Surface and elemental analysis of stainless-steel needles after invasive physiotherapy: an exploratory scanning...

This study evaluated the safety and chemical variations of stainless-steel needles during human tissue application using four electrical stimulation modalities: high-intensity and low-intensity direct current, microcurrents, and compensated biphasic waves. Structural changes and surface integrity of three needle types were also analyzed via SEM. Surface analysis was performed on Type_A, Type_B, and Type_C needles (n = 120) following dry needling interventions on 48 participants using four distinct electrical protocols. SEM evaluation identified carbon, oxygen, chromium, iron, nickel, silicon, manganese, and aluminum across all needles. MANOVA showed that needle type (p < 0.001) and electrical current (p < 0.001) significantly influenced surface composition. A systematic reduction in silicon occurred post-intervention (p < 0.001), while nickel content remained stable (6.1%-7.7%). Qualitatively, Type_A exhibited the most structural irregularities, while percutaneous electrical nerve stimulation caused the greatest organic matter accumulation. These findings indicate that invasive electrotherapy significantly alters the surface elemental composition and morphology of stainless-steel needles, notably through systematic silicon loss. While these changes indicate material loss during procedures, further tissue analysis is required to determine clinical relevance. SEM revealed that Type_A needles developed more surface scratches, whereas Type_B and Type_C accumulated substantial organic matter post-intervention.