PLA-PEG nanocapsules radiolabeled with 99mTechnetium-HMPAO: release properties and physicochemical characterization by atomic force microscopy and photon correlation spectroscopy.

The present work describes the preparation, characterization and labelling of conventional and surface-modified nanocapsules (NC) with 99m Tc-HMPAO. The size, size distribution and homogeneity were determined by photon correlation spectroscopy (PCS) and zeta potential by laser doppler anemometry. The morphology and the structural organization were evaluated by atomic force microscopy (AFM). The stability and release profile of the NC were determined in vitro in plasma. The results showed that the use of methylene blue induces significant increase in the encapsulation efficiency of 99m Tc-HMPAO, from 24.4 to 49.8% in PLA NC and 22.37 to 52.93% in the case of PLA-PEG NC (P<0.05) by improving the complex stabilization. The average diameter of NC calculated by PCS varied from 216 to 323 nm, while the average diameter determined by AFM varied from 238 to 426 nm. The AFM analysis of diameter/height ratios suggested a greater homogeneity of the surface-modified PLA-PEG nanocapsules compared to PLA NC concerning their flattening properties. The in vitro release of the 99m Tc-HMPAO in plasma medium was faster for the conventional PLA NC than for the surface-modified NC. For the latter, 60% of the radioactivity remained associated with NC, even after 12h of incubation. The results suggest that the surface-modified 99m Tc-HMPAO-PLA-PEG NC was more stable against label leakage in the presence of proteins and could present better performance as radiotracer in vivo.     

Characterisation of nanoparticulate systems by hydrodynamic chromatography

Particle size and particle size distribution can have a fundamental effect on the physical properties of colloidal dispersions. For many systems the measurement of average particle size is not sufficient, the presence of different size populations will have a strong influence on properties and could be related to the production process. Hydrodynamic chromatography (HDC) provides a method for the separation of polymers in solution or particles in suspension based on their size. In a packed column, the separation takes place in the inter-particle channels and the elution order is from large to small, analogous to gel permeation chromatography. The dynamic range of packed column HDC is from molecular size up to particles of greater than 1 microm. New instrumentation which can be used to determine the particle size distribution of a range of colloidal dispersions by packed column HDC is described. Data to support accuracy and precision of average particle size determination is presented as well as a number of case studies to illustrate the applicability of the technique to samples with polydisperse or multi-modal particle size distributions.     

Preparation of nanocapsules containing the two-phase core materials

In this study, copolymer nanocapsules containing the two-phase core materials were prepared by mini-emulsion polymerization using styrene (St) and methylmethacrylate (MMA) as comonomer, in which the ZnO nanoparticles organic suspension was prepared by solvothermal synthesis method. The obtained materials were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-visible spectrophotometry and fluorescence spectrometer. The particle size of the prepared ZnO nanoparticles dispersed in the organic solvent was less than 20 nm. The resulting polymer nanocapsules have 100-200 nm in diameter and approximately 10-20 nm in the wall thickness. The surface of the polymer nanocapsules is smooth and clear.     

Preparation of nanocapsules containing the two-phase core materials

In this study, copolymer nanocapsules containing the two-phase core materials were prepared by mini-emulsion polymerization using styrene (St) and methylmethacrylate (MMA) as comonomer, in which the ZnO nanoparticles organic suspension was prepared by solvothermal synthesis method. The obtained materials were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-visible spectrophotometry and fluorescence spectrometer. The particle size of the prepared ZnO nanoparticles dispersed in the organic solvent was less than 20?nm. The resulting polymer nanocapsules have 100–200?nm in diameter and?～?10–20?nm in the wall thickness. The surface of the polymer nanocapsules is smooth and clear.     

A detailed analysis of biodegradable nanospheres by different techniques--a combined approach to detect particle sizes and size distributions

Poly(d,l-lactide-co-glycolide) nanosupensions as intravenous nanosphere systems were produced by solvent deposition in aqueous Poloxamer 188 solutions. Light scattering techniques were applied to these colloidal systems to characterize particle sizes. Regularly shaped spherical particles were received as proved by freeze fracture replica and small-angle X-ray scattering (SAXS). SAXS was performed using intensive synchrotron radiation. Particle sizes were calculated from the small-angle part of scattering curve that were in good agreement with z-average values received from photon correlation spectroscopy (PCS). The flow field-flow fractionation (FlFFF) fractograms in combination with multi-angle light scattering (MALS) allowed an easy detection of maximum particle sizes what is most important for parenteral systems. Furthermore, high quality size distributions were received due to the separation step prior to size characterization. The calculated average size values exhibited a good correlation with z-averages determined by PCS. Only for suspensions of broader size distributions, higher deviations were observed. Comparing particle sizes with and without Poloxamer, differences in diameters resulted that were quantified. The additional Poloxamer shell was not able to be removed by an intensive washing during FlFFF focusing and separation. Especially FlFFF/MALS proved to be a valuable tool to characterize the pharmaceutical nanosuspensions in detail what is of great importance especially for controlled drug delivery systems.     

