Characterization of Poly(vinyl alcohol)/Chitosan Hydrogels as Vascular Tissue Engineering Scaffolds

In this study, PVA/Chitosan hydrogels were fabricated by freeze/thaw cycles and further crosslinking with a KOH/Na₂SO₄ coagulation bath and the effect of freeze/thaw cycle number on cell behaviour was evaluated. The surface of the hydrogels were further modified with Collagen type I adsorption and seeded with bovine aortic vascular smooth muscle and endothelial cells. Increasing the number of freeze/thaw cycles resulted in a marked change in surface morphology, hydrophilicity and protein adsorption. Collagen coating caused an increase in initial attachment and proliferation. We concluded that hydrogels that have undergone 3 freeze/thaw cycles were optimum for cell attachment both in the presence and the absence of coating.     

The effect of external stimuli on the Bovine Serum Albumin adsorption capacity of poly(acrylamide/maleic acid) hydrogels prepared by gamma rays

The effects of external stimuli such as pH of the buffer solution, ionic strength, temperature and the amount of poly-electrolyte monomer in the hydrogel system on the Bovine Serum Albumin (BSA) adsorption capacity of poly(acrylamide/maleic acid) [P(AAm/MA)] hydrogels were investigated. Poly-electrolyte P(AAm/MA) hydrogels with varying compositions were prepared by irradiating acrylamide/maleic acid/water mixtures with γ rays at ambient temperature. Langmuir type adsorption isotherms were observed for all prepared hydrogels. Increase of ionic strength of the buffer solution from 0.01 to 0.1 mol dm⁻³ decreased the adsorption capacity of hydrogels and zero adsorption was observed in the presence of 0.1 mol dm⁻³ Na⁺ and Ca²⁺ ion in the adsorption medium. The adsorption capacity of hydrogels was found to increase from 0 to 120 mg BSA/g dry gel, by changing external stimuli and hydrogel composition.     

Removal of methylene blue with hemicellulose/clay hybrid hydrogels

In this study, we chose corn stover hemicellulose for the preparation of hydrogels with admirable adsorption properties under mild alkaline conditions. Clay nanosheets were introduced to this system and hemicellulose/clay hybrid hydrogels were prepared. Morphological, mechanical properties and the methylene blue adsorption behaviors of the prepared hydrogels were studied. Results suggested that the addition of clay not only improved the mechanical strength of hemicellulose-based hydrogels, but also increased the adsorption capacity on methylene blue. Moreover, the adsorptions were confirmed to follow pseudo-second order equation for both gels with and without clay. The maximum adsorption capacities on methylene blue for hemicellulose-based hydrogels with or without clay reached 148.8 and 95.6 mg/g, respectively. These results implied that hemicellulose-based hydrogels could be used as promising adsorbents for the removal of methylene blue from waste water.     

Swelling equilibria and dye adsorption studies of chemically crosslinked superabsorbent acrylamide/maleic acid hydrogels

Superswelling acrylamide (AAm)/maleic acid (MA) hydrogels were prepared by free radical polymerization in aqueous solution of AAm with MA as comonomer with some multifunctional crosslinkers such as trimethylolpropane triacrylate and 1,4-butanediol dimethacrylate. AAm/MA hydrogels were used in experiments on swelling and adsorption of a water-soluble monovalent cationic dye such as Basic Blue 17 (Toluidin Blue). As a result of dynamic swelling tests, the influence of relative content of MA on the swelling properties of the hydrogel systems was examined. AAm/MA hydrogels were swollen in the range 1660-6050% in water, while AAm hydrogels swelled in the range 780-1360%. Equilibrium water content of AAm/MA hydrogels were calculated in the range 0.8873-0.9837. Water intake of hydrogels followed a non-Fickian type diffusion. The uptake of the cationic dye, BB-17 to AAm/MA hydrogels is studied by batch adsorption technique at 25 °C. In the experiments of the adsorption equilibrium, S-type adsorption in Giles's classification system was found. The binding ratio of hydrogel/dye systems was gradually increased with the increase of MA content in the AAm/MA hydrogels.     

