Carboxymethylated polyethylenimine modified magnetic nanoparticles specifically for purification of His‐tagged protein

Employing immobilized metal‐ion affinity chromatography and magnetic separation could ideally provide a useful analytical strategy for purifying His‐tagged protein. In the current study, a facile route was designed to prepare CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ (CMPEI=carboxymethylated polyethyleneimine) magnetic nanoparticles composed of a strong magnetic core of Fe₃O₄ and a Ni²⁺‐immobilized carboxymethylated polyethyleneimine coated outside shell, which was formed by electrostatic interactions between polyanionic electrolyte of carboxymethylated polyethyleneimine and positively charged surface of 3‐(trimethoxysilyl)propylamin modified SiO₂@Fe₃O₄. The resulting CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ composite nanoparticles displayed well‐uniform structure and high magnetic responsiveness. Hexa His‐tagged peptides and purified His‐tagged recombinant retinoid X receptor alpha were chosen as the model samples to evaluate the adsorption, capacity, and reusability of the composite nanoparticles. The results demonstrated the CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ nanoparticles possessed rapid adsorption, large capacity, and good recyclability. The obtained nanoparticles were further used to purify His‐tagged protein in practical environment. It was found that the nanoparticles could selectively capture His‐tagged recombinant retinoid X receptor protein from complex cell lysate. Owing to its easy synthesis, large binding capacity, and good reusability, the prepared CMPEI‐Ni²⁺@SiO₂@Fe₃O₄ magnetic nanoparticles have great potential for application in biotechnological fields.     

Cancer‐associated pH‐responsive tetracopolymeric micelles composed of poly(ethylene glycol)‐b‐poly(L‐histidine)‐b‐poly(L‐lactic acid)‐b‐poly(ethylene glycol)

To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH‐sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol)‐b‐poly(L ‐histidine)‐b‐poly(L ‐lactic acid)‐b‐poly(ethylene glycol)] consisted of a hydrophobic poly(L ‐histidine) (polyHis) and poly(L ‐lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1–3.5 µg/ml and an average size of 65–80 nm pH 7.4. Importantly, they showed a pH‐dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd.     

Fabrication of poly(ethylene glycol)‐based hydrogels entrapping enzyme‐immobilized silica nanoparticles

In this study, we immobilized enzymes by combining covalent surface immobilization and hydrogel entrapment. A model enzyme, glucose oxidase (GOX), was first covalently immobilized on the surface of silica nanoparticles (SNPs) via 3‐aminopropyltriethoxysilane (APTES), and the resultant SNP‐immobilized enzyme was physically entrapped within photopolymerized hydrogels prepared from two different molecular weights (MWs) (575 and 8000 Da) of poly(ethylene glycol)(PEG). The hydrogel entrapment resulted in a decrease in reaction rate and an increase in apparent K_m of SNP‐immobilized GOX, but these negative effects could be minimized by using hydrogel with a higher MW PEG, which provides higher water content and larger mesh size. The catalytic rate of the PEG 8000 hydrogel was about ten times faster than that of the PEG 575 hydrogel because of enhanced mass transfer. Long‐term stability test demonstrated that SNP‐immobilized GOX entrapped within hydrogel maintained more than 60% of its initial activity after a week, whereas non‐entrapped SNP‐immobilized GOX and entrapped GOX without SNP immobilization maintained less than 20% of their initial activity. Incorporation of SNPs into hydrogel enhanced the mechanical strength of the hydrogel six‐fold relative to bare hydrogels. Finally, a hydrogel microarray entrapping SNP‐immobilized GOX was fabricated using photolithography and successfully used for quantitative glucose detection. Copyright © 2009 John Wiley & Sons, Ltd.     

A pH‐sensitive water‐soluble N‐carboxyethyl chitosan/poly(hydroxyethyl methacrylate) hydrogel as a potential drug sustained release matrix prepared by photopolymerization technique

