Surface-initiated Graft Polymerization Research Articles

Yolk-Shell Encapsulation of Cells by Biomimetic Mineralization and Visible Light-Induced Surface Graft Polymerization.

The pursuit of low-cytotoxicity modification strategies represents a prominent avenue in cell coating research, holding immense significance for the advancement of practical living cell-related technologies. Here, we presented a novel method to fabricate encapsulated yeast cells with a yolk-shell structure by biomimetic mineralization and visible-light-induced surface graft polymerization. In this approach, an amorphous calcium carbonate (ACC) shell was first deposited on the surface of a yeast cell (cell@ACC) modified with 4 layers of self-assembled poly(diallyl dimethylammonium chloride) (PDADMAC)/poly(acrylic acid) (PAA) film using a biomimetic mineralization technique. Subsequently, polyethylenimine (PEI) was absorbed on the surface of cell@ACC by electrostatic interaction. Then, a cross-linked shell was introduced by surface-initiated graft polymerization of poly(ethylene glycol) diacrylate (PEGDA) on cell@ACC under irradiation of visible light using thioxanthone catechol-O,O'-diacetic acid as the photosensitizer. After the removal of the inner ACC shell, the yolk-shell-structured yeast cells (cell@PHS) were obtained. Due to the mild conditions of the strategy, the cell@PHS could retain 98.81% of its original viability. The introduction of the shell layer significantly prolonged the lag phase of yeast cells, which could be tuned between 5 and 25 h by regulating the thickness of the shell. Moreover, the cell@PHS showed improved resistance against lyticase due to the presence of a protective shell. After 30 days of storage, the viability of cell@PHS was 81.09%, which is significantly higher than the 19.89% viability of native yeast cells.

A Versatile Strategy to Coat Individual Cell with Fully/Partially Covered Shell for Preparation of Self-Propelling Living Cells.

Coating living cells with a functional shell has been regarded as an effective way to protect them against environmental stress, regulate their biological behaviors, or extend their functionalities. Here, we reported a facile method to prepare fully or partially coated shells on an individual yeast cell surface by visible light-induced graft polymerization. In this strategy, yeast cells that were surface-absorbed with polyethylenimine (PEI) were deposited on the negatively charged glass slide to form a single layer by electrostatic interaction. Then, surface-initiated graft polymerization of poly(ethylene glycol) diacrylate (PEGDA) on yeast cells under visible light irradiation was carried out to generate cross-linked shells on the cells. The process of surface modification had negligible influence on the viability of yeast cells due to the mild reaction condition. Additionally, compared to the native yeast cells, a 17.5 h of delay in division was observed when the graft polymerization was performed under 15 mW/cm2 irradiation for 30 min. Introducing artificial shell endowed yeast cells with significant resistance against lyticase, and the protection can be enhanced by increasing the thickness of shell. Moreover, the partially coated yeast cells would be prepared by simply adjusting the reaction condition such as irradiation density and time. By immobilizing urease on the functional patch, the asymmetrically modified yeast cells exhibited self-propelling capability, and the speed of directional movement reached 4 μm/s in the presence of 200 mM urea. This tunable coating individual cell strategy with varying functionality has great potential applications in fields of cell-based drug delivery, cell therapy, biocatalysis, and tissue engineering.

Preparation of hybrid particles via surface-initiated polymerization from thiol-functionalized attapulgite and their application in polycarbonate as an efficient processing modifier

ABSTRACT In this work, the thiolized attapulgite (ATP-MTS) particles were prepared by the dealcoholation between hydroxyl and γ-mercaptopropyltrimethoxysilane (MTS). Then, based on the ‘grafting from’ mechanism, the surface-initiated graft polymerization was carried out to give ATP grafted with polymethyl methacrylate hybrid particles (ATP@PMMA). The grafting process was characterized in detail by FTIR, TGA, XRD, XPS, TEM and elemental analysis. The effects of the main polymerization conditions on the grafting ratio were investigated in detail. Finally, polycarbonate (PC) was modified with ATP@PMMA to investigate the effects of hybrid particles on the processability of nanocomposites. The results showed that ATP@PMMA particles with a maximum graft ratio of 23.3% were prepared successfully within 5 h. The optimum polymerization temperature was 60°C, and the ratio of MMA/SH/AIBN was 500/2/1. The surface tailoring improved the dispersion of ATP@PMMA in the matrix. Compared with the pristine PC, the incorporation of ATP@PMMA enhanced the melt flow index (MFI), while reduced the glass transition temperature (T g) and complex viscosity of nanocomposites.

