Microgel particles containing methacrylic acid: pH-triggered swelling behaviour and potential for biomaterial application

pH-responsive microgels are crosslinked polymer particles that swell when the pH approaches the pK(a) of the ionic monomer incorporated within the particles. In recent work from our group it was demonstrated that the mechanical properties of degenerated intervertebral discs (IVDs) could be restored to normal values by injection of poly(EA/MAA/BDDA) (ethylacrylate, methacrylic acid and butanediol diacrylate) microgel dispersions [J.M. Saunders, T. Tong, C.L. Le Maitre, T.J. Freemont, B.R. Saunders, Soft Matter 3 (2007) 486]. In this work we report the pH dependent swelling and rheological properties of poly(MMA/MAA/EGDMA) (methylmethacrylate and ethyleneglycol dimethacrylate) microgel dispersions. This system was investigated because it contains monomers that are already used as biomaterials. The poly(MMA/MAA/EGDMA) particles exhibit pH-triggered volume swelling ratios of up to ca. 250. The swelling onset for these particles occurs at pH values greater than ca. 6.0. A pK(a) for these particles of ca. 6.7 is consistent with titration and swelling data. Fluid-to-gel phase diagrams for concentrated poly(MMA/MAA/EGDMA) dispersions were determined as a function of polymer volume fraction and pH using tube-inversion measurements. The rheological properties for the gelled microgel dispersions were investigated using dynamic rheology measurements. The elastic modulus data for the poly(MMA/MAA/EGDMA) gelled dispersions were compared to data for poly(EA/MAA/BDDA) microgels. A similar pH-dependence for the elastic modulus was apparent. The maximum elastic modulus was achieved at a pH of about 7.0. The elastic modulus is an exponentially increasing function of polymer volume fraction at pH 7.0. Preliminary cell challenge experimental data are reported that indicate that gelled poly(MMA/MAA/EGDMA) microgel dispersions are biocompatible with cells from human intervertebral discs. However, the duration over which these experiments could be performed was limited by gradual redispersion of the gelled microgel dispersions. Based on the results presented it is suggested that poly(MMA/MAA/EGDMA) microgel would be a good candidate as a biomaterial for structural support of soft connective tissues.     

A study of poly(butadiene/methacrylic acid) dispersions: from pH-responsive behaviour to the effects of added Ca2+

This study investigates the effects of added Ca(2+) on the properties of poly(Bd/MAA) dispersions (1,3-butadiene and methacrylic acid) and considers the effect of particle composition on the pK(a). Four latex dispersions are considered in detail. These include poly(Bd/6MAA) and poly(Bd/20MAA) which contain, 6 and 20 wt% MAA, respectively, based on the total monomer mass used for dispersion preparation. Two model systems are also used for comparison. These are poly(Bd) and poly(EA/33MAA/BDDA) (EA and BDDA are ethyl acrylate and butanediol diacrylate). The latter is a well-studied model pH-responsive microgel. The apparent pK(a) of the poly(Bd/MAA) dispersions was determined from potentiometric titrations and found to increase with Bd content. The pH-dependence of the particle size was studied using photon correlation spectroscopy. Electrophoretic mobility measurements were also used. The hydrodynamic diameters and mobilities exhibited major changes as the pH approached the pK(a) for the particles. The critical coagulation concentrations were also measured. The results indicate that Ca(2+) caused pronounced dispersion instability at low pH. Moreover, Ca(2+) prevents swelling of the poly(Bd/MAA) particles at high pH. It was found that efficient ionic binding of all of the RCOO(-) groups within the poly(Bd/20MAA) particles occurred when the mole ratio of RCOO(-) to Ca(2+) was less than or equal to 2.0. Consideration of all the data leads to the suggestion that poly(Bd/MAA) particles have a core-shell structure. It is suggested that the particle core contains mostly poly(Bd) and that the shell is comprised of lightly crosslinked poly(Bd-co-MAA) copolymer.     

