Behavior of Motile Sperm in Taylor-Couette Flow: Effect of Shear Stress on the Behavior of Motile Sperm

doi:10.4236/ojfd.2013.32A002

Paper Menu >>

Journal Menu >>

Open Journal of Fluid Dynamics, 2013, 3, 9-13

http://dx.doi.org/10.4236/ojfd.2013.32A002 Published Online July 2013 (http://www.scirp.org/journal/ojfd)

Behavior of Motile Sperm in Taylor-Couette Flow: Effect

of Shear Stress on the Behavior of Motile Sperm

Yasutaka Hayamizu1, Toru Hyakutake2, Koji Matsuura3, Shinichiro Yanase4,

Shinichi Morita1, Shigeru Ohtsuka1, Takeshi Gonda1

1Department of Mechanical Engineering, Yonago National College of Technology, Tottori, Japan

2Graduate School of Engineering, Yokohama National University, Yokohama, Japan

3Research Core for Interdisciplinary Sciences, Okayama University, Okayama, Japan

4Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan

Email: [email protected]

Received May 27, 2013; revised June 4, 2013; accepted June 11, 2013

cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Infertility is often cited as one of the causes of a declining birthrate, which has become a serious social problem in re-

cent years. Processes by which motile sperm can be safely and easily sorted are therefore important for infertility treat-

ment. Therefore, as a new sorting method, microfluidic sperm sorter using the microfluidic system has been developed.

To improve more separation efficiency of this device, it is necessary to know the behaviors of motile sperm in the mi-

crochannel where the sperm undergo shear flow. The previous study implied the necessity of the modeling of motile

sperm in the shear flow. In the present study, therefore, we experimentally investigated the behavior of the motile sperm

in the Taylor-Couette flow using PTV (Particle Tracking Velocimetry) method. The experimental results showed that

the ascent of the shear stress led to the increase in the sperm velocity, and the direction of the sperm velocity was oppo-

site to that of the flow.

Keywords: Motile Sperm; Taylor-Couette Flow; Shear Stress; PTV

1. Introduction

Infertility is often cited as one of the causes of a declin-

ing birthrate, which has become a serious social problem

in recent years. Approximately 10% of couples were

infertility, and almost 50% of all cases of infertility are

associated with a lack of sperm or sperm abnormalities.

Processes by which motile sperm can be safely and eas-

ily sorted are therefore important for infertility treatment.

Currently, the swim up method or the Percoll method is

employed for sperm sorting. However, these methods

need much time and sort sperm in a non-physiological

environment, so damage such as DNA fragmentation is a

major problem [1], and it might result in the sorting of

sperm that is unsuitable for fertilization [2]. Therefore, as

a new sorting method, microfluidic sperm sorter using

the microfluidic system has been developed (refer to Fig-

ure 1) [3-5]. To improve more separation efficiency of

this device, it is necessary to know the behaviors of mo-

tile sperm in the microchannel where the sperm undergo

shear flow. The previous study implied the necessity of

the modeling of motile sperm in the shear flow.

In the present study, therefore, we experimentally in-

vestigated the behavior of the motile sperm in the Tay-

lor-Couette flow using PTV (Particle Tracking Veloci-

metry) method. In this paper, we report the effect of

shear stress on the behavior of motile sperm.

Figure 1. Microfluidic sperm sorter (Life Science Depart-

ment, Menicon Co., Ltd.) .

Y. HAYAMIZU ET AL.

2. Experimental Procedure

2.1. Experimental Apparatus

The dimension of the curved channel is shown in Table

1. Here, a is the width of the curved channel (gap of the

rotor and the casing), h the height of the curved channel,

R the radius of the rotor (refer to Figures 2 and 3). The

dimensionless parameter concerned is the Taylor number

Ta [6] given by

Ra a

Ta R





, (1)

where ν is the kinematic viscosity and ω the angular ve-

locity of the rotor. Taylor [6] classifies flows by the Tay-

lor number Ta as follows:

Ta < 41.3: Laminar Couette flow;

41.3 < Ta < 400: Laminar flow with the Taylor vortex.

We carried out an experiment by laminar Couette flow

in Ta < 41.3 to examine the effect of shear stress on the

behavior of motile sperm in this study.