Characteristics and advantages of surface-initiated graft-polymerization as a way of “grafting from” method for graft-polymerization of functional monomers on solid particles

In our researches done in recent years, a late-model graft-polymerization way as a means of “grafting from” method was founded, and it is the surface-initiated graft-polymerization. By using this new means, various functional monomers were smoothly grafted on solid particles, getting a variety of functional grafted particles. The key of this way lied on constituting a redox surface-initiating system at the interface between the particle and the solution, so that a great deal of free radicals would be produced on the surfaces of solid particles, and smoothly initiated the monomer to be graft-polymerized on solid particles. In this work, based on a lot of experimental data, the characteristics and advantages of the surface-initiated graft-polymerization way were further summarized, and therelevant mechanisms were analyzed. The system of NH2/S2O82− as a typical surface-initiating system wasused, and the graft-polymerizations of three functional monomers, methacrylic acid (MAA), 2-hydroethyl methacrylate (HEMA) and N,N-dimethylaminoethyl methacrylate (DMAEMA), on silica gel particles were carried out. For comparison, the graft-polymerizations of the above three monomers were also performed by using “grafting through” method. The experimental results show that the graft-polymerizations by using surface-initiated graft-polymerization way can be carried out under mildconditions. More importantly, two distinct characteristics of the surface-initiated graft-polymerization way are displayed as compared with the “grafting through” method, and they are high grafting degree and rapid graft-polymerization rate. For example, for the graft-polymerization of HEMA, as the surface-initiated graft-polymerization way is used, the grafted degree of PHEMA on PHEMA/SiO2 particles at 30 °C in 12 h reaches up to 41 g/100 g, whereas when the “grafting though” method is adopted, the grafted degree of PHEMA on PHEMA/SiO2 particles at 60 °C in 20 h only reaches 15 g/100 g.

Friction Properties of Hydrated Phospholipid Polymer Brush Films Prepared by Surface Initiated Graft Polymerization

Friction Properties of Hydrated Phospholipid Polymer Brush Films Prepared by Surface Initiated Graft Polymerization

Decorating an individual living cell with a shell of controllable thickness by cytocompatible surface initiated graft polymerization.

Surface engineering of individual living cells is a promising field for cell-based applications. However, engineering individual cells with controllable thickness by chemical methods has been rarely studied. This article describes the development of a new cytocompatible chemical strategy to decorate individual living cells. The thicknesses of the crosslinked shells could be conveniently controlled by the irradiation time, visible light intensity, or monomer concentration. Moreover, the lag phase of the yeast cell division was extended and their stability against lysis was improved, which could also be tuned by controlling the shell thickness.

Preparation of cationic functional polymer poly(Acryloxyethyltrimethyl ammonium chloride)/SiO2 and its adsorption characteristics for heparin

Ion-exchange is a widely used purification technology in the heparin manufacturing process. To improve the rate and efficiency, the cationic monomer Acryloxyethyltrimethyl ammonium chloride (DAC) was grafted on silica gel particles by using a surface-initiated graft-polymerization technique, and a novel adsorption polymer of PDAC/SiO2 was prepared. The adsorption experiments of PDAC/SiO2 for heparin show that there are strong electrostatic interactions between heparin with a high density of negative charges and PDAC/SiO2 that exists in many quaternary ammonium cations. Comparing the adsorption kinetics of PDAC/SiO2 with D201 anionic strong alkali exchange resin, PDAC/SiO2 shows higher adsorption capacity and faster adsorption rate. The pH and temperature of solutions have a great influence on the adsorption amount, and there is a maximum adsorption capacity of 121mg/g when pH=7 at 25 °C. The adsorption of PDAC/SiO2 for heparin is an exothermic process and driven by entropy.