Biocompatible pH‐sensitive semi‐interpenetration polymeric network hydrogels (semi‐IPN) based on water‐soluble N‐carboxyethyl chitosan (CECS) and 2‐hydroxyethyl methacrylate (HEMA) were synthesized by the photopolymerization technique. pH‐sensitivity, cytotoxicity, morphology, mechanical property, and water state of hydrogel were investigated by a swelling test, methylthiazolydiphenyl‐tetrazolium bromide (MTT) assay, scanning electron microscopy (SEM), universal testing machine, and differential scanning calorimetry (DSC), respectively. The drug release studies were carried out using 5‐Flurouracil as the model drug. The results indicated that the hydrogels were sensitive to pH of the medium and its wet state had good mechanical properties. The results of cytotoxicity and prolonged drug release characteristics revealed the suitability of the hydrogels as drug delivery matrices. The release kinetics was evaluated by fitting the experimental data to standard release equations, and the best fit was obtained with the Higuchi model of the hydrogel. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(acrylic acid)‐chitosan @ tannic acid double‐network self‐healing hydrogel based on ionic coordination

In this work, poly(acrylic) acid‐chitosan @ tannic acid‐aluminum ion (PAA‐CS@TA‐Al³⁺) double‐network hydrogel was prepared via prefabrication, blending method, and Al³⁺ immersion method. The interaction between chitosan and tannic acid (CS@TA) was analyzed using Fourier transfer infrared spectra and UV‐Vis spectra. The UV‐Vis spectrum was also used to confirm the formation of ionic coordination in the gel. Then, the possible coordination modes were studied and analyzed. The microscopic pore structure and macroscopic strain behavior of the gel were analyzed using SEM and tensile testing, respectively, which verified that the tensile strength (≈32 KPa) and elongation at break (≈1700%) of the gel primarily resulted from its crosslinking structure. In addition, the gel also demonstrated a good self‐healing performance with recovery ≈92.2% at 60 minutes. Hence, the proposed novel self‐healing gel can provide inspiration for the preparation of future self‐healing gels.     

Interpenetrating polymer network hydrogels based on silicone and poly(2‐methacryloyloxyethyl phosphorylcholine)

In the present work, sequential interpenetrating polymer networks (IPNs) based on silicone and poly(2‐methacryloyloxyethyl phosphorylcholine) (PMPC) were developed with improved protein resistance. The structure and morphology of the IPNs were characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The results showed that the IPNs exhibited heterogeneous morphology. The bulk properties such as water content, ion permeability, and mechanical strength of the IPNs were determined by gravimetric method, ionoflux measurement technique, and tensile tester, respectively. The surface characteristics of the IPNs were investigated by X‐ray photoelectron spectroscopy (XPS) and contact angle measurements. XPS analysis suggested that PMPC was present on the surface as well as in the bulk material. The IPNs possessed more hydrophilic surface than pristine silicone revealed by contact angle measurements. Bovine serum albumin (BSA) was used as a model protein to evaluate protein resistance by a bicinchoninic acid assay method. The result revealed that the protein adsorption on the IPNs was significantly reduced compared to pristine silicone. These results suggest that the IPNs based on silicone and PMPC may be developed as novel ophthalmic biomaterials. Copyright © 2010 John Wiley & Sons, Ltd.     

Star‐shaped and photocrosslinked poly(1,5‐dioxepan‐2‐one): Synthesis and characterization

New star‐shaped and photocrosslinked poly(1,5‐dioxepan‐2‐one) (PDXO) has been synthesized through ring‐opening polymerization initiated by SnOct₂/pentaerythritol. The star‐shaped PDXO was end‐functionalized by acrolyol chloride to form acrylate end groups. The end‐functionalized PDXO was photocrosslinked initiated by 2,2‐dimethoxy‐2‐phenylacetophenone. The gel content ranged from 80 to 99%, indicating a high degree of crosslinking. The thermal properties of the star‐shaped PDXO and the photocrosslinked PDXO were analyzed by differential scanning calorimetry. The glass‐transition temperature was determined to approximately ?32 °C for the crosslinked PDXO. The viscosity numbers were determined for star‐shaped PDXO, with reference to linear homologues. The star‐shaped PDXO had lower viscosity numbers than the linear counterparts. The crosslinked PDXO showed a rather hydrophilic surface as compared with other resorbable polyesters. The advancing contact angle was 64 ± 2, and the receding angle was 57 ± 4. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2049–2054, 2002     

Protein‐ and homo poly(amino acid)‐based hydrogels with super‐swelling properties

