Influence of Surfactant on the Skin Permeation of Methylisothiazolinone and Methylchloroisothiazolinone.

Patch tests are often used in safety evaluations to identify the substance causing skin irritation, but the same substance can sometimes give positive or negative results depending on the test conditions. Here, we investigated differences in the skin penetration of two test compounds under different application conditions. We studied the effects of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant polysorbate 80 (PS) on skin penetration of the preservatives methylisothiazolinone (MT) and methylchloroisothiazolinone (MCT), which are used in cosmetics such as shampoos. The skin permeation of MT was enhanced by SDS but was unchanged by PS. Skin impedance decreased in the presence of SDS whereas PS had the same effect as the control aqueous solution, suggesting that SDS reduction of the barrier function of skin affects the permeation of MT, a hydrophilic drug. Application of a mixture of MCT and MT in the presence of SDS did not affect the skin permeation of MCT whereas the permeation of MT was enhanced by SDS, indicating that the skin permeation of MCT is less affected by SDS than is MT. Thus, attention should be paid to the possible effect of co-solutes, especially hydrophilic drugs.

Rheological Properties and Composition Affecting the Skin Permeation of a Model of a Hydrophilic Drug in Lecithin Reverse Wormlike Micelles.

We investigated the effect of the rheological properties and composition of lecithin reverse wormlike micelles (LRWs) on the skin permeation of a model of a hydrophilic drug to determine whether LRWs support uniform hydrophilic drug/oil-based formulations and good drug penetrate into skin. Here, we prepared LRWs with D (-)-ribose (RI) or glycerol (GL) as polar compounds, liquid paraffin (LP) or isopropyl myristate (IPM) as oils, and 6-carboxyfluorescein (CF) as a model for a hydrophilic drug, and evaluated the rheological properties and skin penetration characteristics of the preparations. The LRWs showed moderate viscosity at 25 °C, a typical storage temperature, but decreasing viscosity at 32 °C, the surface temperature of human skin, suggesting that the LRWs would penetrate the microstructure of skin (e.g., wrinkles and hair follicles). The highest skin permeability of CF was observed when IPM was used as the oil, suggesting that both the stratum corneum and hair follicle routes are involved in drug permeation. The penetration of CF into hair follicles is influenced not only by the rheology of the formulation but also by the interaction between IPM and sebum in the hair follicles.

Effect of the Physicochemical Properties of Liquid Paraffin on the Phase State and Rheological Properties of Lecithin Reverse Wormlike Micelles.

Lecithin reverse wormlike micelles (LRWs) have been studied recently for dermal application dosage use but the effects of the physicochemical properties of oils on the formation and rheological properties of LRWs have not been investigated. We studied the effect of oil on the formation of LRWs using 5 types of liquid paraffin (LP) with kinematic viscosities ranging from 4.00 to 88.0 mm2/s. Partial phase diagrams of lecithin/water/LP systems indicated that LPs with low molecular weights could form LRWs with only a small amount of water, but LPs with high molecular weights could not form LRWs, regardless of the water concentration. The solubility of lecithin in LPs was higher for low molecular weight LPs, thus possibly affecting the formation of LRWs. The zero-shear viscosity and relaxation time of LRWs initially increased with increasing water concentration, and then decreased. The water concentration providing the maximum value was dependent on the molecular weight of the LP, whereas the maximum amount and length of the LRWs were independent of the water concentration. Our results indicate that the molecular weight of LP affects the ease of formation and the viscoelasticity of LRWs.

A Method for Measuring the Surface Free Energy of Topical Semi-solid Dosage Forms.

