Electroacupuncture is a combination of acupuncture from oriental medicine and low-frequency (1–1,000 Hz) stimulation, which is a type of physical therapy used in western medicine. Low-frequency stimulation was first proposed in 1816 by Louis Berlioz of France, who suggested that electrical stimulation combined with acupuncture treatment could enhance the effectiveness of the treatment. Later, in 1825, Sarlandiere used this technique to treat gout and neurological diseases, and he published a report in which he referred to the technique as “galvanopuncture,” from which the term electroacupuncture is derived [
Among the metal wires that are commercially available, we selected phosphor bronze (hereafter referred to as PB) and Ni-coated SS 304 (hereafter referred to as SS 304 Ni), which both have superior electrical conductivity as compared to SS 304, which is currently used for electro acupuncture, along with titanium alloy (Ti-6-Al-4V) and SS 316, which have relatively low electrical conductivity but were expected to demonstrate superior stability. Due to the circumstances involved in purchasing, a thickness of 0.25 mm was used for PB and 0.2 mm for Ti-6-Al-4V, and thicknesses of 0.2, 0.25, and 0.3 mm were used for SS 304 Ni and SS 316. All materials were purchased from a company (KOS, Korea) specializing in metal wire.
MTT (3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2H-tetrazolium bromide) assay and cytotoxicity testing were performed in order to assess the biocompatibility of the experimental material. The procedure for each experiment conducted was as follows.
The cytotoxicity test of ISO 10993-5 for assessment of the cytotoxic potential of a test element (medical device) after direct contact was used as the assay standard. The procedure composed with cell seeding, contact of the test element, incubation for more than 24 hours, preparation of the coloring solution of revelation, revelation of cytotoxicity, reading.
The wires were segmented into 10 mm sections, and 40 sections were added to 3 mL of Dulbecco’s Modified Eagle’s Medium: nutrient mixture F-12 (DMEM/F-12, GIBCO). Extraction was performed at 37°C for 48 hours. The assignment of experimental and control groups was as follows (Table
Allocation of experimental group and control group.
No. | Wire | Assignment |
---|---|---|
(1) | Ti-6-Al-4V 0.20 mm | Experimental group |
(2) | Phosphor bronze 0.25 mm | Experimental group |
(3) | SS 304 Ni 20 mm | Experimental group |
(4) | SS 304 Ni 25 mm | Experimental group |
(5) | SS 304 Ni 30 mm | Experimental group |
(6) | SS 316 0.20 | Experimental group |
(7) | SS 316 0.25 | Experimental group |
(8) | SS 316 0.30 | Experimental group |
(9) | DMEM/F-12 | Control group |
Mouse osteoblast (MC3T3 cell) was cultured for 24 hours with DMEM/F-12 (5% FBS, penicillin-streptomycin added). It was inspected for contamination before use. Media of sufficiently grown cells were removed, and media extracts of the experimental group and the control group were cultured separately for 24 hours. The media were then added to a plate with formazan crystal. After the formazan had dissolved, a Dymatech MRX ELISA microplate reader (Dynatech laboratories, Chantilly, VA, USA) was used to measure the absorbance at 540 nm. The average of 3 measurements was used to calculate the percentage of cell solubility. The result of the control group was used as the negative control.
The conditions for extraction and cell culture were performed as in an MTT assay. The cultured cells were stained with 0.3% crystal violet, and a stereoscopic microscope (Leica microsystem DE/EZ4) was used to compare their viability.
We prepared 5 cm of wire for each type. In order to consider body fluid conditions, 1 cm of each wire was dipped separately into 50 mL of Hank’s solution (Table
Chemical composition of Hank’s solution.
Component | Concentration (mol dm−3) |
---|---|
NaCl | 137.0 |
KCl | 5.4 |
Na2HPO4 | 0.25 |
KH2PO4 | 0.44 |
CaCl2 | 1.3 |
MgSO4 | 1.0 |
NaHCO3 | 4.2 |
A stereoscopic microscope (SMZ 1500, Nikon, Japan) and scanning electron microscope (SEM) were used to observe corrosion. The stereoscopic microscope was used to observe changes in color and shape, and SEM was used to observe surface changes due to corrosion.
