Design and fabrication of 3D-printed hard-soft interfaces made from PLA and hydrogel

Abstract

The mechanical properties of biological hard-soft interfaces change gradually over a small surface area to prevent the formation of stress concentrations through variations in the interface’s chemical composition, microstructure and geometry. The bone-tendon/ligament and bone-cartilage interface are the most prominent hard-soft interfaces within the human body and need restoration once injuries occur. It is difficult to repair these interfaces and simultaneously maintain the initial quality of the native tissues. This study used hybrid 3D-printing techniques, i.e., fused deposition modeling (FDM) and an extrusion-based technique, to develop a proof of concept for the fabrication of hard-soft interface structures. The first part of the study concentrates on the design of geometrical interlocking structures. A parametric study with multiple simulations was performed for two specific geometries, an anti-trapezoidal and a double hook design. The double hook design demonstrated the highest stiffness under tensile stress conditions. The second part concentrates on manufacturing hard-soft interface structures, for which 2D and 3D models were fabricated. The 2D models were used to explore different geometrical interlocking designs and validate the computational models. The 3D models were used to create a proof-of-concept for a hard-soft interface made from PLA (FDM technique) and alginate (extrusion-based technique). The 3D-printing techniques were combined by extruding hydrogel into the interlocking system of the PLA part and printing a soft alginate scaffold on top of the interlocking structure. In conclusion, this study suggests several practical solutions to improve interfacial designs and to manufacture hard-soft interface structures. Combining 3D-printing techniques opens up new possibilities for the fabrication of state-of-the-art hard-soft interfaces structures.