Inverse Miniemulsion Research Articles

Design of Cross-Linked Starch Nanocapsules for Enzyme-Triggered Release of Hydrophilic Compounds

Cross-linked starch nanocapsules (NCs) were synthesized by interfacial polymerization carried out using the inverse mini-emulsion technique. 2,4-toluene diisocyanate (TDI) was used as the cross-linker. The influence of TDI concentrations on the polymeric shell, particle size, and encapsulation efficiency of a hydrophilic dye, sulforhodamine 101 (SR 101), was investigated by Fourier transform infrared (FT-IR) spectroscopy, dynamic light scattering (DLS), and fluorescence measurements, respectively. The final NC morphology was confirmed by scanning electron microscopy. The leakage of SR 101 through the shell of NCs was monitored at 37 °C for seven days, and afterwards the NCs were redispersed in water. Depending on cross-linker content, permeable and impermeable NCs shell could be designed. Enzyme-triggered release of SR 101 through impermeable NC shells was investigated using UV spectroscopy with different α-amylase concentrations. Impermeable NCs shell were able to release their cargo upon addition of amylase, being suitable for a drug delivery system of hydrophilic compounds.

Easily recyclable and highly active rice roll-like Au/SiO2 nanocatalysts from inverse miniemulsion

Rice roll-like (RR-like) Au/SiO2 nanocatalysts (NCs) were synthesized through simultaneous sol–gel process of tetramethoxysilane and 3-aminopropyltriethoxysilane (APTES) and in situ reduction of gold salt in inverse miniemulsions. APTES played an important role in formation of RR-like SiO2 nano-supports, reduction of gold salts to narrowly size-distributed sub–10nm Au nanoparticles (NPs), and improved attachment of Au NPs to the SiO2 nano-supports. The prepared RR-like Au/SiO2 NCs displayed a pH-dependent, reversible colloidal stability in water, which facilitated to recycle them through tuning the pH value of the dispersion. Most importantly, the catalytic activity of the RR-like Au/SiO2 NCs towards reduction of p-nitrophenol was about 7–9 times higher than that of the raspberry-like Au/SiO2 NCs reported in our previous paper (Colloids Surf. A, 489, 2016, 223–233). The formation mechanism of the RR-like Au/SiO2 NCs was also discussed.

Development of a Novel Immobilization Method by Using Microgels to Keep Enzyme in Hydrated Microenvironment in Porous Hydrophobic Membranes.

Using colloidal polyacrylamide (PAAm) microgels as carriers, a novel strategy for covalent immobilization of enzymes maintained in hydrated microenvironment on/in a macroporous surface-functionalized hydrophobic polyvinylidene fluoride (PVDF) membrane is developed. The PAAm microgels are synthesized by inverse miniemulsion polymerization, and first the parameters are investigated which are suited to obtain particles in the desired size range, 100-200 nm, with narrow size distribution. Amino functions are then imparted to the microgels applying the Hofmann reaction. The modification is confirmed by Fourier-transform infrared spectroscopy analysis, ninhydrin test, and elemental analysis. In addition, functionalized microgels are characterized by dynamic light scattering. The amino-functionalized PAAm microgels are then immobilized on pre-modified PVDF membrane having aldehyde functionalities on the surface. Afterward, unreacted aldehyde groups still present on the membrane where quenched by ethanolamine and the enzyme lipase from Candida rugosa (LCR) is subsequently immobilized on the microgels loaded PVDF membrane via glutaraldehyde cross-linking, exploiting the free amino groups on immobilized microgels. Catalytic efficiency of LCR immobilized by this strategy is evaluated using para-nitrophenyl palmitate as substrate and compared with LCR directly immobilized on PVDF membrane without microgels. Results show that LCR immobilized by means of microgels exhibits better performance with a 2.3-fold higher specific biocatalytic activity.

Crystallization at Nanodroplet Interfaces in Emulsion Systems: A Soft-Template Strategy for Preparing Porous and Hollow Nanoparticles.

