Swelling-Shrinking Behavior of a Hydrogel with a CO2-Switchable Volume Phase Transition Temperature

Macromolecules exhibit rich phase behavior that may be exploited for advanced material design. In particular, the volume phase transition in certain crosslinked hydrogels is a key property controlling the transition between a collapsed/dehydrated and a swollen/hydrated state, thereby regulating the release and absorption of water via a temperature change. In this work, a simple and tunable system exhibiting a carbon dioxide (CO2)-switchable volume phase transition is introduced, which displays isothermal swelling-shrinking behavior that is activated by addition and removal of CO2, respectively. Through systematic compositional studies, shifts in phase transition temperatures of up to 8.6 °C are measured upon CO2 exposure, which enables pronounced isothermal swelling in response to CO2, reaching up to a fivefold increase in mass. The shift in transition temperature and the extent of swelling are controlled by the hydrogel composition, thus enabling the transition temperature and swelling degree to be tuned a priori for a particular application. Controlled release experiments from these gels upon a CO2-induced phase transition suggest viability for drug delivery applications. It is anticipated that this work will motivate and expand efforts to exploit phase behavior for smart material development.

Visible light triggered controlled formation of rapidly self-healing hydrogels based on thiol-disulfide exchange

The properties of stimuli-responsive hydrogels can be tailored under various external stimuli, but it is difficult to realize the customized adjustment of hydrogel properties since the crosslinking degree in the gelation process is intractable. Here, a visible light triggered thiol-disulfide exchange reaction was applied for constructing disulfide-crosslinked hydrogels from P(EMA-SS-PEG), a poly(ethylene glycol) grafted poly(ethyl methacrylate) derivative with a disulfide linkage as the grafting point. This photochemical method provides mild gelation conditions to handily regulate the morphology, mechanical properties, swelling ratio, and degradation rate of hydrogels by simply varying the irradiation time. Based on this strategy, these disulfide-crosslinked hydrogel coatings showed rapid self-healing in 10 min under ambient conditions, which was dependent on the width of the scratch, temperature, and humidity. Notably, spraying water on these coatings could significantly accelerate the self-healing process of large scratches (360 μm) at room temperature with a self-healing time of 1 hour, enabling the practical application of hydrogel coatings in a natural environment.

Precision polymer nanofibers with a responsive polyelectrolyte corona designed as a modular, functionalizable nanomedicine platform

We describe the development of a modular, functionalizable platform for biocompatible core-shell block copolymer nanofibers of controlled length (22 nm – 1.3 μm) and low dispersity produced via living crystallization-driven...

Stimuli-responsive polymer/nanomaterial hybrids for sensing applications

Chemical and biological/biochemical sensors are capable of generating readout signals that are proportional to the concentration of specific analytes of interest. Signal sensitivity and limit of detection/quantitation can be enhanced through the use of polymers, nanomaterials, and their hybrids. Of particular interest are stimuli-responsive polymers and nanomaterials due to their ability to change their physical and/or chemical characteristics in response to their environment, and/or in the presence of molecular/biomolecular species of interest. Their individual use for sensing applications have many benefits, although this review focuses on the utility of stimuli-responsive polymer and nanomaterial hybrids. We discuss three main topics: stimuli-responsive nanogels, stimuli-responsive network polymers doped with nanomaterials, and nanoparticles modified with stimuli-responsive polymers.

Antimicrobial Activity of Electrospun Polyvinyl Alcohol Nanofibers Filled with Poly[2-(tert-butylaminoethyl) Methacrylate]-Grafted Graphene Oxide Nanosheets

A novel cationic polymer, poly[2-(tert-butylaminoethyl) methacrylate] (PTA), effectively kills various strains of bacteria with low toxicity to tissue cells. Graphene-based materials demonstrate exceptional electron transport capability, antibacterial activity, favorable nontoxicity, and versatile applicability. PTA can be grafted onto the graphene oxide (GO) surface (GO-g-PTA) to enhance the antimicrobial efficiency of the latter against Staphylococcus aureus (S. aureus). In this study, GO-g-PTA powders were successfully synthesized via free radical polymerization (GO-g-PTA-F) and atom transfer radical polymerization (GO-g-PTA-A). The antimicrobial efficiencies of graphene nanosheets (GNSs), GO-g-PTA-F, and GO-g-PTA-A were then investigated. Addition of GNS, GO-g-PTA-F, and GO-g-PTA-A to the PVA nanofibers was carried out elucidate the effects of filler amount and physical treatment on the morphology, microstructure, crystallization behaviors, antimicrobial efficiency, and cytotoxicity of the composite fibers. Finally, the potential applications of electrospun PVA/GNS, PVA/GO-g-PTA-F, and PVA/GO-g-PTA-A composite nanofiber mats to chronic wound care were evaluated. The resulting PVA/GO-g-PTA-A composite nanofiber mats showed enhanced antimicrobial ability against S. aureus compared with the PVA/GNS and PVA/GO-g-PTA-F composite nanofiber mats at the same filler volume percentage.

