Mechanical Properties of 3D Voxel-Printed Materials for Cardiovascular Tissue Imitation

Joël Illi¹Manuel Bergamin¹Marc Ilic¹Anselm Walter Stark¹Stefan Bracher²Martin Hofmann³Juergen Burger³Isaac Shiri¹Andreas Haeberlin^1,2,4Christoph Gräni^1,4*

• ¹Department of Cardiology, University Hospital Bern, Bern, Switzerland
• ²ARTORG Center for Biomedical Engineering Research, Faculty of Medicine, University of Bern, Bern, Bern, Switzerland
• ³School for Biomedical and Precision Engineering, University of Bern, Bern, Bern, Switzerland
• ⁴Translational Imaging Center, Sitem Center, University of Bern, Bern, Bern, Switzerland

Background: Cardiovascular patient-specific phantoms can improve patient care through testing and simulation. However, materials like silicone and 3D-printing polymers differ mechanically from biological tissues. Agilus30Clear, the primary material for 3D-printed phantoms, is much stiffer, nearly isotropic, and lacks strain hardening behaviour. To overcome these challenges, novel 3D voxel-printing approach could potentially address these limitations.Methods/Aim: This study aimed to explore the applicability of 3D voxel-printing and assess how different parameters (strand structure, density, orientation) affect mechanical properties and comparing them to established phantom materials and porcine cardiovascular tissues.Progressive uniaxial cyclic tension tests were performed across 9 stages, varying strain rates and target strain levels, with elastic modulus calculated for comparison. The goal was to stepwise assess, whether the overall material stiffness can be reduced, achieving anisotropy, and replicating strain hardening behaviour.Results: In the first step, varying the strand density the tested samples showed a 0-60% strain modulus of elasticity of 0.215 to 0.278 N/mm 2 , representing a 4-5 fold reduction in elastic modulus in that range, compared to the base material Agilus30Clear. In the second step, varying the orientation of the structures a significant influence on the elastic moduli was measured. The 0-60% modulus of elasticity dropped to 0.161-0.192 N/mm 2 , displaying anisotropic material behaviour. In the third step, two strand structures specifically designed to mimic fibre recruitment were tested. These resulted in slightly flatter (more linear) stress-strain curves compared to the non-linear strain-softening behaviour observed in Agilus30Clear. However, they still fell short of replicating the desired non-linear strain-hardening behaviour characteristic of fibre recruitment in cardiovascular tissuesIn the third step, the two strand structures specifically designed to mimic fibre recruitment were tested, which lead to slightly flatter (linear) stress-strain curves, when compared to the Agilus30Clears non-linear strain softening curves, but far from the desired non-linear strain hardening behaviour, of the fibre recruitment in cardiovascular tissues.The novel 3D voxel-printing material approach resulted in reduced elastic modulus, anisotropic behaviour, and strain hardening, providing a much closer representation of the mechanical behaviour of porcine cardiovascular tissues compared to other available