Diffusion and sorption studies of dyes through PVA cryogel membranes

The capacity of poly(vinyl alcohol) (PVA) to crosslink through freeze/thaw method was used to obtain PVA hydrogel membranes (HG) that were subjected to sorption and diffusion experiments using three dyes: Congo red (CR), methylthymol blue (MTB), and crystal violet (CV). To study the sorption of dyes into the cryogenic membrane, dye solutions at different concentrations were used. After sorption, desorption of dyes from the PVA membrane was monitored to quantify the possible regeneration of the membrane (PVA HG). To have a deep insight on the mechanism behind the desorption process, dye‐release kinetics were studied. The diffusion experiments reveal the fact that CR and MTB do not permeate the PVA HG membrane making it a promising candidate in the advanced purification processes of wastewaters. The effect of the incorporation of dyes (CV, CR, and MTB) on the chemical properties of PVA cryogel matrices has been studied by using several techniques such as: differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of biocompatible spongy cryogels of poly(vinyl alcohol)–gelatin and study of water sorption behaviour

Porous biocompatible spongy hydrogels of poly(vinyl alcohol) (PVA)–gelatin were prepared by the freezing–thawing method and characterized by infrared and differential scanning calorimetry. The prepared so‐called ‘cryogels’ were evaluated for their water‐uptake potential and the influence of various factors, such as the chemical architecture of the spongy hydrogels, pH and the temperature of the swelling bath, on the degree of water sorption by the cryogels was investigated. It was found that the water sorption capacity constantly decreased with increasing concentration of PVA while initially an increase and thereafter a decrease in swelling was obtained with increasing amounts of gelatin in the cryogel. The water sorption capacity decreased with an increase in the number of freeze–thaw cycles. The hydrogels were also swollen in salt solutions and various simulated biological fluids and a fall in swelling ratio was noticed. The effect of the drying temperature of the cryogel on its water sorption capacity was also investigated, and a decrease in swelling was obtained with increasing temperature of drying. The biocompatibility of the prepared materials was assessed by in vitro methods of blood‐clot formation, platelet adhesion, and per cent haemolysis. It was noticed that with increasing concentration of PVA and gelatin the biocompatibility increased, while a reduced biocompatibility was noted with an increasing number of freeze–thaw cycles. Copyright © 2005 Society of Chemical Industry     

Preparation and characterization of poly(vinyl alcohol) cryogel‐silver nanocomposites and evaluation of blood compatibility,cytotoxicity, and antimicrobial behaviors

In this investigation, cryogels composed of poly(vinyl alcohol) (PVA) were prepared by repeated freeze‐thaw method. The prepared cryogels served as templates for producing highly stable and uniformly distributed silver nanoparticles via in situ reduction of silver nitrate (AgNO₃) using alkaline formaldehyde solution as reducing agent. The structure of the PVA/Ag cryogel nanocomposites was characterized by a Fourier transform infrared and Raman spectroscopy. The morphologies of pure PVA cryogels and PVA/Ag nanocomposites were observed by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The SEM analysis suggested that cryogels show a well defined porous morphology whereas TEM micrographs revealed the presence of nearly spherical and well separated Ag nanoparticles with diameter about 100 nm. XRD results showed all relevant Bragg's reflections for crystal structure of silver nanoparticles. The amount of silver in cryogel nanocomposites and thermal stability were determined by inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis measurements. Mechanical properties of nanocomposites were observed in terms of tensile strength. The antibacterial studies of the synthesized nanosilver containing cryogels showed good antibacterial activity against both gram‐negative and gram‐positive bacteria. The prepared PVA/Ag nanocomposites were also investigated for swelling and deswelling behaviors. The results reveal that both the swelling and deswelling process depends on the chemical composition of the cryogel silver nanocomposites, number of freeze‐Thaw cycles and pH and temperature of the swelling medium. The biocompatibility of the prepared nanocomposites was judged by in vitro methods of percent hemolysis and protein (BSA) adsorption. POLYM. COMPOS., 36:1983–1997, 2015. © 2014 Society of Plastics Engineer     

