Characterization and physiochemical studies of crosslinked thiolated polyvinyl alcohol hydrogels

Modification and crosslinking of polyvinyl alcohol (PVA) by thiolation using thioglycolic acid (TGlA) and various crosslinkers were carried out. The crosslinked thiolated PVA (TPVA) hydrogels were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infra red spectroscopy coupled with thermal analysis (TG-FTIR) techniques. The crosslinking of the resultant material was carried out using three crosslinker sodium trimetaphosphate (STMP), glyoxal and boric acid. The influence of esterification and crosslinking on the physical and chemical properties of the material was studied. XRD showed that after crosslinking the crystallinity of TPVA hydrogels decreased. These results were further substantiated by DSC observations. The thermal stability of the TPVA hydrogels is enhanced. A significant variation in the initial decomposition temperature was observed with respect to different STMP crosslinked samples having varying TGlA concentration and different crosslinkers. The coupled TG-FTIR studies of crosslinked samples at different temperatures show that the evolution of sulfur-containing gases (carbon disulfide and carbon monosulfide) is being prominent for this material.     

Studies on Glutaraldehyde Crosslinked Chitosan Hydrogel Properties for Drug Delivery Systems

Chitosan was crosslinked with different amount of glutaraldehyde to prepare appropriate hydrogels to be used as drug delivery system. The swelling behavior of freeze-dried hydrogels in aqueous media at different temperature and pHs has been examined. The swelling, porosity and biocompatibility behavior of samples were investigated to check effects of polymer/polymer and polymer/drug interactions on these system characteristics. Obtained experimental results illustrates that with increasing crosslinking agent from 0.068 to 0.30, swelling of the prepared samples degrees from 1200% to 600% and pore diameters change from 100 to 500 µm. To investigate systems biocompatibility in gastric conditions, effects of crosslinker concentration on the pepsin enzyme activity have been studied using variation of relative viscosity of the system. Presented results also show that with increasing crosslinker agent concentration activity of enzyme reduces considerably and so crosslinker molar ratio to amine functional groups of chitosan must be less than 0.2.     

Effect of crosslinkers on size and temperature sensitivity of poly(N-isopropylacrylamide) microgels

In this work, we study the effect of crosslinkers on the size and swelling properties of temperature sensitive N-isopropylacrylamide (NIPAAm) microgels produced by dispersion polymerization. The crosslinkers studied were N,N′-methylenebisacrylamide (MBA), ethylene glycol dimethacrylate (EGDMA) an 3,9-divinyl-2,4,8,10-tetra-oxaspiro[5.5] undecane (DVA). The type of crosslinker had a major impact on the size and swelling behavior, although the proportion of crosslinker used in each case was low (maximum 5 mol%). The effect can be related to the hydrophilic/hydrophobic characteristics of the crosslinkers. DVA produces smaller hydrogels with reduced swelling ratio, MBA produces bigger microgels with higher swelling ratio, while EGDMA results in an intermediate behavior. With increasing amount of crosslinker used in the synthesis, the extent of the swelling ratio decreases for DVA and EGDMA crosslinked microgels, while increases for MBA crosslinked microgels. There is also a slight effect on the critical transition temperature (T _c) of the microgels from 30 °C (DVA) to 34 °C (MBA) as observed in copolymers of NIPAAm with hydrophilic or hydrophobic comonomers.     

Fast responsive poly(acrylic acid‐co‐N‐isopropyl acrylamide) hydrogels based on new crosslinker

Novel dual temperature‐ and pH‐sensitive poly(acrylic acid‐co‐N‐isopropylacrylamide), AA/NIPAAm, hydrogels were successfully prepared by chemical crosslinking with crosslinkers. Copolymers of AA/NIPAAm were crosslinked in the presence of different mol % of N,N‐methylene bisacrylamide (MBA) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked AA/NIPAAm series are evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MBA concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. The prepared MAAm type AA/NIPAAm hydrogels exhibited a more rapid deswelling rate than MBA type AA/NIPAAm hydrogels in ultra pure water in response to abrupt changes from 20°C to 50°C. The results of this study provide valuable information regarding the development of dual stimuli‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dual‐Crosslinked Human Serum Albumin‐Polymer Hydrogels for Affinity‐Based Drug Delivery

