Biostable Segmented Thermoplastic Polyurethane Shape Memory Polymers for Smart Biomedical Applications

Abstract

The exceptional tunability of chemical, mechanical, and shape memory properties of segmented thermoplastic polyurethanes (STPUs) makes them promising materials in a wide range of biomedical applications. STPUbased shape memory polymers (SMPs) that stably maintain their chemical, thermomechanical, and shape memory properties even after implantation could provide a reliable platform for controlled environmental response. For example, materials could be actuated at set time points to deliver bioactive agents, or cleavable compounds could be incorporated into a stable SMP that responds to wound signals for use in diagnosis. To this end, a library of STPUs with varying ratios of hard to soft segments was synthesized and characterized. It was found that using polypropylene glycol as the soft segment and triethylene glycol as the chain extender with hexamethylene diisocyanate induced sufficient phase separation in STPUs to provide a shape memory system. The polymers had more than 90% shape recovery ability and high enough transition temperatures (56−58 °C under dry and 44−51 °C under wet conditions) to enable maintenance of their temporary shape at body temperature. We tuned chemical, mechanical, thermal, and shape memory properties by changing the composition and characterized their stability in degradation media (more than 94% mass remaining at 40 days under accelerated conditions for polymers with higher hard segment ratios). The cytocompatible STPUs were highly stable (>90%) in their primary and secondary geometries in in vitro degradation media, indicating that they would stay intact after implantation. Then, the materials were actuated by heating at userdefined time points, upon which they returned to their primary shapes. As a proof of concept, we incorporated magnetic nanoparticles into this system to provide a magnetically actuated SMP that induced 44% shape recovery only after 5 min of exposure to a magnetic field. This system provides a platform for future generations of STPUs that include other cleavable or environmentally responsive components so that wound or clinician-controlled signals can act as external stimuli to cause shape and morphological changes.

Domain Structure, Thermal and Mechanical Properties of Polycaprolactone-Based Multiblock Polyurethane-Ureas under Control of Hard and Soft Segment Lengths

“…From the point of view of the ability to control the microdomain structure of multiblock PU, new prospects are opened up for obtaining adaptive functional materials based on them, namely, intelligent medical devices [ 21 ], implants for minimally invasive surgery [ 22 ], self-tightening suture threads [ 23 ], miniature manipulators [ 24 ], “breathable clothing” [ 25 ], etc. However, understanding the phase behavior of such systems is only the first step on the way to the targeted physicochemical design of multiblock copolymers with preprogrammed properties.…”

Tailor-Made Functional Polyolefins of Complex Architectures: Recent Advances, Applications, and Prospects

“…The segmented copolymers, such as polyurethanes composed of hard and soft segments, are an appropriate solution for this problem. 241 Such polymers benefit from the possibility of response temperature control through the structure and soft segment length regulation. In polyethylene, the introduction of the comonomer units into the polymer backbone results in a PE melting point depression.…”

“…One of the exciting topics in the shape memory effect is lowering the response temperature to broaden the application range of SMPs in biological and biomedical areas where high-temperature processes are avoided. The segmented copolymers, such as polyurethanes composed of hard and soft segments, are an appropriate solution for this problem . Such polymers benefit from the possibility of response temperature control through the structure and soft segment length regulation.…”

Magnetically Actuated Shape Memory Polymers for On-Demand Drug Delivery

“…To combine the benefits of prior magnetically responsive and SMP approaches, we hypothesized that magnetically responsive polyurethane-based SMPs could enhance controlled drug delivery. To that end, we selected SMP compositions based on previously developed thermally actuated SMP systems [ 26 , 27 ]. Using these materials, magnetically responsive polymer composites were prepared by incorporating iron oxide magnetic nanoparticles (mnps) into the SMPs.…”