On the barrier properties of the cornea: a microscopy study of the penetration of fluorescently labeled nanoparticles, polymers, and sodium fluorescein

Overcoming the natural defensive barrier functions of the eye remains one of the greatest challenges of ocular drug delivery. Cornea is a chemical and mechanical barrier preventing the passage of any foreign bodies including drugs into the eye, but the factors limiting penetration of permeants and nanoparticulate drug delivery systems through the cornea are still not fully understood. In this study, we investigate these barrier properties of the cornea using thiolated and PEGylated (750 and 5000 Da) nanoparticles, sodium fluorescein, and two linear polymers (dextran and polyethylene glycol). Experiments used intact bovine cornea in addition to bovine cornea de-epithelialized or tissues pretreated with cyclodextrin. It was shown that corneal epithelium is the major barrier for permeation; pretreatment of the cornea with β-cyclodextrin provides higher permeation of low molecular weight compounds, such as sodium fluorescein, but does not enhance penetration of nanoparticles and larger molecules. Studying penetration of thiolated and PEGylated (750 and 5000 Da) nanoparticles into the de-epithelialized ocular tissue revealed that interactions between corneal surface and thiol groups of nanoparticles were more significant determinants of penetration than particle size (for the sizes used here). PEGylation with polyethylene glycol of a higher molecular weight (5000 Da) allows penetration of nanoparticles into the stroma, which proceeds gradually, after an initial 1 h lag phase.

Self-assembly of a Model Peptide incorporating a Hexa-Histidine sequence attached to an Oligo-Alanine sequence, and binding to Gold NTA/Nickel nanoparticles

Amyloid fibrils are formed by a model surfactant-like peptide (Ala)10-(His)6 containing a hexahistidine tag. This peptide undergoes a remarkable two-step self-assembly process with two distinct critical aggregation concentrations (cac’s), probed by fluorescence techniques. A micromolar range cac is ascribed to the formation of prefibrillar structures, whereas a millimolar range cac is associated with the formation of well-defined but more compact fibrils. We examine the labeling of these model tagged amyloid fibrils using Ni-NTA functionalized gold nanoparticles (Nanogold). Successful labeling is demonstrated via electron microscopy imaging. The specificity of tagging does not disrupt the β-sheet structure of the peptide fibrils. Binding of fibrils and Nanogold is found to influence the circular dichroism associated with the gold nanoparticle plasmon absorption band. These results highlight a new approach to the fabrication of functionalized amyloid fibrils and the creation of peptide/nanoparticle hybrid materials.

Observing the in situ chiral modification of Ni nanoparticles using scanning transmission X-ray microspectroscopy

Enantioselective heterogeneous hydrogenation of Cdouble bond; length as m-dashO bonds is of great potential importance in the synthesis of chirally pure products for the pharmaceutical and fine chemical industries. One of the most widely studied examples of such a reaction is the hydrogenation of β-ketoesters and β-diketoesters over Ni-based catalysts in the presence of a chiral modifier. Here we use scanning transmission X-ray microscopy combined with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) to investigate the adsorption of the chiral modifier, namely (R,R)-tartaric acid, onto individual nickel nanoparticles. The C K-edge spectra strongly suggest that tartaric acid deposited onto the nanoparticle surfaces from aqueous solutions undergoes a keto-enol tautomerisation. Furthermore, we are able to interrogate the Ni L2,3-edge resonances of individual metal nanoparticles which, combined with X-ray diffraction (XRD) patterns showed them to consist of a pure nickel phase rather than the more thermodynamically stable bulk nickel oxide. Importantly, there appears to be no “particle size effect” on the adsorption mode of the tartaric acid in the particle size range ~ 90–~ 300 nm.

Polymer protected gold nanoparticles: synthesis, characterization and application in catalysis

This review discusses the stabilization of gold nanoparticles (AuNPs) by nonionic, anionic, cationic and amphoteric polymers. The protocols used for synthesis of AuNPs in aqueous and organic solvents are described. Size, shape and morphology of AuNPs are characterized by various physicochemical methods. Application aspects of polymer-protected AuNPs in catalysis are outlined.

Effective separation of Am(III) and Eu(III) from HNO3 Q1 Q2 solutions using CyMe4-BTPhen-functionalized silica-coated magnetic nanoparticles

It has been shown that CyMe4-BTPhen-functionalized silica-coated maghemite (c-Fe2O3) magnetic nanoparticles (MNPs) are capable of quantitative separation of Am(III) from Eu(III) from HNO3 solutions. These MNPs also show a small but significant selectivity for Am(III) over Cm(III) with a separation factor of around 2 in 4 M HNO3. The water molecule in the cavity of the BTPhen may also play an important part in the selectivity.