A heterophase method to prepare hollow and/or porous crystalline nanoparticles of metal oxides at room temperature is presented, taking cerium(IV) oxide and γ-iron(III) oxide (i.e., maghemite) as representative cases. The crystallization begins at the oil-water interface in aqueous nanodroplets of the precursor in inverse (water-in-oil) miniemulsion systems, and it may continue toward the inner part of the droplets. A poly(styrene-b-acrylic acid) block copolymer is used as a structuring agent because the ability of the carboxylic groups to bind metal ions improves the inorganic shell formation. A precipitating base is added from the continuous phase, generating hydroxide species at the interface that begin the crystallization. We analyze the effects of the synthetic parameters in terms of colloidal stability and morphology of the resulting materials. In the case of maghemite samples, the prepared dispersions of hollow particles present a distinct magnetofluidic behavior.

Stabilization of Inverse Miniemulsions by Silyl-Protected Homopolymers.

Inverse (water-in-oil) miniemulsions are an important method to encapsulate hydrophilic payloads such as oligonucleotides or peptides. However, the stabilization of inverse miniemulsions usually requires block copolymers that are difficult to synthesize and/or cannot be easily removed after transfer from a hydrophobic continuous phase to an aqueous continuous phase. We describe here a new strategy for the synthesis of a surfactant for inverse miniemulsions by radical addition–fragmentation chain transfer (RAFT) polymerization, which consists in a homopolymer with triisopropylsilyl protecting groups. The protecting groups ensure the efficient stabilization of the inverse (water-in-oil, w/o) miniemulsions. Nanocapsules can be formed and the protecting group can be subsequently cleaved for the re-dispersion of nanocapsules in an aqueous medium with a minimal amount of additional surfactant.

Poly(ethylene glycol)-co-methacrylamide-co-acrylic acid based nanogels for delivery of doxorubicin

Polymeric nanogels have been widely explored for their potential application as delivery carriers for cancer therapeutics. The ability of nanogels to encapsulate therapeutics by simple diffusion mechanism and the ease of their fabrication to impart target specificity in addition to their ability to get internalized into target cells make them good candidates for drug delivery. The present study aims to investigate the applicability of poly(ethylene glycol)-co-methacrylamide-co-acrylic acid (PMA)-based nanogels as a viable option for the delivery of doxorubicin (DOX). The nanogels were synthesized by free radical polymerization in an inverse mini-emulsion and characterized by nuclear magnetic resonance spectroscopy (1H NMR), Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), X-ray diffraction and differential scanning calorimetry. DOX was physically incorporated into the nanogels (PMA-DOX) and the mechanism of its in vitro release was studied. TEM experiment revealed spherical morphology of nanogels and the hydrodynamic diameter of the neat nanogels was in the range of 160 ± 46.95 nm. The size of the nanogels increased from 235.1 ± 28.46 to 403.7 ± 89.89 nm with the increase in drug loading capacity from 4.68 ± 0.03 to 13.71 ± 0.01%. The sustained release of DOX was observed upto 80 h and the release rate decreased with increased loading capacity following anomalous release mechanism as indicated by the value of diffusion exponent (n = 0.64–0.75) obtained from Korsmeyer–Peppas equation. Further, cytotoxicity evaluation of PMA-DOX nanogels on HeLa cells resulted in relatively higher efficacy (IC50~5.88 μg/mL) as compared to free DOX (IC50~7.24 μg/mL) thus demonstrating that the preparation is potentially a promising drug delivery carrier.

Redox-responsive biodegradable nanogels for photodynamic therapy using Chlorin e6

Recent advances in drug carrier design in the field of photodynamic therapy (PDT) have stimulated the development of numerous sophisticated drug delivery carriers. We developed novel biodegradable and biocompatible nanogels as PDT carriers. The nanogels were synthesized by ATRP technique using inverse miniemulsion and their biodegradability was determined in the presence of glutathione. The model photosensitizer (PS) was encapsulated in the biodegradable nanogels by simple mixing and sonication. The cellular uptake of the PS-loaded nanogels and the cytotoxicity of the nanogels before and after laser irradiation were determined using HeLa cells. The results showed that the Ce6-nanogel complex was well internalized into the tumor cells, and the Ce6-loaded nanogels did not influence on cellular viability of the cells before light irradiation. Under light exposure, however, the Ce6-nanogel complex-treated HeLa cells revealed strong photoactivity. These nanogels may enhance therapeutic efficacy of PSs without any complex chemical modifications with PSs.

