Polyacrylamide Network Research Articles

Terpyridine-functionalized chemically cross-linked polyacrylamide hydrogel for white emission and multistimuli-responsive behaviour

A highly efficient and multifunctional white-emitting hydrogel was fabricated using a facile copolymerization process by introducing a hydrophilic terpyridine-based chromophore into a polyacrylamide network.

A semi-interpenetrating network ionic hydrogel for strain sensing with high sensitivity, large strain range, and stable cycle performance

Transparent conductive hydrogels with intrinsic flexibility, high sensitivity and outstanding repeatability and nearly real-time response are highly demanded for wearable devices/sensors. Here we report a novel ionic conductor hydrogel consisting of interpenetrating sodium carboxymethylcellulose (CMC) microsheets and polyacrylamide (PAAm) network. Intrinsic interactions between the CMC and PAAm endow the hydrogel with outstanding physical, mechanical robustness. The ionic hydrogel shows a very high transparency (98.2%), high adhesion efficiency (64% in strength), outstanding repeatability (500 cycles at the strain of 300%), sensitivity (Gauge factor = 3.15), and nearly real-time response (360 ms) to a small amount of stress. Additionally, two pieces of the semi-interpenetrating hydrogel can be bonded together with CMC membrane instantly without any external stimulation. Strain sensor based on the semi-interpenetrating network hydrogel has been demonstrated reliable in detecting a small strain caused by a subtle vibration up to a very large deformation by stretching. The hydrogel-based strain sensor may be applied in human motion detection, smart cushion and soft robotics.

3D Meshlike Polyacrylamide Hydrogel as a Novel Binder System via in situ Polymerization for High‐Performance Si‐Based Electrode

AbstractSilicon has been considered as a promising anode material due to its high theoretical capacity (3579 mAh g−1), however, it suffers from capacity degradation owing to the series of multiscale fractures in the electrode caused by the volume variation (≈300%) during phase transitions. The molecular/structural design of polymeric binders has been pivotal in overcoming the challenges to improve the integrity of Si anode via strong interactions between active materials and binders. In this respect, the covalently crosslinked polyacrylamide (PAM) network, which effectively maintains its mechanical strength and shape, is introduced as a novel binder system for Si active materials. Unlike the thermal crosslinking, the abundant polar‐functional groups, related to the strong interactions between Si and polymer, are not sacrificed in their network by virtue of the in situ polymerization. Through the PAM gel, the Si‐based electrode exhibits a superior capacity of ≈1526 mAh g−1 at an optimized crosslinker concentration after 500 cycles. In addition, the effect of the chemical/mechanical properties of PAM gel on the electrochemical properties of Si is adequately elucidated. The results will provide meaningful insight regarding the design of novel binders, especially in the application of the covalently crosslinked structure to Si‐based electrodes.

Fabrication of tough, self‐recoverable, and electrically conductive hydrogels byin situreduction of poly(acrylic acid) grafted graphene oxide in polyacrylamide hydrogel matrix

ABSTRACTDeveloping electrically conductive hydrogels with good electronic properties and excellent mechanical performance is significant to their potential applications. In this article, we present a strategy to fabricate tough, self‐recoverable and electrically conductive hydrogels containing reduced graphene oxide (rGO). Poly(acrylic acid) grafted graphene oxide (GO‐g‐PAA) was synthesized and incorporated into chemically crosslinked polyacrylamide (PAM) networks to obtain GO‐g‐PAA/PAM hydrogels, which were further treated with ascorbic acid solution at ambient temperature to give rGO‐g‐PAA/PAM hydrogels. The interfacial interaction between GO/rGO and hydrogel matrix was improved by reversible hydrogen bonds between the grafted PAA chains and PAM matrix. Consequently, both GO‐g‐PAA/PAM and rGO‐g‐PAA/PAM hydrogels exhibited improved tensile properties, excellent energy dissipation, and rapid self‐recovery. Thein situchemical reduction of GO‐g‐PAA in hydrogel matrix endowed rGO‐g‐PAA/PAM hydrogels with satisfactory electrical conductivity and obvious resistance change upon stretching. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48781.