A dual‐crosslinked in situ gelling drug delivery scaffold based on dextran (DEX), thiolated serum albumin, and poly(ethylene glycol) (PEG) is presented. Dextran–vinyl sulfone conjugates with varied molecular weight and degrees of substitution are synthesized by controlling the reaction time and temperature with divinyl sulfone. Dextran–human serum albumin (sHSA) hydrogels are prepared using a thiol‐vinyl sulfone Michael addition reaction with thiolated albumin as the crosslinker. Poly(ethylene glycol) dithiol is added as a third component to the crosslinked dextran–human serum albumin hydrogel to facilitate additional crosslinking, and reduce gelation time, while modulating the physicochemical properties of the Dex–sHSA–PEG network. The onset of gelation of the modular three‐component dual‐crosslinked hydrogel network ranges from 45 min to 1.5 h depending on gel constituent concentrations and the gelation temperature (25 or 37 °C). All gels remain stable for over a 25 d period under physiological conditions. In vitro drug release assays show that dual‐crosslinked Dex–sHSA–PEG hydrogels can deliver doxorubicin in a sustained manner over 7 d. Finally, a Tetrazolium‐based assay shows the biocompatible nature of the Dex–sHSA–PEG hydrogels and capacity to deliver doxorubicin successfully to MCF‐7 breast cancer cells.     

Preparation and Evaluation of Functionalized Poly(vinyl alcohol)-Based Hydrogels for Arsenite Removal from Water

Cross-linked thiolated polyvinyl alcohol (TPVA) hydrogels were synthesized by a two-step functionalization process, i.e., esterification and cross-linking of polyvinyl alcohol (PVA) hydrogel. PVA was esterified with thioglycolic acid and was subsequently cross-linked with sodium trimeta phosphate (STMP). The cross-linked TPVA was utilized as chelating material for arsenite As(III) binding. Atomic absorption spectroscopy (AAS) was used to detect and monitor As(III) concentration in water. Various parameters affecting the arsenic removal process were investigated. It was observed that the cross-linked TPVA behaves as an excellent chelating material for As(III). A maximum removal efficiency of 94% was achieved under our experimental conditions. To investigate the interaction of As(III) with functional groups before and after the removal process, attenuated total reflectance-infrared (ATR) was used. The microanalysis of elements present in samples was carried out by energy dispersive X-ray microanalysis. The material showed good regeneration ability along with antimicrobial activity against both bacterial and fungal strains.     

Swelling Properties of Chemically Crosslinked Poly(acrylamide-co-maleic acid) Hydrogels

ABSTRACT

Chemically crosslinked poly(acrylamide-co-maleic acid) [poly(AAm-co-MA)] hydrogels were prepared by simultaneous free radical copolymerization of acrylamide (AAm) with maleic acid (MA) in presence of di or tri functional crosslinking agents using ammonium persulfate-N,N,N′,N′-tetramethylethylenediamine (APS-TMEDA) redox-initiating system. The poly(AAm-co-MA) hydrogels formation was confirmed by IR studies. The influence of crosslinkers such as N,N′-methylene-bis-acrylamide (MBA) and 2,4,6-triallyloxy-1,3,5-triazine (TATA) on swelling/de-swelling characteristics were studied in detail for poly(AAm-co-MA) hydrogels containing different amounts of maleic acid. The present investigation also deals with the influence of concentration of crosslinker and initiator on the swelling behavior of poly(AAM-co-MA) hydrogels. The effect of various salts on swelling capacity was studied. In addition, the effect of simulated biological fluids and pH solutions on the swelling of hydrogels was also studied in detail.     