Topography-induced cell adhesion to Acr-sP(EO-stat-PO) hydrogels: the role of protein adsorption

Topographic surface patterning of intrinsically non-adhesive P(EO-stat-PO)-based hydrogels can lead to the adhesion and spreading of fibroblasts. Explanations for this unexpected behavior are discussed, particularly with regard to non-specific protein adsorption from the serum-supplemented culture medium. The presence of serum proteins is shown to be essential for adhesion. Adsorption of plasma and ECM proteins (Fibronectin (FN) and Vitronectin (VN)) to the hydrogels is possible. The effect of VN on initial cell adhesion is analyzed in detail. It appears that VN is the main serum component that is crucial for initial cell adhesion to PEG and that surface topography is essential for further, durable adhesion establishment, and spreading.     

An enhanced immobilization of BSA biomolecule on anionic hydrogels: swelling and adsorption modeling

The three-dimensional structure of hydrogels plays a leading role in several areas of applications. The hydrogels are more and more used as systems of immobilized and controlled release of biomolecules in biotechnology and bio-pharmacy industries. To improve protein adsorption capacity in poly(acrylamide) hydrogels, maleic acid co-monomer was included into the reaction mixture during hydrogel synthesis. So, hydrogels of poly(acrylamide) and its copolymers with diprotic maleic acid were prepared by copolymerization and chemical crosslinking with N,N′-methylene bis-acrylamide. Swelling behavior in distilled water, in physiological saline and in bovine serum albumin (BSA) solutions was studied. Influence of initial BSA concentration on hydrogel swelling and BSA adsorption was investigated. The high amount of maleic acid present in the hydrogels has a significant effect on the swelling behavior and BSA adsorption. Results showed that the pH sensitivity of hydrogels resulted in the high amount of adsorbed BSA. The adsorption isotherms were described by Langmuir and Freundlich models. The thermodynamic parameter (ΔG _ads ⁰ ) was determined for all obtained hydrogels. We demonstrated the favorable character and reversibility of the BSA adsorption process.     

pH/temperature - sensitive imprinted ionic poly(N-tert-butylacrylamide-co-acrylamide/maleic acid) hydrogels for bovine serum albumin

In this study, we have prepared pH/temperature-sensitive imprinted ionic poly(N-tert-butylacrylamide-co-acrylamide/maleic acid) [P(TBA-co-AAm/MA)] hydrogels for bovine serum albumin (BSA) by using molecular imprinting method. BSA adsorption from aqueous BSA solutions was investigated with two types of hydrogel systems prepared by non-imprinted and imprinted methods. Hydrogels imprinted with BSA showed higher adsorption capacity and specificity for BSA than hydrogels prepared by the usual procedure. At all studied conditions, the highest BSA adsorption was observed in the hydrogel imprinted with 8.63 wt.-% BSA. In addition, the imprinted hydrogels exhibited both for good selectivity BSA and high adsorption rate depending on the number of BSA-sized cavities. Adsorption studies showed that other stimuli, such as pH, temperature and initial BSA concentration also influenced the BSA adsorption capacity of both non-imprinted and imprinted hydrogels.     

γ-irradiated chitosan-polyvinyl pyrrolidone hydrogels as pH-sensitive protein delivery system

The effects of pH of the buffer solution and the composition of the hydrogel system on the bovine serum albumin (BSA) adsorption capacity of chitosan (CS)–polyvinyl pyrrolidone (PVP) (CSPVP) hydrogels and release of BSA were investigated. Poly-electrolyte CSPVP hydrogels with different compositions were prepared by irradiating CS/PVP/water mixtures with γ-rays at ambient temperature. The adsorption capacity of hydrogels was found to increase from 0 to 350 mg BSA/g dry gel, by changing external stimuli and hydrogel composition. The adsorption of BSA within CSPVP hydrogels increased with increase in CS content in the hydrogels. When the irradiation doses of hydrogel increased, the adsorption of BSA decreased. The maximum adsorption of BSA was observed at pH 5. A significant amount of the adsorbed BSA (up to 95%) was eluted in the phosphate medium containing 0.1 M NaCl at pH 7.4.     