Application of atomic force microscopy and ultrasonic resonator technology on nanoscale: Distinction of nanoemulsions from nanocapsules

Oily core nanocapsules were prepared by sequential addition of positively and negatively charged polyelectrolytes based on a nanoemulsion and transformation thereof into a core–shell structure. The capsules were well characterized by photon correlation spectroscopy, laser diffraction, ζ-potential and transmission electron microscopy and feature an average size of 150 nm and a negative surface charge. The aim of the current study was to improve the dispersion stability and mechanic rigidity of the capsule wall by depositing an increasing number of up to five layers. Therefore, atomic force microscopy (AFM) and ultrasonic resonator technology (URT) were applied to investigate the shell of the nanoemulsion, the intermediate and final nanocapsules in more detail. AFM was performed to investigate the shape, morphology and mechanic properties of the emulsion and capsule shell. It proved to be a feasible technique to distinguish nanoemulsions from nanocapsules by stiffness analysis. URT was utilized in order to observe the ultrasound velocity and could confirm the AFM results. Both techniques demonstrated that the shell around an oil droplet solidified with increasing number of polyelectrolyte layers. Since a solid wall might have the potential of a strong diffusion barrier, nanocapsules might present a feasible prolonged release drug delivery system in contrast to nanoemulsions.     

纳米雄黄的粒度分析方法

目的：建立纳米雄黄的粒度分析方法。方法：利用原子力显微镜对纳米雄黄的表观形貌进行直接观察测定,用激光光散射法对纳米雄黄的粒度分布范围进行分析测定。结果：首次得到原子力显微镜下纳米雄黄形貌特征图;激光光散射颗粒度测定仪的测量显示．粒径在30nm以下的纳米雄黄约90％。结论：本研究所采用的原子力显微镜法和激光光散射法快速、简便、准确,可用于纳米雄黄的粒度检测。     

Atomic force microscopy and photon correlation spectroscopy: two techniques for rapid characterization of liposomes.

The direct evaluation of the heterogeneity of the particle population of nanometric drug delivery systems as liposomes is difficult to achieve owing to the dimension and the carrier characteristics. The influence of the lipidic ratio and composition on the physical stability of liposomes during their storage was investigated using atomic force microscopy (AFM) and photon correlation spectroscopy (PCS). Liposomes were made by a mixture of different lipids and obtained using distinct methods of preparation. AFM images, acquired immediately after the deposition of the sample on mica surface, clearly showed the spherical shape of the lipidic vesicles. In all the 7 months of the experiment, the average sizes of the different liposomes evaluated using the two techniques were comparable. According to PCS analysis, AFM images confirmed that almost all the diversified vesicular systems tended to form aggregates during their storage; this loss of stability was strengthened by the increase of polydispersity index value. The different behaviours observed were to ascribe to the lipidic composition more than the methods of liposome preparation. In conclusion, AFM technique owing to the relative simplicity cold be useful for the technological control of size distribution profile according to the preparative factors and moreover to the batch-to-batch reproducibility.     

Redispersible spray-dried lipid-core nanocapsules intended for oral delivery: the influence of the particle number on redispersibility

Abstract

This study proposes a new approach to produce easily redispersible spray-dried lipid-core nanocapsules (LNC) intended for oral administration, evaluating the influence of the particle number density of the fed sample. The proposed approach to develop redispersible spray-dried LNC formulations intended for oral route is innovative, evidencing the needing of an optimization of the initial particle number density in the liquid suspension of nanocapsules. A mixture of maltodextrin and L-leucine (90:10 w/w) was used as drying adjuvant. Dynamic light scattering, turbidimetry, determination of surface area and pore size distribution, electron microscopy and confocal Raman microscopy (CRM) were used to characterize the proposed system and to better understand the differences in the redispersion behavior. An easily aqueous redispersion of the spray-dried powder composed of maltodextrin and L-leucine (90:10 w/w) was obtained, depending on the particle number density. Their surface area decreased in the presence of LNC. CRM enabled the visualization of the spatial distribution of the different compounds in the powders affording to better understand the influence of the particle number density of the fed sample on their redispersion behavior. This study shows the need for optimizing initial particle number density in the liquid formulation to develop redispersible spray-dried LNC powders.     

