Structure and protein separation efficiency of poly(N-isopropylacrylamide) gels: Effect of synthesis conditions

Crosslinked poly(N-isopropylacrylamide) (PNIPA) gels with different crosslink densities in the form of rods and beads were prepared by free-radical crosslinking copolymerization. Solution and inverse suspension polymerization techniques were used for the gel synthesis. The gels were utilized to concentrate dilute aqueous solutions of penicillin G acylase (PGA), bovine serum albumin (BSA), and 6-aminopenicillanic acid (6-APA). The discontinuous volume transition at 34°C observed in the gel swelling was used as the basis of concentrating dilute aqueous protein solutions. PNIPA gels formed below 18°C were homogeneous, whereas those formed at higher temperatures exhibited heterogeneous structures. The water absorption capacity of PNIPA gels in the form of beads was much higher, and their rate of swelling was much faster than the rod-shaped PNIPA gels. It was also found that the polymerization techniques used significantly affect the properties of PNIPA gels. The separation efficiency decreased when the protein molecules PGA or BSA in the external solution were replaced with small-molecular-weight compounds, such as 6-APA. The protein separation efficiency by the gel beads increased to 100% after coating the bead surfaces with BSA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 805–814, 1998     

pH‐sensitive uniform gel beads for DNA adsorption

Uniform gel beads 3 mm in diameter were obtained by the suspension polymerization of an amine functionalized monomer, N‐3‐(dimethyl amino)propylmethacrylamide (DMAPM). The polymerization of DMAPM in the form of uniform droplets could be achieved at room temperature in an aqueous dispersion medium by using Ca–alginate gel as the polymerization mold. In this preparation, potassium persulfate/tetramethyl ethylenediamine and sodium alginate/calcium chloride were used as the redox initiator and the stabilizer systems, respectively. The crosslinked DMAPM gel beads exhibited pH‐sensitive, reversible swelling–deswelling behavior. The uniform gel beads were also obtained by the copolymerization of DMAPM and acrylamide (AA) in the same polymerization system. Although copolymer gel beads with higher pH sensitivities were obtained with increasing feed concentration of DMAPM, the total monomer conversion decreased. Crosslinked DMAPM and DMAPM–AA copolymer gel beads were utilized as sorbents for DNA adsorption. The gel beads produced with higher DMAPM feed concentration exhibited higher equilibrium DNA adsorption capacity. The DNA equilibrium adsorption capacities up to 50 mg DNA/g dry gel could be achieved with the crosslinked DMAPM gel beads. This value was reasonably higher relative to the previously reported adsorption capacities of known sorbents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3154–3161, 2000     

Preparation of interpenetrating polymer network gel beads for dye absorption

Preparation of interpenetrating polymer network (IPN) gel beads for dye absorption was carried out by using simultaneous crosslinking method. First, sodium alginate (SA), 3‐(methacrylamido) propyl trimethyl ammonium chloride (MAPTAC), and/or acrylamide (AM), K₂S₂O₈, and N,N′‐methylenebisacrylamide (MBAM) were mixed in aqueous solution. The beads were prepared using K₂S₂O₈ and MBAM as the initiator and crosslinking agent, respectively. Then, the solution was dropped into CaCl₂ solution mixed with N,N,N′,N′‐tetramethylethylenediamine (TMEDA). The former was used as the crosslinking agent of alginate and the latter was used as the accelerator for the polymerization of monomer in the alginate solution. The gel bead composed of only alginate was also prepared to compare the properties with IPN gel bead. The components in IPN gel bead were examined by FTIR analysis. The factors effecting the particle size of alginate and IPN gel beads were investigated. In alginate gel bead, the concentration of solution affected the particle size, whereas type of monomer affected the particle size of IPN gel bead. The IPN gel bead had smooth surface (from SEM results), different from the alginate bead. Alginate content caused the swelling behavior of dried IPN beads. Cationic dye was absorbed by crosslinked alginate gel bead. The absorption of reactive dye by IPN gel bead was a result of its cationic charge. The absorption density of IPN gel beads was the reciprocal of the absorbent dosage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1585–1591, 2006     

Polymethyl methacrylate/montmorillonite nanocomposite beads through a suspension polymerization‐derived process

