In Vivo Measurement of the Mechanical Properties of Facial Soft Tissue Using a Bi-Layer Material Model

In vivo characterization of facial soft tissue is of great significance for facial plastic surgery, animation and dermatology. This paper presents an in vivo experimental method to characterize the macroscopic mechanical properties of facial soft tissue. In this method, a bi-layer material (BLM) model is established with the skeleton as the substrate under the facial soft tissue and the relationship between the mechanical properties of soft tissue and force-displacement curve is obtained. A novel indentation apparatus is also developed to experimentally measure the force-displacement curve of the facial soft tissue in vivo. Using the apparatus, experiments were conducted on artificial skins to verify the theoretical model. Experiments on facial soft tissue were finally conducted on four volunteers to obtain Young's moduli at five facial locations using an optimal indenter whose radius is determined by the verification experiment. Our experiment results indicate that a slight difference is observed in Young's moduli of facial soft tissue among different volunteers and indentation location. At locations of the left-hand cheek near the lips (NE) and center of the left-hand jaw (CJ), Young's moduli E-1 are relatively large ranging from 2.653 kPa to 4.437 kPa. Nevertheless, at other locations of the center of the cheek (CC), left-hand zygomatic region (ZYG) and left-hand cheek near the lips (NL), the contact forces are smaller, and Young's moduli E-1 are between 1.649 kPa and 3.395 kPa.

Automated summary

This paper presents a method for in vivo characterization of facial soft tissue mechanical properties, using a bi-layer material model and a novel indentation apparatus. Experiments on artificial skins and four volunteers showed slight differences in Young's moduli of facial soft tissue at different locations.