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.     

Mechanical properties of interpenetrating polymer network hydrogels based on hybrid ionically and covalently crosslinked networks

Hydrogels are polymer networks swollen in water. Because of their soft and wet nature, and their ability to show large volume changes, hydrogels can be useful in many biomedical and actuator applications. In these applications, it is crucial to tune the mechanical and physical properties of a hydrogel in a controllable manner. Here, interpenetrating polymer networks (IPNs) made of a covalently crosslinked network and an ionically crosslinked network were produced to investigate the effective parameters that control the physical and mechanical properties of an IPN hydrogel. Covalently crosslinked polyacrylamide (PAAm) or poly(acrylic acid) (PAA) networks were produced in the presence of alginate (Alg) that was then ionically crosslinked to produce the IPN hydrogels. The effect of ionic crosslinking, degree of covalent crosslinking, AAm : Alg and AA : Alg ratio on the swelling ratio, tensile properties, indentation modulus, and fracture energy of IPN hydrogels was studied. A hollow cylindrical hydrogel with gradient mechanical properties along its length was developed based on the obtained results. The middle section of this hydrogel was designed as a pH triggered artificial muscle, while each end was formulated to be harder, tougher, and insensitive to pH so as to function as a tendon‐like material securing the gel muscle to its mechanical supports. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2504–2513, 2013     

Thermosensitive elastin-derived polypeptide hydrogels crosslinked by genipin

In this paper, first, elastin-derived peptides (EPs) with low molecular weight were prepared by acid degradation. Second, elastin-derived peptide hydrogels were fabricated by crosslinking EP with genipin. EP exhibited an inverse transition temperature, and the inverse transition temperature (T_t) could be adjusted by changing the concentration and molecular weight of EP, pH, and adding salt. The freeze-dried EP hydrogels were obviously three-dimensional network structure and the property of EP hydrogel can be optimized by dosage of genipin. Differential scanning calorimetry (DSC) tests and the swelling ratio changing with temperature showed the crosslinked EP hydrogels were still thermosensitive and exhibited a negative swelling behavior. The compression modulus of EP hydrogels can even reach 39.4?kPa, surpassing many other elastin-based hydrogels. This genipin crosslinked EP hydrogel is a good biological material and has great potentiality in tissue engineering.     

Polyvinylphosphonic acid copolymer hydrogels prepared with amide and ester type crosslinkers

Crosslinked hydrogels made of poly(vinylphosphonic acid‐co‐N,N′‐methylenebisacrylamide) (P(VPA‐co‐MBAA)) and poly(vinylphosphonic acid‐co‐ethyleneglycol diacrylate) (P(VPA‐co‐EGDA)) were prepared by using precipitation polymerization in water medium. A comparison research was made between the resultant hydrogels containing different loads of vinylphosphonic acid segments when N,N′‐methylenebisacrylamide (MBAA) or ethyleneglycol diacrylate (EGDA) were used as comonomers. Morphological observations indicated that the resultant copolymer appeared as a fine powder at low VPA loadings and strongly aggregated at the high loadings; especially, a copolymer containing 63 mol % of VPA segments in P(VPA‐co‐MBAA) was observed to have a flake‐shaped appearance in its aggregated morphology. The resultant copolymer powders were characterized using FTIR spectroscopy and titrimetric analysis. Also, monomer reactivity ratios, r₁ and r₂, of VPA and MBAA or EGDA were estimated as 0.06 and 0.98 for VPA and MBAA and 0.05 and 1.82 for VPA and EGDA, respectively. This suggested that a large distribution of MBAA and EGDA was present in the resultant copolymer powders. Their crosslinked PVPA structure presented hydrogel properties having high water uptakes and an absorption mechanism independent from pH of bulk solution. The evidence showed that high VPA loadings could strongly interacted through hydrogen bonds between neighbor VPA segments even in the presence of water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Surface characteristics of ionically crosslinked chitosan membranes

