Computational investigation of interface printing patterns within 3D printed multilayered scaffolds for osteochondral tissue engineering.

Osteoarthritis is a highly prevalent rheumatic musculoskeletal disorder that commonly affects many joints. Repetitive joint overloading perpetuates the damage to the affected cartilage, which undermines the structural integrity of the osteochondral unit. Various tissue engineering strategies have been employed to design multiphasic osteochondral scaffolds that recapitulate layer-specific biomechanical properties, but the inability to fully satisfy mechanical demands within the joint has limited their success. Through computational modeling and extrusion-based bioprinting, we attempted to fabricate a biphasic osteochondral scaffold with improved shear properties and a mechanically strong interface. A 3D stationary solid mechanics model was developed to simulate the effect of lateral shear force on various thermoplastic polymer/hydrogel scaffolds with a patterned interface. Additionally, interfacial shear tests were performed on bioprinted polycaprolactone (PCL)/hydrogel interface scaffolds. The first simulation showed that the PCL/gelatin methacrylate (GelMA) and PCL/polyethylene glycol diacrylate (PEGDA) scaffolds interlocking hydrogel and PCL at interface in a 1:1 ratio possessed the largest average tensile (PCL/GelMA: 80.52 kPa; PCL/PEGDA: 79.75 kPa) and compressive stress (PCL/GelMA: 74.71 kPa; PCL/PEGDA: 73.83 kPa). Although there were significant differences in shear strength between PCL/GelMA and PCL/PEGDA scaffolds, no significant difference was observed among the treatment groups within both scaffold types. Lastly, the hypothetical simulations of potential biphasic 3D printed scaffolds showed that for every order of magnitude decrease in Young's modulus (E) of the soft bioink, all the scaffolds underwent an exponential increase in average displacement at the cartilage and interface layers. The following work provides valuable insights into the biomechanics of 3D printed osteochondral scaffolds, which will help inform future scaffold designs for enhanced regenerative outcomes.