Biodegradable magnetic polymer composites. (a) Biodegradable helical microrobot, made of gelatin methacryloyl and fabricated by two-photon polymerization (reproduced with permission from Advanced Healthcare Materials, Wiley) [57]. (b) Biodegradable PLGA/Fe/5-FU microrobots, fabrication process (reproduced with permission from Sensors and Actuators B: Chemical, ScienceDirect) [59]. (c) Biodegradable capsules for drug delivery made of alginate hydrogel, loaded with Fe3O4 particles (reproduced with permission from Journal of Colloid and Interface Science, Elsevier) [60]. (d) Biodegradable microswimmers for drug delivery based on chitosan loaded with iron oxide (magnetite) particles (reproduced with permission from ACS Nano) [61].