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Sensors and Materials, Vol. 29, No. 12 (2017) 1749–1761
MYU Tokyo
S & M 1467

Softening Hard Stool
Using Magnetically Controlled Fe3O4 Nanoparticles
Qian Li, Xiaojun Liu, Ming Chang,1,2* Wei Hsiu Lin,2 and Zhen Lu3
State Key Laboratory of Digital Manufacturing Equipment and Technology,
Huazhong University of Science and Technology, Wuhan 430074, China
1
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, Fujian, China
2
Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li 32023, Taiwan
3
School of Economics and Management, Shanghai University of Electric Power, Shanghai 201300, China(Received May 2, 2017; accepted December 5, 2017)

Keywords: fecal impaction, oscillating magnetic field, Fe3O4 nanoparticle aggregate, hard stool, sway
motionFecal impaction is a gastrointestinal problem that occurs in all age groups. Traditional therapy
with drugs or surgery may result in serious complications for patients. Softening hard stool invitro is realized with swaying Fe3O4 nanoparticle (NP) aggregates controlled by an oscillating
magnetic field generated using a combination of electromagnetic coils and permanent magnets.
The operation mechanism of the combined oscillating magnetic field is analyzed, experiments
on NP manipulation by the magnetic field are conducted, and the morphology and sway motion
characteristics of the aggregates are observed under various experimental parameter settings.
Experimental results show that such NP aggregates manipulated by oscillating magnetic fields canbe applied to soften stool in the rectum for fecal impaction treatment. In addition, diagnosis andsensing of constipation induced by obstruction in the gastrointestinal tract can be executed by thesame approach in the future.

1.

Introduction

Fecal impaction, a symptom of constipation in the presence of hard stool obstructing therectum, is a common serious medical condition for a considerable number of people, with a higher
prevalence in children, incapacitated patients, and the elderly.(1,2) Complications attributable
to fecal impaction include stercoral ulceration, rectovaginal fistula, megacolon, and colonicperforation, which are associated with high morbidity and high mortality.(3) Traditional therapies
include hard stool fragmentation or manual disimpaction, and hard stool softening using enemas
followed by distal colon for evacuation.(1,2,4) The iatrogenic injury of the sphincter muscles leading
to megarectum is occasionally found after manual disimpaction, and bowel necrosis, perforation,and death are occasionally encountered after cleansing using soap-sud enemas.(5,6) Surgery is
reserved for peritonitis induced by bowel perforation. However, patients are required to tolerate
pain and there is a risk of complication.(7) Moreover, clinical sensing of such sickness is usuallybased on reduced defecation frequency or difficulty in defecation, which, however, always indicate*

Corresponding author: e-mail: ming@cycu.edu.tw
http://dx.doi.org/10.18494/SAM.2017.1817
ISSN 0914-4935 © MYU K.K.