Super-tough hydrogels using ionically crosslinked networks

Alginate and polyacrylamide hydrogels were produced by a facile one-pot method with varied ionic crosslinkers in this article. These hydrogels display outstanding mechanical properties compared to the pristine polyacrylamide (PAAm) hydrogels. The alginate network is ionically crosslinked by multivalent cation, whereas N,N′-methylenebis (acrylamide) (MBAA) is used as covalent crosslinker for the PAAm network. Particularly, the obtained hydrogels by using trivalent cations (Fe³⁺ and Al³⁺) as crosslinkers are much stronger than that of using divalent cations (Ca²⁺ and Ba²⁺) as crosslinkers. In addition, with increasing concentration of cations, the compressive properties of gels are improved, whereas when the concentration is higher than 0.3 M, the compressive properties of gels are damaged due to mono-bindings. Interestingly, the hydrogels with higher chemical crosslinker concentration depicts better mechanical properties than those hydrogels with lower chemical crosslinker, which is different from that of common double network hydrogels. These hydrogels with excellent mechanical properties are promising candidates for biomedical application like load-bearing tissues. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48182.     

In situ crosslinked hydrogels formed using Cu(I)‐free Huisgen cycloaddition reaction

BACKGROUND: ‘Click’ chemistry, or the 1,3‐dipolar cycloaddition of organic azides with alkynes, has been evaluated for many biomedical purposes; however, its utility in crosslinking hydrogels in situ is limited by the toxicity of the requisite copper(I) catalyst. We report the first use of catalyst‐free Huisgen cycloaddition to generate crosslinked hydrogels under physiological conditions using multivalent azide‐functionalized polymers and an electron‐deficient dialkyne crosslinker. RESULTS: Water‐soluble azide‐functionalized polymers were crosslinked with an electron‐deficient dialkyne crosslinker to form hydrogels at physiological temperature without the addition of copper(I) catalyst. Crosslinking was confirmed using scanning electron microscopy, Fourier transform infrared and ¹H NMR analyses. Flow by vial inversion and dynamic rheological methodologies were implemented to evaluate gelation kinetics at 37 °C of variable polymer compositions, concentrations and stoichiometric ratios. Kinetic studies revealed gelation in as little as 12 h at 37 °C, although strong gels that withstand inversion were observed by 1–8 days. CONCLUSION: The ability to form hydrogel networks under mild conditions demonstrates the potential viability of the catalyst‐free ‘click’ crosslinking chemistry for in situ gelling and other biological applications. Further chemical modifications in the crosslinking moieties, as well as polymer and crosslinker conformations, are expected to enhance gelation kinetics to a more biomedically practical rate. Copyright © 2009 Society of Chemical Industry     

Swelling and network parameters of high oil‐absorptive network based on 1‐octene and isodecyl acrylate copolymers

Crosslinked 1‐octene‐isodecyl acrylate copolymers were synthesized and evaluated for oil‐absorbency applications. The copolymer was crosslinked at different concentrations of ethylene glycol diacrylate (EGDA) and EG dimethacrylate (EGDMA) crosslinkers via catalytic initiation or by electron‐beam irradiation at a dose rate 80 kGy. The concentration of both crosslinkers was varied from 0.5 to 2%. The effects of the crosslinking conditions such as crosslinker concentration, method of polymerization and monomer concentrations on the conversion and gel fraction were examined through oil‐ absorption tests using petroleum crude oil. It was found that the oil absorbency was influenced mainly by the degree of crosslinking and the hydrophobicity of the copolymer units. The final equilibrium oil content, volume fraction of the polymer, and swelling capacity were determined at 298 K. The effective crosslinking density, average molecular weight between the crosslinks, and polymer–toluene interaction parameter were determined from stress–strain measurements. The crosslinking efficiencies of EGDA and EGDMA toward copolymers were determined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 80–91, 2005     

Swelling and Diffusion Properties of Poly(acrylamide-co-maleic acid) Hydrogels: A Study with Different Crosslinking Agents