Preparation of a surface-grafted imprinted ceramic membrane for selective separation of molybdate anion from water solutions

A surface-grafted imprinted ceramic membrane (IIP-PVI/CM) for recognizing molybdate (Mo(VI)) anion was prepared by surface-initiated graft-polymerization. Firstly, raw alumina ceramic membrane (CM) was deposited with SiO2 active layer by situ hydrolysis deposition method. Subsequently, γ-methacryloxy propyl trimethoxyl silane (MPS) was used as a coupling agent to introduce double bonds onto the SiO2 layer (MPS-CM). Then, 1-vinylimidazole (VI) was employed as a functional monomer to graft-polymerization onto the MPS-CM (PVI-CM). During the graft-polymerization, the influence factors of grafting degree of PVI were investigated in detail. Under optimum conditions (monomer concentration 20wt%, temperature 70°C, initiator amount 1.1wt% and reaction time 8h), the grafting degree of 20.39g/100g was obtained. Further, Mo(VI) anion was used as a template to imprint in the PVI-CM by employing 1,6-dibromohexane as a cross-linking agent, and then Mo(VI) was removed, obtaining the IIP-PVI/CM with many imprinted cavities for Mo(VI). Thereafter, static adsorption and dynamic separation properties of IIP-PVI/CM for Mo(VI) were studied. Results indicate that IIP-PVI/CM shows a specific selectivity for Mo(VI) with the adsorption capacity of 0.69mmol/100g, and the selectivity coefficient of IIP-PVI/CM is 7.48 for molybdate to tungstate anions. During the dynamic separation, IIP-PVI/CM has also good selectivity for separation of Mo(VI) and W(VI) anions.

Preparation and Grafting Functionalization of Self-Assembled Chitin Nanofiber Film

Chitin is a representative biomass resource comparable to cellulose. Although considerable efforts have been devoted to extend novel applications to chitin, lack of solubility in water and common organic solvents causes difficulties in improving its processability and functionality. Ionic liquids have paid much attention as solvents for polysaccharides. However, little has been reported regarding the dissolution of chitin with ionic liquids. The author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to ~4.8 wt % and the higher contents of chitin with AMIMBr gave ion gels. When the ion gel was soaked in methanol for the regeneration of chitin, followed by sonication, a chitin nanofiber dispersion was obtained. Filtration of the dispersion was subsequently carried out to give a chitin nanofiber film. A chitin nanofiber/poly(vinyl alcohol) composite film was also obtained by co-regeneration approach. Chitin nanofiber-graft-synthetic polymer composite films were successfully prepared by surface-initiated graft polymerization technique. For example, the preparation of chitin nanofiber-graft-biodegradable polyester composite film was achieved by surface-initiated graft polymerization from the chitin nanofiber film. The similar procedure also gave chitin nanofiber-graft-polypeptide composite film. The surface-initiated graft atom transfer radical polymerization was conducted from a chitin macroinitiator film derived from the chitin nanofiber film.

Fouling resistance and cleaning efficiency of stimuli-responsive reverse osmosis (RO) membranes

Abstract A series of stimuli-responsive reverse (RO) membranes were prepared by tethering three stimuli-responsive polymers, poly (sulfobetaine methacrylate) (PSBMA), poly (4-(2-Sulfoethyl)-1-(4-vinyl-benzyl) pyridinium betain) (PSVBP) and poly (N-isopropylacrylamide) (PNIPAM) onto the surface of a commercial thin-film (TFC) RO membrane via surface-initiated graft polymerization. The membrane surface was characterized by ATR-FTIR, XPS, zeta potential, water contact angle (WCA), FESEM and AFM. Membrane characterization indicates successful grafting of these polymers, with more negatively-charged, smoother and more hydrophilic surfaces as a result. Long-term fouling-rinsing cycled experiments were conducted to evaluate fouling resistance and cleaning efficiency. With CaCO 3 as the foulant, the modified membranes showed better fouling resistance in the whole testing as long as 320 h; with BSA as the foulant, they only showed better antifouling performance in short term. However, the modified membranes showed much higher cleaning efficiency in both cases, with the PA-g-PSVBP membrane as the best one.

