- Email: [email protected]
Development of a microscopic adhesive evaluation method using a scanning haptic microscope
Journal Pre-proof Development of a microscopic adhesive evaluation method using a scanning haptic microscope Takeshi Moriwaki, Sadao Omata, Yasuhide Nakayama
PII:
S0924-4247(19)31532-8
DOI:
https://doi.org/10.1016/j.sna.2019.111692
Reference:
SNA 111692
To appear in:
Sensors and Actuators: A. Physical
Received Date:
25 August 2019
Revised Date:
9 October 2019
Accepted Date:
22 October 2019
Please cite this article as: Moriwaki T, Omata S, Nakayama Y, Development of a microscopic adhesive evaluation method using a scanning haptic microscope, Sensors and Actuators: A. Physical (2019), doi: https://doi.org/10.1016/j.sna.2019.111692
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Research Paper
Development of a microscopic adhesive evaluation method using a scanning haptic microscope Takeshi Moriwakia*, Sadao Omatab, Yasuhide Nakayamac
Faculty of Science and Technology, Hirosaki University, Aomori, Japan.
b
Over Science & Technology Lab, Fukushima, Japan.
c
Biotube Co., Ltd., Tokyo, Japan
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a
re
*Correspondence to: Dr. Takeshi Moriwaki
Faculty of Science and Technology, Hirosaki University
Tel: +81-172-39-3690 Fax: +81-172-39-3690
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3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
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Email: [email protected] Graphical abstract
We propose a microscopic adhesive evaluation method using a scanning haptic microscope. By focusing on the variation in frequency during the pulling of the probe, the adhesive property
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between sample surface and probe tip could be evaluated quantitatively.
1
ro of -p
Highlights
Microscopic adhesion property was measured by our developed microscope
re
(SHM).
Detection resolution of adhesion property is very high.
Mutations in SWI-SNF complex and inactivated JAK-STAT signaling enriched at relapse
lP
Simultaneous micro-mapping of topography, elasticity and adhesion can be
Jo
ur na
expected.
2
ABSTRACT Single-point measurement methods have been proposed to study both microscopic to macroscopic adhesive properties; however, thus far, a simple and quantitative distribution observation method has not been established. A scanning haptic microscope (SHM) was developed to observe microscopic distribution of the elastic modulus of biological tissue surfaces. The SHM comprises a vibrating glass probe and measures the elastic modulus from the variation in vibration frequency during indentation by the probe. By focusing on the variation in frequency during the pulling of the probe, the adhesive properties between sample
ro of
surface and probe tip could be evaluated. In this study, we examined the possibility of measuring adhesion properties, as a basis study of adhesive property mapping by SHM. The samples used were silicone gels with different adhesive properties by varying the mixing ratio of silicones with high or low adhesion. The sample was indented using a glass probe as in usual
-p
SHM measurements. The time difference during the variation in frequency between indentation
re
and pulling (i.e., adhesion time) of each silicon sample was clearly distinguished. The adhesion time measured by the SHM was closely related to tack indices in rolling ball and probe tack
lP
tests; classical tests were conducted to quantitatively evaluate the tack. SHM is expected to be a powerful mapping tool of adhesive property with microscopic spatial resolution for
ur na
centimeter-level measurement areas.
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Keywords: adhesion, tack, micromechanics, tactile, scanning haptic microscope
3
1. INTRODUCTION Adhesion is a phenomenon related to static or dynamic bonding of contact interfaces, and it is attracting attention as an important parameter for evaluating cell functions such as cellular migration, differentiation, and growth regulation. The cell adhesive force and strength are thought to vary depending on cell activity and the surrounding environment (e.g. culture substrate, medium), affecting cell functions in biological processes. To evaluate adhesive properties, various methods have been proposed, such as micropipette aspiration [1,2], optical tweezer [3], and a shear flow device [4]. Atomic force microscopy (AFM) is a promising
ro of
method for understanding cell adhesive properties. AFM has nanoscale spatial resolution, enabling the detection of the adhesive force between an AFM probe and a cell or biological molecule. Furthermore, AFM enables the detection of adhesive force in both cell–molecule and molecule–molecule adhesion, using a modified probe. Thus, cell adhesion has been widely
-p
studied using AFM [5-7].
