Synthesis and electromechanical actuation of a temperature, pH, and electrically responsive hydrogel

Conducting polymer hydrogels for biomedical application: Current status and outstanding challenges

Conducting polymer hydrogels (CPHs) are composite polymeric materials with unique properties that combine the electrical capabilities of conducting polymers (CPs) with the excellent mechanical properties and biocompatibility of traditional hydrogels. This review aims to highlight how the unique properties CPHs have from combining their two constituent materials are utilized within the biomedical field. First, the synthesis approaches and applications of non-CPH conductive hydrogels are discussed briefly, contrasting CPH-based systems. The synthesis routes of hydrogels, CPs, and CPHs are then discussed. This review also provides a comprehensive overview of the recent advancements and applications of CPHs in the biomedical field, encompassing their applications as biosensors, drug delivery scaffolds (DDSs), and tissue engineering platforms. Regarding their applications within tissue engineering, a comprehensive discussion of the usage of CPHs for skeletal muscle prosthetics and regeneration, cardiac regeneration, epithelial regeneration and wound healing, bone and cartilage regeneration, and neural prosthetics and regeneration is provided. Finally, critical challenges and future perspectives are also addressed, emphasizing the need for continued research; however, this fascinating class of materials holds promise within the vastly evolving field of biomedicine.

Thermo-pH-Salt Environmental Terpolymers Influenced by 2-((Dimethylamino)methyl)-4-methylphenyl Acrylate: A Comparative Study for Tuning Phase Separation Temperature

This study offers a comparison between three different types of thermoresponsive (TR) and thermo-pH-salt (TPR) multiresponsive polymers including homopoly(N-isopropylacrylamide) (PNIPAAm), copolymers with three different monomers, 2-hydroxyethyl methacrylate (HEMA), N,N-dimethylacrylamide (DMAAm), and styrene (S) at three different concentrations (5, 10, and 20 mol %), and a PNIPAAm terpolymer with 5, 10, and 20 mol % 2-((dimethylamino)methyl)-4-methylphenyl acrylate (DMAMCA) and 10 mol % HEMA, DMAAm, and S monomers. All polymers were chemically analyzed with 1H NMR and Fourier transform infrared spectroscopy (FT-IR) as well as gel permeation chromatography (GPC) for the molecular weights and dispersity and differential scanning calorimeter (DSC) for the glass transition temperatures. The cloud point, also known as the phase separation temperature (Cp), was determined for all polymers by a turbidity test using a UV-vis spectrophotometer; a micro-differential scanning calorimeter was used for measuring the cloud point in deionized water. The influence of a tertiary amine cationic group of DMAMCA changed the behavior of TR copolymers into TPR by shifting the cloud point of the TPR to higher values in acidic solutions (lower pH) and to lower values in alkaline solutions. The Cp was measured at different concentrations of Hofmeister kosmotropic and chaotropic anion salt solutions in a range of pH solutions for the terpolymers. It demonstrated the same behavior as mentioned in pH solutions besides the effect of salt ions. By measuring the Tc and Cp of these polymers, we can exploit various applications of stimuli-responsive materials for sensors and biomedical technology.

Functional Materials Made by Combining Hydrogels (Cross-Linked Polyacrylamides) and Conducting Polymers (Polyanilines)-A Critical Review

Hydrogels made of cross-linked polyacrlyamides (cPAM) and conducting materials made of polyanilines (PANIs) are both the most widely used materials in each category. This is due to their accessible monomers, easy synthesis and excellent properties. Therefore, the combination of these materials produces composites which show enhanced properties and also synergy between the cPAM properties (e.g., elasticity) and those of PANIs (e.g., conductivity). The most common way to produce the composites is to form the gel by radical polymerization (usually by redox initiators) then incorporate the PANIs into the network by oxidative polymerization of anilines. It is often claimed that the product is a semi-interpenetrated network (s-IPN) made of linear PANIs penetrating the cPAM network. However, there is evidence that the nanopores of the hydrogel become filled with PANIs nanoparticles, producing a composite. On the other hand, swelling the cPAM in true solutions of PANIs macromolecules renders s-IPN with different properties. Technological applications of the composites have been developed, such as photothermal (PTA)/electromechanical actuators, supercapacitors, movement/pressure sensors, etc. PTA devices rely on the absorption of electromagnetic radiation (light, microwaves, radiofrequency) by PANIs, which heats up the composite, triggering the phase transition of a thermosensitive cPAM. Therefore, the synergy of properties of both polymers is beneficial.