Polyethylene glycol diacrylate-based supermacroporous monolithic cryogel as high-performance liquid chromatography stationary phase for protein and polymeric nanoparticle separation

A supermacroporous monolithic cryogel was directly prepared by in situ cryo-copolymerization in a stainless steel cartridge (70mmx5.0mm I.D.) using methacrylic acid (MAA) as functional monomer and polyethylene glycol diacrylate (PEGDA) as crosslinker. The highly crosslinked (90%, molar ratio) poly(MAA-PEGDA) cryogel had more uniform supermacropores with a mean diameter of 25microm compared to the poly(acrylamide)-based cryogels. The viability of poly(MAA-PEGDA) cryogel as a medium was demonstrated for separations of lysozyme from chicken egg white (CEW) and water-soluble poly(N-isopropylacrylamide-co-3-(dimethylamino) propyl methacrylamide) (NIPAM-DMAPMA) nanoparticles from its crude reaction solution. The dynamic binding capacities of lysozyme and the polymeric nanoparticles were 4.51x10(-3)micromol/ml and 33.4microg/ml, respectively. The lysozyme recovered from the above separations had a purity of more than 85%, and retained 90% of its enzymatic activity.     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4/poly(N‐isopropylacrylamide‐co‐methacrylic acid) two‐shell thermosensitive magnetic composite hollow latex particles

In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe₃O₄/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe₃O₄ nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe₃O₄ latex particles to form the poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891     

Preparation of ion-exchange beads based on poly(methacrylic acid) brush grafted chitosan beads: Isolation of lysozyme from egg white in batch system

Poly(methacrylic acid) brush grafted crosslinked-chitosan (chitosan-g-poly(MAA)) beads were prepared in two sequential steps: in the first step, chitosan beads were prepared by phase-inversion technique and then were crosslinked with epichlorohydrin under alkaline condition; in the second step, the graft copolymerization of methacrylic acid onto the chitosan beads was initiated by ammonium persulfate (APS) under nitrogen atmosphere. The chitosan-g-poly(MAA) beads were first used as an ion exchange support for adsorption of lysozyme (LYZ) from aqueous solution. The influence of pH, equilibrium time, ionic strength and initial LYZ concentration on the adsorption capacity of the chitosan-g-poly(MAA) ion-exchange beads has been investigated in a batch system. Maximum LYZ adsorption onto chitosan-g-poly(MAA) beads was found to be 65.7 mg/g at pH 6.0. The experimental equilibrium data obtained LYZ adsorption onto chitosan-g-poly(MAA) ion-exchange beads fitted well to the Langmuir isotherm model. Kinetics parameters of this adsorption system were also analyzed by using the equilibrium experimental data. The result of kinetic analyzed for LYZ adsorption onto ion-exchange beads showed that the second order rate equation was favourable. Finally, the chitosan-g-poly(MAA) ion-exchange beads were used for the purification of LYZ from egg white in batch system and the purity of the eluted LYZ from ion-exchange chitosan-g-poly(MAA) beads was determined as 94% by HPLC from single step purification.     

Timolol maleate release from pH-sensible poly(2-hydroxyethyl methacrylate-co-methacrylic acid) hydrogels

Multifunctional polymeric materials were obtained from poly(methacrylic acid-co-2-hydroxyethyl methacrylate), to be used as a raw material in the manufacture of contact lens and as drug delivery systems. Poly(methacrylic acid-co-2-hydroxyethyl methacrylate) was prepared by free-radical polymerization in aqueous solution at 60 °C using potassium persulfate (KPS) as initiator and N,N^′-methylenebisacrylamide (BIS) as cross-linker agent. The dynamic and equilibrium swelling properties of dry glassy poly(methacrylic acid-co-2-hydroxyethyl methacrylate) polymeric networks were studied as a function of pH and methacrylic acid (MAA) content. The water content increase as MAA content and pH increase. Timolol maleate delivery from poly(MAA) and poly(2-hydroxyethyl methacrylate) (HEMA) homopolymers was studied and the results show a Fickian diffusion behavior.     