A Novel Phase Inversion-Based Process for the Preparation of Lipid Nanocarriers

Purpose. To develop and subsequently evaluate a novel phase inversion-based method used to formulate lipidic nanocapsules. Methods. Mechanical properties of emulsions prepared by multi-inversion phase processes were investigated using a drop tensiometer. Based on the results obtained, a formulation process was developed and a new type of nanocarrier was prepared. These particulates were sized by photon correlation spectroscopy and were visualized by atomic force microscopy and transmission electronic microscopy. Differential scanning calorimetry was also performed. Results. The marginally cohesive but stable interfacial properties of the initial system led to the formulation of lipidic nanocapsules that were composed of a liquid core surrounded by a cohesive interface and were dispersed in an aqueous medium. These related suspensions were stable upon dilution for several months. The control of the formulation parameters allowed an adjustment of the particle mean diameter in the range of 25-100 nm with a monodisperse size distribution. Conclusions. A novel and convenient process for the preparation of lipidic nanocapsules is described. The structure of these particulates resembles a hybrid between polymeric nanocapsules and liposomes. Such nanocapsules display a strong potential for drug delivery.     

The influence of lipid nanocapsule composition on their size distribution.

A formulation process, based on the inversion phase of an emulsion, was used to prepare lipid nanocapsules. Triglycerides, lecithin, salted water and hydroxy stearate of poly(ethylene glycol) were used in the preparation. The amounts of each that allowed nanocapsules to be formed described a feasibility domain within a ternary diagram. The size distribution of various nanoparticulate carriers has already been shown to influence their applications. An experimental mixture design inside the feasibility domain has been used in order to approximate, through an empirical model, the influence of the quantitative composition of nanocapsules on their size distribution. Reduced cubic polynomial equations successfully modelled the evolution of responses in terms of particle average diameters and coefficients of variation. The results were presented using an analysis of response surface showing a scale of possible particle sizes between 20 and 95 nm and a coefficient of variation between 11 and 40%. Furthermore, this technique showed that the proportion of hydrophilic surfactant had a major influence on the average diameter and the size distribution of the particles decreasing when its proportion increased. On the contrary, the coefficient of variation and the average diameter slightly increase with the proportion of triglycerides. Such a tool offers major advantages to design the formulation of particles as a function of the required size distribution.     

Alkylcyanoacrylate nanocapsules prepared from mini-emulsions: a comparison with the conventional approach

Polyalkylcyanoacrylate nanocapsules are being prepared using two different types of o/w-emulsions: a conventional emulsion generated by intensive stirring with a home-made device and a mini-emulsion produced by the action of ultrasonic dispersion, using the alkylcyanoacrylate monomer as a hydrophobic agent. The emulsions and the resulting nanocapsule dispersions are compared using various methods of physical characterization. The formation of solid capsules is indicated by solid state NMR spectra and atomic force microscopy. Differences between the results of both synthetic approaches are found in terms of particle size distribution, zeta potential and tendency towards particle agglomeration. Capsules prepared by ultrasound via the mini-emulsion pathway tend to be smaller and more monodisperse. Their zeta potential is negative with larger absolute values as compared to capsules obtained from conventional emulsions, leading to stronger repulsive interactions and a higher stability against capsule agglomeration.     

Polyalkyl cyanoacrylate nanocapsules

In-situ polymerized methyl cyanoacrylate (MCA), ethyl cyanoacrylate (ECA), and butyl cyanoacrylate (BCA) were used to prepare nanocapsules of fluorescein or doxorubicin as markers by a w/o emulsion interfacial polymerization technique. Different concentrations of MCA were also used to show the effect of monomer concentration. The nanocapsules were characterized by electron microscopy, particle size analysis, holding capacity and in-vitro release of the marker substances. After selection of the polymerization solvent system, nearly spherical nanocapsules were obtained using each of the monomers. Most of the nanocapsules prepared were in the particle size range 500-1500 nm diameter. They were able to hold 55-74% of the marker initially present in aqueous solution. In-vitro dissolution studies showed that release of marker was retarded variably in an increasing order from nanocapsules containing MCA, ECA then BCA. Increasing the concentration of the monomer in the nanocapsules led to retardation of marker release.     