re
Here, tack is an important adhesive property for evaluating cell functions. Tack is a viscoelastic characteristic measuring the quickness of bonding in the attachment and
lP
detachment process between a viscoelastic sample and substrate. As highly quantitative adhesive tack measurement methods, rolling ball tack test and probe tack test have been commonly conducted, although they are macroscopic tests. In the rolling ball tack test, the
ur na
adhesive tack of sample surfaces is measured as the stopping distance of a rolling ball, and as the tensile load or distance of separation between a plunger and the sample surface in the probe tack test. Regarding the measurement method, the AFM adhesion test is considered a type of nanoscale probe tack test. Because measurement accuracy and sensitivity are closely related to
Jo
the contact area between the probe and sample surface, the quantitative capability of the probe tack test is restricted in the AFM adhesion test. The scanning haptic microscope (SHM) may be a powerful tool to quantitatively evaluate
adhesive tack. The SHM system was developed for precise observation of the topography and distribution of the elastic modulus over slices of natural tissue. This system is based on tactile sensor technology and a phase shift method [8], and the height and elastic modulus of each measurement point are measured by indentation with a vibrating glass probe. In previous 4
studies, the mechanical property of biological tissues such as ovum stiffness [9] and elastic modulus distribution of blood vessel walls [10] was evaluated using an SHM. Because the probe conducts indentation and pulling at each measurement point, SHM serves as a type of microscale probe tack test. Therefore, by focusing on the pulling process of the probe, the SHM could evaluate the tack of a sample surface. In this study, we used the SHM to evaluate microscopic tack. In comparison to the rolling ball tack test and probe tack test, this study reveals the adequate quantitative measurement
2. MATERIALS AND METHODS 2.1. Measurement principle of adhesive tack by SHM
ro of
capability of the SHM adhesion test.
The SHM (SHM-3000, P&M Co., Fukushima, Japan) is a microscopic imaging tool for
-p
topographical imaging and elastic modulus measurements in natural soft tissue. The details of
re
the device configuration and measurement principles have been presented elsewhere [10]. Briefly, the SHM system comprises a microtactile sensor probe, three stages, two cameras, and
lP
two controllers (Fig. 1). The sensor probe has a glass needle and lead zirconate titanate (PZT) sensor element. There are three electrodes in the PZT sensor element: input, output, and ground. The sensor unit operates based on the phase-shift method [8]. The sensor probe is vibrated near
ur na
the resonance frequency by applying an AC voltage to the PZT sensor element. The vibration state is maintained by a phase shift circuit in the controller as a feedback circuit for the vibration phase. A frequency change is generated by the contact between the sensor tip and sample surface; this frequency change rate with indentation depth has an almost linear relationship with
Jo
the elastic modulus of the sample. The pattern mapping of the frequency change at each point across the entire measurement area of a sample was converted to the distribution image of the elastic modulus.
The adhesive property of a sample surface can be evaluated via the oscillation frequency change during the probe pulling process. Figure 2 shows the oscillation frequency change and probe tip motion during the indentation and pulling of the sensor probe in an SHM measurement. During indentation, the sensor probe approaches the sample surface (I), and the oscillation 5
frequency varies as the probe tip indents and establishes contact with the sample surface (II). In general SHM measurement, a topography and an elastic modulus distribution are created by deriving the contact height and the rate of frequency change with indentation distance at each measurement point during indentation. After a short standby time (III), the pulling process begins. During probe pulling (IV), the oscillation frequency returns to that before contact through complete separation of the probe tip and sample surface (V, VI). In a low adhesive sample, the time required for the frequency change is nearly equal during both indentation and pulling. Contrastingly, in a high adhesive sample, the frequency change time during pulling is
ro of
longer than that during indentation due to clinging.
2.2. Sample preparation
Silicone gels were used as adhesion test samples. Adhesive properties of samples were
-p
adjusted by varying the ratios of two silicone materials, namely a high adhesive gel (TSE3062;
re
TANAC Co., Ltd., Gifu, Japan) and low adhesive gel (TSE3450, TANAC Co., Ltd.). Samples were prepared with six different high adhesive gel percentages of 80, 86, 90, 94, 96, and 98
lP
wt%. Each sample was solidified in an oven (50 °C, ca. 24 h), after mixing and degassing.
2.3. Scanning haptic microscope (SHM) measurement
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A microscopic adhesion test was conducted using the SHM. The SHM measurement was conducted according to the procedure in our previous report [10]. Silicone samples were solidified to obtain a cylinder with a 35-mm diameter and a 10-mm height. Three samples were prepared for each mixing ratio of the silicone materials. SHM measurements were conducted
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thrice for each sample, providing nine measurements in total for each mixing ratio of the silicone gels. The tip diameters of the glass probes were 10–38 μm; there were six probes in total. The indentation depth and probe speed were 10 μm and 0.2 mm/s, respectively. To evaluate the tack property quantitatively, adhesion time Tad was defined as follows: 𝑇ad = (𝑡pu10 − 𝑡pu90 ) − (𝑡in90 − 𝑡in10 ).