Adsorption, desorption, and conformational changes of lysozyme from thermosensitive nanomagnetic particles

Adsorption of globular protein, lysozyme, on thermosensitive poly(N-isopropylacrylamide) coated nanomagnetic particles was studied at different temperatures and pHs. It was observed that a maximum amount of lysozyme was adsorbed at a temperature above the lower critical solution temperature (LCST) (32 degrees C ) of the polymer and at the isoelectric point (pI=11) of lysozyme. Desorption was carried out using either NaH2PO4 (pH 4) or NaSCN (pH 6) as the desorbing agents. Conformational changes in lysozyme on desorption from nanomagnetic particles was studied by circular dichroism and intrinsic fluorescence spectroscopy. Lysozyme desorbed by NaH2PO4 showed very little conformational changes while lysozyme desorbed by NaSCN showed significant conformational changes, and 87% enzymatic activity was retained in the desorbed enzyme for desorption by NaH2PO4.     

Microgels containing methacrylic acid: effects of composition on pH-triggered swelling and gelation behaviours

pH-responsive microgels are cross-linked polymer colloids that swell when the pH approaches the pK _a of the particles. In this work, we present a comprehensive investigation of pH-triggered particle swelling and gel formation for a range of microgels containing methacrylic acid (MAA). The microgels investigated have the general composition poly(A/MAA/X), where A and X are the primary co-monomer and cross-linking monomer, respectively. The primary co-monomers were methyl methacrylate (MMA), ethyl acrylate (EA) or butyl methacrylate. The cross-linking monomers were either butanediol diacrylate (BDDA) or ethyleneglycol dimethacrylate (EGDMA). The microgels were studied using scanning electron microscopy, photon correlation spectroscopy (PCS) and dynamic rheology measurements. Gel phase diagrams were also constructed. The particles swelled significantly at pH values greater than approximately 6.0. It was shown that poly(EA/MAA/X) microgels swelled more strongly than poly(MMA/MAA/X) microgels. Furthermore, greater swelling occurred for particles prepared using EGDMA than BDDA. Concentrated dispersions of all the microgels studied exhibited pH-triggered gel formation. It was found that the fluid-to-gel transitions for the majority of the six microgel dispersions investigated could be explained using PCS data. In those cases, gelation was attributed to a colloidal glass transition. Interestingly, the microgels that were considered to have the highest hydrophobic content gelation occurred under conditions where little particle swelling was evident from PCS. The data presented show that gelled poly(EA/MAA/BDDA) and poly(MMA/MAA/EGDMA) microgel dispersions have the strongest elasticities at pH = 7.     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4 thermosensitive magnetic composite hollow latex particles

In this study, the poly(NIPAAm–MAA)/Fe₃O₄ hollow latex particles were synthesized by three steps. The first step was to synthesize the poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. Following the first step, the second step was to polymerize N‐isopropylacrylamide (NIPAAm), MAA, and crosslinking agent (N,N'‐methylene‐bisacrylamide (MBA)) in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly (NIPAAm‐MAA) core‐shell latex particles. After the previous processes, the core‐shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core in order to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, Fe²⁺ and Fe³⁺ ions were introduced to bond with the ? COOH groups of MAA segments in the poly(NIPAAm‐MAA) hollow polymer latex particles. Further by a reaction with NH₄OH and then Fe₃O₄ nanoparticles were generated in situ and the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles were formed. The concentrations of MAA, crosslinking agent (N,N'‐methylene bisacrylamide), and Fe₃O₄ nanoparticles were important factors to influence the morphology of hollow latex particles and lower critical solution temperature of poly(NIPAAm–MAA)/Fe₃O₄ magnetic composite hollow latex particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Morphology of core-shell latex particles

The progressive dissolution of carboxylated latex particles with increasing pH was utilized to investigate the internal structure of core-shell latex particles, in comparison with that of copolymeric latex particles formed from the same monomers. The results indicated that in those latex particles which are formed when ethyl acrylate (EA) -methacrylic acid (MAA) or methyl acrylate (MA) -MAA mixture is polymerized in the presence of poly(MA-MAA) or poly(EA-MAA) seeds the shell is composed of the more hydrophilic poly(MA-MAA) molecules relatively high in MAA content and the core is composed of both poly(MA-MAA) and poly(EA-MAA) molecules, regardless of the order of the stage feed, while the copolymeric latex particles are relatively uniform from surface to center in distribution of all components except MAA. Examination of the distribution of the carboxylic groups in all of the latex particles showed their concentration to be highest at the surface and to decrease with proximity to the center in accordance with other findings reported in the literature.     

