A Strong and Double-sided Self-Adhesive Hydrogel Sensor.

Flexible self-adhesive hydrogel sensors are attracting considerable concerns in recent years. However, creating a self-adhesive hydrogel sensor with excellent mechanical properties remains to be challenging. Herein, a double-sided self-adhesive hydrogel capable of strain sensor with high strength is demonstrated by penetration strategy. The middle poly(acrylic acid)-polyacrylamide/Fe3+ (PAA-PAM/Fe3+ ) tough layer endows the double-sided self-adhesive hydrogel with high mechanical properties, while the bilateral poly[2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide-polyacrylamide (PSBMA-PAM) adhesive layers are used to ensure excellent adhesiveness on diverse substrates. The tough layer of the double-sided self-adhesive hydrogel sensor shows a strong interface bonding force against the adhesive layer. The double-sided self-adhesive hydrogel sensor enables excellent adhesiveness on diverse substrates. More importantly, it can accurately detect different strains and human motions as a self-adhesive hydrogel strain sensor. This work manifests a new route of structural design to develop a self-adhesive hydrogel sensor with excellent mechanical properties that is suitable for a wide range of applications.

Driving Polymer Brushes from Synthesis to Functioning.

The great success of controlled radical polymerizations has encouraged researchers to develop more facile and robust approaches for surface-initiated polymerizations (SIPs) to fabricate polymer brushes, even for non-experts. In recent years, external-stimuli-mediated radical polymerization methods have come to the fore as SIPs because of their less rigorous synthetic procedures and high controllability, which expand the opportunities for synthesizing macromolecules with desired chemical compositions and structures, as well as tailor-made polymers and bioconjugates that show broad applicability and physiological compatibility. This review discusses the latest developments in surface-initiated polymerization methods, in particular, external-stimuli mediated atom transfer radical polymerization (ATRP), photo-induced polymerizations, and reversible addition-fragmentation chain transfer (RAFT) polymerization, as well as other methods and their combination for the application in surface grafting. The implementation of these methods is of great interest due to their unique possibilities to temporally control a polymerization process, fast and straightforward polymerization, and environmentally benign features, which lead to established and emerging applications in biolubrication, antifouling, and biosensing.

Mussel-Inspired Multicomponent Codeposition Strategy toward Antibacterial and Lubricating Multifunctional Coatings on Bioimplants.

Bacterial infections and limited surface lubrication are the two key challenges for bioimplants in dynamic contact with tissues. However, the simultaneous lubricating and antibacterial properties of the bioimplants have rarely been investigated. In this work, we successfully developed a multifunctional coating with simultaneous antibacterial and lubricating properties for surface functionalization of bioimplant materials. The multifunctional coating was fabricated on a polyurethane (PU) substrate via polydopamine (PDA)-assisted multicomponent codeposition, containing polyethyleneimine (PEI) and trace amounts of copper (Cu) as synergistic antibacterial components and zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) as the lubricating component. The obtained PDA(Cu)/PEI/PMPC coating showed excellent antibacterial activity (antibacterial efficiency: ∼99%) to both Escherichia coli and Staphylococcus aureus compared with bare PU. The excellent antibacterial properties were attributed to the combined effect of anti-adhesion capability of hydrophilic PMPC and PEI and bactericidal activity of Cu in the coating. Meanwhile, the coefficient of friction of the coating was significantly decreased by ∼52% compared with bare PU owing to the high hydration feature of PMPC, suggesting the superior lubricating property. Furthermore, the PDA(Cu)/PEI/PMPC coating was highly biocompatible toward human umbilical vein endothelial cells demonstrated by in vitro cytotoxicity tests. This study not only contributes to the chemistry of PDA-assisted multicomponent codeposition but also provides a facile and practical way for rational design of multifunctional coatings for medical devices.

Bioinspired Polysaccharide-Derived Zwitterionic Brush-like Copolymer as an Injectable Biolubricant for Arthritis Treatment.

Developing highly efficient and biocompatible biolubricants for arthritis treatment is extraordinarily demanded. Herein, inspired by the efficient lubrication of synovial joints, a paradigm that combines natural polysaccharide (chitosan) with zwitterionic poly[2-(methacryloyloxy) ethyl phosphorylcholine] (PMPC), to design a series of brush-like Chitosan-g-PMPC copolymers with highly efficient biological lubrication and good biocompatibility is presented. The Chitosan-g-PMPC copolymers are prepared via facile one-step graft polymerization in aqueous medium without using any toxic catalysts and organic solvents. The as-prepared Chitosan-g-PMPC copolymers exhibit very low coefficient of friction (µ < 0.01) on Ti6 Al4 V alloy substrate in both pure water and biological fluids. The superior lubrication is attributed primarily to the hydrated feature of PMPC side chains, interface adsorption of copolymer as well as to the hydrodynamic effect. In vivo experiments confirm that Chitosan-g-PMPC can alleviate the swelling symptom of arthritis and protect the bone and cartilage from destruction. Due to their facile preparation, distinctive lubrication properties, and good biocompatibility, Chitosan-g-PMPC copolymers represent a new type of biomimetic lubricants derived from natural biopolymer for promising arthritis treatment and artificial joint lubrication.