We used bull sperm (AG Japan Co., Ltd.), which is

Table 1. Dimension of curved channel.

a [mm] h [mm] R [mm]

1 4 20

Figure 2. Experimental apparatus.

Figure 3. Enlargement of the test section.

enclosed in a straw by 0.5 ml, and cryopreserved by liq-

uid nitrogen (77.15 K). A saccharide, penicillin, citric

acid for pH adjustment, and glycerin to prevent cell de-

struction in the fusion are added in the semen. A test for

evaluate vitality of sperm is performed just after the ex-

tract and the fusion, and only sperms which meet a stan-

dard are enclosed in a straw, and they are cryopreserved

again. Therefore, the motility of the sperm in the ex-

periment is high.

2.2. Experimental Method

The working fluid mixed a fluorescent dye (Pyronin Y)

and buffer solution (Modified HTF Medium) with semen.

We diluted semen with the buffer solution, changed the

viscosity of the working fluid and carried out an experi-

ment. We used Pyronin Y as the fluorescence of sperms.

For an experiment procedure, we dissolved freeze se-

men in hot water of 310.15 K in 40 seconds. We scat-

tered the fluorescent dyes in the buffer solution, and add

it to sperms. Then, we filled the working fluid in the

channel. The channel is formed of the casing and the

rotor. The velocity gradient occurs between the rotor

wall and the casing wall by rotating the rotor and thereby

produces constant shear stress (refer to Figure 3). The

rotor is rotated by the motor.

We next explain the method of visualization. The laser

sheet lights up a cross-section of the channel normal to

the channel side wall and the photographs are taken of

the fluorescence patterns by a high speed camera. We

used Davis7.2 (LaVision GmbH) for PTV and PIV, and

used a fluorescent particle (FLUOSTAR: particle diame-

ter 15 μm) of specific gravity 1.1 for a tracer of PIV. We

calculated the sperm velocity by the PTV analysis of the

fluorescence image of the sperm using the high speed

camera with the high-pass filter (570 nm or more trans-

mitted wave length) (refer to Figure 4). Also, we calcu-

lated the flow velocity by tracing the PIV analysis of the

fluorescent particles (refer to Figure 5).

Figure 4. Fluorescence image of the sperm.

Y. HAYAMIZU ET AL. 11

Figure 5. Fluorescence image of the particle.

We measured the viscosity of working fluid using the

precision rotational viscometer before and after experi-

ment and confirmed that there was not a viscosity change.

Also, we calculated the density of the working fluid from

the gravimeter.

3. Experimental Results and Discussion

3.1. Physical Property

Figures 6 and 7 show physical property of the working

fluid at 310.15 K. Figure 6 shows the relationship be-

tween the shear stress τ of each dilution rate n and the

shear velocity γ. The figure shows the relations of τ



in all dilution rates. This result means that the working

fluid is Newtonian fluid even if dilution rate changes. In

addition, a similar tendency was seen at other tempera-

fluid is

310.15 K constant, which is suited for the sperm.

measured values in this ex-

velocity v* = {v(a/R)1/2}/(Rω) and the horizontal axis is

re.

Figure 7 shows the relationship between the viscosity

μ and the dilution rate n. As the dilution rate of the

working fluid increases, the viscosity decreases. There-

fore, we carried out an experiment at dilution rate n = 2

and 6 to examine the influence of the viscosity of the

working fluid. The temperature of the working

3.2. Sperm Velocity

Comparison between the experimental result and the

theoretical result of the dimensionless flow velocity dis-

tribution in this present device is shown in Figure 8. The

vertical axis of the figure is dimensionless flow velocity

u* = u/(Rω) and the horizontal axis is dimensionless co-

ordinate x/a. The mean error rate of the experimental

result to the theoretical result was approximately 9.3%.

Therefore, reliability of the

riment is around 90.7%.

The sperm velocity of n = 2 and 6 is shown in Figure

9. The vertical axis of the figure is dimensionless sperm

(a)

(b)

(c)

(d)

(e)

Figure 6. Relationship between τ and γ. (a) n = 2; (b) n = 3;

Y. HAYAMIZU ET AL.

0.0012

0.0014

0.0016

0.0018

0.002

01234567

μ[Pa・s]

Figure 7. Relationship between μ and n.