Lysozyme purification from tobacco extract by polyelectrolyte precipitation

Tobacco is widely used as a model plant for feasibility studies of recombinant protein production from transgenic plants. However, dealing with large quantities of biomass to recover recombinant proteins is a challenge for down-stream processing. In this study, the effect of isoelectric precipitation on native tobacco protein was first studied. Among the three acids studied, hydrochloric acid is shown to be more effective than acetic or citric acid, and at pH 4, 60% of native tobacco protein was precipitated by HCl. Egg white lysozyme was used as the model protein to test the feasibility of polyelectrolyte precipitation in protein recovery from tobacco extract. Precipitation of lysozyme at pH 7 was shown ineffective probably because of the interference of polyphenolic acids. However, after isoelectric precipitation at pH 5 poly(acrylic) acid (PAA) was shown to precipitate 85% of the soluble lysozyme when the polymer dosage was increased to 1.5 mg polymer/mg lysozyme, while negligible amounts of native tobacco protein was co-precipitated. Lysozyme precipitation by PAA in tobacco extract obtained at pH 5 was also studied, and lysozyme yield was significant improved.     

Preparation and Characterization of Poly(N‐Vinylpyrrolidone‐co‐Methacrylic Acid) Hydrogels

In this study, N‐vinylpyrrolidone (VP)/methacrylic acid (MAA) copolymers have been prepared at three different mole percents, the methacrylic acid composition being around 5, 10, 15%. MAA and VP monomer mixtures have been irradiated in ⁶⁰Co‐γ source at different irradiation doses and percent conversions have been determined gravimetrically. ～80% conversion of monomers into hydrogels were performed at 3.4 kGy irradiation dose. These hydrogels were swollen in distilled water at pH 4.0, 7.0, and 9.0. P(VP/MAA) hydrogel which contains 5% methacrylic acid showed the maximum % swelling at pH 9.0 in water. Diffusion of water was found to be of non‐Fickian character. Diffusion coefficients of water in P(VP/MAA) hydrogels were calculated. Initial swelling rates of P(VP/MAA) hydrogels increased with increasing pH and MAA content in hydrogels. Swelling kinetics of P(VP/MAA) hydrogels was found to be of second order. Thermal behavior of PMAA, PVP and P(VP/MAA) hydrogel were investigated by thermal analysis. P(VP/MAA) hydrogel gained new thermal properties and the temperature for maximum weight loss and temperature for half‐life of P(VP/MAA) hydrogel were determined.     

Effects of pH,salt, surfactant and composition on phase transition of poly(NIPAm/MAA) nanoparticles

The volume phase transition of poly(NIPAm/MAA) copolymer nanoparticles in buffer solutions at various pH and in aqueous solutions of KCl or ionic surfactants (SDS and DTMAB) was systematically studied using dynamic laser scattering technique. It was found that ionizable MAA groups imparted a responsiveness of the particles to pH and electrolytes. At pH > pKa of the copolymer, electrostatic repulsion of negative charges, mostly from COO⁻ groups, was a governing mechanism for preventing the particles from collapse at T > T_tr. The particles exhibited a sharp volume phase transition upon elimination of the negative charges by decreasing the pH of the medium or by the addition of cationic surfactant. At pH < pKa, the presence of MAA groups enhanced the hydrophobicity of the particles as indicated by a lower T_tr and a sharper volume phase transition. A pH 4 buffer at the same ionic strength exhibited the most significant effect on the particle size and phase transition, followed by the ionic surfactant with an opposite charge (e.g., DTMAB), KCl, and finally the ionic surfactant with the same charge (e.g. SDS). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2667–2676, 1999     

Optically Triggered Dissociation of Kinetically Stabilized Block Copolymer Vesicles in Aqueous Solution

We demonstrate a strategy for using an optical stimulus to trigger the dissociation of block copolymer (BCP) vesicles in aqueous solution. The BCP, comprising hydrophilic poly(ethylene oxide) (PEO) and a block of poly(methacrylic acid) bearing a number of spiropyran methacrylate comonomer units (P(MAA‐co‐SPMA)), was allowed to firstly self‐assemble into large vesicles in aqueous solution at pH = 3 with protonated carboxylic acid groups, and then become kinetically stable at pH = 8 due to the glassy vesicle membrane of P(MAA‐co‐SPMA). Fast dissociation of the vesicles was achieved through a cascade of events triggered by UV‐induced isomerization from neutral spiropyran to charged merocyanine in the membrane.

