Stimuli-responsive smart materials for biomedical applications

The convergence of materials science and biomedicine has driven a paradigm shift towards personalized, responsive medical solutions. This review focuses on three pivotal classes of stimuli-responsive smart materials: shape memory polymers (SMPs), stimuli-responsive hydrogels (SRHs), and liquid crystal elastomers (LCEs), for transformative biomedical applications. SMPs offer programmable shape recovery triggered by stimuli (e.g., temperature, light), enabling minimally invasive procedures and adaptive scaffolds. SRHs combine the biocompatibility and softness of traditional hydrogels with dynamic, multifunctional responses to environmental cues like heat, light, or pH. LCEs uniquely integrate liquid crystal order with elastomeric networks, exhibiting reversible deformation and actuation ideal for biomimetic prosthetics and tissue engineering. Critically, the emergence of 4D printing technology, integrating these SRMs with additive manufacturing, overcomes limitations of static fabrication by enabling the creation of structures that dynamically transform in situ under specific triggers. This allows precise spatiotemporal control for complex, personalized medical devices across scales. The review systematically summarizes recent advancements in SMPs, SRHs, and LCEs, elucidates their fundamental stimulus-responsive mechanisms, explores their integration with 4D printing, and examines diverse biomedical applications. Key challenges and future prospects are thoroughly analyzed to guide the strategic development of next-generation intelligent biomedical materials.