The device presented could give convincing results. The in vivo mechanical properties of human facial skin obtained by our modified formula agree well with open literature, and a better reliability than classical Hertz theory is evidenced.

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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 [Formula: see text] are relatively large ranging from 2.653[Formula: see text]kPa to 4.437[Formula: see text]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 [Formula: see text] are between 1.649[Formula: see text]kPa and 3.395[Formula: see text]kPa.