Preparation and storage stability of rutin nanosuspensions

Formulations of the rutin nanosuspensions have been prepared by high pressure homogenization (HPH). A Micron LAB 40 was used for HPH to obtain rutin nanosuspensions. Photon correlation spectroscopy (PCS) and laser diffraction were employed to analyze the particle size. Morphology of the particles was analyzed by light microscopy. The HPH technique produced rutin nanosuspensions having PCS size average of 547–912 nm and zeta potential range about ?30 mV in water. Aqueous rutin nanosuspension stabilized by SDS and Tween 80 were stable over 12 months. The nanosuspensions produced via HPH not only could prevent large particle size and particle growth, but also protect the drugs from chemically degradation. The molecules of the surface stabilizer are able to shield the chemical compound. The crystalline structure in a nanoparticulate sized formulation results in improved drug chemical-stability.     

Scanning electron microscopy and atomic force microscopy imaging of solid lipid nanoparticles derived from amphiphilic cyclodextrins.

Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been applied to the imagery of solid lipid nanoparticles (SLNs) formulated from an amphiphilic cyclodextrin, 2,3-di-o-alkanoyl-beta-cyclodextrin, beta-CD21C6. Comparison of the results shows that the vacuum drying technique used in sample preparation for SEM causes shrinkage in the size of the SLNs, whereas the deposition method used for AFM causes the SLNs to form small clusters. The hydrodynamic diameter determined from photon correlation spectroscopy (PCS) is 359+/-15 nm and the zeta potential is -25 mV.     

Analysis of titanium dioxide and zinc oxide nanoparticles in cosmetics

There have been rapid increases in consumer products containing nanomaterials, raising concerns over the impact of nanoparticles (NPs) to humankind and the environment, but little information has been published about mineral filters in commercial sunscreens. It is urgent to develop methods to characterize the nanomaterials in products. Titanium dioxide (TiO₂) and zinc oxide (ZnO) NPs in unmodified commercial sunscreens were characterized by laser scanning confocal microscopy, atomic force microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that laser scanning confocal microscopy evaluated primary particle aggregates and dispersions but could not size NPs because of the diffraction limited resolution of optical microscopy (200 nm). Atomic force microscopy measurements required a pretreatment of the sunscreens or further calibration in phase analysis, but could not provide their elemental composition of commercial sunscreens. While XRD gave particle size and crystal information without a pretreatment of sunscreen, TEM analysis required dilution and dispersion of the commercial sunscreens before imaging. When coupled with energy-dispersive X-ray spectroscopy, TEM afforded particle size information and compositional analysis. XRD characterization of six commercial sunscreens labeled as nanoparticles revealed that three samples contained TiO₂ NPs, among which two listed ZnO and TiO₂, and displayed average particle sizes of 15 nm, 21 nm, and 78 nm. However, no nanosized ZnO particles were found in any of the samples by XRD. In general, TEM can resolve nanomaterials that exhibit one or more dimensions between 1 nm and 100 nm, allowing the identification of ZnO and TiO₂ NPs in all six sunscreens and ZnO/TiO₂ mixtures in two of the samples. Overall, the combination of XRD and TEM was suitable for analyzing ZnO and TiO₂ NPs in commercial sunscreens.     

Release profiles and morphological characterization by atomic force microscopy and photon correlation spectroscopy of 99mTechnetium-fluconazole nanocapsules