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Sensors and Materials, Vol. 29, No. 12 (2017)that the patients are in a serious condition. Early diagnosis and a fast and painless treatment for
fecal impaction are thus desirable.
Magnetic nanomaterials have been applied in various biomedical applications, such as in cell
marking and separation, targeted drug delivery, thermotherapy, and magnetic resonance contrast
enhancement, and have been found to be biocompatible and suitable for pain-free microsurgery.(8–10)
The noncontact motion control of magnetic nanomaterials has been investigated. Fan et al.(11)observed the rotation of gold, platinum, and nickel nanowires in an alternating electric field.
Wang et al.(12) controlled the rotation and translation of microrods using ultrasonic waves. Rikken
et al.(13) reviewed the manipulation of micro- and nanostructure motion using magnetic fields,
including homogeneous and inhomogeneous magnetic fields, and rotating and oscillating magnetic
fields. These investigations showed that the motion of magnetic materials can be controlled byvarious noncontact methods. Shaalan et al.(10) reported that the major trend in nanomaterials
is to make them multifunctional and controllable using external signals or in accordance withthe local environment. Many biological and biomedical experiments that utilize these motions
have been carried out, with encouraging results. Zhang et al.(14) controlled the motion of blood
cells with rotational nickel nanowires. Zhou and Metin(15) proposed an approach for the fluidic
trapping and two-dimensional transport of swimming microorganisms, which utilizes a rotating
magnetic microrobot. Gabayno et al.(16,17) developed thrombolysis technology, in which a strong
vortex is induced by rotating magnetic aggregates for breaking a thrombus. These experiments
indicate that micro- and nanomaterials can impact the target indirectly with the help of a rotational
fluid induced by fast rotating micro- or nanomaterials. Simultaneously, controlling a microrobot
to move with a magnetic field and a field gradient has been reported in many studies. Chanu
and Martel(18) proposed a magnetic resonance imaging (MRI)-system-based method for driving
microrods. Yesin et al.(19) and Choi et al.(20) actuated a ferromagnetic microrobot with Helmholtz
and Maxwell coil pairs.
Similar to previous biological experiments on the manipulation of micro- and nanostructures,
we propose a swaying nanoparticle (NP) aggregate approach to break and soften hard stools bycontact. Experiments are carried out in a microfluidic channel. Fe3O4 NPs are first magnetized
to form aggregates by a static magnetic field generated by two permanent magnets and then theseaggregates are controlled to sway around their centroid by a perpendicular oscillating magnetic
field produced by two electromagnetic coils driven by an alternating current. The magnetic
force guides the aggregate forward onto the target to break the stool block and sweep the pieces
away. Experiments show that various sizes of the aggregates formed by the magnetic field can beused to perform the breaking action. Because of the good characteristics of the contrast agent of
Fe3O4 NPs, it is also possible to incorporate the proposed approach with MRI or other bioimaging
technologies to achieve the target of early detection of fecal impaction by magnetically controllingthe movement of the magnetic nanomaterials.

2.

Materials and Methods

2.1

Preparation of Fe3O4 NPs

Fe3O4 NPs were prepared by the coprecipitation method. 100 ml of a 0.1 M FeCl2 solution and100 ml of a 0.2 M FeCl3 solution were mixed in a 500 ml beaker and stirred with a glass rod. 100
ml of a 0.8 M NaOH solution was continuously added and then the mixture was stirred vigorously1751

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for about 30 min. Finally, a strong permanent magnet was used to attract the black precipitatesto the bottom and then the supernatant was removed. Deionized water was added to purify theprecipitates five to six times to ensure a pH of about 7.0. The precipitates were then dried andground to obtain Fe3O4 particles. After the particles were dispersed in deionized water again, they
were broken into nanometer scale with an ultrasonic processor.
2.2

Experimental methods

2.2.1 Experimental setup
A schematic diagram of the experimental setup is shown in Fig. 1. Two permanent magnets
are placed to generate a static unidirectional magnetic field Hs. Magnetic NPs in the microfluidic
capillary magnetized by the unidirectional field tend to aggregate owing to the action of dipolar
attractive forces. A pair of electromagnetic coils, into which an alternating current from a
programmable source (not shown) is input, are placed orthogonally to the static field andgenerate a sinusoidal dynamical field Hv with an amplitude of Hp and a frequency of f, i.e., Hv =Hpsin(2πft). Under such a magnetic field configuration, the combined oscillating magnetic field is = H si + Hv j , in which i and j are unit vectors in the x- and y-axes. The phase angle trajectoryH(denoted as φ) of the combined oscillating field is

ϕ = tan−1
H p sin(2π f t)
.
Hs

(1)

The magnetic NP aggregates tend to align their easy axis along the orientation of the final
magnetic field and will oscillate (denoted as a sway motion) under this combined oscillating
magnetic field. A high-speed camera is used to observe the experimental process in a microfluidic
capillary surrounded by magnets and coils.

Fig. 1. (Color online) Schematic diagram of experimental setup consisting of two permanent magnets, twoelectromagnetic coils into which AC current is applied, a high-speed camera, and microfluidic capillary.

