A Processable Shape Memory Polymer System for Biomedical Applications

Abstract

Polyurethane shape memory polymers (SMPs) with tunable thermomechanical properties and advanced processing capabilities have been synthesized, characterized, and implemented in the design of a microactuator medical device prototype. The ability to manipulate glass transition temperature (Tg) and crosslink density in low-molecular weight aliphatic thermoplastic polyurethane SMPs is demonstrated using a synthetic approach that employs UV catalyzed thiol-ene “click” reactions to achieve post-polymerization crosslinking. PUs containing varying C=C functionalization are synthesized, solution blended with polythiol crosslinking agents and photoinitiator and subjected to UV irradiation, and the effects of number of synthetic parameters on crosslink density are reported. Thermomechanical properties are highly tunable, including glass transitions tailorable between 30 and 105°C and rubbery moduli tailorable between 0.4 and 20 MPa. This new SMP system exhibits high toughness for many formulations, especially in the case of low crosslink density materials, for which toughness exceeds 90 MJ/m3 at select straining temperatures. To demonstrate the advanced processing capability and synthetic versatility of this new SMP system, a laser-actuated SMP microgripper device for minimally invasive delivery of endovascular devices is fabricated, shown to exhibit an average gripping force of 1.43 ± 0.37 N and successfully deployed in an in vitro experimental setup under simulated physiological conditions.

3D printing of shape memory poly(d,l‐lactide‐co‐trimethylene carbonate) by direct ink writing for shape‐changing structures

“…The 4D shape‐changing behavior was achieved by deforming it in a small‐sized temporary shape in advance. Once triggered by an external stimulus such as water bath or infrared diode laser, the structure could recover and show self‐expanding behavior, as illustrated in Figure (d).…”

Influence of the soft segment nature on the thermomechanical behavior of shape memory polyurethanes

“…Among them, shape memory polyurethanes (SMPUs) have been widely studied as thermal‐induced shape memory polymers . By modifying their chemical composition, thermomechanical properties of SMPUs can be triggered for promising applications in biomedicine, automotive, aerospace, and also in textile sector .…”

4D Printing of Shape Memory‐Based Personalized Endoluminal Medical Devices

“…This stent is thermally actuated and in vitro we accomplish this with heating the stent in a custom thermal chamber. Other in vitro methods that have been demonstrated to actuate endoluminal devices use an infrared diode laser or resistive heating . The most elegant approach, based on patient safety and efficacy, is Curie‐regulated inductive heating, which requires a ferromagnetic filler phase .…”

“…For that reason, while SMPs have generated much academic interest, engineering them in clinically useful form factors for biomedical devices has been challenging. Though multiple studies have reported proofs‐of‐concept for several thermally induced SMP devices, such as catheters, microgrippers, vascular stents, aneurysmal foams, orthodontic wires, and surgical sutures, the processing methods utilized to fabricate these devices were ad hoc and/or were used to obtain structures that are characterized by simple geometries. Melt stereolithography (SLA), in contrast, generates a 3D structure by sequentially UV polymerizing via a free radical mechanism molten (meth)acrylated resin, layer‐by‐layer.…”