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  • Elastic modulus and viscoelastic properties of full thickness skin characterised at micro scales.

Elastic modulus and viscoelastic properties of full thickness skin characterised at micro scales.

Biomaterials (2012-12-25)
Michael L Crichton, Xianfeng Chen, Han Huang, Mark A F Kendall
ABSTRACT

The recent emergence of micro-devices for vaccine delivery into upper layers of the skin holds potential for increased immune responses using physical means to target abundant immune cell populations. A challenge in doing this has been a limited understanding of the skin elastic properties at the micro scale (i.e. on the order of a cell diameter; ~10 μm). Here, we quantify skin's elastic properties at a micro-scale by fabricating customised probes of scales from sub- to super-cellular (0.5 μm-20 μm radius). We then probe full thickness skin; first with force-relaxation experiments and subsequently by elastic indentations. We find that skin's viscoelastic response is scale-independent: consistently a ~40% decrease in normalised force over the first second, followed by further 10% reduction over 10 s. Using Prony series and Hertzian contact analyses, we determined the strain-rate independent elastic moduli of the skin. A high scale dependency was found: the smallest probe encountered the highest elastic modulus (~30 MPa), whereas the 20 μm radius probe was lowest (below 1 MPa). We propose that this may be a result of the load distribution in skin facilitated by the hard corneocytes in the outermost skin layers, and softer living cell layers below.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Tungsten, foil, thickness 0.25 mm, ≥99.9% trace metals basis
Sigma-Aldrich
Tungsten, powder, 12 μm, 99.9% trace metals basis
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Tungsten, foil, thickness 0.127 mm, ≥99.9% trace metals basis
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Tungsten, foil, thickness 0.5 mm, ≥99.9% trace metals basis
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Tungsten, powder, ≤10 μm, ≥99.99% trace metals basis
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Tungsten, wire, diam. 1.0 mm, 99.99% trace metals basis
Sigma-Aldrich
Tungsten, wire, diam. 0.25 mm, ≥99.9% trace metals basis