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2.2.2 Principle of softening stool
The mechanism of softening stool is the sway motion of Fe3O4 NP aggregates. Under theaction of a combination of a fluid field and a magnetic field, the forces applied to magnetic
aggregates include contributions from drag force, magnetism, buoyancy force, gravitational
force, Brownian force, thermophoretic force, Saffman’s lift force, and Basset force.(21) Since only
forces in the horizontal plane should be considered, buoyancy force and gravitational force in thevertical direction are neglected. Brownian force can be negligible since Brownian motion is not
obvious for these aggregates. As there is almost no temperature difference in the capillary, thethermophoretic force is not taken into consideration. Saffman’s lift force and Basset force are also
neglected because they are generally much less than the drag force.( 21)The force and torque exerted on a Fe3O4 aggregate, which is simplified as an ellipsoid witha half-major axis of a and a minor axis of b, are shown in Fig. 2. τm and τD are, respectively, themagnetic torque and drag torque. θ is the angle between the combined magnetic field H and theeasy axis (dashed line in the figure). Fmx and Fmy are the components of magnetic force in the xand y-axes, respectively. FD is the fluidic resistance when assuming that the aggregate moves inthe x direction. Fx and Fy are the interaction forces between the aggregate and the stool. Figure2(b) shows the force acting on the stool from the aggregate.
The total drag torque exerted by the fluid on the ellipsoid aggregate rotating along the minor
axis is(22)τD = 8πωka3 (s20 + 1)

3/2

,

(2)

 
−1

1
2 2
where s0 is a parameter that can be obtained in Ref. 22, k =2s0 + 1 (1 − s0 )2 tan−1+ s0 ,3s0and ω is the rotational speed of the ellipsoid.
For a magnetic aggregate placed in a magnetic field H, the driving magnetic torque is(16)τm = µ0(a)χ2
V H 2 sin(2θ) ,2(2 + χ)(3)(b)

Fig. 2. (Color online) (a) Free-body diagram of swaying Fe3O4 aggregate when breaking stool. (b) Force acting
on the stool from the aggregate.

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Sensors and Materials, Vol. 29, No. 12 (2017)

where V = 4πab2/3 is the volume of the magnetic aggregate and χ is magnetic susceptibility.
Supposing that the aggregate rotates at a constant speed, τm is equal to τD at low Reynolds
numbers and then the rotational speed can be obtained as(23)ω=µ0 χ2 V H 2 sin(2θ)
16πka3 (2 + χ)(s20 + 1)

3/2

.

(4)

When the aggregate moves at velocity v, the fluidic drag force applied to the aggregate is
FD = 6πηrv,(24) where η is the viscosity coefficient and r is the equivalent radius of the aggregate.
However, when the aggregate presses against the stool, the motion of the aggregate is blocked by
the stool, i.e., FD can be seen as zero. Therefore,(25,26)


3χ
∂H



F = Fmx =,µ0 V H


 x
3+χ
∂x


∂H
3χ



Fy = Fmy = 3 + χ µ0 V H ∂y ,

(5)

∂H
∂H
and
are, respectively, the magnetic gradients in the x and y directions.
∂x∂yEquations (4) and (5) constitute the force model for the breaking of stool by a swaying aggregate.
Six dry and hard stool blocks were prepared to check the strength of the stool. Experiments werecarried out with the universal material testing machine WDW3200. Experimental results show thatthe tensile strength of these dry blocks is 0.02 ± 0.001 MPa. More conservatively, we may assume
the contact force component Fx to be an axial force applied to the stool and neglect Fy. Under the∂H= 0.2 T/m, the induced Fx is approximately 2 × 10−8 N. In the caseconditions of H = 22 Oe and∂xof a stool block with a cross-sectional area of 1 × 10−12 m2, the resulting maximum normal stressand shear stress applied to the stool are 0.02 and 0.01 MPa, respectively. Since stool in solution iscomposed of loose and softer structures, the resulting stresses caused by impact can break thesestructures. Certainly, the aggregates formed of NPs will be employed to provide a combined
breaking force in the process. The interaction forces between the aggregate and bulk stool are not
only to break the stool but also to push the aggregate to another target. Sometimes the aggregate
will also be damaged by the collision. However, the NPs will aggregate again owing to the actionof the magnetic field. Moreover, the direction of motion of the NP aggregate can be controlled bychanging the direction of the magnetic gradient.
where

3.

