Experimental study of TPU and SEBS additively manufactured leaflets for novel aortic valve polymer TAVI prosthesis

Background and Objective Transcatheter valve implantation is a cutting-edge technology for high and low risk patients with aortic stenosis. Bioprosthetic valves are limited due to several disadvantages as a long-term durability and structural valve degeneration. Polymeric aortic valve leaflet devices represent state-of-the-art technology to overcome limitations of bioprostheses. Nevertheless, more recent biocompatible and biostable polymers have revealed a significant potential. Additionally, 3D additive manufacturing opens new paths for patient-specific design of biomedical implants. Flexible polymers may not only mimic native aortic valve, but also may improve long-term durability. Polyurethanes and styrene polymers are promising materials for modern polymer valves. Nevertheless, mechanical properties of additive manufactured TPU or SEBS leaflets are not properly studied. Methods Experimental study of TPU and SEBS samples and aortic valve leaflets for novel aortic valve polymer TAVI prosthesis is presented. Tensile tests and compression tests of three types of FDM-printed samples with various filament alignments (axial alignment, transversal alignment, diagonal alignment) were performed. The results of tests confirmed that longitudinal axial alignment achieve a maximum stress compared to transversal and diagonal directions. Compressive tests of TPU and SEBS 3D-manufactured aortic valve leaflets with digital image correlation technology were performed. Young’s modulus and Poisson’s ratio were evaluated. Moreover, parameters of constitutive models were found. Results The TPU tensile specimen exhibits the highest stress/strain values at a speed of 100 mm/min, regardless of the filament alignment pattern. Slightly lower results are observed at a speed of 50 mm/min, which is likely associated with a wide range of plastic deformation. In the case of SEBS, a different pattern is observed: at 500 mm/min, it demonstrates high resistance to fracture, unlike TPU. A comparison of TPU and SEBS specimens at the same speeds and with the same alignment, based on maximum stress values, shows a minimal difference of 4% with the axial alignment at a speed of 50 mm/min; however, when comparing strains, the difference increases to 90%. The results of the compression experiment on aortic valve specimens made of TPU and SEBS at a speed of 30 mm/min showed that TPU force values for is considerably lower (4% of the maximum case), while for SEBS the spread increases to 20% of the maximum case. Conclusion SEBS aortic valve leaflets were shown to be stiffer than TPU. It can be a step for choice of stiffer/softer leaflets for patient-specific device. The proposed approach can help manufacturers in elaboration and manufacturing of new TAVI polymer devices design made of TPU and SEBS polymers for clinical applications.