Simultaneously improved strength and toughness in κ-carrageenan/polyacrylamide double network hydrogel via synergistic interaction

Hybrid double network (DN) hydrogels have been fabricated by combining a physically cross-linked κ-carrageenan network, where various cations were used as cross-linker, with a covalently cross-linked polyacrylamide (PAAm) network. Compared to monovalent K+ and divalent Ca2+ cations, the presence of K+/Ca2+ mixture cations produced a well interconnected porous structure due to the synergistic effect, which simultaneously improved the strength and toughness of the resulting DN hydrogel. A model has been proposed considering the dissociation asynchronism of double-helical aggregates, which well interpret the fracture process and toughening mechanism of the K+/Ca2+-cross-linked κ-carrageenan/PAAm DN hydrogel. Moreover, the synergistic effect of K+/Ca2+ mixture cations also improved the recovery efficiency at room temperature and self-healing ability of DN hydrogel. The strategy of synergistic interaction presented here provides an alternative view for the fabrication of hybrid DN hydrogels with desirable mechanical performance and functional property.

Reinforcing effect of graphene oxide on mechanical properties, self-healing performance and recoverability of double network hydrogel based on κ-carrageenan and polyacrylamide

Double network (DN) hydrogels are considered as one of the toughest group of materials with unique structural platforms which exhibit a combination of different mechanical properties into a single material. However, it is highly favorable yet challenging to design a hydrogel that combines required levels of mechanical properties as recovery efficiency, toughness, stretchability, and fatigue resistance with self-healing property for potential applications. Here we successfully synthesize a new kind of κ-carrageenan (κ-Car)/polyacrylamide (PAm)/graphene oxide (GO) nanocomposite double network (NCDN) hydrogel with desired mechanical properties and self-healing performance by using GO as the network crosslinking reinforcement. As compared to the DN hydrogel without GO nanosheets, the NCDN hydrogel containing an optimized amount of 0.3 wt% GO exhibited excellent mechanical properties (compression strength: 21.7 MPa, failure tensile stress: 0.64 MPa, failure tensile strain: 2398% and fracture energy: 5.7 MJ/m3), significant hysteresis (0.98 MJ/m3 at λ = 10), enhanced toughness recovery (~97.23% at 90 °C and ~67.07% at room temperature), and good fatigue resistance simultaneously. This could be explained in terms of the synergistic effect of the reversible interactions induced by bridging of the GO nanosheets between the κ-Car and PAm networks. This not only allowed an additional load transfer between the two networks but also had a great contribution to energy dissipation of the hydrogels through desorption of anchored polymer chains from the surface of the GO together with GO amplification effect on molecular orientation. Moreover, multi-reinforcing action of GO and thermo-reversible property of the κ-Car network enabled the NCDN hydrogel to exhibit self-healing capability, thermo-responsive property, and remarkable thermal stability at elevated temperature. The results of this work provided a great insight into understanding the correlation between microstructure and mechanical performance of hydrogels and extend hydrogel applications, especially for the stimuli-responsive load-bearing.

Combination of the Silver-Ethylene Interaction and 3D Printing To Develop Antibacterial Superporous Hydrogels for Wound Management.

Due to insufficient biomedical functions of hydrogels for wound management, the exploitation of available methods to expand the biomedical functions of hydrogels always becomes the cutting-edge research. Here, we report on the use of the silver-ethylene interaction and 3D printing technique to develop the antibacterial superporous polyacrylamide (PAM)/hydroxypropyl methylcellulose (HPMC) hydrogel dressings. Experiments demonstrated that the silver-ethylene interaction played significant roles in mediating the formation, dispersion, and cross-linking of silver nanoparticles (AgNPs) in the hydrogel matrix as well as the cross-linking of the PAM networks. At the same time, such organometallic complexes also controlled the release of AgNPs to balance the cytocompatibility and antibacterial activity of the AgNP-cross-linked hydrogels. On the other hand, the use of 3D printed templates and HPMC as the pore-making materials demonstrated could tailor hydrogels into 91.4% porosity and the formed pores into open channels, endowing hydrogels with rapid water uptake rate and 14 times dead-weight of uptake capacity. Furthermore, experiments showed that the regular large pores arisen from 3D printed templates could buffer the swelling of superporous hydrogel dressings, thus decreasing the detachment risk of dressings from wounds. In vivo experiments demonstrated that the AgNP-cross-linked superporous hydrogel dressings could promote the healing of the infected wounds and restrain scar tissue formation.