Our aim was to determine the surface free energy (SFE) of semi-solid dosage forms (SSDFs) by establishing a reproducible method for measuring the contact angle of liquids to SSDFs. Four SSDFs were used: petrolatum, an oil/water (O/W) and a water/oil (W/O) cream, and an alcohol-based gel. The SSDFs were evenly spread on a glass slide, and the change in contact angle over time was measured by dropping water, glycerol, diiodomethane and n-hexadecane as the test liquids. Depending on the combination of test liquid and SSDF, the contact angle was either constant or decreased in an exponential manner. Contact angles may have decreased in an exponential manner because the reaction between the test liquid and the SSDF altered the interfacial tension between the two phases and changed the surface tension of the test liquid and the SFE of the SSDF. The contact angle of the test liquid to the SSDF could be determined reproducibly using the initial contact angle immediately after dropping the liquid on the SSDF as the contact angle before reaction. Using the obtained contact angles and the Owens-Wendt-Rabel-Kaelble equation, we calculated the SFE and its component for the SSDFs tested and found that the results reflect the physicochemical properties of SSDFs. Furthermore, the work of adhesion (WA) of the SSDF to Yucatan micropig skin was calculated using the SFE for the SSDFs. Interestingly, the WA values for all SSDFs tested were comparable.

Characteristics of an Emulsion Obtained Using Hydrophobic Hydroxypropyl Methylcellulose as an Emulsifier and a High-Pressure Homogenizer.

Hydrophobically modified hydroxypropyl methylcellulose (HM-HPMC), a polymer in which a small amount of HPMC is stearoxyl substituted, was used as an emulsifier of emulsion-type lotion. A high-pressure homogenizer (microfluidizer) was used. The viscosity of the 1% HM-HPMC aqueous gel decreased after passing through the microfluidizer from 5.5 to 2.7 Pa·s. When liquid paraffin (LP) was used as the oil phase, a stable emulsion was obtained with an LP ratio of 1-40%. The apparent viscosity decreased with LP ratios up to 20%, and then increased with increasing LP concentration. The emulsions with an LP ratio <20% presented a pseudo-viscous flow, similar to that of the diluted polymer solution. HM-HPMC likely adsorbed onto the oil with a stearoxyl group; thus, the interaction between the stearoxyl group, which explained the high viscosity of HM-HPMC, decreased, reducing the viscosity of the emulsion. The LP ratio was 40%, and the emulsion presented a plastic flow, which is typical of concentrated emulsions. The size of the droplet in the emulsion was approximately 1 µm regardless of the LP ratio. When low-viscosity LPs or monoester-type oils such as isopropyl myristate were used, some of the emulsions presented creaming. An emulsion using HM-HPMC as an emulsifier and an appropriate oil homogenized with a microfluidizer is stable, has low viscosity, and can be easily spread on skin.

The Molecular Mechanisms Underlying Prostaglandin D2-Induced Neuritogenesis in Motor Neuron-Like NSC-34 Cells.

Prostaglandins are a group of physiologically active lipid compounds derived from arachidonic acid. Our previous study has found that prostaglandin E2 promotes neurite outgrowth in NSC-34 cells, which are a model for motor neuron development. However, the effects of other prostaglandins on neuronal differentiation are poorly understood. The present study investigated the effect of prostaglandin D2 (PGD2) on neuritogenesis in NSC-34 cells. Exposure to PGD2 resulted in increased percentages of neurite-bearing cells and neurite length. Although D-prostanoid receptor (DP) 1 and DP2 were dominantly expressed in the cells, BW245C (a DP1 agonist) and 15(R)-15-methyl PGD2 (a DP2 agonist) had no effect on neurite outgrowth. Enzyme-linked immunosorbent assay demonstrated that PGD2 was converted to 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) under cell-free conditions. Exogenously applied 15d-PGJ2 mimicked the effect of PGD2 on neurite outgrowth. GW9662, a peroxisome proliferator-activated receptor-gamma (PPARγ) antagonist, suppressed PGD2-induced neurite outgrowth. Moreover, PGD2 and 15d-PGJ2 increased the protein expression of Islet-1 (the earliest marker of developing motor neurons), and these increases were suppressed by co-treatment with GW9662. These results suggest that PGD2 induces neuritogenesis in NSC-34 cells and that PGD2-induced neurite outgrowth was mediated by the activation of PPARγ through the metabolite 15d-PGJ2.