(1)
6
Here, tin10 [s] and tin90 [s] are durations exceeding 10% and 90% of the maximum frequency change during the indentation process, respectively, and tpu10 [s] and tpu90 [s] are durations less than 10% and 90% of the maximum frequency change during the probe pulling process, respectively.
2.4. Rolling ball tack test The rolling ball tack test was conducted with reference to ASTM D3121, the standard adhesive tack test used for adhesive tapes (Fig. 3A). As the test ball, a stainless-steel ball with
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a 1-mm diameter was used. The rolling ball apparatus was specially designed using a 3D printer (Projet HD3000; 3D Systems, RockHill, SC, USA). The running distance and incline angle were 150 mm and 21°, respectively. Silicone samples were solidified to form sheets with a 280mm length, 30-mm width, and 3-mm height. Three samples were prepared for each mixing ratio
-p
of the silicone materials, and the stopping distance was measured thrice for each sample,
re
providing a total of nine distance measurements for each mixing ratio.
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2.5. Probe tack test
The probe tack test was conducted with reference to ASTM D2979, using a creep meter (Rheoner II; Yamaden, Tokyo, Japan) (Fig. 3B). A stainless-steel rod with a 7-mm tip diameter
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was used as the plunger. The same silicon samples used in the SHM measurements were used, with the test conducted thrice for each sample, providing a total of nine probe tack test measurements. Before the test, the plunger was pushed into the silicone samples to a depth of 0.5 mm to establish adhesion between the plunger and sample surface. The plunger was then
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lifted at a rate of 0.05 mm/s until failure, i.e., separation of the plunger and sample surface.
3. RESULTS
3.1. Scanning haptic microscope (SHM) measurement The changes in oscillation frequency with respect to time are shown in Fig. 4A. The frequency change time during the indentation process ( 𝑡in90 − 𝑡in10 ) did not change significantly depending on the sample. However, the frequency change time during the pulling 7
process (𝑡pu10 − 𝑡pu90 ) increased as the proportion of the high adhesive gel increased. The adhesion time Tad was longer at instances of higher proportions of the high adhesive gel (Fig. 4B). Adhesion time in the measurement of the same sample tended to be longer for a probe with a thicker tip (Fig. 4C).
3.2. Macroscopic tests The results of the rolling ball tack test are shown in Fig. 5. The stopping distance was shorter in samples with a high tack. Accordingly, the stopping distance was shorter in samples
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with higher proportions of the high adhesive gel.
The relationships between the removed distance and adhesive force obtained in the probe tack test are shown in Fig. 6A. The maximum adhesive force tended to be smaller for higher proportions of the high adhesive gel; however, the variation in the maximum value was larger
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for low proportions of the high adhesive gel (Fig. 6B). The adhesive distance, the removed
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distance detected by the maximum adhesive force, is longer at higher proportions of the high
4. DISCUSSION
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adhesive gel (Fig. 6C).
In this study, the feasibility of a microscopic adhesion test using an SHM was investigated.
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In the SHM measurements, the frequency change time during the pulling process was longer for sticky gels, resulting in a longer adhesion time Tad. The sticky samples had a higher tack index, taking more time for the sample surface and glass tip to separate during the pulling process, as shown in Fig. 2 and 4A. Accordingly, the adhesion time Tad provided a measure of
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the tack shown by the sample surface.
Based on the value of Tad, it appears that tack can be measured with good quantification
using an SHM. The relationship between Tad and the results of both the rolling ball tack test and probe tack test is shown in Fig. 7. Tad sufficiently correlated with the indices of general macroscopic tack tests, showing that an SHM measurement can quantitatively evaluate the tack of a sample surface. Because the variation in the average Tad is small, SHM has a tack detection resolution that can express differences in the level of several centimeters in the rolling ball tack 8
test. When measuring the same sample, Tad tended to be larger when using a thicker probe (Fig. 4C). This shows that thicker probes have higher tack detection resolutions. The adhesive property can be clearly observed because a thicker probe establishes contact with a larger area. AFM is widely used to understand the adhesive properties of biological sample surfaces from the molecular to the cellular level. Although AFM is devised to better detect sensitivity such as cantilever rigidity and optical lever detection, an SHM with a sufficient probe size is considered to have a tack detection resolution that is equal to or greater than that of AFM. However, a
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comparison of tack detection resolution between SHM and AFM is left as future work.
