Small Polydispersity Research Articles

Size-Controlled Polyelectrolyte Complexes: Direct Measurement of the Balance of Forces Involved in the Triggered Collapse of Layer-by-Layer Assembled Nanocapsules

Polyelectrolyte multilayers composed of poly(allylamine hydrochloride) and poly(styrene sulfonate) were assembled on 13 nm gold nanoparticles and characterized by Transmission Electron Microscopy and Atomic Force Microscopy. The direct measurement of the interactions at the molecular level using a Surface Force Apparatus revealed that the colloidal stability of such coated particles in aqueous media is brought about concomitantly by electrostatic and steric repulsive interactions. The cyanide induced dissolution of the gold cores yields either hollow nanocapsules or collapsed nanospheres, two species which are very difficult to distinguish. In contrast to the established micron sized hollow capsules, the dissolution of the nanosized gold cores may induce a substantial swelling of the polyelectrolyte complex into the central void as induced by the temporary local increase of the ionic strength. At least three layer pairs are required to maintain the structural integrity of the polyelectrolyte shells to yield hollow nanospheres. At about three layer pairs, thin nanocapsules are mechanically compressible and may collapse on themselves following mechanical stimulation to form even smaller spherical polyelectrolyte complex particles that retain the small polydispersity of the gold cores. Thus, the templating of polyelectrolyte shells around, e.g., gold nanoparticles followed by the dissolution of the respective cores constitutes a new method for the synthesis of extremely small polyelectrolyte complex particles with very low polydispersity.

Modelling the size and polydispersity of magnetic hybrid nanoparticles for luminescent sensing of oxygen

We report on a strategy to model both the size (d) and the polydispersity (PdI) of magnetic oxygen-sensitive nanoparticles with a typical size of 200 nm in order to increase the surface area. The strategy is based on experimental design and Response Surface Methodology. Nanoparticles were prepared by miniemulsion solvent evaporation of solutions of poly(styrene-co-maleic anhydride). Features of this strategy include (1) a quick selection of the most important variables that govern d and PdI; (2) a better understanding of the parameters that affect the performance of the polymer; and (3) optimized conditions for the synthesis of nanoparticles of targeted d and PdI. The results were used to produce nanoparticles in sizes that range from 100 to 300 nm and with small polydispersity. The addition of a platinum porphyrin complex that acts as a luminescent probe for oxygen and of magnetite (Fe3O4) to the polymeric particles, did not affect d and PdI, thus demonstrating that this strategy simplifies their synthesis. The resulting luminescent and magnetic sensor nanoparticles respond to dissolved oxygen with sensitivity (Stern-Volmer constant) of around 35 bar−1.

Fluorescence studies on potential antitumor 6-(hetero)arylthieno[3,2-b]pyridine derivatives in solution and in nanoliposomes

Abstract The photophysical properties (absorption and fluorescence) of four 6-(hetero)arylthieno[3,2- b ]pyridine derivatives, the methyl 3-amino-6-(thien-3-yl)thieno[3,2- b ]pyridine-2-carboxylate 1 , the methyl 3-amino-6-(2,2′-bithienyl-5-yl)thieno[3,2- b ]pyridine-2-carboxylate 2 , the methyl 3-amino-6-(thien-2-yl)thieno[3,2- b ]pyridine-2-carboxylate 3 and the methyl 3-amino-6-(fur-3-yl)thieno[3,2- b ]pyridine-2-carboxylate 4 , evaluated previously as potential antitumor compounds, were studied in solvents of different polarity. All compounds have reasonable fluorescence quantum yields and exhibit a solvatochromic behaviour. The thienopyridine derivatives were incorporated in lipid membranes of neat egg-yolk phosphatidylcholine (egg-PC), dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylglycerol (DPPG) and dioctadecyldimethylammonium bromide (DODAB). Fluorescence measurements indicate that all compounds are mainly located in the lipid bilayer, feeling the transition from the rigid gel phase to the liquid-crystalline phase. The most promising antitumor compounds, the thien-3-yl and the 2,2′-bithienyl-5-yl thienopyridine derivatives 1 and 2 , were encapsulated in different nanoliposome formulations, considering future drug delivery applications using liposomes as carriers. Almost all the liposomes with incorporated compounds have diameters lower than 165 nm and generally low polydispersity. The formulation DPPC:DMPG:DSPE-PEG (1:1:0.1) exhibits a small diameter (below 100 nm), low polydispersity and reasonable negative zeta-potential values for both thienopyridines 1 and 2 .