At-Line Monitoring of Conversion in the Inverse Miniemulsion Polymerization of Acrylamide by Raman Spectroscopy

This work studied the at-line Raman spectroscopy monitoring for the inverse miniemulsion polymerization of acrylamide. The conversion was determined from the Raman spectra without previous calibration using the peaks corresponding to —CH2— and C═C functional groups of acrylamide. Gravimetric data was used to validate the results of conversion obtained with the Raman spectra. Dynamic light scattering was used to measure the particle size. The results show that high energy in the homogenization step increases the surface area of the droplets and generates a lack of surfactant, which results in larger diameters. It is possible to make at-line monitoring of monomer conversion directly from the Raman spectra without using calibration models. The data obtained show an incomplete conversion that is also confirmed by gravimetric analysis.

Preparation, characterization and biological evaluation of curcumin loaded alginate aldehyde–gelatin nanogels

Curcumin, a natural polyphenol exhibits chemopreventive and chemotherapeutic activities towards cancer. In order to improve the bioavailability and therapeutic efficacy, curcumin is encapsulated in alginate aldehyde–gelatin (Alg Ald-Gel) nanogels. Alginate aldehyde–gelatin nanogels are prepared by inverse miniemulsion technique. Physicochemical properties of the curcumin loaded nanogels are evaluated by, Dynamic light scattering (DLS), NMR spectroscopy and Scanning electron microscopy (SEM). Curcumin loaded nanogels show hydrodynamic diameter of 431±8nm and a zeta potential of −36±4mV. The prepared nanogels exhibit an encapsulation efficiency of 72±2%. In vitro drug release studies show a controlled release of curcumin from nanogels over a period of 48h. Hemocompatibility and cytocompatibility of the nanogels are evaluated. Bare nanogels are cytocompatible and curcumin loaded nanogels induce anticancer activity towards MCF-7 cells. In vitro cellular uptake of the curcumin loaded nanogels using confocal laser scanning microscopy (CLSM) confirms the uptake of nanogels in MCF-7 cells. Hence, the developed nanogel system can be a suitable candidate for curcumin delivery to cancer cells.

Rheological evaluation of synthesized template‐hydrophobically modified acrylamide based copolymers in brine

ABSTRACTThe newly hydrophobically modified associating acrylamide‐based copolymers were prepared by the inverse miniemulsion polymerization method in order to investigate the copolymers rheological and associating properties in water and brine solutions. Dimethyldodecane (2‐acrylamidopropyl) ammonium bromide (DDPAB) was synthesized and used as a hydrophobic monomer and was later copolymerized with acrylamide in the presence of poly(acrylic acid‐co‐maleic acid) and various molecular weights of poly(acrylic acid) as templates. The chemical compositions and functional groups of the resulting hydrophobic monomer and copolymers were characterized using the 1H nuclear magnetic resonance and Fourier transform‐infrared spectroscopy. According to the studies on the solutions viscosity behavior, incorporation of small amount of hydrophobic monomer improved the thickening properties due to the intermolecular hydrophobic association. The apparent viscosity of the copolymers with a template was much greater than those prepared without a template. The molecular weight of the template strongly influenced the thickening behaviors of the copolymers. A template copolymer with 1 mol % of a hydrophobic monomer was the one most efficient. The addition of electrolyte saline improved the polarization of the solutions and enhanced the thickening ability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43588.

