Biomedical Engineering Reference
In-Depth Information
Fig. 11.14
Muscle-driven simulations of different facial expressions. From Ref. [
11
]. Copyright
2013 by Taylor & Francis. Adapted with permission
11.4.5 Facial Expression Simulations
We also used our face-jaw-tongue-hyoid model to simulate a series of facial expres-
sions and compared the displacement of landmarks with experimental measurements
in the literature [
11
]. For these simulations, the hypodermis, represented by the inner
and middle layer of elements in the face model, was simulated using a Mooney-
Rivlin material. The outer layer of elements representing the epidermis and dermis
was modeled using an anisotropic material with parameters based on in vivo tests as
described above.
For these simulations, a novel aspect of the face model was the imposition of a
pre-stress corresponding to the tension inherent in living skin. The inner nodes of the
facial elements were scaled prior to the finite element analysis. During the first step
of the analysis, they were displaced back to their reference positions. This resulted
in a tension field similar to the RSTLs observed by Borges [
33
].
The simulated facial expressions included a closed-mouth smile, an open-mouth
smile, pursing of the lips, and lips turned downwards (Fig.
11.14
). These were
achieved by activating appropriate sets of orofacial muscles. For all facial expres-
sions, the mouth corner experienced the largest displacement, which was in agree-
ment with experimental observations. The simulated landmark displacements were
within a standard deviation of the measured displacements (Fig.
11.15
). For open
and closed-mouth smiles, increasing the stiffness of the skin layer resulted in smaller
landmark displacements (Fig.
11.15
). Increasing the in vivo skin tension had a vari-
able effect on landmark displacements.
