Access to this full-text is provided by Springer Nature.
Content available from Scientific Reports
This content is subject to copyright. Terms and conditions apply.
1
Vol.:(0123456789)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports
Moisture retention of glycerin
solutions with various
concentrations: a comparative
study
H. J. Chen1,2,7, P. Y. Lee3,7, C. Y. Chen4, S. L. Huang4,5, B. W. Huang5, F. J. Dai1,2, C. F. Chau1,
C. S. Chen1 & Y. S. Lin4,5,6*
Various methods of evaluating a humectant’s moisture retention have unique mechanisms. Hence, for
designing advanced or ecient ingredients of cosmetic products, a clear understanding of dierences
among methods is required. The aim of this study was to analyze the moisture-retention capacity
of glycerin, a common ingredient in cosmetic products. Specically, this study applied gravimetric
analysis, transepidermal water loss (TEWL) analysis, and dierential scanning calorimetry (DSC)
to examine the evaporation of glycerin solutions of dierent concentrations. The results revealed
that the moisture-retention capacity of glycerin increased with the glycerin concentration from 0
to 60 wt%, and glycerin at concentration of 60–70 wt% did not exhibit weight change during the
evaporation process. When the glycerin concentration exceeded 70 wt%, moisture sorption occurred
in the glycerin solution. Furthermore, the results revealed a deviation between the evaporation
rates measured using gravimetric analysis and those measured using TEWL analysis. However,
normalizing the results of these analyses yielded the relative evaporation rates to water, which
were consistent between these two analyses. DSC thermograms further conrmed the consistent
results and identied two hydrated water microstructures (nonfreezable water and free water) in the
glycerin solutions, which explained why the measured evaporation rate decreased with the glycerin
concentration. These ndings can be applied to prove the moisture-retention capacity of a humectant
in cosmetic products by dierent measuring methods.
e moisture-retention capacity of ingredients is crucial in cosmetics1. An eective moisture-retaining agent
in cosmetic products can be benecial against skin aging2,3. A humectant is a hygroscopic substance that can
maintain skin moisture and hydration3,4. Loss of skin hydration engenders skin dryness, wrinkling, sagging, and
laxity. Accordingly, several studies have sought humectants that exhibit high ecacy in retaining moisture on
the human stratum corneum5.
A humectant’s moisture-retention capacity can be measured through various methods such as gravimetric
analysis, transepidermal water loss (TEWL) analysis, dierential scanning calorimetry (DSC), thermogravimetric
analysis, dilatometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy–based relaxation
time analysis6–9. Among these methods, gravimetric analysis can be easily applied to measure the weight change
of an analyte in a material through evaporation within a specic period; a low level of weight loss indicates high
moisture retention. However, because of the detection limit of balance machines used for gravimetric analy-
sis, considerable time is required for accumulating detectable weight changes in order to measure a solution’s
OPEN
1Department of Food Science and Biotechnology, National Chung Hsing University, No. 145, Xingda Rd.,
South Dist., Taichung City 402204, Taiwan, ROC. 2Healthmate Co., Ltd., No. 14, Pinghe 1st St., Changhua
City 500016, Taiwan, ROC. 3Department of Optoelectronics and Materials Technology, National Taiwan Ocean
University, No. 2, Beining Rd., Zhongzheng Dist., Keelung City 202301, Taiwan, ROC. 4Ph.D. Program in
Materials and Chemical Engineering, National United University, No. 2, Lienda Rd., Miaoli City 360302, Taiwan,
ROC. 5Department of Chemical Engineering, National United University, No. 2, Lienda Rd., Miaoli City 360302,
Taiwan, ROC. 6Institute of Food Safety and Health Risk Assessment, National Yang Ming Chiao Tung University,
No. 155, Sec. 2, Linong St. Beitou Dist., Taipei City 112304, Taiwan, ROC. 7
These authors contributed equally:
H. J. Chen and P. Y. Lee. *email: linys@nuu.edu.tw
Content courtesy of Springer Nature, terms of use apply. Rights reserved
2
Vol:.(1234567890)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
evaporation rate, which is an indicator of the solution’s moisture-retention10. erefore, in gravimetric analysis,
obtaining accurate evaporation rates is a time-consuming process11.