Results

3.1

Characterization of Fe3O4 NPs

The morphology and magnetic characteristics of the obtained Fe3O4 NPs are shown in Fig.
3. Figure 3(a) shows a transmission electron microscopy (TEM) image of the Fe3O4 NPs. The
diameters of these spherical particles are about 10–20 nm. The size distribution of the NPs
measured with a dynamic light-scattering particle size distribution analyzer (Horiba LB-550) is
shown in Fig. 3(b). The iron oxide concentration of the tested dispersions is 0.5%. The vibrating
sample magnetometer (VSM) data shown in Fig. 3(c) indicate that there is almost no hysteresis

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Sensors and Materials, Vol. 29, No. 12 (2017)

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 3. (Color online) (a) TEM image of NPs, which are spherical in shape and have diameters of about 10–20
nm. (b) Size distribution of the NPs measured by dynamic light scattering. (c) Magnetic hysteresis loops from
VSM measurements showing good magnetic characteristics. (d) SEM image of ellipsoid-like aggregate formed
after permanent magnets were placed close to Fe3O4 suspension. (e) Relationship between ellipsoid-like aggregate
concentration and Fe3O4 NP concentration under a magnetic field of 25 Oe.  (f) Relationship between ellipsoid-likeaggregate concentration and external magnetic field at the NP concentration of 0.5%.

when the magnetic field ranges from −15000 to 15000 Oe.  This result confirms the good magnetic
characteristics of the as-prepared Fe3O4 NPs. Figure 3(d) shows that the NPs form an ellipsoidlike aggregate with an irregular surface when exposed to an external static magnetic field in the x
direction.  The lengths of the obtained aggregates in our experiment are roughly from 15 to 50 μm.  
The concentration of ellipsoid-like aggregates reveals a quadratic dependence on the concentrationof Fe3O4 NPs under a static magnetic field of 25 Oe, as shown in Fig. 3(e). The concentrations of
aggregates were determined using an Olympus BX53 microscope. At the NP concentration of 0.5%,
Fig. 3(f) shows that the concentration of ellipsoid-like aggregates is also quadratically dependent
on the static magnetic field.
3.2

Motion of magnetically controlled Fe3O4 NP aggregates

To understand the motion behavior of Fe3O4 aggregates, aggregates with lengths of 15, 25,
and 50 μm (denoted as L15, L25, and L50, respectively) under the combined oscillating magnetic
field were observed. Figure 4 shows the sequential images of three aggregates of L25 (marked
as A, B, and C) subjected to a combined oscillating magnetic field with Hs = 25 Oe, Hp = 8 Oe,and f = 45 Hz. The observation lasts for 7 s to ensure that the motion process can be properly
measured. The motion trajectories of the aggregates were observed and recorded with a highspeed camera (Teledyne Dalsa Genie HM640). The video was then divided into separate images

Sensors and Materials, Vol. 29, No. 12 (2017)

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Fig. 4. (Color online) Image sequences show the swaying and translational motion of three ellipsoid-likeaggregates (L25) under Hs = 22 Oe, Hp = 8 Oe, and f = 45 Hz.

