Magnetic Nanocomposite Scaffolds with Four-Dimensional Response in Bone Tissue Engineering – From Mechanisms to Applications

Bone tissue engineering has undergone a paradigm shift from static, replacement-based approaches toward dynamic and bioactive systems. Despite advances in three-dimensional scaffolds, these structures cannot dynamically adapt to the changing biological environment, particularly in critical-sized bone defects requiring stem cell differentiation, angiogenesis, and gradual matrix mineralization. Magnetic nanoparticles, especially superparamagnetic iron oxide nanoparticles (Fe₃O₄ and γ-Fe₂O₃), provide remote control and spatiotemporal regulation of regenerative processes through mechanical, thermal, and chemical stimulation. Four-dimensional (۴D) tissue engineering adds "time" as the fourth dimension, creating dynamic scaffolds that can adapt to irregular bone defects through magnetic field‑induced shape recovery. However, challenges remain, including dose- and time-dependent toxicity (especially at doses above ۳۵ mg/kg), heterogeneous nanoparticle distribution, lack of standardized magnetic stimulation protocols, and inadequate control over ۴D shape changes. This review article systematically analyzes the fundamentals, current challenges, specific clinical applications, and future perspectives to provide a roadmap for developing next-generation magnetic‑stimuli‑based regenerative therapies.

Keywords:

Magnetic nanocomposite scaffold , four‑dimensional tissue engineering , superparamagnetic iron oxide nanoparticles , bioprinting , bone repair , shape‑memory polymer , magnetic stimulation