In this study, homogenous dense chitosan membranes were prepared by solution‐casting procedure. Then the membranes were ionically crosslinked by sulfuric acid. The surfaces of chitosan membranes before and after crosslinking were characterized by using FTIR‐ATR, X‐ray photoelectron spectroscopy (XPS), and atomic‐force microscopy (AFM) techniques. The XPS data suggest that the surface composition of crosslinked membrane does not change significantly with respect to uncrosslinked membrane and the most important evidence is a certain amount of sulfur, coming from the crosslinker. The result from FTIR‐ATR data shows the effectiveness of the crosslinking procedure by the shift in amide I and amide II bands. The investigation of membrane surfaces by AFM indicates that the crosslinking procedure modifies the surface morphology of chitosan. After crosslinking, the surface topography becomes more homogenous and relatively flat. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Novel preparative method for porous hydrogels using overrun process

Porous poly(vinyl alcohol) (PVA) hydrogels were prepared using the overrun process which is usually used in manufacturing ice cream. The pores in the hydrogel formed exhibit dual‐pore structure due to the injection of air bubbles and ice recrystallization. Morphological investigation revealed that overrun‐processed hydrogels had closed pore structures and that their pore size and size distribution had been influenced by the impeller rate and concentration of polymer solution. The closed‐pore structure was reformed into interconnected open‐pore structure at lower concentrations of the solution. The freeze–thawing process, which takes place in PVA cross‐linking, has no effect on the bubble structure, but removes the small pores formed during ice recrystallization. Besides the swelling ratio of overrun‐processed PVA hydrogels is increased tenfold in comparison with non‐porous hydrogels. Overrun‐processed hydrogels showed more rapid swelling kinetics than freeze‐dried and film‐like hydrogels due to their larger surface area. In the future, the overrun process can be applied to prepare porous scaffolds containing proteins, such as growth factors and other cytokines, without denaturation, because it operates at a low temperature. Copyright © 2004 Society of Chemical Industry     

Swollen behavior of crosslinked network hydrogels based on poly(vinyl alcohol) and polydimethylsiloxane

Poly(vinyl alcohol) (PVA) was dissolved in the water to make a 10 wt % aqueous solution, and polydimethylsiloxane (PDMS) was mixed with 1 wt % 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and 0.5 mol % methylenebisacrylamide (MBAAm) in isopropyl alcohol. This mixture was added to a PVA aqueous solution and heated at 90°C for 7 h. Various crosslinked networks were prepared at different molar ratios of PVA/PDMS (1:1, 1:3, and 3:1). The characterization of PVA/PDMS crosslinked networks was determined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), a universal testing machine (UTM), and the equilibrium water content (EWC). The DSC melting endotherms showed, at 219.49°C, a sharp endothermic peak of PVA, and PVA/PDMS crosslinked networks had melting peaks close to this point. The value of EWC increased with the content of PVA in the crosslinked networks, simultaneously depending on the temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 957–964, 2002     

Cellulose hydrogels physically crosslinked by glycine: Synthesis,characterization, thermal and mechanical properties

Biopolymers are very efficient for significant applications ranging from tissue engineering, biological devices to water purification. There is a tremendous potential value of cellulose because of its being the most abundant biopolymer on earth, swellability, and functional groups to be modified. A novel, highly efficient route for the fabrication of mechanically stable and natural hydrogels is described in which cellulose and glycine are dissolved in an alkaline solution of NaOH and neutralized in an acidic solution. The dissolving temperature and the glycine amount are essential parameters for the self-assembly of cellulose chains and for tuning the morphology and the aggregate structures of the resulting hydrogels. Glycine plays the role of a physical crosslinker based on the information obtained from FTIR and Raman spectra. Among the prepared set of hydrogels, CL5Gly30 hydrogels have the highest capacity to absorb water. The prepared CL5Gly30 gels can absorb up to seven times their dry weight due to its porous 3-D network structure. CL5Gly10 hydrogel exhibits 80% deformation under 21 N force executed. The method developed in this article can contribute to the application of heavy metal adsorption in aqueous solutions for water purification and waste management. © 2019 The Authors. 137 published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48380.     

