Papers by Gerald B Kasting
Impact of solvent dry down, vehicle pH and slowly reversible keratin binding on skin penetration of cosmetic relevant compounds: I. Liquids
International Journal of Pharmaceutics, Aug 1, 2022
Dynamics of glycerine and water transport across human skin from binary mixtures
International Journal of Cosmetic Science, Sep 26, 2016
Skin transport properties of glycerine and water from binary mixtures contacting human skin were ... more Skin transport properties of glycerine and water from binary mixtures contacting human skin were determined to better understand the mechanism of skin moisturization by aqueous glycerine formulations.
Journal of Controlled Release, Aug 1, 1986
Transient transport through skin is analyzed in order to estimate the contribution of appendageal... more Transient transport through skin is analyzed in order to estimate the contribution of appendageal diffusion to the observed penetration rate. Theoretical curves for transport through shunts and directly across the skin are fit employing a least-squares procedure to experimental data obtained with excised human skin. For ibuprofen in pH 7.4 saline solutions, the data can be fit well with a two-route diffusion model. The mean shunt lag time (+ SD) calculated by this method was 8.6 f 3.3 min (range 2-20) while that for transcutaneous penetration was 92 + 14 min (range 50-l 70). The percent of steady state transport attributable to shunt diffusion was 25 * 7 (range 11-44). The latter result may be explained by the combined transport of ionized ibuprofen (mostly through the shunts) and neutral ibuprofen (mostly through the skin).
Lab on a Chip, 2017
Eccrine sweat has rapidly emerged as a non-invasive, ergonomic, and rich source of chemical analy... more Eccrine sweat has rapidly emerged as a non-invasive, ergonomic, and rich source of chemical analytes with numerous technological demonstrations now showing the ability for continuous electrochemical sensing.
The origin and elimination of spurious peaks in threshold electron photoionization spectra
Journal of Electron Spectroscopy and Related Phenomena, 1975
Abstract Autoionization electrons in threshold photoionization spectra are known to occur. The ef... more Abstract Autoionization electrons in threshold photoionization spectra are known to occur. The effect of such electrons on the interpretation of threshold electron spectra is discussed and a new method is described which enables one to discriminate between zero kinetic energy electrons and energetic electrons in photoionization experiments with little ambiguity. The method largely overcomes the main problem present in some previously described threshold electron studies; namely, the line-of-sight transmission of energetic electrons which gives rise to non-threshold electron peaks. A rejection ratio of 25 is readily obtained for 0.038 eV electrons compared with threshold (zero kinetic energy) electrons and the (small) transition probability for energetic electrons falls off more rapidly than for analysers previously described. Design parameters based on electron trajectory calculations are given for the analyser used, and photoionization results on argon are presented.
Evaluation of Stratum Corneum Heterogeneity
CRC Press eBooks, Jun 8, 2021
Absorption of solvent-deposited weak electrolytes and their salts through human skin in vitro
International Journal of Pharmaceutics, May 1, 2022
Permeation of a weak acid (benzoic acid) and a weak base (propranolol) in various stages of ioniz... more Permeation of a weak acid (benzoic acid) and a weak base (propranolol) in various stages of ionization through human skin in vitro was measured from 0-72 h following solvent deposition of radiolabeled doses ranging from 11-11,000 nmol/cm2 and 1.93-1930 nmol/cm2, respectively. For the twenty combinations tested for each compound, mean permeation into the receptor fluid over 72 hours ranged from 1.5-40.7 percent of dose for benzoic acid and 1.3-35.5 percent of dose for propranolol. For all but the lowest doses, permeation increased with increasing fraction of nonionized permeant in the dose solution. Generally, this trend became stronger as the dose increased. Recovery of radioactivity averaged 94.3 ± 5.5% for propranolol and was independent of ionization state and dose. Recovery of radioactivity for benzoic acid ranged from 40 to >100%, increasing with fraction nonionized and with dose. These effects can be qualitatively explained in terms of the low permeability of ionized species through stratum corneum, the volatility of free benzoic acid, and a buffer capacity of the stratum corneum deposition region on the order of 10-20 nmol/cm2.
