Experimental investigation on additively manufactured polymeric hybrid auxetic tubes for biomedical applications

Purpose Polymeric auxetic metamaterials have shown immense progress in their application as bioresorbable stents in the biomedical sector because of their superior mechanical and biocompatible properties. This paper aims to propose the implementation of novel hybrid auxetic structure in cylindrical stent prototypes. The proposed design is characterized by uniaxial tensile testing of standard specimens, axial and radial compression and three-point bending tests. The test outcomes made them suitable for stent fabrication in biomedical applications. Design/methodology/approach This research paper focuses on fabricating biodegradable hybrid auxetic tubes of transparent PLA and white PLA Pro+ by Fused Filament Fabrication (FFF). This novel polymeric hybrid auxetic tube (PHAT) design comprises re-entrant, hexagonal, meta-chiral auxetic unit cells. They are repeatedly arranged in a planar structure, rolled to form the cylindrical tube. Their deformation mechanisms are studied through experimental tests for stent applications. Findings The deformation pattern showcases half-wave and full-wave transformations on ligaments caused by anti-chiral and chiral circular nodes rotation, resulting in auxetic behavior due to Negative Poisson Ratio (NPR). The load displacement curves are plotted to evaluate axial, radial and bending stiffness as a measure of buckling resistance, crush resistance and bending flexibility to determine their suitability for stent applications. The axial foreshortening, radial recoil and dogboning rate are calculated to confirm their feasibility through the experimental test results. Originality/value The NPR values attained are −2.25 and −3.43 for transparent and white PLA Pro+ specimens, respectively. The axial stiffness of 166.18 N/mm and 105.96 N/mm, radial stiffness of 33.75 N/mm and 28.86 N/mm, bending stiffness value of 14.31 N.mm2 and 18.89 N.mm2 and bending flexibility of 69.93 × 10–3 1/N.mm2 and 52.94 × 10–3 1/N.mm2 are found for transparent PLA and white PLA Pro+, respectively. The foreshortening effects of 0.57% and 0.64%, radial recoil of 4.12% and 3.64% and dogboning effects of 9.67% and 10.56% are observed from experimental results.