Interpenetrating polymer networks based on ionically crosslinked polymers: Reacidification and annealing as morphological variables

A carboxylic elastomer based on butadiene, styrene, and methacrylic acid was polymerized and neutralized to form an ionomeric network I. Sequential IPNs were formed by synthesizing in situ polystyrene crosslinked with divinylbenzene as network II. Annealing studies were carried out, with and without reacidification, to ascertain the role played by ionic crosslinks in influencing morphology and mechanical behavior. Finally, the product is reneutralized, resulting in are arranged, relaxed structure. Ionic crosslinks in polymer I provide an in situ decrosslinking mechanism which permits molecular rearrangements to be induced. By annealing the material, a more cocontinuous phase morphology with concomitant modulus increases is attained. This investigation suggests an alternative method of inducing dual phase continuity in multipolymer combinations.     

Synthetic polymeric absorbent for dye based on chemically crosslinked acrylamide/mesaconic acid hydrogels

Adsorption properties of copolymers of acrylamide and mesaconic acid (CAME) in aqueous Basic Blue 12 (Nile blue chloride) solution have been investigated. Chemically crosslinked CAME hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), mesaconic(ME) acid, and water by free radical polymerization in aqueous solution, using a multifunctional crosslinker such as ethylene glycol dimethacrylate (EGDMA). Dynamic swelling tests in water was applied to the hydrogels. Weight swelling ratio (S) values have been calculated. Sorption of Basic Blue 12 (BB 12) onto CAME hydrogels was studied by batch sorption technique at 25°C. In the experiments of the sorption, L type sorption in the Giles classification system was found. Some binding parameters such as initial binding constant (K_i), equilibrium constant (K), monolayer coverage (n), site‐size (u), and maximum fractional occupancy (Ô) for CAME hydrogels‐BB 12 binding system were calculated by using Klotz, Scatchard, and Langmuir linearization methods. Finally, the amount of sorbed BB 12 per gram of dry hydrogel (q) was calculated to be 2.28 × 10^?6–7.91× 10^?6 mol BB 12 per gram for hydrogels. Sorption % was changed range 16.09–58.86%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 405–413, 2006     

Observations by DSC on bound water structure in some physically crosslinked hydrogels

Linear, compositionally homogeneous copolymers containing 23–62 wt% N-vinyl-2-pyrrolidone (VP) were prepared by a semi-continuous copolymerisation with methyl methacrylate (MMA) in the absence of chemical crosslinker. Films cast from solution in chloroform were swollen in water at various temperatures (T) within the range 283–343 K. The total water content (11–80 wt%) of the resultant hydrogels at swelling equilibrium, as well as its subdivision into freezing and non-freezing water components, were measured and found to be dependent on copolymer composition and T. The network structure of these hydrogels is considered to arise from a combination of normal VP–water interactions with physical crosslinking due to hydrophobic MMA sequences, and the novel, albeit only semi-quantitative, findings are discussed on this basis.     

Electrochemical behavior of ionically crosslinked polyampholytic gel electrolytes

An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate (DEA) with acrylic acid (AAc). Free radical copolymerization of the ionic complex and acrylamide (AAm), yielded the ionically crosslinked polyampholytic gel electrolytes [poly(AAc-DEA-AAm), designated as PADA] using two types of organic solvents containing a lithium salt. The PADA gel electrolyte exhibited good thermal stability shown by the DSC thermogram. The impedance analysis at temperatures ranging from −30 to 75 °C indicated that the ionic conductivities of the PADA gel electrolytes were rather close to those of liquid electrolytes. The temperature dependence of the ionic conductivities was found to be in accord with the Arrhenius equation. Moreover, the ionic conductivities of PADA gel electrolytes increased with an increase of the molar ratios of cationic/anionic monomers. The ionic conductivities of PADA gels prepared in solvent mixtures of propylene carbonate, ethyl methyl ether and dioxolane (3:1:1, v/v) were higher than those of PADA gels prepared in propylene carbonate only. Significantly, the ionic conductivities of two kinds of PADA gel electrolytes were in the range of 10⁻³ and 10⁻⁴ S cm⁻¹ even at −30 °C. The electrochemical windows of PADA gel electrolytes measured by cyclic voltammetry were in the range from −1 V to 4.5 V.     