Preparation of CdFe2O4-polymeric nanoparticles by inverse miniemulsion and its film properties

Abstract CdFe2O4-polymeric nanoparticles were prepared by inverse miniemulsion in order to achieve an acceptable grain size on the formed spin-coated film at a low calcination temperature. Sodium polyacrylate latex (PAANa) was synthesized by inverse miniemulsion polymerization using NaOH as a co-stabilizer. The effects of the NaOH content added to the inverse miniemulsion on the size and distribution of droplets and the latex particles were studied. The Cd-Fe salt droplets from the miniemulsion were absorbed by the PAANa latex particles, and the films formed by CdFe2O4-polymeric nanoparticles were characterized. The nucleation mechanism was characterized based on the ratio of the final number of latex particles to the initial number of droplets in a volume unit (Np/Nd). The increased NaOH dosage efficiently enhanced the stability of droplets, and Np/Nd approached 1. CdFe2O4-polymeric nanoparticles were formed using PAANa latex particles as a nano-reactor. The CdFe2O4-polymeric film prepared by inverse miniemulsion exhibits high reaction activity, as evidenced by the highly crystalline spinel structure formed at a low calcination temperature. The height of the film before and after calcination at 500 °C was 79 nm and 3.2 μm, respectively. The high reaction activity of CdFe2O4-polymeric nanoparticles can be successfully achieved by the inverse miniemulsion method.

Morphology control of silica/poly(methyl methacrylate-co-styrene) hybrid nanoparticles via multiple-miniemulsion approach

AbstractAn appropriate approach has been used for the preparation of silica/P(MMA-co-St) hybrid nanoparticles through converting previously prepared inverse miniemulsions into a direct miniemulsion and consequently, using the droplet nucleation polymerization technique. In the early stage of the procedure, silica particles were synthesized from TEOS in the presence of NH4OH or HCl as a catalyst through a base or acid-catalyzed sol-gel process. TEOS, ethanol and tirmethoxyvinylsilan were mixed in MMA:St (50:50) to create the inverse miniemulsion I, similarly CTAB, NH4OH/HCl and distilled water were dispersed into MMA:St (50:50) and called inverse miniemulsion II. Then, the two mentioned inverse miniemulsions were emulsified in water to achieve direct miniemulsion. The nature of the catalyst and TEOS concentration varied, for the aims of investigation, their effect on the morphology and size of hybrid nanoparticles. This route provided a unique process for silica/polymer hybrid nanoparticles production, avoiding organic solvents. Transmission electron microscopy micrographs revealed that, the morphology of the hybrid nanoparticles can be controlled by the nature of the catalyst.

Solid lipid nanoparticles for encapsulation of hydrophilic drugs by an organic solvent free double emulsion technique

Encapsulation of hydrophilic compounds for drug delivery systems with high loading efficiency is not easily feasible and remains a challenge, mainly due to the leaking of the drug to the outer aqueous phase during nanoparticle production. Usually, encapsulation of hydrophilic drugs is achieved by using double emulsion or inverse miniemulsion systems that often require the use of organic solvents, which may generate toxicological issues arising from solvent residues. Herein, we present the preparation of solid lipid nanoparticles loaded with a hydrophilic compound by a novel organic solvent free double emulsion/melt dispersion technique. The main objective of this study was to investigate the influence of important process and formulation variables, such as lipid composition, surfactant type, sonication parameters and lipid solidification conditions over physicochemical characteristics of SLN dispersion. Particle size and dispersity, as well as dispersion stability were used as responses. SLN dispersions with average size ranging from 277 to 550nm were obtained, showing stability for over 60 days at 4°C depending on the chosen emulsifying system. Entrapment efficiency of fluorescent dyes used as model markers was assessed by fluorescence microscopy and UV–vis spectrophotometry and results suggest that the obtained lipid based nanoparticles could be potentially applied as a delivery system of water soluble drugs.

Glutathione Responsive Hyaluronic Acid Nanocapsules Obtained by Bioorthogonal Interfacial "Click" Reaction.