Water‐swellable, tough, and stretchable inorganic–organic sulfoaluminate cement/polyacrylamide double‐network hydrogel composites

ABSTRACTEffectively improving the mechanical properties of the hydrogel can greatly broaden its application range. The design concept of forming a double‐network structure by organic–inorganic hybridization can greatly enhance the mechanical properties of traditional hydrogels. Here, a series of organic–inorganic double‐network (OIDN) polyacrylamide/(sulfoaluminate cement) (PAM/SAC) composite gels by solution polymerization were synthesized at room temperature. The OIDN composite gels not only retain the characteristics of water swelling but also exhibit excellent tensile properties (stress and strain are 12 MPa and 2500%, respectively) and compressive strength (stress and strain are 65 MPa and 80%, respectively). In the preparation process, a brittle inorganic network of hydrated sulfoaluminate (hydra‐SAC) and a ductile network of polyacrylamide (PAM) were formed by the manner of interpenetrating. The phase composition and thermal stability of the OIDN composite gels were characterized and determined by FTIR, XRD, SEM, and TGA, respectively. The effect of SAC on swelling and mechanical performance of the OIDN composite gels was also investigated. The results show that the use of SAC hybrid hydrogels can effectively improve the mechanical strength, and the OIDN composite gels are expected to be a potential grouting and plugging functional material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47905.

Double-layer hydrogel with photoresponsive shape memory features for controllable catalysis

Abstract

Thermoresponsive double network hydrogels composed of poly(N-isopropylacrylamide) and polyacrylamide

Temperature response of double network (DN) hydrogels composed of thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) and hydrophilic polyacrylamide (PAAm) was studied by a combination of swelling and mechanical measurements, differential scanning calorimetry (DSC) and 1H nuclear magnetic resonance (NMR) spectroscopy. A series of DN hydrogels with tightly crosslinked first network of PNIPAAm and loosely crosslinked second network of PAAm was prepared. In the series, crosslinking density of the first PNIPAAm network was varied while crosslinking density of the second PAAm network was kept constant. Presence of the second hydrophilic PAAm component in DN hydrogels strongly affects their behavior. Both, degree of deswelling and specific enthalpy of demixing in DN hydrogels are strongly reduced relative to corresponding single network (SN) hydrogels. Presence of the second network shows a reinforcing effect on DN hydrogels. From NMR results it follows that mobility of a great part of PNIPAAm in DN hydrogels is significantly reduced due to agglomeration of PNIPAAm induced by formation of the second network already at low temperature. A certain portion of water confined in agglomerated structures and a slow exchange regime between ‘‘confined” and ‘‘free” water were established by NMR methods for all investigated SN and DN hydrogels.

Robust hydrogel of regenerated cellulose by chemical crosslinking coupled with polyacrylamide network

ABSTRACTRegenerated cellulose/polyacrylamide (RC/PAAm) double network (DN) hydrogels are composed of cellulose crosslinked by epichlorohydrin (ECH) and chemical‐crosslinked PAAm. The prepared RC/PAAm DN hydrogels present enhanced strength, good shape recovery property, excellent energy dissipation properties, decreased equilibrium water content, and low equilibrium swelling ratio (SR). The compressive strength and modulus of RC/PAAm hydrogel are about 4.3 and 11.5 times compared to that of RC hydrogel, respectively. Intriguingly, the chemical crosslinking between ECH and cellulose chains could increase the distance between cellulose chains. Consequently, the increasing molar ratio of ECH to glucose leads to larger SRs and decreased mechanical strength of the hydrogels. Additionally, higher PAAm contents lead to more densely crosslinked networks, and thus decreasing the SRs and improving the mechanical strength of the hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47811.

