Fe-Fe<sub>3</sub>O<sub>4</sub> nanoparticles with core-shell structure for the fabrication of polylactic acid-based composites with low toxicity and high radiopacity
Polylactic acid (PLA) has the elastic modulus comparable to that of human bone and shows high biocompatibility. These properties make it an ideal matrix for biodegradable materials used in implantable devices. However, the polymer has insufficient mechanical properties and low radiopacity, making it difficult to evaluate the degradation and position of the implanted device by magnetic resonance imaging and computed tomography. This paper reports that the introduction of magnetic Fe-Fe3O4 nanoparticles into the PLA matrix can increase the mechanical strength, radiopacity and promote uniform biodegradation of the resulting material. Fe-Fe3O4 nanoparticles with an average size of 68 nm were synthesized by electric explosion of an iron conductor in an oxygen atmosphere. The nanoparticles have a core-shell morphology: an a-Fe enriched core and an Fe<sub>3</sub>O<sub>4</sub> magnetite shell (=4 mass %). Fe-Fe<sub>3</sub>O<sub>4</sub>@PLA composite with different content of nanoparticles was synthesized using polymerization filling technique, and test samples of a given size were made by 3D printing. It was found that the introduction of nanoparticles into PLA in an amount of up to 10 mass % increases the strength of the material and prevents fracture from printing defects. In the case of a high content of nanoparticles (above 15%) they form agglomerates that become additional effective stress concentrators in the material. The large size of the agglomerates reduces their mobility during the plastic flow of the deformed polymer matrix. The presence of Fe-Fe3O4 nanoparticles significantly improves the radiopacity of images and stimulates the growth of fibroblast cell line 3T3. The developed material is promising for the manufacture of 3D printed bone scaffolds and screws.