A Photothermal-Responsive Soft Actuator Based on Biomass Carbon Nanosheets of Synergistic Bilateral Polymers

Currently, polymer actuators capable of photothermal response are being developed to be more sensitive and repeatable. In this work, a three-layered structured soft film actuator (NA/PET/NI-3) was designed by combining poly(N-isopropylacrylamide) (PNIPAM), poly(N-(2-aminoethyl)-acrylamide) (PANGA) and poly(ethylene glycol-co-terephthalate) (PET) film. Coconut water and PEI were used to synthesize a new kind of carbon nanosheet (PEI-CCS), which, when triggered by near-infrared light, will enable photothermal bending behavior in the micrometer-scale NA/PET/NI-n film, while PET served as the supporting and heat conducting layer. This three-layered actuator utilized the synergistic effects of two kind of polymers, PNIPAM and PNAGA, on either side of PET, with the upper critical solution temperatures and lower critical solution temperatures when subjected to temperature changes. This bilateral polymer design exhibited a rapid response under near-infrared light stimulation, bending to 180° within 4 s and recovering to its original shape within 30 s. When the bending process was set to 90° as in the standard experiment, NA/PET/NI-3 responded within 2 s and recovered within 8 s. NA/PET/NI-3 also demonstrated good reversibility and repeatability, capable of undergoing reversible driving over 120 times. The design and preparation of this actuator provided new ideas for the development of polymer soft actuators.

H-bond-type thermo-responsive schizophrenic copolymers: The phase transition correlation with their parent polymers and the improved protein co-assembly ability

Schizophrenic copolymers are one type of the popular smart polymers that show invertible colloidal structures in response to temperature stimulus. However, the lack of principles to predict the phase transition temperature of a schizophrenic copolymer from its corresponding parent thermo-responsive polymers limits their development. Additionally, studies on their applications remain scarce. Herein, a series of schizophrenic copolymers were synthesized by polymerization of a RAFT-made polymer precursor poly(acrylamide-co-N-acryloxysuccinimide-co-acrylic acid) (P(AAm-co-NAS-co-AAc)) with the mixture of N-isopropylmethacrylamide (NIPAm) and acrylamide (AAm) in varying molar ratios. In aqueous solution, the block P(AAm-co-NAS-co-AAc) and the block poly(NIPAm-co-AAm) exhibited upper and lower critical solution temperature (UCST and LCST) behavior, respectively. The schizophrenic copolymers featured either UCST-LCST, LCST-UCST, or only LCST thermo-responsive transition. A preliminary correlation of phase transition between the schizophrenic copolymers and their parent polymers was summarized. Furthermore, the co-assembly of the schizophrenic copolymers and proteins were conducted and the kinetics of protein loading and protein activity were investigated, which showed that the schizophrenic copolymers were efficient platforms for protein co-assembly with ultra-high protein loading while preserving the protein bioactivities. Additionally, all the materials were non-toxic towards NIH 3T3 and MCF-7 cells. This work offers the prospects of the schizophrenic polymers in soft colloidal and assembly systems, particularly in guiding the design of new materials and their use in biomedical applications.

The UCST phase transition of a dextran based copolymer in aqueous media with tunable thermoresponsive behavior

A hydrogen bonded UCST polymer has been developed by grafting of methacrylamide and acrylic acid on dextran via free radical polymerization.

A Smart Patch with On-Demand Detachable Adhesion for Bioelectronics

A smart ionic skin patch with on-demand detachable adhesion has been developed as human-machine interface for physiological signal monitoring. In spite of the multifunctions demonstrated by existing ionic skin, it is still difficult to distinguish different signals simultaneously. Moreover, the secondary damages to the tissues are often overlooked when the adhesive materials are removing from the wound. Herein, a multifunctional biomimetic hydrogel with temperature, mechanical, electrical, and pH response is developed. This hydrogel is designed by in situ polymerizing of hydrophilic anion monomers in a natural cationic polysaccharide to construct multifunctional biomimetic ionic channel. Due to the reversible physical cross-linked network and thermosensitivity, the mechanical properties, adhesion, and visual effect of the hydrogel can be tuned by changing hydrogen bonding density via phase transition, thus making it an excellent biosafe material for wearable device. The hydrogel is utilized as skin patch intended for monitoring physiological signals stimulated by physical and chemical changes involving pressure, temperature, pH value, and electrocardiograph. Especially, this ionic skin patch can recognize temperature change signals precisely either in broad or extremely narrow temperature range. This smart skin patch can even recognize the pressure and temperature signals in real time and differentiate the signals simultaneously.

Phase Transition Behavior and Catalytic Activity of Poly(N-acryloylglycinamide-co-methacrylic acid) Microgels

Poly(N-acryloyl glycinamide) is a well-known thermoresponsive polymer possessing an upper critical solution temperature (UCST) in water. By copolymerizing N-acryloyl glycinamide (NAGA) with methacrylic acid (MAA) in the presence of a crosslinker, poly(N-acryloyl glycinamide-co-methacrylic acid) [P(NAGA-MAA)] copolymer microgels with an MAA molar fraction of 10-70 mol % were obtained. The polymerization kinetics suggests that the copolymer microgels have a random structure. The size of the microgels was between 60 and 120 nm in the non-aggregated swollen state in aqueous medium and depending on the solvent conditions, they show reversible swelling and shrinking upon temperature change. Their phase transition behavior was studied by a combination of methods to understand the process of the UCST-type behavior and interactions between NAGA and MAA. P(NAGA-MAA) microgels were loaded with silver nanoparticles (AgNPs) by the reduction of AgNO₃ under UV light. Compared with the chemical reduction of AgNO₃, the photoreduction results in smaller AgNPs and the amount and size of the AgNPs are dependent on the comonomer ratio. The catalytic activity of the AgNP-loaded microgels in 4-nitrophenol reduction was tested.

One-pot surfactant-free modulation of size and functional group distribution in thermoresponsive microgels

Control over the size and functional group distribution of soft responsive hydrogel particles is essential for applications such as drug delivery, catalysis and chemical sensing. Traditionally, targeted functional group distributions are achieved with semi-batch techniques which require specialized equipment, while the preparation of size-tailored particles typically involves the use of surfactants. Herein, we present a simple and robust surfactant-free method for the modulation of size and carboxylic acid functional group distribution in poly(N-isopropylacrylamide) thermoresponsive microgels, employing reaction pH as the single experimental parameter. The varying distributions of carboxylic acid residues arise due to differences in kinetic reactivity, which are a function of the degree of dissociation of methacrylic acid, and thus of reaction pH. Incorporated charged residues induce a surfactant-like action during the particle nucleation stage, and impact the final particle size. Characterization with dynamic light scattering, and electron microscopy consistently supports the pH-tailored morphology of the microgels. A mathematical model which accounts for particle deformation on the imaging substrate also shows excellent agreement with the experimental results.

Visible light controlled aqueous RAFT continuous flow polymerization with oxygen tolerance

A fast visible light controlled RAFT polymerization system without the prior removal of oxygen was successfully carried out in a continuous tubular reactor with water as a green solvent.