In general, TEWL refers to the amount of water vapor that permeates a certain area of membrane per unit of
time and can be measured using a probe. A TEWL probe is an open-chamber system that applies two pairs of
temperature and moisture sensors on a cylinder to determine water loss (in grams per hour per square meter)
through evaporation12. e measuring principle of a TEWL probe is based on Fick’s law of diusion, which relates
to the mass transfer rate of water per unit area within a specic period. Compared with water loss measurement
methods that involve weighing an analyte, a TEWL probe can aord a more stable measurement of water loss
in a few minutes13.
DSC is a powerful tool for exploring the microstructure and thermal behavior of a liquid sample14; it can
also be applied for evaluating the moisture retention of a humectant15. According to the freezing temperature
criterion, the microstructure of water in a humectant can be categorized into three types: nonfreezable water,
intermediate water, and free water8,16–19, as shown in Fig.1 for three hydrated water types. Nonfreezable water
and intermediate water can easily bind to a humectant through hydrogen bonding and are thus called bound
water. Intermediate water and free water can exhibit phase transitions and are thus called freezable water20. Non-
freezable water tightly binds to the hydrophilic sites of a humectant and has low mobility because of the strong
water–humectant interactions. Specically, nonfreezable water involves very weak free water–water interactions.
Intermediate water is oriented around nonfreezable water and the humectant as a hydration shell, forming cage-
like structures through which the maximum number of hydrogen bonds is achieved in the available space21.
e molecular interactions of intermediate water involve both water–humectant and water–water interactions.
Molecular interactions of free water mainly involve water–water interactions.
Various methods of evaluating a humectant’s moisture retention have unique mechanisms. Hence, for design-
ing advanced or ecient ingredients of cosmetic products, a clearer understanding of the dierences among
such methods is required. Accordingly, this study used glycerin—a common humectant—as a model to examine
moisture retention; specically, the study examined the moisture-retention capacity of glycerin solutions of dif-
ferent concentrations by using three convenient methods, namely; gravimetric analysis, TEWL assessment and
DSC, for comparison.
Materials and methods
Glycerin (First Cosmetics Manufacture Co., Ltd., Taiwan) and deionized water were used in this study. Glycerin
solutions of dierent concentrations (wt%) were prepared by diluting glycerin with various amounts of deion-
ized water; these solutions were then subjected to evaporation experiments. Each evaporation experiment was
conducted by placing 3mL glycerin solution in a vial with an internal diameter of 9mm. ese experiments
were conducted in a closed system at 30°C and 70% relative humidity.
e weight change of the glycerin solutions during evaporation was automatically monitored using a precise
ve-digit electronic balance machine (AS 60/220.R2, Radwag Wagi Elektroniczne, Poland) for 35h. Additionally,
a well-known TEWL probe (Courage + Khazaka Electronic, Köln, Germany) was used to detect the evaporation
rate of the glycerin solutions at the beginning of the evaporation process according to the international guidelines.
A single measurement was collected every 2s until the standard deviation was below 0.1g/hr/m2.
DSC experiments were performed using a dierential scanning calorimeter (Q10, TA Instruments, New
Castle, USA) with a ermo Model FC100AX0TA refrigerated cooling system and ermal Advantage Universal
Analysis soware. A 5-mg sample was weighed and sealed in the aluminum pan of the calorimeter. e sample
pan along with a reference pan was then placed in the DSC instrument, cooled from 40 to − 50°C, and heated up
again to 40°C at a rate of 1°C/min to avoid the response time lag caused by a faster heating rate. e temperature
and enthalpy peak associated with the phase transition during the heating process were analyzed. e enthalpy
in unit of J/g was calculated by integration of enthalpy peak and normalization of water weight in the glycerin
solution6. e experiments were repeated at least three times to ensure the reproducibility of the DSC results.
Results and discussion
Gravimetric analysis. Figure2a illustrates the uctuation of the instantaneous evaporation rate of a water
solution with time; the rate was measured using an electronic balance. e weight of the water solution was
measured automatically every minute during the evaporation process to calculate the instantaneous evaporation
rate. e instantaneous evaporation rate uctuated considerably because of a limited change in the weight of the
water solution during the evaporation process and detection limitation of the balance. Figure2b displays the
accumulative average evaporation rate dened as the overall evaporation rate from start to a certain time, pre-
sented in Fig.2a. As indicated in this gure, the accumulative average evaporation rate also uctuated consider-
Figure1. ree hydrated water types in a humectant.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
3
Vol.:(0123456789)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
ably during the early phases of the evaporation process due to the small weight change; however, the uctuation
decreased gradually with evaporation time because of the relatively large accumulated weight change. A stable
accumulative average evaporation rate may be obtained aer more than 5h. erefore, the gravimetric analysis
was determined to consume considerable time before yielding a stable evaporation rate.