ZnO microparticle‐loaded chitosan/poly(vinyl alcohol)/acacia gum nanosphere‐based nanocomposite thin film wound dressings for accelerated wound healing

The present study deals with the development of novel ZnO microparticle‐loaded chitosan/poly(vinyl alcohol)/acacia gum nanosphere‐based nanocomposite thin films through electrospraying and evaluation of their potential use in wound healing applications for skin. ZnO microparticles were synthesized and used as bioactive agents. Morphology, size distribution, structure, and dispersion of the synthesized ZnO microparticles were analyzed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM). ZnO microparticles were incorporated into the ternary nanocomposite films by electrospraying technique. Thermogravimetric analyses reveal that incorporation of ZnO microparticles into the nanocomposite structure improves the thermal stability. Mechanical analyses show that tensile strength reaches to the maximum value of 12.75 MPa with 0.6 wt % ZnO content. SEM and TEM micrographs demonstrate that the nanocomposite films consist of nanospheres with nanocapsular structures whose sizes are mostly between 250 and 550 nm. Viability tests established prevailing cellular performance of the fibroblasts on 0.6 wt % ZnO microparticle‐loaded nanocomposite films with a viability percentage of 160% compared to the control group. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48445.

Highly water-dispersible calcium lignosulfonate-capped MnO nanoparticles as a T 1 MRI contrast agent with exceptional colloidal stability, low toxicity and remarkable relaxivity

A simple and efficient method to synthesize highly water-dispersible calcium lignosulfonate-coated manganese oxide nanoparticles as a potential candidate for the current magnetic resonance imaging (MRI) T 1 contrast agents was reported. Hydrophobic MnO nanoparticles with dimensions of about 10 nm were prepared by thermal decomposition of manganese(ii)acetylacetonate in the presence of oleic acid as a surfactant. The characteristics of the synthesized nanoparticles, cytotoxicity assay and in vitro MRI properties were investigated in detail. Results showed that calcium lignosulfonate has a great influence on the colloidal stability and biocompatibility of MnO nanoparticles in water. Furthermore, this coating agent ensures abundant exposure of external Mn ion with protons of water, which endows the nanoparticles with a longitudinal molar relaxivity (r 1) of 4.62 mM-1 s-1. An efficient contrast enhancement effect was observed in the study of MRI investigations.

Synergistic Effect and Characterization of Graphene/Carbon Nanotubes/Polyvinyl Alcohol/Sodium Alginate Nanofibrous Membranes Formed Using Continuous Needleless Dynamic Linear Electrospinning

In this study, a self-made continuous needleless dynamic linear electrospinning technique is employed to fabricate large-scale graphene (Gr)/carbon nanotubes (CNT)/polyvinyl alcohol (PVA)/sodium alginate (SA) nanofibrous membranes. The synergistic effect of Gr and CNT fillers in the PVA/SA membrane is explored in depth by changing the volume ratio (v/v) of Gr and CNT as 10:0, 8:2, 6:4, 4:6, 2:8, and 0:10. Microstructure, functional group, conductivity, and hydrophilicity of PVA/SA/Gr/CNT membranes was characterized. Results show that the linear electrode needleless electrospinning technique can be spun into 200-nm diameter fibers. The PVA/SA/Gr/CNT fibrous membrane has good hydrophilicity and thermal stability. A Gr/CN ratio of 6:4 possessed the optimal synergistic effect, which showed the lowest surface resistivity of 2.53 × 103 Ω/m2. This study will provide a reference for the large-scale preparation of nanofibrous membrane used as a artificial nerve conduit in the future.

Characterization and Microstructure of Linear Electrode-Electrospun Graphene-Filled Polyvinyl Alcohol Nanofiber Films

With the aim of achieving controllable mass production of electrospun nanofiber films, this study proposes and investigates the feasibility of using a custom-made linear electrode- electrospun device to produce conductive graphene (GR)-filled polyvinyl alcohol (PVA) nanofibers. The film morphology and diameter of nanofibers are observed and measured to examine the effects of viscosity and conductivity of the PVA/GR mixtures. Likewise, the influence of the content of graphene on the hydrophilicity, electrical conductivity, electromagnetic interference shielding effectiveness (EMSE), and thermal stability of the PVA/GR nanofiber films is investigated. The test results show that the PVA/GR mixture has greater viscosity and electric conductivity than pure PVA solution and can be electrospun into PVA/GR nanofiber films that have good morphology and diameter distribution. The diameter of the nanofibers is 100 nm and the yield is 2.24 g/h, suggesting that the process qualifies for use in large-scale production. Increasing the content of graphene yields finer nanofibers, a smaller surface contact angle, and higher hydrophilicity of the nanofiber films. The presence of graphene is proven to improve the thermal stability and strengthens the EMSE by 20 dB at 150–1500 MHz. Mass production is proven to be feasible by the test results showing that PVA/GR nanofiber films can be used in the medical hygiene field.

