Stimuli-responsive polymers and their applications in separation science

A self-healing thermogelling polymer with tunable transparency based on biomolecule alginate grafting phenylboronic acid

Thermogelling polymers with transparency, structure stability and biocompatibility are promising for biomedicine application. In this study, a thermogelling polymer P-C5PEG with tunable transparency was developed by the reaction between alternating copolymer C5PEG and chemically modified biomolecule Alg-PBA via boronic ester bonds. The sol-to-gel transition of P-C5PEG aqueous solution sensitively responded to changes in temperature, and the critical value could be adjusted between 15 and 40 °C by varying the content of C5PEG and Alg-PBA. As the weight ratio of Alg-PBA to C5PEG was over 0.3, the transparency of as-synthesized hydrogel kept above 75 % at 37 °C. Meanwhile, immersion P-C5PEG hydrogel in CaCl2 solution significantly increased its mechanical strength by 3 times due to chelation effect. The shear-resistance and self-healing properties were ensured by dynamic boronic ester bonds due to the protective effect of hydrophobic gel network. As a drug delivery, P-C5PEG hydrogel had a swelling rate of 3748.7 ± 103 % in PBS and could continuously release fluorescein sodium within 24 h. Moreover, the in vitro degradability and cytotoxicity of P-C5PEG was confirmed. Finally, the mechanisms behind the thermogelling property and tunable transparency were revealed. Overall, this thermogelling P-C5PEG polymer, with tunable transparency and thermo-responsiveness, exhibits great potential for biomedicine application.

Nanocellulose-based membranes with pH- and temperature-responsive pore size for selective separation

Smart gating membranes have drawn much attention due to the controllable pore structure. Herein, a smart gating membrane with dual responsiveness was prepared from bacteria cellulose (BC) grafted with pH- and temperature-responsive polymers. By external stimulation, the average pore size of the membrane can be controlled from 33.75 nm to 144.81 nm, and the pure water flux can be regulated from 342 to 2118 L·m-2·h-1 with remarkable variation in the pH range of 1-11 and temperature range of 20-60 °C. The adjustability of pore size is able to achieve the gradient selective separation of particles and polymers with different sizes. In addition, owing to the underwater superoleophobicity and the nanoscale pore structure, the membrane separation efficiencies of emulsified oils are higher than 99 %. Moreover, the controllable pore size endows the membrane with good self-cleaning performance. This nanocellulose-based smart gating membrane has potential applications in the fields of controllable permeation, selective separation, fluid transport, and drug/chemical controlled release systems.

Comprehensive review on pH and temperature-responsive polymeric adsorbents: Mechanisms, equilibrium, kinetics, and thermodynamics of adsorption processes for heavy metals and organic dyes

Wastewater treatment technologies have been developed to address the health and environmental risks associated with toxic and cancer-causing dyes and heavy metals found in industrial waste. The most commonly used method to mitigate and treat such effluents is adsorption, which is favored for its high efficiency, low costs, and ease of operation. However, traditional adsorbents have limitations in terms of regeneration and selectivity compared to smart adsorbents. Smart polymeric adsorbents, on the other hand, can undergo physical and chemical changes in response to external factors like temperature and pH, enabling a selective adsorption process. These adsorbents can be easily regenerated and reused with minimal generation of secondary pollutants during desorption. The unique properties acquired by stimuli-responsive adsorbents have encouraged researchers to investigate their potential for the selective and efficient removal of organic dyes and heavy metals. This comprehensive review focuses on two common stimuli, pH and temperature, discussing the fabrication methods and characteristics of smart adsorbents responsive to these factors. It also provides an overview of the mechanisms, isotherms, kinetics, and thermodynamics of the adsorption process for each type of stimuli-responsive adsorbent. Finally, the review concludes with discussions on future perspectives and considerations.

A review of electrophoretic separations in temperature-responsive Pluronic thermal gels

Gel electrophoresis is a ubiquitous bioanalytical technique used in research laboratories to validate protein and nucleic acid samples. Polyacrylamide and agarose have been the gold standard gel materials for decades, but an alternative class of polymer has emerged with potentially superior performance. Pluronic thermal gels are water-soluble polymers that possess the unique ability to undergo a change in viscosity in response to changing temperature. Thermal gels can reversibly convert between low-viscosity liquids and high-viscosity solid gels using temperature as an adjustable parameter. The properties of thermal gels provide unmatched flexibility as a dynamic separations matrix to measure analytes ranging from small molecules to cells. This review article describes the physical and chemical properties of Pluronic thermal gels to provide a fundamental overview of polymer behavior. The performance of thermal gels is then reviewed to highlight their applications as a gel matrix for electrokinetic separations in capillary, microfluidic, and slab gel formats. The use of dynamic temperature-responsive gels in bioanalytical separations is an underexplored area of research but one that holds exciting potential to achieve performance unattainable with conventional static polymers.

Synthesis and Characterization of Thermoresponsive Chitosan-graft-poly(N-isopropylacrylamide) Copolymers

Thermoresponsive chitosan-graft-poly(N-isopropylacrylamide) (CS-g-PNIPAAm) copolymers of different composition were synthesized by free-radical polymerization of chitosan (CS) and N-isopropylacrylamide (NIPAAm) in aqueous solution using potassium persulfate (PPS) as an initiator. By changing the molar ratio of CS:NIPAAm from 1:0.25 to 1:10 graft copolymers with a CS backbone and different amounts of PNIPAM side chains were prepared. The chemical structure of the obtained CS-g-PNIPAAm copolymers was confirmed by FTIR and 1H NMR spectroscopy. 1H NMR spectra were also used to calculate the content of attached PNIPAAm side chains. Moreover, the lower critical solution temperature (LCST) behavior of synthesized copolymers was assessed by cloud point, differential scanning calorimetry and particle size measurements. The aqueous solutions of copolymers containing ≥12 molar percent of PNIPAAm side chains demonstrated LCST behavior with the phase separation at around 29.0-32.7 °C. The intensity of thermoresponsiveness depended on the composition of copolymers and increased with increasing content of poly(N-isopropylacrylamide) moieties. The synthesized thermoresponsive chitosan-graft-poly(N-isopropylacrylamide) copolymers could be potentially applied in drug delivery systems or tissue engineering.

Ion-Imprinted Polymeric Materials for Selective Adsorption of Heavy Metal Ions from Aqueous Solution

The introduction of selective recognition sites toward certain heavy metal ions (HMIs) is a great challenge, which has a major role when the separation of species with similar physicochemical features is considered. In this context, ion-imprinted polymers (IIPs) developed based on the principle of molecular imprinting methodology, have emerged as an innovative solution. Recent advances in IIPs have shown that they exhibit higher selectivity coefficients than non-imprinted ones, which could support a large range of environmental applications starting from extraction and monitoring of HMIs to their detection and quantification. This review will emphasize the application of IIPs for selective removal of transition metal ions (including HMIs, precious metal ions, radionuclides, and rare earth metal ions) from aqueous solution by critically analyzing the most relevant literature studies from the last decade. In the first part of this review, the chemical components of IIPs, the main ion-imprinting technologies as well as the characterization methods used to evaluate the binding properties are briefly presented. In the second part, synthesis parameters, adsorption performance, and a descriptive analysis of solid phase extraction of heavy metal ions by various IIPs are provided.