Design and preparation of matrine surface-imprinted material and studies on its molecule recognition selectivity

A matrine molecule surface-imprinted material was designed and prepared using an effective surface-imprinting technique developed by our group, and its molecular recognition performance and mechanism were investigated in depth. Monomer glycidyl methacrylate (GMA) was first graft-polymerized on the surfaces of micron-sized silica gel particles in surface-initiated graft polymerization manner, obtaining the grafted particles PGMA/SiO2 with high grafting degree. Subsequently, the ring-opening reaction of the epoxy groups of the grafted macromolecules PGMA with 5-aminosalicylic acid (5-ASA) was carried out, resulting in the functional grafted particle SA-PGMA/SiO2, on whose surfaces salicylic acid as functional group was chemically bonded. By right of the mutual strong secondary bond forces, electrostatic interaction and hydrogen bonding, SA-PGMA/SiO2 particles produced strong adsorption for matrine. Finally, with this strong adsorption, matrine molecule surface imprinting was carried out on the surfaces of SA-PGMA/SiO2 particles with ethylene glycol diglycidyl ether as cross-linking agent, resulting in the matrine molecule surface-imprinted material MIP-SAP/SiO2. The binding characteristic of MIP-SAP/SiO2 toward matrine was investigated in depth with both batch and column methods and using oxymatrine and cytisine as two contrast alkaloids. The experimental results show that MIP-SAP/SiO2 has special recognition selectivity and excellent binding affinity for matrine. Relative to oxymatrine and cytisine, the selectivity coefficients of MIP-SAP/SiO2 for matrine are 5.66 and 11.17, respectively.

Synthesis of a highly dense and selective imprinted polymer via pre-irradiated surface-initiated graft polymerization

A highly dense and selective U(vi)-imprinted polymer was prepared by pre-irradiated surface-initiated graft polymerization.

Adsorption and recognition characteristics of surface molecularly imprinted polymethacrylic acid/silica toward genistein

In this paper, on the basis of surface-initiated graft polymerization, a new surface molecular imprinting technique is established by molecular design. And molecularly imprinted polymer MIP-PMAA/SiO2 is successfully prepared with genistein as template. The adsorption and recognition characteristics of MIP-PMAA/SiO2 for genistein are studied in depth by using static method, dynamic method and competitive adsorption experiment. The experimental results show that MIP-PMAA/SiO2 possesses very strong adsorption affinity and specific recognition for genistein. The saturated adsorption capacity could reach to 0.36mmolg−1. The selectivity coefficients relative to quercetin and rutin are 5.4 and 11.8, respectively. Besides, MIP-PMAA/SiO2 is regenerated easily and exhibits excellent reusability.

Facile preparation of SiO2 hybrid nanoparticles via Cu2+-amine redox-initiated radical polymerization

The CuSO4-catalyzed surface-initiated conventional radical graft polymerization of electron-deficient monomers such as N,N-dimethylacryamide (DMAAm) was carried out from amino-functionalized SiO2 nanoparticles (SiO2–NH2) to directly prepare hybrid SiO2 nanoparticles (SiNPs) chemically grafted with functional poly(N,N-dimethylacryamide) (SiO2-g-PDMAAm) in aqueous media with trimethyltetradecylammonium chloride (TTAC) added as a surfactant. The optimum reaction conditions were as follows: weight feed ratio CuSO4·5H2O:DMAAm:H2O:SiO2–NH2:TTAC of 1:500:5,000:1,000:100 and reaction temperature at 80 °C. Spectroscopy and microscopy confirmed the successful graft polymerization and the formation of hybrid SiNPs with PDMAAm chains. Thermogravimetric analysis indicated the grafting yield could be up to 15.39 wt%. As the active radicals only formed on the SiNP surfaces, there was no free polymer in the reacting mixture. Because of the presence of PDMMAm chains, the hybrid SiO2-g-PDMAAm nanoparticles exhibited an enhanced dispersion stability in aqueous media over the pristine SiO2–NH2, and a thermoresponsive settlement behavior. The parallel experiments with other electron-deficient monomers suggest that the current strategy requires less post-treatment, mild conditions and affords universal applicability.

