Recent advances in soft magnetic nanocomposites have enabled myriads of magnetic robots with programmable shape transformation, shedding light on various biomedical applications. However, the complex shape transformation of magnetic hydrogels remains a challenge because of their ultralow magnetization and simple geometry. Here we demonstrate an approach to meet this challenge by fabricating composite structures of magnetic hydrogels and elastomers with extrusion-based 3D printing. Under an alternating magnetic field, magneto-thermo-sensitive hydrogels — poly(N-isopropylacrylamide) (PNIPAm) embedding Fe₃O₄ nanoparticles, can undergo abrupt volume collapse due to magnetothermal effect. The mismatch in the responsiveness of magnetic hydrogels and elastomers enables the shape transformation of the composite structure. We have printed magnetic hydrogels with various geometries and achieved complex shape transformation of the composite structure. The shape transformative structure can simultaneously encase and kill cancer cells (human malignant melanoma cells) through magnetic hyperthermia. $\sim$50% of cancer cells can be killed by the heated magnetic hydrogel during deformation. This approach may open opportunities for applications in medicine and bioengineering.

软磁性纳米复合材料的最新进展使无数的磁性机器人具有可编程的形状转换功能，从而在各种生物医学应用中大放光彩。然而，由于磁性水凝胶的超低磁化强度和简单的几何形状，其复杂的形状转换仍然是一个挑战。在这里，我们展示了一种通过基于挤压的3D打印制造磁性水凝胶和弹性体的复合结构来应对这一挑战的方法。在交变磁场下，磁热敏水凝胶—嵌入Fe ₃ O _4的聚（N-异丙基丙烯酰胺）（PNIPAm）由于磁热效应，纳米粒子可能会发生突然的体积塌陷。磁性水凝胶和弹性体的响应度不匹配，可实现复合结构的形状转换。我们已经印制了具有各种几何形状的磁性水凝胶，并实现了复合结构的复杂形状转换。形状转化结构可以通过磁性热疗同时包裹和杀死癌细胞（人类恶性黑色素瘤细胞）。$〜$在变形过程中，加热的磁性水凝胶可杀死50％的癌细胞。这种方法可能为医学和生物工程中的应用打开机会。