This study revealed that an SHM can measure the tack of sample surface. The only arrangement to evaluate the tack was calculation of Tad; SHM measurement was conducted in the same matter as previous studies. This means that the height, elastic modulus, and tack of
-p
the sample can be measured simultaneously using SHM. The tack on the sample surface may
re
also affect the frequency change during the indentation process, decreasing the detection accuracy of the elastic modulus. According to Figure 4A, however, the effect of the tack of the
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sample surface on frequency change appears to be much smaller in the indentation process than in the pulling process. Therefore, it is considerable that SHM can achieve both high-accuracy tack and elastic modulus measurements. By developing a software that calculates and displays
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Tad at each measurement point, the mapping of tack distribution of the sample surface is possible. Furthermore, the biomolecules of the SHM probe can be modified in a similar manner to AFM studies [11,12]. If the SHM probe is modified with the antigen and the sample is coated with the antibody, the specific adhesive reaction can be detected along with topographic and
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elasticity details using an SHM. Thus, the SHM is expected to be a powerful mapping tool for adhesion property of living tissue surfaces.
5. CONCLUSION We used an SHM to evaluate the microscopic adhesive properties as a first step to observe the distribution of the adhesive properties of natural tissue. The SHM sufficiently evaluated the tack of a sample surface. This is done by calculating the adhesion time, which is measured as 9
the time difference for the variation in frequency between the indentation and pulling processes. The adhesion time measured using the SHM was closely related to the measured tack values in the rolling ball tack and probe tack tests. Therefore, an SHM can evaluate the microscale adhesive properties of sample surfaces quantitively. COMPETING INTERESTS There are no conflicts of interests to declare.
ACKNOWLEDGMENTS
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This study was funded in part by a Grant-in-Aid for Scientific Research (26289127) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and a Grant from the
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Nakatani Foundation.
10
REFERENCES 1.
B. Hogan, A. Babataheri, Y. Hwang, A.I. Barakat, J. Husson, Biophys. J. 109 (2015), 209219.
2.
X. Lian, S. Liu, L. Liu, R. Xu, M. Du, S. Whang, H. Zhu, Q. Lu, Q. Zhang, Y. Wu, D. Huang, Y. Wei, Regen. Biomater. 5 (2018), 151-157.
3.
A.A. Khalili, M.R. Ahmad, Int. J. Mol. Sci. 16 (2015), 18149-18184
4.
H. Wang, J. Xia, Z. Zheng, Y.P. Zhuang, X. Yi, D. Zhang, P. Whang, Bioprocess Biosyst. Eng. 41 (2018), 1371-1382. T.D. Nguyen, Y. Gu, Sci. Rep. 6 (2016), 38059.
6.
J. Han, L. Xu, S. Qian, X. Hu, T. Guo, S. Wu, Y. Liu, Z. Jiang, Sens. Actuators A. Phys.
ro of
5.
267 (2017), 127-134. 7.
H. Kim, A. Yamagishi, M. Imaizumi, Y. Onomura, A. Nagasaki, Y. Miyagi, T. Okada, C.
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Nakamura, Colloids Surf. B Biointerfaces 155 (2017), 366-372.
S. Omata, Y. Terunuma, Sens. Actuators A. Phys. 35 (1992), 9-15.
9.
Y. Murayama, C.E. Constantinou, S. Omata, J. Biomech. 37 (2004), 67-72.
re
8.
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10. T. Moriwaki, T. Oie, K. Takamizawa, Y. Murayama, T. Fukuda, S. Omata, K. Kanda, Y. Nakayama, J. Artif. Organs 14 (2011), 276-283. 11. Z. Hong, K.J. Reeves, Z. Sun, Z. Li, N.J. Brown, G.A. Meininger, PLoS One 10 (2015),
ur na
e0119533.
12. N. Kamprad, H. Witt, M. Schröder, C.T. Kreis, O. Bäumchen, A. Janshoff, M. Tarantola,
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Nanoscale 10 (2018), 22504-22519.
11
BIOGRAPHY
Dr. Takeshi Moriwaki Takeshi Moriwaki is Assistant Professor (Ph. D) of Faculty of Science and Technology, Hirosaki University. His research interests include evaluation of physical properties at soft
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tissue, and development of film-type force sensors.
Dr. Sadao Omata
Sadao Omata is Director (Ph. D) of Over Science & Technology Lab. His research interests
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include ultrasonic or optical evaluation and development of haptic devices.
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Dr. Yasuhide Nakayama
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Yasuhide Nakayama is Chief Technical Officer (Ph. D) of Biotube Co., Ltd. His research interests include the development of biological artificial tissues and stent for aneurysm
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treatment.
12
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Figure 1.
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FIGURE LEGENDS
(A) Photograph of scanning haptic microscope system (bar = 50 mm). (B) Samples and sensor probe (bar = 10 mm). (C) Magnification image of glass probe tip (bar = 50 μm).
13
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Figure 2.
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Change of oscillation frequency (A) and tip motion (B) of an SHM probe.
14
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Figure 3.