Surface-initiated atom transfer radical polymerization from chitin nanofiber macroinitiator film

This paper reports the preparation of chitin nanofiber-graft-poly(2-hydroxyethyl acrylate) (CNF-g-polyHEA) films by surface-initiated atom transfer radical polymerization (ATRP) of HEA monomer from a CNF macroinitiator film. First, a CNF film was prepared by regeneration from a chitin ion gel with an ionic liquid. Then, acylation of the CNF surface with α-bromoisobutyryl bromide was carried out to obtain the CNF macroinitiator film having the initiating moieties (α-bromoisobutyrate group). The surface-initiated graft polymerization of HEA from the CNF macroinitiator film by ATRP was performed to produce the CNF-g-polyHEA film. The IR, XRD, and SEM measurements of the resulting film indicated the progress of the graft polymerization of HEA on surface of CNFs. The molecular weights of the grafted polyHEAs increased with prolonged polymerization times, which affected the mechanical properties of the films under tensile mode.

Preparation of Molybdate Anion Surface-Imprinted Material for Selective Removal of Molybdate Anion from Water Medium

A MnO4– anion surface-imprinted material was prepared with the new surface-imprinting technique of “pre-graft polymerizing and post-crosslinking/imprinting” for the selective removal of molybdate anions from a water medium. Monomer dimethylaminoethyl methacrylate (DMAEMA) was first graft-polymerized on micron-sized silica gel particles by using a surface-initiated graft-polymerization method, resulting in the grafted particles PDMAEMA/SiO2. Subsequently, the grafted macromolecule PDMAEMA was quaternized with epichlorohydrin as a reagent, and the quaternization transform of the grafted particles was realized, obtaining the functional grafted particles QPDMAEMA/SiO2, on which original tertiary amine groups had been transformed into quaternary ammonium groups. The adsorption property of the functional grafted particles for molybdate (MoO42– anion) was examined. On this basis, the MoO42– anion imprinting toward the functional macromolecules QPDMAEMA was conducted with 1,6-hexanediamine as a cross-linker, and MoO42– anion surface-imprinted material IIP-QPDMAEMA/SiO2 was obtained, namely, MoO42– anion surface-imprinted material IIP-QPDMAEMA/SiO2 was prepared with the “pre-graft polymerizing and post-crosslinking/imprinting” method. The ion recognition and combination characters of IIP-QPDMAEMA/SiO2 particles were researched in depth. The experimental results show that this MoO42– anion surface-imprinted material has specific recognition selectivity and combination affinity for the template ion, the MoO42– anion. Relative to the two contrast anions, WO42– and MnO4–, the selectivity coefficients of IIP-QPDMAEMA/SiO2 for the MoO42– anion were 6.41 and 5.39, respectively, displaying high ion recognition ability of this imprinted material.

Preparation of grafted particles PGMA/SiO2 with a new surface-initiating system of mercapto group/BPO and their functionalization transformation

A new surface-initiating system for free radical graft-polymerization of lipophilic vinyl monomer was designed. The coupling agent γ-mercaptopropyl trimethoxysilane (MPMS) was first bonded onto the surfaces of silica gel particles, obtaining the modified particles MPMS-SiO2. So a new surface-initiating system was constituted by mercapto group on the surfaces of MPMS-SiO2 and dibenzoyl peroxide (BPO) in the solution. Through the proton transfer of mercapto groups to the decomposition product of BPO, a great deal of primary sulfur free radicals were produced on the surfaces of the particles, leading to the graft-polymerization of glycidyl methacrylate (GMA) on silica gel particles, obtaining the grafted particles PGMA/SiO2 with a high PGMA grafting degree (about 26 g/100 g) . The effects of the main factors on the graft polymerization of GMA were examined and the corresponding mechanism was investigated. The functionalization transformations of the grafted particles PGMA/SiO2 were conducted via ring-opening reaction of the epoxy groups with 5-aminosalicylic acid (5-ASA) and iminodiacetic acid (IDAA) as reagents, respectively, obtaining two functional composite materials, SA-PGMA/SiO2 and IDAA-PGMA/SiO2. The new route of surface-initiated graft-polymerization is feasible and effective. The suitable temperature is 55 °C and the appropriate used amount of BPO is 1.0 % of the monomer mass. The grafted particles PGMA/SiO2 are easy to be transformed into functional composite particles via the ring-opening reaction of epoxy groups. SA-PGMA/SiO2 particles have excellent extracting ability for alkaloids, and have an adsorption capacity of 87 mg/g for matrine; IDAA-PGMA/SiO2 particles have strong chelating adsorption action for heavy metal ions, and have an adsorption capacity of 360 mg/g for Pb2+ ion.

