Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bonds

Four amino acid-bearing acrylamides, N-acryloyl-l-threonine (AThrOH), N-acryloyl-l-glutamic acid (AGluOH), N-acryloyl-l-phenylalanine (APheOH), and N-acryloyl-l, l-diphenylalanine (APhePheOH), were selected for copolymerization with n-butyl acrylate (nBA) to develop amino acid-based self-healable copolymers. A series of copolymers comprising amino acid-bearing acrylamides and nBA with tunable comonomer compositions and molecular weights were synthesized by free radical and reversible addition-fragmentation chain-transfer copolymerization. Self-healing and mechanical properties originated from the noncovalent bonds between the carboxyl, hydroxyl, and amide groups, and π-π stacking interactions among the amino acid residues in the side chains were evaluated. Among these copolymers, P(nBA-co-AGluOH) with suitable comonomer compositions and molecular weights (nBA : AGluOH = 82 : 18, Mn = 18 300, Mw/Mn = 2.58) exhibited good mechanical properties (modulus of toughness = 17.3 MJ m-3) and self-healing under ambient conditions. The multiple noncovalent bonds of P(nBA-co-AGluOH)s were also efficient in improving the optical properties with an enhanced refractive index and good transparency.

Mechanically Tunable Hydrogels with Self-Healing and Shape Memory Capabilities from Thermo-Responsive Amino Acid-Derived Vinyl Polymers

In this study, we report the fabrication and characterization of self-healing and shape-memorable hydrogels, the mechanical properties of which can be tuned via post-polymerization crosslinking. These hydrogels were constructed from a thermo-responsive poly(N-acryloyl glycinamide) (NAGAm) copolymer containing N-acryloyl serine methyl ester (NASMe) units (5 mol%) that were readily synthesized via conventional radical copolymerization. This transparent and free-standing hydrogel is produced via multiple hydrogen bonds between PNAGAm chains by simply dissolving the polymer in water at a high temperature (~90 °C) and then cooling it. This hydrogel exhibited moldability and self-healing properties. The post-polymerization crosslinking of the amino acid-derived vinyl copolymer network with glutaraldehyde, which acts as a crosslinker between the hydroxy groups of the NASMe units, tuned mechanical properties such as viscoelasticity and tensile strength. The optimal crosslinker concentration efficiently improved the viscoelasticity. Moreover, these hydrogels exhibited shape fixation (~60%)/memory (~100%) behavior owing to the reversible thermo-responsiveness (upper critical solution temperature-type) of the PNAGAm units. Our multifunctional hydrogel, with moldable, self-healing, mechanical tunability via post-polymerization crosslinking, and shape-memorable properties, has considerable potential for applications in engineering and biomedical materials.

Transparent Electronics for Wearable Electronics Application

Recent advancements in wearable electronics offer seamless integration with the human body for extracting various biophysical and biochemical information for real-time health monitoring, clinical diagnostics, and augmented reality. Enormous efforts have been dedicated to imparting stretchability/flexibility and softness to electronic devices through materials science and structural modifications that enable stable and comfortable integration of these devices with the curvilinear and soft human body. However, the optical properties of these devices are still in the early stages of consideration. By incorporating transparency, visual information from interfacing biological systems can be preserved and utilized for comprehensive clinical diagnosis with image analysis techniques. Additionally, transparency provides optical imperceptibility, alleviating reluctance to wear the device on exposed skin. This review discusses the recent advancement of transparent wearable electronics in a comprehensive way that includes materials, processing, devices, and applications. Materials for transparent wearable electronics are discussed regarding their characteristics, synthesis, and engineering strategies for property enhancements. We also examine bridging techniques for stable integration with the soft human body. Building blocks for wearable electronic systems, including sensors, energy devices, actuators, and displays, are discussed with their mechanisms and performances. Lastly, we summarize the potential applications and conclude with the remaining challenges and prospects.