Pullulan/poly(N-vinylimidazole) cryogel: An efficient adsorbent for methyl orange

Pullulan/poly(N-vinylimidazole) (PNVI) hybrid cryogels were synthesized under free radical polymerization and chemical crosslinking conditions in an alkaline, aqueous solution of pullulan (PUL), N-vinylimidazole (NVI), ammonium persulfate and epicholorohydrin (ECH) at −18°C. PUL and PNVI cryogels alone were also synthesized under similar conditions. Optimum cryogel formation conditions were determined by considering product yields and gel fractions of the samples. The products were characterized by elemental analysis, FTIR-ATR spectrometry, Thermal gravimetric analysis, and scanning electron microscopy (SEM) analyses. It has been found that PUL/PNVI hybrid samples bear improved physicochemical properties compared to ECH crosslinked PUL and PNVI samples alone. They act as hydrogels in aqueous medium reaching equilibrium swelling capacity values of the order of 600%. Dried PUL/PNVI cryogels show higher thermal stability than the dried cryogels of the parent polymers and maintain their physical integrity over a prolonged time period. Macroporous morphology was revealed by SEM analysis. Having 54.2 mg/g maximum equilibrium adsorption capacity in 200 ppm methyl orange solution and maintaining 95% of its adsorption capacity at the end of seven consecutive adsorption/desorption cycles, PUL/PNVI cryogel proved to be an efficient and durable dye adsorbent using methyl orange as the model compound in aqueous solution.     

Removal of organic water pollutant using magnetite nanomaterials embedded with ionic copolymers of 2‐acrylamido‐2‐methylpropane sodium sulfonate cryogels

Magnetite cryogel composites as macroporous crosslinked matrices have received wide attention and attract much interest in the water purification and desalination industry. They can be used to produce effective adsorbents with high adsorption rate, capacity and desorption for water pollutants. In this work, the incorporation of magnetite nanoparticles into cryogels by the in situ method is proposed to increase the dispersion of nanoparticles in the gel composites and to produce effective magnetic materials with high adsorption capacities. Ionic sodium‐2‐acrylamido‐2‐methylpropane sulfonate (Na‐AMPS) monomer was selected to prepare cryogels as the homopolymer or copolymers with 2‐hydroxyethyl methacrylate (HEMA) or N‐vinyl pyrrolidone (VP) by the crosslinking polymerization technique in the frozen state. Magnetite nanoparticles were introduced into the cryogel by the in situ co‐precipitation method after introducing iron cations into the cryogel networks. The surface morphologies, crystal structure, magnetite content, thermal stability and magnetic properties were determined for the cryogels and their magnetite composites. The magnetite cryogel composites show significantly enhanced methylene blue dye removal in short times with higher adsorption efficiencies and good regeneration to form an effective adsorbent for water treatment. © 2017 Society of Chemical Industry     

Preparation and characterization of spongy cryogels of poly(vinyl alcohol)–casein system: water sorption and blood compatibility study

Polyvinyl alcohol (PVA) and casein are biocompatible and biodegradable macromolecules, which have been widely applied in biomedical fields. In this paper, novel physically crosslinked hydrogels composed of PVA and casein were prepared by repeated freezing–thawing treatment of aqueous solutions of PVA and casein and characterized by IR, differential scanning calorimetry and scanning electron microscopy techniques. The prepared so‐called ‘cryogels’ were evaluated for their water uptake, and the influences of various factors, such as their chemical architecture and the pH and temperature of the swelling bath, were investigated in terms of water sorption. The effect of salt and various simulated biological fluids on the swelling of cryogels was investigated. The in vitro biocompatibility of the prepared cryogels was also judged by methods such as protein (bovine serum albumin) adsorption, blood clot formation and percentage haemolysis measurements. Copyright © 2005 Society of Chemical Industry     

Structural,morphological and thermal characterization of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) Cryogels: evaluation of water sorption potential and cytotoxicity

