The combination of the first-line standard chemotherapeutic drug doxorubicin hydrochloride (DOX) and the molecular-targeted drug Herceptin (HCT) has emerged as a promising strategy for human epidermal growth receptor 2 (HER-2) overexpressing breast cancer treatment. However, insufficient drug accumulation and severe cardiotoxicity are two major challenges that limit its clinical application. Herein, an in situ forming gold nanorods (AuNRs)-sodium alginate (ALG) hybrid hydrogel encapsulating DOX and HCT was engineered for tumor synergistic therapy involving injectable, dual-stimuli-responsive drug release, photothermal ablation, and drug-antibody synergistic therapy. The photothermal agent AuNRs, anticancer drug DOX, and anticancer antibody HCT were mixed in ALG solution, and after injection, the soluble ALG was quickly transformed into a hydrogel in the presence of Ca2+ in the body. Significantly, the hybrid hydrogel exhibits an extremely high photothermal conversion efficiency of 70% under 808 nm laser irradiation. The thermal effect can also provide photothermal stimulation to trigger the drug release from the gel matrix. In addition, the drug release rate and the releasing degree are also sensitive to the pH. In vitro studies demonstrated that the PEI-AuNR/DOX/HCT/ALG hydrogel has facilitated the therapeutic efficiency of each payload and demonstrated a strong synergistic killing effect on SK-BR-3 cells. In vivo imaging results showed that the local drug delivery system can effectively reduce the nonspecific distribution in normal tissues and increase drug concentration at tumor sites. The proposed hydrogel system shows significant clinical implications by easily introducing a sustainable photothermal therapy and a potential universal carrier for the local delivery of multiple drugs to overcome the challenges faced in HER-2 overexpressing cancer therapy.
Development and understanding of highly mechanically robust and electronically conducting hydrogels are extremely important for ever-increasing energy-based applications. Conventional mixing/blending of conductive additives with hydrophilic polymer network prevents both high mechanical strength and electronic conductivity to be presented in polymer hydrogels. Here, we proposed a double-network (DN) engineering strategy to fabricate PVA/PPy DN hydrogels, consisting of a conductive PPy-PA network via in-situ ultrafast gelation and a tough PVA network via a subsequent freezing/thawing process. The resultant PVA/PPy hydrogels exhibited superior mechanical and electrochemical properties, including electrical conductivity of ~6.8 S/m, mechanical strength of ~0.39 MPa, and elastic moduli of ~0.1 MPa. Upon further transformation of PVA/PPy hydrogels into supercapacitors, they demonstrated a high capacitance of ~280.7 F/g and a cycle life of 2000 galvanostatic charge/discharge cycles with over 94.3% capacity retention at the current density of 2 mA/cm2 and even subzero temperatures of −20 °C. Such enhanced mechanical performance and electronic conductivity of hydrogels are mainly stemmed from a synergistic combination of continuous electrically conductive PPy-PA network and the two interpenetrating DN structure. This in-situ gelation strategy is applicable to the integration of ionic-/electrical-conductive materials into DN hydrogels for smart-soft electronics, beyond the most commonly used PEDOT:PSS-based hydrogels.
Herein, we fabricated a flexible semidry electrode with excellent mechanical performance, satisfactory self-adhesiveness, and low-contact impedance using physical/chemical crosslinked polyvinyl alcohol/polyacrylamide dual-network hydrogels (PVA/PAM DNHs) as an efficient saline reservoir. The resultant PVA/PAM DNHs showed admirable adhesive and compliance to the hairy scalp, facilitating the establishment of a robust electrode/skin interface for biopotential signal transmission. Moreover, the PVA/PAM DNHs steadily released trace saline onto the scalp to achieve the minimized potential drift (1.47 ± 0.39 mV/min) and low electrode–scalp impedance (18.2 ± 8.9 kΩ @ 10 Hz). More importantly, the application feasibility of real-world brain−computer interfaces (BCIs) was preliminarily validated by 10 participants using two classic BCI paradigms. The mean temporal cross-correlation coefficients between the semidry and wet electrodes in the eyes open/closed and the N200 speller paradigms are 0.919 ± 0.054 and 0.912 ± 0.050, respectively. Both electrodes demonstrate anticipated neuroelectrophysiological responses with similar patterns. This semidry electrode could also effectively capture robust P-QRS-T peaks during electrocardiogram recording. Considering their outstanding advantages of fast setup, user-friendliness, and robust signals, the proposed PVA/PAM DNH-based electrode is a promising alternative to wet electrodes in biopotential signal acquisition.
