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Materials 2015, 8(4), 1841-1857; doi:10.3390/ma8041841

Collagen Fibrils in Skin Orient in the Direction of Applied Uniaxial Load in Proportion to Stress while Exhibiting Differential Strains around Hair Follicles

Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
These authors contributed equally to this work.
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Author to whom correspondence should be addressed.
Academic Editor: Amir A. Zadpoor
Received: 4 March 2015 / Revised: 9 April 2015 / Accepted: 14 April 2015 / Published: 20 April 2015
(This article belongs to the Special Issue Mechanics of Biomaterials)
View Full-Text   |   Download PDF [1185 KB, uploaded 20 April 2015]   |  

Abstract

We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast Fourier Transforms (FFT) while strain inhomogeneity was determined at different distances from hair follicles using Digital Image Correlation (DIC). A parameter, defined as the Collagen Orientation Index (COI), is introduced that accounts for the increasingly ellipsoidal nature of the FFT amplitude images upon loading. We show that the COI demonstrates two distinct mechanical regimes, one at low strains (0%, 2.5%, 5% strain) in which randomly oriented collagen fibrils align in the direction of applied deformation. In the second regime, beginning at 5% strain, collagen fibrils elongate in response to applied deformation. Furthermore, the COI is also found to be linearly correlated with the applied stress indicating that collagen fibrils orient to take the applied load. DIC results indicated that major principal strains were found to increase with increased load at all locations. In contrast, minimum principal strain was dependent on distance from hair follicles. These findings are significant because global and local changes in collagen deformations are expected to be changed by disease, and could affect stem cell populations surrounding hair follicles, including mesenchymal stem cells within the outer root sheath. View Full-Text
Keywords: second harmonic generation microscopy (SHG); fast fourier transform (FFT); collagen orientation index; digital image correlation (DIC); strain mapping second harmonic generation microscopy (SHG); fast fourier transform (FFT); collagen orientation index; digital image correlation (DIC); strain mapping
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Nesbitt, S.; Scott, W.; Macione, J.; Kotha, S. Collagen Fibrils in Skin Orient in the Direction of Applied Uniaxial Load in Proportion to Stress while Exhibiting Differential Strains around Hair Follicles. Materials 2015, 8, 1841-1857.

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