Towards the development of a shape memory polymer for individualized endovascular therapy of intracranial aneurysms using a 3D-printing/leaching method

Abstract

Endovascular treatment of intracranial aneurysms (ICA) aims to occlude the aneurysm space for preventing ICA growth/rupture. Modern endovascular techniques are still limited by lower complete occlusion rates, frequently leading to aneurysm growth, rupture and re-operation. In this work, we propose shape memory polymer (SMP)-based embolic devices that could advance the effectiveness of ICA therapy by facilitated individualized ICA occlusion. Specifically, we develop an 3D-printing/leaching method for the fabrication of 3D-SMP devices that can be tailored to patient-specific aneurysm geometries that are obtained from computed tomography angiography. We demonstrate that this method allows the fabrication of highly porous, compressible foams with unique shape memory properties and customizable microstructure. In addition, the SMP foams exhibit great shape recovery, anisotropic mechanical properties, and the capability to occlude in-vitro models with individualized geometries. Collectively, this study indicates that the proposed method will have the potential to advance the translation of coil- and stent-free embolic devices for individualized treatment of saccular ICAs, targeting complete and long-term durable aneurysm occlusion.

Keywords: 3D printing; biomaterials; endovascular therapy; patient-specific; shape memory polymers.

Figure 1:

(a) Schematics showing the steps for the fabrication of SMP foams using templates 3D printed with polyvinyl alcohol (PVA) (see Section 1). (b) Pipeline for the production of individualized PVA templates and phantoms obtained from patient’s CTA imaging. The white arrow indicates the parent vessel, which has a diameter of 2.45 mm. (The 3D model was enlarged twofold.)

Figure 2:

Photographs and SEM micrographs of the 3DSMP foams from the (a) top view and (b) side view.

Figure 3:

(a) SEM micrographs of PVA templates (top) and 3DSMP foams (bottom) at different infill densities (columns). (b) Measurements of the wall thickness between the PVA templates and 3DSMP foams.

Figure 4:

(a) Experimental $T_g$ measurements of the solid SMP and 3DSMP. (b) $T_g$ exponential models (i.e., as a function of TEA molar ratio) used to predict the TEA content of 3DSMP foams with $T_g\approx {41}^{\circ }\mathrm{C}$.

Figure 5:

(a) FTIR spectra of solid SMP and 3DSMP of the SMP-X ratio. (b) Zoomed spectra showing the altered urethane chemistry of the 3DSMP foams due to the 3D-printing & PVA-leaching process.

Figure 6:

(a) Representative compressive stress-strain curves of the 3DSMP foams at different infill densities, and (b) derived mechanical parameters: peak stress, CSR, and elastic modulus.

Figure 7:

Shape recovery properties of the 3DSMP foams: Shape storage at (a) room temperature $\left(T={23}^{°}\mathrm{C}\right)$ and (b) $T=-{20}^{°}\mathrm{C}$. (c) Shape recovery triggering using a heating ramp at $T=T_g+{10}^{°}\mathrm{C}$.

Figure 8:

Proof-of-concept demonstration of the occlusion of aneurysm phantoms with patient-specific geometries using 3DSMP foams. Aneurysm geometries were enlarged threefold from original CTA imaging to facilitate delivery of the foam.