     

Synthesis and characteristics of poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive semi‐hollow latex particles and their application to drug carriers

In this work, the poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite semi‐hollow latex particles was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate‐co‐methacrylic acid) (poly (MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second process was to polymerize methacrylic acid (MAA), N‐isopropylacrylamide (NIPAAm), and crosslinking agent, N,N′‐methylenebisacrylamide, in the presence of poly(MMA‐MAA) latex particles to form the linear poly(methyl methacrylate‐co‐methacrylic acid)/crosslinking poly(methacrylic acid‐co‐N‐isopropylacrylamide) (poly(MMA‐MAA)/poly(MAA‐NIPAAm)) core–shell latex particles with solid structure. In the third process, part of the linear poly(MMA‐MAA) core of core–shell latex particles was dissolved by ammonia to form the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles. The morphologies of the semi‐hollow latex particles show that there is a hollow zone between the linear poly(MMA‐MAA) core and the crosslinked poly(MAA‐NIPAAm) shell. The crosslinking agent and shell composition significantly influenced the lower critical solution temperature of poly(MMA‐MAA)/poly(MAA‐NIPAAm) semi‐hollow latex particles. Besides, the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles were used as carriers to load with the model drug, caffeine. The processes of caffeine loaded into the semi‐hollow latex particles appeared four situations, which was different from that of solid latex particles. In addition, the phenomenon of caffeine released from the semi‐hollow latex particles was obviously different from that of solid latex particles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3441–3451     

Synthesis of pH‐sensitive surfactants by the terpolymerization of methacrylic acid,methoxy poly(ethylene glycol) methacrylate,and lauryl methacrylate: Initiator effect and reactivity ratio study

For the development of pH‐sensitive surfactants to be used in water‐in‐oil fermentation, the free‐radical terpolymerization of methacrylic acid (MAA), methoxy poly(ethylene glycol) methacrylate (MPEGMA), and lauryl methacrylate (LMA), at a molar ratio of 1.0:0.04:0.76, was studied with two initiators, azobisisobutyronitrile (AIBN) and hydrogen peroxide, at different concentrations. The polymer synthesized with 0.45% AIBN as the initiator was the most promising, giving similar conversions of all three monomers throughout the 10‐h polymerization. The subsequent study on AIBN‐initiated systems indicated that MPEGMA caused an increase‐then‐decrease profile of the MAA conversion with a plateau around an ethylene glycol/MAA ratio of 1–2. This observation was fairly consistent with the well‐known type II template polymerization of poly(ethylene glycol) (PEG)–MAA systems. The reactivity ratios obtained in this study suggested that the polymer synthesized with AIBN as the initiator had a structure of alternating blocks of MAA and LMA, with isolated PEG grafts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2950–2959, 2004     

Selective extraction based on poly(MAA‐VB‐EGMDA) monolith followed by HPLC for determination of hordenine in plasma and urine samples

Hordenine is an active compound found in several foods, herbs and beer. In this work, a novel sorbent was fabricated for selective solid‐phase extraction (SPE) of hordenine in biological samples. The organic polymer sorbent was synthesized in one step in the plastic barrel of a syringe by a pre‐polymerization solution consisting of methacrylic acid (MAA), 4‐vinylphenylboronic acid (VB) and ethylene glycol dimethacrylate (EGDMA). The conditions for preparation were optimized to generate a poly(MAA‐VB‐EGMDA) monolith with good permeability. The monolith exhibited good enrichment efficiency towards hordenine. By using tyramine as the internal standard, a poly(MAA‐VB‐EGMDA)‐based SPE‐HPLC method was established for analysis of hordenine. Conditions for SPE, including volume of eluting solvent, pH of sample solution, sampling rate and sample volume, were optimized. The proposed SPE‐HPLC method presented good linearity (R² = 0.9992) within 10–2000 ng/mL and the detection limits was 3 ng/mL, which is significantly more sensitive than reported methods. The method was also applied in plasma and urine samples; good capability of removing matrices was observed, while hordenine in low content was well extracted and enriched. The recoveries were from 90.6 to 94.7% and from 89.3 to 91.5% for the spiked plasma and urine samples, respectively, with the relative standard deviations <4.7%. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and stability of BODIPY‐based fluorescent polymer brushes at different pHs