for the analysis of the instantaneous displacement and velocity of aggregates. Before alternating
current is input into the coils, Fe3O4 NPs aggregate into ellipsoid-like aggregates under a static
magnetic field. After the AC current is input into the coils, the aggregates start to oscillate withthe orientation of the combined magnetic field. An amplitude of 20.5° of the oscillating magnetic
field can be obtained. The observed swaying amplitude of aggregates is almost the same as theamplitude of the combined magnetic field, which means that there exists no phase angle lag. The
aggregates are driven towards the magnetic gradient. The translational motion trajectories offive aggregates of L25 in the x-axis direction are shown in Fig. 5. The translational velocities
of aggregates are varied at different time intervals. This may be caused by the changing fluid
resistance induced by the sway motion.
Ureña et al.(27) established the theoretical critical frequency for micro-NPs rotating at low
Reynolds numbers. The experiments to observe the critical frequency of these ellipsoid-likeaggregates in the combined oscillating magnetic field have been performed. The comparable
measurements of Fe3O4 aggregates are carried out from the observations of L15, L25, and L50
and shown in Fig. 6. Figure 6(a) shows the swaying frequencies and amplitudes of L15, L25, andL50 at Hs = 22 Oe and Hp = 8 Oe, varying the magnetic frequencies from 0 to 90 Hz. As shown,
the swaying frequencies of L15 and L25 are the same as the magnetic field, and their swaying
amplitudes are maintained at 20–22°. The swaying frequency and amplitude of L50 are coincident
with those of L15 and L25 when the magnetic field frequency f is lower than 45 Hz. However,they suddenly decrease once the frequency is higher than 45 Hz. This phenomenon is observed
when the increased magnetic frequency is beyond the critical frequency of aggregate L50, which
agrees with the theoretical result obtained by Ureña et al.(27) Figure 6(b) shows that if Hs is fixedat 22 Oe, L15 and L25 maintain the same values as the magnetic field amplitude even when Hp
is over 50 Oe. This illustrates that the inertia of these aggregates has little impact on the motion
and can be ignored. In addition, the swaying amplitude of L50 gradually becomes lower than themagnetic field amplitude beyond 25 Oe. A bending deformation of aggregate L50 was observedat this stage. This may result in the decline of the amplitude. Figure 6(c) shows the relationshipbetween the swaying amplitude of aggregates and the static magnetic field Hs at Hp = 25 Oe andf = 45 Hz. Accordingly, the swaying amplitudes of L15 and L25 agree with the magnetic field
curve very well but the swaying amplitude of L50 is much lower than the magnetic field curve
until Hs exceeds 22 Oe. This shows that a stronger static magnetic field is favorable for stabilizing
and stiffening the structure. When the static magnetic field is weaker than the alternating
magnetic field, the aggregates with larger length are likely deformed by the oscillating field, as
has also been found by many researchers.(28–31) The swaying amplitude of aggregate L25 is almost
linearly dependent on the relative angle between Hs and Hv, as depicted in Fig. 6(d). This angle can1756

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Fig. 5. (Color online) Translational motion trajectories of five aggregates of L25 in the x-axis direction for aperiod of 7 s. The centroid of aggregate “A” at 0 s is set as the original point.

(a)

(b)

(c)

(d)

Fig. 6. (Color online) (a) Swaying frequencies and amplitudes of L15, L25, and L50 vary with the magnetic
field frequency at Hs = 22 Oe and Hp = 8 Oe. (b) Swaying amplitudes of L15, L25, and L50 vary with Hp at thefrequency of 45 Hz and Hs = 22 Oe. (c) Swaying amplitudes of L15, L25, and L50 vary with the static magnetic
field Hs at Hp = 25 Oe and f = 45 Hz. (d) Swaying amplitude of L25 varies with the relative angle between Hs andHv.

