## 1 Introduction
The collagen reorientation and mechanical properties were compared at each indentation step between different groups, and significant differences were observed in the relaxation behavior and fiber orientation. Significant differences were observed in the collagen fiber alignment due to differences in mold geometries. The relative strength of alignment for the isotropic group was very low, whereas the relative strength for the anisotropic group was significantly higher, demonstrating a more strongly aligned network. Results demonstrated that the slower the relaxation rate, the more highly aligned the samples, the smaller the changes in collagen fiber orientation, and the larger the strain magnitudes compared to isotropic samples. He analyzed the mechanics and kinematics of soft tissues under indentation. The purpose of performing indentation tests on soft biological tissues varies in several studies including evaluation of biomechanical properties such as the Young's modulus, puncture force, and displacement, as well as variations in the collagen fiber orientation upon indentation, and mechanics of dynamic needle insertions into soft biological tissues [7]. In general, understanding the mechanical properties of soft tissue will help scientists to predict and analyze the behavior of the tissue subjected to various biological forces, or the forces that they need to bear or respond to during the surgical procedure; this insight leads to a better device design and improvement [8; 9]. Needle insertion procedures involve several transitions between tissue layers that give rise to rupture events. These events involve large forces and tissue deformations that lead to crack extensions. [PERSON] et al. presented the theory behind the mechanics of rupture events and determined the impact of insertion velocity on needle force and tissue deformation [10]. Needle insertion experiments were performed on porcine heart tissues and the non-linear viscoelastic properties of the tissues were determined through implementation of the Kelvin-Voight model. This helped in analyzing the relationship between tissue deformation and rupture force at different velocities [10]. Another study conducted by [PERSON] et al. was aimed at establishing a relationship between the fiber orientation and tensile strength of an artificial collagen model made of porcine skin. The model was subjected to uniaxial tensile tests and the collagen fiber orientation (parallel or perpendicular) was determined prior to testing using small-angle light scattering (SALS). This helps in characterizing the microstructure without damaging the material [11]. Results illustrated the stress-elongation response, where the collagen fibers in the parallel direction were observed to be less extensible compared to fibers aligned in the perpendicular direction. It was also observed that the stiffness significantly varies with respect to the direction of orientation [11]. Collagen is the most important protein responsible for the mechanical framework of the myocardium [12]. There are two types of collagens dominantly in myocardium: collagen I and collagen III; where collagen I is stiffer compared to collagen III and responsible for regulating the mechanical properties of the myocardium under large deformation. Collagen IV, V, and VI play significant roles in fiber formation and cell-ECM interactions. However, they do not directly contribute to the mechanical properties of tissues. Collagen fibers consist of bundles of proteins that are cross-linked together. Collagen fibers exhibit a coiled structure. When stretched, they change from crimpled state to an uncrumpled state (straight) creating a toe region. At the end of this region, the fibers respond linearly to the load. When stretched to a high level, the fibers completely straighten [12; 13]. Lamb hearts were chosen because of their biological and physiological similarities with human hearts.