Journal of Pharmaceutical Sciences, 2019
A porous pathway feature has been added to an existing skin diffusion model to extend the range o... more A porous pathway feature has been added to an existing skin diffusion model to extend the range of applicability to highly polar solutes that do not readily diffuse across the stratum corneum (SC) lipid/ corneocyte matrix. The porous pathway consists of 2 components: Pathway A is appendageal and is implemented as an array of aqueous shunts (the macropores), which themselves have microporous walls with transient aqueous pores (the micropores). Two varieties of shunts are discussed, one representing a terminal hair follicle and the other representing an eccrine sweat duct; however, the focus here is on the hair follicle. Pathway B is transcellular, with lipid-phase transport accomplished through defects or breaks in the bilayer lipid structure. The composite model admits polar solutes into the skin in a sizeselective manner with an effective micropore radius of 1.6 nm. Steady-state permeabilities, desorption rates from isolated SC, and SC/water partition coefficients of both polar and lipophilic solutes are effectively explained.
Mycoses, Jan 18, 2017
The topical treatment of nail fungal infections has been a focal point of nail research in the pa... more The topical treatment of nail fungal infections has been a focal point of nail research in the past few decades as it offers a much safer and focused alternative to conventional oral therapy. Although the current focus remains on exploring the ways of enhancing permeation through the formidable nail barrier, the understanding of the nail microstructure and composition is far from complete. This article reviews our current understanding of the nail microstructure, composition and diseases. A few of the parameters affecting the nail permeability and potential causes of the recurrence of fungal nail infection are also discussed.
International Journal of Pharmaceutics, Oct 1, 2011
Mathematical models of skin permeability play an important role in various fields including predi... more Mathematical models of skin permeability play an important role in various fields including prediction of transdermal drug delivery and assessment of dermal exposure to industrial chemicals. Extensive research has been performed over the last several decades to yield predictions of skin permeability to various molecules. These efforts include the development of empirical approaches such as quantitative structure-permeability relationships and porous pathway theories as well as the establishment of rigorous structure-based models. In addition to establishing the necessary mathematical framework to describe these models, efforts have also been dedicated to determining the key parameters that are required to use these models. This article provides an overview of various modeling approaches with respect to their advantages, limitations and future prospects.
Dermal Exposure and Absorption of Chemicals
Elsevier eBooks, 2018
Human skin behaves as a semipermeable membrane, permitting uptake of chemicals from the external ... more Human skin behaves as a semipermeable membrane, permitting uptake of chemicals from the external environment. Negative consequences of dermal exposure to chemicals are well documented and include both local and systemic effects. Evaluation and management of potential toxicity and risk associated with dermal exposure requires prediction of the rate and extent of chemical absorption. Historically, both experimental and mathematical approaches have been applied to the investigation of absorption processes. This chapter reviews factors influencing the outcome of absorption experiments and describes rudimentary characteristics of mathematical models. It is intended to provide useful perspective to persons responsible for conducting, interpreting, or implementing occupational or environmental health risk assessments that involve dermal exposure.
Skin Research and Technology, Mar 13, 2017
Background: Experimental work on skin hydration is technologically challenging, and mostly limite... more Background: Experimental work on skin hydration is technologically challenging, and mostly limited to observations where environmental conditions are constant. In some cases, like diapered baby skin, such work is practically unfeasible, yet it is important to understand potential effects of diapering on skin condition. To overcome this challenge, in part, we developed a computer simulation model of reversible transient skin hydration effects. Methods: Skin hydration model by Li et al. (Chem Eng Sci, 138, 2015, 164) was further developed to simulate transient exposure conditions where relative humidity (RH), wind velocity, air, and skin temperature can be any function of time. Computer simulations of evaporative water loss (EWL) decay after different occlusion times were compared with experimental data to calibrate the model. Next, we used the model to investigate EWL and SC thickness in different diapering scenarios. Results: Key results from the experimental work were: (1) For occlusions by RH=100% and free water longer than 30 minutes the absorbed amount of water is almost the same; (2) Longer occlusion times result in higher water absorption by the SC. The EWL decay and skin water content predictions were in agreement with experimental data. Simulations also revealed that skin under occlusion hydrates mainly because the outflux is blocked, not because it absorbs water from the environment. Further, simulations demonstrated that hydration level is sensitive to time, RH and/or free water on skin. In simulated diapering scenarios, skin maintained hydration content very close to the baseline conditions without a diaper for the entire duration of a 24 hours period. Conclusion: Different diapers/diaper technologies are known to have different profiles in terms of their ability to provide wetness protection, which can result in consumer-noticeable differences in wetness. Simulation results based on published literature using data from a number of different diapers suggest that diapered skin hydrates within ranges considered reversible.
