Biofunctional surface modification of duplex stainless steel using powder-mixed electrical discharge machining: In-vitro cytotoxicity and hemolysis evaluation

Duplex stainless steel (DSS) possesses favorable mechanical and corrosion-resistant properties; however, its limited surface biofunctionality restricts its application in biomedical environments. Moreover, the biological performance of powder-mixed electrical discharge machining (PMEDM)-modified DSS surfaces remains insufficiently explored. This study investigates the effect of multi-walled carbon nanotubes (MWCNTs) and μ-hydroxyapatite (μHAp) mixed dielectrics on surface modification and biocompatibility of DSS. Experiments were designed using a Taguchi L18 orthogonal array by varying peak current, pulse duration, dielectric composition, polarity, and electrode material. The modified surfaces were evaluated through in-vitro cytotoxicity (MG-63 and MCF-7 cell lines) and hemolysis tests. The results indicate that dielectric composition, peak current, and electrode material significantly affect biological responses. The optimal condition, achieved at 10 A using a copper-tungsten electrode with a dielectric containing 75% MWCNTs and 25% μHAp, exhibited maximum cell viability (~97.9%) and minimum hemolysis (~9.84%). Surface morphology revealed a porous structure, while X-ray diffraction (XRD) analysis confirmed the formation of bioactive oxide and carbide phases. The findings demonstrate that MWCNT-enriched PMEDM is an effective approach for improving DSS surface biofunctionality for potential biomedical applications.