Stretching skin: The physiological limit and beyond.

Area of Science:

• Computational mechanics
• Biomaterials science
• Tissue engineering

Background:

• Skin exhibits complex, nonlinear, and anisotropic behavior within physiological limits.
• Beyond physiological limits, mechanical stretch induces irreversible skin growth.
• Understanding these behaviors is crucial for applications like tissue expansion in reconstructive surgery.

Purpose of the Study:

• To develop a novel computational model for skin's constitutive behavior under stretch.
• To characterize reversible and irreversible skin responses, including growth.
• To simulate stretch-induced skin growth during tissue expansion procedures.

Main Methods:

• A transversely isotropic chain network model with eight wormlike chains for physiological behavior.
• A transversely isotropic growth model using a scalar-valued growth multiplier for irreversible growth.
• Implicit Euler backward scheme for temporal discretization and finite element method for spatial discretization, with nested Newton iterations.

Main Results:

• The model accurately captures skin's nonlinear, anisotropic, and stretch-locking properties.
• It simulates irreversible area growth as a transversely isotropic process.
• Simulations of tissue expander geometries reveal spatio-temporal evolution of stress, strain, and area gain.

Conclusions:

• The proposed computational model provides a robust framework for understanding skin mechanics and growth.
• It has the potential to advance reconstructive surgery by optimizing tissue expansion parameters.
• The model can inform decisions on expander geometry, size, placement, and inflation timing.