A Single Electrical Acupuncture Needle with Bipolar Electrodes for

Biotissue Discrimination

Giseok Kang

, Jae-Cheon Kim

, Sohee Kim

1,2

and Jong-Hyun Lee

1,2

Department of Medical System Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

Department of Mechatronics, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

Keywords: Bipolar Electrodes, Acupuncture Needle, Biotissue, Electrical Impedance, MEMS, Flexible Photomask,

Parylene C.

Abstract: In oriental medicine, acupuncture is an essential treatment for the muscle tissue relaxation. For treatment,

electrical stimulations to the tissue conducted with multiple electrical acupuncture needles have generally

been used. However, the sting depth of a needle can be handled only by the sense of the oriental medicine

doctor. Moreover, it is difficult to use multiple needles to focus the electrical stimulation on a tissue of small

volume, and, likewise difficult to distinguish various tissues. In order to overcome the aforementioned

shortcomings, we developed a single acupuncture needle that has bipolar electrodes on the surface of the

needle tip by using a novel flexible parylene C film photomask. The interdigitated electrodes, 31.25 m in

width and 32.00 m in gap, were passivated by parylene C film to prevent metal debris from spreading into

the tissue. The electrical acupuncture needle was developed based on the conventional acupuncture needle

(400 m in diameter), so that the needle will give a familiar sensation to patients. We demonstrate the metal

patterning technique with a high resolution that has less than 2.95 % dimensional error compared to the

designed metal pattern dimensions. The biotissues were well distinguished by phase angle at 1 MHz of

14.6°, -32.7°, and 43.6° for skin, muscle, and ligament of a chicken, respectively.

1 INTRODUCTION

Acupuncture is an Asian alternative medicine

methodology that uses metal needles inserted into

the skin for patient treatment. The treatment, based

on traditional medicine theory, insists that human

body imbalances, due to unstable flow of the qi, can

be controlled by acupuncture (Langevin and

Yandow, 2002). Though current scientific research

has reported the physiological efficacy of the

acupuncture, some studies have still concluded that

the efficacy of acupuncture can be explained by the

placebo effect (White et al., 2003). In order to clear

up this controversy, acupuncture needs more

research from the scientific point of view.

Most of acupuncture treatments are focused on

muscle tissue relaxation, additionally supported by

electrical stimulations (Sandberg et al., 2003). In this

conventional stimulation, multiple needles are

needed because a single needle acts as only one

electrode. When the volume of tissue to be treated is

small, it is difficult to use a conventional electrical

acupuncture needle to locate the designated tissue in

a one shot. Therefore, it is difficult to distinguish

between various tissues by means of electrical

signals. In addition, the single conventional needle is

not efficient in stimulation of the target tissue

because the electrical signal tends to disperse into

the surrounding tissue. For effective acupuncture

treatment, thus, accuracy of detection and

localization of electrical stimulation are

indispensable.

In this paper, we have developed bipolar

electrodes on a single acupuncture needle surface

using micro-electromechanical systems (MEMS)

technology. In order to fabricate the acupuncture

needle, a novel flexible photomask made of parylene

C film is used. The flexible photomask is designed

to make direct contact with a curved substrate,

which makes it possible to pattern the electrodes on

the surface of conventional acupuncture needles

with high resolution. Parylene C is a material

featuring high biocompatibility and good electrical

insulation for the electrode passivation.

To validate the developed electrical acupuncture

needle, various biotissues (skin, muscle, and

Kang G., Kim J., Kim S. and Lee J..

A Single Electrical Acupuncture Needle with Bipolar Electrodes for Biotissue Discrimination.

DOI: 10.5220/0004237700470050

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2013), pages 47-50

ISBN: 978-989-8565-34-1

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

ligament of a chicken) were characterized in terms

of electrical impedance. For steady and precise

results, every test was conducted using an automated

real-time measurement system under identical

conditions.

Figure 1: Schematics of the conventional acupuncture

needle and bipolar electrodes pattern [dimensions in m];

(a) overall view of the conventional acupuncture needle

(400 m in diameter, 30 mm in length) and cross-section

view of the electrodes on the needle surface, (b) overall

view of the bipolar electrode pattern made of Ti/Au (200

m in width, 10 mm in length), and (c) detailed view of

the interdigitated electrode (2 mm in length; both width

and gap are 30 m).

2 DEVICE CONFIGURATION

A flexible parylene C film photomask has been

developed to fabricate high resolution patterns on

the curved surface of the conventional acupuncture

needle, whose diameter can be as small as 400 um.

Compared to the previous flexible polydimethly-

siloxane (PDMS) photomask (Kim et al., 2009), the

patterning capability in this study was greatly

improved, showing a smaller pattern size and no

cracks in the metal layer. This improved patterning

was achieved by locating the parylene masking layer

on the neutral axis (geometric centroid of the beam

or membrane) that contains no longitudinal stresses

or strains (Bedford and Liechti, 2000). The Cr layer

(around 150 nm thick) can be located in the centroid

of the parylene C layers with a very low eccentricity.

This is because the parylene C is deposited by

chemical vapor deposition (CVD), which shows a

few tens of nm error in thickness (Yang et al., 1998).

The dimensions of the designed electrical

acupuncture needle are illustrated in Figure 1.

Considering the dimensions of the biotissue under

testing the interdigitated electrode (IDE), the

electrical sensing part on the acupuncture needle,

was designed to have 30

m

both in width and gap,

and to have 2 mm in length. The acupuncture needle

was electrically insulated by the biocompatible

polymer, parylene C (Schmidt et al., 1988). This will

also prevent metal debris from spreading into the

living tissue during operation. Figure 2 shows the

electrical acupuncture needle passivated with

parylene C.