Adsorption of methyl violet in aqueous solutions by poly(N-vinylpyrrolidone-co-methacrylic acid) hydrogels

N-vinylpyrrolidone(VP)/methacrylic acid (MAA) monomer mixtures containing different quantities of methacrylic acid were irradiated with gamma-radiation to form hydrogels. Mixtures which contain 5, 10, 15% and irradiated with 3.4 kGy were used for swelling and diffusion studies in water and solutions of methyl violet and for the adsorption of methyl violet from aqueous solutions. Diffusion of water and methyl violet within hydrogels were found to be of non-Fickian character. In the dye adsorption experiments, the effects of pH, concentration of aqueous solution of dye and the composition of hydrogels on the adsorption process were investigated. When the pH and concentration of aqueous solutions of dye and the MAA content in hydrogels increased, the adsorption increased.     

Metal adsorption of carboxymethyl cellulose/carboxymethyl chitosan blend hydrogels prepared by Gamma irradiation

Blend hydrogels based on the carboxymethyl cellulose (CMC) and carboxymethyl chitosan (CMCts) were prepared by γ-irradiation of a high concentrated CMC/CMCts aqueous solution. Properties of the hydrogels, such as gel fraction, swelling ratio, gel strength, and metal adsorption for Pb and Au were investigated. The gel fraction increased with increasing dose, while the swelling ratio decreased with increasing it. The obtained blend hydrogels had high adsorption performance which was controlled by adjusting the composition of CMC/CMCts.     

Cyclodextrin-Cross-Linked Hydrogels for Adsorption and Photodegradation of Cationic Dyes in Aqueous Solution

Possessing three-dimensional porous structures and tunable mechanical strengths, cyclodextrin-containing polymeric hydrogels are one of the most promising water-based adsorbent materials due to their easy availability, simple chemical modification and environmental friendliness. In this work, two kinds of hydrogels were prepared via the copolymerization with acrylic acid and vinyl-derivatized β-cyclodextrins in water. These two gels have showed good adsorption performance towards cationic dyes through the noncovalent interactions with their anionic backbones and porous network. Meanwhile, pseudo-second-order model was selected to clarify the adsorption kinetics process. Moreover, nano-scaled TiO₂ was doped into these resultant cyclodextrins-based hydrogels to achieve efficient degradation of dyes upon light irradiation. The obtained TiO₂-loaded hydrogels could exhibit improved adsorption performance and make the adsorbed dyes photo-degraded with the decolorization rates above 95%. It can be envisioned that such cyclodextrin-based soft materials may find applications in dye clearance and water treatment.     

Efficient Adsorption and Recovery of Pb(II) from Aqueous Solution by a Granular pH-Sensitive Chitosan-based Semi-IPN Hydrogel