Liquid Crystallinity of Random Copolymers of Polymethacrylates Containing Biphenyl Moieties Synthesized by Atom Transfer Radical Polymerization

4-(4′-Cyanobiphenyloxy)butyl methacrylate, MA(4OCB), was copolymerized with 8-(4′-hexyloxybiphenyloxy)octyl methacrylate, MA(8O6RB), or butyl methacrylate, MA(Bu), by atom transfer radical polymerization. Phase transition behaviors and liquid crystalline properties of the random copolymers with small polydispersity were compared with those of respective homopolymers. The thermal analysis suggested that both biphenyl mesogens in the p[MA(4OCB)-co-(8O6RB)] random copolymers were oriented together rather than segregated. In the case of the p[MA(4OCB)-co-MA(Bu)] random copolymers, the butyl side-chains worked to diminish liquid crystallinity by disturbing orientation of the biphenyl mesogen due to thermal fluctuation.

Synthesis of Poly(3-Hexylthiophene) with High Molecular Weight and Small Polydispersity

Regioregular head-tail poly(3-hexylthiophenes) (HT-P3HT) with a controlled high molecular weight and a small polydispersity have been synthesized via an improved Kumada catalyst-transfer polycondensation (KCTP) by using the new-prepared hexylmagnesium bromide as the Grignard reagent. As the amount of nickel catalyst dichloro[1,3-diphenylphosphinopropane] nickel (Ni(dppp)Cl2) was 0.5% mol of the amount of monomer 2,5-dibromo-3-hexylthiophene (DBHT) we can obtain a HT-P3HT with a high molecular weight Mn (38 449) and a small polydspersity (1.18). By using of LiCl as a co-catalyst, the regioregularity of the P3HT with high molecular weight (40 270) is maintained and the PDI (1.03) is smaller than that of the P3HT polymerized in the absence of LiCl but the conversion ratio of the monomer is promoted. The HT-P3HT with high molecular weight and small polydispersity will be an attractive candidate applied in solar cells.

Fabrication of vitamin E-enriched nanoemulsions: Factors affecting particle size using spontaneous emulsification

Oil-in-water nanoemulsions are finding increasing use as delivery systems to encapsulate lipophilic bioactive components in functional food, personal care, and pharmaceutical products. We have investigated the influence of system composition and preparation conditions on the particle size of vitamin E acetate (VE)-loaded nanoemulsions prepared by spontaneous emulsification. This method relies on the formation of very fine oil droplets when an oil/surfactant mixture is added to water. The oil-to-emulsion ratio content was kept constant (10wt.%) while the surfactant-to-emulsion ratio (%SER) was varied (from 2.5 to 10wt.%). Oil phase composition (vitamin E to medium chain triglyceride ratio) had a major effect on particle size, with the smallest droplets being formed at 8wt.% VE and 2wt.% MCT. Surfactant type also had an appreciable impact on particle size, with TWEEN® 80 giving the smallest droplets from a group of food-grade non-ionic surfactants (TWEEN® 20, 40, 60, 80, and 85). Surfactant-to-emulsion ratio also had to be optimized to produce fine droplets, with the smallest droplets being formed at SER=10wt.%. Particle size could also be reduced by increasing the temperature and stirring speed used when the oil/surfactant mixture was added to water. By optimizing system composition and homogenization conditions we were able to form VE-loaded nanoemulsions with small mean droplet diameters (d<50nm) and low polydispersity indexes (PDI<0.13). The spontaneous emulsification method therefore has great potential for forming nanoemulsion-based delivery systems for food, personal care, and pharmaceutical applications.

