title: Elastic modulus and viscoelastic properties of full thickness skin characterised at micro scales.
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.
authors.affiliation: The University of Queensland, Delivery of Drugs and Genes Group, Australian Institute for Bioengineering and Nanotechnology, QLD 4072, Australia.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Crichton
authors.forename: Xianfeng
authors.initials: X
authors.lastname: Chen
authors.forename: Han
authors.initials: H
authors.lastname: Huang
authors.forename: Mark A F
authors.initials: MA
authors.lastname: Kendall
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D055119:Elastic Modulus / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D036103:Nanotechnology; D012867:Skin / Q000648:ultrastructure; D012879:Skin Physiological Phenomena; D014414:Tungsten; D014783:Viscosity
chemical_list: D014414:Tungsten