Thermal barrier, skin

Double-Skinned Sheet Double-skinned or hollow-core polycarbonate sheet is available in two thicknesses, 0.220 in. and 0.625 in., in widths of 36 and 48 in. for thin material and 47.25 in. wide for thick material. Standard lengths range from 8 to 16 ft. Double-skinned sheet that is 0.220 in. thick is used primarily as a thermal barrier when light transmission is also required. The thicker sheet has more substantial stiffness and is used as primary glazing. 

Chitrphiromsri and Kuznetsov [47] presented a model that couples heat and moisture transport in firefighters protective clothing during a flash fire exposure. The garment consists of three fabric layers (outer shell, moisture barrier and thermal barrier). The skin also has three layers epidermis, dermis and subcutaneous. Finite diflerence method methodology is used to solve the differential equations (equations 12.38-40, 12.47). The equations are the energy equation for the fabric (based on Gibson s [15] and Torvi s [48] models) ... 

Epidermis Complete removal of the dermis may be achieved by several mechanical, thermal, and chemical techniques. Most commonly, the epidermal-dermal junction is split by heating the skin to 60 C for 30-120 s [83, 84], Pitman et al. [85] could show that such a treatment does not impair the barrier function. The use of ethylene diamine tetraacetic acid, sodium bromide, or ammonia fumes has also been reported [80, 83, 86], It may, however, be suspected that the use of sufficiently strong acids or bases may change the buffer capacity of skin, which would especially influence the penetration behavior of ionizable drugs. 

Microscopically, the skin is a multilayered organ composed of many histological layers. It is generally subdivided into three layers the epidermis, the dermis, and the hypodermis [1]. The uppermost nonviable layer of the epidermis, the stratum corneum, has been demonstrated to constitute the principal barrier to percutaneous penetration [2,3]. The excellent barrier properties of the stratum corneum can be ascribed to its unique structure and composition. The viable epidermis is situated beneath the stratum corneum and responsible for the generation of the stratum corneum. The dermis is directly adjacent to the epidermis and composed of a matrix of connective tissue, which renders the skin its elasticity and resistance to deformation. The blood vessels that are present in the dermis provide the skin with nutrients and oxygen [1]. The hypodermis or subcutaneous fat tissue is the lowermost layer of the skin. It supports the dermis and epidermis and provides thermal isolation and mechanical protection of the body. 

Tanojo, EL, et al. 1997. In vitro human skin barrier perturbation by oleic acid Thermal analysis and freeze fracture electron microscopy studies. Thermochim Acta 293 77. 

H. Tanojo, J. A. Bouwstra, H. E. Junginger, and H. E. Bodde, In vitro human skin barrier modulation by fatty acids skin permeation and thermal analysis studies, Pharm Res. 14 42-49 (1997). 

Relatively little is known about the structure of stratum corneum, even though it is considered the primary barrier in transdermal permeation of most permeants. Traditional permeability studies of full-thickness skin (1-12) have implied molecules permeated through the skin by various polar or nonpolar pathways depending on the hydrophilicity or lipophilicity of the permeant. Coupling of macroscopic and molecular-level investigations of thermally induced alterations of the stratum corneum are beginning to provide insight into the molecular structure and barrier function of the stratum corneum. 

Permeability changes in full-thickness skin have been associated with temperature or solvent pretreatment. The molecular basis of these permeability changes has been attributed to lipid melting or protein conformational changes. The current studies have probed the role of lipid fluidity in the permeability of lipophilic solutes, and examined the effects of temperature on the physical nature of the stratum corneum by differential scanning calorimetry and thermal perturbation infrared spectroscopy. Combining molecular level studies that probe the physical nature of the stratum corneum with permeability results, a correlation between flux of lipophilic solutes and nature of the stratum corneum barrier emerges. 

Further recent developments in DSC and IR techniques, with respect to the study of SC barrier properties, include step-scan FT-IR photoacoustic spectroscopy [195] and combined microscopic differential calorimetry-Four-ier transform infrared (DSC-FTIR) spectroscopy [196]. The former allows depth profiling of the membrane the latter enables the simultaneous detection of calorimetric and structural modifications during a thermal transition. Technological advances in DSC and IR will, no doubt, continue to expand the application of these techniques to the study of skin barrier function. 

The use of ultrasound (US) to enhance percutaneous absorption (so-called sonophoresis or phonophoresis) has been studied over many years, and is the basis of US propagation and US effects on tissue, and the use of US in transdermal delivery have been reviewed in detail. The proposed mechanisms by which US enhances skin penetration include cavitation, thermal effects and mechanical perturbation of the SC that is, US acts on the barrier function of the membrane. ... 

Additional work, however, has addressed mechanistic aspects of the effects of low-frequency US. Cavitation and thermal effects have been postulated and, to a certain extent, characterized, but further work is clearly needed to define exactly how US interacts with the skin barrier to increase its permeability. 

After dermal exposure, the skin should be irrigated copiously with water. Topical application of freshly made 10% ascorbic acid solution or of a barrier cream containing 2% glycine and 1% tartaric acid has been beneficial in reducing thermal and chemical burns. 

Tanojo H, BosvanGeest A, Bouwstra JA, Junginger HE, and Bodde HE. In Vitro Human Skin Barrier Perturbation by Oleic Acid Thermal Analysis and Freeze Fracture Electron Microscopy Studies, Tlwrmochim Acta 1997 293 77-85. 

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