Cryogels are macroporous hydrogels which are synthesized through cryogelation method. In the present study cryogels of poly (2-hydroxyethyl methacrylate-co-acrylonitrile) (P (HEMA-co-AN)) were synthesized by copolymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylonitrile (AN) monomers by redox polymerization using cryogelation technique. The synthesized cryogels were characterized by FTIR, SEM, XRD, DSC and TGA techniques. Different compositions of the cryogels were prepared by varying concentrations of the monomers and redox initiators in the feed mixture. These cryogels were then subjected to swelling studies and porosity determination. The swelling behavior was studied as function of concentration of the monomers, redox initiators, temperature, pH, and simulated biological fluids. The prepared cryogels were also characterized for their network parameters using water sorption data. The biocompatibility of P (HEMA-co-AN) cryogel was evaluated by in vitro cytotoxicity test. The results indicated that the P (HEMA-co-AN) cryogel had macroporous morphology and exhibited good water absorption capacity. Moreover, the cryogel was thermally stable and biocompatible in nature.     

Influence of grafting conditions on the properties of polyacrylamide-based cation-exchange cryogels grafted with 2-acrylamido-2-methyl-1-propanesulfonic acid

The effects of grafting conditions on the properties of a novel cation-exchange cryogel by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogel (pAAm cryogel) using potassium diperiodatocuprate (Cu(III) solution) as initiator were investigated experimentally. The basic cryogels were saturated with the initiator solution followed by the solution of monomers to get the expected sulfo groups under various grafting conditions, such as concentrations of monomers and initiator, graft reaction time, graft temperature and the volume ratio of Cu(III) to NaOH. The results showed that these factors influenced the liquid dispersion behaviors and the flow resistance as well as the protein binding capacity of the grafted cryogels. Protein binding capacity increased with the increase of concentration of AMPSA and Cu(III), the graft temperature and the graft reaction time in a wide range under the present conditions. Compared with these factors, the volume ratio of Cu(III) to NaOH in the initiator solution in the considered situations had a relatively weaker influence on the cryogel microstructures and protein binding capacity. The maximum binding capacity of lysozyme reached 2.5 mg/mL cryogel in these grafted cryogels.     

Study of cryostructurization of polymer systems. IX. Poly(vinyl alcohol) cryogels filled with particles of crosslinked dextran gel

The influence of deformable disperse filler on rheological and thermal properties of poly(vinyl alcohol) cryogels (obtained by freezing–thawing of concentrated aqueous solutions of the polymer) was studied. Spherical particles of crosslinked dextran gel—the Sephadex beads of two types: G-25 and G-100—were used as filler. It was found that an increase in the filler concentration from 0 to 20 wt% produced and increase in the composite cryogel strength; the greater reinforcement effect was observed with large-pore Sephadex beads into the cryogel matrix. An increase in the fraction of disperse phase also leads to an increase in fusion temperatures of these composites, such effect being determined mainly by the filler type. The filling of cryogels with G-100 beads improves the thermostability of composite samples to a higher extent as compared with the use of G-25 particles. Several possible reasons for the trends observed in rheological and thermal properties of Sephadexfilled PVA cryogels were revealed.     

Silver hydroxyapatite reinforced poly(vinyl alcohol)—starch cryogel nanocomposites and study of biodegradation,compressive strength and antibacterial activity

In the present work polyvinyl alcohol‐starch/silver hydroxyapatite (PVA‐starch/AgHap) cryogel nanocomposites were prepared by successive freezing‐thawing of a blend of PVA and starch solutions to fabricate a cryogel followed by its reinforcement with silver hydroxyapatite (AgHap). The prepared macroporous cryogel nanocomposites were characterized by Infra‐red spectroscopy (FTIR), environmental scanning electron microscopy (ESEM), and particle size and charge analysis. The amylase induced enzymatic degradation of nanocomposites was studied gravimetrically in phosphate buffer saline (PBS) and effect of various parameters like chemical composition of the nanocomposite, number of freeze‐thaw cycles, and enzyme activity were assessed on the extent of degradation of the nanocomposite. The influence of chemical composition and experimental conditions like the number of freeze thaw cycles was studied on the elastic modulii of the cryogels. The in vitro cytotoxicity and antibacterial activity of nanocomposites was also evaluated against L‐529 fibroblast cells and gram positive and gram negative bacteria, respectively. POLYM. ENG. SCI., 59:254–263, 2019. © 2018 Society of Plastics Engineers     