Photographs of (A) rolling ball tack test apparatus (bar = 50 mm) and (B) probe tack test
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apparatus (bar = 20 mm).
15
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SHM measurement results. (A) Oscillation frequency of sensor probe during indentation and pulling processes. (B) The relationship between a sample’s adherence property and its adhesion time with the sensor probe (tip diameter: 20.1 μm). (C) The relationship between the tip size and adhesion time for 98% high adhesive gel. The error bars denote standard deviation.
16
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Figure 5.
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Stop distances in rolling ball tack test. The error bars denote standard deviation.
17
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(A) Adhesive force-displacement relationships in the probe tack test, (B) maximum adhesive force, and (C) removed distance detected at maximum adhesive force at each gel sample. The error bars denote standard deviation.
18
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Figure 7.
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Relationships among values measured using SHM and (A) rolling ball tack test and (B) probe tack test. The error bars denote standard deviation. The squares of correlation coefficient were
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0.995 for the rolling ball tack test, and 0.991 for the probe tack test.
19
PII:
S0924-4247(19)31532-8
DOI:
https://doi.org/10.1016/j.sna.2019.111692
Reference:
SNA 111692
To appear in:
Sensors and Actuators: A. Physical
Received Date:
25 August 2019
Revised Date:
9 October 2019
Accepted Date:
22 October 2019
Please cite this article as: Moriwaki T, Omata S, Nakayama Y, Development of a microscopic adhesive evaluation method using a scanning haptic microscope, Sensors and Actuators: A. Physical (2019), doi: https://doi.org/10.1016/j.sna.2019.111692
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Research Paper
Development of a microscopic adhesive evaluation method using a scanning haptic microscope Takeshi Moriwakia*, Sadao Omatab, Yasuhide Nakayamac
Faculty of Science and Technology, Hirosaki University, Aomori, Japan.
b
Over Science & Technology Lab, Fukushima, Japan.
c
Biotube Co., Ltd., Tokyo, Japan
-p
ro of
a
re
*Correspondence to: Dr. Takeshi Moriwaki
Faculty of Science and Technology, Hirosaki University
Tel: +81-172-39-3690 Fax: +81-172-39-3690
lP
3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
ur na
Email: [email protected] Graphical abstract
We propose a microscopic adhesive evaluation method using a scanning haptic microscope. By focusing on the variation in frequency during the pulling of the probe, the adhesive property
Jo
between sample surface and probe tip could be evaluated quantitatively.
1
ro of -p
Highlights
Microscopic adhesion property was measured by our developed microscope
re
(SHM).
Detection resolution of adhesion property is very high.
Mutations in SWI-SNF complex and inactivated JAK-STAT signaling enriched at relapse
lP
Simultaneous micro-mapping of topography, elasticity and adhesion can be
Jo
ur na
expected.
2
ABSTRACT Single-point measurement methods have been proposed to study both microscopic to macroscopic adhesive properties; however, thus far, a simple and quantitative distribution observation method has not been established. A scanning haptic microscope (SHM) was developed to observe microscopic distribution of the elastic modulus of biological tissue surfaces. The SHM comprises a vibrating glass probe and measures the elastic modulus from the variation in vibration frequency during indentation by the probe. By focusing on the variation in frequency during the pulling of the probe, the adhesive properties between sample
ro of
surface and probe tip could be evaluated. In this study, we examined the possibility of measuring adhesion properties, as a basis study of adhesive property mapping by SHM. The samples used were silicone gels with different adhesive properties by varying the mixing ratio of silicones with high or low adhesion. The sample was indented using a glass probe as in usual
-p
SHM measurements. The time difference during the variation in frequency between indentation
re
and pulling (i.e., adhesion time) of each silicon sample was clearly distinguished. The adhesion time measured by the SHM was closely related to tack indices in rolling ball and probe tack
lP
tests; classical tests were conducted to quantitatively evaluate the tack. SHM is expected to be a powerful mapping tool of adhesive property with microscopic spatial resolution for
ur na
centimeter-level measurement areas.
