Synthesis of poly(N,N‐diethylacrylamide‐co‐acrylic acid) hydrogels with fast response rate in NaCl medium

A series of thermo‐ and pH‐sensitive poly (N,N‐diethylacrylamide‐co‐acrylic acid) (P(DEA‐co‐AA)) hydrogels were prepared in NaCl aqueous solutions with different concentrations. Swelling and deswelling studies showed that in comparison with conventional P(DEA‐co‐AA) hydrogels (prepared in distilled water), the P(DEA‐co‐AA) hydrogels thus prepared had almost the same volume phase transition temperature (VPTT), but exhibited much faster response rates as the temperature was raised above their VPTT. Besides, the hydrogels prepared by this method had faster response rates in low pH buffer solutions, and the response rates increased with the increased concentration of the NaCl solutions used during the polymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and pH dual‐responsive hydrogels based on semi‐interpenetrating network of poly(N‐isopropylacrylamide) and collagen nanofibrils

Hydrogels with environment‐sensitive properties have great potential applications in the controlled drug release field. In this paper, hybrid hydrogels with semi‐interpenetrating polymer networks (semi‐IPNs), composed of poly(N‐isopropylacrylamide) (PNIPAM) as the thermo‐sensitive component by in situ polymerization and self‐assembled collagen nanofibrils as the pH‐sensitive framework, were prepared for controlled release of methyl violet as a model drug. From Fourier transform infrared spectroscopy and scanning electron microscopy, it was indicated that the crosslinking of PNIPAM in the presence of collagen nanofibrils led to the formation of semi‐IPNs with homogeneous porous structure, and the semi‐IPNs showed improved thermal stability and elastic properties compared with the native collagen as determined using differential scanning calorimetry and rheologic measurements. Furthermore, the semi‐IPNs possessed swelling behaviors quite different from those of neat collagen or PNIPAM hydrogel under various pH values and temperatures. Correspondingly, as expected, the drug release behavior in vitro for semi‐IPNs performed variously compared with that for single‐component semi‐IPNs, which revealed the tunable performance of semi‐IPNs for release ability. Finally the thermo‐ and pH‐responsive mechanism of the semi‐IPNs was illuminated to provide guidance for the application of the thermo‐ and pH‐sensitive collagen‐based hybrid hydrogels in controlled drug delivery systems. © 2019 Society of Chemical Industry     

Thermo‐ and pH‐sensitive poly(vinylmethyl ether)/carboxymethylchitosan hydrogels crosslinked using electron beam irradiation or using glutaraldehyde as a crosslinker

BACKGROUND: Stimuli‐sensitive or intelligent hydrogels have been investigated for many biomedical and pharmaceutical applications. Those hydrogels with dual sensitivity will have more extensive potential applications. The aim of the work presented was to prepare a series of thermo‐ and pH‐sensitive hydrogels based on poly(vinylmethyl ether) (PVME) and carboxymethylchitosan (CMCS). The hydrogels were crosslinked using electron beam irradiation (EB) or using glutaraldehyde (GA) as a crosslinker at room temperature. RESULTS: The structures of the PVME/CMCS hydrogels obtained using the two crosslinking methods are proposed. The effects of component polymer ratio, GA content, irradiation dose, temperature and pH on the swelling behavior of the PVME/CMCS hydrogels were studied. There is a sharp decrease in the swelling ratios when the temperature increases from 25 to 37 °C. At low pH and also at high pH, the hydrogels have a higher swelling ratio; however, deswelling occurs evidently at a pH of around 3. CONCLUSION: The study shows that both EB and GA crosslinked hydrogels are thermo‐ and pH‐ sensitive, simultaneously. Thus, they may be potential candidates for both thermo‐ and pH‐sensitive applications. Copyright © 2009 Society of Chemical Industry     

Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent. RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy. CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry     

pH‐ and temperature‐responsive IPN hydrogels based on soy protein and poly(N‐isopropylacrylamide‐co‐sodium acrylate)

pH‐ and temperature‐responsive interpenetrating polymer network (IPN) hydrogels based on soy protein and poly(N‐isopropylacrylamide‐co‐sodium acrylate) were successfully prepared. The structure and properties of the hydrogels were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analyzer. The equilibrium and dynamic swelling/deswelling behaviors and the drug release properties of the hydrogels responding to pH and/or temperature were also studied in detail. The hydrogels have the porous honeycomb structures, good miscibility and thermal stability, and good pH‐ and temperature‐responsivity. The volume phase transition temperature of the hydrogels is ca. 40°C. Changing the soy protein or crosslinker content could be used to control the swelling behavior and water retention, and the hydrogels have the fastest deswelling rate in pH 1.2 buffer solutions at 45°C. Bovine serum albumin release from the hydrogels has the good pH and temperature dependence. The results show that the proposed IPN hydrogels may have potential applications in the field of biomedical materials such as in drug delivery systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39781.     

Effects of microgel content and n‐methylolacrylamide on the properties of microgel composite hydrogels prepared by postcrosslinking method

Acrylamide co 2‐acrylamido‐2‐methylpropane sulfonic acid microgel composite (MC) hydrogels were prepared by heating MC polymer with 50% water content. Crosslinking reaction occurred in the heating process and reactive microgels with hydroxymethyl groups introduced by N‐methylolacrylamide (NMA) were used as postcrosslinkers. Microgel swollen size is influenced by NMA content. Both microgel and its NMA content affect MC hydrogel properties, which relates to the crosslinking chain length and the crosslinking density. The tensile strength of MC hydrogels increases and their elongation decreases as the microgel content increases from 0.1 to 0.5 g. Both the tensile strength and the elongation decrease as the microgel content further increases from 0.5 to 1.1 g. The MC hydrogel tensile strength increases and the elongation decreases as the NMA content of microgels increases from 5.0 to 14.8%. However, they both decrease when the NMA content of microgels exceeds 14.8%. Although the crosslinking chains υ calculated from tensile stress–strain curves were very high, MC hydrogels were elastic and had the highest tensile strength of 127 kPa and considerably moderate elongation of 427%. Their excellent mechanical properties attributed to their unique structure crosslinked by microgel particles. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Rapid pH‐dependent phase transition and elasticity of stimuli‐responsive cationic poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli‐responsive hydrogels prepared from poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH‐dependent swelling and elasticity, a series of cationic hydrogels based on N,N‐dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH‐dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH‐dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10‐ to 40‐fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry     

Thermally crosslinked anionic hydrogels composed of poly(vinyl alcohol) and poly(γ‐glutamic acid): Preparation,characterization, and drug permeation behavior

pH‐sensitive anionic hydrogels composed of poly(vinyl alcohol) (PVA) and poly(γ‐glutamic acid) (γ‐PGA) were prepared by the freeze drying method and thermally crosslinked to suppress hydrogel deformation in water. The physical properties, swelling, and drug‐diffusion behaviors were characterized for the hydrogels. In the equilibrium swelling study, PVA/γ‐PGA hydrogels shrunk in pH regions below the pK_a (2.27) of γ‐PGA, whereas they swelled above the pK_a. In the drug‐diffusion study, the drug permeation rates of the PVA/γ‐PGA hydrogels were directly proportional to their swelling behaviors. The cytocompatibility test showed no cytotoxicity of the PVA/γ‐PGA hydrogels for the 3T3 fibroblast cell lines. The results of these studies suggest that hydrogels prepared from PVA and γ‐PGA could be used as orally administrable drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of poly(acrylic acid)–Fe3+/gelatin/poly(vinyl alcohol) triple‐network supramolecular hydrogels with high toughness,high strength and self‐healing properties