3 BIOTISSUE EXPERIMENTS

To evaluate the fabricated electrical acupuncture

needle, an ex-vivo efficiency test of the biotissues

was conducted. Arrows in Figure 3 indicate the

biotissues (skin,

muscle, and ligament) of the chicken.

(a)

(b)

(c)

Figure 2: Configuration of the electrical acupuncture

needle passivated by parylene C: (a) fabricated electrical

acupuncture needle, (b) schematic of the Ti/Au bipolar

electrodes (bright yellow), the conventional acupuncture

needle (dark gray) and parylene C electrical insulation

layer (translucent green), and (c) SEM image of a part of

the IDE.

(a) (b)

Figure 3: Chicken biotissues: (a) skin (white) and muscle

(pink), and (b) ligament (white line).

BIODEVICES2013-InternationalConferenceonBiomedicalElectronicsandDevices

The test maintained identical environment

conditions (room temperature of 26 °C, room

humidity of 50%) in a clean booth. The bipolar

electrodes of the electrical acupuncture needle were

connected to an impedance analyzer (HP4294A,

USA) and a laptop in order to automatically measure

the electrical signals of the biotissues. Constant

voltage (0.5 V

) and current (0.1 mA) were applied

to the biotissues from the impedance analyzer at 7

frequencies from 1 kHz to 1 MHz, as shown in

Figure 4. The sinusoidal electrical signal was

applied to the electrodes located on the needle

through the impedance probe kit (HP42941A, USA).

The probe kit performs a 4-wire (or Kelvin)

measurement method which automatically

compensates the lead and contact resistance to

measure impedance characteristics accurately

(Siegal and Galloway, 2008). Visual basic for

application (VBA) in Excel (Microsoft, USA) was

used to control the impedance analyzer and to

collect raw data into text files.

To verify the effectiveness of the developed

needle for the biotissue discrimination, a

conventional method using two electrical

acupuncture needles (separation distance 5 mm) was

evaluated as well. The tip of the conventional needle,

whose diameter is identical to that of the developed

needle, was not electrically passivated

The validation of the electrical acupuncture

needles as a sensor was performed by measuring the

electrical impedances of various biotissues (skin,

muscle, and ligament of a chicken). The electrical

impedances of the tissues, the magnitude, and the

phase angle were measured, with results as shown in

Figure 4. All the data points corresponding to each

frequency indicate the average values calculated

with 200 data points of electrical response data for

each biotissue. Furthermore, the data points,

including the error bar (a standard deviation value),

are clearly differentiated between the biotissues at

the particular frequencies of the components of the

electrical impedance.

As shown in Figure 4, only the developed needle

can distinguish the biotissues both in the magnitude

and phase. We believe that the high performance of

the developed needle as an electrical sensor is

attributed to the electrodes in micro scale. In the test

using the bipolar needle, impedance magnitude of

the skin is larger than that of the muscle. That can be

explained by the fact that electrical signals is easily

conducted through each fiber (very large individual

cells) of muscle, but the skin is highly

inhomogeneous resulting in the most resistive tissue

in the human body (Miklavcic et al., 2006).

(a) magnitude in the developed needle test.

(b) magnitude in the conventional needle test.

(d) phase in the conventional needle test.

Figure 4: Electrical impedance responses as a function of

the frequency for the skin, muscle, and ligament of the

chicken: (a) magnitude in the developed needle test, (b)

magnitude in the conventional needle test, (c) phase in the

developed needle test, and (d) phase in the conventional

needle test. The vertical bars represent the error, defined

by the standard deviation. The arrows indicate the

frequency at which the differentiation index reaches the

maximum value.

In order to quantitatively evaluate the

effectiveness of the differentiation, differentiation

index (D), was used, as in our previous work:

ASingleElectricalAcupunctureNeedlewithBipolarElectrodesforBiotissueDiscrimination

D = G/D

, (1)

where G and D

are the gap and the average

difference, respectively (Kang, Yoo, Kim and Lee,

2012). A negative value of D means that the data

points overlapped, while a positive value of D close

to 1.0 (the maximum value of D) means that the data

points are well distinguished with a low-variance.

To validate the difference of the electrical

impedance between the biotissues, the D values

were estimated following the sequence of tissues as

the needle penetrated the tissues; D

corresponds to

the differentiation index between the skin and

muscle; D

corresponds to the differentiation index

between muscle and ligament. The maximum D

values of the magnitude and phase angle for the

biotissues are summarized in Table 1. The best case

for the biotissue discrimination took place for the

phase angle at 1 MHz; 0.97 for both D

and D

The differentiation indices, based on the

electrical impedances, were confirmed to have

efficiently distinguished the biotissues. This electro-

thermal acupuncture needle, integrated with a

microheater to focus heat-effects on a localized area,

can be a good medical appliance for a precision

treatment.

Table 1: Maximum differentiation index values of

magnitude and phase angle for biotissue discrimination.

Biotissue

Differentiation

index

Magnitude Phase angle

at 50 kHz at 1 MHz

Skin & muscle D

0.95 0.97

Muscle &

ligament

0.93 0.97

4 CONCLUSIONS

We designed and fabricated a novel electrical

acupuncture needle with bipolar electrodes for

biotissue discrimination. With the developed

acupuncture needle, various biotissues were

electrically characterized, and were definitely

distinguished at a particular frequency in real-time.

It is expected that the developed electrical

acupuncture needle with enhanced sensing accuracy

will be greatly beneficial to patients.

ACKNOWLEDGEMENTS

The research was supported by a grant from the

Institute of Medical System Engineering (iMSE) in

the GIST, Korea.

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BIODEVICES2013-InternationalConferenceonBiomedicalElectronicsandDevices