Growing skin: tissue expansion in pediatric forehead reconstruction

Abstract

Tissue expansion is a common surgical procedure to grow extra skin through controlled mechanical over-stretch. It creates skin that matches the color, texture, and thickness of the surrounding tissue, while minimizing scars and risk of rejection. Despite intense research in tissue expansion and skin growth, there is a clear knowledge gap between heuristic observation and mechanistic understanding of the key phenomena that drive the growth process. Here, we show that a continuum mechanics approach, embedded in a custom-designed finite element model, informed by medical imaging, provides valuable insight into the biomechanics of skin growth. In particular, we model skin growth using the concept of an incompatible growth configuration. We characterize its evolution in time using a second-order growth tensor parameterized in terms of a scalar-valued internal variable, the in-plane area growth. When stretched beyond the physiological level, new skin is created, and the in-plane area growth increases. For the first time, we simulate tissue expansion on a patient-specific geometric model, and predict stress, strain, and area gain at three expanded locations in a pediatric skull: in the scalp, in the forehead, and in the cheek. Our results may help the surgeon to prevent tissue over-stretch and make informed decisions about expander geometry, size, placement, and inflation. We anticipate our study to open new avenues in reconstructive surgery, and enhance treatment for patients with birth defects, burn injuries, or breast tumor removal.

Mathematical and computational modelling of skin biophysics: a review

“…An attractive feature of computational models is the ability to quantify physical parameters required to obtain a specific outcome. For example, Prof. Kuhl's group at Stanford University has pioneered the development of mechanobiological adaptation models for skin to optimize the outcome of reconstructive surgery procedures in children [61][62][63][64][65][66][67] Streamline plots representing the maximum (coloured) and minimum (white) principal strain vectors in a finite deformation 2D plane-strain image-based finite-element model of the skin subjected to 20% in-plane compression (adapted from [20]). Grey arrows indicate the direction and location of the applied load.…”

On the mechanics of thin films and growing surfaces

“…In particular, our surface energy not only accounts for the elastic behavior of the surface itself, but also for its growth or shrinkage with respect to the bulk [36]. To kinematically characterize the amount of surface growth, we adopt the multiplicative decomposition of the surface deformation gradient into an elastic tensor and a growth tensor [59]. A conceptually elegant approach to experimentally characterize the surface growth tensor in plants is the classical peel test [10] as demonstrated in Figure 4.…”

A framework for studying dynamics and stability of diffusive–reactive interfaces with application to Cu 6 Sn 5 intermetallic compound growth

“…Examples of such phenomena include dendritic growth in Li-ion batteries [1,2], growth of brittle intermetallic compounds in solder joints [3], tissue growth [4][5][6] and growth of compounds under chemicalvapour deposition [7]. The interplay between the aforementioned driving forces can not only affect the growth rate of the materials involved, but can also change the interface morphology from being flat, to scalloped to even dendritic.…”

“…The growth of these materials can have significant physical as well as physiological effect. For example, the growth of dendrites on the negative electrode in the Li-ion battery can make it unsafe for commercial use [1] and moderating the growth of malignant tissues can aid in recovery of diseased individuals [6]. Recently, cracking of micrometre-scale solder joints has been attributed as the cause for an aircraft crash [8].…”

“…A framework for studying dynamics and stability of diffusive-reactive interfaces with application to Cu 6 Often during phase growth, the rate of accretion, on the one hand, is determined by a competition between bulk diffusion and surface reaction rate. The morphology of the phase interface, on the other hand, is determined by an interplay between surface diffusivity and surface reaction rate.…”