[Preparation and physicochemical properties of nano-silver acupuncture needles]

To explore the preparation of nano-silver acupuncture needles and evaluate the appearance, structure and properties.

Stainless steel acupuncture needles were pretreated by polishing with sandpaper and cleaning with ultrapure water and absolute ethanol. As the working electrodes, the needles were placed in an electrolyte solution contained silver nitrate (AgNO₃), potassium nitrate (KNO₃), and polyvinylpyrrolidone (PVP); and the silver nanoparticles were deposited at a constant voltage of -0.2 V for 1 200 s. The heat-treatment was conducted at 600 ℃ for 15 min in an argon atmosphere to strengthen the adhesion between the nanoparticles and the substrate. The surface appearance and structure of nano-silver acupuncture needles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrical conductivity, thermal conductivity and biocompatibility of the needles were evaluated. The cytotoxicity and biocompatibility of the sample were assessed using the CCK-8 assay. According to the national standard, Acupuncture Needles (GB 2024-2016), the other physicochemical performances of nano-silver acupuncture needles were tested.

①By controlling the AgNO₃ concentration and the molar ratio of AgNO₃ to PVP, it was found that at an AgNO₃ concentration of 2 mmol/L and a molar ratio of 5∶1, silver nanoparticles with the diameter of 50-100 nm, regular appearance, and uniform distribution were obtained. At a lower concentration, the size of silver nanoparticles was smaller and unevenly distributed particles, whereas a higher concentration tended to produce a dendritic structure. ②By sandpaper polishing, acid etching pretreatment, and heat-treatment at 600 ℃ under argon for 15 min, the adhesion of silver nanoparticles on the surface of the needle body was strengthened, and the simulated pig skin puncture test showed the intact coating without shedding. ③SEM found that the silver nanoparticles were uniformly deposited, forming a nanofilm approximately 1.5 μm thick; XRD analysis showed the diffraction peaks corresponding to cubic crystal silver (111), (200), (220) and (311); and XPS detected characteristic peaks of Ag 3d3/2 and Ag 3d5/2, confirming the successful deposition and good crystallinity of the silver nanoparticles. ④Resistivity measurements indicated that the nano-silver acupuncture needles exhibited a resistivity of approximately 0.15 Ω·cm, about three times lower than that of unmodified stainless steel needles. The infrared thermography demonstrated that their thermal conductivity was superior to that of traditional acupuncture needles. In vitro CCK-8 cytotoxicity assay showed that the nano-silver acupuncture needles had no adverse effects on human skin fibroblasts and possessed good biocompatibility. ⑤ The key parameters such as needle tip performance, hardness, and the adhesion between the needle body and handle were in compliance with the requirements in Acupuncture Needles (GB 2024-2016), ensuring a quality guarantee provided for clinical applications.

The preparation of nano-silver acupuncture needles effectively overcomes the insufficient toughness of traditional silver needles and improves the electrical and thermal conductivity of stainless acupuncture needles.