The University of Queensland, Delivery of Drugs and Genes Group, Australian Institute for Bioengineering and Nanotechnology, QLD 4072, Australia.
Biomaterials. 2013 Mar;34(8):2087-97. doi: 10.1016/j.biomaterials.2012.11.035. Epub 2012 Dec 20.
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.
最近出现的用于将疫苗递送到皮肤上层的微设备,通过物理手段靶向大量免疫细胞群体,具有提高免疫反应的潜力。在这样做的过程中,一个挑战是对微尺度(即细胞直径的量级;10μm)下皮肤弹性性质的理解有限。在这里,我们通过制造从亚细胞到超细胞(0.5μm-20μm 半径)的鳞片的定制探针,定量了微尺度上皮肤的弹性性质。然后,我们用探针探测全厚度皮肤;首先进行力松弛实验,然后进行弹性压痕实验。我们发现皮肤的粘弹性响应是与尺度无关的:在最初的一秒内,归一化力持续下降约 40%,随后在 10 秒内进一步下降 10%。通过 Prony 级数和赫兹接触分析,我们确定了皮肤的应变率无关弹性模量。发现了很高的尺度依赖性:最小的探针遇到的弹性模量最高(30MPa),而 20μm 半径的探针最低(低于 1MPa)。我们提出,这可能是由于最外层皮肤角质细胞中的硬细胞和下面更柔软的活细胞层有助于皮肤中的负载分布。