Wires selected for corrosion stability and biocompatibility were evaluated for travel speed and straightness with respect to thermal treatment conditions, and tensile strength was calculated with respect to the evaluated straight line. For the evaluation of straightness, the gap length was defined as the deviation from a reference line at a distance of 100 mm, to measure the extent of bending. The tensile strength was calculated by dividing the maximum tensile load before material breakdown by that of an original cross-sectional area of the sample.
Ti-6Al-4V is a Ti alloy with excellent biocompatibility that is used as a material for dental implants. Its electrical conductivity, however, is low, at 1.01% (IACS—International Annealed Copper Standard), and it is also expensive. SS 304 Ni is an existing SS 304 wire that is coated with Ni, whose high electrical conductivity, at 25% (IACS), improves the wire’s conductivity. It is expected that this higher electrical conductivity can improve the effectiveness of electro acupuncture. SS 316 is the most commonly used stainless steel, along with SS 314. Compared to SS 314, SS 316 has a lower Cr- and a higher Ni-content, and Mo is added to it. It has a higher resistance to corrosion and creep but has inferior electrical conductivity, at 2.5% (IACS), as compared to 3.0% for SS 304 (IACS) (Table
Comparison of cost, conductivity, and tensile strength of wire material (1st of July, 2010).
Material | Diameter (mm) | Material | Tensile strength (N/mm2) | Electrical conductivity | Unit cost (1000 won/Kg) |
---|---|---|---|---|---|
Ti-6Al-4V | 0.25 | C 0.08%, Al 5.5~6.5%, Ni 0.05%, O 0.13%, Ti 88~90.08%, V 3.5~4.5%, Fe 0.25%, H 0.013% | 2005 | 1.01 | 1720 |
Phosphor bronze | 0.25 | 2131 | 15 | 16 | |
SS 304 Ni | 0.2 | C 0.075%, Si 0.45%, Mn 1.25%, | 1685 | 25 | 22.5 |
SS 316 | 0.25 | C below 0.08%, Si below 1.0%, Mn below 2.0%, Cr 16~18%, Ni 10~14%, Mo 2.0~3% | 999 | 2.5 | 24.5 |
The results of the corrosion stability tests of new acupuncture needle materials in simulated body fluid are as follows (Table
Corrosion assessment of wire material in Hank’s solution (x: corrosion was not observed. o: corrosion was observed).
Diameter (mm) | Ti-6Al-4V | Phosphor bronze | SS 304 Ni | SS 316 |
---|---|---|---|---|
0.2 | x | — | o | x |
0.25 | — | o | o | x |
0.3 | — | — | o | x |
Corrosion test of Ti-6Al-4V: no corrosion was identified on the thickness of 0.20 mm (B is the control).
Corrosion test of PB: corrosion was identified on the thickness of 0.25 mm (B is the control).
Corrosion test of STS 304 Ni: corrosion was identified on all thicknesses (A: 0.20 mm, B: 0.25 mm, C: 0.30 mm, D: control).
Corrosion test of STS 316: no corrosion was identified on any of the thicknesses (A: 0.20 mm, B: 0.25 mm, C: 0.30 mm, D: control).
When cell viability was expressed as a percentage with respect to the negative control, PB showed the lowest viability (50.5%) and SS 316 (0.25 mm) showed the highest viability (Table
Because there is no separate standard of cell viability for oriental medicine equipment, the standards of the Federation Dentaire Internationale (FDI) were used for our evaluation (Tables
The absorbance (540 nm) from MTT assay and viability.