Controlled release of berberine hydrochloride from alginate microspheres embedded within carboxymethyl chitosan hydrogels

Berberine hydrochloride is a natural medicine with wide clinical application. In this article, berberine hydrochloride was entrapped into alginate microspheres via an emulsification/gelation method. The size distribution of the microspheres was determined by a laser particle sizer. Drug distribution within the microspheres was determined by confocal laser scanning microscopy. Those drug‐loaded microspheres were further entrapped into carboxymethyl chitosan (CMC) hydrogel to form a new drug‐delivery system (DDS). The surface morphology of the DDS was observed using metallographic microscopy and scanning electron microscopy (SEM). The compression strength of the DDSs with alginate microspheres was found significantly higher than that of the pure hydrogel. The drug‐release performances of the DDS in phosphate buffer solution (PBS, pH 7.4), saline solution (pH 6.3), and hydrochloric acid solution (HAS, pH 1.2) were also studied. Decay of the DDS in PBS within 72–80 h results in a faster release; however, the steady release in saline solution could last for all the testing period without cleavage of the DDS. In HAS, because of the shrinkage of the DDS, release is fast in the first period and remains steady later. The DDS exhibits prospective in controlled steady release of drugs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Characterization and possible agricultural application of polyacrylamide/sodium alginate crosslinked hydrogels prepared by ionizing radiation

Polyacrylamide/sodium alginate (PAAm/Na‐alginate) crosslinked copolymers were prepared by using electron beam irradiation. The gel content and the swelling behavior of the obtained copolymers were investigated. The thermal and morphological properties of the prepared copolymers were studied using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The thermal stability of PAAm significantly changed when mixed with Na‐alginate. The addition of PAAm/Na‐alginate copolymer in small quantities to sandy soil increased its ability to retain water. The growth and other responses of the faba bean plant cultivated in a soil treated with PAAm and PAAm/Na‐alginate copolymer were investigated. The growth of the bean plant cultivated in a soil containing PAAm/Na‐alginate was better than that cultivated in soil treated with PAAm. The most significant difference between the PAAm and its alginate copolymer is that the latter partially undergoes radiolytic and enzymatic degradation to produce oligo‐alginate, which acts as a plant growth promoter. The increase in faba bean plant performance by using PAAm/Na‐alginate copolymer suggested its possible use in the agriculture field as a soil conditioner, providing the plant with water as well as oligo‐alginate growth promoter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3572–3580, 2006     

Novel physically crosslinked hydrogels of carboxymethyl chitosan and cellulose ethers: Structure and controlled drug release behavior

Novel hydrogels, physically crosslinked by hydrogen bonding of component polymers, were obtained by mixing aqueous solutions of carboxymethylchitosan (CMCS) with cellulose ethers including hydroxyethylcellulose (HEC) and methylcellulose (MC). The hydrogels were characterized by IR, XPS, WAXD, and SEM. The swelling and controlled drug release behaviors of hydrogels were also studied. The results indicate that intermacromolecular hydrogen bonding in CMCS/HEC is stronger than that in CMCS/MC. The swelling and drug release rate of hydrogels decrease as the interaction of component polymers increases. Both the swelling and drug release from hydrogels can be controlled by component polymer ratio. The hydrogels may be potential candidates for biomedical applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Swelling and dye sorption studies of AAm/SA hydrogels crosslinked by glutaraldehyde and divinylbenzene

