4D Printed Bifurcated Stents with Kirigami-Inspired Structures

Summary

Using a 3D printer, a shape memory polymer filament is extruded to form a branched tubular structure. The structure is patterned and shaped such that it can contract into a compact form once folded and then return to its formed shape when heated.

Abstract

Branched vessels, typically in the form of the letter "Y," can be narrowed or blocked, resulting in serious health problems. Bifurcated stents, which are hollow in the interior and exteriorly shaped to the branched vessels, surgically inserted inside the branched vessels, act as a supporting structure so that bodily fluids can freely travel through the interior of the stents without being obstructed by the narrowed or blocked vessels. For a bifurcated stent to be deployed at the target site, it needs to be injected inside the vessel and travel within the vessel to reach the target site. The diameter of the vessel is much smaller than the bounding sphere of the bifurcated stent; thus, a technique is required so that the bifurcated stent remains small enough to travel through the vessel and expands at the targeted branched vessel. These two conflicting conditions, that is, small enough to pass through and large enough to structurally support narrowed passages, are extremely difficult to satisfy simultaneously. We use two techniques to fulfill the above requirements. First, on the material side, a shape memory polymer (SMP) is used to self-initiate shape changes from small to large, that is, being small when inserted and becoming large at the target site. Second, on the design side, a kirigami pattern is used to fold the branching tubes into a single tube with a smaller diameter. The presented techniques can be used to engineer structures that can be compacted during transportation and return to their functionally adept shape when activated. Although our work is targeted on medical stents, biocompatibility issues need to be solved before actual clinical use.

Introduction

Stents are used to widen narrowed or stenosed passages in humans, such as blood vessels and airways. Stents are tubular structures that resemble the passages and mechanically support the passages from further collapsing. Typically, self-expanding metal stents (SEMS) are widely adopted. These stents are made from alloys composed of cobalt-chromium (stainless-steel) and nickel-titanium (nitinol)^1,2. The downside of metal stents is that pressure necrosis can exist where the metal wires of the stent come into contact with the live tissues and the stents are impacted. Furthermore, the vessels of the body can be irr....

Protocol

1. Blood vessel mock-up design for the demonstration

1. Set the diameter of the proximal main vessel to 25 mm, the diameters of the distal main vessel and the side branch equal to 22 mm. Set the total length of the vessels equal to 140 mm. Set the length of the proximal main vessel, the distal main vessel and the side branch to 65 mm, 75 mm and 65 mm, respectively. The complete blood vessel is shown in Figure 2 and Figure 3.
2. Print the computer model of the branched vessel by using an FDM 3D printer. Use a polycarbonate filament.

2. Blood vessel mock-up fabri....

Results

In this protocol, we showed the procedures required to fabricate a bifurcated stent. The stent uses a kirigami structure to allow the bifurcated stent to fold into a compact cylindrical tube, which is very suitable for sliding through the narrow pathways of blood vessels. The SMP allows the folded structure to return to its original shape when the temperature reaches the glass transition temperature. The original shape, 3D printed using the SMP material, closely matches the branched vessels. In other words, the interior .......

Discussion

Stents are often used to clear the clogged internal pathways such as the blood vessels and airways of patients. Surgical operation of inserting stents requires the careful consideration of the patient’s illness and human anatomical characteristics. The shape of the vessel is complex, and diverse branching conditions exist. However, the standard stent operational procedures are based on mass-produced stents with standard sizes. In this protocol, we showed how to personally tailor the fabrication of the stent based o.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Fortus380mc	Stratasys	Fortus 380mc	FDM 3D printer for printing blood vessel mock-up
Moment1 3D printer	Moment	Moment 1	FDM 3D printer for printing bifurcated stent
PC(white) Filament Canister	Stratasys	PC(white) Filament Canister	PC filament for printing blood vessel mock-up
PLM software NX 10.0	Siemens	NX 10.0	3D CAD modeling software
Sandpaper	DAESUNG	CC-600CW	Smooting out the surface of the bifurcated stent
Shape Memory Polymer filament	SMP Technologies Inc	MM-5520	Shape memory polymer filament
silicon	Shinetus	KE-1606	silicon for blood vessel mock-up
Simplify3D	Simplify3D	Simplify3D 4.0.1	Slicing software for model slicing