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

Abstract

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.

Shape memory polyurethane potentially used for vascular stents with water-induced stiffening and improved hemocompatibility

“…As a commercial material widely used in blood-contact fields, 52,53 Pellethane 2363-80AE (80AE) was used as a control. PEG is often used for surface modification to reduce the adhesion and activation of platelets for blood-contact materials, 54–56 thus PEG-based PU (PEGPU) was synthesized according to our reported method 14 as another control in our study (detailed information of PEGPU is shown in Table S4, ESI†). The results showed that the number of platelets adhered to the surface of TAPU1020 was slightly lower than that of 80AE.…”

“…Histocompatibility assessments were conducted according to the literature. 14 The detailed method is shown in the ESI †…”

“…Our group recently synthesized a series of polyurethane (PU) featuring main chains consisting of only hard segments and side chains of dangling PEG soft segments (PEGPU). 14 This new design of PU containing hard main chains and hydrophilic soft side chains (HMHS) realized the dramatically promoted microphase separation and soft-to-stiff transition in water. However, the shape recovery ratio ( R r ) and antithrombotic ability of the unique SMPUs should be further promoted to be qualified for specific applications such as self-expanding vascular stents.…”

4D Printed Biocompatible Magnetic Composite for Minimally Invasive Deployable Structures

“…Thus, athermal heating, which is possible by careful selection of the nanofillers incorporated in the polymer matrix, is a potentially viable means of exploiting the shape memory materials for remote actuation. The stimulus could be light 17 , ultrasound 18 , water 19 , microwaves 20 , etc. Magnetic stimulation is a potential means of remote actuation of these materials via indirect heating.…”

Hydration Activates Dual‐Confined Shape‐Memory Effects of Cold‐Reprogrammable Photonic Crystals

“…[23] On the other hand, the powerful capillary pressure created by water evaporation forces the skeleton to deform. [24] Furthermore, the hydration/dehydration of copolymer regulates the interchain binding forces (energy storage for shape recovery), [25] relieving/locking internal stresses. If the interchain binding can be controlled directionally by prestimulation, it is likely to obtain the activatable shape-memory property.…”