Synthesis of charged chitosan nanoparticles as functional biolubricant.

Osteoarthritis has been a major disease in recent years, which is mainly related to the breakdown of the lubrication function of the cartilage sliding interface, along with the inflammation of the joint capsule. In this paper, one kind of novel biomimetic nanoparticles (NPs) lubricant, named CS-PS, is synthesized through chemically grafting hydrophilic sulfonic acid (SO3-) groups onto the surface of biocompatible and biodegradable chitosan (CS) NPs. Compared with control CS NPs, the as-synthesized CS-PS NPs exhibits excellent hydration and stability because of negatively charged surface zeta potential, along with extraordinary lubrication performance in water for realizing a super-low friction coefficient (COF) as ∼0.01 at the sliding interface of PDMS elastomer-Ti6Al4V disk. Correspondingly, the CS-PS NPs can also be used as a drug carrier for aspirin, which presents very good drug loading and release behavior in PBS (pH = 7.4). MCS cells culture experiment proves that this kind of novel lubricant is nontoxic and biocompatible, for which may be expected to use as potential articular injective material for the treatment of osteoarthritis.

Surface Engineering of Liquid Metal Nanodroplets by Attachable Diblock Copolymers.

Liquid metal (LM) micro/nano droplets have promising applications in various fields such as flexible electronics, catalysis, and soft composites as well as biomedicines. However, the preparation of highly stable LM nanodroplets suspension based on eutectic gallium/indium (EGaIn) alloys is still challenging. Herein, we report a general and robust strategy to fabricate EGaIn nanodroplets stabilized by polymer brushes (polymer brushes/EGaIn nanodroplets) via in situ attachment of well-defined diblock copolymers with short poly(acrylic acid) (PAA) anchoring segments. Under ultrasonication, the anchoring PAA block is in situ attached onto the gallium oxide "skin" layer of EGaIn nanodroplets to form polymer brushes. The attachable diblock copolymer surfactants allow for highly efficient formation of EGaIn nanodroplets in high yield and with narrow size distribution. The polymer brushes/EGaIn nanodroplets contain very low fractions of attached polymer (<1 wt %) and exhibit high colloidal stability (>30 days) and good redispersibility. Precise control of polymer architecture by atom-transfer radical polymerization was employed to prepare various block copolymers for suspensions in a variety of solvents.

Embedded polyzwitterionic brush-modified nanofibrous membrane through subsurface-initiated polymerization for highly efficient and durable oil/water separation.

HYPOTHESIS: Developing separation membranes functionalized by polymer brushes with high separation efficiency and good cycling stability is of great importance for oil/water separation, yet is still challenged. EXPERIMENTS: In this work, the covalently embedded polyzwitterionic brush-functionalized nanofibrous membrane was developed for efficient and durable oil/water separation. The nanofibrous membrane was prepared by the electrospinning method using initiator-embedded polyacrylonitrile (PAN) resin, followed by novel subsurface-initiated atom transfer radical polymerization (SSI-ATRP) to graft embedded poly(sulfobetaine methacrylate) brushes (PSBMA). The hydration ability, underwater oil adhesion, oil/water separation performance as well as self-cleaning properties of the as prepared membrane (PAN-sg-PSBMA) were systematically studied. FINDINGS: The PAN-sg-PSBMA membrane exhibited extraordinary hydration ability and underwater superoleophobicity with extremely low oil adhesion, which outperformed conventional polymer brush-modified membrane (PAN-g-PSBMA). The PAN-sg-PSBMA membrane was able to separate both oil/water mixture and surfactant-stabilized emulsions with ultrahigh permeation flux and separation efficiency. Moreover, compared with PAN-g-PSBMA, PAN-sg-PSBMA membrane exhibited unprecedented recycling stability in both permeation flux and separation efficiency, which is attributed to mechanical robustness of embedded polymer brushes and outstanding antifouling ability. The current findings revealed that embedded polymer brushes from SSI-ATRP could offer a promising design of functionalized nanofibrous membrane for highly efficient and durable oil/water separation.

Mussel-Inspired One-Step Fabrication of Ultralow-Friction Coatings on Diverse Biomaterial Surfaces.

Low-friction and hydrophilic surfaces have critical applications in biomedical devices and implants. Existing methods to achieve such surfaces, for example, grafting polymer brushes, usually suffer from tedious steps and harsh reaction conditions, which limit practical applications. In this work, we propose a set of versatile ultralow-friction coatings applicable for diverse biomaterial surfaces via a one-step simple codeposition strategy with dopamine and hydrophilic monomers. The polymer coatings show ultralow-friction performance together with hydrophilic feature and antifouling property. The coefficient of friction of the as-prepared coating can be as low as 0.003 in pure water. The coating also provides superior and stable lubrication in biological fluids due to antifouling capability. Furthermore, the versatility of this strategy allows fabrication of multiple lubricious polymer coatings with different hydrophilic monomers and on diverse material surfaces. The typical application of this low-friction coating on a medical catheter was further demonstrated, which dramatically improved surface wettability and reduced friction of the outer surface of the catheter. In view of the versatility and remarkable lubrication ability, the multifunctional coatings may find important applications in biomedical devices and implants.

