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End functionalization of homopolymers by noncovalent binding units is a straightforward approach to prepare supramolecular polymers with a broad application scope as stimuli-responsive functional m...

Stretchable strain sensors have promising applications in many fields, including soft robotic skin, health monitoring, wearable electronics, and so on. Among the various properties of stretchable strain sensors, the low detection limit and wide sensing range are the two most critical properties that determine their practical application in the above fields. However, it is still a great challenge to achieve both an ultralow detection limit and ultrawide sensing range at the same time, and there often needs to be a tradeoff between them. Herein, we propose a simple route to design a stretchable strain sensor with both an ultralow detection limit and an ultrawide sensing range by the combination of the electrospinning technique and ultrasonication anchoring technique. Specifically, thermoplastic polyurethane (TPU) is fabricated into a highly stretchable porous film and carbon nanotubes (CNTs) are anchored onto the surface of TPU nanofibers assisted by ultrasonication, and then assembled with two Cu electrodes to fabricate the strain sensor. Attributed to the multiscale evolution of the conductive network under stretching, the designed strain sensor exhibits many outstanding merits, such as an ultra-low detection limit (0.05%), an ultrawide sensing range from 0.05% to 600%, a fast response time of 75 ms, and excellent durability. Because of these outstanding merits, the TPU@CNT strain sensor can detect both the subtle strain change caused by the sound of a piano and the large strain change caused by the large-scale motions of joints. Moreover, it is found that TPU@CNT sensor responds to temperature and humidity, which has great potential in temperature sensors and humidity sensors.

In this work, we proposed an effective route, i.e., three-dimensional (3D) confined co-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) within organic emulsion droplets, to efficiently encapsulate high-density and large-size NPs into the wall of BCP vesicles. Attributed to the interfacial instability, the aqueous phase could spontaneously enter into the organic emulsion droplets, thus inducing the formation of BCP vesicles encapsulated with NPs. Moreover, it is found that the encapsulation of NPs into the vesicle wall is mainly dominated by the ratio (DN/dw0) of the NP diameter (DN) to the layer thickness of the affinitive blocks (dw0). Utilizing the 3D confined co-assembly of polystyrene-block-poly(4-vinylpyridine) and PS-coated gold nanoparticles (AuNPs) with different diameters, the high-efficiency encapsulation of AuNPs in the BCP vesicle wall at a DN/dw0 value of 0.66 can be achieved, which is greater than the previous reported critical value (i.e., DN/dw0 ≈ 0.5). Although the conformational entropy loss of the polymer chains increases with the introduction of AuNPs, the NPs can still be successfully encapsulated into the vesicle wall because the oil–water interface can suppress the diffusion of NPs to the aqueous phase. However, as the DN/dw0 value is further increased to 1.04, AuNPs will be repelled out of the vesicles because of the extremely strong entropic repulsion arising from the drastic loss in conformational entropy of PS blocks, thus forming some spherical hybrid micelles independently. Our results provide a new and facile route to realize the efficient encapsulation of large size NPs into polymeric vesicles.

Thermoresponsive polymers that exhibit a cloud point temperature (Tcp) are an important class of stimuli-responsive polymers that have great potential for biomedical applications. Precise tuning of the Tcp is of fundamental importance for designing thermoresponsive polymers. However, tuning the Tcp generally requires sophisticated control over the chemical and assembled structures of thermoresponsive polymers. Here, we report a simple yet effective method to tune the Tcp of thermoresponsive polymers only by mixing and varying the mixing ratios of amphiphilic copolymer pair that contains l- and d-configured hydrophobic blocks in a dilute solution. Stereocomplex (SC) crystallization of the l- and d-configured blocks led to form core–shell micelles with a larger size, a bigger core, and a higher aggregation number, which facilitated the intermicellar aggregation upon heating due to improved intermicellar attractions. SC crystallization of the hydrophobic blocks improved the separation efficacy of the thermor...

