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

Abstract

Skin expansion is a common surgical technique to correct large cutaneous defects. Selecting a successful expansion protocol is solely based on the experience and personal preference of the operating surgeon. Skin expansion could be improved by predictive computational simulations. Towards this goal, we model skin expansion using the continuum framework of finite growth. This approach crucially relies on the concept of incompatible configurations. However, aside from the classical opening angle experiment, our current understanding of growth-induced incompatibilities remains rather vague. Here we visualize and characterize incompatibilities in living systems using skin expansion in a porcine model: We implanted and inflated two expanders, crescent, and spherical, and filled them to 225 cc throughout a period of 21 days. To quantify the residual strains developed during this period, we excised the expanded skin patches and subdivided them into smaller pieces. Skin growth averaged 1.17 times the original area for the spherical and 1.10 for the crescent expander, and displayed significant regional variations. When subdivided into smaller pieces, the grown skin patches retracted heterogeneously and confirmed the existence of incompatibilities. Understanding skin growth through mechanical stretch will allow surgeons to improve— and ultimately personalize—preoperative treatment planning in plastic and reconstructive surgery.

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

“…This methodology has been successfully employed to study the deformation induced by different expander geometries: rectangle, sphere and crescent expanders 31,32 . The results corresponding to the sphere and crescent expanders are discussed next.…”

“…If the expanded area moves outside of the grid, the expander should be deflated and removed. This problem has been encountered using the protocol in one out of eight grids 31,32 . Expanders can also leak if they are defective or punctured during the inflation protocol.…”

“…This also compromises the validity of the experiment and the safety of the animal, therefore the expander should be removed. This problem has been encountered using this protocol in one out of eight grids 31,32 .…”

“…The protocol presented here addresses existing knowledge gaps by quantifying expansion-induced deformation in a porcine animal model of tissue expansion. To the author’s knowledge, this is the first protocol to quantify continuous deformation maps on sizable patches of skin tissue 31,32 .…”

“…The protocol was approved by the IRB of Ann and Robert H. Lurie Children’s Hospital of Chicago Research Center Animal Care and Use Committee to guarantee humane treatment of animals. The results for two expansion studies using this protocol have been published elsewhere 16,31 .…”