[Preparation and Rheological Properties of Cross-linked Liposomes Using Hydroxypropylmethylcellulose Bearing a Hydrophobic Anchor].

Hydrophobically-modified hydroxypropylmethylcellulose (HM-HPMC) is a thickener with a long hydrophobic alkyl side chain. In this study, we investigated the gelation ability and rheological properties of a liposome/HM-HPMC mixed solution. The liposome suspension and the HM-HPMC aqueous solution each had low viscosities, but the viscosity increased rapidly when they were mixed. This is thought to be due to the formation of a 3D network structure caused by the hydrophobic group of HM-HPMC penetrating into the liposomal bilayer membrane, crosslinking the liposomes together. This hypothesis was supported by the fact that gelation did not occur when hydroxypropylmethylcellulose without a hydrophobic group was used. The viscosity of the liposome/HM-HPMC mixed solution decreased rapidly when a shear was applied, but immediately returned to the original gel state when the shear was removed, indicating a reversible reaction. When a strong shear is applied, the hydrophobic group of HM-HPMC detaches from the liposome. When the shear is removed, the liposome is again cross-linked by HM-HPMC. From these results, it was revealed that liposome cross-linked gels can be prepared when HM-HPMC is used.

[Prediction of Wettability and Adhesion of Lotion to Skin Based on the OWRK Method].

In this study, we propose a new technique for evaluating wetting and adhesion of lotions to skin using surface tension measurements, contact angle measurements and calculations based on the Owens-Wendt-Rabel-Kaelble (OWRK) method. Three prescription lotions (Napageln® Lotion 3%, Sumilu® Lotion 3% and Felbinac Lotion 3% ï½¢Rakool｣） and two over-the-counter lotions (Feitas® Lotion and Salomethyl® FB Lotion α) were used. Based on the dispersive and polar components of the surface free energy of Yucatan micro pig (YMP) skin, isograms of contact angle (wetting envelope) and adhesion work of the YMP skin surface were constructed. Plotting the surface tension and its polar component of lotions on this isogram revealed that it is possible to predict the wettability and adhesion of lotions to YMP skin. Such diagrams can be easily constructed even using the surface free energy of other types of skin, such as that of humans and hairless mice. This evaluation method may be applicable to other external use medicines.

[Optimum Volume of Water Needed for the Paste State of Pediatric Powders: Considerations Based on Yield Values and Applications to Generic Medicine].

To clarify the volume of water required to paste pediatric powders, we herein established a standard for the powder paste state by measuring yield values when water was added to powders. The powders used in the present study were selected from 8 types including original and generic drugs. Tipepidine hibenzate is prescribed in the pediatric field in combination with ambroxol hydrochloride and l-carbocysteine. The volumes of water needed to achieve the paste state of ambroxol hydrochloride between the original and generic drugs were similar. However, the volumes of water needed for l-carbocysteine markedly differed between the original and generic drugs due to differences in their additives. The spreadability of the mixture when water was added to the powders was evaluated using a spread meter. Among the powders tested in the present study, the yield value to achieve a paste state with the addition of water was approximately 1000 dyne/cm2. The optimum volume of water estimated from this yield value using the linear proportional relationship for the amount of powder may be applied to the mixture of each pediatric power for dosage/body weight.

The Comparison of Surface Free Energy of Human, Yucatan Micropig, and Hairless Mouse Skins and Influence of Surfactant on Surface Free Energy of the Skin.

