The Clinical Context
Endovascular Aneurysm Repair (EVAR) is a minimally invasive procedure to treat aortic aneurysms. Surgeons navigate a stent-graft through the femoral artery to the aorta, guided by imaging alone. The procedure demands high tactile precision: the surgeon must feel the compliance of the aortic wall to correctly position and deploy the stent without rupture.
Training simulators for EVAR exist, but most use silicone or latex vessels with mechanical properties that poorly match real aortic tissue. The goal of this project was to design a bio-mimetic aortic wall that replicates the mechanical compliance of human tissue, to be integrated into a full EVAR training simulator developed by a PhD researcher at LMPS.
The Design Approach
The key insight was that aortic tissue compliance cannot be replicated by a homogeneous material alone. Human aortic walls have a layered, anisotropic structure, stiffer in the circumferential direction and more compliant in the longitudinal direction, due to the organization of elastin and collagen fibers.
My approach was to design a parametric woven mesostructure: a repeating geometric lattice pattern, printed in a bi-material combination, that mimics this anisotropy at the structural level rather than relying on bulk material properties alone.
Simulation and Validation
The mesostructure geometry was modeled in SolidWorks as a fully parametric design, with pitch, strand width, and interlocking angle all adjustable independently to tune the effective stiffness.
FEA simulation in COMSOL modeled Von Mises stress and deformation under physiological blood pressure loads. The simulation confirmed that the woven architecture distributes stress more uniformly than a solid wall, reducing peak stress concentrations at the simulated vessel boundary conditions.
Material Calibration
The physical validation used a Stratasys PolyJet printer with a bi-material approach: VeroRigid for the structural strands and AgilusBlack for the compliant matrix. Calibration prints were fabricated to characterize the printer's resolution at 0.3 mm (the minimum feature size) and determine the optimal material ratio.
The fabricated samples demonstrated that the mesostructure can be reliably printed at the target resolution, validating the manufacturing feasibility of the design. Integration into the full EVAR simulator and in-vitro pressure testing remain as next steps.