Hydrogels with good mechanical and self‐healing properties are of great importance for various applications. Poly(acrylic acid)–Fe³⁺/gelatin/poly(vinyl alcohol) (PAA‐Fe³⁺/Gelatin/PVA) triple‐network supramolecular hydrogels were synthesized by a simple one‐pot method of copolymerization, cooling and freezing/thawing. The PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogels exhibit superior toughness, strength and recovery capacity compared to single‐ and double‐network hydrogels. The mechanical properties of the synthesized hydrogels could be tailored by adjusting the compositions. The PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogel with 0.20 mmol Fe³⁺, 3% gelatin and 15% PVA could achieve good mechanical properties, the tensile strength and elongation at break being 239.6 kPa and 12.8 mm mm^?1, respectively, and the compression strength reaching 16.7 MPa under a deformation of about 91.5%. The synthesized PAA‐Fe³⁺/Gelatin/PVA triple‐network hydrogels have good self‐healing properties owing to metal coordination between Fe³⁺ and carboxylic groups, hydrogen bonding between the gelatin chains and hydrogen bonding between the PVA chains. Healed PAA‐Fe³⁺(0.20)/Gelatin3%/PVA15% triple‐network hydrogels sustain a tensile strength of up to 231.4 kPa, which is around 96.6% of the tensile strength of the original samples. Therefore, the synthesized triple‐network supramolecular hydrogels would provide a new strategy for gel research and expand the potential for their application. © 2019 Society of Chemical Industry     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Hollow poly(N‐isopropylacrylamide)‐co‐poly(acrylic acid) microgels with high loading capacity for drugs

A convenient approach has been developed for the preparation of microsize hydrogels composed of crosslinked poly(acrylic acid) (PAA) and poly(N‐isopropylacrylamide) (PNIPAm). First, semi‐interpenetration polymer networks of hydropropylcellulose (HPC) and PNIPAm‐co‐PAA copolymer are formed through the copolymerization and crosslinking of monomer acrylic acid and N‐isopropylacrylamide in HPC aqueous solution. After the selective removal of HPC from networks due to ionization of PAA units and disruption of hydrogen bonding with increasing pH, PNIPAm‐co‐PAA microgels are obtained, whose volume is confirmed to be responsive to both temperature and pH. Doxorubicin hydrochloride (Dox) can be encapsulated in PNIPAm‐co‐PAA microgels with high drug loading driven by the electrostatic interaction, and a sustained‐release characteristic of Dox from the microgels is observed under physiological pH value and temperature. In vitro cell experiments, the drug‐loaded microgels can be taken up by LoVo cells and release their payload in cell cytoplasm without loss of drug efficacy. This indicates that PNIPAm‐co‐PAA microgels might be a potential drug delivery carriers especially for water‐soluble or polypeptide drugs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Multi‐responsive hydrogels based on N‐isopropylacrylamide and sodium alginate

Hydrogels consisting of sodium alginate and N‐isopropylacrylamide covalently crosslinked with N,N′‐methylenebisacrylamide were prepared. The mixed‐interpenetrated networks obtained were characterized using elemental analysis, Fourier transform infrared and Raman spectroscopy, swelling measurements and environmental scanning electron microscopy. The thermo‐ and pH‐responsive properties of these hydrogels were evidenced by their swelling behaviour, which depended also on the amount of crosslinking agent and hydrogel composition. Copyright © 2010 Society of Chemical Industry     

Volume phase transition temperature tuning and investigation of the swelling–deswelling oscillation of responsive microgels

Temperature‐ and pH‐responsive polyampholyte microgels were prepared by an aqueous dispersion polymerization. Scanning electron microscopy and dynamic laser light scattering (DLS) were employed for the characterization of the morphology and size distribution of the microgels. Temperature‐ and pH‐dependent volume phase transitions of the polyampholyte microgels were also investigated using DLS. The microgels showed an interesting swelling–deswelling oscillatory behavior when the pH was varied. An interpretation was proposed for the phenomenon in terms of Coulombic repulsion and hydrophobic hydration. It is of great interest that the volume phase transition temperature (VPTT) of the polyampholyte microgels can be varied by changing the pH. This could be a convenient approach for tuning the VPTT of N‐isopropylacrylamide‐based hydrogels. Copyright © 2007 Society of Chemical Industry     

Characterization of degraded hydrogels based on poly(vinyl alcohol) grafted with poly(lactide‐co‐glycolide)