Absorbance | ||||||
1st | 2nd | 3rd | Average | S.D. | Viability (average/control) | |
Ti-6Al-4V (0.20 mm) | 0.337 | 0.34 | 0.336 | 0.338 | 0.002 | *90.2% |
PB (0.25 mm) | 0.188 | 0.189 | 0.191 | 0.189 | 0.002 | ***50.58% |
SS 304 Ni (0.20 mm) | 0.289 | 0.295 | 0.29 | 0.291 | 0.003 | **77.83% |
SS 304 Ni (0.25 mm) | 0.321 | 0.315 | 0.319 | 0.318 | 0.003 | **85.049% |
SS 304 Ni (0.30 mm) | 0.304 | 0.306 | 0.304 | 0.305 | 0.001 | **81.39% |
SS 316 (0.20 mm) | 0.362 | 0.361 | 0.355 | 0.36 | 0.004 | 95.99% |
SS 316 (0.25 mm) | 0.36 | 0.359 | 0.365 | 0.362 | 0.003 | 96.52% |
SS 316 (0.30 mm) | 0.358 | 0.357 | 0.362 | 0.359 | 0.003 | 95.9% |
Control | 0.376 | 0.374 | 0.373 | 0.374 | 0.002 | 100% |
(*
Definition of index values.
0 | No observable lysis |
1 | Up to 20 percent |
2 | 20–40 percent |
3 | 40–60 percent |
4 | 60–80 percent |
5 | Over 80 percent |
Response index and cytotoxicity.
Response index | Cytotoxicity |
---|---|
0 | None |
1 | Mild |
2-3 | Moderate |
4-5 | Severe |
MTT assay result (*:
In the MTT assay, the degree of cell viability was high, except for PB and SS 304 Ni 0.2 mm, but in the cell stain testing, PB and SS 314 Ni for all thicknesses showed low cell viability compared to the control group (Figure
Stain test of each material. B (Ti-6Al-4V) and E (SS 316) show higher rate of survival, while (c) (PB) and (d) (SS 304 Ni) show a lower rate ((a) is the control).
In our evaluation of corrosion, only Ti-6Al-4V and SS 316 were not corroded. In the MTT assay, Ti-6Al-4V, SS 316, and SS 314 Ni showed excellent cell viability of grade 1 or higher. However, only Ti-6Al-4V and SS 316 showed moderate cell viability in the stain test. In terms of cost, Ti alloy (1720 KRW/kg) is about 70 times more expensive than SS 316 (24.5 KRW/kg) (Table
Results of safety and economic evaluation according to the material (x: corrosion was not observed. o: corrosion was observed).
Material | Thickness | Corrosion | Viability (MTT assay) | Viability (stain test) | Cost effectiveness |
---|---|---|---|---|---|
Ti-6Al-4V | 0.20 mm | x | 90.20% | High | Low |
PB | 0.25 mm | o | 50.58% | Low | High |
Ni co | 0.20 mm | o | 77.83% | Low | Normal |
Ni co | 0.25 mm | o | 85.04% | Low | Normal |
Ni co | 0.30 mm | o | 81.39% | Low | Normal |
SS 316 | 0.20 mm | x | 95.99% | High | Normal |
SS 316 | 0.25 mm | x | 96.52% | High | Normal |
SS 316 | 0.30 mm | x | 95.90% | High | Normal |
As a result of the linearization of SS 316 wire, wires with thicknesses of 0.20, 0.25, and 0.30 mm were all appropriate at a temperature condition of 700°C ± 3°C. The most appropriate straight product under 2.0 mm was obtained at a travel speed of 0.58 m/s ± 0.01 m/s (Table
Process in accordance with the conditions of the wire straightness evaluation.
