In vivo Nail Water Loss Measurement by Biox

Assessment of fingernail health is imperative for the validation of nail cosmetic products and for evaluating the treatment of diseases. However, in vivo measurement of properties such as transonychial water loss (TOWL) or nail water content (hydration) is not straightforward.

Biox Systems Ltd, in collaboration with London South Bank University’s Bioengineering Research Centre, develops instrumentation for skin near-surface characterization. Biox’s highly sensitive condenser-chamber AquaFlux [1] is easily adapted for TOWL measurement. The in vivo nail insert accessory has a compliant probe tip that conforms to the roughness and curvature of rigid nail plate surfaces to form a contact seal.

Researchers at LSBU were thus able to conduct experiments that combine AquaFlux TOWL data with measurements of hydration within the fingernail, and show how these data corelate. Local measurements of hydration levels (spatially resolved to ≈1 mm, to a depth of ≈20 μm into the dorsal outer layer) were made using opto-thermal transient emission radiometry (OTTER) [2,3]. A flash laser beam delivers harmless optical energy impulses to the test surface, whose absorption is dissipated as slight heating.

This sets up a thermal wave that migrates through the surface of the test medium, causing a characteristic transient thermal emission, lasting milliseconds, and whose form is determined by the opto-thermal properties of the test media. This radiant thermal transient is collected and focussed onto a liquid nitrogen cooled infrared sensor that converts it into a weak electrical signal, which is amplified and stored digitally. Parameters such as surface hydration, hydration gradient and hydration depth profiling within a nail plate are revealed by mathematical analysis of the digitised transient decay curve.

Figure 1. (A) Surface hydration and hydration gradient, and (B) water diffusion coefficients and TOWL at the centres of Left- and Right-hand fingernails of two different individuals.

The figures presented here are side-by-side examples of TOWL and OTTER measurements as described above. Figure 1A shows surface hydration (H₀) and hydration gradient (W) at the centre of two sets of fingernails. The data plotted in Figure 1B compare AquaFlux TOWL and OTTER’s water diffusion coefficient property (D) of each nail. D is found by combining the hydration gradient within the nail with the water vapour flux density evaporating from its surface, i.e. TOWL. A connection between D and TOWL has been discussed elsewhere [4], and may have implications for drug delivery [5]. TOWL values tend to be high; similar to TEWL for palm or heel.

Figure 2. (A) The hydration distribution and (B) TOWL distribution on the surface of the same ring finger nail.

Figures 2A and 2B indicate hydration and TOWL distribution, respectively, across the surface of the same nail. This demonstrates the heterogeneity of these parameters – both decreasing with distance from the nail proximal. Intra-nail hydration heterogeneity tends to be larger than inter-nail heterogeneity, while TOWL differences within the same nail appear smaller than that of different nails measured at the same locations, perhaps due to the larger measurement zone of the AquaFlux (≈5 mm diameter), relative to OTTER.

References:

E. Imhof, M.E.P. De Jesus, P. Xiao, L.I. Ciortea, E.P. Berg, “Closed-chamber transepidermal water loss measurement: microclimate, calibration and performance”, Int J Cosmet Sci, Vol 31, Issue 2, 97-118, 2009.
E. Imhof, A.D. McKendrick, P. Xiao, “Thermal emission decay Fourier transform infrared spectroscopy“, Rev. Sci. Instrum., Vol. 66, Issue 11, 5203-5213, 1995.
Xiao, R.E. Imhof, “Opto-thermal measurement of water distribution within the stratum corneum“, in Skin Bioengineering Techniques and Applications in Dermatology and Cosmetology, Curr Probl Dermatol, Basel, Karger, Vol 26, 48-60, 1998.
Murdan, D. Hinsu, M. Guimier, “A few aspects of transonychial water loss (TOWL): Inter-individual, and intra-individual inter-ﬁnger, inter-hand and inter-day variabilities, and the inﬂuence of nail plate hydration, ﬁling and varnish”, Eur. J. Pharm. Biopharm, Vol 70, 684–689, 2008.
S. Chiua, N.A. Belsey, N.L. Garrett, J. Moger, M.B. Delgado-Charro, R.H. Guy, “Molecular diffusion in the human nail measured by stimulated Raman scattering microscopy”, Proc. Natl. Acad. Sci., Vol 112 Issue 25, 7725–7730, 2015.