Jo
Keywords: adhesion, tack, micromechanics, tactile, scanning haptic microscope
3
1. INTRODUCTION Adhesion is a phenomenon related to static or dynamic bonding of contact interfaces, and it is attracting attention as an important parameter for evaluating cell functions such as cellular migration, differentiation, and growth regulation. The cell adhesive force and strength are thought to vary depending on cell activity and the surrounding environment (e.g. culture substrate, medium), affecting cell functions in biological processes. To evaluate adhesive properties, various methods have been proposed, such as micropipette aspiration [1,2], optical tweezer [3], and a shear flow device [4]. Atomic force microscopy (AFM) is a promising
ro of
method for understanding cell adhesive properties. AFM has nanoscale spatial resolution, enabling the detection of the adhesive force between an AFM probe and a cell or biological molecule. Furthermore, AFM enables the detection of adhesive force in both cell–molecule and molecule–molecule adhesion, using a modified probe. Thus, cell adhesion has been widely
-p
studied using AFM [5-7].
re
Here, tack is an important adhesive property for evaluating cell functions. Tack is a viscoelastic characteristic measuring the quickness of bonding in the attachment and
lP
detachment process between a viscoelastic sample and substrate. As highly quantitative adhesive tack measurement methods, rolling ball tack test and probe tack test have been commonly conducted, although they are macroscopic tests. In the rolling ball tack test, the
ur na
adhesive tack of sample surfaces is measured as the stopping distance of a rolling ball, and as the tensile load or distance of separation between a plunger and the sample surface in the probe tack test. Regarding the measurement method, the AFM adhesion test is considered a type of nanoscale probe tack test. Because measurement accuracy and sensitivity are closely related to
Jo
the contact area between the probe and sample surface, the quantitative capability of the probe tack test is restricted in the AFM adhesion test. The scanning haptic microscope (SHM) may be a powerful tool to quantitatively evaluate
adhesive tack. The SHM system was developed for precise observation of the topography and distribution of the elastic modulus over slices of natural tissue. This system is based on tactile sensor technology and a phase shift method [8], and the height and elastic modulus of each measurement point are measured by indentation with a vibrating glass probe. In previous 4
studies, the mechanical property of biological tissues such as ovum stiffness [9] and elastic modulus distribution of blood vessel walls [10] was evaluated using an SHM. Because the probe conducts indentation and pulling at each measurement point, SHM serves as a type of microscale probe tack test. Therefore, by focusing on the pulling process of the probe, the SHM could evaluate the tack of a sample surface. In this study, we used the SHM to evaluate microscopic tack. In comparison to the rolling ball tack test and probe tack test, this study reveals the adequate quantitative measurement
2. MATERIALS AND METHODS 2.1. Measurement principle of adhesive tack by SHM
ro of
capability of the SHM adhesion test.
The SHM (SHM-3000, P&M Co., Fukushima, Japan) is a microscopic imaging tool for
-p
topographical imaging and elastic modulus measurements in natural soft tissue. The details of
re
the device configuration and measurement principles have been presented elsewhere [10]. Briefly, the SHM system comprises a microtactile sensor probe, three stages, two cameras, and
lP
two controllers (Fig. 1). The sensor probe has a glass needle and lead zirconate titanate (PZT) sensor element. There are three electrodes in the PZT sensor element: input, output, and ground. The sensor unit operates based on the phase-shift method [8]. The sensor probe is vibrated near
ur na
the resonance frequency by applying an AC voltage to the PZT sensor element. The vibration state is maintained by a phase shift circuit in the controller as a feedback circuit for the vibration phase. A frequency change is generated by the contact between the sensor tip and sample surface; this frequency change rate with indentation depth has an almost linear relationship with
Jo
the elastic modulus of the sample. The pattern mapping of the frequency change at each point across the entire measurement area of a sample was converted to the distribution image of the elastic modulus.
The adhesive property of a sample surface can be evaluated via the oscillation frequency change during the probe pulling process. Figure 2 shows the oscillation frequency change and probe tip motion during the indentation and pulling of the sensor probe in an SHM measurement. During indentation, the sensor probe approaches the sample surface (I), and the oscillation 5
frequency varies as the probe tip indents and establishes contact with the sample surface (II). In general SHM measurement, a topography and an elastic modulus distribution are created by deriving the contact height and the rate of frequency change with indentation distance at each measurement point during indentation. After a short standby time (III), the pulling process begins. During probe pulling (IV), the oscillation frequency returns to that before contact through complete separation of the probe tip and sample surface (V, VI). In a low adhesive sample, the time required for the frequency change is nearly equal during both indentation and pulling. Contrastingly, in a high adhesive sample, the frequency change time during pulling is
ro of
longer than that during indentation due to clinging.
2.2. Sample preparation
Silicone gels were used as adhesion test samples. Adhesive properties of samples were
-p
adjusted by varying the ratios of two silicone materials, namely a high adhesive gel (TSE3062;
re
TANAC Co., Ltd., Gifu, Japan) and low adhesive gel (TSE3450, TANAC Co., Ltd.). Samples were prepared with six different high adhesive gel percentages of 80, 86, 90, 94, 96, and 98
lP
wt%. Each sample was solidified in an oven (50 °C, ca. 24 h), after mixing and degassing.