Evaporation rates measured using gravimetric and TEWL analyses. e evaporation rate of a
humectant can be an indicator of the moisture-retention capacity of the humectant. Figure3 presents evapora-
tion rates measured through gravimetric and TEWL analyses for glycerin solutions of dierent concentrations
(wt%). e evaporation rate of 10wt% glycerin measured through TEWL analysis was determined to be consist-
ent with that revealed by an invivo report on 20 healthy volunteers22. e results of the two analyses indicated
that the evaporation rate decreased with the glycerin concentration, demonstrating that a concentrated glycerin
solution has a high moisture-retention capacity. No obvious evaporation rate could be measured when the glyc-
erin concentration was at 60–70wt%. is phenomenon can be attributed to the equilibrium between glycerin
evaporation and moisture sorption. A glycerin molecule has three hydroxyl groups and is hygroscopic. When
the glycerin concentration exceeded 70wt%, a considerable amount of moisture sorption occurred, resulting in
an increase in the weight of the glycerin solution and a negative evaporation rate.
is study revealed a deviation between the evaporation rates measured using gravimetric analysis and those
measured using TEWL analysis. e rates measured using gravimetric analysis were higher than those meas-
ured using TEWL analysis. is deviation can be attributed to the dierent mechanisms of these two analyses.
In gravimetric analysis, the direct evaporation rate of a solution is measured in terms of weight loss (in grams
per hour per square meter) during the evaporation process. By contrast, in TEWL analysis, evaporation rate is
0
10
20
30
40
50
60
70
Instantaneous evaporation rate (g/hr/m2)
Time (hr)
0
10
20
30
40
50
60
70
80
0510 15 20 25 30 35 0510 15 20 25 30
35
Accumulated average evaporation rate (g/hr/m2
)
Time (hr)
(a() b)
Figure2. Gravimetric analysis of water evaporation rate with time: (a) instantaneous evaporation rate and (b)
accumulative average evaporation rate.
-40
-30
-20
-10
0
10
20
30
40
0102030405060708090
100
Gravimetric
TEWL
Glycerin concentration (wt %)
Evaporation rates (g/hr/m²)
Figure3. Evaporation rate of glycerin solutions of various concentrations measured by using gravimetric and
TEWL analyses.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
4
Vol:.(1234567890)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
evaluated as the rate of water vapor diusion through a TEWL probe, as determined through the calculation of
vapor density gradient using Fick’s law of diusion.
To ensure a fair comparison between the analyses, this study normalized their results. e relative evapora-
tion rate to water (RERW) was dened as the ratio of the water evaporation rate of glycerin solution to the water
evaporation rate of pure water. Figure4 displays the RERW measured using gravimetric and TEWL analyses.
e rates derived from the two analyses were consistent, verifying the accuracy of this evaporation experiment.
According to the denition of RERW, moisture sorption started when the RERW was less than 0%, where no
water loss occurred. erefore, as revealed in Fig.4, when the RERW was 0%, the glycerin concentration was
approximately 60–70wt%. Glycerin concentrations that were lower than 60wt% were associated with positive
and less than 100% RERWs, indicating that glycerin at this concentration can achieve moisture retention and
reduced evaporation. However, when the glycerin concentration was higher than 70wt%, the RERW became
negative, demonstrating that glycerin at this concentration can gain water. is nding agrees with the reports
of Fluhr etal.23 and Kiran etal.24 that glycerin is an excellent humectant and hygroscopic agent. Humectancy
or hygroscopicity is the tendency of a substance to absorb moisture from the surrounding atmosphere. Pure
glycerin absorbs its own weight in water over 3 days23.
DSC analysis. DSC analysis was conducted to investigate the microstructure of water in the glycerin solu-
tions. Figure5 displays DSC thermograms of the glycerin solutions of dierent concentrations. e melting
curves varied considerably with the glycerin concentration, with an obvious peak appearing at a glycerin con-
centration of 0wt% and no signal appearing aer a glycerin concentration of 70wt% indicating existence of
nonfreezable water. ese peaks were ascribed to the melting of frozen water including bulk water and free
water18. Dierent types of frozen water have dierent transition temperatures and peak shapes. e transition
-150
-100
-50
0
50
100
150
0102030405060708090
100
Gravimetric
TEWL
Glycerin concentration (wt %)
Relative evaporation rate to water (%)
Figure4. RERWs of glycerin solutions of various concentrations measured by using gravimetric and TEWL
analyses.