Crosslinked hydrogels comprising acrylamide (AAm) and maleic acid (MA) were synthesized by free radical polymerization in presence of a crosslinker using ammonium persulfate (APS) and N,N,N¹,N¹-tetramethylethylenediamine (TMEDA) as initiator and activator, respectively. The crosslinked hydrogel formation was confirmed by IR analysis. The swelling/de-swelling characteristics were studied in detail for crosslinked poly(acrylamide-co-maleic acid) [poly(AAM-co-MA)] hydrogels containing different amounts of maleic acid. Four different crosslinkers such as 1,2-ethyleneglycol dimethacrylate (EGDMA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), and diallyl phthalate (DP) were utilized to study their influence on the swelling behavior of the hydrogels. The effect of reaction parameters such as the concentration of crosslinker and initiator on swelling capacity of the crosslinked poly(AAm-co-MA) hydrogels was also investigated. Further, the influence of various salts, simulated biological fluids, and pH solutions on the swelling pattern of hydrogels was studied extensively. Phase separation morphology of crosslinked hydrogels was also studied by differential scanning calorimetry. The morphology of crosslinked hydrogels were revealed using scanning electron microscopy (SEM).     

Zwitterionic hydrogels crosslinked with novel zwitterionic crosslinkers: Synthesis and characterization

Two novel zwitterionic sulfobetaine dimethacrylate crosslinkersN,N-bis(methacryloxyethyl)-N-methyl-N-(3-sulfopropyl)ammonium (CL1) and N,N-bis(methacryloxyethyl)-N-methyl-N-(4-sulfobutyl)ammonium (CL2) betaines were synthesized and used for preparation of zwitterionic hydrogels formed from N-(methacryloxyethyl)-N,N-dimethyl-N-(3-sulfopropyl)ammonium betaine (SBDMA) via redox-initiated free-radical polymerization. The commercially available crosslinkers N,N′-methylene bisacrylamide (BIS) and ethylene glycol dimethacrylate (EDMA) were also used. Equilibrium water content, sorption degree, diffusion coefficient of water, state of water, degree of crosslinking and mechanical properties were determined for hydrogels crosslinked using different crosslinking conditions. A minor difference in the spacer length between the charged moieties in CL1 and CL2 crosslinkers, respectively, was shown to influence the hydrogel properties. The CL1 and CL2 crosslinkers with chemical structure similar to SBDMA resulted in hydrogels with higher stiffness, mechanical strength and crosslink density compared to hydrogels crosslinked by BIS and EDMA. This difference was assigned to suppression of the compositional drift during the hydrogel formation when crosslinkers with chemical structure similar to monomer were used. PolySBDMA hydrogels exhibited a low adhesion of RAT-2 fibroblasts-like cells.     

Synthesis and characterization of reinforced acrylic‐based superabsorbents crosslinked with divinylbenzene

A series of superabsorbent polymers were synthesized by an inverse suspension polymerization, with potassium persulfate as the initiator, Span60 as the dispersant, and N,N′‐methylene bisacrylamide (BIS) and divinylbenzene (DVB) as multiple crosslinkers. The synthesis conditions, including the amount of dispersant, concentration of crosslinkers, oil‐to‐water phase ratio (O/W) of the polymerization system, total monomer concentration, and acrylamide (AM) content were studied. The results indicated that there were optima for the following properties: BIS crosslinker concentration (0.075 wt %), O/W (3 : 1), total monomer concentration (37.5 wt %), and AM content (5 wt %). In addition, the particle size had a significant influence on the absorption speed, and the absorption speed increased with decreasing particle size. In comparison with the conventional sample crosslinked only by BIS, the superabsorbent with the same particle size but crosslinked by multiple crosslinkers had the higher absorption rate because of surface crosslinking. It also showed that the salt resistance and antihydrolyzing property of the superabsorbent crosslinked by multiple crosslinkers (BIS and DVB) were enhanced, which was also attributed to surface crosslinking by DVB. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1594–1600, 2006     