Surface free energy (SFE) is an important factor for evaluation of wettability or adhesion. Thus, the SFE of a Yucatan micropig (YMP) skin and a hairless mouse (HM) skin, which are commonly used in skin permeation studies instead of human skin, were compared with the human skin. Contact angles of water and 1-bromo naphthalene to skin were measured and the SFE was calculated using the Owens-Wendt equation. The SFE of the human abdominal skin was 40 mN/m and its polar component σsp was as low as 2 mN/m, which was similar to that of the low sebum skin reported previously. In the case of the YMP skin, σsp was high on the surface but similar to that obtained after the skin was tape-stripped twice. The HM skin showed similar SFE as that of the human skin. When the surfactant was applied on the skin, wiped, and dried, the remaining surfactant increased the SFE in σsp; however, the original SFE was obtained after rinsing with water. The YMP skin and HM skin is similar to the human abdominal skin with a low sebum level. Thus, they are also good skin models for studying wettability or adhesion of a substance.

Application of Pickering Emulsion with Cyclodextrin as an Emulsifier to a Transdermal Drug Delivery Vehicle.

The emulsion prepared with ß-cyclodextrin as an emulsifier (ßCDE) is considered to be a Pickering emulsion. We examined the characteristics of ßCDEs using captopril (CP) as a model drug, and studied the in vitro skin permeation of CP from ßCDEs through hairless mouse skin. The stability of ßCDE was increased with increasing ßCD concentration and conversely decreased with increasing CP concentration. The yield stress value from the rheological measurement results was suggested to be one of the factors determining the stability of the ßCDE, and ßCDEs with higher yield stress values were more stable. We found that the skin permeability of CP could be improved by using ßCDE with isopropyl myristate as the oil phase and that the flux of CP depended on the free CP concentration in the water phase of ßCDE.

Highly Viscoelastic Reverse Wormlike Micellar Systems from a Mixture of Lecithin, Polyglycerol Fatty Acid Monoesters, and an Oil.

We report new lecithin reverse wormlike micelles with high viscoelasticity formed using lecithin/polyglycerol fatty acid monoester (PGLFA)/oil systems. In this study, the influence of the amphiphilicity (i.e., hydrophile-lipophile balance, HLB) of PGLFA on the phase behavior and rheological properties of reverse wormlike micelles was investigated in detail. PGLFAs with degrees of polymerization of polyglycerol varying between 6-40 and constituent fatty acids with chains between 6-18 carbon atoms long were used. Partial phase diagrams of the lecithin/PGLFA/n-decane systems indicated that the appropriate PGLFA could change the lecithin/oil solution into a highly viscoelastic solution comprising reverse wormlike micelles. Rheological measurements showed that all systems that formed reverse wormlike micelles exhibited an unusual phenomenon called "shear-thickening". Furthermore, reverse wormlike micelles grew as the PGLFA concentration increased and the zero-shear viscosity (η0) of the solution rapidly increased. Our results indicate that the magnitude of the maximum η0 depends on the degree of polymerization of the constituent polyglycerol in the PGLFA, while the size of the reverse micellar region and the highly viscous region in the phase diagram depends on the HLB value of the PGLFA.

Influence of Characteristics of Oily Vehicle on Skin Penetration of Ufenamate.

Skin penetration amounts of a highly lipophilic drug, ufenamate, prepared in four oily vehicles, including white petrolatum (WP), liquid paraffin (LP), isopropyl myristate (IPM), and isocetyl stearate (ICS), were compared. Ufenamate was mixed in each vehicle at 5% and applied at a rate of 2 mg/cm2 to intact, stripped, and delipidized Yucatan micropig skin. The amounts of ufenamate and IPM in the stratum corneum (SC), epidermis, and dermis were determined. The skin penetration amounts of ufenamate from liquid oils were significantly higher than those from WP; the amounts of ufenamate were in the order WP

Skin Permeation of Testosterone from Viscoelastic Lecithin Reverse Wormlike Micellar Solution.

