Polyurethane as smart biocoatings: Effects of hard segments on phase structures and properties

Development of smart polyurethane (PU) coatings for enhancing the biocompatibility of the metal scaffold has attracted great interest in the past few years, and the investigation of the relationship between phase structure and smart properties is necessary. Herein, two series of PU biocoatings with different hard segment structures and soft segment length were prepared, and the soft segments consist of the polycaprolactone diols (PCL) with different molecular weights, and the hard segments were made of 1, 4-butanediol (BDO) and hexamethylene diisocyanate (HDI) with linear structure, or BDO and isophorone diisocyanate (IPDI) with alicyclic structure, respectively. To understand the phase structures, the chemical structure, surface micromorphology, and segmental incompatibility of the PU films were characterized, which reveals that IPDI-based PU possesses a phase compatible structure with a single-phase transition above 0 °C. Besides, the IPDI-based PU shows the thermal-responsive deformation at the temperature of 45 °C, slightly higher than the human body temperature. In contrast, the HDI-based PU possesses the excellent shape memory property caused by the microphase separation structure, because of the crystallization of soft and hard segments from the melt. Further, based on the characteristics of phase structure, the potential application of the IPDI-based PU and HDI-based PU is explored, offering a useful approach to effectively design the structures and properties of PU coatings.