Precipitation Polymerization Of N-isopropylacrylamide Research Articles

Stimuli-sensitive and degradable capsules as drug carriers with decreased toxicity against healthy cells

Novel hollow hydrogel capsules, stimuli-sensitive and degradable polymer-based, were synthesized. These capsules were prepared by a facile method based on precipitation polymerization of N-isopropylacrylamide (NIPA) with crosslinking agent -N,N′-bis(acryloyl)cystine (BISS) on -C = C- modified sacrificial dimethyldiethoxysilane emulsion templates (DMDES). The capsules were formed after the removal of the silica core by ethanol. The presence of carboxylic groups from BISS gave the capsules stability and sensitivity to pH. The presence of the -S-S- groups, in turn, made the polymer network susceptible to degradation by the reducing agent glutathione, which is present at elevated concentration in some cancer cells. The anticancer drug Doxorubicin (DOX) was loaded and released from capsules after their degradation. The highest release of drug was observed at 37 °C and cGSH = 40 mM, which corresponds well with the conditions present in most cancer cells. The MTT assay indicated that the DOX-loaded capsules were more cytotoxic against MCF-7 breast cancer cells than DOX alone. Importantly, they were less toxic against the healthy MCF-10A cells. The unloaded gel nanoparticles did not inhibit proliferation of the cells.

Preparation of Temperature-Responsive Antibody-Nanoparticles by RAFT-Mediated Grafting from Polymerization.

Herein, we report the preparation of temperature-responsive antibody-nanoparticles by the direct polymerization of N-isopropylacrylamide (NIPAAm) from immunoglobulin G (IgG). To this end, a chain transfer agent (CTA) was introduced into IgG, followed by the precipitation polymerization of NIPAAm in an aqueous medium via reversible addition-fragmentation chain transfer polymerization above the lower critical solution temperature (LCST). Consequently, antibody-polymer particles with diameters of approximately 100-200 nm were formed. Owing to the entanglement of the grafted polymers via partial chemical crosslinking, the antibody-nanoparticles maintained their stability even at temperatures below the LCST. Further, the dispersed nanoparticles could be collected by thermal precipitation above the LCST. Additionally, the antibody-nanoparticles formulation could maintain its binding constant and exhibited a good resistance against enzymatic treatment. Thus, the proposed antibody-nanoparticles can be useful for maximizing the therapeutic potential of antibody-drug conjugates or efficacies of immunoassays and antibody recovery and recycling.

Specific Binding of Ligand-Functionalized Thermoresponsive Microgels: Effect of Architecture, Ligand Density, and Hydrophobicity.

The biomolecular interaction of ligand-presenting switchable microgels is studied with respect to the polymer type, composition, and structure of the microgels. Monodisperse microgels are prepared through precipitation polymerization of N-isopropylacrylamide (PNIPAM microgels) or oligo(ethylene glycol methacrylamide)s (POEGMA microgels) in the presence of crosslinkers or in their absence (self-crosslinked). Functionalization with mannose or biotin as model ligands and affinity measurements upon heating/cooling are conducted to obtain mechanistic insights into how the microgel phase transition affects the specific interactions. In particular, we are interested in adjusting the crosslinking, swelling degree, and ligand density of mannose-functionalized microgels to reversibly catch and release mannose binding Escherichia coli by setting the temperature below or above the microgels' volume phase transition temperature (VPTT). The increased mannose density for collapsed microgels above the VPTT results in stronger E. coli binding. Detachment of E. coli by reswelling the microgels below the VPTT is achieved only for self-crosslinked microgels showing a stronger decrease in ligand density compared to microgels with dedicated crosslinkers. Owing to a reduced mannose density in the shell of POEGMA microgels, their E. coli binding was lower compared to PNIPAM microgels, as supported by ultraresolution microscopy. Importantly, an inverse temperature-controlled binding of microgels decorated with hydrophilic mannose and hydrophobic biotin ligands is observed. This indicates that hydrophobic ligands are inaccessible in the collapsed hydrophobic network above the VPTT, whereas hydrophilic mannose units are then enriched at the microgel-water interface and thus are more accessible.

