Facile and Scalable Fabrication of High-Performance Polylactide-Based Medical Microparts through Combining the Microinjection Molding Intense Shear Stress Field and Annealing Strategy

The second surgery for removing metallic internal fixation devices causes unbearable pain to orthopedic patients. Fortunately, poly(L-lactic acid) (PLLA), a bioabsorbable aliphatic polyester, has exhibited certain advantages in practical application due to its degradation over time in vivo with a minimal inflammatory response. However, the use of a PLLA bone screw for repairing defective bones is actually limited by the difficulty in realizing the balance between stiffness and toughness in current products. Herein, we report a novel strategy to fabricate the microbone screw from a blend of PLLA and poly[(butylene succinate)-co-adipate] (PBSA) by adopting the combination of the microinjection molding process featured with an intensive shear stress field and the subsequent annealing strategy. Accordingly, the hybrid shish-kebab structures consisting of flexible PBSA fibers attached by well-aligned lamellar crystals of PLLA could be generated, which prove to be able to overcome the difficulties well in keeping the balance between stiffness strength and toughness of the regular PLLA microparts. Thanks to the above-formed unique hybrid shish-kebab structures, the bone-mimicking PLLA/PBSA (90/10) blend material not only possesses excellent ductility (elongation at break of 51%) but also exhibits high stiffness (Young's modulus of 2.32 GPa) and balanced tensile strength (61.2 MPa). Moreover, the flexural measurements show that the fabricated PLLA/PBSA microbone screw also possesses good flexural properties (comparable flexural strength and much better toughness) compared to that of the pure PLLA bone screw. The strategy proposed in this work for fabrication of the PLLA-based microbone screw could be industrially scalable and shows good application prospects.