Discontinuous fibers are commonly added to matrix materials in additive manufacturing to enhance properties, but such benefits may be constrained by print and fiber orientation. The additive processes of forming rasters and layers in powder bed fusion inherently cause anisotropy in printed parts. Many print parameters, such as laser, temperature, and hatch pattern, influence the anisotropy of tensile properties. This study characterizes fiber orientation attributed to recoating non-encapsulated fibers and the resulting anisotropic tensile properties. Tensile and fracture properties of polyamide 12 reinforced with 0%, 2.5%, 5%, and 10% discontinuous carbon fibers by volume were characterized in two primary print/tensile loading orientations: tensile loading parallel to the recoater (“horizontal specimens”) and tensile load along the build axis (“vertical specimens”). Density and fractographic analysis indicate a homogeneous mixture with low porosity and primary fiber orientation along the recoating direction for both print orientations. Neat specimens (zero fiber) loaded in either direction have similar tensile properties. However, fiber-reinforced vertical specimens have significantly reduced consistency and tensile strength as fiber content increased, while the opposite is true for horizontal specimens. These datasets and results provide a mechanism to tune material properties and improve the functionality of selectively laser-sintered fiber-reinforced parts through print orientation selection. These datasets could be used to customize functionally graded parts with multi-material selective laser-sintering manufacturing.

Additive manufacturing has enhanced medical trainers and their functionality, but synthetic tissues that are both anatomically accurate and capable of replicating musculoskeletal load responses remain largely unexplored. The purpose of this study is to demonstrate fabrication of synthetic tissue using active filament-mixing fabrication to enable local composition control with thermoplastic compositions tuned to match the modulus of elasticity of the respective tissues and functionally graded transitions between ligament and bone. Synthetic femoral anterior cruciate ligament (ACL) tibial complexes were fabricated and tested at 30° flexion along the tibial and anatomical load orientations matching the test procedure performed on cadaveric femoral ACL tibial complexes by Woo et al. in 1991. Load parameters were facilitated by section grips integrated into the design of test specimens without requiring a multi-axis jig. Anatomical accuracy was achieved by modeling tissues from magnetic resonance imaging data. Specimens loaded in the tibial orientation have an ultimate load of 287 ± 37 N and stiffness of 62.8 ± 11 N/mm. Specimens loaded in the anatomical orientation have an ultimate load of 312 ± 6.5 N and a stiffness of 43.5 ± 3.4 N/mm. Although load response in the synthetic tissue was less than its cadaveric counterpart due to bending load from flexion, the methods of this study are versatile, repeatable, and compatible with a wide variety of printable thermoplastics and composites which can be applied to other tissues, joints, and load conditions.