Control of Dispersity and Grafting Density of Particle Brushes by Variation of ATRP Catalyst Concentration.

Silica particles with grafted poly(methyl methacrylate) brushes, SiO2-g-PMMA, were prepared via activator regeneration by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The grafting density and dispersity of the polymer brushes was tuned by the initial ATRP catalyst concentration ([CuII/L]0). Sparsely grafted particle brushes, which also displayed an anisotropic string-like structure in TEM images, were obtained at very low catalyst concentrations, [CuII/L]0 < 1 ppm. The effect of the initial catalyst concentration on dispersity and initiation efficiency in the particle brush system was similar to that observed in the synthesis of linear PMMA homopolymers. The kinetic study revealed a transition from controlled radical polymerization to a less controlled process at low monomer conversion, when the [CuII/L]0 decreased below about 10 ppm.

Mussel-Inspired Thermoresponsive Polypeptide-Pluronic Copolymers for Versatile Surgical Adhesives and Hemostasis.

Inspired by marine mussel adhesive proteins, polymers with catechol side groups have been extensively explored in industrial and academic research. Here, Pluronic L-31 alcoholate ions were used as the initiator to prepare a series of polypeptide-Pluronic-polypeptide triblock copolymers via ring-opening polymerization of l-DOPA-N-carboxyanhydride (DOPA-NCA), l-arginine-NCA (Arg-NCA), l-cysteine-NCA (Cys-NCA), and ε-N-acryloyl lysine-NCA (Ac-Lys-NCA). These copolymers demonstrated good biodegradability, biocompatibility, and thermoresponsive properties. Adhesion tests using porcine skin and bone as adherends demonstrated lap-shear adhesion strengths up to 106 kPa and tensile adhesion strengths up to 675 kPa. The antibleeding activity and tissue adhesive ability were evaluated using a rat model. These polypeptide-Pluronic copolymer glues showed superior hemostatic properties and superior effects in wound healing and osteotomy gaps. Complete healing of skin incisions and remodeling of osteotomy gaps were observed in all rats after 14 and 60 days, respectively. These copolymers have potential uses as tissue adhesives, antibleeding, and tissue engineering materials.

Stratified polymer brushes from microcontact printing of polydopamine initiator on polymer brush surfaces.

Stratified polymer brushes are fabricated using microcontact printing (µCP) of initiator integrated polydopamine (PDOPBr) on polymer brush surfaces and the following surface initiated atom transfer radical polymerization (SI-ATRP). It is found that the surface energy, chemically active groups, and the antifouling ability of the polymer brushes affect transfer efficiency and adhesive stability of the polydopamine film. The stickiness of the PDOPBr pattern on polymer brush surfaces is stable enough to perform continuous µCP and SI-ATRP to prepare stratified polymer brushes with a 3D topography, which have broad applications in cell and protein patterning, biosensors, and hybrid surfaces.

Parallel array of nanochannels grafted with polymer-brushes-stabilized Au nanoparticles for flow-through catalysis.

Smart systems on the nanometer scale for continuous flow-through reaction present fascinating advantages in heterogeneous catalysis, in which a parallel array of straight nanochannels offers a platform with high surface area for assembling and stabilizing metallic nanoparticles working as catalysts. Herein we demonstrate a method for finely modifying the nanoporous anodic aluminum oxide (AAO), and further integration of nanoreactors. By using atomic transfer radical polymerization (ATRP), polymer brushes were successfully grafted on the inner wall of the nanochannels of the AAO membrane, followed by exchanging counter ions with a precursor for nanoparticles (NPs), and used as the template for deposition of well-defined Au NPs. The membrane was used as a functional nanochannel for novel flow-through catalysis. High catalytic performance and instantaneous separation of products from the reaction system was achieved in reduction of 4-nitrophenol.

Noncovalent microcontact printing for grafting patterned polymer brushes on graphene films.

This article describes a simple and universal approach to prepare patterned polymer brushes on graphene-based substrate surfaces by microcontact printing (µCP) of initiator molecules and subsequent surface initiated atom transfer radical polymerization (SI-ATRP) method. Four different initiators are designed and have strong adhesion with graphene-based substrates through noncovalent interaction. Optical and fluorescence microscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the successful polymerization of vinyl monomers on substrate surfaces. To demonstrate the broad applicability of this strategy, polymer brushes with different functionalities including cationic and anionic polyelectrolyte, thermally and pH responsive polymers, as well as polymer patterns on different graphene-based surfaces are fabricated. Binary polymer brushes can also be easily prepared by further initiating the initiator backfilled in the bare areas.