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
-50-40 -30-20 -100 10 20
0 % glycerin
10 % glycerin
20 % glycerin
30 % glycerin
40 % glycerin
50 % glycerin
60 % glycerin
70 % glycerin
80 % glycerin
90 % glycerin
100 % glycerin
Temperature (℃)
Heat flow (mW)
Endo
Figure5. Heating curves of DSC thermograms at a 1°C/min scanning rate for glycerin solutions of various
concentrations.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
5
Vol.:(0123456789)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
temperature of intermediate water is lower than that of free water19. Nevertheless, no melting peak was observed
for intermediate water in this study. is result corresponded to a previous study reporting that poly(2-meth-
oxyethylacrylate) analogous polymers had just two hydrated water types, nonfreezable water and free water18.
Table1 presents a summary of the peaks observed for the glycerin solutions of dierent concentrations. e
melting enthalpy observed for 0wt% glycerin was noted to be consistent with the value obtained for pure water
in a previous study25, indicating that the DSC method and conditions considered in the present study could be
applicable to other study settings. e results also revealed that the peak temperature decreased with the glycerin
concentration and that only 0wt% glycerin was associated with a positive peak temperature. e positive melting
peak indicates that the microstructure type of the water in 0wt% glycerin was bulk water18. However, the melt-
ing peaks associated with 10–60wt% glycerin were lower than 0°C, signifying that the microstructure type of
the water in the material also included free water except bulk water. When the glycerin concentration exceeded
70wt%, no melting peak was observed, revealing that the microstructure of the water was nonfreezable water.
Figure6 illustrates the microstructure type of the water in the glycerin solutions at dierent concentrations.
e melting enthalpy peak decreased with the glycerin concentration, and no melting enthalpy was observed
when the glycerin concentration exceeded 70wt% (Table1). is nding was consistent with the results of the
evaporation experiments conducted using gravimetric analysis and the TEWL probe. e melting enthalpy
resulted from frozen water (bulk water and free water), which can evaporate. e melting enthalpy increases with
the amount of frozen water evaporating. is thus explains why the evaporation rate of the glycerin solutions
decreased with the glycerin concentration. For concentrated glycerin solutions, the microstructure of the water
tended to be nonfreezable water without evaporation.
To more clearly demonstrate the microstructures of water, the DSC thermograms for glycerin solutions with
concentrations of < 10wt% are displayed in Fig.7 for comparison. e curves for 0.1, 1, and 5wt% glycerin were
between those for 0 and 10wt% glycerin. e melting peaks associated with 0.1, 1, and 5wt% glycerin shied
le from 0wt% glycerin toward lower temperature regions; additionally, the melting temperatures ranged from
Table 1. DSC thermogram analysis of 0 to 100wt% glycerin solutions.
Glycerin concentration (wt%) Peak temperature (°C) Enthalpy (J/g)
0 0.64 334.3
10 − 2.28 213.8
20 − 5.48 167.0
30 − 9.80 112.1
40 − 15.77 67.7
50 − 23.50 50.8
60 − 32.45 8.5
70 – –
80 – –
90 – –
100 – –
Figure6. A schematic diagram to illustrate the microstructure type of the water in the glycerin solutions with
various concentrations.
Content courtesy of Springer Nature, terms of use apply. Rights reserved
6
Vol:.(1234567890)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
both above and below 0°C. is phenomenon signies that free water was formed when glycerin molecules were
added to the bulk water solution18. When the glycerin concentration reached 10wt%, the melting peak was in
the negative temperature region because of the large amount of free water. Furthermore, as revealed in Table2,
in addition to the peak temperature, the melting enthalpy decreased with the glycerin concentration.