Poly(vinyl alcohol) (PVA) grafted with poly(lactide‐co‐glycolide) and cross‐linked as a material of increased hydrophobicity relative to PVA was produced. The properties were examined with respect to the mass loss, water uptake, hydrophilicity, and mechanical characteristics upon hydrolytical degradation. The hydrogels investigated display water uptake increasing with degradation time because of increasing hydrophilicity. The mass loss amounts up to 15% after eight weeks of degradation. The mechanical properties of the hydrogels are within the range of those of natural tissue, the E modulus is 18 MPa, or even 100–200 MPa, depending on the structure of material. The mechanical characteristic and their dependence degradation show the most recognizable correlation with the chemical structure. Studies of the topography of degraded samples (scanning electron microscopy) and IR measurements demonstrate the degradation to occur at slow rate due to the high degree of grafting. The mass loss is rather low and a bulk degradation mechanism takes place. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of cetirizine‐containing,pH‐sensitive acrylic acid/poly(vinyl alcohol) hydrogels

In this study, interpenetrated acrylic acid (AA)/poly(vinyl alcohol) (PVA) hydrogels were prepared by free‐radical polymerization with N,N‐methylene bisacrylamide (MBAAm) as a crosslinker. The basic structural parameters, such as the molecular weight between crosslinks, volume interaction parameter, number of crosslinks, Flory–Huggins solvent interaction parameter, and diffusion coefficient, were calculated. Cetirizine dihydrochloride was loaded as a model drug in selected samples. The prepared hydrogels were evaluated for swelling, sol–gel fraction, and porosity. The swelling of the AA/PVA hydrogels was found to be directly proportional to the pH, that is, 1.2–7.5, depending on composition. The percentage of cetirizine hydrochloride was found to be directly proportional to the buffer pH and was at its maximum at pH 7.5, that is, 90–95%, and its lowest at pH 1.2, that is, 20–30%. The gel fraction increased with increasing concentration of AA and MBAAm, whereas the porosity showed the same response with AA, but an inverse relationship was observed with MBAAm. The drug‐release data were fitted into various kinetics models, including the zero‐order, first‐order, Higuchi, and Peppas models, which showed non‐Fickian diffusion. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, and no interaction was found among the polymer ratio and the drug. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43407.     

Synergistic effect of graphene oxide and sodium carboxymethylcellulose on the properties of poly(vinyl alcohol) hydrogels

Hydrogels are a promising candidate for applications in biomedicine and bioengineering, but their mechanical properties often restrict their applications. To improve the mechanical performance of poly(vinyl alcohol) (PVA) hydrogels, we introduced sodium carboxymethylcellulose (CMC), and graphene oxide (GO) into them. We prepared a series of composite hydrogels composed of PVA, CMC, and GO with epichlorohydrin as a chemical crosslinker. We used Fourier transform infrared spectroscopy and X-ray diffraction to characterize the chemical structures of GO and the hydrogel. The dynamic mechanical analysis results show the synergistic enhancement effects of CMC and GO on the PVA hydrogel. The swelling process of the hydrogels also fit well with the second-order kinetic equation. Scanning electron microscopy results suggest that the neat mesh structure facilitated superior mechanical properties in the hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47644.     

Effects of end groups on the thermal response of poly(N‐isopropylacrylamide) microgels

Poly(N‐isopropylacrylamide) (PNIPAM) microgels were prepared through soap‐free emulsion polymerization using 2, 2′‐ azobisobutyronitrile and potassium persulfate as initiator respectively. The thermal response of microgels was researched by measuring the transmittance and the hydrodynamic diameter of the microgels at different temperatures. The result shows that the different structure of the end groups of polymer that come from residues of initiator result in the different thermal response of PNIPAM microgels. The LCST (lower critical solution temperature) of AIBN‐initiator microgels is 5°C lower than that of the KPS‐initiator microgels, whereas the AIBN‐initiated PNIPAM microgels have better thermal response sensitivity. The scanning electron microscope characterization shows that the morphology of AIBN‐initiated PNIPAM microgels is more regular than that of KPS‐initiated. Furthermore, the T_g of the microgels was measured by differential scanning calorimeter and the result indicates that the end groups influences the T_g of microgels severely. This work demonstrated that the hydrophobic end group coming from initiators can decreases the LCST of PNIPAM microgels and increases the thermal response sensitivity, which providing a newly simple but effective method to regulate the thermal response of PNIPAM microgels. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1164‐1171, 2013     