Thermo-responsive membranes fabricated by immobilization of microgels with enhanced gating coefficinent and reversible behavior

Thermo-responsive smart gating membranes have much potential applications in many fields, such as controlled release of drug, chemical/biological separation, sensors and water purification. In this study, a series of novel thermo-responsive membranes were fabricated through immobilization of thermo-responsive microgels into commercial microfiltration membranes via dynamic adsorption. The microgels were synthesized via precipitation polymerization of N-isopropylacrylamide (NIPAm), which can be reversibly expanded and shrunken upon the temperature change. This thermo-responsive behavior was preserved after incorporation of them into the membrane, indicating reversible water flux between the pore closure state at 25 °C and the pore opening state at 40 °C and high stimuli-responsive gating coefficient of 41 under narrow temperature range (25 °C–40 °C). More importantly, the resultant membrane exhibits good thermo-tunable separation performance for the polystyrene (PS) nanoparticles with different size, which has bright potential for the application in water gating and controlled release systems.

Temperature-Responsive Poly(N-Isopropylacrylamide) Nanogels: The Role of Hollow Cavities and Different Shell Cross-Linking Densities on Doxorubicin Loading and Release.

Smart polymers with extraordinary characteristics are studied in drug-delivery applications. In the current study, temperature-responsive hybrid core-shell nanoparticles were synthesized by precipitation polymerization of N-isopropylacrylamide and vinyl-modified silica nanoparticles. These temperature-responsive hybrid core-shells were prepared with different cross-linking densities by using 2, 4, and 8 mol % of N,N-methylene bisacrylamide (MBA). Hydrolysis of the silica cores of the hybrid core-shells resulted in hollow poly(N-isopropylacrylamide) (PNIPAM) nanogels. Functionalization of silica nanoparticles with vinyl-containing silane modifier of 3-(trimethoxysilyl) propyl methacrylate (MPS) in two different contents was proven by Fourier transform infrared spectroscopy. Preparation of the hybrid PNIPAM nanogels and etching of the silica cores were studied using thermogravimetric analysis and also electron microscopy imaging. Sensitivity of the PNIPAM nanogel samples to temperature was studied using ultraviolet-visible (UV-vis) spectroscopy. In addition, dynamic light scattering was used for investigation of the squeezing and expansion of the hybrid and hollow samples against variation of temperature. The UV-vis spectroscopy results display higher absorption intensities in higher contents of MPS modifier and MBA cross-linker. The swelling content of the nanogels with hollow cavities was higher than that of the hybrid samples. The hybrid nanogels with 2 and 8 wt % silica content and different cross-linking densities and also their hollow nanoparticles were used for loading and release of doxorubicin (DOX). The release characteristics of the DOX-loaded nanogels were studied at different temperatures using UV-vis spectroscopy. The DOX release was higher at temperatures lower than the gel collapse temperature of the PNIPAM network. Although the nanogels with hollow cavities displayed higher loading capacities, the release percentage was higher for the hybrid PNIPAM nanogels, which was confirmed by the experimental release profiles and mathematical models. The most appropriate fitting of the DOX release data from the PNIPAM nanogel samples was observed for the Korsmeyer-Peppas model. Cytotoxicity studies on HeLa cell line showed that drug-loaded hollow samples showed higher toxicity due to loading of a higher amount of DOX.

Biocatalytically Initiated Precipitation Atom Transfer Radical Polymerization (ATRP) as a Quantitative Method for Hemoglobin Detection in Biological Fluids.

The hemoglobin content of blood is an important health indicator, and the presence of microscopic amounts of hemoglobin in places where it normally does not occur, e.g. in blood plasma or in urine, is a sign of diseases such as hemolytic anemia or urinary tract infections. Thus, methods to detect and quantify hemoglobin are important for clinical laboratories, blood banks, and for point-of-care diagnostics. The precipitation polymerization of N-isopropylacrylamide by hemoglobin-catalyzed atom transfer radical polymerization (ATRP) is used as an assay for hemoglobin quantification relying on the formation of turbidity as a simple optical read-out. Dose-response curves for pure hemoglobin and for hemoglobin in blood plasma, in urine, in erythrocytes, and in full blood are obtained. Turbidity formation increases with the concentration of hemoglobin. Concentrations of hemoglobin as low as 6.45 × 10-3 mg mL-1 in solution, 4.88 × 10-1 mg mL-1 in plasma, and 1.65 × 10-1 mg mL-1 in urine could be detected, which is below the clinically relevant concentrations in the respective body fluids. Total hemoglobin in full blood is also accurately determined. The reaction can be regarded as a polymerization-based signal amplification for the sensing of hemoglobin, as the analyte catalyzes the formation of radicals which add many monomer units into detectable polymer chains. While most established hemoglobin tests involve the use of highly toxic reagents such as potassium cyanide, the polymerization-based test uses simple and stable organic reagents. Thus, it is an environmentally friendlier alternative to established chemical assays for hemoglobin.