Highly swollen acrylamide (AAm)/sodium acrylate (SA) hydrogels were prepared by free radical solution polymerization in aqueous solution of AAm with SA as comonomer and two multifunctional crosslinkers such as glutaraldehyde (GL) and divinylbenzene (DVB). Water absorption and percentage swelling were determined gravimetrically. The influence of SA content in hydrogels was examined. Percentage swelling ratio of AAm/SA hydrogels was increased up to 2946–12,533%, while AAm hydrogels swelled up to 1326–1618%. The values of equilibrium water content of the hydrogels are between 0.9297–0.9921. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Adsorption properties of AAm/SA hydrogels in aqueous thionin solution have been investigated. Finally, the amount of sorbed thionin per gram of dry hydrogel (q_e) was calculated to be 4.81 × 10^?6?11.69 × 10^?6 mol thionin per gram for hydrogels. Removal efficiency (RE%) of the AAm/SA hydrogels was changed range 37.03–68.82%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthetic hydrogels. 1. Effects of solvent on poly(acrylamide) networks

Acrylamide hydrogels were synthesized in a series of hydro-organic solvents to examine how solvent affects the network structure by influencing properties of the first formed polymer in the reaction mixture. The looser and more heterogeneous network structure of gels formed in aqueous solutions of ethylene glycol or propylene glycol was found to be largely due to the reduced chain lengths of the primary polymer molecules. Results from NMR analysis of the monomer, and intrinsic viscosity measurements of the polymer in various solvents indicate that solvent effects on the reactivity of the monomer and the propagating radical impose an overriding control over properties of the resultant networks.     

Removal of toxic metals using superabsorbent polyelectrolytic hydrogels

Because of the presence of carboxylic acid moieties, poly(acrylic acid) possesses a unique ability to form stable complexes with divalent metal ions. However, its practical use for the removal of heavy metals from aqueous solutions is restricted because of its inherent water solubility. To address this issue, crosslinking of this polymer has been attempted to synthesize hydrogel, which is stable in aqueous medium over a wide range of pH values. The hydrogels, prepared by redox polymerization of acrylic acid in the presence of polyethylene glycol diacrylate as the crosslinker, were characterized by Fourier transform infrared spectrometry, elemental analysis, thermal analysis, and swelling studies. This chelating hydrogel‐bearing O, O donor groups exhibited high‐metal sorption capacity of 41.1, 58.2, 43.1, and 81.2 mg/g for Cr⁶⁺, Ni²⁺, Cu²⁺, and Pb²⁺, respectively, under optimum conditions. The effect of parameters including pH, concentration, and interference of common ions on metal uptake was also investigated. Langmuir and Freundlich adsorption isotherms have been used to validate the metal uptake data. High recovery (>97%) was achievable for all metal ions with 1N HCl as eluting agent, and the regeneration tests revealed that the sorbent could be used repeatedly for at least 10 cycles without any loss in chelating efficiency. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

利用二醛木聚糖一锅法制备纳米银抗菌水凝胶

利用二醛木聚糖(DAX)可与羧甲基壳聚糖(CMCS)以及银氨溶液同时反应的特性,即DAX的醛基与CMCS的氨基发生席夫碱反应形成亚胺键,同时,DAX含有的大量醛基与银氨溶液发生银镜反应,在室温条件下很快地还原出银纳米粒子(SNPs),一锅法制备出了具有优异抗菌性能的羧甲基壳聚糖-纳米银抗菌水凝胶。加入生物相容性良好的聚乙烯醇(PVA)并通过冻融法形成了与CMCS互穿的双网络结构,进一步提高了水凝胶的结构稳定性。采用FTIR、热重、TEM、XRD和SEM对DAX,SNPs和水凝胶的形貌、结构进行了表征。结果表明DAX在整个反应中起到了十分有效的双功能作用,成功的与CMCS和PVA发生反应,共同构成了双网络结构的水凝胶,从而提高了水凝胶的力学性能。同时,DAX将银氨溶液中的SNPs还原出来,且粒径在20-80 nm之间,具有较好的分散性,从而显著提高了水凝胶的抗菌性。本文中所制备的水凝胶具有伤口敷料方面的应用潜力。