Azide-functionalized hyaluronic acid and disulfide dialkyne have been used for "click" reaction polymerization at the miniemulsion droplets interface leading to glutathione responsive nanocapsules (NCs). Inverse miniemulsion polymerization was chosen, due to its excellent performance properties, for example, tuning of size and size distribution, shell thickness/density, and high pay loading efficiency. The obtained size, size distribution, and encapsulation efficiency were checked via fluorescent spectroscopy, and the tripeptide glutathione was used to release an encapsulated fluorescent dye after cleavage of the nanocapsules shell. To show the glutathione-mediated intracellular cleavage of disulfide-containing NC shells, CellTracker was encapsulated into the nanocapsules. The cellular uptake in dendritic cells and the cleavage of the nanocapsules in the cells were studied using confocal laser scanning microscopy. Because of the mild reaction conditions used during the interfacial polymerization and the excellent cleavage properties, we believe that the synthesis of glutathione responsive hyaluronic acid NCs reported herein are of high interest for the encapsulation and release of sensitive compounds at high yields.

Inverse miniemulsion-based preparation of raspberry-like Au/SiO 2 nanocomposite particles with high catalytic activity towards reduction of p -nitrophenol

Abstract A convenient method based on the inverse miniemulsion technique was proposed to prepare raspberry-like Au/SiO2 nanocomposite particles (NCPs). HAuCl4 was incorporated into porous SiO2 nano-supports through a sol–gel process of a silica precursor in inverse miniemulsions. Raspberry-like Au/SiO2 NCPs were subsequently obtained through in situ reduction of the incorporated HAuCl4 by hydrazine at the surface of SiO2 nano-supports. Most of Au nanoparticles (NPs) were half-embedded in the SiO2 nano-supports and were covered by a thin layer of porous SiO2, offering a good morphological stability to the Au/SiO2 NCPs. The content of Au NPs of the Au/SiO2 NCPs could be adjusted by the loading of HAuCl4. The influences of the HAuCl4 loading on the particle size and particle morphology of the Au/SiO2 NCPs, the pore properties of the SiO2 nano-supports, as well as the properties of the Au NPs were systematically investigated. The formation mechanism of the raspberry-like Au/SiO2 NCPs was discussed. All the synthesized Au/SiO2 NCPs displayed a high catalytic activity towards the reduction of p-nitrophenol.

RAFT inverse miniemulsion periphery polymerization in binary solvent mixtures for synthesis of nanocapsules

Herein we report the synthesis of polymeric nanocapsules with an aqueous core via inverse miniemulsion periphery RAFT polymerization (IMEPP) of styrene/divinyl benzene in binary solvent mixtures using an amphiphilic macroRAFT species comprising N-(2-hydroxypropyl) methacrylamide and styrene as dual steric stabilizer and RAFT agent. Inverse miniemulsions were prepared using various ratios of toluene and n-hexane as the continuous phase. For toluene:hexane volume ratios of 100:0–60:40, hollow polymeric nanocapsules were successfully obtained with average diameters generally well below 300nm. Issues with poor colloidal stability were encountered using toluene:hexane=50:50. Moreover, the particle size distributions exhibited the greatest uniformity in pure toluene. It is rationalized that the presence of (excessive) amounts of n-hexane in the continuous phase leads to poor steric stabilization of miniemulsion droplets as well as the formation of solid (non-hollow) particles in the continuous phase.

Highly dispersed spherical Bi3.25La0.75Ti3O12 nanocrystals via topotactic crystallization of aggregation-free gel particles from an effective inverse miniemulsion sol–gel approach

Aggregation-free spherical lanthanum-doped bismuth titanate (Bi3.25La0.75Ti3O12, BLT) gel particles with an average size of about 150 nm were successfully obtained from an inverse miniemulsion sol–gel process, with Span-80 acting as surfactant, n-butanol as co-surfactant, cyclohexane as continuous phase, and submicro-droplets of aqueous solution containing Bi3+, La3+ and Ti4+ ions as dispersed phase, and then topotactically transformed into highly dispersed spherical BLT nanocrystals after an in situ crystallization at 600 °C for 8 h. It has been found that the BLT gel particles can be obtained via a moderate sol–gel reaction inside the miniemulsion droplets at 65 °C, but their morphology and aggregation degree are strongly affected by the relative amounts of Span-80 and n-butanol. The perfect spherical BLT gel particles with no aggregation can be achieved only under the condition of 3 wt% n-butanol relative to the mass of cyclohexane, with excessive amount of n-butanol leading to the formation of ill-gelled particles with irregular shapes, while insufficient addition of n-butanol resulting in terrible aggregation of gel particles. To understand the formation of aggregation-free spherical BLT gel particles, a tentative mechanism is proposed and discussed, which reveals that a well-coordinated oil–water interfacial film made up of Span-80 and n-butanol molecules and the appropriately enhanced evaporation of water from such interfaces should be responsible for the formation of aggregation-free spherical BLT gel particles. Aggregation-free spherical BLT (Bi3.25La0.75Ti3O12) gel particles can be prepared from an effective inverse miniemulsion sol–gel process, and subsequently topotactically transformed into spherical BLT nanocrystals through an in situ crystallization.

