Development and validation of an analytical method for the quantification of cytochrome c in skin transport studies

A simple isocratic HPLC method for the quantification of Cytochrome c in skin permeation samples was developed and validated. The mobile phase comprised a 41 : 59 mixture of an organic phase A (0.1% trifluoroacetic acid in a 90 : 10 mixture of MeCN–H₂O) and an aqueous phase B (0.1% trifluoroacetic acid in H₂O). The Cytochrome c retention and run times were 2.62 and 8.0 min, respectively—much shorter than those for existing gradient methods. The response was accurate, precise and linear from 2.5 to 25 μg/mL. The mean recoveries for intra‐day and inter‐day analysis ranged from 88.5 to 103.8% and the RSD varied from 0.05 to 1.55%. The assay was used to quantify transport of Cytochrome c across intact and laser‐microporated porcine skin in vitro. Cytochrome c permeation and the amount of protein retained within the membrane over 24 h were quantified as a function of the number of micropores. Although no Cytochrome c permeation was observed across intact skin, laser microporation enabled delivery of 22.9 ± 3.3 and 56.0 ± 15.9 μg/cm² of the protein across skin samples with 300 and 1800 micropores, respectively. In conclusion, the HPLC method provided a fast, efficient means to quantify Cytochrome c in samples from skin transport studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Quality by Design for Development,Optimization and Characterization of Brucine Ethosomal Gel for Skin Cancer Delivery

Natural products have been extensively used for treating a wide variety of disorders. In recent times, Brucine (BRU) as one of the natural medications extracted from seeds of nux vomica, was investigated for its anticancer activity. As far as we know, this is the first study on BRU anticancer activity against skin cancer. Thus, the rational of this work was implemented to develop, optimize and characterize the anticancer activity of BRU loaded ethosomal gel. Basically, thin film hydration method was used to formulate BRU ethosomal preparations, by means of Central composite design (CCD), which were operated to construct (3²) factorial design. Two independent variables were designated (phospholipid percentage and ethanol percentage) with three responses (vesicular size, encapsulation efficiency and flux). Based on the desirability function, one formula was selected and incorporated into HPMC gel base to develop BRU loaded ethosomal gel. The fabricated gel was assessed for all physical characterization. In-vitro release investigation, ex-vivo permeation and MTT calorimetric assay were performed. BRU loaded ethosomal gel exhibited acceptable values for the characterization parameters which stand proper for topical application. In-vitro release investigation was efficiently prolonged for 6 h. The flux from BRU loaded ethosome was enhanced screening optimum SSTF value. Finally, in-vitro cytotoxicity study proved that BRU loaded ethosomal gel significantly improved the anticancer activity of the drug against A375 human melanoma cell lines. Substantially, the investigation proposed a strong motivation for further study of the lately developed BRU loaded ethosomal gel as a prospective therapeutic strategy for melanoma treatment.     

Kinetic investigations on the basis of isothermal DSC measurements of hydrogenation and dehydrogenation of magnesium hydride

Results of kinetic investigations on the basis of isothermal DSC measurements by means of defined pressure changes are presented and interpreted for the Mg/MgH₂ system. From an evaluation of the experimentally obtained DSC-signals, the dependence of reaction rate on hydrogen pressure p₀, temperature and sample morphology could be described. Under certain conditions, it is possible to visualise individual rate-determining steps and, thus, to arrive at conclusions on the reaction mechanism.     

Sustained release of BSA from a novel drug delivery matrix -- bullfrog skin collagen film

A novel drug delivery system, bullfrog skin collagen film, was employed to release bovine serum albumin (BSA). The biophysical properties of bullfrog skin collagen film used were evaluated by thermal denaturation temperature and percentage water loss. The film obtained exhibited good stability and can be taken as a good candidate for drug delivery matrix. Compared with conventional collagen from molecular weight and amino acid composition, bullfrog skin collagen showed significant differences. For safety considerations, bullfrog skin collagen has great advantages. The release kinetics of BSA from bullfrog skin collagen film was measured in vitro. The results indicated bullfrog skin collagen film could be used for sustained release of BSA. Thus, bullfrog skin collagen film can be taken as a novel drug delivery system.     

