An anistropic, viscoelastic model of in vivo facial skin

Accurate knowledge of the mechanical properties of facial skin can lead to better face models. These in turn can result in improved prediction of maxillofacial surgical outcome, enhanced artificial skin , and more realistic animations

Comparison of anisotropic models to simulate the mechanical response of facial skin

Physically-realistic models of the face can be applied in a wide range of domains, including biomedicine, computer animation, and forensics. There has been significant improvement in the anatomical accuracy of face models with better representation of the mimetic muscles, and realistic contact and attachments between soft and bony tissues [1,2]. Face simulations can also benefit from improved constitutive models of the skin layer. For example, better representation of the mechanical properties of facial skin can lead to improved predictions of deformations as a result of maxillofacial surgical procedures. The objective of this work is to compare and evaluate constitutive models’ ability to simulate the mechanical response of facial skin subjected to a rich set of deformations using a probe. We developed a finite element model to simulate the facial skin experiments of Flynn et al [3]. Several anisotropic constitutive equations were tested for their suitability to represent facial skin, including models proposed by Gasser et al [4], and Tong and Fung [5]. To represent in vivo tension, we applied a prestress to the model prior to simulating the full set of deformations. The reaction forces due to the displaced probe were calculated. A non-linear optimization procedure determined model parameters and in vivo tensions that best fit the model reaction forces to the measured experimental reaction forces. The finite element model simulated the force-displacement response of facial skin under a rich set of deformations. Use of an anisotropic constitutive law in place of an isotropic law resulted in a better fit between the models and experiments. For example, using the Gasser et al [4] anisotropic material model results in a 0.87 variance accounted for compared to 0.79 variance using an isotropic Ogden material model [3]. Future developments include the incorporation of the structure inferior to the skin in the model. We believe this will have the most significant effect on the model performance. References: [1] Flynn et al. Comput Methods Biomech Biomed Eng, 18: 571-582, 2015 [2] Wu et al. IEEE Trans Vis Comput Graph, 20:1519-1529, 2014 [3] Flynn C et al. J Mech Behav Biomed Mater, 28: 484-494, 2013. [4] Gasser T et al. J R Soc Interface, 3: 15-35, 2006.” [5] Tong, P and Fung Y-C. J Biomech, 9: 649-657, 197

A finite element model of the face including an orthotropic skin model under in vivo tension

Computer models of the human face have the potential to be used as powerful tools in surgery simulation and animation development applications. While existing models accurately represent various anatomical features of the face, the representation of the skin and soft tissues is very simplified. A computer model of the face is proposed in which the skin is represented by an orthotropic hyperelastic constitutive model. The in vivo tension inherent in skin is also represented in the model. The model was tested by simulating several facial expressions by activating appropriate orofacial and jaw muscles. Previous experiments calculated the change in orientation of the long axis of elliptical wounds on patients’ faces for wide opening of the mouth and an open-mouth smile (both 30 degrees). These results were compared with the average change of maximum principal stress direction in the skin calculated in the face model for wide opening of the mouth (18o) and an openmouth smile (25 degrees). The displacements of landmarks on the face for four facial expressions were compared with experimental measurements in the literature. The corner of the mouth in the model experienced the largest displacement for each facial expression (11–14 mm). The simulated landmark displacements were within a standard deviation of the measured displacements. Increasing the skin stiffness and skin tension generally resulted in a reduction in landmark displacements upon facial expression

Face

The face is probably the part of the body, which most distinguishes us as individuals. It plays a very important role in many functions, such as speech, mastication, and expression of emotion. In the face, there is a tight coupling between different complex structures, such as skin, fat, muscle, and bone. Biomechanically driven models of the face provide an opportunity to gain insight into how these different facial components interact. The benefits of this insight are manifold, including improved maxillofacial surgical planning, better understanding of speech mechanics, and more realistic facial animations. This chapter provides an overview of facial anatomy followed by a review of previous computational models of the face. These models include facial tissue constitutive relationships, facial muscle models, and finite element models. We also detail our efforts to develop novel general and subject-specific models. We present key results from simulations that highlight the realism of the face models

Netpot: easy meal enjoyment for distant diners

Abstract. We capture key factors of a group meal with communication and interface technologies to make a meal more enjoyable for diners who cannot be collocated. We determined three factors of a popular group meal, Chinese hotpot, that are essential for a group meal experience: interacting as a group with food, a central shared hotpot, and a feeling that others are nearby. We developed a prototype system to maintain these factors for an online meal with remote friends. Our technique is of interest to designers creating technology for isolated diners