Mechanical behavior of full-thickness burn human skin is rate-independent

Abstract

Skin tissue is recognized to exhibit rate-dependent mechanical behavior under various loading conditions. Here, we report that the full-thickness burn human skin exhibits rate-independent behavior under uniaxial tensile loading conditions. Mechanical properties, namely, ultimate tensile stress, ultimate tensile strain, and toughness, and parameters of Veronda-Westmann hyperelastic material law were assessed via uniaxial tensile tests. Univariate hypothesis testing yielded no significant difference (p > 0.01) in the distributions of these properties for skin samples loaded at three different rates of 0.3 mm/s, 2 mm/s, and 8 mm/s. Multivariate multiclass classification, employing a logistic regression model, failed to effectively discriminate samples loaded at the aforementioned rates, with a classification accuracy of only 40%. The median values for ultimate tensile stress, ultimate tensile strain, and toughness are computed as 1.73 MPa, 1.69, and 1.38 MPa, respectively. The findings of this study hold considerable significance for the refinement of burn care training protocols and treatment planning, shedding new light on the unique, rate-independent behavior of burn skin.

Figure 1

(a) The dog-bone shape skin samples are shown on the left and debrided or discarded full-thickness burn human skin is shown on the right. (b) The dimensions of the dog-bone specimen created using the ASTM D638 Type V die. (c) The experimental set up for the uniaxial tensile test of dog-bone shape full-thickness burn human skin sample held between the grips and fixtures in a 37 °C PBS bath in a transparent container using TA Instruments ElectroForce TestBench.

Figure 2

A typical nominal stress–strain curve of the full-thickness burn ex vivo human skin tissue sample undergoing the uniaxial tensile test. The applied force (F), initial length (L₀), and initial cross-section area (A₀) of the dog bone sample are shown in the inset.

Figure 3

The box plots of (a) ultimate tensile stress (UT stress), (b) ultimate tensile strain (UT strain), (c) toughness, and parameters (d) μ and (e) γ of the Veronda–Westmann model for the full-thickness burn human skin tissue at loading rates of 0.3 mm/s, 2.0 mm/s, and 8.0 mm/s. The ‘*’ indicates a significant difference in the Wilcoxon rank-sum test.

Figure 4

Contribution of each material property in the multiclass classification of full-thickness burn human skin tissue samples into the three loading rate classes of 0.3 mm/s, 2 mm/s, and 8 mm/s.