Material extrusion 3D-printing of thermoplastic polyurethane-based small diameter vascular grafts: Tunable compliance design with varying shore hardness

Fabrication of small-diameter vascular grafts (SDVGs) remains a significant clinical challenge because currently available synthetic grafts exhibit poor long-term patency due to thrombosis, intimal hyperplasia, insufficient endothelialization, and compliance mismatch with native vessels. Thermoplastic polyurethane (TPU) offers tunable elasticity and processability, but the relationship between Shore hardness, printability, and vascular compliance remains insufficiently understood for material extrusion (MEX)-based fabrication. In this study, we systematically investigated the mechanical properties and printability of four commercially available TPU grades (60 A, 70 A, 82 A, and 95 A) using MEX 3D printing, specifically fused filament fabrication (FFF). Printing parameters were optimized to minimize under-extrusion and surface defects. Tensile testing and digital image correlation (DIC) were used to determine Young’s modulus, ultimate tensile stress, and Poisson’s ratio, which were subsequently used to estimate graft compliance. Lower Shore hardness TPU demonstrated substantially higher compliance, with TPU 60 A achieving compliance of 2.35 ± 0.10%/100 mmHg for a 4 mm inner diameter graft, closely matching native saphenous vein. A compliance design chart was developed to assist in selecting appropriate wall thickness across various graft diameters. The study further highlights the trade-off between enhanced biomimetic compliance and reduced printability associated with softer TPU grades. These findings demonstrate the feasibility of fabricating mechanically compatible TPU-based SDVGs using accessible FFF platforms and provide a practical framework for compliance-tailored vascular graft design.