Polymethyl methacrylate (PMMA) polymer beads with montmorillonite (MMT) were prepared using a suspension polymerization method for applying acrylic bone cements. The polymer beads were characterized by X‐ray diffraction and transmission electron microscopy to examine MMT dispersion. The change in the shape and size of the polymer beads due to the preparation conditions, such as stirring speed, degree of polymerization, and concentration of polyvinyl alcohol (PVA) as a suspension stabilizer, and MMT contents, etc. was observed by scanning electron microscopy and particle size analysis. The prepared polymer beads were composed of polymer‐intercalated nanocomposites with partially exfoliated MMT layers. The size of the polymer beads was decreased by increasing the stirring speed. The bead size was decreased with increasing the degree of polymerization and the concentration of PVA molecules. MMT addition into the monomer portion increased the size of the corresponding polymer beads. The bead size was slightly reduced by adding of styrene to the MMA solution. The incorporation of PMMA into monomer portion enlarged the bead size. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2340–2349, 2005     

Preparation and characterization of molecularly imprinted polymer of bovine serum albumin

Molecularly imprinted polymer beads of bovine serum albumin (BSA) were prepared via inverse phase suspension polymerization, using BSA as the template molecule, a combination of acrylamide and methacrylic acid (MAA) as double functional monomers, and N, N′‐methylene bisacrylamide as the crosslinker. The effect of different monomer ratios and degrees of crosslinking were investigated. When both selectivity and physical properties of the resultant polymer beads were taken into account, the ratio of MAA in the total monomers was chosen at 40% (m/m) and the degree of crosslinking at 30% (n/n), the resultant polymer beads had good selectivity (α = 2.77) and good physical properties. The effects of pH and temperature were studied. It turned out that the functionalization of polymers of BSA prepared via inverse‐phase suspension polymerization exhibited specific recognition for BSA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

医用多孔聚丙烯酰胺微球的制备与表征

以反相悬浮聚合法制备出适合医用的多孔载体材料——聚丙烯酰胺微球，经正交实验得到反应体系所需的最佳聚合条件。所得微球的检测结果表明，产物具有不同粒径和特定孔径的规则球形结构。     

Investigation of the surface area and polarity of porous copolymers of maleic anhydride and divinylbezene

Porous copolymers of maleic anhydride (MA) and divinylbezene (DVB) in the form of regular microspheres were prepared by suspension polymerization. During copolymerization the mixture of 1,4-dioxane and n-dodecane as a pore-forming diluent was used. It was found that specific surface area of the obtained beads is strongly dependent on the diluent system and polymerization medium and achieves a value from 4 to 535 m²/g. To determine the influence of polymerization medium on the selectivity and polarity of the copolymers, inverse gas chromatography (IGC) was applied. To determine these parameters, three procedures were applied: overall polarity, the selectivity triangle, and the ΔC method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characterization of the structure and diffusion behavior of calcium alginate gel beads

A simple and novel method using gel shrinkage to indirectly characterize the structure of calcium alginate gel (CAG) beads during the calcium alginate gelation process was presented in this study. The effect of preparation process parameters (gelling cations, bead diameter, and alginate M _w and concentration) on the structure of the CAG bead formation process was thoroughly investigated. It was found that (a) the concentration of the Na⁺ and Ca²⁺ ion in gel bath was found to be the determining factor in the gel structure formation process by regulating the dissociation of alginate and the complexation of the calcium; (b) Na⁺ acts as a competitor with calcium and a screen in the electrostatic repulsion; (c) the effect of beads size below 700 μm on the structure of CAG beads can be neglected; and (d) the sodium alginate concentration has no significant effect on the gel formation process. Furthermore, the diffusion of bovine serum albumin (BSA) was controlled by the density of CAG bead. Consequently, a faster diffusion rate of BSA within the looser structure of beads can be observed. These results are keys to understanding the behavior and performance of beads in their utilization medium. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48923.     