Figure 8. Velocity distribution of laminar Couette flow.

-0.02

-0.015

-0.01

-0.005

012345678

(a)

-0.02

-0.015

-0.01

-0.005

012345678

(b)

Figure 9. Sperm velocity in laminar Couette flow. (a) n = 2;

(b) n = 6.

Taylor number Ta. As Taylor number (shear stress) in-

creases, the sperm velocity shows the tendency of in-

creasing in all dilution rates. Then, the propulsion direc-

tion of the sperm is opposite to the flow. In addition, in

the difference of the sperm velocity is small in each Ta

even if they compare it at dilution rate. In other words,

even if the viscosity of working fluid is different, the

sperm velocity shows not changing too much and agrees

with the study of Smith et al. [7].

4. Conclusions

In the present paper, we experimentally investigated the

behavior of the motile sperm in the Taylor-Couette flow

using PTV method, and obtained following results:

The ascent of the shear stress led to the increase in the

sperm velocity, and the direction of the sperm velocity is

opposite to that of the flow.

Even if the viscosity of working fluid is different, the

sperm velocity doesn’t change too much.

5. Acknowledgements

The authors would like to express their cordial thanks to

Hiroki Endo and Yuka Matsuda for their help in the ex-

periments.

REFERENCES

[1] E. V. Younglai, D. Holt, P. Brown, A. Jurisicova and R.

F. Casper, “Sperm Swim-Up Techniques and DNA Frag-

mentation,” Human Reproduction, Vol. 16, No. 9, 2001,

pp. 1950-1953. doi:10.1093/humrep/16.9.1950

[2] S. Smith, S. Hosid and L. Scott, “Use of Postseparation

Sperm Parameters to Determine the Method of Choice for

Sperm Preparation for Assisted Reproductive Technol-

ogy,” Fertility and Sterility, Vol. 63, No. 3, 1995, pp.

591-597.

[3] B. S. Cho, T. G. Schuster, X. Zhu, D. Chang, G. D. Smith

and S. Takayama, “Passively Driven Integrated Micro-

fluidic System for Separation of Motile Sperm,” Analyti-

cal Chemistry, Vol. 75, No. 7, 2003, pp. 1671-1675.

doi:10.1021/ac020579e

[4] T. G. Schuster, B. S. Cho, L. M. Keller, S. Takayama,

and G. D. Smith, “Isolation of Motile Spermatozoa from

Semen Samples Using Microfluidics,” Reproductive Bio-

Medicine, Vol. 7, No. 1, 2003, pp. 75-81.

doi:10.1016/S1472-6483(10)61732-4

[5] T. Hyakutake, Y. Hashimoto, S. Yanase, K. Matsuura and

K. Naruse, “Application of a Numerical Simulation to

Improve the Separation Efficiency of a Sperm Sorter,”

Biomedical Microdevices, Vol. 11, No. 1, 2009, pp. 25-

33. doi:10.1007/s10544-008-9207-2

[6] H. Schlicting, “Boundary Layer Theory,” 7th Edition,

McGraw-Hill Pub. Co., New York, 1987, pp. 525-529,

[7] D. J. Smith, E. A. Gaffney, H. Gadelha, N. Kapur and J.

C. Kirkman-Brown, “Bend Propagation in the Flagella of

Migrating Human Sperm, and Its Modulation by Viscos-

ity,” Cell Motility and the Cytoskeleton, Vol. 66, No. 4,

2009, pp. 220-236. doi:10.1002/cm.20345

Y. HAYAMIZU ET AL.

Nomenclature

a: width of the curved channel [mm]

h: height of the curved channel [mm]

n: dilution rate

R: radius of the rotor [mm]

Ta: Taylor number

u: flow velocity [mm/s]

u*: dimensionless flow velocity = u/(Rω)

v: sperm velocity [mm/s]

v*: dimensionless sperm velocity = {v(a/R)1/2}/(Rω)

x: distance from rotor wall [mm]

Greek Letters

γ: shear velocity [1/s]

μ: viscosity [Pa·s]

ν: kinematic viscosity [mm2/s]

τ: shear stress [Pa]

ω: angular velocity of the rotor [rad/s]