Some remarks on heat capacity measurements by temperature-modulated calorimetry

In temperature-modulated calorimetry, the condition in sample amount, especially thickness, required for high-accuracy heat capacity measurement should be made clear. We propose the condition of maximum thickness of a sample for measuring heat capacity within an accuracy of 1%. The other important factor for high-accuracy heat capacity measurement is thermal contact conductance between a sample and a sample pan and also that between a pan and a base plate of an apparatus. The conditions in these thermal contact conductances required for high-accuracy heat capacity measurement are discussed. Among them, if only thermal contact conductance between a pan and a base plate is significant, there is an ingenious method to measure heat capacity with high accuracy. Furthermore, if the thermal contact conductance between a pan and a base plate is infinite, we offer a simple method to obtain complex heat capacity.     

Films based on chitosan polyelectrolyte complexes for skin drug delivery: Development and characterization

Novel chitosan based polyelectrolyte complexes (PEC) were developed and optimized in order to obtain films possessing the optimal functional properties (flexibility, resistance, water vapour transmission rate and bioadhesion) to be applied on skin. The development was based on the combination of chitosan and two polyacrylic acid (PAA) polymers with different crosslinkers and crosslinking densities. The interaction between the polymers was maximized controlling the pH, and by forming the films at a pH value close to the pK_a of the respective components as identified by potentiometric and turbidimetric titrations. The action of glycerol, PEG200, Hydrovance and trehalose upon the functional properties of the films was also evaluated. Glycerol was found to improve the film properties in terms of flexibility, resistance and water vapour transmission rate (WVTR) with a maximum effect at 30%. The application of a pressure sensitive adhesive (PSA) significantly improved bioadhesion with a negligible influence in the resistance and flexibility of the films.The optimized film, including adhesive, has shown very good properties for application in the skin and represents a very promising formulation for further incorporation of drugs for topical and transdermal administration.     

Hierarchical structure in polymer‐based drug delivery systems as probed by calorimetric measurements

Thermoporosimetry (TPM), a differential scanning calorimetry technique that relies on the shift of transition temperatures caused by the confinement of liquids, was applied to elucidate the complex morphology of drug‐loaded polymeric microcapsules prepared by the emulsion solvent evaporation method. For the very first time, TPM has been applied simultaneously with two liquids as structural probes. It was found that Miglyol, which dissolves the selected drug (Ibuprofen), is confined inside vesicles having a mean radius of 26.3 nm, whereas water, which is the continuous phase, is trapped inside a swollen polymeric network of Eudragit with an average mesh radius of 1.7 nm. A proposed hierarchical structure is given, which predicts that Eudragit microcapsules are formed from a collection of inert oil vesicles partitioned by polymeric Eudragit membranes swollen by water. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1939–1945, 2010     

Considerations of the intermediate oxides via XPS elemental quantitative analysis for the thickness measurements of ultrathin SiO2 on Si

The thicknesses of intermediate oxides at the interface between ultrathin SiO₂ and Si substrates have been measured via XPS elemental quantitative analysis for some SiO₂/Si(100) and SiO₂/Si(111) samples with the silicon oxide thickness less than 2 nm. The measurements involve XPS determination of the Si relative atomic ratio, calculation of Si atomic densities for the intermediate oxide, etc. and then the intermediate oxide thicknesses and the number of monolayers are obtained by referencing the thickness data from two international comparisons for these samples. The results show that the thickness of the intermediate oxides is in the range 0.14–0.16 nm with an average value of 0.15 nm. The number of monolayers for the intermediate oxides at the interface is less than one monolayer with an average value of 0.60. In the present work, there are a series of approximations. By making these approximations many parameters, including L and R₀, used in the conventional calculation method are removed to give a simpler equation, which is valid when the thicknesses of SiO₂ overlayer and the intermediate oxides are very small. This, therefore, appears to be a simple and quick method to obtain approximate oxide thicknesses of modest accuracy. The present work does not in any way replace or improve on Eqns ( 2 –6) cited in the text. Copyright © 2010 John Wiley & Sons, Ltd.     