Synthesis and Physical Properties of Proton Conducting Polymer Electrolytes Comprising PAM Cross-Linked Flexible Spacers

The design of novel proton exchange membranes with high conductivity and better dimensional stability has become increasingly important due to the need for applications in different devices. The present work shows the acid-doped and crosslinked polyacrylamide (PAM) networks including flexible spaces. To this end PAM was modified with 1,4-butanediol diglycidyl ether (BG) to form PAM35BG and PAM50BG networks, which would afford more space for protonated solvents. The reaction of PAM with BG was monitored by FTIR and 13C CP-MAS NMR. The polymer electrolytes were produced by acid doping at several stoichiometric ratios with respect to the monomer repeat unit of a host polymer. The resulting materials exhibited better thermal, chemical, and electrochemical stabilities and had distinct Tg values. Additionally, the pores of the PAM-BG materials were filled with H3PO4 to get PAM35BG0.5H3PO4 and PAM50BG1.0H3PO4. The doping enhanced the proton conductivities of the membranes as high as 0.003 S/cm at 120 °C under an anhydrous atmosphere. The proton diffusion mechanism and the dielectric relaxation were further examined using the complex modulus formalism, M*.

A strong, tough, and osteoconductive hydroxyapatite mineralized polyacrylamide/dextran hydrogel for bone tissue regeneration

The design of hydrogels with adequate mechanical properties and excellent bioactivity, osteoconductivity, and capacity for osseointegration is essential to bone repair and regeneration. However, it is challenging to integrate all these properties into one bone scaffold. Herein, we developed a strong, tough, osteoconductive hydrogel by a facile one-step micellar copolymerization of acrylamide and urethacrylate dextran (Dex-U), followed by the in situ mineralization of hydroxyapatite (HAp) nanocrystals. We show that the soft, flexible, and hydrophobically associated polyacrylamide (PAAm) network is strengthened by the stiff crosslinked Dex-U phase, and that the mineralized HAp simultaneously improves the mechanical properties and osteoconductivity. The obtained HAp mineralized PAAm/Dex-U hydrogel (HAp-PADH) has extremely high compressive strength (6.5 MPa) and enhanced fracture resistance (over 2300 J m−2), as compared with pure PAAm hydrogels. In vitro, we show that the mineralized HAp layer promotes the adhesion and proliferation of osteoblasts, and effectively stimulates osteogenic differentiation. Through the in vivo evaluation of hydrogels in a femoral condyle defect rabbit model, we show regeneration of a highly mineralized bone tissue and direct bonding to the HAp-PADH interface. These findings confirm the excellent osteoconductivity and osseointegration ability of fabricated HAp-PADH. The present HAp-PADH, with its superior mechanical properties and excellent osteoconductivity, should have great potential for bone repair and regeneration. Statement of SignificanceWe developed a strong, tough, and osteoconductive hydrogel by a facile one-step micellar copolymerization of acrylamide and urethane methacrylate dextran (Dex-U), followed by the in situ mineralization of hydroxyapatite (HAp) nanocrystals. The hydrophobic micellar copolymerization and introduction of the stiff crosslinked Dex-U phase endowed the soft polyacrylamide (PAAm) network with enhanced strength and toughness. The in situ mineralized HAp nanocrystals on the hydrogels further improved the mechanical properties of the hydrogels and promoted osteogenic differentiation of cells. Mechanical tests together with in vitro and in vivo evaluations confirmed that the HAp mineralized PAAm/Dex-U hydrogel (HAp-PADH) achieved a combination of superior mechanical properties and excellent osseointegration, and thus may offer a promising candidate for bone repair and regeneration.