The use of super‐swelling polymers is steadily increasing and the applications in industry are continuing to grow. With the authorization of the superabsorbents in food packaging by the Food and Drug Administration recently, demand may soon take off in the market. However, the increase in prices of petroleum products in recent years may be a drawback for these acrylic‐based materials. Thus, there is now a need to develop natural‐based super‐swelling hydrogels which are more economical and environment friendly. In addition, the super‐swelling gels are promising novel functions in the biomedical and pharmaceutical applications. This review is aimed to highlight research and trends in protein‐ and homo poly(amino acid)‐based super‐swelling hydrogels. Thus, the proteinaceous hydrogels, including chemically modified soy‐, fish‐ and collagen‐based proteins, are discussed. The protein‐polysaccharide, protein‐synthetics, and the inorganic composites are also investigated as hybrid materials. Finally, the super‐swelling hydrogels based on homo polypeptides, i.e. poly(aspartic acid), poly(glutamic acid), and poly(ε‐L‐lysine) are reviewed. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and thermal properties of a novel lactose‐containing poly(N‐isopropylacrylamide‐co‐acrylamidolactamine) hydrogel

An improved, simple, and efficient method for the synthesis of lactose‐containing monomer acrylamidolactamine (LAM) has been reported. Free radical copolymerization of this monomer with N‐isopropylacrylamide (NIPAM) in the presence of the crosslinking reagent N,N′‐methylenebisacrylamide (BisA) (1.2 mol %) proceeded smoothly in an aqueous solution using potassium persulfate (KPS) and N,N,N′,N′‐tetramethylethylenediamine (TMEDA) as the initiating system and gave transparent hydrogels. Reactivity ratios were estimated from copolymerization reactions carried out in solution without BisA crosslinker and at low conversion, by using both linearization and nonlinearization methods. They were found to be r_LAM = 0.75 and r_NIPAM = 1.22. The swelling behavior of the hydrogels was studied by immersion of the hydrogels in deionized water at different temperatures. Equilibrium water uptake was increased when the LAM content was higher than 47 mol %, and reached ≈ 44‐fold with 100 mol % LAM at room temperature. Depending on the composition, the gels showed sharp swelling transitions with small changes in temperature. Differential scanning calorimetry (DSC) was used to characterize the swelling transition and the organization of water in the copolymer hydrogels. The amounts of freezable water in these hydrogels ranged from 81 to 89%, and was not correlated to the content of the sugar monomer. These gels have potential applications as biocompatible materials. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1393–1402, 1999     

Cobalt(III)‐Mediated Permanent and Stable Immobilization of Histidine‐Tagged Proteins on NTA‐Functionalized Surfaces

We present the cobalt(III)‐mediated interaction between polyhistidine (His)‐tagged proteins and nitrilotriacetic acid (NTA)‐modified surfaces as a general approach for a permanent, oriented, and specific protein immobilization. In this approach, we first form the well‐established Co²⁺‐mediated interaction between NTA and His‐tagged proteins and subsequently oxidize the Co²⁺ center in the complex to Co³⁺. Unlike conventionally used Ni²⁺‐ or Co²⁺‐mediated immobilization, the resulting Co³⁺‐mediated immobilization is resistant toward strong ligands, such as imidazole and ethylenediaminetetraacetic acid (EDTA), and washing off over time because of the high thermodynamic and kinetic stability of the Co³⁺ complex. This immobilization method is compatible with a wide variety of surface coatings, including silane self‐assembled monolayers (SAMs) on glass, thiol SAMs on gold surfaces, and supported lipid bilayers. Furthermore, once the cobalt center has been oxidized, it becomes inert toward reducing agents, specific and unspecific interactions, so that it can be used to orthogonally functionalize surfaces with multiple proteins. Overall, the large number of available His‐tagged proteins and materials with NTA groups make the Co³⁺‐mediated interaction an attractive and widely applicable platform for protein immobilization.     

Preparation and characterization of poly(acrylic acid)‐iron rich smectite superabsorbent composites

A novel poly(acrylic acid)‐iron rich smectite (IRS) superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) in the presence of N,N‐methylenebisacrylamide (MBA) as a crosslinker. IRS was used to strengthen the hydrogel products in the polymerization process. Water absorbencies for these superabsorbent composites in water and saline solutions were investigated. IRS caused a reduced equilibrium swelling as low as 8–26%. However, grafted IRS particles resulted in improved gel strength as high as 66% compared to the IRS‐free sample. IRS modified superabsorbent hydrogel composites exhibited higher thermal stability compared to the IRS‐free sample. The pH dependent reversible swelling behavior of hydrogels was also investigated. It is found that the swelling process is pH dependent and reversible for synthesized superabsorbent. Superabsorbent hydrogel composites were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR spectroscopy was confirmed grafting of acrylic chains onto the surface of IRS particles. From the standpoint of these results, these strengthened and thermostabilized hydrogels may be considered as good candidates for a controlled release study and agricultural applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and characterization of poly(acrylic acid‐co‐acrylamide)/hydrotalcite nanocomposite hydrogels for carbonic anhydrase immobilization

