Comparative Analysis of Promising Hydrophobic Polymers for Biomedical Applications: Mechanical Properties and Susceptibility to Lipid-Induced Plasticization

Recent advances in biocompatible elastomeric polymers have expanded the design possibilities for long-term implantable medical devices, yet systematic comparison across relevant candidate families remain limited. Herein, we present a comparative evaluation of four promising biomedical elastomers: a siloxane-based polyurethane (Si–PU), a polyisobutylene-based polyurethane (PIB–PU), cross-linked poly(styrene- block -isobutylene- block -styrene) (xSIBS), and poly(styrene-ethylene-butylene-styrene) (SEBS). Tensile mechanical properties, viscoelastic relaxation, creep behavior, fracture toughness, thrombogenicity, and lipid-induced property deterioration were assessed to elucidate structure–property relationships relevant to blood-contacting applications. Marked differences in stiffness, deformation kinetics, and fracture energy were observed across the materials, reflecting variations in segmental chemistry, phase morphology, and network connectivity. For example, the styrene-dominant SEBS demonstrated greater stiffness than the urethane-dominant PIB–PU (65.70 MPa ± 12.63 MPa vs 8.13 MPa ± 0.36 MPa), while simultaneously demonstrating lower fracture toughness (10.89 kJ/m 2 ± 1.55 kJ/m 2 vs 50.39 kJ/m 2 ± 5.32 kJ/m 2 ). Following lipid immersion, Si–PU, PIB–PU, and xSIBS demonstrated measurable swelling (1.86 ± 0.08, 1.25 ± 0.00, and 1.07 ± 0.03, respectively) and mechanical softening (e.g., a 32.29% ± 6.13% toughness decrease for Si–PU) while SEBS remained unaffected. Lipid susceptibility increased in the order SEBS → xSIBS → PIB–PU → Si–PU, with mechanical responses theorized to be a result of lipid-mediated plasticization disrupting intermolecular domains. Collectively, these findings establish a preliminary framework linking molecular composition and viscoelastic behavior to environmental susceptibility, highlighting critical trade-offs in the design of implantable medical devices.