Tearing a hydrogel of complex rheology

Tough hydrogels of many chemical compositions are being discovered, and are opening new applications in medicine and engineering. To aid this rapid and worldwide development, it is urgent to study these hydrogels at the interface between mechanics and chemistry. A tough hydrogel often deforms inelastically over a large volume of the sample used in a fracture experiment. The rheology of the hydrogel depends on chemistry, and is usually complex, which complicates the crack behavior. This paper studies a hydrogel that has two interpenetrating networks: a polyacrylamide network of covalent crosslinks, and an alginate network of ionic (calcium) crosslinks. When the hydrogel is stretched, the polyacrylamide network remains intact, but the alginate network partially unzips. We tear a thin layer of the hydrogel at speed v and measure the energy release rate G. The v–G curve depends on the thickness of the hydrogel for thin hydrogels, and is independent of the thickness of the hydrogel for thick hydrogels. The energy release rate approaches a threshold, below which the tear speed vanishes. The threshold depends on the concentration of calcium. The threshold may also depend on the thickness when the thickness is comparable to the size of inelastic zone. The threshold determined by slow tear differs from the threshold determined by cyclic fatigue. We discuss these experimental findings in terms of the mechanics of tear and the chemistry of the hydrogel.

Fabrication of 3D PDMS Microchannels of Adjustable Cross-Sections via Versatile Gel Templates.

Flexible gel fibers with high stretchability were synthesized from physically cross-linked agar and covalently cross-linked polyacrylamide networks. Such gel material can withstand the temperature required for thermal curing of polydimethylsiloxane (PDMS), when the water in the gel was partially replaced with ethylene glycol. This gel template supported thermal replica molding of PDMS to produce high quality microchannels. Microchannels with different cross sections and representative 3D structures, including bifurcating junction, helical and weave networks, were smoothly fabricated, based on the versatile manipulation of gel templates. This gel material was confirmed as a flexible and reliable template in fabricating 3D microfluidic channels for potential devices.

Thermo-modulated Hela cell release from an elastic and biocompatible hydrogel.

Cell growth and release from the hydrogel scaffolds are critical steps in cell culture and cell therapies. Herein a double network hydrogel with one thermosensitive P(AEtMA-Cl-DEAEA) network and the other polyacrylamide network is reported. The diad hydrogel is elastic and maintains its structural integrity under large deformation. BSA is adsorbed onto the hydrogel at body temperature and subsequently released from the hydrogel at lower temperature. Hela cells proliferate on the hydrogel scaffolds at 37°C. When the scaffold is incubated at low temperature (20°C), 32.6% ± 6.4% of its population are detached from the scaffolds. The detached cells remain active in cell culture. This hydrogel with excellent mechanical properties and unique biological function has promising biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1786-1791, 2019.

Synthesis, structure and mechanical properties of nanocomposites based on exfoliated nano magnesium silicate crystal and poly(acrylamide)

In this study, hydrolyzed polyacrylamide based nanocomposite (HPAM-NC) hydrogels crosslinked by chromium (III) acetate, was synthesized using free radical polymerization. The introduction of magnesium silicate nanocrystals (MSNCs) into the hydrolyzed polyacrylamide (HPAM) network endows the system with enhanced mechanical properties. The successful formation and crystalline behavior of HPAM-NC hydrogels was verified by Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Diffraction (XRD) analyses. Field-Emission Scanning Electron Microscopy (FESEM) and rheology tests showed that the morphology and mechanical properties of HPAM-NC hydrogels were strongly influenced by different content of parameters including concentration of copolymer, nanoparticle and cross-linker. The results showed that this nanocomposite hydrogel is a moldable material so it can expand its application as value-added product.