A novel fabrication method of temperature-responsive poly(acrylamide) composite hydrogel with high mechanical strength

High strength, stimuli-responsive poly(acrylamide) composite hydrogels (PAAm CH gels) were prepared by grafting polymerization of acrylamide (AAm) onto temperature-sensitive core–shell microgels. These microgels, composing of poly(N-isopropylacrylamide) as core and polyvinylamine (PVAm) as shell, were used as both initiator and crosslinker to form a robust three-dimensional network via bonding the poly(acrylamide) (PAAm) backbone. The CH gels exhibited a remarkably rapid shrinking rate and transmittance switch in response to the environmental temperature change, which the conventional chemically cross-linking PAAm hydrogels (PAAm OR) were short of. Even compared to the bulk PNIPAAm hydrogels (PNIPAAm OR) crosslinked with N,N′-methylenebisacrylamide (MBA), the CH gels were featured with faster responsive rate, which could be attributed to the formation of interconnected water transportation channels between the microspheres and PAAm gel matrix due to the fast shrinking of microgels. Moreover, the effects of microgel species and content on swelling and mechanical properties of CH gels were also systematically investigated. The results elaborated that the CH gels could be compressed almost 99% without breaking and completely recovered their original shape when the stress was removed. And the optimized compressive strength of CH gels could be up to 21.94 MPa. Based on the analysis of CH gel mechanical properties, the influence of microsphere content on effective network chains density of CH gels was discussed through rheology measurements. Finally, the essential reinforcement on mechanical properties was mainly contributed to the homogeneous microstructure of hydrogel network and the energy dissipation mechanism of microgels in gel matrix.     

Self‐healing hydrogel of poly(vinyl alcohol)/graphite oxide with pH‐sensitive and enhanced thermal properties

Supramolecular hydrogel is a fascinating polymeric material composed of three‐dimensional noncovalent networks with many outstanding properties, especially reversible relevant performances. A self‐healing supramolecular hydrogel of poly(vinyl alcohol)/graphite oxide, with reversible pH responsiveness and good thermal stability, was prepared. The morphology, functional group changes, swelling performance, thermal stability, rheological performance, and self‐healing property of the PVA/GO hydrogel were investigated. A probable mechanism between the components and potential applications were also examined in our study. The experimental results show that the PVA/GO hydrogel was not only self‐healable without external stimulus or addition of any healing agents, but also pH sensitive and with good thermal stability. Green ingredients (PVA and GO) and a simple synthesis method (a freezing/thawing treatment) may pose little threat to the environment and also promote the production of such hydrogels. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46143.     

Carboxymethyl cellulose reinforced poly(vinyl alcohol) with trimethylol melamine as a chemical crosslinker

In this investigation, carboxymethyl cellulose (CMC)‐reinforced poly(vinyl alcohol) (PVA) were prepared with trimethylol melamine as a chemical crosslinker. The structure and property of hydrogels were measured by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), texture analysis, and rheometry. The FTIR spectra demonstrated that the etherification reaction successfully occurred in the PVA–CMC hydrogels, and the SEM figures exhibited the homogeneous porous structure of the CMC–PVA hydrogels. The compression strength of the PVA–CMC hydrogels was 15 times higher than that of the PVA hydrogels. Moreover, the PVA–CMC hydrogels exhibited a higher storage modulus than that of the PVA hydrogels; this illustrated better elasticity for the PVA–CMC hydrogels. As a result, CMC‐modified PVA hydrogels with high mechanical behavior will broaden the potential applications of hydrogels, such as in wound dressings, facial masks, and skin‐protection layers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44590.