Conclusions
is study compared three methods used to evaluate the moisture-retention capacity of glycerin solutions of
dierent concentrations. e results indicate that the moisture-retention capacity of glycerin increases with the
glycerin concentration. Although a deviation was observed between the results of gravimetric analysis and TEWL
analysis, normalizing the results of these analyses revealed reasonably high consistency levels between them. In
addition to conrming the consistency between the gravimetric and TEWL analyses results, this study gener-
ated DSC thermograms to further identify two hydrated water forms in the glycerin solutions, which explained
the measured evaporation rates of the glycerin solutions. ese ndings can be applied to prove the moisture-
retention capacity of a humectant in cosmetic products by dierent measuring methods.
Data availability
All data generated or analysed during this study are included in this published article.
Received: 9 April 2022; Accepted: 13 May 2022
References
1. Kim, H. et al. Seeking better topical delivery technologies of moisturizing agents for enhanced skin moisturization. Expert Opin.
Dr ug. D eliv. 15, 17–31 (2018).
2. C hoi, S. Y. et al. Protective eects of fermented honeybush (Cyclopia intermedia) extract (HU-018) against skin aging: a randomized,
double-blinded, placebo-controlled study. J. Cosmet. Laser er. 20, 313–318 (2018).
3. Wang, H. et al. Novel confocal Raman microscopy method to investigate hydration mechanisms in human skin. Skin Res. Technol.
25, 653–661 (2019).
4. Spada, F., Barnes, T. M. & Greive, K. A. Skin hydration is signicantly increased by a cream formulated to mimic the skin’s own
natural moisturizing systems. Clin. Cosmet. Investig. Dermatol. 11, 491–497 (2018).
5. Chen, K., Guo, B. & Luo, J. Quaternized carboxymethyl chitosan/organic montmorillonite nanocomposite as a novel cosmetic
ingredient against skin aging. Carbohydr. Polym. 173, 100–106 (2017).
6. Li, W., Xue, F. & Cheng, R. States of water in partially swollen poly(vinyl alcohol) hydrogels. Polymer 46, 12026–12031 (2005).
7. Kataoka, Y., Kitadai, N., Hisatomi, O. & Nakashima, S. Nature of hydrogen bonding of water molecules in aqueous solutions of
glycerol by attenuated total reection (ATR) infrared spectroscopy. Appl. Spectrosc. 65, 436–441 (2011).
-50 -40-30 -20-10 01020
0 % glycerin
0.1 % glycerin
1 % glycerin
5 % glycerin
10 % glycerin
Temperature (℃)
Heatflow (mW)
Endo
Figure7. Heating curves of DSC thermograms at a 1°C/min scanning rate for glycerin solutions with the
concentrations of 0–10wt%.
Table 2. DSC thermogram analysis of glycerin solutions with low concentrations.
Glycerin concentration (wt%) Peak temperature (°C) Enthalpy (J/g)
0 0.64 334.3
0.1 0.48 295.3
1 0.42 269.4
5− 0.68 259.8
10 − 2.28 213.8
Content courtesy of Springer Nature, terms of use apply. Rights reserved
7
Vol.:(0123456789)
Scientic Reports | (2022) 12:10232 | https://doi.org/10.1038/s41598-022-13452-2
www.nature.com/scientificreports/
8. Bag, M. A. & Valenzuela, L. M. Impact of the hydration states of polymers on their hemocompatibility for medical applications: a
review. Int. J. Mol. Sci. 18, 1422 (2017).
9. Jiménez-Pérez, Z. E. et al. Applications of Panax ginseng leaves-mediated gold nanoparticles in cosmetics relation to antioxidant,
moisture retention, and whitening eect on B16BL6 cells. J. Ginseng Res. 42, 327–333 (2018).
10. Lin, Y. S. & Chen, C. Y. A novel evaporation detection system using an impedance sensing chip. Analyst 139, 5781–5784 (2014).
11. Chou, W. L., Lee, P. Y., Chen, C. Y., Lin, Y. H. & Lin, Y. S. A high performance impedance-based platform for evaporation rate
detection. J. Vis. Exp. 116, e54575 (2016).
12. Cristiano, M. C. et al. Invitro and invivo trans-epidermal water loss evaluation following topical drug delivery systems application
for pharmaceutical analysis. J. Pharm. Biomed. Anal. 186, 113295 (2020).
13. De Paepe, K., Houben, E., Adam, R., Wiesemann, F. & Rogiers, V. Validation of the VapoMeter, a closed unventilated chamber
system to assess transepidermal water loss vs. the open chamber Tewameter®. Skin. Res. Technol. 11, 61–69 (2005).
