Triggered by light and magnetism: smart foam PLLA/HAP/Fe₃O₄ scaffolds for heat-controlled biomedical applications

Ternary composite foam materials containing poly-L-lactic acid (PLLA), calcium hydroxyapatite (HAP) (20 nm), and morphologically controlled Fe₃O₄ nanoparticles (80 nm) were fabricated using the thermally induced phase separation (TIPS) technique over a broad concentration range of the magnetic component (1-30 wt%). The foam scaffolds were highly porous (>95%), and lightweight, with a high capacity for soaking in Ringer's solution. The foam density varied with the inorganic component content, ranging from 0.02 to 0.079 g mL^-1, while the mean pore size was approximately 330 μm. The magnetic behavior of Fe₃O₄ nanocubes and the foam composites was characterized. The presence of the inorganic filler caused a shift towards a lower decomposition temperature of PLLA. The conversion energy of both dry and Ringer's solution soaked foams was studied in detail demonstrating that the fabricated ternary composites are highly temperature-responsive under the influence of an alternating magnetic field (AMF), near-infrared (NIR) laser radiation (808, 880, and 1122 nm), and the synergistic effect of both external stimuli. This synergy resulted in faster heating and a higher maximum temperature (T_max ≈ 80 °C). Biological characterization and heating ability analysis enabled the selection of the most reliable foam, which contained 15% magnetic filler, based on its appropriate microstructure, sufficient biocompatibility, and ability to reach biologically relevant temperatures under AMF exposure and the combined action of NIR and AMF. The fabricated materials exhibit high potential for biomedical applications as well as other areas requiring temperature-controlled stimulation of various processes.