Synthesis of lysozyme imprinted column with macroporous structure and enhanced selectivity: Utilization of cryogelation technique and electrostatic functional monomers

Applicability of molecularly imprinted polymers (MIP) in conventional protein separation processes demands monolithic construction of columns with macroporous structure in addition to the high specificity and adsorption capacity. In this study, therefore, lysozyme (Lyz) imprinted monolithic cryogel columns were synthesized using electrostatic functional monomers (EFMs) to provide strong interactions between template and polymer, leading to specific recognition and capture of Lyz. SEM images and FTIR spectroscopy analysis confirmed the macroporous structure and presence of EFMs in the samples. Adsorption isotherms, heterogeneity, and breakthrough curves as well as selectivity of the molecularly imprinted cryogels (EFMs‐MIC) and non‐imprinted cryogels (EFMs‐NIC) were investigated. Results showed effective imprinting with a maximum adsorption capacity of 211 mg/g and a high imprinting factor (IF) of 4.2 at low Lyz concentrations. A high relative selectivity coefficient of 7.24 was obtained for Lyz over cytochrome c, a competing protein, indicating that the imprinted sites could well distinguish Lyz. Reusability of MICs was also examined, where insignificant changes were observed in the cryogel adsorption/desorption characteristics after four cycles. Therefore, it is suggested to use EFMs and cryogelation in the synthesis of imprinted monolithic cryogels column for application in conventional protein separation processes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42880.     

Hyaluronic acid microneedles-laden collagen cryogel plugs for ocular drug delivery

Particle loaded hydrogels have shown to provide prolonged delivery of drug in a controlled manner. We propose that embedding drug-loaded hyaluronic acid (HA) microneedles in supermacroporous collagen type-I (Col-I) cryogel plugs may enhance the hydration and provide prolonged release of drug for ocular diseases. In this study, we have fabricated Col-I cryogel and HA-microneedles embedded Col-I cryogel at sub-zero temperature using 4S-arm Star-PEG as a crosslinker. The fabricated novel Col-I cryogels have shown supermacroporous morphology with solvent uptake capacity of nearly 90% due to large pore volume and high interconnectivity. These features of the cryogel enable the release the drug in a controlled and sustained manner. The fabricated cryogels have demonstrated nearly 50% degradation in simulated tear fluid within 15 days of duration. Moreover, the microneedles incorporated cryogels have shown prolonged release of required therapeutic concentration of drug that may satisfy the present dire need for antibacterial drug delivery in eyes. The variation in the drug release kinetics from Col-I cryogel and HA-microneedles-laden-Col-I cryogels have been studied in different release media (PBS and Simulated tear fluid).     

Complexation of macroporous amphoteric cryogels based on N,N‐dimethylaminoethyl methacrylate and methacrylic acid with dyes,surfactant, and protein

Macroporous amphoteric cryogels based on N,N‐dimethylaminoethylmethacrylate and methacrylic acid p(DMAEM‐co‐MAA) crosslinked by N,N′‐methylenebisacrylamide (MBAA) were synthesized by radical copolymerization of monomer mixtures in cryoconditions. The structure and morphology of cryogels were evaluated by FTIR and SEM. Cryogels exhibited interconnected porous structure with pore size ranging from 40 to 80 µm, which depended on their crosslinking degree. The value of the isoelectric point (IEP) of equimolar amphoteric cryogel determined from the water flux was equal to 4.4, while the IEP of cryogel with the excess of DMAEM units was equal to 7.1. The mechanical strength of equimolar amphoteric cryogels increases with increasing amount of crosslinking agent. The complexation ability of amphoteric cryogels with respect to surfactant, dyes, and protein was demonstrated. The adsorption isotherms with respect to anionic surfactant—sodium dodecylbenzene sulfonate (SDBS) and protein—lysozyme correspond to Langmuir equation, while adsorption isotherms of anionic and cationic dyes—methylene blue (MB) and methyl orange (MO) are well described by Freundlich equation. It was found that the binding ability of p(DMAEM‐co‐MAA) with respect to various low‐ and high‐molecular weight compounds changes in the following order: SDBS > lysozyme ? MO > MB. The preferential adsorption of MB from the mixture of protein and MB was shown. The quantitative release of protein, surfactant and dye molecules from the matrix of cryogels takes place at the IEP of cryogel. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43784.     

