Occlusive Properties

Jenning, V., et al., Vitamin A loaded solid lipid nanoparticles for topical use occlusive properties and drug targeting to the upper skin. Eur. J. Pharm. Biopharm., 49, 211-18, 2000. 

Evaluation of the occlusive properties of different pastes in vitro 2 g of test product were carefully spread over the surface of agar-filled Petri dishes. The dishes were weighed and kept at room temperature in a box covered by a protecting cloth (start values). Further weighings were taken at days 1,2, and 5 thereafter. For control purposes, white petrolatum and a plate without any test product were included in the test. Each experiment was conducted in triplicate. 

Evaluation of the occlusive properties of different pastes in vivo these were evaluated in vivo on tape-stripped skin exactly as described in Reference 10. Briefly, the stratum corneum of the forearm of healthy volunteers was tape stripped until the transepidermal water loss (TEWL) attained values between 40 and 50 g/m2/h. After a rest period of 1 h, 2.5 mg/cm2 of the test products were carefully applied on the stripped sites using a gloved finger, and the TEWL was measured at different times until 120 min after application. Percent changes relative to a nontreated control site were calculated over time. Positive control was white petrolatum. 

FIGURE 22.4 Occlusive properties of different pastes on stripped skin in vivo (percent decrease in transepi-dermal water loss) of n = 6 healthy volunteers. HP3 hydrophilic paste LP1 and LP2 lipophilic pastes. For the sake of clarity, means are shown +HSD (HP3) or —HSD (white petrolatum) only. 

Shiu K-B, Lee H-C, Lee G-H, Wang Y (2002) Synthesis, structures, and solvent-occlusion properties of a molecular loop and a molecular square using tetracarbonyl- and diphosphine-ligated diruthenium(I) as building blocks and dicarboxylates as linkers. Organometallics 21 4013 1016... 

When an agent such as formaldehyde or urea is applied to the skin, changes in the skin s impedance are observed [18]. It is believed that formaldehyde increases the ratio of unbound to bound water, thus possibly explaining why formaldehyde lowers the skin s resistance [18]. In contrast, urea is observed to increase the skin s resistance. It is speculated that this results because urea increases the amount of bound water in the skin [ 18]. Also, it appears that the most hydrophilic material does not necessarily produce the greatest effect on the skin s impedance [7]. For example, glycerol decreases the skin s impedance to greater extent than does pyrrolidone carboxylic acid. In addition, it was observed that petrolatum has an occlusive property [15]. 

A. Casiraghi, P. Minghetti, E Cilurzo, L. Montanari, and A. Naik, Occlusive properties of monolayer patches In vitro and in vivo evaluation, Pharm. Res., 19,423-426, 2002. 

Ascorbic acid (vitamin C) has been incorporated in both W/O/W and O/ W/O multiple-emulsions systems (Silva et al., 1997 Gallarate et al., 1999 Farahmand et al., 2006). In the first system, vitamin C was dissolved in the inner aqueous phase of a W/O/W multiple emulsion. In this case, improved protection against oxidation was reported when compared with O/W microemulsion, O/W and W/O emulsions, both at 45°C and 20 0. Incorporating vitamin C in the intermediate aqueous phase of an O/W/O multiple emulsion improved the occlusive properties, the acceptability and durability on skin. 

The final polymerised product is formed in particles much smaller (50-500 nm) than produced with suspension polymerisation. Emulsion polymerisation can lead to rapid production of high molecular weight polymers but the unavoidable occlusion of large quantities of soap adversely affects the electrical insulation properties and the clarity of the polymer. 

The basic biology of chemokines and their receptors is well covered in Chapters 2 and 3 of this book, and we will focus hereafter upon the roles of individual chemokines and receptors in atherosclerosis. The largest amount of data on the roles of chemokines in cardiovascular disease (C VD) has been obtained from in vitro studies and murine models, which will be discussed in detail. In man, genetic polymorphisms in chemokine and chemokine-receptor genes have pointed to an important role for specific chemokines in various atherosclerotic diseases including coronary artery disease and carotid artery occlusive disease. For properties see Table 1. 

Although HU may mediate some of its clinical benefits through its positive effect on HbF expression, these data also suggest that it may, by a yet-to-be defined mechanism of action, modulate the clinical severity of SCA. One possible pathway is that among the two incriminated interacting cell partners (sickle erythrocyte and endothelial cell) involved in vaso-adhesion and occlusion, HU may also affect the phenotype status of endothelial cells so that its adhesogenic (structural) and/or vasoregulatory (functional) properties are modified in a favorable manner. 

The suitable materials for the above mentioned domains are polymers, metals and ceramics. Among these, polymers play an important role. Even the polymers have a lot of remarkable properties that could be used in biomaterials design, the interaction between these artificial materials and tissues and blood could create serious medical problems such as clot formation, activating of platelets, and occlusion of tubes for dialysis or vascular grafts. In the last few years, novel techniques of synthesis have been used to correlate desirable chemical, physical and biological properties of biomaterials. 

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