RSM-CCD optimized In-air synthesis of photocatalytic nanocomposite: Application in removal-degradation of toxic brilliant blue

The present research work describes the synthesis of a nanocomposite hydrogel [BFO/Mr-cl-poly(AAm)-IPN-poly(AA)] from nano bismuth iron oxide (BFO) synergistically coupled with interpenetrating network (IPN: Mr-cl-poly(AAm)-IPN-poly(AA)) of acrylic acid (AA) created within crosslinked network of a semi-IPN (Mr-cl-poly(AAm)). Semi-IPN was previously synthesized from N, N′-methylene bisacrylamide (MBA) crosslinked (cl) network of polyacrylamide (poly(AAm)) grafted onto aqueous extract of Commiphora mukul (Mr). The synthesized sample was efficient in removal-degradation of Coomassie brilliant blue G-250 (CBB) dye. Nanocomposite (NC) was magnetic as well as photocatalytic. Initially, optimization of the reaction parameters was carried out using Response Surface Methodology (RSM) design. Significant variables were accessed using Minimum Resolution V design and further optimized conditions were evaluated with central composite design (CCD). Semi-IPN showed maximum % swelling of 833.8% showing interdependence of time-temperature and solvent-crosslinker concentration. IPN synthesized gave maximum swelling of 285.8%. On insertion of BFO nanoparticles, the NC synthesized could remove-degrade a maximum of 90.4% dye in sunlight and 88.6% in UV–visible light under optimized parameters: 600 mg NC dose, 10 ppm initial dye concentration, pH 7.0, removal and degradation time 25 h and 4 h, respectively. The whole process showed second order kinetics with Elovich model criteria and followed Langmuir adsorption isotherm. GC-MS analysis gave low molecular weight products as an evidence of degradation process. Also, the NC synthesized can be recycled for industrial use.

Fabrication of Activity-Reporting Glucose Oxidase Nanocapsules with Oxygen-Independent Fluorescence Variation.

Glucose oxidase (GOx) has seen large-scale technological applications, and the determinations of its activity that is directly related to the enzymatic functions are extremely important. However, conventional methods to analyze the enzymatic activity involving high oxygen dependency and indirect redox reactions are usually tedious and restricted in complicated environments. For analyzing enzymatic activity by direct detection of the electron signals from the active centers, mediators are often used for facilitating the electron transfer. Differing from common methods of preparing electron mediators-contained GOx composites, a strategy aiming at remolding of the enzyme itself has been proposed in this work. Cofactor-like molecule 2'-diallyamino-ethyl flavin (DAA-flavin) derived from riboflavin is synthesized and incorporated as cross-linker into the polyacrylamide (PAAm) network around GOx surface by in situ polymerization to obtain enzyme nanocapsules termed as GOx@Fla-c-PAAm. The peripheral polymer shell confines the orientation of GOx and prevents it from denaturing, whereas incorporated DAA-flavin can replace the oxygen as an alternative electron acceptor to interact with the active centers of GOx in the presence of the substrate, thus giving the nanocapsules oxygen-independent characteristics. The introduced unlimited cofactor-like molecules endow the nanocapsules redox-related fluorescence, and the intensity variation is closely correlated with the enzymatic activity. There is a high goodness of fitting ( R2 ∼ 0.990) between the slope of linear fluorescence-time plots and enzymatic activity, thereby making the nanocapsules a reliable activity-reporting enzymatic nanosystem with oxygen-independent fluorescence variation for further extended potential application in biofuel cells and biosensors.

Interpenetrated Networks of Nanocellulose and Polyacrylamide with Excellent Mechanical and Absorptive Properties

AbstractComposites based on interpenetrating networks (IPNs) of cellulose nanofibril (CNF) aerogels and polyacrylamide are prepared and exhibit robust mechanical, water retaining, and re‐swelling capacities. Furthermore, their swelling behavior is not affected by an increased ionic strength of the aqueous phase. These unprecedented IPNs combine the water retaining capacity of the polyacrylamide with the mechanical strength provided by the CNF aerogel template. The CNF aerogel/polyacrylamide composites exhibit a compressive stress at break greater than 250% compared with a neat polyacrylamide hydrogel. Furthermore, the composites retain their wet compression properties after drying and re‐swelling, whereas the neat polyacrylamide hydrogels fail at a significantly lower stress and strain after drying and re‐swelling. These composite materials highlight the potential of CNF aerogels to strengthen the mechanical properties and reduce the number of fracture defects during the drying and re‐swelling of a hydrogel. These composites show the potential of being optimized for a plethora of applications, especially in the hygiene field and for biomedical devices.