To combine the advantages of a biopolymer with hydrotalcite in an enzyme immobilization system, the intercalation polymerization was used to prepare poly(acrylic acid‐co‐acrylamide)/hydrotalcite (PAA‐AAm/HT) nanocomposite hydrogels using sodium methyl allyl sulfonate as intercalation agent. Transmission electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy results revealed that sodium methyl allyl sulfonate chains entered into the interlayer of HT, the interaction between them has taken place, and HT was dramatically exfoliated into nanoscale and homogeneously dispersed in the PAA‐AAm matrix. Transmission electron microscopy and cryo scanning electron microscope results showed that dried hydrogels were regular spherical particles, and swollen hydrogels revealed homogeneous porous network structures. Then, PAA‐AAm/HT nanocomposite hydrogels were used to immobilize carbonic anhydrase (CA), and the CO₂ hydration activities of free enzyme and immobilized enzyme were evaluated. Results showed that immobilized CA retained the majority of the enzyme activity. The reason may be the formation of a microenvironment almost all of which is composed of free water inside the porous network structures. Therefore, the immobilized CA is of great potential in the removal of trace CO₂ from the closed spaces. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3232–3240, 2009     

Thermo‐/moisture‐responsive shape‐memory effect of poly(2‐ethyl‐2‐oxazoline) networks

In this work, poly(2‐ethyl‐2‐oxazoline) (PEtOx) is crosslinked to realize a moisture‐ and thermo‐responsive shape‐memory polymer. The obtained PEtOx networks exhibit excellent shape‐memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape‐memory cycles. The trigger temperature (T_trig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1053–1061     

Rheology and phase behavior of thermo‐reversible pentablock terpolymer hydrogel

Thermo‐reversible phase behaviors and rheological properties of a pentablock terpolymer solution, poly(N‐isopropylacrylamide)‐b‐poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PNIPAM₁₅₀‐PEO₁₃₆‐PPO₄₅‐PEO₁₃₆‐PNIPAM₁₅₀), are investigated in comparison with its precursor, PEO₁₃₆‐PPO₄₅‐PEO₁₃₆ (F108). It is found that the critical gelation concentration of the terpolymer solution is only about 11 wt %, which is significantly lower than that of F108 solution (～22 wt %). The 11 wt % terpolymer solution displays higher viscosity, stronger gel strength, and fast thermo‐responsive behavior compared with the 22 wt % F108 solution. The 11 wt % terpolymer solution shows a typical Newtonian fluid behavior at 30 °C due to the presence of individual spherical micelles, and presents an elastic gel property at 41 °C because of the formation of the close‐packed micelle aggregates. Cryogenic transmission electron microscopy (cryo‐TEM) and variable‐temperature ¹H NMR results demonstrate that the sol–gel phase transition mechanism is mainly related to the hydrophilic/hydrophobic transition of PPO and PNIPAM groups by external temperature stimulus. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1335–1342     

A thermodynamic analysis of specific interactions in homoblends of poly(styrene‐co‐4‐vinylpyridine) and poly(styrene‐co‐methacrylic acid)

Miscibility and strong specific interactions that occurred within homoblends of poly(styrene‐co‐4‐vinylpyridine) containing 15 mol % of 4‐vinylpyridine (PS4VP15) and poly(styrene‐co‐methacrylic acid) containing 15 mol % of methacrylic acid (PSMA15) have been examined by Fourier Transform infrared spectroscopy and DSC. The observed positive deviation of the glass transition temperature of the blends from the linear average line, was analyzed by the frequently used theoretical conventional approaches including the one very recently proposed by Brostow. A better fit was obtained when this latter is used. A reasonable agreement with experimental values was also obtained when the theoretical fitting parameter free method developed by Coleman, is applied to predict the composition dependence of the T_g of this system. A thermodynamic analysis of hydrogen bonding in this system was carried using the Painter‐Coleman association model and the variation of the Gibbs function of mixing and its different contributions and corresponding phase diagrams as a function of temperature and composition were estimated. This analysis predicted PSMA15 to be miscible with PS4VP15 in the whole composition range up to 150 °C. Above this temperature, a partial miscibility is predicted when the PS4VP15 is in excess. The DSC results are in agreement with these predictions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 923–931, 2009     