Constructing noncovalent interactions has been a benign method to tune the stimuli responsivity and assembled structure of polymers in solution; this is essential for controlling the functions and properties of stimuli-responsive materials. Herein, we demonstrate a novel supramolecular strategy to manipulate the cloud point (

Stereocomplexation of complementary chiral blocks has been a feasible way to prepare thermoresponsive physical gels (or thermogels). Understanding the thermoresponsive phase behavior of stereocomplexable amphiphilic copolymers in water is essential to prepare thermogels with tunable physical properties. Herein, we use an enantiomeric mixture of the poly(D-lactic acid) (PDLA)/poly(ethylene glycol) (PEG) diblock copolymer and the poly(L-lactic acid) (PLLA)/PEG triblock copolymer as a stereocomplexable system and report a novel thermogel that exhibits unique gel–sol–gel multiple transitions upon heating. The thermally-induced phase transition of the PEG–PDLA/PLLA–PEG–PLLA thermogel was governed by the copolymer composition and the stereocomplexation of PLLA/PDLA segments. The molecular motion of PEG segments enhances during the gel–sol transition but slows down in the subsequent sol–gel transition. The gel–sol and sol–gel transitions that occurred at low and high temperatures are driven by the increased mobility of PEG segments and micelles and the promoted PLLA/PDLA stereocomplexation, respectively. PEG–PDLA/PLLA–PEG–PLLA gels can be used to capsulate and release a hydrophobic drug; the drug release rate increases as the content of hydrophilic blocks increases.

Skin-like sensor has recently emerged for its promising applications in human motion monitoring and healthcare. However, it is challenging to develop flexible skin-like sensors multifunctionally coupled with high transparency and strain sensitivity, accurate thermosensation, and good antibacterial activity. Herein, we fabricate flexible and transparent (94.3%) ionogels by facilely mixing ionic liquid (IL) and thermal-plastic polyurethane (TPU) to be as skin-like sensors. The prepared TPU@IL ionogel-based sensor exhibits wide strain range (0.1–500%) and fast response (96 ms) to strain stimuli. Attributed to the temperature-dependent conductivity and low freezing point of IL, the ionogels can be served as stretchable temperature sensor, containing wide operating temperature window (−40-100 °C) and high detecting accuracy (0.1 °C). Moreover, the ionogels exhibit excellent antibacterial activity. This work may inspire future research to design full-featured skin-like sensors.

Stretchable strain sensor and temperature sensor are two essential components for the integration of wearable electronics and electrical skins, which have great potentials in healthcare monitoring, human motion monitoring and human-machine interfaces. Up to now, it is still a challenge to fabricate the stretchable and multifunctional sensor with both the capabilities of strain sensing and temperature sensing by an effective and economical method. Herein, a simple route is provided to design multifunctional sensors with high sensing performances for strain and temperature, which combines the electrospun technique and ultrasonication anchoring technique. Specifically, fibrous thermoplastic polyurethane (TPU) film is fabricated by electrospun technique at first, and then is saturated by ionic liquid (IL) to design the stretchable sensor. Attributed to the stable response and fast reconstruction of conductive pathways of ionic liquid under the stretching-releasing process, the TPU/IL sensor can serve as strain sensor, which exhibits various merits, including fast response time of 67 ms, ultra-low detection limit (0.1%), ultra-wide sensing range from 0.1% to 400% and excellent durability for long-term usage. In addition, it is noteworthy that TPU/IL sensor has great advantages in temperature sensing, which possesses a lowest temperature accuracy of 0.5 °C. This work provides a novel route for manufacturing stretchable multifunctional sensor with both temperature and strain sensing functions, which may accelerate the development of the emerging wearable electronics and electrical skins.