Investigation into the effect of varying l-leucine concentration on the product characteristics of spray-dried liposome powders

Spray-dried formulations offer an attractive delivery system for administration of drug encapsulated into liposomes to the lung, but can suffer from low encapsulation efficiency and poor aerodynamic properties. In this paper the effect of the concentration of the anti-adherent l-leucine was investigated in tandem with the protectants sucrose and trehalose. Two manufacturing methods were compared in terms of their ability to offer small liposomal size, low polydispersity and high encapsulation of the drug indometacin. Unexpectedly sucrose offered the best protection to the liposomes during the spray drying process, although formulations containing trehalose formed products with the best powder characteristics for pulmonary delivery; high glass transition values, fine powder fraction and yield. It was also found that l-leucine contributed positively to the characteristics of the powders, but that it should be used with care as above the optimum concentration of 0.5% (w/w) the size and polydispersity index increased significantly for both disaccharide formulations. The method of liposome preparation had no effect on the stability or encapsulation efficiency of spray-dried powders containing optimal protectant and anti-adherent. Using l-leucine at concentrations higher than the optimum level caused instability in the reconstituted liposomes.

Large-Scale Synthesis of Lipid–Polymer Hybrid Nanoparticles Using a Multi-Inlet Vortex Reactor

Lipid-polymer hybrid nanoparticles combine the advantages of both polymeric and liposomal drug carriers and have shown great promise as a controlled drug delivery platform. Herein, we demonstrate that it is possible to adapt a multi-inlet vortex reactor (MIVR) for use in the large-scale synthesis of these hybrid nanoparticles. Several parameters, including formulation, polymer concentration, and flow rate, are systematically varied, and the effects of each on nanoparticle properties are studied. Particles fabricated from this process display characteristics that are on par with those made on the lab-scale such as small size, low polydispersity, and excellent stability in both PBS and serum. Using this approach, production rates of greater than 10 g/h can readily be achieved, demonstrating that use of the MIVR is a viable method of producing hybrid nanoparticles in clinically relevant quantities.

Polymer brush with pendent glucosylurea groups constructed on a glass substrate by RAFT polymerization

A polymer brush with pendent d-glucosylurea groups (Poly(glucosylureaethyl methacrylate), PolyGUMA) was obtained by surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization of GUMA on a glass substrate. The linear relationship between the loge ([M]o/[M]) value and the reaction conversion, and the small polydispersity in Mw/Mn value of PolyGUMA produced in liquid phase at the same time suggested that the polymerization proceeded in a living manner. The bicinchoninic acid method indicated that the PolyGUMA brush was significantly resistant against non-specific adsorption of albumin (bovine serum) and lysozyme (egg white). Furthermore, the adhesion of cells such as HepG2, and HEK293 cells was strongly suppressed by the presence of PolyGUMA brush. The glucosylurea group-carrying polymer brush prepared here might be quite useful to provide a “bio-inert (anti-biofouling)” surface in bio-medical fields.

Quantitative SNP genotyping by affinity capillary electrophoresis using PEG‐oligodeoxyribonucleotide block copolymers with electroosmotic flow

Quantitative SNP detection was demonstrated with an ACE using a PEG-oligodeoxyribonucleotide block copolymer (PEG-b-ODN) as a probe in the presence of an EOF. The probe's PEG segment with large molecular weight and small polydispersity yielded a high resolution in the separation of a chemically synthesized 60-base ssDNA (WT) and its single-base-substituted mutant (MT). A mixture of WT and MT was clearly separated within 10 min by simultaneously using two types of PEG-b-ODN probes whose ODN segments were complementary to WT and MT and whose PEG segments were of different lengths. The peak area ratio between WT and MT was in good agreement with the feed ratio. The averaged difference between the feed and observed ratio of MT was determined to be 0.23%, which is lower than that of any other methods. The ACE using the PEG-b-ODN probes in the presence of EOF could be utilized as a facile method for estimating SNP allele frequency in various research fields.