Direct Monitoring of Microgel Formation during Precipitation Polymerization of N-Isopropylacrylamide Using in Situ SANS.

Poly(N-isopropylacrylamide) microgels have found various uses in fundamental polymer and colloid science as well as in different applications. They are conveniently prepared by precipitation polymerization. In this reaction, radical polymerization and colloidal stabilization interact with each other to produce well-defined thermosensitive particles of narrow size distribution. However, the underlying mechanism of precipitation polymerization has not been fully understood. In particular, the crucial early stages of microgel formation have been poorly investigated so far. In this contribution, we have used small-angle neutron scattering in conjunction with a stopped-flow device to monitor the particle growth during precipitation polymerization in situ. The average particle volume growth is found to follow pseudo-first order kinetics, indicating that the polymerization rate is determined by the availability of the unreacted monomer, as the initiator concentration does not change considerably during the reaction. This is confirmed by calorimetric investigation of the polymerization process. Peroxide initiator-induced self-crosslinking of N-isopropylacrylamide and the use of the bifunctional crosslinker N,N′-methylenebisacrylamide are shown to decrease the particle number density in the batch. The results of the in situ small-angle neutron scattering measurements indicate that the particles form at an early stage in the reaction and their number density remains approximately the same thereafter. The overall reaction rate is found to be sensitive to monomer and initiator concentration in accordance with a radical solution polymerization mechanism, supporting the results from our earlier studies.

High-Speed AFM Reveals the Detailed Mechanism of Dynamic Protein Adsorption Onto Individual Hydrogel Microspheres

Hydrogel microspheres, i.e., microgels have both colloidal and hydrogel properties, which are composed of cross-linked hydrophilic polymer network. Due to the colloidal size property and biocompatibility, microgels are promising for advanced bio-nanomaterials such as protein drug delivery vehicles [1]. In order to establish the design concept of such protein carrier, understanding the dynamic interaction between the protein and microgels is essential. Up to now, the dynamic interaction between protein and microgels is well characterize by means of scattering, spectroscopy, and sensor [2]. However, to the best of our knowledge, there are no study that direct visualization during protein adsorption to individual microgels at nanoscale in real-time. Against this background, we visualized individual microgels during protein adsorption onto the microgels at nanoscale in real-time for the first time [3]. This approach, which enabled us to monitor the moment of protein adsorption to individual microgels, was realized by high-speed atomic force microscopy (HS-AFM) [4]. This method allows the direct visualization of the dynamics of biological molecules in action, without significantly disturbing the physiological function of the molecules [5]. We have already monitored the dynamic adsorption behavior of microgels onto solid/liquid interface [6]. The microgels were synthesized through aqueous free-radical precipitation polymerization of N-isopropyl acrylamide, the cross-linker N,N'-methylenebis (acrylamide), and acrylic acid with different content. In this presentation, the effect of protein interaction on the microgels’ dynamics will be discussed. Partially reproduced with permission from [6] Copyright (2017) John Wiley and Sons.