Traditional multicolor fluorescent hydrogels are generated through the assembly of discrete fluorescent hydrogels, which is not a complete integration much distinct from living organisms. On the basis of aggregation-induced emission (AIE), a special solvent polar-responsive AIE molecule possessing a twisted intramolecular charge transfer (TICT) effect was noticed. By incorporating it into the gel network, an AIE gel that displays continuous gradient fluorescence was fabricated. First, hydrogel A containing the solvent polar-responsive AIE-gen was prepared to show orange fluorescence. After soaking in the organic solvents, the fluorescence color transition of hydrogel A ranging from orange to green occurred when being immersed in high-polarity organic solvents ascribed to the embedded AIE-gen owning TICT effect. Then, hydrogel A was successively lifted up from organic solvents. Due to the different immersion time of each section for the hydrogel, the polarity difference occurred. Then, the produced gel B showed continuous gradient fluorescence ranging from orange to green under the irradiation of UV light.
Biomimetic intelligent polymeric hydrogel actuators with cooperative fluorescence-color switchable behaviors are expected to find great potential applications in soft robotics, visual detection/display, and camouflage applications. However, it remains challenging to realize the spatial manipulation of synergistic shape/color-changing behaviors. Herein, we report an interfacial supramolecular assembly (ISA) approach that enables the construction of robust fluorescent polymeric hydrogel actuators with spatially anisotropic structures. On the basis of this ISA approach, diverse 2D/3D soft fluorescent hydrogel actuators, including chameleon- and octopi-shaped ones with spatially anisotropic structures, were facilely assembled from two different fluorescent hydrogel building blocks sharing the same physically cross-linked agar network. Spatially control over synergistic shape/color-changing behaviors was then realized in one single anisotropic hydrogel actuator. The proposed ISA approach is universal and expected to open promising avenues for developing powerful bioinspired intelligent soft actuators/robotics with selective spatial shape/color-changing behaviors.
Booming sophisticated robotics and prosthetics put forward high requirements on soft conductive materials that can bridge electronics and biology, those soft conductive materials should imitate the mechanical properties of biological tissues and build information transmission networks. Until now, it remains a great challenge to handle the trade-off among ease of preparation, high conductivity, processability, mechanical adaptability, and external stimuli responsiveness. Herein, a kind of readily prepared and processed multifunctional MXene nanocomposite hydrogel is reported, which is prepared via the fast gelation of cationic monomer initiated by delaminated MXene sheets. The gelation time can be adjusted (several seconds to minutes) based on the MXene loadings. By adjusting the MXene ratio, the resulting nanocomposites are ultrastretchable (>5000%), three-dimensional (3D) printable, and show outstanding mechanical and electrical self-healing. As expected, the integration of multifunctional systems onto various substrates (e.g., gloves and masks) is further demonstrated via 3D printing and could achieve diverse sensory capabilities toward strain, pressure, and temperature, showing great prospects as smart flexible electronics.
Despite extensive efforts in designing and preparing switchable underwater adhesives, it is not easy to regulate the underwater adhesion strength locally and remotely. Here, we design and synthesize photoreversible copolymer of poly[dopamine methacrylamide-co-methoxyethyl-acrylate-co-7-(2-methacryloyloxyethoxy)-4-methylcoumarin]. Due to the dynamic formation and breaking of chemical crosslinking networks within the smart adhesives, the material shows widely tunable adhesion strength from ∼150 to ∼450 kPa and long-range reversible maneuverability under orthogonal 254 and 365 nm ultraviolet light stimulation via the coumarin dimerization and cycloreversion. Moreover, the adhesive exhibits good circulation performance and stability in an acid–base environment. It also demonstrated that the bolt can be coated with the smart adhesive material for on-demand bonding. This design principle opens the door to the development of remotely controllable high-performance smart underwater adhesives.
This study marks the birth of visible and selective click covalent assembly. It is achieved by amplifying orthogonal alkyne−azide click chemistry through interfacial multisite interactions between azide/alkyne functionalized polymer hydrogels. Macroscopic assembly of hydrogels via host−guest chemistry or noncovalent interactions such as electrostatic interactions has been reported. Unlike macroscopic supramolecular assembly, here we report visible and selective “click” covalent assembly of hydrogels at the macroscale. LEGO-like hydrogels modified with alkyne and azide groups, respectively, can click together via the formation of covalent bonds. Monomer concentration-dependent assembly and selective covalent assembly have been studied. Notably, macroscopic gel assembly clearly elucidates click preferences and component selectivity not observed in the solution reactions of competing monomers.
