Multi-view stereo analysis reveals anisotropy of prestrain, deformation, and growth in living skin

Abstract

Skin expansion delivers newly grown skin that maintains histological and mechanical features of the original tissue. Although it is the gold standard for cutaneous defect correction today, the underlying mechanisms remain poorly understood. Here we present a novel technique to quantify anisotropic prestrain, deformation, and growth in a porcine skin expansion model. Building on our recently proposed method, we combine two novel technologies, multi-view stereo and isogeometric analysis, to characterize skin kinematics: Upon explantation, a unit square retracts ex vivo to a square of average dimensions of 0.83 × 0.83. Upon expansion, the unit square deforms in vivo into a rectangle of average dimensions of 1.40 × 1.34. Deformations are larger parallel than perpendicular to the dorsal midline suggesting that skin responds anisotropically with smaller deformations along the skin tension lines. Upon expansion, the patch grows in vivo by 1.62 × 1.40 with respect to the explanted, unexpanded state. Growth is larger parallel than perpendicular to the midline, suggesting that elevated stretch activates mechanotransduction pathways to stimulate tissue growth. The proposed method provides a powerful tool to characterize the kinematics of living skin. Our results shed light on the mechanobiology of skin and help us to better understand and optimize clinically relevant procedures in plastic and reconstructive surgery.

The Incompatibility of Living Systems: Characterizing Growth-Induced Incompatibilities in Expanded Skin

“…However, we refined this approach to account for prestrain and natural growth. 11 Figure 4 summarizes the important configurations during tissue expansion. The complete kinematic description of tissue adaptation under supra-physiological stretch required the analysis of both the control and expanded patches.…”

“…32 When carried over to the experimental characterization of skin expansion, this conceptual approach is capable of revealing detailed regional variations of anisotropic skin stretch and growth. 11 Here we adopt this methodology to study the kinematics of skin expansion in a chronic porcine model using three basic ingredients: multi-view stereo, isogeometric description, and the continuum theory of finite growth.…”

“…9,15 Here we present the results of an experiment, which was designed as a natural follow up to our earlier publications. 10,11 The first novel contribution of the present study is the use of three expander geometries instead of one: spherical, rectangular, and crescent. For all three, we retain a strong interest in understanding the basic mechanisms of tissue adaptation with the ultimate goal of establishing a constitutive equation that links tissue stretch to growth over time.…”

Isogeometric Kirchhoff–Love shell formulations for biological membranes

“…This type of deformation agrees with experimental observations. We have conducted controlled experiments of skin expansion and found significant differences in strains parallel and orthogonal to Langer’s lines, which are associated with collagen fiber orientations [10]. …”

Quantification of Strain in a Porcine Model of Skin Expansion Using Multi-View Stereo and Isogeometric Kinematics

“…Employing splines, representation of smooth surfaces leads to the calculation of the corresponding deformation maps by means of an isogeometric (IGA) description. The analysis of the geometry is based on the theoretical framework of continuum mechanics of membranes having an explicit parameterization 16 .…”