Gas‐forming poly(ethylene glycol)‐b‐poly(L‐lactic acid) micelles

In this study, a novel drug‐carrying micelle composed of methoxy poly(ethylene glycol) (mPEG)‐b‐poly(L‐lactic acid) (PLLA) with gas‐forming carbonate linkage was fabricated. Here, the gas‐forming carbonate linkage was formed by the chemical coupling of the terminal hydroxyl group of the PLLA block and benzyl chloroformate (BC). mPEG‐b‐PLLA‐BC was self‐organized in aqueous solution: the PEG block on the hydrophilic outer shell and the PLLA‐BC block in the hydrophoboic innor core. The cleavage of carbonate linkage by hydrolysis and formation of carbon dioxide nanobubbles in the micellar core enabled an accelerated release of the encapsulated anticancer drug (doxorubicin: DOX) from the mPEG‐b‐PLLA‐BC micelles. The amount of drug (DOX) released from the mPEG‐b‐PLLA‐BC micelle was higher than that from the conventional mPEG‐b‐PLLA micelle, which allowed for increased in vitro toxicity against KB tumor cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Robust solvent‐free fabrication and characterization of (polydimethylsiloxane‐co‐2‐hydroxyethylmethacrylate)/poly (ethylene glycol) methacrylate (PDMS‐HEMA)/PEGMA hydrogels

Combining hydrophobic materials such as polydimethylsiloxane (PDMS), a natural hydrophobic material with typical hydrophilic monomers without using organic solvent remains a big challenge due to their extreme different properties; hence, fabricating a class of silicone hydrogels with two extremes without use of organic solvents could bring us a novel class of silicone hydrogels. Herein, a range of PDMS‐HEMA‐PEGMA hydrogels was prepared from hydroxyl‐terminated PDMS, 2‐hydroxyethylmethacrylate (HEMA), poly (ethylene glycol) methacrylate (PEGMA), and isophorone diisocyanate via condensation and radical copolymerization reactions. The infrared results confirmed the PDMS‐HEMA‐PEGMA network formation, while the hydrophilicity of the as‐prepared block copolymer was dependent on (PDMS‐HEMA)/PEGMA ratio. Increasing the PEGMA content resulted in increased equilibrium water content, phase separation, surface roughness, and tensile strength, while the tensile modulus, elongation at break, optical transmittance, water contact angle, and oxygen permeability (Dk) were decreasing. At PEGMA content of 28.3%, the relative protein adsorption ratio decreased to 20% and 36% for bovine serum albumin and lysozyme, respectively, compared with that of the control (PDMS‐HEMA), suggesting antiprotein adsorption ability. In overall, the results showed that the PDMS‐HEMA‐PEGMA hydrogels not only exhibited remarkable hydrophilicity and suppressed protein adsorption but also maintained higher optical transparency and oxygen permeability (Dk).     

Novel biomimetic composite based on collagen and poly(γ‐benzyl L‐glutamate)‐co‐poly(glutamic acid)

Novel biomimetic composite was prepared by the reaction of collagen and poly(γ‐benzyl L ‐glutamate)‐co‐poly(glutamic acid) (PBLG‐co‐PGA), which were crosslinked by non‐toxic crosslinking reagents 1‐ethyl‐(dimethylaminopropyl) carbodiimide (EDC) and N‐hydroxysuccinimide (NHS). The composite was characterized by FTIR and DSC. FTIR results confirmed that the collagen in the composite was successfully crosslinked with PBLG‐co‐PGA. DSC results showed that the composites possessed higher shrinkage temperature and higher thermal stability than the collagen. The water absorption test showed that the water absorbency of the composites increased with the increase in PBLG‐co‐PGA content in the composite. The studies of collagenase degradation and the tensile strength showed that the biostability and the tensile strength of the composites were significantly improved in comparison with that of the collagen. According to the investigations of cell adherent ratio and cell proliferation in vitro, the composite possessed good biocompatibility. Copyright © 2007 John Wiley & Sons, Ltd.