Preparation of uniform calcium alginate gel beads by membrane emulsification coupled with internal gelation

With the objective of making calcium alginate gel beads with small and uniform size, membrane emulsification coupled with internal gelation was proposed. Spherical gel beads with mean size of about 50 μm, and even smaller ones in water, and with narrow size distribution were successfully obtained. Experimental studies focusing mainly on the effect of process parameters on bead properties were performed. The size of the beads was mainly dependent on the diameter of the membrane pores. High transmembrane pressure made for large gel beads with wide size distribution. Low sodium alginate concentration produced nonspherical beads, whereas a high concentration was unsuitable for the production of small beads with narrow distribution. Thus 1.5% w/v was enough. A high surfactant concentration favored the formation of small beads, but the adverse effect on mass transfer should be considered in this novel process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 848–852, 2003     

Surface morphology evaluation of polymer beads based on divinylbenzene by atomic force microscopy

Macroporous poly(styrene‐co‐divinylbenzene) and poly(divinylbenzene) beads were synthesized by modified suspension polymerization in the presence of different mixtures of toluene and heptane as porogen agent. Through atomic force microscopy, it was possible to identify the microspheres and the channels between them that constitute the bead pores. It was also possible to make a comparison with the results obtained by nitrogen desorption, a traditional technique used to determine the porosity of macroporous copolymers in the dry state. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 541–551, 2002; DOI 10.1002/app.10290     

2‐Hydroxypropylmethacrylate based mono‐ and bifunctional gel beads prepared by suspension polymerization

Spherical and swellable gel beads in the size range 35–200 µm were prepared by suspension polymerization of 2‐hydroxypropylmethacrylate (HPMA). In the proposed method, a mixture of cyclohexanol and octanol was used as a diluent phase dispersed in an aqueous medium including poly(vinyl pyrrolidone) (PVP) as the stabilizer. The polymerization was initiated within the organic phase including the monomer and the crosslinker (ethylene glycol dimethacrylate) by an oil soluble initiator benzoyl peroxide. Spherical and swellable gel beads carrying both hydroxyl and carboxyl functional groups were also prepared by suspension copolymerization of HPMA and a water soluble comonomer (methacrylic acid). For this purpose, the suspension polymerization method proposed for HPMA was modified by using poly(vinyl alcohol) as a stabilizer instead of PVP. The effect of initiator concentration, polymerization temperature, monomer/diluent ratio, crosslinker concentration, stirring rate on yield, average size, size distribution, and carboxyl content of the HPMA based gel beads, were investigated. The swelling characteristics of the gel beads were defined. © 2000 Society of Chemical Industry     

Metal recovery using immobilized cell suspension from a brewery

Lead, copper, and cadmium were adsorbed onto calcium alginate beads containing the cell suspension discarded from a brewery. In the cell suspension, there were many cells under lysis. The cell-suspension immobilized beads were prepared by adding 0.6% (w/v) sodium alginate into the cell suspension from the brewery and then making the cell suspension fall dropwise into the swirling 1% (w/v) calcium alginate solution. The dry weight of insoluble solid in the cell suspension was 96 g dry weight/l and the dry density of the bead containing cell suspension was 140 g dry weight/l of the bead. The specific metal uptake of the cell-suspension immobilized bead was 23.7 mg Pb²⁺, 14.3 mg Cu²⁺, and 13.4 mg Cd²⁺/g bead dry weight, respectively. The cell-suspension immobilized beads retained the initial metal-uptake capacity after 20 repeated batches of adsorption and desorption, but the fraction of metal desorbed from the beads by 1 M HCl solution was only 70% of the adsorbed metal. The beads, which had been contained for 14 successive days in the 0.5% (w/v) CaCl₂ solution at 4 °C just after 20 cycles of adsorption/desorption, retained the initial metal-uptake capacity after 30 repeated cycles, and more than 90% of the copper and cadmium adsorbed on the beads was desorbed by the 1 M HCl solution.     

Thermosensitive poly(N‐isopropylacrylamide) hydrogel for refolding of recombinant bovine prethrombin‐2 from E. coli inclusion bodies