Enhancing the crystallization and orientation of electrospinning poly (lactic acid) (PLLA) by combining with additives

PLLA is a thermoplastic biopolymer and can be used in industrial applications for medical and filtration applications. The brittleness of PLLA is attributed to slow crystallization rates and its glass transition temperature (Tg) is high (60 °C); for this reason, its applications are limited. The orientation, morphology, and crystal structure of the electrospun fibers was investigated by SEM, POM, DSC, FTIR, XRD, and SAXS. Combining with additives leads to a large decrease of fiber diameter, viscosity, and changes of fiber morphology and crystal structure compared to pure PLLA. DSC showed that the Tg of PLLA decreased about 15 °C and there was no change in relaxation enthalpy by the addition of plasticizer. FT-IR indicate a strong interaction between PLLA and additives; a new band appears in the PLLA blend at 1,756 cm−1 at room temperature as a crystalline band without any annealing. In addition, WAXD indicated that the intensities of the two peaks at (200/110) and (203) increased for the blend at room temperature without any annealing in comparison with PLLA; this means that PHB crystallizes in the amorphous region of PLLA. The POM experiments agree with the results from DSC, FTIR, and WAXS measurements, confirming that adding PHB results in an increase in the number of nuclei with much smaller spherulites and enhances the crystallization behavior of this material, thereby improving its potential for applications.

Remarkable dynamics of nanoparticles in the urban atmosphere

Nanoparticles emitted from road traffic are the largest source of respiratory exposure for the general public living in urban areas. It has been suggested that adverse health effects of airborne particles may scale with airborne particle number, which if correct, focuses attention on the nanoparticle (less than 100 nm) size range which dominates the number count in urban areas. Urban measurements of particle size distributions have tended to show a broadly similar pattern dominated by a mode centred on 20–30 nm diameter emitted by diesel engine exhaust. In this paper we report the results of measurements of particle number concentration and size distribution made in a major London park as well as on the BT Tower, 160 m aloft. These measurements taken during the REPARTEE project (Regents Park and BT Tower experiment) show a remarkable shift in particle size distributions with major losses of the smallest particle class as particles are advected away from the traffic source. In the Park, the traffic related mode at 20–30 nm diameter is much reduced with a new mode at <10 nm. Size distribution measurements also revealed higher number concentrations of sub-50 nm particles at the BT Tower during days affected by higher turbulence as determined by Doppler Lidar measurements and are indicative of loss of nanoparticles from air aged during less turbulent conditions. These results are suggestive of nanoparticle loss by evaporation, rather than coagulation processes. The results have major implications for understanding the impacts of traffic-generated particulate matter on human health.

Improving survival of probiotic bacteria using bacterial poly-γ-glutamic acid

A major hurdle in producing a useful probiotic food product is bacterial survival during storage and ingestion. The aim of this study was to test the effect of γ-PGA immobilisation on the survival of probiotic bacteria when stored in acidic fruit juice. Fruit juices provide an alternative means of probiotic delivery, especially to lactose intolerant individuals. In addition, the survival of γ-PGA-immobilised cells in simulated gastric juice was also assessed. Bifidobacteria strains (B. longum, B. breve), immobilised on 2.5 % γ-PGA, survived significantly better (P < 0.05) in orange and pomegranate juice for 39 and 11 days respectively, compared to free cells. However, cells survived significantly better (P < 0.05) when stored in orange juice compared to pomegranate juice. Moreover, both strains, when protected with 2.5 % γ-PGA, survived in simulated gastric juice (pH 2.0) with a marginal reduction (<0.47 log CFU/ml) or no significant reduction in viable cells after four hours, whereas free cells died within two hours. In conclusion, this research indicates that γ-PGA can be used to protect Bifidobacteria cells in fruit juice, and could also help improve the survival of cells as they pass through the harsh conditions of the gastrointestinal tract (GIT). Following our previous report on the use of γ-PGA as a cryoprotectant for probiotic bacteria, this research further suggests that γ-PGA could be used to improve probiotic survival during the various stages of preparation, storage and ingestion of probiotic cells.

Effective separation of Am(III) and Eu(III) from HNO3 solutions using CyMe4-BTPhen-functionalized silica-coated magnetic nanoparticles

It has been shown that CyMe4-BTPhen-functionalized silica-coated maghemite (c-Fe2O3) magnetic nanoparticles (MNPs) are capable of quantitative separation of Am(III) from Eu(III) from HNO3 solutions. These MNPs also show a small but significant selectivity for Am(III) over Cm(III) with a separation factor of around 2 in 4 M HNO3. The water molecule in the cavity of the BTPhen may also play an important part in the selectivity.

Mesomorphic behaviour in copoly(ester-imide)s of poly(butylene-2,6-naphthalate) (PBN)

Copolycondensation of N,N’-bis(4-hydroxybutyl)-biphenyl-3,4,3',4'-tetracarboxylic diimide at 20 and 25 mol% with bis(4-hydroxybutyl)-2,6-naphthalate produces PBN-based copoly(ester-imide)s that not only crystallise but also form a (smectic) mesophase upon cooling from the melt. Incorporation of 25 mol% imide in PBN causes the glass transition temperature (measured by DSC) to rise from 51 to 74 °C, a significant increase relative to PBN. Furthermore, increased storage- (G'), loss- (G'') and elastic (E) moduli are observed for both copoly(ester-imide)s when compared to PBN itself. Structural analysis of the 20 mol% copolymer by X-ray powder and fibre diffraction, interfaced to computational modelling, suggests a crystal structure related to that of α-PBN, in space group P-1, with cell dimensions a = 4.74, b = 6.38, c = 14.45 Å, α = 106.1, β = 122.1, γ = 97.3°, ρ = 1.37 g cm-3.

