Improving tissue expansion protocols through computational modeling

Abstract

Tissue expansion is a common technique in reconstructive surgery used to grow skin in vivo for correction of large defects. Despite its popularity, there is a lack of quantitative understanding of how stretch leads to growth of new skin. This has resulted in several arbitrary expansion protocols that rely on the surgeon's personal training and experience rather than on accurate predictive models. For example, choosing between slow or rapid expansion, or small or large inflation volumes remains controversial. Here we explore four tissue expansion protocols by systematically varying the inflation volume and the protocol duration in a porcine model. The quantitative analysis combines three-dimensional photography, isogeometric kinematics, and finite growth theory. Strikingly, all four protocols generate similar peak stretches, but different growth patterns: Smaller filling volumes of 30 ml per inflation did not result in notable expander-induced growth neither for the short nor for the long protocol; larger filling volumes of 60 ml per inflation trigger skin adaptation, with larger expander-induced growth in regions of larger stretch, and more expander-induced growth for the 14-day compared to the 10-day expansion protocol. Our results suggest that expander-induced growth is not triggered by the local stretch alone. While stretch is clearly a driver for growth, the local stretch at a given point is not enough to predict the expander-induced growth at that location. From a clinical perspective, our study suggests that longer expansion protocols are needed to ensure sufficient growth of sizable skin patches.

Multifactorial analysis of the surgical outcomes of giant congenital melanocytic nevi: Single versus serial tissue expansion

“…Even in anatomically challenging areas such as the extremities, we found no significant differences in complications between single and serial expansion. It is generally believed that rectangular-shaped expanders could enable faster expansion [22]; however, we did not observe an increased risk of complications in the present study. Multifactorial analysis demonstrated that implantation of a larger expander and a high inflation volume were associated with a significantly higher rate of complications after expander insertion.…”

Transcriptomic analysis reveals dynamic molecular changes in skin induced by mechanical forces secondary to tissue expansion

“…To better understand the molecular response of skin following TE, we performed an in vivo study using a porcine TE model 34 and evaluated the skin transcriptome profile at 1 h (TE.1h), 24 h (TE.24h), 3 days (TE.3d) and 7 days (TE.7d) of expansion (Fig. 1 a).…”

Personalized Computational Models of Tissue-Rearrangement in the Scalp Predict the Mechanical Stress Signature of Rotation Flaps

“…Therefore, MVS offers a flexible and easy-to-use methodology to create accurate preoperative models of reconstructive surgery (Lee et al, 2018). Alternatives include 3D cameras, which are becoming common in clinical practice (Camison et al, 2018; Lee et al, 2018).…”

“…Our methodology relies on obtaining 3D patient-specific geometries using multi-view stereo (MVS) (Hiep et al, 2009; Tepole et al, 2015), a flexible and powerful algorithm from computer vision that relies on feature matching across photographs taken from different angles. A commercial finite element (FE) analysis framework is used to perform the virtual procedure (Lee et al, 2018). To investigate the effect of anisotropy, a fiber distribution field according to Cox’s lines is imposed (Cox, 1941).…”