Emerging Sustainable Lead-Free X-ray Shielding Materials: Design Strategies and Future Perspectives

X-rays play an essential role in medical diagnostics, nondestructive testing, and material characterization; nevertheless, their strong ionizing nature presents substantial risks to human health and the environment. Consequently, the development of shielding materials with superior attenuation efficiency, mechanical robustness, and environmental sustainability is of critical importance. In this context, sustainable lead-free X-ray shielding materials have recently emerged as promising alternatives to their conventional lead-based counterparts, providing comparable or even superior attenuation performance while enabling flexible control over composition and structure. This review summarizes recent progress in carbon-, metal-, and ceramic-based lead-free shielding composites, emphasizing their shielding mechanisms, composition-property relationships, and comparative performance, while also highlighting structural engineering strategies (such as micro/nanostructures, core-shell architectures, and multilayer configurations) that further enhance attenuation efficiency, mechanical robustness, and functional versatility. Finally, critical challenges and future opportunities are presented to chart pathways toward the rational design of next-generation X-ray shielding materials featuring advanced architecture, superior performance, and seamless multifunctional integration.