Several classes of antifungal have been employed in candidiasis treatment, but patients with advanced immunodeficiency can present unsatisfactory results after therapy. In these cases, high doses of drugs or the use of multiple agents are sometimes used, and hence increasing the risk of serious side effects. Considering theses difficulties, the encapsulation of antifungal agents in nanoparticulate carriers has been used with the objective of modifying the pharmacokinetic of drugs resulting in more efficient treatments with less side effects. The purpose of this work was the preparation, characterization and the investigation of the release profiles of radiolabeled fluconazole nanocapsules. The size, homogeneity and zeta potential of NC preparations were determined with a Zetasizer 3000HS. The morphology and the structural organization were evaluated by atomic force microscopy (AFM). The release study in vitro of NC was evaluated in physiologic solution with or without 70% mouse plasma. The labeling yield of fluconazole with 99mTc was 94% and the radiolabeled drug was stable within 24h period. The encapsulation percentage of 99mTc-fluconazole in PLA-POLOX NC and PLA-PEG NC was approximately of 30%. The average diameter calculated by photon correlation spectroscopy (PCS) varied from 236 to 356 nm, while the average diameter determined by AFM varied from 238 to 411 nm. The diameter/height relation decreased significantly when 25% glutaraldehyde was used for NC fixation on mica. The zeta potential varied from -55 to -69 nm and surface-modified NC showed lower absolute values than conventional NC. The in vitro release of 99mTc-fluconazole in plasma medium of the conventional and surface-modified NC was greater than in saline. The drug release in plasma medium from conventional NC was faster than for surface-modified NC. The results obtained in this work suggest that the nanocapsules containing fluconazole could be used to identify infectious foci, due to the properties, such as size, zeta potential and controlled release of (99m)Tc-fluconazole. The surface-modified nanocapsules could constitute a long-circulating intravenous formulation of fluconazole for treating sepsis caused by disseminated form of candidiasis. However, in vivo studies should be considered and are under investigation.     

两性霉素B脂质体粒度测定方法研究

目的：建立两性霉素B脂质体粒度检测方法，通过测定一组性质不同的样品，找出最佳测定方法。方法：用计算机的图像一数字处理技术结合扫描电镜、透射电镜和激光光散射粒度测定仪分别测定两性霉素B脂质体的粒度。结果：电镜法测定两性霉素B脂质体的粒度为20—100nln，平均粒径为55—75nm；激光光散射法测定两性霉素B脂质体的粒度为30—200nm，平均粒径为50—180nm。结论：激光光散射法能较好反映两性霉素B脂质体在使用时的真实粒度，且方法快速、简便，是一种较好的两性霉素B脂质体粒度测定方法。     

Microstructure and Elution of Tetracycline from Block Copolymer Coatings

A critical metrology issue for pharmaceutical industries is the application of analytical techniques for the characterization of drug delivery systems to address interrelationships between processing, structure, and drug release. In this study, cast coatings were formed from solutions of poly(styrene-b-isobutylene-b-styrene) (SIBS) and tetracycline in tetrahydrofuran (THF). These coatings were characterized by several imaging modalities, including time- of-flight secondary ion mass spectrometry (TOF-SIMS) for chemical imaging and analysis, atomic force microscopy (AFM) for determination of surface structure and morphology, and laser scanning confocal microscopy (LSCM), which was used to characterize the three-dimensional structure beneath the surface. The results showed phase separation between the drug and copolymer regions. The size of the tetracycline phase in the polymer matrix ranged from hundreds of nanometers to tens of microns, depending on coating composition. The mass of drug released was not found to be proportional to drug loading, because the size and spatial distribution of the drug phase varied with drug loading and solvent evaporation rate, which in turn affected the amount of drug released.     

Spray-dried indomethacin-loaded polyester nanocapsules and nanospheres: development, stability evaluation and nanostructure models

The industrial development of polymeric nanoparticle suspensions, as drug delivery systems, is limited due to the problems in maintaining stability of suspensions. In this work, a spray-drying technique was applied to dry nanocapsule and nanosphere suspensions prepared by nanoprecipitation of polyesters using SiO₂ as adjuvant. Powders obtained from nanocapsules presented stable drug recoveries and morphological characteristics after 5 months. For nanocapsules, nanostructures around 200 nm were observed by scanning electron microscopy (SEM) on the surface of microparticles of SiO₂, whereas for the nanosphere formulation, nanostructures with a reduced diameter (60–90 nm) were observed, despite the particle sizes of each original suspension being similar, when measured by photon correlation spectroscopy (PCS). In order to investigate the morphological aspects of nanocapsule and nanosphere powders, several nanosphere formulations were spray-dried using different concentrations of SiO₂ and a comparative study of the different colloidal systems (nanocapsules, nanospheres, nanoemulsion or nanodispersion) was carried out by PCS. SEM analyses showed that nanostructures with reduced diameter are formed independently of the adjuvant concentration. The dynamic properties of these systems allowed to suggest that the structure of the nanosphere particle (polymer, sorbitan monostearate and polysorbate 80) was a polymeric matrix dispersing the sorbitan monostearate which, when submitted to the spray-drying process in the presence of SiO₂, gave nanostructures presenting diameters around 80 nm covering the microparticles due to the release of lipophilic surfactant from the polymeric matrix.