We report a simple strategy for the grafting of poly(methacrylic acid) [poly(MAA)] brushes from silicon substrate by surface‐initiated RAFT polymerization and the subsequent coupling of BODIPY to these brushes to render them fluorescent. The poly(MAA) brushes were first generated by functionalization of hydrogen‐terminated silicon substrate with methyl‐10‐undecenoate which both leads to the formation of an organic layer covalently linked to the surface via Si? C bonds without detectable reaction of the carboxylate groups and couples to the polymerization initiator, followed by surface‐initiated RAFT polymerization of tert‐butyl methacrylate from these substrate‐bound initiator centers, and finally conversion of tert‐butyl groups to carboxylic acid groups. The poly(MAA) brushes were then made fluorescent by grafting a BODIPY derivative via an ester linkage. The stability of the BODIPY‐based fluorescent polymer brushes in buffer solutions at pH 6.0 to 12.0 with added salt was investigated by ellipsometry, fluorescence microscopy, grazing angle‐Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy. The results of these measurements indicated that the organic molecule‐initiator bond (ester linkage) is unstable and can be hydrolyzed resulting in detaching of the immobilized polymer from the silicon substrate. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3586–3596     

Protein recognition via ion-coordinated molecularly imprinted supermacroporous cryogels

Molecular imprinting is a method for making selective binding sites in synthetic polymers using a molecular template. The aim of this study is to prepare lysozyme-imprinted supermacroporous cryogels which can be used for the purification of lysozyme (Lyz) from egg white. N-Methacryloyl-(L)-histidinemethylester (MAH) was chosen as the metal-coordinating monomer. In the first step, Cu2+ was complexed with MAH and the lysozyme-imprinted poly(HEMA-MAH) [Lyz-MIP] cryogel were produced by free radical polymerization initiated by N,N,N',N'-tetramethylene diamine (TEMED) in an ice bath. After that, the template (i.e., lysozyme) was removed using 0.05 M phosphate buffer containing 1M NaCl (pH 8.0). The maximum lysozyme adsorption capacity was 22.9 mg/g polymer. The relative selectivity coefficients of Lyz-MIP cryogel for lysozyme/bovine serum albumin and lysozyme/cytochrome c were 4.6 and 3.2 times greater than non-imprinted poly(HEMA-MAH) (NIP) cryogel, respectively. Purification of lysozyme from egg white was also monitored by determining the lysozyme activity using Micrococcus lysodeikticus as substrate. The purity of the desorbed lysozyme was about 94% with recovery about 86%. The Lyz-MIP cryogel could be used many times without decreasing the adsorption capacity significantly.     

Synthesis and Characterization of Novel pH‐Responsive Polyampholyte Microgels

Summary: We synthesized for the first time novel pH‐responsive polyampholyte microgels consisting of poly(methacrylic acid) and poly(2‐(diethylamino)ethyl methacrylate) (PMAA‐PDEA) that are sterically stabilized with poly(ethylene glycol) methyl ether methacrylate (PEGMEM). These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH but become hydrophobic and compact between pH 4 and 6 near the isoelectric point. Dynamic‐light scattering measurements showed that the hydrodynamic radius, R_h of these microgels is approximately 100 nm between pH 4 and 6 and increases to around 140 and 170 nm at pH 2 and 10, respectively. It is evident that the cross‐linked MAA‐DEA microgel that is sterically stabilized with PEGMEM retains the polyampholyte properties in solution.

Sterically stabilized cross‐linked MAA‐DEA microgel.