Measuring and Modeling Contractile Drying in Human Stratum Corneum

Summary

This article describes a method of quantifying the dynamic drying behavior and mechanical properties of stratum corneum by measuring spatially resolved in-plane drying displacements of circular tissue samples adhered to an elastomer substrate. This technique can be used to measure how different chemical treatments alter drying and tissue mechanical properties.

Abstract

Stratum corneum (SC) is the most superficial skin layer. Its contact with the external environment means that this tissue layer is subjected to both cleansing agents and daily variations in ambient moisture; both of which can alter the water content of the tissue. Reductions in water content from severe barrier dysfunction or low humidity environments can alter SC stiffness and cause a build-up of drying stresses. In extreme conditions, these factors can cause mechanical rupture of the tissue. We have established a high throughput method of quantifying dynamic changes in the mechanical properties of SC upon drying. This technique can be employed to quantify changes in the drying behavior and mechanical properties of SC with cosmetic cleanser and moisturizer treatments. This is achieved by measuring dynamic variations in spatially resolved in-plane drying displacements of circular tissue samples adhered to an elastomer substrate. In-plane radial displacements acquired during drying are azimuthally averaged and fitted with a profile based on a linear elastic contractility model. Dynamic changes in drying stress and SC elastic modulus can then be extracted from the fitted model profiles.

Introduction

The outer most layer of the epidermis, or stratum corneum (SC) consists of cohesive corneocyte cells surrounded by a lipid rich matrix^1,2. The composition and structural integrity of SC is essential for maintaining correct barrier functionality³, which prevents invasion from microorganisms and resists both mechanical forces and excessive water loss⁴. The capacity of personal care products to maintain or degrade skin barrier function is of great interest to skin healthcare and the cosmetic industry⁵. The daily application of person....

Protocol

An exempt approval (3002-13) to carry out research using de-identified tissue samples pursuant to the Department of Health and Human Services regulations, 45 CFR 46.101(b)(4) was granted. Full thickness skin is received from elective surgery. In this article, the tissue source is 66-year-old Caucasian female breast.

1. Preparation of Elastomer Coated Coverslips

1. In a 20 mL glass vial, mix 0.107 g of Sylgard 184 curing agent with 5.893 g base. The total mixture mass is 6 g with a base to curing agent ratio of 55:1.
2. After mixing with a glass rod to ensure homogeneity, place the glass vial in a vacuum chamber and degas to ....

Results

Figure 1(a) shows a representative fluorescent image of an SC sample coated with fluorescent beads (section 3). The corresponding transmitted light image of the sample is shown in Figure 1(b) overlaid with a quiver plot of spatially resolved drying displacements that form after 16 h drying at 25% R.H. Due to the circular symmetry of the samples, these displacements can be azimuthally averaged. Figure 1(c) shows radial (u_r, soli.......

Discussion

In this article, we describe a technique that can be used to measure the dynamic drying behavior and mechanical properties of human SC. Previous studies have demonstrated that this technique can be used to quantify the effects of environmental conditions and chemical products commonly used in cosmetic cleansers and moisturizers on the dynamic drying behavior of SC^7,8. There are a number of key steps in the protocol. Firstly, SC swells notably with water content; .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Silicone elastomer base	Dow-Corning	1064291
Silicone elastomer Curing Agent	Dow-Corning	1015311
FluoSpheres Carboxylate 0.1 µm yellow green fluorescent 505/515	Thermo Fisher	F8803
FluoSpheres Carboxylate 1 µm yellow green fluorescent 505/515	Thermo Fisher	F8823
FluoSpheres Carboxylate 1 µm nile red fluorescent 535/575	Thermo Fisher	F8819
Trypsin from porcine pancreas	Sigma-Aldrich	T6567
Trypsin inhibitor type II-s	Sigma-Aldrich	T9128
(3-aminopropyl)triethoxysilane	Sigma-Aldrich	440140
Sodium tetraborate	Sigma-Aldrich	221732
Boric acid	Sigma-Aldrich	B0294
Phosphate buffered saline	Sigma-Aldrich	P7059
N-(3-Dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride	Sigma-Aldrich	E7750
Vortexer mixer	VWR	58816-123
6 mm diameter hole punch	Sigma-Aldrich	Z708860
SOLA 6-LCR-SB	Lummencor light engine	No.3526
Cfi Plan Achro Uw 1X Objective	Nikon Plan UW	MRL00012
CFI Plan Fluor 40X Oil Objective 1.3 na - 0.20 mm wd	Nikon Plan Fluor	MRH01401
Nikon Eclipse Ti-U inverted microscope	Nikon	MEA53200
Clara-E Camera	Andor	DR-328G-C02-SIL
Remote Focus Attachment E-RFA Ergo Design	Nikon	99888
Ti-S-E Motorized Stage	Nikon	MEC56110