Ordered Hard-Segment Polyurethanes: Structural Design, Functional Regulation, Biomedical Applications, and Perspectives

Biomedical polyurethanes (PUs) are widely investigated for blood-contacting devices, soft-tissue repair, tissue-engineering scaffolds, and smart implants owing to their tunable segmented structures, elasticity, and processability. However, aromatic PUs may generate potentially harmful degradation products, while conventional aliphatic PUs often suffer from insufficient hard-segment association, limited microphase separation, and inadequate long-term mechanical stability. Ordered hard-segment PUs, constructed from monodisperse, uniform-sized, or structurally well-defined hard segments, provide a molecular-level strategy to address these challenges by enabling cooperative hydrogen bonding and enhanced soft-hard segment microphase separation. This Review summarizes recent progress in their structural design, molecular construction, functional regulation, biomedical applications, and translational evaluation of ordered hard-segment PUs. Particular emphasis is placed on how hard-segment length, sequence regularity, symmetry, and content, together with soft-segment chemistry, surface/interface functionalization, blending or composite strategies, and network-based designs, regulate microstructure, mechanical performance, biocompatibility, and degradation behavior. The distinction between hard-segment ordering and hard-segment chemistry is further discussed, highlighting the importance of molecular regularity and packing capability rather than simply increasing hard-segment content. Finally, current challenges associated with biological validation, standardized evaluation, device-oriented design, and clinical translation are discussed, underscoring the need for structurally precise, interface-stable, application-specific ordered hard-segment PUs as advanced biomedical elastomers.