Vibrational spectroscopy and microscopic imaging of skin: I. collagen hydration in type i collagen and dermal tissue II. lateral diffusion of exogenous agents in human SC III. ceramide permeation into human skin

Confocal Raman spectroscopy and dynamic vapor sorption (DVS) measurements of human Type I collagen and pigskin dermis were performed to probe relative humidity (RH) dependent differences in the nature and level of collagen hydration. Raman spectra were also acquired as a function of time for both Type I collagen and pigskin dermis samples upon exchange of a 100% RH H2O to deuterium oxide (D2O) environment. Alterations in Amide I and III modes were consistent with anticipated changes in hydrogen bonding strength as RH increased and upon H → D exchange. Of note is the identification of a Raman spectral marker (band at 938 cm-1) which appears to be sensitive to alterations in collagen-bound water. Analysis of DVS isotherms provided a quantitative measure of adsorbed and absorbed water vapor consistent with the Raman results. Infrared (IR) spectroscopic imaging was utilized to evaluate lateral diffusion in stratum corneum (SC) and elucidate intermolecular interactions between exogenous agents and SC constituents. In separate experiments, acyl chain perdeuterated oleic acid (OA-d) and deuterated dimethyl sulfoxide (DMSO-d) were applied to the surface of isolated human SC. The lateral distribution of permeant concentrations was monitored using the time-dependence of IR images. Diffusion coefficients (D) were estimated from Fick’s second law. Networked glyphs served as the major pathway for lateral distribution of OA-d. In glyph-poor regions, D values 0.3-1 x 10-8 cm2/s bracketed the OA-d data and apparently decreased with time and diffusion of DMSO-d suggests D values of ~10-7 cm2/s. Interactions between the exogenous agents and the SC were tracked from changes in CD2 and Amide I stretching frequencies. OA-d spectral changes suggest penetration into the ordered lipids of the SC; DMSO-d penetration results in perturbation of SC keratin structure. IR imaging was also used to investigate permeation properties of two types of ceramides in human skin. IR images were acquired after incubating for 24 or 48 H with deuterated ceramide suspended in oleic acid. IR images of ceramide concentration were obtained after applying Beer’s Law. Analysis of IR spectra and concentration images suggest the detection limit of both ceramide around 3.5 mM, and most of the ceramide reside in concentrated localized pockets on skin surface, and in deep glyphs. Further analysis indicates the permeation of both ceramide into top layers of SC.Ph.D.Includes bibliographical referencesIncludes vitaby Qihong Zhan