Modeling and optimization of cranial suture anisotropic material properties using a response surface methodology

The present study aimed to develop and validate a transversely isotropic finite element (FE) model of the cranial suture that predicts suture mechanics, validated using ex-vivo data from the swine internasal suture. A 2D displacement-controlled FE model of the bone-suture-bone complex was constructed using microcomputed tomography (μCT) images, with a uniform cross-section and boundary conditions replicating experimental tensile tests. Suture geometry was modeled at three evenly spaced positions to explore how material anisotropy captures regional mechanical variation. Collagen fiber orientation was quantified from histological sections based on fiber angles relative to the suture-bone interface. Transversely isotropic material parameters were identified and optimized to match ex-vivo experimental outcomes using response surface methodology (RSM) with a five-level central composite design. Nodal forces at the displaced bone face were used from FE simulations to compare with experimental force-displacement measurements. Analysis of variance revealed that shear modulus (G_xy), and Young's moduli (E_y, and E_x) significantly influenced force response (p < 0.05). Transitioning from isotropic to transversely isotropic material behavior led to a reduction in strain energy within the suture. Regional variation in suture interdigitation and thickness affected fiber alignment, enabling greater deformation and influencing mechanical behavior. The presented study developed a 2D FE model that incorporated transversely isotropic material properties to better predict the mechanical behavior of the region-specific internasal suture geometry. By incorporating histology-based collagen fiber orientation and optimizing transversely isotropic material properties using experimental data, the model captured region-specific mechanical responses, offering new insight into the structural role of anisotropy in cranial suture mechanics.