526 Computational modeling of two methods of histologic embedding during Mohs micrographic surgery

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Skin cancer is the most common malignancy in the United States. Mohs micrographic surgery (MMS) combines surgical excision with oriented microscopic evaluation to provide the highest cure rate for non-melanoma skin cancers. Despite a theoretical 100% margin assessment, the recurrence rate for large skin cancers is as high as 41%. One potential reason for high recurrence rates is unanticipated tissue deformation during histologic processing. Two methods of embedding are the glass-slide and the heat sink embedding method. In the glass-slide method, tissue is manipulated onto a two-dimensional surface and then immobilized by freezing. In the heat sink method, tissue is applied to a frozen two-dimensional surface that immobilizes the tissue on contact. Despite new techniques for studying tissue biomechanics, few biomechanical studies have been applied to dermatology nor MMS. We propose computational modeling of excised skin tissue to describe deformations that arise during MMS tissue processing. We hypothesize that the model of skin tissue embedded with the glass-slide will reveal distinct strain patterns relative to the heat sink embedded tissue. An anisotropic Prandtl-Reuss elastoplastic material model was applied to assess Young’s modulus, Poisson’s ratio, and yield stress. The three-dimensional shape of a Mohs layer of skin tissue was created with a mesh of hexahedral elements as a three-dimensional solid. Force parameters were collected with a microscopic cantilever force indenter on fresh skin tissue to define the strain on the elements. Different types of strain, including normal and von Mises effective strain were assessed. The models support our hypothesis of distinct strain patterns for the two embedding methods. Further modeling is needed to define the clinical scenarios that would be negatively impacted by these differences.