Interface Performance Enhancement in 3D-Printed Biphasic Scaffolds with Interlocking Hourglass Geometry

The cartilaginous surfaces in ginglymus (hinge) joints such as the knee, elbow, and the ginglymoarthrodial temporomandibular joint (TMJ) primarily function under unidirectional shear and orthogonal compression. Regenerative medicine approaches to treat injured or arthritic joints include biphasic scaffolds, which must withstand the joint's biomechanical demands. In the current study, we leveraged computational modeling to design a 3D-printed biphasic scaffold with enhanced biomechanical performance for ginglymus joints. A sinusoidal hourglass tube geometry was introduced to support shear stresses at the hydrogel-substrate interface and to support orthogonal compression. Biphasic constructs were evaluated with both empirical and in silico interface shear experiments. A thermal extrusion 3D-printed polylactic acid (PLA) hourglass interface was infilled with a hydrogel, comprised of either (1) agarose or (2) pentenoate-modified hyaluronic acid (PHA), polyethylene glycol diacrylate (PEGDA), and devitalized cartilage (DVC). Shear loads were applied either parallel to the tube's long axis (i.e., 1-direction) or orthogonally (i.e., 2-direction). Additionally, the hourglass tube architecture without any hydrogel was evaluated in compression in the 1- and 3-directions. Empirically, ultimate interface shear stresses up to 51 ± 7 kPa were observed for the infilled PHA-PEGDA-DVC hydrogels, with higher values in both loading directions compared to a crosshatch scaffold as a standard-of-comparison control (p < 0.05). The computer model suggested a geometry-dependent shear load transfer. The ultimate compressive stress for the hourglass architecture in the 3-direction reached 6.9 ± 1.8 MPa, which was 39% higher than the crosshatch architecture. The hourglass design enhanced performance under shear in the 1-direction and compression in the 3-direction, which may add value for future designs employed for regenerating tissues in ginglymus joints that primarily function under unidirectional shear and orthogonal compression.