2.3. Scanning haptic microscope (SHM) measurement
ur na
A microscopic adhesion test was conducted using the SHM. The SHM measurement was conducted according to the procedure in our previous report [10]. Silicone samples were solidified to obtain a cylinder with a 35-mm diameter and a 10-mm height. Three samples were prepared for each mixing ratio of the silicone materials. SHM measurements were conducted
Jo
thrice for each sample, providing nine measurements in total for each mixing ratio of the silicone gels. The tip diameters of the glass probes were 10–38 μm; there were six probes in total. The indentation depth and probe speed were 10 μm and 0.2 mm/s, respectively. To evaluate the tack property quantitatively, adhesion time Tad was defined as follows: 𝑇ad = (𝑡pu10 − 𝑡pu90 ) − (𝑡in90 − 𝑡in10 ).
(1)
6
Here, tin10 [s] and tin90 [s] are durations exceeding 10% and 90% of the maximum frequency change during the indentation process, respectively, and tpu10 [s] and tpu90 [s] are durations less than 10% and 90% of the maximum frequency change during the probe pulling process, respectively.
2.4. Rolling ball tack test The rolling ball tack test was conducted with reference to ASTM D3121, the standard adhesive tack test used for adhesive tapes (Fig. 3A). As the test ball, a stainless-steel ball with
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a 1-mm diameter was used. The rolling ball apparatus was specially designed using a 3D printer (Projet HD3000; 3D Systems, RockHill, SC, USA). The running distance and incline angle were 150 mm and 21°, respectively. Silicone samples were solidified to form sheets with a 280mm length, 30-mm width, and 3-mm height. Three samples were prepared for each mixing ratio
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of the silicone materials, and the stopping distance was measured thrice for each sample,
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providing a total of nine distance measurements for each mixing ratio.
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2.5. Probe tack test
The probe tack test was conducted with reference to ASTM D2979, using a creep meter (Rheoner II; Yamaden, Tokyo, Japan) (Fig. 3B). A stainless-steel rod with a 7-mm tip diameter
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was used as the plunger. The same silicon samples used in the SHM measurements were used, with the test conducted thrice for each sample, providing a total of nine probe tack test measurements. Before the test, the plunger was pushed into the silicone samples to a depth of 0.5 mm to establish adhesion between the plunger and sample surface. The plunger was then
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lifted at a rate of 0.05 mm/s until failure, i.e., separation of the plunger and sample surface.
3. RESULTS
3.1. Scanning haptic microscope (SHM) measurement The changes in oscillation frequency with respect to time are shown in Fig. 4A. The frequency change time during the indentation process ( 𝑡in90 − 𝑡in10 ) did not change significantly depending on the sample. However, the frequency change time during the pulling 7
process (𝑡pu10 − 𝑡pu90 ) increased as the proportion of the high adhesive gel increased. The adhesion time Tad was longer at instances of higher proportions of the high adhesive gel (Fig. 4B). Adhesion time in the measurement of the same sample tended to be longer for a probe with a thicker tip (Fig. 4C).
3.2. Macroscopic tests The results of the rolling ball tack test are shown in Fig. 5. The stopping distance was shorter in samples with a high tack. Accordingly, the stopping distance was shorter in samples
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with higher proportions of the high adhesive gel.
The relationships between the removed distance and adhesive force obtained in the probe tack test are shown in Fig. 6A. The maximum adhesive force tended to be smaller for higher proportions of the high adhesive gel; however, the variation in the maximum value was larger
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for low proportions of the high adhesive gel (Fig. 6B). The adhesive distance, the removed
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distance detected by the maximum adhesive force, is longer at higher proportions of the high
4. DISCUSSION
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adhesive gel (Fig. 6C).
In this study, the feasibility of a microscopic adhesion test using an SHM was investigated.
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In the SHM measurements, the frequency change time during the pulling process was longer for sticky gels, resulting in a longer adhesion time Tad. The sticky samples had a higher tack index, taking more time for the sample surface and glass tip to separate during the pulling process, as shown in Fig. 2 and 4A. Accordingly, the adhesion time Tad provided a measure of
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the tack shown by the sample surface.
Based on the value of Tad, it appears that tack can be measured with good quantification
using an SHM. The relationship between Tad and the results of both the rolling ball tack test and probe tack test is shown in Fig. 7. Tad sufficiently correlated with the indices of general macroscopic tack tests, showing that an SHM measurement can quantitatively evaluate the tack of a sample surface. Because the variation in the average Tad is small, SHM has a tack detection resolution that can express differences in the level of several centimeters in the rolling ball tack 8
test. When measuring the same sample, Tad tended to be larger when using a thicker probe (Fig. 4C). This shows that thicker probes have higher tack detection resolutions. The adhesive property can be clearly observed because a thicker probe establishes contact with a larger area. AFM is widely used to understand the adhesive properties of biological sample surfaces from the molecular to the cellular level. Although AFM is devised to better detect sensitivity such as cantilever rigidity and optical lever detection, an SHM with a sufficient probe size is considered to have a tack detection resolution that is equal to or greater than that of AFM. However, a
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comparison of tack detection resolution between SHM and AFM is left as future work.
