The mechanical response of human skin and underlying tissue (hereafter, referred to as only skin) is a subject that has been studied by professionals and scientists for many years. However, the current methods require large specialized equipment in a laboratory to measure the response of skin. Handheld devices that perform compression and extension measurements of skin have the potential to replace bulky lab equipment and have the advantage of making in vivo measurements. In this research we explore the use of handheld devices to measure the mechanical response of skin in compression and extension. Further, this research aims to use simulation and optimization techniques to develop a method of determining material parameters based on the measurements recorded by the handheld devices.
This work has two major components. First, we study the use of two proprietary handheld devices on a viscoelastic foam material, and second we research the use of the handheld devices on human skin. Using the handheld devices on a viscoelastic foam holds a three-fold purpose. First, the device’s accuracy and precision are determined. Second, simple compression and extension tests are used to determine a constitutive material model for the foam. Third, a combination of the physical handheld device results and constitutive material model are used to study a simulation model that replicates the handheld device’s boundary conditions. Once these three steps are completed, an optimization method is used to determine the material parameters needed to replicate the physical test. In this process, we find that the handheld devices can provide test data that then can be used with the simulation and optimization methods to determine the material parameters to replicate the viscoelastic foam response.
In the second major part of this work, the handheld devices are used to study the response of human skin in vivo. The optimization methods are then applied to two different simulation models. First, a model that represents the skin as a single bulk material is considered. Second, a model that represents the skin as two layers is considered. It is found that the bulk material model is able to replicate either the compression or extension tests, but not both. On the other hand, the two-layer model is able to replicate both the compression and extension tests simultaneously. The simulation and optimization techniques studied in this work, along with the results from the handheld devices, can be used to determine the material parameters needed to replicate the response of human skin.