Micropatch‐arrayed pads for non‐invasive spatial and temporal profiling of topical drugs on skin surface

Micropatch‐arrayed pads (MAPAs) are presented as a facile and sensitive sampling method for spatial profiling of topical agents adsorbed on the surface of skin. MAPAs are 28 × 28 mm sized pieces of polytetrafluoroethylene containing plurality of cavities filled with agarose hydrogel. They are affixed onto skin for 10 min with the purpose to collect drugs applied topically. Polar compounds are absorbed by the hydrogel micropatches. The probes are subsequently scanned by an automated nanospray desorption electrospray ionization mass spectrometry system operated in the tapping dual‐polarity mode. When the liquid junction gets into contact with every micropatch, polar compounds absorbed in the hydrogel matrix are desorbed and transferred to the ion source. A 3D‐printed interface prevents evaporation of hydrogel micropatches assuring good reproducibility and sensitivity. MAPAs have been applied to follow dispersion of topical drugs applied to human skin in vivo and to porcine skin ex vivo, in the form of self‐adhesive patches. Spatiotemporal characteristics of the drug dispersion process have been revealed using this non‐invasive test. Differences between drug dispersion in vivo and ex vivo could be observed. We envision that MAPAs can be used to investigate spatiotemporal kinetics of various topical agents utilized in medical treatment. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultra‐thin SiO2 on Si IX: absolute measurements of the amount of silicon oxide as a thickness of SiO2 on Si

Results from a study conducted between National Metrology Institutes (NMIs) for the measurements of the absolute thicknesses of ultra‐thin layers of SiO₂ on Si are reported. These results are from a key comparison and associated pilot study under the auspices of the Consultative Committee for Amount of Substance. ‘Amount of substance’ may be expressed in many ways, and here the measurand is the thickness of the silicon oxide layers with nominal thicknesses in the range 1.5–8 nm on Si substrates, expressed as the thickness of SiO₂. Separate samples were provided to each institute in containers that limited the carbonaceous contamination to approximately < 0.3 nm. The SiO₂ samples were of ultra‐thin on (100) and (111) orientated wafers of Si. The measurements from the laboratories which participated in the study were conducted using ellipsometry, neutron reflectivity, X‐ray photoelectron spectroscopy or X‐ray reflectivity, guided by the protocol developed in an earlier pilot study. A very minor correction was made in the different samples that each laboratory received. Where appropriate, method offset values attributed to the effects of contaminations, from the earlier pilot study, were subtracted. Values for the key comparison reference values (agreed best values from a Consultative Committee study) and their associated uncertainties for these samples are then made from the weighted means and the expanded weighted standard deviations of the means of these data. These results show a dramatic improvement on previous comparisons, leading to 95% uncertainties in the range 0.09–0.27 nm, equivalent to 0.4–1.0 monolayers over the 1.5–8.0 nm nominal thickness range studied. If the sample‐to‐sample uncertainty is reduced from its maximum estimate to the most likely value, these uncertainties reduce to 0.05–0.25 nm or ～1.4% relative standard uncertainties. The best results achieve ～1% relative standard uncertainty. It is concluded that XPS has now been made fully traceable to the SI, for ultra‐thin thermal SiO₂ on Si layers, by calibration using wavelength methods in an approach that may be extended to other material systems. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Critical review of the current status of thickness measurements for ultrathin SiO2 on Si Part V: Results of a CCQM pilot study

Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in the amount of thermal oxide on (100) and (111) orientation silicon wafer substrates in the thickness range 1.5–8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium—energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing—incidence x‐ray reflectometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterized by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters. The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The data sets correlate with the NPL data with average root‐mean‐square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonaceous contamination equivalent to ～ 1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X‐ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. The XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2), deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy. Copyright © 2004 John Wiley & Sons, Ltd.     

Effect of Penetration Enhancers on Toenail Delivery of Efinaconazole from Hydroalcoholic Preparations

The incorporation of permeation enhancers in topical preparations has been recognized as a simple and valuable approach to improve the penetration of antifungal agents into toenails. In this study, to improve the toenail delivery of efinaconazole (EFN), a triazole derivative for onychomycosis treatment, topical solutions containing different penetration enhancers were designed, and the permeation profiles were evaluated using bovine hoof models. In an in vitro permeation study in a Franz diffusion cell, hydroalcoholic solutions (HSs) containing lipophilic enhancers, particularly prepared with propylene glycol dicaprylocaprate (Labrafac PG), had 41% higher penetration than the HS base. Moreover, the combination of hydroxypropyl-β-cyclodextrin with Labrafac PG further facilitated the penetration of EFN across the hoof membrane. In addition, this novel topical solution prepared with both lipophilic and hydrophilic enhancers was physicochemically stable, with no drug degradation under ambient conditions (25 °C, for 10 months). Therefore, this HS system can be a promising tool for enhancing the toenail permeability and therapeutic efficacy of EFN.