Supramolecular polymers (SMPs) have quite different crystallization behavior from the conventional polymers, because of the confinement effects of supramolecular units. Crystallization of SMPs undergoes in a “confined” and “dynamic” manner. Herein, we selected the 2-ureido-4[1H]-pyrimidione (UPy)-bonded poly(l-lactic acid) (PLLA) as a model SMP and investigated the crystallization kinetics, polymorphic crystalline structure and phase transition of supramolecular PLLAs (SM-PLLAs). SM-PLLAs were synthesized by the end functionalization of hydroxyl-terminated 2- and 3-arm PLLA precursors with different molecular weights. Crystallization rate and crystallinity of SM-PLLAs are strongly depressed in both nonisothermal and isothermal crystallizations, as compared to the nonfunctionalized PLLA precursors. Crystalline structure of SM-PLLAs is sensitive to the crystallization temperature (Tc). A low Tc (75–95 °C) facilitates the formation of metastable β crystals of PLLA in SM-PLLAs; while a high Tc (100–130 °C) fa...

Precipitation (or solvent displacement) method has been a simple yet efficient way to prepare the micro- and nanoparticles of polymers. However, control over the particle morphology of semicrystalline polymer is extremely challenging in the precipitation method, due to the interplay of polymer crystallization with liquid–liquid phase separation in solution. This limits the preparation of polymer particles with well-controlled morphology. Herein we report on the preparation of flower-shaped and spherical biodegradable polymer particles by precipitating the ureido-4[1H]-pyrimidione-functionalized supramolecular poly(lactic acid) (PLA) from a good solvent to an antisolvent. Morphology of PLA particles was successfully manipulated by the solution crystallization, molecular weight, and intermolecular interactions of polymer precursors. Homocrystallization of supramolecular poly(l-lactic acid) yielded the flower-shaped particles in precipitation; yet stereocomplex crystallization of PLA supramolecular copolymer...

Physical hydrogels crosslinked by non-covalent interactions have attained increasing attention due to their good mechanical properties and processability. However, the use of feasible and controllable non-covalent interactions is highly essential for preparing such hydrogels. In this article, we report on stereocomplexed physical hydrogels prepared by simple casting and swelling of amphiphilic graft copolymers bearing a poly(acrylic acid) (PAA) backbone and poly(l-lactic acid) (PLLA) or poly(d-lactic acid) (PDLA) stereocomplexable side chains. The microstructure, swelling behavior, and mechanical and shape memory properties of the obtained hydrogels can be tuned by varying the copolymer composition and stereocomplex (SC) crystallization of PLLA/PDLA enantiomeric chains. The long PLLA or PDLA chains segregate to form hydrophobic, crystallized domains in water, serving as physical crosslinking junctions for hydrogels. SC crystallization between PLLA and PDLA further enhances the number density of physical crosslinkers of enantiomerically mixed hydrogels. The SC content increases as the PLLA/PDLA ratio approaches 1/1 in enantiomerically mixed hydrogels. The average distance between crosslinking junctions declines for the hydrogels with a high PLLA (or PDLA) mass fraction (MPLA) and SC content, due to the increased number density of physical crosslinkers. Accordingly, the tensile strength and the Young's modulus increase but the swelling ratio and the elongation-at-break of the hydrogels decrease with an increase in MPLA and SC content. The hydrogels exhibit shape memory behavior; the shape fixing ability is enhanced by the SC crystallization of PLLA/PDLA side chains in the hydrogels.

Thermoresponsive block copolymer (BCP) micelles have attracted increasing attentions due to their potential in biological applications. Many studies have investigated facile strategies to tune the cloud point (Tcp) of thermoresponsive polymer, such as changing hydrophobic/hydrophilic block ratio, micelle concentration and addition of salt. Considering the dependence of properties and functions of BCPs on thermal-induced structural transition, it is necessary to understand the universal mechanism of structural changes during temperature-induced phase transition; whereas it is challenging to achieve precise structure and properties of BCP micelles with Tcp changes. Herein, we choose thermoresponsive poly (L-lactide-co-glycolide)-poly (ethylene glycol)-poly (L-lactide-co-glycolide) (PLGA-PEG-PLGA) block copolymer as a model system and utilize synchrotron-radiation small-angle X-ray scattering (SAXS) technique to systematically investigate the assembled structure of PLGA-PEG-PLGA and the mechanism for thermally induced structural transition of BCP micelle. With the increase of PLGA hydrophobic block, the Tcp significantly decreases, ascribed to the enhancement of the core size, aggregation number, as well as the packing density of PLGA in micelle core. Moreover, the increase of micelle concentration and the addition of salt also decreases the Tcp. Furthermore, temperature-induced drug release is also investigated, the release rate is much faster at above Tcp.

