Structural, Magnetic and Microwave Characterization of Polycrystalline Z-Type Sr3Co2Fe24O41 Hexaferrite

We report results on the structural and microwave properties and magnetic phase transitions in polycrystalline Sr₃Co₂Fe₂₄O₄₁ hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave absorbing material. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves revealed a change in the magnetization behavior at 293 K. The reflection losses in the 1-20 GHz range of the Sr₃Co₂Fe₂₄O₄₁ powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in both the absence and presence of a magnetic field. In the latter case, a dramatic rise in the attenuation was observed. The microwave reflection losses reached the maximum value of 32.63 dB at 17.29 GHz in the Ku-band. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the appearance of new reflection losses maxima. At a fixed thickness t_m of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field.

Characterization Methods for Solid Lipid Nanoparticles (SLN) and Nanostructured Lipid Carriers (NLC)

BACKGROUND

Solid lipid nanoparticles (SLN) and the next generation of nanostructured lipid carriers (NLC) seem to be a very promising alternative to other colloidal carriers such as liposomes, microemulsions, and polymeric nanoparticles. These combine the advantages of the cited nanocarriers and can improve the dissolution rate in biological fluids, increase the drug absorption, improve the tissue distribution in the target organ, enhance the drug bioavailability and ensure controlled drug release. SLN and NLC can ensure higher drug stability in the harsh environment, cover the bitter taste of the drug, and reduce the first-pass-effect after oral administration. However, these carriers suffer from some disadvantages such as low drug loading capacity, drug expulsion, and unpredictable gelation tendency.

METHODS

This article aims to provide detail information about the process of complex characterization of SLN and NLC to produce an effective, quality and safe colloidal DDS with desired properties, based on the literature published in the period from 2000 to 2017.

RESULTS

Characterization techniques in terms of size and particle size distribution; surface morphology, functionalization, and zeta potential; structure, depending on the degree of crystallinity, lipid modification, drug incorporation and loading capacity; drug release; co-existence of other nano- and microstructures; and toxicity assessment according to the process of production, lipids and surfactants used and route of administration are discussed in the article.

CONCLUSION

The precise characterization of lipid nanocarriers as drug delivery systems ensures guarantees for the quality of the product as an effective and safe form. The typical composition of SLN and NLC requires a comprehensive approach of characterization and in-depth analysis of the results to perform a drug delivery system with desired properties.

Ketoprofen-loaded polymer carriers in bigel formulation: an approach to enhancing drug photostability in topical application forms

The purpose of the study was to investigate the stability and biopharmaceutical characteristics of ketoprofen, loaded in polymeric carriers, which were included into a bigel in a semisolid dosage form. The polymer carriers with in situ-included ketoprofen were obtained by emulsifier-free emulsion polymerization of the monomers in aqueous medium or a solution of the polymers used. The morphological characteristics of the carriers, the in vitro release and the photochemical stability of ketoprofen were evaluated. The model with optimal characteristics was included in a bigel formulation. The bigel was characterized in terms of pH, rheological behavior, spreadability, and in vitro drug release. Acute skin toxicity, antinociceptive activity, anti-inflammatory activity, and antihyperalgesic effects of the prepared bigel with ketoprofen-loaded polymer carrier were evaluated. The carriers of ketoprofen were characterized by a high yield and drug loading. The particle size distribution varied widely according to the polymer used, and a sustained release was provided for up to 6 hours. The polymer mixture poly(vinyl acetate) and hydroxypropyl cellulose as a drug carrier, alone or included in the bigel composition, improved the photostability of the drug compared with unprotected ketoprofen. The bigel with ketoprofen-loaded particles provided sustained release of the drug and had optimal rheological parameters. In vivo experiments on the bigel showed no skin inflammation or irritation. Four hours after its application, a well-defined analgesic, anti-inflammatory, and antihyperalgesic effect was registered. The polymer mixture of poly(vinyl acetate) and hydroxypropyl cellulose as a carrier of ketoprofen and the bigel in which it was included provided an enhanced photostability and sustained drug release.