Water‐Triggered Stiffening of Shape‐Memory Polyurethanes Composed of Hard Backbone Dangling PEG Soft Segments

• Published in: Advanced materials (Weinheim) Vol. 34; no. 46; pp. e2201914 - n/a
• Main Authors: Liu, Wenkai, Wang, Ao, Yang, Ruibo, Wu, Hecheng, Shao, Shuren, Chen, Jinlin, Ma, Yan, Li, Zhen, Wang, Yanchao, He, Xueling, Li, Jiehua, Tan, Hong, Fu, Qiang
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 17.11.2022
• Subjects: Biocompatibility; Biomedical materials; Glass transition temperature; Incompatibility; Materials science; microphase separation; Modulus of elasticity; Molecular structure; morphology transformation; Polyethylene glycol; Polyurethane; Polyurethane resins; Recovery; Segments; shape‐memory polyurethanes; Stiffening; Stress transfer; water‐triggered stiffening; morphology transformation; microphase separation; biocompatibility; water-triggered stiffening; shape-memory polyurethanes
• DOI: 10.1002/adma.202201914
• ISSN: 0935-9648; 1521-4095

Shape‐memory polymers (SMPs) induced by heat or water are commonly used candidates for biomedical applications. Shape recovery inevitably leads to a dramatic decrease of Young's modulus due to the enhanced flexibility of polymer chains at the transition temperature. Herein, the principle of phase‐transition‐induced stiffening of shape‐memory metallic alloys (SMAs) is introduced to the design of molecular structures for shape‐memory polyurethane (SMPUs), featuring all‐hard segments composed of main chains that are attached with poly(ethylene glycol) (PEG) dangling side chains. Different from conventional SMPs, they achieve a soft‐to‐stiff transition when shape recovers. The stiffening process is driven by water‐triggered segmental rearrangement due to the incompatibility between the hard segments and the soft PEG segments. Upon hydration, the extent of microphase separation is enhanced and the hard domains are transformed to a more continuous morphology to realize more effective stress transfer. Meanwhile, such segmental rearrangement facilitates the shape‐recovery process in the hydrated state despite the final increased glass transition temperature (Tg). This work represents a novel paradigm of simultaneously integrating balanced mechanics, shape‐memory property, and biocompatibility for SMPUs as materials for minimally invasive surgery such as endoluminal stents. Inspired by the thermally triggered phase transformation process and “soft‐to‐stiff” transition achieved by lattice distortion of shape‐memory alloys, a series of water‐triggered stiffening shape‐memory polyurethanes is developed. They can achieve “soft‐to‐stiff” transition by forming more continuous hard domains upon hydration.