Thymine-terminated poly(lactic acid) (PLA-THY) and diaminotriazine-terminated poly(ethylene glycol) (PEG-DAT) are synthesized and they can form the supramolecular amphiphilic diblock copolymers in solution through the thymine/diaminotriazine complementary hydrogen bonding interactions. Such supramolecular copolymers self-assemble into the stimuli-responsive micelles in aqueous solution. Micelle size, crystalline state, stimuli responsibility, drug loading and release behavior of the supramolecular micelles can be readily tuned from the block length, stereostructure, homo and stereocomplex crystallizations of hydrophobic PLA blocks. The enantiomerically-mixed supramolecular copolymers with both poly( l -lactic acid) (PLLA) and poly( d -lactic acid) (PDLA) blocks assemble into the stereocomplexed micelles, while those having the isotactic PLLA (or PDLA) and atactic poly( d , l -lactic acid) (PDLLA) blocks form the homocrystalline and amorphous micelles, respectively. The stereocomplexed and amorphous micelles exhibit smaller size than their homocrystalline analogs, all of which are much larger than the micelles formed from the conventional covalently-bonded diblock copolymers. The supramolecular micelles are sensitive to the external stimuli such as pH and ion. The homocrystalline and stereocomplexed micelles undergo fast aggregation in the acidic and salted solutions due to the disassociation of complementary hydrogen bonds. The stereocomplexed micelles exhibit larger drug loading content and slower drug release rate than the amorphous and homocrystalline ones, because of the larger polymer/drug interactions and tighter chain packing inside the micelle cores.

Promoting the stereocomplexation ability of high-molecular-weight poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) is an efficient way to improve the thermal resistance of the resulting materials. Herein, we studied the competing crystallization kinetics, polymorphic crystalline structure, and lamellae structure of the PLLA/PDLA component in its miscible blends with poly(vinyl acetate) (PVAc) and proposed a method to improve the stereocomplexation ability of PLLA and PDLA through miscible blending with the other polymer. Crystallization of the PLLA/PDLA component is suppressed after the addition of PVAc, due to the dilution effect. The stereocomplexation ability of PLLA and PDLA is enhanced by blending with PVAc; this becomes more obvious at a high PVAc content (≥50 wt %) but less significant with the further increase of PLLA, PDLA molecular weights. Almost exclusive formation of SCs is achieved for PLLA and PDLA after blending with a large proportion of PVAc (e.g., 75 wt %). Incorporation of PVAc also facilitates the HC-to-SC structural reorganization upon heating. The increased chain mobility, decreased equilibrium melting point, and enhanced intermolecular interactions may account for the preferential stereocomplexation in PLLA/PDLA/PVAc blends.

Constructing dual or multiple noncovalent crosslinks is highly effective to improve the mechanical and stimuli-responsive properties of supramolecular physical hydrogels, due to the synergistic effects of different noncovalent bonds. Herein, a series of tough physical hydrogels are prepared by solution casting and subsequently swelling the films of poly(ureidopyrimidone methacrylate-co-stearyl acrylate-co-acrylic acid). The hydrophobic interactions between crystallizable alkyl chains and the quadruple hydrogen bonds between ureidopyrimidone (UPy) motifs serve as the dual crosslinks of hydrogels. Synergistic effects between the hydrophobic interactions and hydrogen bonds render the hydrogels excellent mechanical properties, with tensile breaking stress up to 4.6 MPa and breaking strain up to 680%. The UPy motifs promote the crystallization of alkyl chains and the hydrophobic alkyl chains also stabilize UPy-UPy hydrogen bonding. The resultant hydrogels are responsive to multiple external stimuli, such as temperature, pH, and ion; therefore, they show the thermal-induced dual and metal ion-induced triple shape memory behaviors.