Poly(N-acryloyl glycinamide-co-N-acryloxysuccinimide) Nanoparticles: Tunable Thermo-Responsiveness and Improved Bio-Interfacial Adhesion for Cell Function Regulation

Poly(N-acryloyl glycinamide) (PNAGA) can form high-strength hydrogen bonds (H-bonds) through the dual amide motifs in the side chain, allowing the polymer to exhibit gelation behavior and an upper critical solution temperature (UCST) property. These features make PNAGA a candidate platform for biomedical devices. However, most applications focused on PNAGA hydrogels, while few focused on PNAGA nanoparticles. Improving the UCST tunability and bio-interfacial adhesion of the PNAGA nanoparticles may expand their applications in biomedical fields. To address the issues, we established a reactive H-bond-type P(NAGA-co-NAS) copolymer via reversible addition-fragmentation chain transfer polymerization of NAGA and N-acryloxysuccinimide (NAS) monomers. The UCST behaviors and the bio-interfacial adhesion toward the proteins and cells along with the potential application of the copolymer nanoparticles were investigated in detail. Taking advantage of the enhanced H-bonding and reactivity, the copolymer exhibited a tunable UCST in a broad temperature range, showing thermo-reversible transition between nanoparticles (PNPs) and soluble chains; the PNPs efficiently bonded proteins into nano-biohybrids while keeping the secondary structure of the protein, and more importantly, they also exhibited good adhesion ability to the cell membrane and significantly inhibited cell-specific propagation. These features suggest broad prospects for the P(NAGA-co-NAS) nanoparticles in the fields of biosensors, protein delivery, cell surface decoration, and cell-specific function regulation.

Medical Applications of Hydrogels in Skin Infections: A Review

Skin infections are common diseases for which patients seek inpatient and outpatient medical care. Globally, an increasing number of people are affected by skin infections that could lead to physical and psychological damage. Skin infections always have a broad spectrum of clinical presentations that require physicians to make an aggressive and accurate diagnosis for prescribing the proper symptomatic antimicrobials. In most instances, the treatment for skin infections mainly includes oral or topical anti-infective drugs. However, some of the classical anti-infective drugs have limitations, such as poor water solubility, low bioavailability, and poor targeting efficiency, which can lead to poor efficacy, adverse effects, and drug resistance. Therefore, research priorities should focus on the development of more effective drug delivery systems with new materials. Hydrogels are a highly multifunctional class of medical materials with potential applications in dermatology. Several hydrogel dressings with anti-infective functions have been formulated and demonstrated to improve the efficacy and tolerance of oral or topical classical anti-infective drugs to a certain degree. In this study, the medical applications of hydrogels for the treatment of various skin infections are systematically reviewed to provide an important theoretical reference for future research studies on the treatment options for skin infections.

Process intensified synthesis of luminescent poly(9,9-dioctylfluorene-alt-benzothiadiazole) and polyvinyl alcohol based shape memory polymeric nanocomposite sensors toward cold chain logistics information monitoring

Luminescent shape memory polymeric nanocomposite sensors prepared using poly(9,9-dioctylfluorene-alt-benzothiadiazole) and polyvinyl alcohol for cold chain logistics information monitoring.

Triple crosslinking conductive hydrogels with digitally printable and outstanding mechanical stability for high-resolution conformable bioelectronics

Soft, conductive, and stretchable hydrogels offer a broad variety of applications, including skin-interfacing electrodes, biomonitoring patches, and electrostimulation. Despite rapid developments over the last decades, a combination of good electrical and mechanical properties, low-cost fabrication, and biocompatibility is yet to be demonstrated. Also, the current methods for deposition and patterning of these hydrogels are manual, and there is a need toward autonomous and digital fabrication techniques. In this work, we demonstrate a novel Gallium (Ga) embedded sodium-alginate-polyacrylamide-LAPONITE® (Ga-SA-PAAM-La) hydrogel, that is ultra-stretchable (Maximum strain tolerance of∼985%), tough (toughness ∼30 kJ m^-3), bio-adhesive (adhesion energy ∼216 J m^-2), conductive, and digitally printable. Ga nanoparticles are used as radical initiators. By adjusting the sonication parameters, we control the solution viscosity and curing time, thus allowing us to prepare pre-polymers with the desired properties for casting, or digital printing. These hydrogels benefit from a triple-network structure due to the role of Ga droplets as crosslinkers besides BIS (N,N'-methylene-bis-acrylamide) and LAPONITE®, thus resulting in tough composite hydrogels. The inclusion of LAPONITE® into the hydrogel network improved its electrical conductivity, adhesion, digital printability, and its mechanical properties, (>6× compared to the same hydrogel without LAPONITE®). As electrodes in the electrocardiogram, the signal-to-noise ratio was surprisingly higher than the medical-grade Ag/AgCl electrodes, which are applied for monitoring muscles, heart, respiration, and body joint angle through EMG, ECG, and bioimpedance measurements. The results obtained prove that such digitally printed conductive and tough hydrogels can be used as potential electrodes and sensors in practical applications in the next generation of printed wearable computing devices.

