Biocompatibility—the ability of a material to perform its intended function without causing undesirable local or systemic host responses—is a critical challenge for long-term biomedical sensors. It depends on chemical composition, surface morphology, and physical properties. Implantable materials must be non-toxic, non-allergenic, non-irritating, non-genotoxic, and non-carcinogenic, with no adverse effects on tissues, blood, or the immune system.