A series of granular pH-sensitive semi-interpenetrating polymer network (semi-IPN) hydrogels based on chitosan (CTS), acrylic acid (AA) and gelatine (GE) were utilized for the adsorption and recycle of Pb(II) from aqueous solutions. The composite hydrogels have been characterized by FT-IR and TGA. The effects of contact time, pH value and initial Pb(II) concentration on the adsorption were investigated. Results indicated that the adsorption capacity of the hydrogel increased with increasing pH value and initial Pb(II) concentration, and a pH-sensitive adsorption characteristic was presented. The adsorption rate of the semi-IPN hydrogels on Pb(II) is fast with an adsorption rate constant of 14.9790 mg/(g·s), and adsorption equilibrium could be reached within 10 min. The adsorption isotherms of the hydrogels for Pb(II) could be described well by the Langmuir equation, rather than the Freundlich equation. The as-prepared hydrogels showed good reusability with 0.05 mol/l HNO₃ solutions as the desorbing agent and 0.1 mol/l NaOH solutions as the regeneration agent, respectively. After five consecutive adsorption-desorption processes, the semi-IPN hydrogel with 20 wt% GE may reach 85.26% of its initial adsorption capacity. In addition, the adsorbed Pb(II) can be quantitatively recovered by simply eluting the hydrogel with dilute HNO₃ solution, and a recovery ratio of 89.27% was reached for the semi-IPN hydrogel. The satisfactory adsorption amount is mainly derived from the chelating of functional groups (i.e. –COO^? and –NH₂) with Pb(II) ions. The hydrogel adsorbents exhibited excellent affinity for Pb(II), and can be applied to treat wastewater containing heavy metal ion and simultaneously recover the valuable metal sources.     

Cationic dye adsorption by poly(N-isopropylacrylamide/maleic acid) copolymeric hydrogels prepared by gamma rays

N-isopropylacrylamide/maleic acid hydrogels containing different quantities of maleic acid have been synthesized with γ-radiation. The hydrogels were used in experiments on swelling, diffusion and adsorption of a cationic dye methylene blue. The diffusion of MB into the hydrogels was found to be the non-Fickian type. The factors influencing adsorption capacity of the hydrogel such as gel composition, and irradiation dose were systematically investigated. The equilibrium data for dye adsorption was better described by the Freundlich isotherm than Langmuir isotherm model. The kinetic studies showed that the pseudo-second-order kinetic model fits better than the data obtained from pseudo-first-order model.     

Synthesis,characterization and properties of pineapple peel cellulose-<Emphasis Type="Italic">g</Emphasis>-acrylic acid hydrogel loaded with kaolin and sepia ink

Novel composite hydrogels were synthesized by grafting of acrylic acid onto pineapple peel cellulose and addition of kaolin or sepia ink in ionic liquid 1-butyl-3-methylimidazolium chloride, using potassium persulfate as a free radical initiator and N,N′-methylenebisacrylamide as a crosslinking agent. The structure and morphology of the prepared hydrogels were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscope, X-ray diffraction, thermogravimetry and differential scanning calorimetry. Kaolin and sepia ink improved the thermal stability of the hydrogels. Swelling studies on the prepared hydrogels indicated sepia ink and kaolin affected the swelling ratio and pH-responsive properties. The optimum swelling pH value for the hydrogels was shifted from 7.0 to 12.0 in the presence of sepia ink. The effects of kaolin and sepia ink contents on methylene blue adsorption capacity of the prepared hydrogels were also investigated. The optimum methylene blue adsorption capacity reached 153.85 mg/g at 10% of kaolin and 142.21 mg/g at 20% of sepia ink. The pseudo-second-order kinetic model fit well with the experimental results, indicating the adsorption was chemisorption behavior.     

聚离子液体水凝胶用于中性水中Cr(VI)的去除

随着经济的快速发展,水污染已成为全球关注的紧迫问题。其中,Cr（VI）在废水中含量较高且毒性较强,可引起多种严重疾病。而大多数污染地表水和地下水的pH往往是接近中性的。因此,开发具有近中性pH值下有效去除Cr（VI）的吸附剂对生态系统和公众健康至关重要。本文设计并制备了具有不同结构的三氮唑鎓聚离子液体水凝胶,并将其应用于CrO42-的吸附和释放。该水凝胶可在中性条件下实现水中CrO42-的100%去除,最大吸附量高达356 mg/g。等温吸附结果表明,在较低浓度下CrO42-在聚离子液体水凝胶中为单层吸附。此外,可进一步通过离子交换将吸附于水凝胶中的CrO42-释放出来,实现吸附剂的再生。     

Cationic dye adsorption by acrylamide/itaconic acid hydrogels in aqueous solutions