Electrospun Mat of Poly(vinyl alcohol)/Graphene Oxide for Superior Electrolyte Performance

Here, we describe an electrospun mat of poly(vinyl alcohol) (PVA) and graphene oxide (GO) as a novel solid-state electrolyte matrix, which offers better performance retention upon drying after infiltrated with aqueous electrolyte. The PVA-GO mat overcomes the major issue of conventional PVA-based electrolytes, which is the ionic conductivity decay upon drying. After exposure to 45 ± 5% relative humidity at 25 °C for 1 month, its conductivity decay is limited to 38.4%, whereas that of pure PVA mat is as high as 84.0%. This mainly attributes to the hygroscopic nature of GO and the unique nanofiber structure within the mat. Monolithic supercapacitors have been derived directly on the mat via a well-developed laser scribing process. The as-prepared supercapacitor offers an areal capacitance of 9.9 mF cm^-2 at 40 mV s^-1 even after 1 month of aging under ambient conditions, with a high device-based volumetric energy density of 0.13 mWh cm^-3 and a power density of 2.48 W cm^-3, demonstrating great promises as a more stable power supply for wearable electronics.

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.

Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core–shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase.

Epoxy resin composites with improved thermal resistance and flame retardancy were fabricated based on P(H) microcapsules.

Nanocarbons in Electrospun Polymeric Nanomats for Tissue Engineering: A Review

Electrospinning is a versatile process technology, exploited for the production of fibers with varying diameters, ranging from nano- to micro-scale, particularly useful for a wide range of applications. Among these, tissue engineering is particularly relevant to this technology since electrospun fibers offer topological structure features similar to the native extracellular matrix, thus providing an excellent environment for the growth of cells and tissues. Recently, nanocarbons have been emerging as promising fillers for biopolymeric nanofibrous scaffolds. In fact, they offer interesting physicochemical properties due to their small size, large surface area, high electrical conductivity and ability to interface/interact with the cells/tissues. Nevertheless, their biocompatibility is currently under debate and strictly correlated to their surface characteristics, in terms of chemical composition, hydrophilicity and roughness. Among the several nanofibrous scaffolds prepared by electrospinning, biopolymer/nanocarbons systems exhibit huge potential applications, since they combine the features of the matrix with those determined by the nanocarbons, such as conductivity and improved bioactivity. Furthermore, combining nanocarbons and electrospinning allows designing structures with engineered patterns at both nano- and microscale level. This article presents a comprehensive review of various types of electrospun polymer-nanocarbon currently used for tissue engineering applications. Furthermore, the differences among graphene, carbon nanotubes, nanodiamonds and fullerenes and their effect on the ultimate properties of the polymer-based nanofibrous scaffolds is elucidated and critically reviewed.

Hollow polymer particles: a review

Herein, the basic principles, such as the definitions, classifications, and properties, of hollow polymer particles (HPPs) are critically investigated.

Facile polypyrrole thin film coating on polypropylene membrane for efficient solar-driven interfacial water evaporation

Facile dip-coating method to fabricate robust polypyrrole thin film coating on thermal insulation polypropylene membrane with solar vapor generation efficiency of 72%.

UV-triggered thiol–disulfide exchange reaction towards tailored biodegradable hydrogels

Biodegradable hydrogels were constructed by a UV-triggered thiol–disulfide exchange reaction with temporal and spatial precision.

Effect of the MWCNTs selective localization on the dielectric properties for PVDF/PS/HDPE ternary blends with in situ formed core–shell structure

This work demonstrated the selective localization of multiwall carbon nanotubes (MWCNTs) in poly(vinylidene fluoride) (PVDF)/poly(styrene) (PS)/high-density poly(ethylene) (HDPE) blends to be an effective method to reduce the dielectric loss.

Hydrophobization of silver nanoparticles through surface-initiated atom transfer radical polymerization

Poly(methyl methacrylate) (PMMA)-coated Ag@SiO₂core–shell particles with enhanced dispersibility in non-polar solvents were synthesized by surface-initiated atom transfer radical polymerization.

Thickness and substrate dependences of phase transition, drug release and antibacterial properties of PNIPAm-co-AAc films

Normalized absorption coefficient at 590 nm of solutions of extracted CV from 50 nm and 500 nm thick PNIPAm-co-AAc films deposited on Au substrates. Releases were measured for temperatures below (25 °C) and above (40 °C) the LCST.