Influence of electro-polishing characteristics on needle-tissue interaction forces

Abstract

The electro-polishing process was applied to stainless steel 304 with the aim of improving its surface texture. The electrolyte was a mixture of H₂O, H₂SO₄ (98%) and H₃PO₄ (85%) at a volume ratio of 2:3:5. Gravimetric analysis and stylus profilometry were used to analyze the samples. It was observed that the material removed during the electro-polishing process could be controlled to an error limit of 6%. The surfaces obtained showed improved cleanness and reduced surface roughness (Ra). Hypodermic needles were then electro-polished using the same parameters with the aim of reducing forces during needle insertion into tissue. The needle tips were analyzed using a SEM. The needles were tested using silicone phantoms as a tissue substitute. The forces during insertion were less for all the electro-polished needles, with the most consistent results obtained at a current density of 0.66 A/cm². A theoretical model of the needle insertion forces at different insertion depths was developed.