The poly(N‐isopropylacrylamide) (PNIPA) hydrogel, which is a kind of temperature‐sensitive polymer, was synthesized by inverse suspension polymerization. The microscopy and scan electron microscopy (SEM) of PNIPA hydrogel were studied. The microscope photograph showed that the particles were in the range of 0.2–0.5mm in diameter, with numerous conjoint pores about 1–2μm spreading all over the surface of the beads. The swelling properties of PNIPA gel beads indicated that the lower critical solution temperature (LCST) of the gel was 33°C. The PNIPA prepared was applied to the renaturation of bovine prethrombin‐2 (pThr‐2) from inclusion bodies produced in E. coli. It was observed that PNIPA was quite efficient in assisting protein renaturation at high protein concentration. When mixing with 105mg/mL PNIPA hydrogel during the refolding, the total activity of the thrombin was about 6222U/mL, compared with only 2800U/mL by simple dilution refolding. The kinetics of pThr‐2 refolding with the absence or the presence of PNIPA was also studied respectively. The time required for the refolding with PNIPA gel was a little bit longer than that by the dilution method owing to the diffusion resistance of the protein into the network of the gel and the hydrophobic interaction between the protein and the polymer. The mechanism of the enhancement for the PNIPA gel to the refolding was further discussed. The porosity of the PNIPA hydrogel allows penetration of the unfolded protein into the inside of the polymer with a hydrophobic side chain, which can facilitate the formation of intermediate via hydrophobic interaction with the unfolded protein and the folding intermediate that are liable to re‐aggregation. About 1.2mg of purified active thrombin could be recovered from 1 L of cells, which greatly facilitated the scale‐up to the quantities of protein necessary for further functional and structural studies. A novel protein renaturation method mediated by PNIPA hydrogel beads, which highly increases the refolding efficiency with easy handling, recycling, and low cost, was proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1734–1740, 2005     

Synthesis and characterization of thermally-responsive hydroxypropyl methylcellulose gel beads

Thermally responsive gels of hydroxypropyl methylcellulose (HPMC) were produced in spherical form by a suspension crosslinking technique. The suspension crosslinking of HPMC with divinylsulfone was accomplished by dispersing aqueous polymer droplets, containing all of the reactants, in a continuous organic phase. The gel beads were characterized in terms of their swelling properties and particle size distribution. The swelling degrees at 25°C of different formulations of the gel beads ranged from 12 to 123 times their dry volume and shrank to 4 to 18 times dry volume at 75°C. The spherical beads were made in diameters ranging from 500 to 3000 μ. Bead size generally decreased with use of a larger impeller, suspending at high stirring speeds, or at a lower phase ratio. As bead size decreased, the size distribution also narrowed. When compared with bulk HPMC gels, the gel beads demonstrated the same swelling properties and crosslinked network formation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1279–1290, 1997     

Adsorption of Ni2+ from aqueous solutions by novel polyethyleneimine‐attached poly(p‐chloromethylstyrene) beads

In this study Ni²⁺ adsorption properties of polyethyleneimine (PEI)‐attached poly(p‐chloromethylstyrene) (PCMS) beads were investigated. Spherical beads with an average size of 186 μm were obtained by the suspension polymerization of p‐chloromethylstyrene conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, PCMS beads had a specific surface area of 14.1 m²/g. PEI chains could be covalently attached onto the PCMS beads with equilibrium binding capacities up to 208 mg PEI/g beads, via a direct chemical reaction between the amine and chloro‐methyl groups. After PEI adsorption with 10% (w/w) initial PEI concentration, free amino content of PEI‐attached PCMS beads was determined as 0.91 mEq/g. PEI‐attached PCMS beads were utilized as adsorbents in the adsorption/desorption of Ni²⁺ ions from synthetic solutions. The adsorption process was fast; 90% of adsorption occurred within 90 min, and equilibrium was reached at around 2 h. Adsorption capacity was obtained to be 78.2 mg/g at a pH of about 6.0. The chelating beads can be easily regenerated by 0.1 M HNO₃ with higher effectiveness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2467–2473, 2002     

Synthesis of thermosensitive copolymer beads containing pyridinium groups and their antibacterial activity

Thermosensitive 4VP‐NIPAAm‐4G copolymer beads containing pyridyl groups were first prepared by suspension copolymerization of 4‐vinylpyridine (4VP), N‐isopropylacrylamide(NIPAAm), and tetraethylene glycol dimethacrylate (4G; crosslinking reagent) in a saturated Na₂SO₄ aqueous solution in the presence of surfactant and MgCO₃ as dispersants. Then the copolymer beads containing pyridinium groups were obtained by the quaternization of the copolymer beads with various alkyl iodides (CH₃I, C₄H₉I, C₈H₁₇I) in N,N‐dimethylformamide. The 4VP‐NIPAAm‐4G (15 : 97 : 3) copolymer bead and the 4VP‐NIPAAm‐4G copolymer beads quaternized with butyl iodide exhibited high thermosensitivity in water, although the 4VP‐NIPAAm‐4G copolymer beads quaternized with methyl iodide or octyl iodide hardly exhibited thermosensitivity. All the quaternized copolymer beads exhibited antibacterial activity against Escherichia coli (E. coli), although the 4VP‐NIPAAm‐4G copolymer bead did not. In particular, the copolymer bead quaternized with butyl iodide exhibited the highest antibacterial activity against E. coli at 30°C. It was also found that the antibacterial activity of the quaternized 4VP‐NIPAAm‐4G copolymer beads was greatly affected by not only chain length of alkyl groups in alkyl iodides, with which the 4VP‐NIPAAm‐4G copolymer beads were quaternized, but also by temperature of the solutions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Highly improved adsorption selectivity of L-phenylalanine imprinted polymeric submicron/nanoscale beads prepared by modified suspension polymerization