Sensors and Materials, Vol. 29, No. 12 (2017)1757

be adjusted by changing the position of the permanent magnets. The largest swaying amplitude
occurs when Hs is orthogonal to Hv. The swaying amplitude is significantly different from themagnetic field amplitude, which shows a quadratic relationship with the relative angle until theangle approximately equals 90°. In short, the aggregates can be effectively controlled to sway andtranslate with the proper configuration of static and dynamic fields.
3.3

Softening hard stool with magnetically controlled swaying Fe3O4 NP aggregates

The analogy of a broom clearing rubbish is usually associated with this motion of Fe3O4 NP
aggregates. These aggregates were used for the softening of hard stool in an artificial intestinal
tract. An in vitro experiment using a microfluidic capillary with an inner diameter of 0.9 mm wascarried out. The permanent magnets and coaxial electromagnetic coils were placed orthogonallyto each other. The permanent magnets produced a static magnetic field of Hs = 22 Oe. A current
with a frequency of 45 Hz was input into the electromagnetic coils to produce an alternating
magnetic field with the amplitude varying from 0 to 33 Oe. Stool from a healthy volunteer wasdried into a hard block on an alcohol burner. A small piece of the dried stool and the as-prepared
Fe3O4 NP solution were successively placed into the microfluidic capillary. Then, the ends ofthe capillary were sealed with plasticine. The sequential images in Fig. 7 show the softening ofa large mass of hard stool in the microcapillary. Observations were made using a 10× microobjective. As shown, with an increase in current amplitude, the hard stool was gradually subjected
to perturbation. The center of the stool started to break up when Hp reached 16.5 Oe. With further
increase in the current amplitude, the whole stool block started to shake and broke into pieces.
These pieces moved up and down, aiding the breaking up of the remaining stool. After about 38s, the primary stool block had turned into scattered fragments. Here, quantities of aggregates withalmost all sizes were used to soften the stool. The results show that various aggregates of any size
formed by a magnetic field can be used to break stool.

Fig. 7. Image sequences display the softening of hard stool adhesions in microfluidic capillary by magneticallycontrolled Fe3O4 aggregates in a microfluidic capillary.  A large hard block was broken into pieces within 40 s.

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To observe the process more closely, an experiment in a petri dish with a 50× micro-objective
was conducted. The sequential images in Fig. 8 show the softening of stool with a single Fe3O4
NP aggregate. Before the sway-inducing magnetic field was activated, Fe3O4 NPs formed into an
ellipsoid-like aggregate under a static magnetic field of Hs = 22 Oe and was surrounded by messily
distributed stool. When a sway-inducing alternating magnetic field with an amplitude of Hp = 33
Oe and a frequency of 45 Hz was activated, the microrod swayed rapidly, breaking up the stool.
By adjusting the position of the permanent magnets, the microrod can be pushed forward or pulledback to break the stool in other positions. The aggregate was guided, by varying the magnetic
gradient, to come into contact with the stool on the right. The stool was gradually reduced withthe movement of the aggregate and cleared at about 24 s. In the whole process, the stool was
broken from left to right, which is coincident with the principle described. The aggregate wasalso damaged by the intense collision. However, the continuous strike results in the formation ofan empty space to the right so that the stool pellets can be removed from the clear region of thechannel.

4.

Discussion

Fecal impaction is a gastrointestinal problem in which hard stool obstructs the rectum. The
obstruction caused by hard stool has been softened and evacuated to open up a passageway using
Fe3O4 NP aggregates in vitro. As is known, Fe3O4 is also one of the most important spinel-typematerials and has gained much attention in the field of bioimaging. Such an operation mechanism
is promising for applications in sensing and treating fecal impaction because of the characteristics
of being a good MRI contrast agent and high biocompatibility of Fe3O4 NPs. However, someproblems must be solved before they can be applied in vivo. The heat generation during hard stool
softening may affect the rectum content with possible pain. The control of the temperature risein vivo induced by the magnetic NP motion in an alternating magnetic field is still being studied.
However, in our system, the delivered power is not high because of the low frequency of theexternal magnetic field. Thus, the evacuation of NP residues in the wrinkles of the rectum after
the completion of the process should be further studied.

Fig. 8. (Color online) Image sequences display the breaking of stools with swaying Fe3O4 aggregates observedwith a 50× micro-objective.

