Capturing sclera anisotropy using direct collagen fiber models: linking microstructure to macroscopic mechanical...

Collagen fibers are essential to the mechanical behavior of soft tissues, including sclera. Conventional models often represent these fibers statistically, potentially missing crucial aspects of their role in tissue behavior. In this study, we expand on a direct fiber modeling approach that we recently presented based on explicitly representing the sclera long, interwoven fiber bundles. Specifically, our goal was to capture specimen-specific 3D fiber architecture and anisotropic mechanics of four ovine sclera samples (superior from Eye-1, temporal and superior from Eye-2, and temporal from Eye-3), each tested under five conditions: equi-biaxial (1:1) and four non-equi-biaxial (1:0.75, 0.75:1, 1:0.5, and 0.5:1). Fiber architecture was extracted using polarized light microscopy and reconstructed model fiber orientations agreed well with the histological information (adjusted R² > 0.89). Material parameters were determined via inverse fitting to the equi-biaxial tests. Remarkably, the parameters obtained from equi-biaxial fitting also accurately predicted the mechanical response of the same sample under all four non-equi-biaxial conditions. This indicates that the models inherently captured tissue anisotropy through its fiber structure, unlike conventional continuum models which require simultaneous multi-condition fitting. Our findings support direct fiber modeling as a promising tool approach for linking tissue fibrous structure and macroscopic mechanical behavior.