a robust, fast optical actuation system tunable in both speed and magnitude. The material design can easily be extended to other temperature-memory semicrystalline polymers in combination with various light-absorbing and heat-generating additives.

A new strategy for enhancing the photoinduced mechanical force is demonstrated using a reprocessable azobenzene-containing liquid crystalline network (LCN). The basic idea is to store mechanical strain energy in the polymer beforehand so that UV light can then be used to generate a mechanical force not only from the direct light to mechanical energy conversion upon the trans–cis photoisomerization of azobenzene mesogens but also from the light-triggered release of the prestored strain energy. It is shown that the two mechanisms can add up to result in unprecedented photoindued mechanical force. Together with the malleability of the polymer stemming from the use of dynamic covalent bonds for chain crosslinking, large-size polymer photoactuators in the form of wheels or spring-like “motors” can be constructed, and, by adjusting the amount of prestored strain energy in the polymer, a variety of robust, light-driven motions with tunable rolling or moving direction and speed can be achieved. The approach of prestoring a controllable amount of strain energy to obtain a strong and tunable photoinduced mechanical force in azobenzene LCN can be further explored for applications of light-driven polymer actuators.

Direct interference between the induced magnetic and electric moments in a hybrid metal-dielectric nanodisk is demonstrated for the realization of unidirectional forward scattering in the near-infrared region. Specifically, the unidirectional forward scattering with high efficiency of the designed nanoantennas is not limited to one specific wavelength but can fit multiwavelengths. The scattering properties of the metal-dielectric hybrid nanodisk at a specific wavelength can be adjusted to meet the Kerker’s type condition. In addition, the simulated optical properties of the nanoantennas reveal that the nanodisk arranged in an array exhibits efficient absorption leading to enhanced directionality. Our results provide insights into the design and engineering of highly directive nanoantennas.

A series of biodegradable poly(L-lactide) (PLLA) and its copolymers with poly(e-caprolactone) (PCL) is synthesized and characterized. The mechanical properties and shape memory effects are studied by means of dynamic mechanical analysis (DMA) and tensile tests. It is found that the mechanical properties are significantly affected by the polymer compositions. With the e-caprolactone (e-CL) content increasing, the maximum stress decreases linearly and the strain at break increases gradually. By adjusting the compositions, the polymers exhibit excellent shape memory effects and a maximum recovery stress of about 6.2 MPa can be obtained for the PCLA70 copolymer. Structure of the polymers during the shape memory process is investigated using differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The polymers are observed to consist of the PLLA crystal and amorphous phase which serve as physical cross-links and reversible phase, respectively. Shape memory effect is attributed to be the deorientation of the oriented amorphous chains due to thermodynamic entropy effect.

Poly(L-lactide) (PLLA) was synthesized by the ring-opening polymerization of L-lactide and the shape memory behavior was studied using DSC and bending test experiments. The results indicate that the specimen shows the shape memory effect (SME), the small crystalline phase of PLLA and the mobility of amorphous phase may be responsible for the SME. The shape recovery of samples decreases and approaches to steady with the testing number increases.

Two different site-specific cleavage mechanisms for copolymer micelles under ultrasound and redox were confirmed. The finding that ultrasound induced mechanochemical cleavage of central ester bonds can open up a new way in the design of novel ultrasound responsive copolymer micelles for drug release.