智能型聚甲基丙烯酸凝胶的合成与表征

以甲基丙烯酸(MAA)为单体,过硫酸钾(KPS)为引发剂,无机纳米粒子Laponite或者N,N'-亚甲基双丙烯酰胺(BIS)为交联剂,通过原位自由基聚合的方法分别合成了纳米复合聚甲基丙烯酸凝胶和传统型聚甲基丙烯酸凝胶,并利用红外、流变、溶胀性能测试、剥离强度测试等手段对凝胶的性能进行了表征。比较了在不同单体(MAA)含量、体系pH值下,Laponite含量和BIS含量对物理交联法和化学交联法制备的凝胶的交联密度的影响,以及两种凝胶溶胀度随溶液pH值以及温度的变化关系。研究表明:增加单体MAA的含量、增加交联剂Laponite或BIS的含量,以及降低体系的pH值有利于凝胶网状结构的形成。化学交联的传统型聚甲基丙烯酸凝胶具有明显的pH敏感性和温度敏感性,而物理交联的纳米复合聚甲基丙烯酸凝胶具有良好的粘结性能。     

Swelling of High Oil-Absorptive Network Based on 1-Octene and Isodecyl Acrylate Copolymers

Crosslinked 1-octene-isodecyl acrylate copolymers were synthesized and evaluated for oil-absorbency application. The copolymer was crosslinked at different concentrations of ethylene glycol diacrylate (EGDA) and ethylene glycol dimethacrylate (EGDMA) crosslinkers via catalytic initiation or by electron-beam irradiation at dose rate 80 kGy. The concentration of both crosslinkers was varied from 0.5% to 2%. The effect of crosslinking conditions, such as crosslinker concentration, method of polymerization and monomers concentration on conversion and gel fraction was examined through an oil-absorption test using petroleum crude oil. It was found that, the oil absorbency was influenced mainly by the degree of crosslinking and the hydrophobicity of the copolymer units. The final equilibrium oil content, volume fraction of polymer and swelling capacity were determined at 298 K. The effective crosslinking density V_e, the average molecular weight between the crosslinks M_c and the polymer-toluene interaction parameter were determined from stress–strain measurements. The crosslinking efficiencies of EGDA and EGDMA towards copolymers were determined.     

Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

Treatment of gray wastewater and heavy metal removal from aqueous medium using hydrogels based on novel crosslinkers

Water contamination by heavy metals is a serious environmental problem. Several adsorbents with high adsorption capacity have been reported by researchers. In this paper we report the application of a new crosslinker allyl sorbitol (AS), and two other crosslinkers viz. allyl mannitol (AM) and allyl pentaerythritol (AP), toward the synthesis of polymer hydrogels. These hydrogels have been utilized for the removal of heavy metal ions from water. Chemically crosslinked polyacrylic acid hydrogels have been prepared using these crosslinkers viz. AS or AM or AP. The synthesized crosslinked hydrogels have been utilized for the removal of heavy metal ions from water. The maximum copper (Cu) metal ion removal of 81.8, 81.6, 86.8% and adsorption capacity of 409, 408, 434 mg/g were found with AS, AM and AP crosslinker based hydrogels respectively. While the maximum nickel (Ni) metal ion removal of 96.8, 96.6, 99.0% and adsorption capacity of 484, 483, 495 mg/g were found with AS, AM and AP crosslinkers based hydrogels respectively. The maximum chemical oxygen demand (COD) reduction of 72, 74, 78% and total dissolved solids reduction of 86%, 83%, 95% were found with AS, AM, AP based polymer gel respectively. Approximately, 439.2, 451.4, and 475.8 (mg COD removed/g polymer gel) of pollutants reduction capacity was achieved during their treatment.     

