3D printing and mechanical characterization of polylactic acid scaffolds for bone tissue engineering

Abstract

In bone tissue engineering, the use of biocompatible scaffolds mimicking the mechanical behavior of healthy human bones, is key to bone tissue regeneration and new bone growth. The design of scaffolds for bone tissue engineering requires the identification and employment of proper microstructural parameters which may tune the scaffold’s mechanical properties for the control of healthy tissue growth. This study is focused on the design and fabrication of biocompatible poly lactic acid (PLA) scaffolds with various porosity, pore sizes, and pore geometries to investigate their effect on the mechanical properties of the scaffold, with an emphasis on elastic behavior and compressive strength. The selection of structural parameters for the designed PLA scaffolds was performed on the basis of a critical literature review, focusing on the structural characteristics of human bones and state of the art in PLA scaffold fabrication. The generated designs were constructed via additive manufacturing with the use of three dimensional (3D) printing technology at the Department of Biomedical Engineering of the University of West Attica. Compressive testing of the 3D PLA imprints was conducted in collaboration with the Department of Mechanical Engineering of the University of West Macedonia. Results show that, as scaffold porosity increased, both Young modulus and compressive strength decreased, pointing a shift towards greater elasticity but reduced load bearing capacity; yet, the obtained values were comparable to trabecular bone mechanical testing results found in the literature, thus, making the designed PLA scaffolds able to mimic trabecular bone mechanical behavior. Elaboration of the results also indicated the importance of pore geometry, with rectangular pores generally providing greater strength and stiffness, while cylindrical pores, at similar porosity levels, exhibited greater elasticity and enhanced plastic deformation. Although the fabricated PLA scaffolds were found to mimic the mechanical behavior of trabecular bone, the created imprints did not meet the higher mechanical requirements of cortical bone. Our results suggest future research should focus on improving the mechanical strength of the PLA scaffolds by means of using new composite materials and advanced printing techniques.