Study of cryostructuration of polymer systems. XX. Foamed poly(vinyl alcohol) cryogels

Foamed poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze–thaw treatment of whipped PVA water solutions (polymer with MW of 69,000 Da and DD ～99 mol % was used), were obtained and their properties were studied. The rheological characteristics and macrostructure of these gel materials were controlled by the same factors as for the ordinary nonfoamed PVA cryogels (initial polymer concentration and freezing–thawing regimes) and also by the conditions of generation of fluid PVA foams. The study of the kinetics of the freeze–thaw‐induced gel formation of these foams revealed that the temperature dependence of the efficiency of cryotropic gelation showed a maximum at about ?1.5°C. The presence of low molecular weight admixtures in the initial polymer solution appears to be a rather important factor because the admixtures were capable of decreasing the stability of fluid PVA foams and weakening both foamed and nonfoamed cryogel samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1609–1619, 2001     

PVA cryogel membranes as a promising tool for the retention and separation of metal ions from aqueous solutions

The sorption and transport of metal ions by poly(vinyl alcohol) hydrogel membranes (PVA HG), obtained by physical crosslinking through the freezing/thawing method, was analyzed using aqueous nitrate solutions of copper, lead, and nickel, at concentrations ranging from 1 to 100 mM, at 25°C. The sorption of heavy metal by PVA HG has been characterized by swelling and loading degrees. The effect of the heavy metals incorporation on the chemical properties of PVA HG matrices has been studied using SEM, to observe changes in the surface morphology of PVA HG membranes, and FTIR–ATR, aiming to monitor the heavy metals ions sorption into PVA hydrogel membranes. The analysis of permeation and diffusion coefficients of 100 mM aqueous solutions of Cu²⁺, Ni²⁺, and Pb²⁺ show that the diffusion process may be mainly described by hydrodynamic models; however, the transport process shows that the distribution coefficient for the different heavy metals are always higher than one, in agreement, with the sorption studies. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ag+ ions imprinted cryogels for selective removal of silver ions from aqueous solutions

ABSTRACT

The removal of heavy metal ions from aquatic media or any conditions is crucial. Silver ions turn out to be the important example of this problem on earth when these are released to the environment. In the present study, silver ions (Ag⁺) imprinted poly(hydroxyethyl methacrylate) (PHEMA)-based cryogels were prepared using N-methacryloyl-L-cysteine as functional monomer, to be chelated with Ag⁺ ions. The maximum adsorption capacity of Ag⁺-imprinted polymeric cryogel was found to be 49.27 mg/g from aqueous solutions. To investigate the affinity of Ag⁺-imprinted PHEMAC cryogel column, photographic film material from the natural silver ion source was used. The recovery results were 72.8% for the Ag⁺-imprinted PHEMAC cryogel and 0.62% for the non-imprinted PHEMAC cryogels. These values clearly showed the selectivity of the Ag⁺-imprinted PHEMAC cryogel column. The adsorption–desorption cycle was performed more 10 times with use of the same Ag⁺-imprinted PHEMAC cryogel for the determination of reuse. These molecularly imprinted cryogels were used in adsorption process for a long time with no significant loss.     

