Novel design of tubular metamaterials with sign-switchable Poisson's ratio and tunable mechanical properties for intestinal stents.

Introduction: Current intestinal stents used to restore patency face limitations due to the rigidity of metal structures and the premature degradation of biopolymer alternatives. Therefore, there is a critical need to develop stents that are flexible, radially strong, and able to adapt to the dynamic conditions within the body. Methods: This study introduces a novel tubular mechanical metamaterial featuring a sign-switchable Poisson's ratio and tunable mechanical properties, achieved by integrating hexagonal unit cells with positive Poisson's ratio and re-entrant unit cells with negative Poisson's ratio. Experimental uniaxial compression tests and finite element analyses were performed to validate the proposed design and assess its mechanical performance. Results: The structure exhibits a negative Poisson's ratio under tensile loading across all configurations, whereas under compression, the Poisson's ratio was transited from negative to positive due to self-contact between triangular struts, enabling the distinctive sign-switching behavior. Experimental uniaxial compression tests and finite element analyses were performed to validate the proposed design and assess its mechanical performance. Results reveal that the geometric gap between the horizontal struts in the concave unit cells serves as a crucial tuning parameter: increasing this gap delays the onset of sign-switching during compression while exerting minimal influence on the tensile response. The stiffness, yield strength, and energy absorption capacity are shown to be highly adjustable through this geometric control. Discussion: Overall, the metamaterial demonstrates superior energy absorption and tunable stiffness, making it a promising candidate for applications in intestinal stents.