Redox- and glucose-responsive hydrogels from poly(vinyl alcohol) and 4-mercaptophenylboronic acid

Novel redox- and glucose-responsive hydrogels have been synthesized by simple mixing of poly(vinyl alcohol) (PVA) and 4-mercaptophenylboronic acid (MPBA) in aqueous solutions (pH > 9) in an oxidative aqueous media. These hydrogels are produced through the formation of disulfide linkages between MPBA molecules in an oxidative environment (oxygen dissolved in solution or hydrogen peroxide added to the reaction mixture) and complexation via dynamic covalent bonds between PVA and MPBA dimer. These hydrogels show degradation in solutions of l-glutathione and d-glucose.

POZylation: a new approach to enhance nanoparticle diffusion through mucosal barriers

The increasing use of nanoparticles in the pharmaceutical industry is generating concomitant interest in developing nanomaterials that can rapidly penetrate into, and permeate through, biological membranes to facilitate drug delivery and improve the bioavailability of active pharmaceutical ingredients. Here, we demonstrate that the permeation of thiolated silica nanoparticles through porcine gastric mucosa can be significantly enhanced by their functionalization with either 5 kDa poly(2-ethyl-2-oxazoline) or poly(ethylene glycol). Nanoparticle diffusion was assessed using two independent techniques; Nanoparticle Tracking Analysis, and fluorescence microscopy. Our results show that poly(2-ethyl-2-oxazoline) and poly(ethylene glycol) have comparable abilities to enhance diffusion of silica nanoparticles in mucin dispersions and through the gastric mucosa. These findings provide a new strategy in the design of nanomedicines, by surface modification or nanoparticle core construction, for enhanced transmucosal drug delivery.

Controlled variation of monomer sequence-distribution in the synthesis of aromatic poly(ether ketone)s

The effects of varying the alkali metal cation in the high-temperature nucleophilic synthesis of a semi-crystalline, aromatic poly(ether ketone) have been systematically investigated, and striking variations in the sequence-distributions and thermal characteristics of the resulting polymers were found. Polycondensation of 4,4'-dihydroxybenzophenone with 1,3-bis(4-fluorobenzoyl)benzene in diphenylsulfone as solvent, in the presence of an alkali metal carbonate M2CO3 (M= Li, Na, K, or Rb) as base, affords a range of different polymers that vary in the distribution pattern of 2-ring and 3-ring monomer units along the chain. Lithium carbonate gives an essentially alternating and highly crystalline polymer, but the degree of sequence-randomisation increases progressively as the alkali metal series is descended, with rubidium carbonate giving a fully random and non-thermally-crystallisable polymer. Randomisation during polycondensation is shown to result from reversible cleavage of the ether linkages in the polymer by fluoride ions, and an isolated sample of alternating-sequence polymer is thus converted to a fully randomised material on heating with rubidium fluoride.

The partial oxidation of methane over Pd/Al2O3 catalyst nanoparticles studied in-situ by near ambient-pressure x-ray photoelectron spectroscopy

Near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is used to study the chemical state of methane oxidation catalysts in-situ. Al2O3{supported Pd catalysts are prepared with different particle sizes ranging from 4 nm to 10 nm. These catalysts were exposed to conditions similar to those used in the partial oxidation of methane (POM) to syn-gas and simultaneously monitored by NAP-XPS and mass spectrometry. NAP-XPS data show changes in the oxidation state of the palladium as the temperature in- creases, from metallic Pd0 to PdO, and back to Pd0. Mass spectrometry shows an increase in CO production whilst the Pd is in the oxide phase, and the metal is reduced back under presence of newly formed H2. A particle size effect is observed, such that CH4 conversion starts at lower temperatures with larger sized particles from 6 nm to 10 nm. We find that all nanoparticles begin CH4 conversion at lower temperatures than polycrystalline Pd foil.

Enzymatically-triggered, isothermally responsive polymers: re-programming poly(oligoethylene glycols) to respond to phosphatase

Polymers which can respond to externally applied stimuli have found much application in the biomedical field due to their (reversible) coil–globule transitions. Polymers displaying a lower critical solution temperature are the most commonly used, but for blood-borne (i.e., soluble) biomedical applications the application of heat is not always possible, nor practical. Here we report the design and synthesis of poly(oligoethylene glycol methacrylate)-based polymers whose cloud points are easily varied by alkaline phosphatase-mediated dephosphorylation. By fine-tuning the density of phosphate groups on the backbone, it was possible to induce an isothermal transition: A change in solubility triggered by removal of a small number of phosphate esters from the side chains activating the LCST-type response. As there was no temperature change involved, this serves as a model of a cell-instructed polymer response. Finally, it was found that both polymers were non cytotoxic against MCF-7 cells (at 1 mg·mL–1), which confirms promise for biomedical applications.