Modification of gold electrode with a monolayer of self-assembled microgels

A new method of modification of the gold-electrode surface with a microgel monolayer was developed. Microgel particles contained –S-S– groups to enable modification of the gold surface by self-assembly via the chemisorption process. The particles were obtained by precipitation polymerization of N-isopropylacrylamide with N,N′-bis(acryloyl)cystine cross-linker. Their spherical shape and highly uniform dispersion were confirmed by electron microscopies (SEM and TEM). Thermosensitivity of the microgel was investigated with dynamic light scattering (DLS). The formation of monolayers was monitored with a quartz-crystal microbalance. The morphology of the modified surface in its dry state and in aqueous environment was investigated with atomic force microscopy (AFM). At temperatures below the volume-phase-transition temperature the microgels formed a densely packed structure that well covered the entire surface. A significant change in morphology was observed after raising temperature above the volume-phase-transition temperature. The observed increase in roughness of the modified surface suggested that the surface of electrode could be locally, between the microgel particles, uncovered. The electrochemical properties of the modified electrode were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A strong influence of the volume phase transition in the microgels attached to the Au surface on CV and EIS responses of the modified electrode was found. The observed behavior was reversed to that of the electrodes modified with a thin thermosensitive gel film based on N-isopropylacrylamide, i.e. the volume phase transition led to a significant increase in the voltammetric current and to a drop in electron transfer resistance. That was related to partial uncovering of the electrode surface after the shrinking process in the microgels.

The next step in precipitation polymerization of N-isopropylacrylamide: particle number density control by monochain globule surface charge modulation

Many applications of poly(N-isopropylacrylamide) microgels necessitate robust control over particle size.

Poly(N-isopropylacrylamide-co-methacrylic acid) microgel stabilized copper nanoparticles for catalytic reduction of nitrobenzene

Abstract Poly(N-isopropylacrylamide-co-methacrylic acid) microgels [p(NIPAM-co-MAAc)] were synthesized by precipitation polymerization of N-isopropylacrylamide and methacrylic acid in aqueous medium. These microgels were characterized by dynamic light scattering and Fourier transform infrared spectroscopy. These microgels were used as micro-reactors for in situ synthesis of copper nanoparticles using sodium borohydride (NaBH4) as reducing agent. The hybrid microgels were used as catalysts for the reduction of nitrobenzene in aqueous media. The reaction was performed with different concentrations of cat­alyst and reducing agent. A linear relationship was found between apparent rate constant (kapp) and amount of catalyst. When the amount of catalyst was increased from 0.13 to 0.76 mg/mL then kapp was increased from 0.03 to 0.14 min-1. Activation parameters were also determined by performing reaction at two different temperatures. The catalytic process has been discussed in terms of energy of activation, enthalpy of activation and entropy of activation. The synthesized particles were found to be stable even after 14 weeks and showed catalytic activity for the reduction of nitrobenzene.

High-performance composite membranes incorporated with carboxylic acid nanogels for CO2 separation

Composite membranes were fabricated by incorporating carboxylic acid nanogels (CANs) into a Pebax MH 1657 matrix for potential applications in CO2/CH4 (or N2) separation. CANs were synthesized by precipitation polymerization of N-isopropylacrylamide (NIPAM), acrylic acid (AA) monomer and N,N′-methylenebisacrylamide (BIS) crosslinker. The incorporation of CANs simultaneously tailored favorable water environment and increased CO2 transport sites within the membranes. With increasing CANs loading, the homogeneously dispersed CANs in the Pebax matrix offered more favorable water environment and the additional carboxyl group sites for efficient CO2 transport, thus constructing interconnected preferential CO2 transport passageways. The Pebax-CANs-30 composite membrane exhibited the highest gas separation performance, with the CO2/CH4 and CO2/N2 selectivities of 33 and 85 respectively, and a CO2 permeability of 2026 Barrer (1 Barrer=10−10cm3 (STP) cm/(cm2scmHg), well surpassing the Robeson's upper bound limit reported in 2008. This effort will give rise to a new option to tailor water environment and increase CO2 transport sites for fabricating high-performance CO2 separation membranes.

Effect of carbon nanotubes on free radical polymerization of N-isopropylacrylamide in supercritical carbon dioxide and in methanol