Classification | Temperature (°C) | Travel speed (m/s) | Result (mm) | Note |
---|---|---|---|---|
0.20 | 670 | 0.50 | 2.2 | Fail |
0.20 | 670 | 0.58 | 2.4 | Fail |
0.20 | 670 | 0.66 | 2.5 | Fail |
0.20 | 700 | 0.50 | 1.2 | Pass |
0.20 | 700 | 0.58 | 0.8 | Pass |
0.20 | 700 | 0.66 | 1.0 | Pass |
0.20 | 720 | 0.50 | 2.6 | Fail |
0.20 | 720 | 0.58 | 2.4 | Fail |
0.20 | 720 | 0.66 | 2.3 | Fail |
0.25 | 670 | 0.50 | 2.0 | Pass |
0.25 | 670 | 0.58 | 2.1 | Fail |
0.25 | 670 | 0.66 | 2.3 | Fail |
0.25 | 700 | 0.50 | 1.2 | Pass |
0.25 | 700 | 0.58 | 1.0 | Pass |
0.25 | 700 | 0.66 | 1.2 | Pass |
0.25 | 720 | 0.50 | 2.0 | Pass |
0.25 | 720 | 0.58 | 1.9 | Pass |
0.25 | 720 | 0.66 | 1.6 | Pass |
0.30 | 670 | 0.50 | 2.1 | Fail |
0.30 | 670 | 0.58 | 2.3 | Fail |
0.30 | 670 | 0.66 | 2.4 | Fail |
0.30 | 700 | 0.50 | 1.7 | Pass |
0.30 | 700 | 0.58 | 1.4 | Pass |
0.30 | 700 | 0.66 | 1.5 | Pass |
0.30 | 720 | 0.50 | 2.5 | Fail |
0.30 | 720 | 0.58 | 2.2 | Fail |
0.30 | 720 | 0.66 | 2.1 | Fail |
Measurements of the tensile strength of the qualified wire showed that the range of tensile strength was 183~210 kgf/mm2, which is superior to the range of tensile strength of currently used SS 304, which is 170~190 kgf/mm2 (Table
Result of tensile test.
No. | Sample size | Sectional area | Maximum load | Tensile strength | Maximum displacement | Required time |
---|---|---|---|---|---|---|
SS 316-0.20-1 | 0.1997 | 0.03 | 6.28 | 209.333 | 7.540 | 00:00:45 |
SS 316-0.20-2 | 0.1997 | 0.03 | 6.32 | 210.667 | 7.070 | 00:00:42 |
SS 316-0.20-3 | 0.1997 | 0.03 | 6.32 | 210.657 | 7.200 | 00:00:43 |
SS 316-0.25-1 | 0.248 | 0.05 | 9.54 | 190.880 | 6.390 | 00:00:38 |
SS 316-0.25-2 | 0.248 | 0.05 | 9.46 | 189.200 | 7.310 | 00:00:43 |
SS 316-0.25-3 | 0.248 | 0.05 | 9.56 | 191.200 | 6.890 | 00:00:41 |
SS 316-0.30-1 | 0.297 | 0.07 | 12.86 | 183.714 | 6.510 | 00:00:39 |
SS 316-0.30-2 | 0.297 | 0.07 | 12.86 | 183.714 | 7.170 | 00:00:43 |
SS 316-0.30-3 | 0.297 | 0.07 | 12.90 | 184.285 | 6.530 | 00:00:39 |
Tensile graph of SS 316(0.20, 0.25, 0.30 mm); result of tensile strength was 183~210 kgf/mm2, which is superior to the range of tensile strength of currently used SS 304.
Electro acupuncture is a technique that applies an electrical stimulus to an inserted needle, and it is currently applied to a variety of illnesses in clinics worldwide [
In order to develop new material for an acupuncture needle that is safe for electrical current stimulus, 4 types of commercially available materials were tested for their biological safety and risk of corrosion caused by applied current. Based upon our results, the following conclusions were reached. SS 316 showed best biological safety and cost effectiveness as an electro acupuncture needle material. Testing for straightness and tensile strength of SS 316 showed that it is suitable as an acupuncture needle under the condition of 0.58 m/s ± 0.01 m/s.
In summary, it was confirmed that a disposable needle capable of transmitting electrical stimulus can be manufactured using SS 316. If an animal study using an SS 316 needle is performed in the future to study the degree of corrosion under various electrical stimulus conditions and to research the materials capacity to provide safe treatment, this will facilitate the development of safer and more effective acupuncture treatment.
This work was supported by a grant from the Korea Institute of Oriental Medicine for the development of disposable and sterile needles for electro acupuncture (C11020) and Developement of Acupuncture, Moxibustion and Meridian Standard Health Technology (K11010).