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Sensors and Materials, Vol. 29, No. 12 (2017)

Certainly, the limitations of our model should be improved for a more realistic in vivo
environment. Primarily, an isotonic dispersion medium, which is the survival environment of
human tissue, should be used in place of the deionized water in the experiment since magnetic
NPs behave almost the same in these two media. Moreover, because the characteristics of thedehydrated stool material after heat drying may differ from those of naturally dehydrated stool, theapplication of NPs to the latter should be investigated next.
However, the stool softening method using Fe3O4 NPs in a combined oscillating magnetic fieldhas been proposed in this study and verified in vitro. Its application in fecal impaction treatment invivo is forecasted in the future. The next step is to explore how to implement early diagnosis andsensing of fecal impaction by combining the motion manipulation of Fe3O4 NPs and MRI or otherbioimaging technologies. Since both motion control and imaging are based on the same materials,
such a combination is also expected.

5.

Conclusions

In the study, we demonstrated the motion of swaying Fe3O4 NP aggregates using a combined
oscillating magnetic field generated by two electromagnetic coils and two permanent magnets.
The swaying Fe3O4 aggregates were employed to soften hard stool in a microfluidic capillary. The
whole process was rapid (about 38 s) and required no other artificial intervention than the appliedmagnetic field. Although only a small block of hard stool was broken in the microfluidic capillary,
the softening efficiency is encouraging. Fecal impaction is a common and serious gastrointestinal
medical condition involving hard stool obstructing the rectum. Therefore, the detection andsoftening of hard stool in vivo via the noncontact control of biocompatible Fe3O4 NPs for thetreatment of fecal impaction is important and can be expected in the near future.

Acknowledgments
The authors gratefully acknowledge the support of the State Key Laboratory of Digital
Manufacturing Equipment and Technology, Huazhong University of Science and Technology,
China and Program for Research Foundation for Advanced Talents of Huaqiao University (Grant
No. 16BS504).

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About the Authors
Qian Li received his B.S. degree from Wuhan University of Science andTechnology, China, in 2012 and his M.S. degree from Huazhong University of
Science and Technology, China, in 2015. He is now a Ph.D. candidate in
Huazhong University of Science and Technology. His research interests include
nanomaterials and bioengineering.

Xiaojun Liu received his B.S. degree from Harbin Institute of Technology,
China, in 1990, his M.S. degree from Huazhong University of Science andTechnology, China, in 1996, and his Ph.D. degree from The Hong Kong
University of Science and Technology, China, in 2003. He is currently a full
professor in the School of Mechanical Science and Engineering at Huazhong
University of Science and Technology, China. At present he is a deputy directorof the research center for international standards of manufacturing technology,
Ministry of Education and a member of a specialized committee of the China Metrology andMeasurement Society. His research interests are in optical precision measuring techniques andinstruments, surface measurement and analysis, precision engineering, and bioengineering.

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Ming Chang received his B.S. degree from National Central University, Taiwan,
in 1976 and his M.S. and Ph.D. degrees from National Taiwan University,
Taiwan, in 1980 and 1986, respectively. Since 1994, he has been a full professor
in the Department of Mechanical Engineering at Chung Yuan Christian
University, Taiwan. At present he is also a director of the Chinese Metrology
Society and vice president of the Taiwan Automatic Optical Inspection
Equipment Association. His research interests include automated opticalinspection, precision metrology, and bioengineering.
Wei Hsiu Lin received his B.S. degree from I-Shou University, Taiwan, in 2009,and his M.S. degree from Chung Yuan Christian University, Taiwan, in 2011.
He is now is a Ph.D. candidate in Chung Yuan Christian University, Taiwan.
His research interests include automated optical inspection, application of
nanomaterials, and system integration.

Zhen Lu received her B.S. degree from Henan Normal University, China, in2012 and her M.S. degree from Huazhong University of Science and Technology,
China, in 2015. She is now an instructor at Shanghai University of ElectricPower, China. Her research interests include nanomaterials and bioengineering.