Effect of carbon nanotubes (CNT) on free radical polymerization of N-isopropylacrylamide (NIPAAm) initiated by azobisisobutyronitrile at 55°C in supercritical carbon dioxide (scCO2) of 27.6MPa and in methanol (MeOH) was investigated. The weight average molecular weight (Mw) of PNIPAAm polymerized in scCO2 for 10h was 1.2×106g/mol but that of PNIPAAm in MeOH was 0.3×106g/mol as determined by the intrinsic viscosity. Yield of the polymerization for 10h in scCO2 was higher than that in MeOH. Gel permeation chromatography was not effective for molecular weight characterization of PNIPAAm, with a higher Mw giving a larger discrepancy as compared to the viscometric method. PNIPAAm of higher Mw as prepared in scCO2 giving more chain entanglements that could enhance formations of intrachain and interchain hydrogen bonds resulted in a decrease of the lower critical solution temperature of PNIPAAm. CNT reduced yield but raised Mw of PNIPAAm much more in scCO2 than in MeOH, an indication that radical scavenging efficiency of CNT in the precipitation polymerization of NIPAAm in scCO2 was higher than that in the solution polymerization of NIPAAm in MeOH.

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Smart surface imprinting polymer nanospheres for selective recognition and separation of glycoprotein

Through covalent immobilization of template and surface imprinting, smart molecularly imprinted polymer nanospheres were developed for selective separation of the glycoprotein ovalbumin (OB). First, a boronic acid group-bearing poly (methyl methacrylate) (b-PMMA) nanosphere was synthesized directly at the high temperature of 70°C. The b-PMMA nanosphere could pre-immobilize the template OB on its surface by forming reversible covalent bonds. Then the precipitation polymerization of N-isopropylacrylamide (NIPAAm) and acrylamide (AAm) readily occurred on the b-PMMA nanosphere as a core at room temperature, leading to the formation of core–shell molecular imprinting nanosphere. The experiments showed the rebinding affinity of the imprinted nanospheres was thermo- and pH-dependent. The resulting imprinted nanospheres showed high adsorption capacity and good specific recognition behavior toward the template molecule, and no obvious reusability deterioration was observed. Most notably, the imprinted nanospheres reached saturated adsorption within 20min, indicating faster rebinding kinetics. In addition, the imprinted nanospheres were successfully applied to selectively separate the target OB from an egg white sample.

Preparation of wormlike PNIPAM microcontainers with magnetic nanoparticle inclusions

Wormlike poly(N-isopropylacrylamide) (PNIPAM) microcontainers with magnetic nanoparticle inclusions were prepared. First, wormlike iron oxide/SiO2 nanostructures were prepared based on one-dimensional chainlike self-assembly of magnetic nanoparticles followed by a sol-gel process of tetraethyl orthosilicate on the surface of the assemblies. Then, the wormlike iron oxide/SiO2 nanostructures were grafted with linear copolymer of N-isopropylacrylamide (NIPAM) and γ-methacryloxypropyltrimethoxysilane (MPS). PNIPAM shell was fabricated on the P(NIPAM-co-MPS)-modified wormlike iron oxide/SiO2 nanostructures by precipitation polymerization of NIPAM and N,N′-methylenebisacrylamide (MBA). At last, wormlike PNIPAM microcontainers with magnetic nanoparticle inclusions were obtained by removing the middle silica layer with NaOH. The microcontainers have potential applications in drug delivery system, protective shield for bioactive materials, etc.

A versatile method for the preparation of rigid submicron hollow capsules containing a temperature responsive shell

This paper presents a novel method for the preparation of temperature responsive and hollow polymer microcapsules consisting of a rigid cross-linked primary layer on the hollow core and temperature responsive shell. Temperature responsive and perfect core–shell structured magnetic polymer particles were prepared first by a two step seed emulsion polymerization process. i) Divinylbenzene (DVB) cross-linked magnetic@P(DVB) particles were obtained by the emulsion polymerization of DVB using potassium persulfate (KPS) as an initiator in the presence of an oil-in-water magnetic emulsion. ii) The magnetic@P(DVB) composite particles were then functionalized by the precipitation polymerization of N-isopropylacrylamide (NIPAm) with functional co-monomer aminoethylmethacrylate hydrochloride (AEMH) and cross-linker N,N′-methylenebisacrylamide (MBA). 2,2′-azobis(2-methylpropionamidine) dihydrochloride (V-50) was used as an initiator. Core–shell magnetic@P(DVB)@P(NIPAm-AEM) particles were then treated with concentrated HCl. The treatment with HCl dissolved the iron oxide nanoparticles from the magnetic core to form hollow P(DVB)@P(NIPAm-AEM) particles. The hollow structure of temperature responsive P(DVB)@P(NIPAm-AEM) particles prepared was confirmed by Transmission Electron Microscopy (TEM). Dynamic light scattering (DLS) results prove that the P(DVB)@P(NIPAm-AEM) hollow microcapsules are submicron in size with a narrow size distribution, cationic surface charge and most importantly, volume phase transition above its lower critical solution temperature (LCST) of P(NIPAm-AEM) shell. This volume phase transition behaviour of the P(NIPAm-AEM) shell can be utilised as an on/off switch in controlling the permeability of biomolecules or drugs into/from the hollow capsules.