Colloidal astaxanthin: Preparation, characterisation and bioavailability evaluation

Astaxanthin colloidal particles were produced using solvent-diffusion technique in the presence of different food grade surface active compounds, namely, Polysorbate 20 (PS20), sodium caseinate (SC), gum Arabic (GA) and the optimum combination of them (OPT). Particle size and surface charge characteristics, rheological behaviour, chemical stability, colour, in vitro cellular uptake, in vitro antioxidant activity and residual solvent concentration of prepared colloidal particles were evaluated. The results indicated that in most cases the mixture of surface active compounds lead to production of colloidal particles with more desirable physicochemical and biological properties, as compared to using them individually. The optimum combination of PS20, SC and GA could produce the astaxanthin colloidal particles with small particle size, polydispersity index (PDI), conductivity and higher zeta potential, mobility, cellular uptake, colour intensity and in vitro antioxidant activity. In addition, all prepared astaxanthin colloidal particles had significantly (p<0.05) higher cellular uptake than pure astaxanthin powder.

Formation of Pegylated Polyurethane and Lysine-Coated Polyurea Nanoparticles Obtained from O/W Nano-emulsions

The present work describes the formation of Pegylated polyurethane and Lysine-coated polyurea nanoparticles obtained from O/W nano-emulsions via an interfacial polycondensation process in the aqueous solution/polysorbate 80/diisocyanate/medium chain triglyceride systems. The initial nano-emulsions were prepared using the phase inversion composition (PIC) method. Dynamic light scattering studies revealed the changes in the particle size occurring during the process of nanoparticle formation. Well-defined polymeric nanoparticles with a small particle diameter (below 80 nm) and low polydispersity index were obtained using a highly hydrophilic component (polyethylene glycol or lysine) and an aliphatic diisocyante monomer. FT-IR and AFM studies showed that the polymeric matrix of nanoparticles was built by copolymers derived from reaction between the diisocyanate and the hydroxyl groups of both nonionic surfactant and the highly hydrophilic component. Pegylated-polyurethane and lysine-coated polyurea nanoparticles designed in this study are promising tools for future applications in biomedical sciences.

In situ surface functionalization of magnetic nanoparticles with hydrophilic natural amino acids

The surface of magnetic iron oxide nanoparticles has been modified with hydrophilic natural amino acids via an in situ method. A rapid ligand exchange reaction was induced at elevated temperatures to replace the original labile solvent layer with amino acids. The functionalized nanoparticles were quasi-spherical and well separated with an average diameter around 7nm. The resulted products were examined to be highly crystalline and phase-pure Fe3O4. The present of amino acids on the surface of the nanoparticles was verified by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, which indicated successful ligand exchange. Zeta potential and dynamic light scattering measurement suggested that functionalized magnetic nanoparticles were well dispersed in both basic and acidic aqueous solution with small polydispersity. The uncoordinated amine groups are highly reactive and available for either conjugation with biocompatible polymers or attachment of small gold nanocrystals, so as to prepare dual-functional nanocomposite.