Polymer ionogel (PIG) is a new type of flexible, stretchable, and ion-conductive material, which generally consists of two components (polymer matrix materials and ionic liquids/deep eutectic solvents). More and more attention has been received owing to its excellent properties, such as nonvolatility, good ionic conductivity, excellent thermal stability, high electrochemical stability, and transparency. In this review, the latest research and developments of PIGs are comprehensively reviewed according to different polymer matrices. Particularly, the development of novel structural designs, preparation methods, basic properties, and their advantages are respectively summarized. Furthermore, the typical applications of PIGs in flexible ionic skin, flexible electrochromic devices, flexible actuators, and flexible power supplies are reviewed. The novel working mechanism, device structure design strategies, and the unique functions of the PIG-based flexible ionic devices are briefly introduced. Finally, the perspectives on the current challenges and future directions of PIGs and their application are discussed.
Fluorescent poly(N-isopropylacrylamide-co-Nile blue) (pNIPAm-co-NB) microgels were synthesized that exhibited fluorescence intensity changes in a water temperature-dependent fashion. NB is well known to exhibit fluorescence intensity that depends on the hydrophobicity of the environment, while pNIPAm-based microgels are well known to transition from swollen (hydrophilic) to collapsed (relatively hydrophobic) at temperatures greater than 32 °C; hence, we attribute the above behavior to the hydrophobicity changes of the microgels with increasing temperature. This phenomenon is ultimately due to NB dimers (relatively quenched fluorescence) being broken in the hydrophobic environment of the microgels leading to relatively enhanced fluorescence. We went on to show that the introduction of cucurbit[7]uril (CB[7]) into the pNIPAm-co-NB microgels enhanced their fluorescence allowing them to be used for polyamine (e.g., spermine [SPM]) detection. Specifically, CB[7] forms a host–guest interaction with NB in the microgels, which prevents NB dimerization and enhances their fluorescence. When SPM is present, it forms a host–guest complex that is favored over the CB[7]-NB host–guest interaction, which frees the NB for dimerization and leads to fluorescence quenching. As a result, we could generate an SPM sensor capable of SPM detection down to ~0.5 µmol/L in complicated matrixes such as serum and urine.
Patterning diversified properties and surface structure of polymer materials are of great importance toward their potential in biology, optics, and electronics. However, achieving both the patternability of stiffness and microstructure in a reconfigurable manner remains challenging. Here, we prepare amphigels crosslinked by dynamic disulfide bonds, which can be reversibly swollen by immiscible water or liquid paraffin. In the paraffingel form, the materials exhibited a high modulus of 130 MPa due to densified hydrogen bonds. Whereas swollen by water, the modulus fell over two orders of magnitude owing to the destruction of the hydrogen bonds. Via regionalized swelling of the solvents, well-controlled and rewritable soft/stiff mechanical patterns can be created. On the other hand, the dynamic exchange of the disulfide crosslinking enables mechanophoto patterning to fabricate sophisticated macrogeometries and microstructures. The reconfigurable stiffness-structure patterning can be manipulated orthogonally, which will create more application opportunities beyond conventional hydrogels and organogels.
Thermochromic smart windows have gained increasing popularity in light modulation and energy management in buildings. However, the fabrication of flexible thermochromic smart windows with high luminous transmittance (Tlum), tailorable critical temperature (τc), strong solar modulation ability (ΔTsol), and long-term durability remains a huge challenge. In this study, hydrogel-based thermochromic smart windows are fabricated by sandwiching thermochromic hydrogels of polyallylamine hydrochloride, polyacrylic acid, and carbonized polymer dots (CPDs) complexes between two pieces of transparent substrates. Benefiting from the incorporation of nanosized CPDs, the thermochromic hydrogel has an ultrahigh Tlum of ~98.7%, a desirable τc of ~24.2 °C, a ΔTsol of ~89.3% and a rapid transition time of ~3 s from opaque state to transparent state. Moreover, the thermochromic hydrogel exhibits excellent anti-freezing ability, tight adhesion toward various substrates, and excellent self-healing capability. The self-healing capability enables the fabrication of large-area smart windows by welding multiple hydrogel pieces. The smart windows retain their original thermochromic properties after being stored under ambient conditions for at least 147 days or undergoing 10,000 uninterrupted heating/cooling cycles. The model houses with smart windows can achieve a temperature reduction of 9.2 °C, demonstrating the excellent indoor temperature modulation performance of the smart windows.