Preparation of highly flexible chitin nanofiber-graft-poly(γ-l-glutamic acid) network film

In the previous study, we successfully prepared a chitin nanofiber film by regeneration from a chitin ion gel with an ionic liquid using methanol. In this study, we performed surface-initiated graft polymerization of γ-benzyl l-glutamate N-carboxyanhydride (BLG-NCA) from amino groups on a partially deacetylated chitin nanofiber (PDA-CNF) film. First, the chitin nanofiber film was immersed in 40 % NaOH aq. at 80 °C for 7 h for partial deacetylation. Then, the PDA-CNF film was immersed in a solution of BLG-NCA in ethyl acetate at 0 °C for 24 h for graft polymerization from amino groups on nanofibers to give a chitin nanofiber-graft-poly(γ-benzyl l-glutamate) (CNF-g-PBLG) film. The analytical results of the film indicated that graft polymerization of BLG-NCA occur on surface of nanofibers. Furthermore, the film was treated with 1.0 mol/L NaOH aq. to convert PBLG on nanofibers into poly(γ-l-glutamic acid sodium salt) (PLGA). Then, condensation of the resulting carboxylates with amino groups at the terminal ends of PLGAs or the remaining amino groups on nanofibers was performed using the condensing agent to produce a CNF-g-PLGA network film. The resulting film showed the good mechanical properties with high flexibility, which has potentials as promising materials for practical applications.

Polymer-Grafted Cellulose Nanocrystals as pH-Responsive Reversible Flocculants

Cellulose nanocrystals (CNCs) are a sustainable nanomaterial with applications spanning composites, coatings, gels, and foams. Surface modification routes to optimize CNC interfacial compatibility and functionality are required to exploit the full potential of this material in the design of new products. In this work, CNCs have been rendered pH-responsive by surface-initiated graft polymerization of 4-vinylpyridine with the initiator ceric(IV) ammonium nitrate. The polymerization is a one-pot, water-based synthesis carried out under sonication, which ensures even dispersion of the cellulose nanocrystals during the reaction. The resultant suspensions of poly(4-vinylpyridine)-grafted cellulose nanocrystals (P4VP-g-CNCs) show reversible flocculation and sedimentation with changes in pH; the loss of colloidal stability is visible by eye even at concentrations as low as 0.004 wt %. The presence of grafted polymer and the ability to tune the hydrophilic/hydrophobic properties of P4VP-g-CNCs were characterized by Fourier transform infrared spectroscopy, elemental analysis, electrophoretic mobility, mass spectrometry, transmittance spectroscopy, contact-angle measurements, thermal analysis, and various microscopies. Atomic force microscopy showed no observable changes in the CNC dimensions or degree of aggregation after polymer grafting, and a liquid crystalline nematic phase of the modified CNCs was detected by polarized light microscopy. Controlled stability and wettability of P4VP-g-CNCs is advantageous both in composite design, where cellulose nanocrystals generally have limited dispersibility in nonpolar matrices, and as biodegradable flocculants. The responsive nature of these novel nanoparticles may offer new applications for CNCs in biomedical devices, as clarifying agents, and in industrial separation processes.

Preparation of Arsenate Anion Surface-Imprinted Material IIP-PDMC/SiO2 and Study on Its Ion Recognition Property

By molecular design, a new ion surface-imprinting technique was set up based on surface-initiated graft-polymerization, and arsenate anion surface-imprinted material with high performance was prepared for the first time. A redox initiating system was constituted by the amino groups on the surface-modified silica gel particles and the ammonium persulphate in the solution. The cationic monomer 2-methacryloyloxyethyl-trimethyl ammonium chloride (DMC) was used as functional monomer and N,N′-methylenebisacrylamide (MBA) was used as cross-linker. In the solution, the monomer molecules were arranged around the template ion, arsenate anion, via ion exchange action, and then the arsenate anion surface-imprinting was carried out along with the surface-initiated graft-polymerization of DMC and MBA, forming arsenate anion surface-imprinted material IIP-PDMC/SiO₂. The experimental results show IIP-PDMC/SiO₂ possesses specific recognition selectivity and excellent binding affinity for arsenate anion. The selectivity coefficients of IIP-PDMC/SiO₂ for arsenate anion are 8.814 and 7.898 relative to chromate and nitrate ions, respectively.