Biocompatible Glycopolymer Nanocapsules via Inverse Miniemulsion Periphery RAFT Polymerization for the Delivery of Gemcitabine.

Encapsulation of hydrophilic cancer drugs in polymeric nanocapsules was achieved in a one-pot process via the inverse miniemulsion periphery RAFT polymerization (IMEPP) approach. The chosen guest molecule was gemcitabine hydrochloride, which is used as the first-line treatment of pancreatic cancer. The resulting nanocapsules were confirmed to be ∼200 nm, with excellent encapsulation (∼96%) and loading (∼12%) efficiency. Postpolymerization reaction was successfully conducted to create glyocopolymer nanocapsules without any impact on the loads as well as the nanocapsules size or morphology. The loaded nanocapsules were specifically designed to be responsive in a reductive environment. This was confirmed by the successful disintegration of the nanocapsules in the presence of glutathione. The gemcitabine-loaded nanocapsules were tested in vitro against pancreatic cancer cells (AsPC-1), with the results showing an enhancement in the cytotoxicity by two fold due to selective accumulation and release of the nanocapsules within the cells. The results demonstrated the versatility of IMEPP as a tool to synthesize functionalized, loaded-polymeric nanocapsules suitable for drug-delivery application.

Superparamagnetic Fe3O4/Poly(N-isopropyl acrylamide) Nanocomposites Synthesized in Inverse Miniemulsions: Magnetic and Particle Properties.

In the present study, superparamagnetic Fe3O4/poly(N-isopropyl acrylamide) nanocomposites were synthesized by one-step inverse miniemulsion copolymerization of N-isopropyl acrylamide and N,N'-methylene diacrylamide. The loading of Fe3O4 nanoparticles in the nanocomposites was 27 wt%, and the saturation moment of the nanocomposites was 12.4 emu x g(-1). Fe3O4 nanoparticles were prepared through a coprecipitation method. The amount of stabilizer (poly(acrylic acid)) significantly influenced the size and size distribution of the Fe3O4 nanoparticles, and, therefore, their magnetic properties. Superparamagnetism of the Fe3O4 nanoparticles was preserved in the nanocomposites. The effects of synthetic parameters on the particle properties, namely surfactant loading, concentration of ferrofluid, type of lipophobe and initiator, and amount of cross-linker were investigated. Nanocomposites of Fe3O4/poly(N-isopropyl acrylamide) displayed a guava-like morphology, which they could retain after being redispersed in polar solvents.

SAXS Analysis of Shell Formation During Nanocapsule Synthesis via Inverse Miniemulsion Periphery RAFT Polymerization.

Currently available methods for synthesis of polymeric nanocapsules only offer limited control over the shell thickness, even though it is an important parameter for various applications. Furthermore, suitable methods to critically measure this parameter in a facile way are still nonexistent. Here, lab-scale small-angle X-ray scattering (SAXS) is utilized to in situ measure the evolution of shell thickness during nanocapsule synthesis via inverse miniemulsion periphery reversible addition-fragmentation chain transfer (RAFT) polymerization (IMEPP). The measured shell thickness is consistent with estimates from the commonly used transmission electron microscopy (TEM) technique. Moreover, the individual thicknesses of two concentric shells comprising different polymeric materials (the outer shell formed via IMEPP chain extension of the inner shell) can be determined, thus further demonstrating the versatility of this approach.