Star-Shaped Peptide-Polymer Hybrids as Fast pH-Responsive Supramolecular Hydrogels

Significant challenges have gone into the design of smart hydrogels, with numerous potential applications in the industrial, cosmetic, and biomedical fields. Herein, we report the synthesis of novel 4-arm self-assembling peptide-polyethylene glycol (PEG) hybrid star-shaped polymers and their comprehensive hydrogel properties. β-sheet-forming oligopeptides with alternating hydrophobic Leu/ionizable Glu repeats and Cys residues were successfully conjugated to 4-arm PEG via a thiol-maleimide click reaction. The hybrid star-shaped polymers demonstrated good cytocompatibility and reversible β-sheet (lightly acidic pH)-to-random coil (neutral and basic pH) transition in dilute aqueous solutions. At increasing polymer concentrations up to 0.5 wt %, the star-shaped polymers formed transparent hydrogels with shear-thinning and self-healing behaviors via β-sheet self-assembly, as well as a conformation-dependent gel-sol transition. Interestingly, the star-shaped polymers responded rapidly to pH changes, causing gelation to occur rapidly within a few seconds from the change in pH. Hydrogel characteristics could be modulated by manipulating the length and net charge of the peptide blocks. Furthermore, these star-shaped polymers served as satisfactory network scaffolds that could respond to dynamic environmental changes in the pH-oscillation system, owing to their excellent gelation capability and pH sensitivity. As such, they are highly favorable for diverse applications, such as pH-responsive controlled release.

Paclitaxel-nanocrystals-loaded network thermosensitive hydrogel for localised postsurgical recurrent of breast cancer after surgical resection

The recurrence of cancer after local surgery has been a difficult problem in the clinic for a long time. In recent years, local treatment via drug-loaded thermosensitive hydrogels have become a promising strategy to prevent cancer recurrence. Thus, a thermosensitive hydrogel based on poloxamer 407, poloxamer 188 and the bioadhesive excipient carbomer 974P was designed to locally release paclitaxel and prevent local tumour recurrence after direct smearing of the hydrogel at the site of injury in the surgical cavity. To improve the local drug concentration, paclitaxel was prepared into nanocrystals via a wet mill process. A series of studies were performed on this paclitaxel nanocrystal thermosensitive hydrogel (PTX-NCS-gel), including examination of its rheological properties and in vitro release and dissolution studies. Moreover, a postoperative tumour recurrence mouse model was established to evaluate the antitumour effects of this thermosensitive hydrogel. The results showed that PTX-NCS-gel had a clear, regular network structure with excellent temperature sensitivity and could be gelated within minutes at 33.1 °C. Additionally, the rheological property investigation indicated that the hydrogel has proper viscoelasticity and self-recovery ability. In vivo imaging showed that PTX-NCS-gel inhibited both local tumour recurrence and distant metastasis. Moreover, PTX-NCS-gel has the following advantages: it is more convenient to administer, avoids strong allergic responses, and has fewer side effects on the liver and spleen. This hydrogel has the potential to serve as a powerful auxiliary medication to prevent postoperative local tumour recurrence.

Dually cross-linked single networks: structures and applications

Cross-linked polymers have attracted an immense attention over the years, however, there are many flaws of these systems, e.g. softness and brittleness; such materials possess non-adjustable properties and cannot recover from damage and thus are limited in their practical applications. Supramolecular chemistry offers a variety of dynamic interactions that when integrated into polymeric gels endow the systems with reversibility and responsiveness to external stimuli. A combination of different cross-links in a single gel could be the key to tackle these drawbacks, since covalent or chemical cross-linking serve to maintain the permanent shape of the material and to improve overall mechanical performance, whereas non-covalent cross-links impart dynamicity, reversibility, stimuli-responsiveness and often toughness to the material. In the present review we sought to give a comprehensive overview of the progress in design strategies of different types of dually cross-linked single gels made by researchers over the past decade as well as the successful implementations of these advances in many demanding fields where versatile multifunctional materials are required, such as tissue engineering, drug delivery, self-healing and adhesive systems, sensors as well as shape memory materials and actuators.