We evaluated testosterone-containing lecithin reverse wormlike micelles (reverse worms) composed of a polar substance/lecithin/isopropyl myristate for transdermal application. Water, D-ribose, or tetraglycerol were used as the polar substance and were key ingredients for forming the reverse worms. Using the reverse worms, 1 wt% of testosterone could be stably solubilized. When using D-ribose as polar substance, the maximum zero-shear viscosity of the reverse worms solution was higher than that of systems using water or tetraglycerol as the polar substance. The mechanism of skin permeation of testosterone from reverse worms solution was elucidated using skin permeation experiments with hairless mouse skin. When the structure of the reverse worms transitioned to lamellar liquid crystals at the skin/formulation interface, testosterone became supersaturated in the formulations. The structural transition occurred in systems using water or D-ribose as the polar substance, increasing the flux of testosterone. The flux of testosterone from reverse worms solution thus depends on the type of polar substance used.

Rheological properties of elastomeric impression materials for selective pressure impression technique.

PURPOSE: The selective impression technique is recommended for removable prosthodontics. However, the viscoelastic rheological properties of impression materials, particularly the time-dependent viscoelastic changes in impression material immediately after tray seating, are unknown. The objective of this study is to clarify the viscoelastic rheological properties of impression materials by focusing on tray seating. METHODS: In this study, eight types of polyvinylsiloxane (PVS), two types of polyether, and two types of alginate impression materials were used. The storage modulus (G'; degree of stiffness) and loss tangent (tanδ; degree of hardening) were determined as functions of time from 0 to 360 s, commencing immediately after the completion of mixing, using a stress control-type rheometer. Thus, G' and tanδ at 0s and 20 s were compared. RESULTS: Stiffness was found to be widely distributed (4.49-0.26 × 10(4)Pa) among PVS-types, even immediately after mixing the impression material. There was also variation among polyethers (1.55-0.5 × 10(4)Pa) and among alginates (0.64-0.21 × 10(4)Pa). The hardening of all impression materials progresses beyond 20 s after the completion of mixing. CONCLUSIONS: The G' values varied with each impression material, even immediately after mixing, and the accurate impression-taking time was determined from the results of tanδ. These results provide unique insight into the selective impression technique.

A new reverse worm-like micellar system from a lecithin, multivalent carboxylic acid and oil mixture.

We developed new lecithin organogels composed of reverse worm-like micelles with lecithin/multivalent carboxylic acid/oil systems, and discussed their phase behavior and rheological properties. The most important findings in this study are the following. From a screening test of many carboxylic acids for gelation, it was found that the number and position of the carboxyl groups of the multivalent carboxylic acids are the determinants for the formation of reverse worm-like micelles, and appropriate carboxylic acids such as citric acid and 1,2,3-propanetricarboxylic acid can change the lecithin/oil solution into a gel. Furthermore, upon addition of these carboxylic acids, the zero-shear viscosity of solutions increased monotonically until phase separation or cloudiness occurred. For example, when citric acid was used, the maximum zero-shear viscosity of the solution was 70,000,000 times larger than that of n-decane. From studies on the scaling of rheological parameters, it was found that further addition of multivalent carboxylic acids not only induced the formation of linear reverse worm-like micelles but also brought about their branching.

New lecithin organogels from lecithin/polyglycerol/oil systems.

New liquid substances that induce the formation of lecithin organogels composed of reverse worm-like micelles were studied. The phase behavior and rheological properties of lecithin/polyglycerol (PGL)/oil systems were investigated in detail; the polymerization degrees of the glycerol residues were 3, 4, 6, 10, 20, and 40. From the partial phase diagrams of the lecithin/PGL/n-decane systems, it was apparent that highly viscoelastic reverse worm-like micelles formed upon the addition of small amounts of the PGL, except in the case of the PGL with a polymerization degree of 40. Steady-flow viscosity measurements showed that the zero-shear viscosity (η0) of the reverse worm-like micelles rapidly increased with the concentration and polymerization degree of the PGLs, reaching a maximum value that was 750,000 times the viscosity of n-decane and thus resulting in the growth of these micelles. It is noteworthy that the η0 values of lecithin organogels formed using PGLs were higher than the η0 value of the lecithin organogel formed using glycerol (GL). From dynamic viscoelasticity measurements, it was shown that the viscoelastic behavior of the reverse worm-like micelles was consistent with the single Maxwell model, which is the basic model of a viscoelastic body. It follows from this study that PGLs are useful liquids because they can induce the formation of lecithin organogels with high viscoelasticity, as do other liquids such as water, glycerol, ethylene glycol, and formamide.