Polymer electrolyte membranes prepared by EB‐crosslinking of sulfonated poly(ether ether ketone) with 1,4‐butanediol

Crosslinked sulfonated poly(ether ether ketone) (SPEEK) membranes were prepared through the electron beam (EB)‐irradiation crosslinking of SPEEK/1,4‐butanediol under various irradiation conditions and used as a proton exchange membrane (PEM) for fuel cell applications. The crosslinked membranes were characterized by gel fraction, a universal testing machine (UTM), dynamic mechanical analysis (DMA), and small‐angle X‐ray scattering (SAXS). The gel fraction of the crosslinked membranes was used to estimate the degree of crosslinking, and the gel fraction was found to be increased with an increase of the crosslinker content and EB‐absorbed dose. The UTM results indicate that a brittle EB‐crosslinked membrane becomes more flexible with an increase in the crosslinker content. The DMA results show that the EB‐crosslinked membranes have well‐developed ionic aggregation regions and the cluster T_g of membranes decrease with an increase in the 1,4‐butanediol crosslinker content. The SAXS results show that the Bragg and persistence distance of crosslinked membranes increase with an increase in the crosslinker content. The proton conductivities of the EB‐crosslinked membranes were more than 9 × 10^?2 S/cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41760.     

Crosslinking structures of gelatin hydrogels crosslinked with genipin or a water‐soluble carbodiimide

It was suggested in our previous studies that carbodiimide‐ and genipin‐crosslinked gelatin hydrogels could be used as bioadhesives to overcome the cytotoxicity problem associated with formaldehyde‐crosslinked gelatin hydrogels. In this study, we investigated the crosslinking structures of carbodiimide‐ and genipin‐crosslinked gelatin hydrogels. We found that crosslinking gelatin hydrogels with carbodiimide or genipin could produce distinct crosslinking structures because of the differences in their crosslinking types. Carbodiimide could form intramolecular crosslinks within a gelatin molecule or short‐range intermolecular crosslinks between two adjacent gelatin molecules. On the basis of gel permeation chromatography, we found that the polymerization of genipin molecules could occur under the conditions used in crosslinking gelatin hydrogels via a possible aldol condensation. Therefore, besides intramolecular and short‐range intermolecular crosslinks, additional long‐range intermolecular crosslinks could be introduced into genipin‐crosslinked gelatin hydrogels. Crosslinking a gelatin hydrogel with carbodiimide was more rapid than crosslinking with genipin. Therefore, the gelation time for the carbodiimide‐crosslinked gelatin hydrogels was significantly shorter than that of the genipin‐crosslinked gelatin hydrogels. However, the cohesive (interconnected) structure of the carbodiimide‐crosslinked gelatin hydrogels was readily broken because, unlike the genipin‐crosslinked gelatin hydrogels, there were simply intramolecular and short‐range intermolecular crosslinks present in the carbodiimide‐crosslinked hydrogel. In the cytotoxicity study, the carbodiimide‐crosslinked gelatin hydrogels were dissolved into small fragments in the cultural medium within 10 min. In contrast, the genipin‐crosslinked gelatin hydrogels remained intact in the medium throughout the entire course of the study. Again, this may be attributed to the differences in their crosslinking structures. The genipin‐crosslinked gelatin hydrogels were less cytotoxic than the carbodiimide‐crosslinked gelatin hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4017–4026, 2004     

Preparation and characterization of PAM/SA tough hydrogels reinforced by IPN technique based on covalent/ionic crosslinking

In order to fabricate tough hydrogels with superior formability, polyacrylamide/sodium alginate (PAM/SA) interpenetrating polymer network (IPN) hydrogels were produced with ionically crosslinked SA interpenetrated in covalently crosslinked PAM. TGA results show that the heat resistance of PAM/SA IPN hydrogel is improved as compared to that of the individual component. Swelling studies indicate that increasing either chemical crosslinker content or ionic crosslinking via adding more N,N′‐methylenebisacrylamide (MBA) or SA results in lower ESR. It is concluded by tensile test that loosely crosslinked PAM coupled with tightly crosslinked SA improve mechanical strength for hydrogels based on covalent/ionic crosslinking. PAM/SA hydrogels via “one‐pot” method can form different complex shapes with mechanical properties comparable to conventional double network (DN) gels. The fracture strength of PAM_0.05/SA₂₀ reaches level of MPa, approaching 2.0 MPa. The work strives to provide method to tune mechanical and physical properties for hydrogels, which is hopefully to guide the design of hydrogel material with desirable properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41342.