TAVI-Mimic for testing of heart valve leaflet materials in physiological loading situations

Abstract

The loading situation of the aortic valve is complex, complicating the identification of innovative approaches for heart valve leaflet materials, e.g. for transcatheter aortic valve implantation (TAVI). Materials engineering experiments allow for screening of materials but especially for durability testing, the consideration of physiological loads is vital/critical for the suitability-assessment of innovative leaflet materials. For this reason, a framework structure for the testing of leaflet materials in physiological loading (TAVI-Mimic) was developed. The exemplary use case for the TAVI-Mimic was a test for calcification propensity of pericardium during durability testing. The TAVI-Mimic was designed as a fourparted frame, based on previous work of our group. The leaflet material can be attached between inner and outer shells without sewing. In a second step, the TAVI-Mimic was optimized regarding radial load-deformation in comparison to a commercial TAVI by means of finite element analysis (FEA) and hydrodynamic characterization in a pulse duplicator system. Mechanical properties dependent on water uptake of different materials for 3D-printing of the TAVI-Mimic were investigated. After optimization, TAVI-Mimics were equipped with glutaraldehyde-fixated pericardial tissue and prototypes were calcified by using a heart valve durability tester and a metastable calcification-liquid, developed in earlier studies. The development of the TAVI-Mimic using FEA and experiments was successful, leading to a radial load dependent deformation of 0.6 mm which correlates with commercial TAVI. Two methacrylic photopolymers were identified for 3D-printing of the TAVI-Mimic and prototypes attached with pericardial tissue were manufactured. Pericardium TAVI-Mimics were calcified in vitro for one week and an average calciumphosphate precipitate of 0.34- 0.54 mg/cm² was measured. The optimization of the TAVR-Mimic led to an improved load-dependent behaviour compared to a commercial prosthesis while testing. The calcification method, combining the TAVI-Mimic, the metastable calcification solution and the durability tester enabled a successfully calcification of pericardial tissue, approaching the in vivo situation.

Keywords

• finite element analysis
• transcatheter aortic valve implantation
• calcification tendency