[Adhesion loss of syrups in a metering glass which consists of a low surface free energy material].

We previously reported a strong positive correlation between syrup viscosity and the rate of syrup loss due to adhesion to a glass metering device. In this study, we examined differences in the surface free energies of metering devices made of different polymeric materials, since reducing adhesion loss to metering devices could improve the efficiency of drug preparation involving highly viscous syrups. Among metering devices made of glass only, glass with a silicone coating (SLC), polypropylene (PP), and polymethylpentene (PMP) the surface free energy of the glass-only metering device was the highest (49.2 mN/m). The adhesion loss obtained for highly viscous syrups in the PP and PMP metering devices was significantly lower than that of the glass metering device. Measurements of syrup contact angles suggested that in metering devices made of PP and PMP, which have low surface free energies, a decrease in the spreading wetting of syrups was a factor in reducing the rate of adhesion loss. Thus irrespective of the syrup viscosity being measured, metering devices produced from materials with low surface free energies can reduce the time required to prepare prescriptions without compromising the accuracy of drug preparation.

Effects of temperature on the rheological behavior of worm-like micelles in a mixed nonionic surfactant system.

We examined the effects of temperature on the rheological behavior of worm-like micelles in a nonionic surfactant system consisting of polyoxyethylene (10) phytosterol (PhyEO(10))/glyceryl monocaprylate (GFA-C(8))/Water. First, the phase diagram of a PhyEO(10)/GFA-C(8)/Water system was examined when the weight ratio, R, of GFA-C(8) to the total surfactants was changed keeping the total concentration of the surfactants at 5 wt%. The formation of worm-like micelles was confirmed over a wide temperature range. Next, the effect of temperature on the rheological properties of the worm-like micelles was examined. From steady-flow viscosity measurements of the worm-like micelles, it was found that the zero-shear viscosity (eta(0)) gave a maximum value more than 1,000 times greater than the minimum value in the temperature range 20-50 degrees C. Further, the temperature at which the maximum eta(0) was observed decreased with increasing R value. These results indicate that there is an optimal temperature at which the entanglement of worm-like micelles is at its greatest. From dynamic viscoelasticity measurements, it was shown that the viscoelastic behavior observed for the worm-like micelles was consistent with the Maxwell model, which is the basic model for a viscoelastic body. In addition, the plateau modulus (G(0)), which reflects the volume fraction of entangled worm-like micelles, gradually increased with increasing temperature, while the relaxation time (tau), which reflects the disentanglement time of the worm-like micelles, rapidly decreased with increasing temperature. From these results, it was clarified that, for a nonionic worm-like micelle, tau influences the change in eta(0) more strongly than G(0).

Preparation and characterization of n-alkane/water emulsion stabilized by cyclodextrin.

Emulsions consisting of n-alkane/water using alpha, beta, and gamma-cyclodextrin (alpha, beta, and gamma-CD) as an emulsifier were prepared and characterized by means of several physicochemical techniques. A phase diagram of the n-alkane/CD/water system showed that an oil in water (O/W) emulsion can be prepared from a mixture of the appropriate composition. The dissolved n-alkane/CD complexes formed at low CD concentrations showed surface-activity, but emulsions could not be prepared from these complexes. On the other hand, the precipitated complexes formed at high CD concentrations when adsorbed to the oil/water interface, and served as an emulsifier for formation of emulsions. These results showed that the emulsions formed were of the Pickering emulsion. In addition emulsion formation was governed by the wettability and the surface free energy of the precipitated complexes.