This study revealed that an SHM can measure the tack of sample surface. The only arrangement to evaluate the tack was calculation of Tad; SHM measurement was conducted in the same matter as previous studies. This means that the height, elastic modulus, and tack of
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the sample can be measured simultaneously using SHM. The tack on the sample surface may
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also affect the frequency change during the indentation process, decreasing the detection accuracy of the elastic modulus. According to Figure 4A, however, the effect of the tack of the
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sample surface on frequency change appears to be much smaller in the indentation process than in the pulling process. Therefore, it is considerable that SHM can achieve both high-accuracy tack and elastic modulus measurements. By developing a software that calculates and displays
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Tad at each measurement point, the mapping of tack distribution of the sample surface is possible. Furthermore, the biomolecules of the SHM probe can be modified in a similar manner to AFM studies [11,12]. If the SHM probe is modified with the antigen and the sample is coated with the antibody, the specific adhesive reaction can be detected along with topographic and
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elasticity details using an SHM. Thus, the SHM is expected to be a powerful mapping tool for adhesion property of living tissue surfaces.
5. CONCLUSION We used an SHM to evaluate the microscopic adhesive properties as a first step to observe the distribution of the adhesive properties of natural tissue. The SHM sufficiently evaluated the tack of a sample surface. This is done by calculating the adhesion time, which is measured as 9
the time difference for the variation in frequency between the indentation and pulling processes. The adhesion time measured using the SHM was closely related to the measured tack values in the rolling ball tack and probe tack tests. Therefore, an SHM can evaluate the microscale adhesive properties of sample surfaces quantitively. COMPETING INTERESTS There are no conflicts of interests to declare.
ACKNOWLEDGMENTS
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This study was funded in part by a Grant-in-Aid for Scientific Research (26289127) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and a Grant from the
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Nakatani Foundation.
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10. T. Moriwaki, T. Oie, K. Takamizawa, Y. Murayama, T. Fukuda, S. Omata, K. Kanda, Y. Nakayama, J. Artif. Organs 14 (2011), 276-283. 11. Z. Hong, K.J. Reeves, Z. Sun, Z. Li, N.J. Brown, G.A. Meininger, PLoS One 10 (2015),
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e0119533.
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Nanoscale 10 (2018), 22504-22519.
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BIOGRAPHY
Dr. Takeshi Moriwaki Takeshi Moriwaki is Assistant Professor (Ph. D) of Faculty of Science and Technology, Hirosaki University. His research interests include evaluation of physical properties at soft
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tissue, and development of film-type force sensors.
Dr. Sadao Omata
Sadao Omata is Director (Ph. D) of Over Science & Technology Lab. His research interests
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include ultrasonic or optical evaluation and development of haptic devices.
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Dr. Yasuhide Nakayama
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Yasuhide Nakayama is Chief Technical Officer (Ph. D) of Biotube Co., Ltd. His research interests include the development of biological artificial tissues and stent for aneurysm
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treatment.
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Figure 1.
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FIGURE LEGENDS
(A) Photograph of scanning haptic microscope system (bar = 50 mm). (B) Samples and sensor probe (bar = 10 mm). (C) Magnification image of glass probe tip (bar = 50 μm).
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Figure 2.
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Change of oscillation frequency (A) and tip motion (B) of an SHM probe.
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Figure 3.
Photographs of (A) rolling ball tack test apparatus (bar = 50 mm) and (B) probe tack test
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apparatus (bar = 20 mm).
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SHM measurement results. (A) Oscillation frequency of sensor probe during indentation and pulling processes. (B) The relationship between a sample’s adherence property and its adhesion time with the sensor probe (tip diameter: 20.1 μm). (C) The relationship between the tip size and adhesion time for 98% high adhesive gel. The error bars denote standard deviation.
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Figure 5.
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Stop distances in rolling ball tack test. The error bars denote standard deviation.
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(A) Adhesive force-displacement relationships in the probe tack test, (B) maximum adhesive force, and (C) removed distance detected at maximum adhesive force at each gel sample. The error bars denote standard deviation.
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Figure 7.
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Relationships among values measured using SHM and (A) rolling ball tack test and (B) probe tack test. The error bars denote standard deviation. The squares of correlation coefficient were
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0.995 for the rolling ball tack test, and 0.991 for the probe tack test.
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