Thermal/Near-Infrared Light Dual-Responsive Reversible Two-Way Shape Memory cEVA/2D-MoO2 Composite for Multifunctional Applications

Light-responsive reversible two-way shape memory polymers (2W-SMPs) are highly promising for many fields due to indirect heating, clean, and remote control. In this work, a composite with both thermal- and near-infrared (NIR) light-induced reversible two-way shape memory effect (2W-SME) is prepared by doping extremely little quantities of 2D non-layered molybdenum dioxide nanosheets (2D-MoO₂ ) into semicrystalline poly(ethylene-co-vinyl acetate) (EVA) networks. This is the first report on light-induced reversible two-way shape memory composites employing 2D-MoO₂ as photothermal fillers. Upon switching the NIR light on and off, due to the excellent photothermal feature and stability of 2D-MoO₂ , the composite exhibits remarkable light-induced reversible 2W-SME. A light-driven actuator for sensing applications is designed based on the composite and the circuit, where the lamp acting as an alarm can raise and fade upon responding to NIR light. A completely flexible, fuel-free self-walking soft robot is designed based on the advantages of the light-responsive reversible 2W-SMPs. Additionally, the composite acting as a light-fueled crane is able to lift and lower a load that is 3846 times its own weight. The results demonstrate that the prepared composite has a promising prospect for applications as actuators, self-walking soft robot and crane.

Nature-inspired semi-IPN hydrogels with tunable mechanical properties and multi-responsiveness

Tough hydrogels (PAP hydrogels) with high mechanical properties and multi-responsiveness.

Gamma Radiation-Induced Unsaturated P(VDF-CTFE) Membranes with Improved Mechanical Properties

Poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) membranes were prepared by drop-casting with tetrahydrofuran (THF), and were then radiated by a low dose of gamma radiation without any other reagents. The apparent colour of the freshly prepared film was a semi-transparent white, which gradually darkened and finally turned black after 10.2kGy gamma radiation. Meanwhile, the yield and breaking strength of the membrane both improved. X-Ray diffraction (XRD) spectra showed that the structure of the microcrystal of the irradiated P(VDF-CTFE)-THF membrane was not changed. FT-IR analysis showed that the structure of the newly formed double bonds was dominated by –CF2–CF=CH–CF2–, which was formed by both dehydrofluorination and dehydrochlorination. This structure was further confirmed by 1H NMR spectra. The intermediates, such a radical-containing double bonds (–(CF=CH)n–C•F–) formed in this process were traced by electron paramagnetic resonance (EPR) spectroscopy. The thermal and mechanical properties were studied by gel permeation chromatography (GPC), thermogravimetric analysis (TGA), stress–strain and dynamic mechanical analysis (DMA), and all the changes of microstructure and optimization of apparent properties were not found in the corresponding membrane prepared by a solution-cast method with ethyl acetate (EtOAc). Therefore, this paper briefly analyses the probable mechanism of using low dose of gamma radiation to improve the mechanical properties of the P(VDF-CTFE) film prepared with THF.

Advances and trends of hydrogel therapy platform in localized tumor treatment: A review

Due to limitations of treatment and the stubbornness of infiltrative tumor cells, the outcome of conventional antitumor treatment is often compromised by a variety of factors, including severe side effects, unexpected recurrence, and massive tissue loss during the treatment. Hydrogel-based therapy is becoming a promising option of cancer treatment, because of its controllability, biocompatibility, high drug loading, prolonged drug release, and specific stimuli-sensitivity. Hydrogel-based therapy has good malleability and can reach some areas that cannot be easily touched by surgeons. Furthermore, hydrogel can be used not only as a carrier for tumor treatment agents, but also as a scaffold for tissue repair. In this review, we presented the latest researches in hydrogel applications of localized tumor therapy and highlighted the recent progress of hydrogel-based therapy in preventing postoperative tumor recurrence and improving tissue repair, thus proposing a new trend of hydrogel-based technology in localized tumor therapy. And this review aims to provide a novel reference and inspire thoughts for a more accurate and individualized cancer treatment.

Unique Self-Assembly of Sequence-Controlled Amino Acid Derived Vinyl Polymer with Gradient Thermoresponsiveness along a Chain

A novel water-soluble amino acid derived vinyl polymer whose block sequence was designed to achieve a gradient thermoresponsiveness along a chain was accurately prepared through an ultrarapid reversible addition-fragmentation chain-transfer polymerization. The polymer exhibited unique temperature-regulated self-assembly in water, leading to multiple nanostructural transformations including disassembly-to-ordered and ordered-to-ordered transitions. The morphologies were drastically changed by heating the solution from 4 °C (soluble form) to 20 °C (spherical micelle) to 70 °C (vesicle). Moreover, such transitions exhibited hysteresis upon cooling, namely, from 70 °C (vesicle) to 20 °C (wormlike micelle) to 4 °C (soluble form). In this polymer system, the specific monomer sequence contributed to the self-assembly behavior. These findings provide significant insight into the design of new thermoresponsive nanomaterials with potential applications in biomedical chemistry.