Molecularly imprinted polymer (MIP) submicron/nanoscale beads selective for L-Phenylalanine (L-Phe) and D-Phe as well as non-imprinted beads were prepared by modified suspension polymerization involving agitation of the reaction mixture at high rotation speed under safe radical conditions. The effects of pH, template and concentration of racemate solution on the performance of the phenylalanine (Phe) imprinted polymeric submicron/nanoscale beads were studied. L-Phe-imprinted submicron/nanoscale beads prepared for the first time by modified suspension polymerization showed enhanced adsorption capacity and selectivity over those of D-Phe imprinted and non-imprinted beads. Maximum adsorption capacity, 0.35 mg/g, and selectivity, 1.62, of L-Phe imprinted submicron/nanoscale beads were higher than the adsorption capacities, 0.30 and 0.19mg/g, and selectivities, 1.59 and 1.02, of D-Phe imprinted and nonimprinted submicron/nanoscale beads, respectively. FE-SEM analyses revealed that L- and D-Phe imprinted beads were larger (100 nm–1.5 μm) than non-imprinted nanobeads (100–800 nm). ¹³C CP-MAS NMR spectroscopy helped in correlating the bead sizes and the extent of reaction during polymerization. Similarly, FT-IR study was used for evaluation of structural characteristics of the prepared Phe-imprinted and non-imprinted beads. The preparation of Phe-imprinted submicron/nanoscale beads with improved adsorption and separation properties and the study of effect of template on the size and performance of the prepared beads are suitable from both economical and research point of view in MIP field.     

Pressure Cycling to Enhance an Immobilized Enzymic Reaction by Enzyme Entrapment in a Pressure-Sensitive Gel

The enzyme β-galactosidase was entrapped in poly(N-isopropylacrylamide) gel. The gel swelled or collapsed sharply upon the rise or fall of environmental pressure. The gel beads, prepared by reverse suspension polymerization, were placed in a stirred batch reactor filled with a solution of the substrateo-nitrophenol β-D -galactopyranoside. Operations under constant or cycling pressure were performed. A considerable increase in conversion rate was observed under pressure cycling operation, compared with isobaric operations at either atmospheric or high pressure. This result could be explained by the enhancement of mass transfer inside the gel beads during the pressure cycling operation.     

Preparation of functionalized Kraft lignin beads

Kraft lignin from black liquor wastes have been converted into epichlorohydrin‐crosslinked beads by inverse suspension polymerization. A careful control of the different parameters allowed the preparation of spherical beads with a relatively narrow diameter size distribution. The obtained beads, without permanent porosity, swell well in hydroalcoholic media. Grafting of the sulfonylhydrazine moiety using a two‐step route was further performed to apply them to carbonyl compounds scavenging. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of polymerization conditions on particle size distribution in styrene‐graphite suspension polymerization process

Suspension polymerization in the presence of graphite has been studied in order to determine the effects of some operational parameters on the particle size distribution (PSD). The results showed that, with increasing graphite content, the particle size of the polystyrene/graphite (PS/G) beads increased. Moreover, instability of the suspension polymerization system was found at high amounts of graphite. With increasing initiator concentration, the particle size of the polymer beads increased and the PSD became slightly narrower. Changing the concentration of the suspending agent proved to be an efficient way of controlling the particle size, although its increase led to a broadening of the PSD. Adding the suspending agent in two portions at different times decreased the particle size, maintained a lower concentration of suspending agent, and kept the suspension polymerization system stable. Adjusting the stirring speed proved to be a very efficient means of manipulating the PSD of the PS/G composite beads. The Sauter mean diameter decreased and the PSD was broadened with increasing stirring speed; 400 rpm was identified as an appropriate value to obtain polystyrene/graphite beads with desirable particle size and distribution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44270.