On the Three-Dimensional Mechanical Behavior of Human Breast Tissue.

As the human breast undergoes complex, large-scale, fully three dimensional deformations in vivo, three-dimensional (3D) characterization of its mechanical behavior is fundamental to its diagnosis, treatment, and surgical modifications. Its anisotropic, heterogeneous fibrous structure results in complex behavior at both the tissue and organ levels. Mathematically modeling of this complex anisotropic behavior is thus critical to the proper simulation of the human breast. Yet, current breast tissue constitutive models do not account for these complexities, so that there is a pressing need for more detailed fully 3D analysis. To this end, we performed a full 3D kinematic mechanical evaluation of human fibroglandular and adipose breast tissues. We utilized our recently developed 3D kinematic numerical-experimental approach to acquire force-displacement data from both breast tissue subtypes. This was done by subjecting cuboidal test specimens, aligned to the anatomical axes,to both pure shear and simple compression loading paths. We then developed novel constitutive model that was able to simulate the unique anisotropic tension/compression behaviors observed. Constitutive model parameters were determined using a detailed finite element model of the experimental setup coupled to nonlinear optimization. We found that human breast tissues displayed complex anisotropic behavior, with strong, directionally dependent non-linearities. This was especially true for the fibroglandular tissue. The novel constitutive model was also able fully capture these behaviors, including states of combined tension and compression (i.e. in pure shear). The results of this study suggest that human breast tissue is complex in its mechanical response, exhibiting varying levels of anisotropy. Future studies will be required to link the observed anisotropy to the physical structure of the tissue, as well as mapping this heterogeneity and anisotropy across individuals.