Comparison of additive effects on the PVA/starch cryogels: Synthesis,characterization, cytotoxicity,and genotoxicity studies

The research goal of this study is to produce suitable scaffolds for tissue engineering applications. Different ratios of polyvinyl alcohol (PVA)/starch (90:10, 70:30, 50:50) and crosslinking methods have been used to prepare cryogels. Chemically crosslinked cryogels were synthesized using glutaraldehyde as the crosslinking agent. For the physically crosslinked cryogels, sodium dodecyl sulfate was used during cryogelation as the foaming agent. Chemical structure and pore morphology were demonstrated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Swelling ratio and degradation profile of the scaffolds were also determined. 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazolium bromide assay and SEM were used to investigate the biocompatibility of the scaffolds and cell morphology. Genotoxicity test was performed to show DNA fragmentation. The overall results demonstrated that PVA/starch cryogels could have potentially appealing application as scaffolds for tissue engineering applications and additives affect the architecture and characteristic properties of the cryogels.     

Supermacroporous hybrid polymeric cryogels for efficient removal of metallic contaminants and microbes from water

A supermacroporous cryogel column of chitosan-dimethylaminoethyl methacrylate (DMAEMA)-magnetite has been synthesized. The cationic and magnetic properties of chitosan/DMAEMA and magnetite, respectively, allow the adhesion of metals and microbes to the matrix. The large interconnected pores (20–100 µm) with porosity greater than 85% of the cryogels facilitate fast water movement. At lab scale (approximately 2 mL bed volume), static binding capacity of 100% (load: 4.5 ppm arsenic and 2300 ppm chromium) and dynamic binding capacity of 65% for arsenic (load: 58 ppm) was observed. The binding capacity at pilot scale (approximately 300 mL bed volume) was found to be 11.5 mg arsenic and 14.22 mg chromium. There was 100% binding of microbes (Escherichia coli and Streptococci) both at lab and pilot scale. The results were propitious and indicated the suitability of cryogel filter as a single device for the removal of arsenic, chromium, and microbes in field samples.     

Study of cryostructuration of polymer systems. XVII. Poly(vinyl alcohol) cryogels: Dynamics of the cryotropic gel formation

Freeze‐thaw treatment of concentrated (>5 g/dL) aqueous solutions of poly(vinyl alcohol) (PVA) (MW 115,000; DD ≈100%) resulted in the formation of opaque gels. The extent of such a cryostructuration process was exhibited in the rheological properties of similar PVA cryogels. The gels' strength depended on the initial polymer concentration in the solution to be frozen and on the conditions of a cryogenic influence. The key factor was the defrostation dynamics: the slower the thawing rate, the stronger the cryogel sample formed, provided other parameters of the process were identical. The observation for the kinetics of the freeze‐thaw–induced gel formation revealed the extreme character of the temperature dependence of the efficacy of PVA cryotropic gelation, the maximum point being in the vicinity of −2°C. It was shown that the effect of the strengthening of PVA cryogels prepared by means of a single‐cycle cryogenic treatment could be reached either with use of as slow as possible thawing regimes, or by the prolonged frozen storage of the samples at “high” subzero temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2017–2023, 2000     

Super-macroporous composite cryogels based on biodegradable dextran and temperature-responsive poly(N-isopropylacrylamide)

This contribution describes the fabrication of super-macroporous cryogels comprising an interpenetrating network of biodegradable dextran and temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) segments. Cryogels were prepared from nonmodified dextran and N-isopropylacrylamide (NIPAAm) via cryogenic treatment of their aqueous solutions and subsequent irradiation with Ultraviolet light. The weight ratio of the two precursors was varied in order to find out the proper conditions for producing cryogels of high gel fraction yield and favorable physico-mechanical properties. Temperature-responsive behavior and enhanced elastic modulus were established for cryogel materials containing ≥50 wt% PNIPAAm. Scanning electron microscopy study revealed an open-porous structure of cryogels below and above the temperature of volume phase transition. Such morphology featured a very quick response of the material to temperature changes. The capability of dextran/PNIPAAm cryogels for instant release of water-soluble substances was demonstrated as well.