Acrylamide/itaconic acid (AAm/IA) hydrogels containing different quantities of itaconic acid have been irradiated with γ radiation. The hydrogels were used in an experiment concerning the adsorption of cationic dyes such as Basic Blue 9, Basic Violet 1 and Basic Blue 12. In the experiments of the adsorption of dyes from their synthetic aqueous solutions, type S adsorption isotherms were found. One mole of monomeric unit of AAm/IA hydrogels adsorbed 78.5–513.1 μmole of Basic Blue 9, 60.2–641.1 μmole of Basic Violet 1 and, 28.8–593.3 μmole of Basic Blue 12, while acrylamide hydrogel did not adsorb any cationic dye. As a result, it was shown that the AAm/IA hydrogels could be used as an adsorbent for water pollutants such as dyes, and immobilization of these organic contaminants in the hydrogels from waste water can solve one of the most important environmental problems of the textile industry. © 1997 John Wiley & Sons, Ltd.     

Adsorption of bovine serum albumin to acrylamide–itaconic acid hydrogels

In this study, acrylamide–itaconic acid hydrogels containing different amounts of itaconic acid prepared by irradiating with γ radiation are discussed. They have been used in experiments of swelling, diffusion and bovine serum albumin (BSA) adsorption. Maximum and minimum swellings were observed with water (1520%) and BSA (890%), respectively. Diffusion of water, NaCl and BSA within hydrogels were found to be non-Fickian in character. In the experiments of BSA adsorption, type III adsorption was found. The hydrogel prepared with 60 mg itaconic acid and irradiated at 2.00 kGy was found to be the best adsorption system for BSA. The adsorption capacity of acrylamide–itaconic acid hydrogel was found to exceed that of acrylamide hydrogel by more than 80–100%.     

Aam/Aac水凝胶对碱性藏花红染料的吸附特性研究

以丙烯酰胺(AAm)、丙烯酸(AAc)合成了单体配比分别为1，2、1／1、2，1的AAm/AAcc水凝胶，采用分光光度计法研究了此水凝胶对水溶性单价阳离子染料碱性藏花红的吸附特性，测定了它们的吸附动力学曲线和吸附等温线：探讨了水凝胶单体组成对该染料吸附性能的影响：并且用静电场理论解释了解吸后水凝胶更优的再吸附特性，研究表明，AAm，AAc水凝胶可作为染料污水处理中一种良好的吸附剂。     

Adsorption and controlled release of Chlortetracycline HCl by using multifunctional polymeric hydrogels

Adsorption and controlled release of Chlortetracycline HCl to and from multifunctional polymeric materials (HEMA/MAA) hydrogels were investigated. P(HEMA/MAA) hydrogels were synthesized by gamma radiation-induced copolymerization of 2-hydroxyethylmethacrylate (HEMA) and methacrylic acid (MAA) in aqueous solution. The influence of copolymer composition and pH value of the surrounding medium on the type of water diffusion into the glassy polymer were discussed. Drug, Chlortetracycline HCl containing hydrogels, with different drug concentration to polymer ratios, was loaded by direct adsorption method. The influence of MAA content in the gel on the adsorption capacities of hydrogel was studied. Chlortetracycline HCl adsorption capacity of hydrogels was found to increase from 8 to 138 mg Chlortetracycline HCl per gram dry gel with increasing amount of MAA in the gel system and drug concentration. The effect of pH on the releasing behavior of Chlortetracycline HCl from gel matrix was investigated. In vitro drug release studies in different buffer solutions show that the basic parameters affecting the drug release behavior of hydrogel are the pH of the solution and MAA content of hydrogel.     

Molecular imprinting of protein in Pickering emulsion

A new strategy of molecular imprinting to prepare spherical hydrogels via water-in-oil Pickering emulsion polymerization was developed. The imprinted hydrogels exhibited fast adsorption kinetics and significant selectivity for the target protein.