Formation of hollow spherical and doughnut microcapsules by evaporation induced self-assembly of nanoparticles: effects of particle size and polydispersity

Understanding the role of various physicochemical parameters is essential in order to control the microstructure during evaporation induced self-assembly in drying colloidal droplets. In the present work, the effect of particle size and its distribution on formation of spherical and doughnut shaped hollow microcapsules during rapid evaporation induced self-assembly of colloidal droplets has been elucidated. It has been demonstrated that hollow spherical microcapsules with substantial shell thickness are formed for small size and low polydispersity of the nanoparticles in a virgin dispersion. A few of such microcapsules, even with relatively significant shell thickness, burst in order to equilibrate force balance during drying. In contrast, when the size and polydispersity are relatively high, a morphological transformation occurs and the drying droplets release the strain through formation of doughnut shaped grains. Two levels of structural hierarchy and ageing effects of the assembled microcapsules are investigated using small-angle neutron/X-ray scattering and scanning electron microscopy.

Influence of a mixed ionic/nonionic surfactant system and the emulsification process on the properties of paraffin emulsions

Particle size of paraffin emulsions depends mainly on surfactant availability and could be well predicted by a simple theoretical model for calculating the minimum droplet size. ► Experimental data and theoretical model are on good agreement. ► Theoretical model considers surfactant concentration in continuous phase equal to CAC. ► The model could be used as a tool to predict stability of emulsions. Paraffin emulsions are important in technological applications such as coating in the food packaging industry or to provide waterproof properties to particleboard panels. Small particle size (about 1.0 μm) and low polydispersity are required to form stable paraffin emulsions for these applications. In this context, the main objective of the present work is to study the influence of the surfactant system and the emulsification process on the properties of paraffin emulsions. A high pressure homogenizer was used to prepare the emulsions and its characterization was made by means of optical microscopy, laser diffraction and electrophoretic mobility measurements. Emulsions were prepared as a function of the ionic/nonionic surfactant ratio, the total surfactant concentration and the homogenization pressure. A simple theoretical model to predict the minimum particle size was used, assuming that surfactant is either at the oil–water interface or as monomer in the external phase. Experimental and theoretical data are on good agreement and the formation of stable emulsions is explained according to such model. This result could be of prime importance in order to formulate new paraffin emulsions.

Chitosan Nanogels by Template Chemical Cross-Linking in Polyion Complex Micelle Nanoreactors

Chitosan covalent nanogels cross-linked with genipin were prepared by template chemical cross-linking of chitosan in polyion complex micelle (PIC) nanoreactors. By using this method, we were able to prepare chitosan nanogels using only biocompatible materials without organic solvents. PIC were prepared by interaction between chitosan (X(n) = 23, 44, and 130) and block copolymer poly(ethylene oxide)-block-poly[sodium 2-(acrylamido)-2-methylpropanesulfonate] (PEO-b-PAMPS) synthesized by single-electron transfer-living radical polymerization (SET-LRP). PIC with small size (diameter about 50 nm) and low polydispersity were obtained up to 5 mg/mL. After cross-linking of chitosan with genipin, the nanoreactors were dissociated by adding NaCl. The dissociation of the nanoreactors and the formation of the nanogels were confirmed by (1)H NMR, DLS, and TEM. The size of the smallest nanogels was about 50 nm in the swollen state and 20 nm in the dry state. The amount of genipin used during reticulation was an important parameter to modulate the size of the nanogels in solution.

Mixed micelle formation with hydrophobic and hydrophilic Pluronic block copolymers: Implications for controlled and targeted drug delivery