Highly temperature responsive core–shell magnetic particles: Synthesis, characterization and colloidal properties

Temperature responsive magnetic polymer submicron particles were prepared by two step seed emulsion polymerization process. First, magnetic seed polymer particles were obtained by emulsion polymerization of styrene using potassium persulfate (KPS) as an initiator and divinylbenzne (DVB) as a cross-linker in the presence of oil-in-water magnetic emulsion (organic ferrofluid droplets). Thereafter, DVB cross-linked magnetic polymer particles were used as seed in the precipitation polymerization of N-isopropylacrylamide (NIPAM) to induce thermosensitive PNIPAM shell onto the hydrophobic polymer surface of the cross-linked magnetic polymer particles. To impart cationic functional groups in the thermosensitive PNIPAM backbone, the functional monomer aminoethylmethacrylate hydrochloride (AEMH) was used to polymerize with NIPAM while N,N′-methylenebisacrylamide (MBA) and 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (V-50) were used as a cross-linker and as an initiator respectively. The effect of seed to monomer (w/w) ratio along with seed nature on the final particle morphology was investigated. Dynamic light scattering (DLS) results demonstrated particles swelling at below volume phase transition temperature (VPTT) and deswelling above the VPTT. The perfect core (magnetic) shell (polymer) structure of the particles prepared was confirmed by Transmission Electron Microscopy (TEM). The chemical composition of the particles were determined by thermogravimetric analysis (TGA). The effect of temperature, pH, ionic strength on the colloidal properties such as size and zeta potential of the micron sized thermo-sensitive magnetic particles were also studied. In addition, a short mechanistic discussion on the formation of core–shell morphology of magnetic polymer particles has also been discussed.

Effect of thiol-containing monomer on the preparation of temperature-sensitive hydrogel microspheres

The main objective of this study is to prepare, thermally, sensitive microgel particles bearing thiol groups via precipitation polymerization of N-isopropylacrylamide (NIPAM), methylenebisacrylamide (MBA) and vinylbenzylisothiouronium chloride (VBIC) using 2-2′-azobis(2-amidinopropane)-dihydrochloride (V50) as initiator. The influence of various parameters has been investigated as a systematic study to point out the role of each reactant on polymerization conversion, and consequently, on particles and water-soluble polymer formation. The final microgel particles were characterized with respect to particle size and swelling ability. The aim of this paper is to complete our first short communication; Macromolecular symposia, 2000. 150: p. 283–290.

Enzyme immobilization on thermosensitive hydrogel microspheres

Precipitation polymerization of N-isopropylacrylamide, acrylamide, and methylenebisacrylamide in water at 70°C resulted in thermosensitive hydrogel microspheres. Carboxyl groups on the microspheres were introduced by hydrolysis, and amino groups by the Hofmann reaction of amide units on the microspheres. Trypsin was immobilized on the carboxylated microspheres using carbodiimide. Phase transitions were detected using a hydrophobic fluorescence probe. The temperatures at which a phase transition occurred were increased by immobilizing enzymes. The enzymatic activity of the immobilized enzymes decreased above the transition temperature. This was attributed to (i) a decrease in the diffusion of substrate; and (ii) entrapment of enzyme in the surface layer of the microspheres. In an attempt to overcome the entrapment, enzymes were immobilized via a hydrophilic spacer (α-(carboxymethyl)-ω-(carboxymethoxy)-poly(oxy-1,2-ethanediyl), PEO acid) to the microspheres. These enzyme-carrying hydrogel microspheres were found to show an enzymatic activity independent of temperature, even though these conjugates show a phase transition at the lower critical solution temperature.