Transdermal and lateral effective diffusivities for drug transport in stratum corneum from a microscopic anisotropic diffusion model
European Journal of Pharmaceutics and Biopharmaceutics, Jul 1, 2023
Lipid Solubility and Molecular Weight: Whose Idea Was That
Skin Pharmacology and Physiology, 2013
Gene Cooper was a bright theoretician, a skilled product developer, and a motivational leader who... more Gene Cooper was a bright theoretician, a skilled product developer, and a motivational leader who applied his talents to the skin science area early in his career. His work led to the development of finite dose skin absorption models, chemical penetration enhancer technologies and quantitative structure-penetration relationships for chemicals contacting human skin. His ideas regarding the impact of molecular weight and lipid solubility on skin transport catalyzed the later development by Potts and Guy of the first successful skin permeability model. But Gene's most important contribution to the field was as a scientific role model and an inspirational leader who launched the careers of several young scientists, including the author of this article.
Physical Review Letters, Nov 5, 1979
PHYSICAI. REVIEW I.ETTKRS 5 NQvEMBER 1979 tion length and u, -4628t "" cm/sec for the sec- ond-so... more PHYSICAI. REVIEW I.ETTKRS 5 NQvEMBER 1979 tion length and u, -4628t "" cm/sec for the sec- ond-sound velocity one obtains Dg D p withD, =(0.3 or 0.5)xl0 ' cm'/sec from the two values of R,. The dashed lines in Fig. correspond to these two theoretical estimates. For t & 5x10 4 they are consistent arith the neer meas- urements. For larger t, background contributions to D, presumably dominate and are expected to ex- plain the difference between the theoretical asymp- totic result and the data of Ref. 9.
Nature Biomedical Engineering, Jan 19, 2023
An in vitro method for studying the iontophoretic enhancement of drug transport through skin
Journal of Membrane Science, 1988
Abstract An electrodiffusion cell and measurement system has been developed to study the factors ... more Abstract An electrodiffusion cell and measurement system has been developed to study the factors governing the transport of ionized drugs through skin under the influence of an electric field. The system allows the determination of transport rates in vitro under conditions of either constant current or constant voltage across the skin. Both accelerating and retarding voltages may be applied. To test the method, the iontophoretic transport of a negatively charged bone resorption agent, etidronate disodium (ethanehydroxydiphosphonate, EHDP) was measured across excised human skin. An enhancement factor of 50-70 over passive diffusion was obtained using a constant current density of 140 μA-cm−2, and a factor of approximately 100 was obtained with a constant applied voltage of -0.5 V. At the lowest power levels tested (14 μA-cm−2 or -0.25 V) the enhancements were in reasonable agreement with the predictions of a constant field model for electrodiffusion; however, at higher power levels a phenomenological parameter, the drug transference number in the membrane, appeared to be more useful. Neither the constant current nor the constant voltage mode was found to be a completely satisfactory way of controlling drug delivery in this model. A current-voltage regimen in which both parameters are varied may be required in order to achieve consistent results.
Chemischer Informationsdienst, Sep 18, 1979
ChemInform Abstract Es wird eine Extraktionsmethode zur Abtrennung der dreiwertigen Actiniden (ha... more ChemInform Abstract Es wird eine Extraktionsmethode zur Abtrennung der dreiwertigen Actiniden (hauptsächlich Am und Cm) von den dreiwertigen Lanthaniden mit nur 2 Solventextraktionsmitteln beschrieben. Das erste Solvens [Di-(2-ethylhexyl)orthophosphorsäure in n-Heptan] entfernt die schweren Lanthanide aus der wässrigen Lösung , während das zweite (5.7-Dichloroxin-oder S-Nitroxin in CHCl3) Am und Cm extrahiert. Da zusätzliche komplexierende Reagenzien nicht erforderlich sind, werden Abfallbeseitigungs-und Korrosionsprobleme reduziert. Die Methode ist für die effektive Abtrennung der Actiniden von den Lanthaniden in Reaktorspaltprodukten geeignet.
Estimating the Absorption of Volatile Compounds Applied to Skin
92181131 Retention of etidronate in human, dog, and rat
Maturitas, Dec 1, 1992
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Papers by Gerald B Kasting