Acrylamide Hydrogel-Modified Silicon Nanowire Field-Effect Transistors for pH Sensing

In this study, we report a pH-responsive hydrogel-modified silicon nanowire field-effect transistor for pH sensing, whose modification is operated by spin coating, and whose performance is characterized by the electrical curve of field-effect transistors. The results show that the hydrogel sensor can measure buffer pH in a repeatable and stable manner in the pH range of 3–13, with a high pH sensitivity of 100 mV/pH. It is considered that the swelling of hydrogel occurring in an aqueous solution varies the dielectric properties of acrylamide hydrogels, causing the abrupt increase in the source-drain current. It is believed that the design of the sensor can provide a promising direction for future biosensing applications utilizing the excellent biocompatibility of hydrogels.

Techniques and Processes for the Realization of Electrically Conducting Textile Materials from Intrinsically Conducting Polymers and Their Application Potential

This review will give an overview on functional conducting polymers, while focusing on the integration of intrinsically conducting, i.e., self-conducting, polymers for creating electrically conducting textile materials. Thus, different conduction mechanisms as well as achievable electrical properties will be introduced. First, essential polymers will be described individually, and secondly, techniques and processes for the realization of electrically conducting textile products in addition to their application potential will be presented.

Study of the pore structure and size effects on the electrochemical capacitor behaviors of porous carbon/quinone derivative hybrids

We demonstrate the hybridization of a redox-active quinone derivative, 2,5-dichloro-1,4-benzoquinone (DCBQ), and porous carbons with different pore structures for aqueous electrochemical capacitor electrodes. The hybridization is performed in the gas phase, which enables accurate porous carbon/DCBQ weight ratios. This method is advantageous over conventional liquid phase adsorption, in terms of facile optimization of the porous carbon/DCBQ weight ratio to obtain high-performance aqueous electrochemical capacitor electrodes, dependent on the kind of porous carbons; moreover, complete adsorption in the liquid phase cannot be achieved by the conventional liquid phase adsorption method. Their electrochemical capacitor performances are evaluated using an aqueous 1 M H2SO4 electrolyte, and the adsorbed DCBQ undergoes redox reactions inducing pseudocapacitance within the pores of porous carbons. To study the effect of the pore size on the electrochemical capacitor behavior, two kinds of activated carbon (AC) with different pore sizes are examined: the microporous AC and the AC with both micro- and mesopores. Additionally, we examine ordered microporous carbon with a uniform pore size of 1.2 nm and a three-dimensionally (3D) ordered and mutually connected pore structure. The results reveal that mesopores facilitate proton conduction inside the DCBQ-constrained carbon pores, whereas the 3D-ordered and mutually connected micropores balance high volumetric capacitance enhancement with excellent rate capability. Such high proton conduction inside such constrained spaces can be explained only by the Grotthuss mechanism.

Electrochemical polymerization of pyrene and aniline exclusively inside the pores of activated carbon for high-performance asymmetric electrochemical capacitors

An asymmetric polymer capacitor was prepared from pyrene (PY), aniline (ANI), and commercially available activated carbon (AC) through a solvent-free preparation. PY and ANI were adsorbed into the AC host material in the gas phase and electrochemically polymerized exclusively inside the AC pores in an aqueous H2SO4 electrolyte (1 M). No volumetric expansion of the AC particles occurred upon the adsorption of monomers and their subsequent polymerizations; thus, the volumetric capacitance was enhanced by the inclusion of pseudocapacitive polypyrene (PPY) and polyaniline (PANI). The PPY and PANI structures formed inside the AC pores are very thin and have a large contact area with the conductive carbon surfaces. Therefore, the charge transfer distance between the polymers and the carbon surfaces was drastically shortened, significantly reducing the charge transfer resistance; i.e., high power density. The maximum volumetric capacitances for the PPY- and PANI-hybridized AC reached 314 and 299 F cm-3, respectively. Moreover, the strong adhesion derived from their large contact areas and adsorption capability of AC endow these materials with long cycle lifetimes. The PPY- and PANI-hybridized AC have different redox potentials and can be assembled into an asymmetric capacitor. The volumetric capacitance obtained for the asymmetric capacitor further surpassed that of the symmetric capacitor consisting of pristine AC, with high power density and long cycle lifetimes.

Electrochemical synthesis of polyaniline in the micropores of activated carbon for high-performance electrochemical capacitors

Polyaniline synthesized exclusively inside the micropores of activated carbon exhibits excellent energy and power densities.