Pluronic block copolymers offer affluent phase behavioral characteristics and are extensively investigated for drug delivery applications. Hydrophobic Pluronics produce larger aggregates whereas hydrophilic Pluronics often generate small-sized micelles in aqueous milieu. To overcome the limitations and combine the advantages of different kinds of Pluronics the mixing of such two types of Pluronics is studied here, especially for hydrophobic Pluronic L81 and relatively hydrophilic Pluronic P123. Critical micelle concentration (CMC) of the developed binary mixtures was 0.032 mg/ml as evidenced from pyrene fluorescence spectroscopy and is located in between that of the individual Pluronics. Dynamic light scattering (DLS) showed very small particle sizes (∼20 nm) and low polydispersity indices for most of the mixed micelles. Transmission electron microscopy (TEM) demonstrated spherical shape of micelles. Based upon the ratio of hydrophobic and hydrophilic Pluronics, dispersions of varied stability were obtained. With 0.1/1.0 wt.% and 0.5/3.0 wt.% of Pluronic L81/P123, stable dispersions were obtained. Stability was assessed from turbidity measurement, size analysis and clarity of dispersion on standing. Micelles were also found to be stable in bovine serum albumin (BSA) solution. Mixed micelles showed fairly high entrapment efficiency, loading capacity and sustained release profile for aceclofenac (Acl), a model hydrophobe. Presence of salt lowered Acl solubilization in micelles. Thermodynamic parameters for Acl solubilization in mixed micelles revealed high partition coefficient values and spontaneity of drug solubilization. Thus, the developed novel mixed micelles hold promise in controlled and targeted drug delivery owing to their very small size, high entrapment efficiency and stability.

Anti-biofouling properties of an amphoteric polymer brush constructed on a glass substrate

An amphoteric copolymer brush of methacrylic acid (MA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) was prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization using both a free chain transfer agent ( n-butylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid) and a radical initiator (4,4′-azobis(4-cyanopentanoic acid)) covalently fixed to a glass substrate. An aqueous solution of the copolymer, Poly(MA- r-DMAEMA), which was simultaneously obtained in liquid phase, had a sufficiently small polydispersity in its molecular weight. The copolymer brush showed effective suppression of non-specific adsorption of bovine serum albumin and egg white lysozyme to the brush. In contrast, both negatively charged PolyMA and positively charged PolyDMAEMA brushes significantly adsorbed the proteins irrespective of their net charges. Upon ion beam irradiation, furthermore, a hollow space with a designed shape could be made on the glass substrate, and both HEK293 and HepG2 cells non-specifically adhered to the space, forming aggregates, while no adhesion to the non-treated area on the brush was observed. These results suggest that the amphoteric polymer brushes will be useful materials for biomedical applications.

Synthesis and characterization of poly(arylene ether ketone)s containing triazole units through click chemistry

In order to develop a novel process for poly(arylene ether ketone)s with high thermal and chemical stability, a series of poly(aylene ether ketone)s containing triazloe moieties were synthesized via the click chemistry of 4,4′-bis(azidomethyl) diphenyl ketone (BADPK) and bisethynyl compounds (BEAE1-5). The resulting polymers were characterized by using IR and 1H NMR techniques. The solubility data showed that samples possessed good solubility in highly polar solvents. Molecular mass of these samples was determined by GPC which indicated they exhibited reasonable molecules weights and relatively small polydispersity. Furthermore, thermal stability of the samples was evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which indicated that they possessed good thermal stability and high T g (100–140 °C). All the polymers were amorphous confirmed by DSC and X-ray diffraction (WAXD).

Silica-supported quinine-CuBr catalyzed atom transfer radical polymerization of methyl methacrylate

9-Amino epi -quinine was used as a ligand in the atom transfer radical polymerization (ATRP) for the first time, and high monomer conversion as well as small polydispersity could be obtained. The 9-amino epi -quinine-containing organosilane was synthesized and immobilized onto three different silica supports, i.e., fumed SiO 2 , SBA-15, and MCM-48, followed by complexing with CuBr. With the MCM-48 supported catalyst, polymerization of methyl methacrylate achieved high monomer conversion, small polydispersity, and low residual copper content in the product. This heterogeneous catalyst could also be recycled effectively. To form heterogeneous catalysts, a new ligand was immobilized on three different silica supports to complex with CuBr. And these heterogeneous catalysts could catalyze the reaction effectively. ► 9-amino epi -quinine was used as the ligand in the ATRP. ► A 3D mesoporous material, MCM-48, was used as the support and got good results. ► Only 2 equivalent support could complex with almost all the Cu(I) species. ► The catalyst supported by MCM-48 was still effective after the regeneration.