Mechanical characterization of materials for the manufacture of microvessel-mimicking phantoms

Microvascular phantoms are promising tools employable in simulations of realistic surgical scenarios for the development of surgical experience. Being free of ethical issues and customizable to patient-specific anatomies, they represent optimal alternatives to animal and cadaver training and a good solution for preoperative planning. Nevertheless, the adoption and the effectiveness of these simulations heavily relies on the ability of the phantoms to accurately mimic the biomechanical properties of human blood vasculature. In order to achieve this goal, available manufacturing technologies are successfully used to produce phantoms with reduced thickness, but with the limitation of resembling only a limited range of real conditions due to manufacturing methods constraints. This research thesis focuses on materials suitable for the production of microvascular phantoms through different manufacturing techniques and their mechanical characterization. Materials and manufacturing methods, with new potential applicability to the field, have been evaluated and selected. In particular, materials resembling human vessels characteristics have been employed for traditional and additive manufacturing methods. Standardized tests have then been performed on the materials, including shore hardness tests, uniaxial tensile tests and needle-insertion tests. The mechanical properties of the selected materials have been assessed and compared to those of human blood vessels. The results showed the significant impact of the manufacturing process on the mechanical characteristics of the materials. For the additive manufacturing methods, samples were produced with different printing directions and assessed. A sub-selection of materials demonstrated suitable characteristics with respect to biological samples: seven materials presented hardness shore inferior to 10A; six showed tensile strength between 1MPa and 6MPa and an elongation at break between 60% and 290%; eleven materials resulted in an elastic modulus of 0.3-3.5 MPa; of the materials tested also with needle-puncturing, four presented a realistic needle-insertion force of 1- 10 N. The best vasculature-mimicking material was the commercially available DragonSkin 10 fast (Smooth-On Inc., Macungie, USA), with hardness Shore A 13.62 ± 0.57, tensile strength 1.07 ± 0.04 MPa, elongation at break 221.39 ± 10.99 %, elastic modulus 221.39 ± 10.99 MPa and needle-puncturing force 14.70 ± 1.81 N. Prospectively, employing silicones with these characteristics with additive manufacturing methods holds great potential. The research highlights the need for continued investigation into the development of advanced materials and fabrication techniques for improved phantom production.