14. Sambale, A., Kurkowski, M. & Stommel, M. Determination of moisture gradients in polyamide 6 using StepScan DSC. ermochim.
Acta 672, 150–156 (2019).
15. Lin, C. P. & Tsai, S. Y. Dierences in the moisture capacity and thermal stability of Tremella fuciformis polysaccharides obtained
by various drying processes. Molecules 24, 2856 (2019).
16. Utoh, S. Nonfreezing water conned in water layer of multilamellar L-α, distearoyl phosphatidylcholine in temperature range
between 0 °C and −190 °C. J. Chem. Phys. 115, 601–607 (2001).
17. Tranoudis, I. & Efron, N. Water properties of so contact lens materials. Cont. Lens Anterior Eye 27, 193–208 (2004).
18. Tanaka, M. & Mochizuki, A. Eect of water structure on blood compatibility-thermal analysis of water in poly(meth)acrylate. J.
Biomed. Mater. Res. A 68, 684–695 (2004).
19. Abasi, S., Davis, R., Podstawczyk, D. A. & Guiseppi-Elie, A. Distribution of water states within poly(HEMA-co-HPMA)-based
hydrogels. Polymer 185, 121978 (2019).
20. Tahmasebi, A. et al. A dierential scanning calorimetric (DSC) study on the characteristics and behavior of water in low-rank
coals. Fuel 135, 243–252 (2014).
21. Qu, X., Wirsén, A. & Albertsson, A. C. Novel pH-sensitive chitosan hydrogels: swelling behavior and states of water. Polymer 41,
4589–4598 (2000).
22. Polaskova, J., Pavlackova, J. & Egner, P. Eect of vehicle on the performance of active moisturizing substances. Skin Res. Technol.
21, 403–412 (2015).
23. Fluhr, J. W., Bornkessel, A. & Berardesca, E. Glycerol—Just a moisturizer? Biological and biophysical eects. In Dry skin and
moisturizers: chemistry and function 2nd edn (eds Loden, M. & Maibach, H. I.) 227 (CRC Press, 2005).
24. Kiran, M., Mane, A., Banerjee, B., Mehta, H. & Yadav, P. A comparative study to evaluate the ecacy of carboxy methyl cellulose
with glycerin and balanced electrolytes as excipients vs plain carboxy methyl cellulose, for keeping the eye moist. J. Med. Sci. Clin.
Res. 5, 18316–18322 (2017).
25. Faroongsarng, D. & Sukonrat, P. ermal behavior of water in the selected starch- and cellulose-based polymeric hydrogels. Int.
J. Pharm. 352, 152–158 (2008).
Author contributions
C.Y. Chen and B.W. Huang did data curation. H.J. Chen, P.Y. Lee, S.L. Huang, F.J. Dai, C.F. Chau, C.S. Chen,
and Y.S. Lin performed formal analysis and discussion. Y.S. Lin wrote the main manuscript text. All authors
reviewed the manuscript.
Funding
is research was funded by the Ministry of Science and Technology, Grant Number 110-2622-E-239-003.
Competing interests
e authors declare no competing interests.
Additional information
Correspondence and requests for materials should be addressed to Y.S.L.
Reprints and permissions information is available at www.nature.com/reprints.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and
institutional aliations.
Open Access is article is licensed under a Creative Commons Attribution 4.0 International
License, which permits use, sharing, adaptation, distribution and reproduction in any medium or
format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the
Creative Commons licence, and indicate if changes were made. e images or other third party material in this
article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the
material. If material is not included in the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from
the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
© e Author(s) 2022
Content courtesy of Springer Nature, terms of use apply. Rights reserved
1.
2.
3.
4.
5.
6.
Terms and Conditions
Springer Nature journal content, brought to you courtesy of Springer Nature Customer Service Center GmbH (“Springer Nature”).
Springer Nature supports a reasonable amount of sharing of research papers by authors, subscribers and authorised users (“Users”), for small-
scale personal, non-commercial use provided that all copyright, trade and service marks and other proprietary notices are maintained. By
accessing, sharing, receiving or otherwise using the Springer Nature journal content you agree to these terms of use (“Terms”). For these
purposes, Springer Nature considers academic use (by researchers and students) to be non-commercial.
These Terms are supplementary and will apply in addition to any applicable website terms and conditions, a relevant site licence or a personal
subscription. These Terms will prevail over any conflict or ambiguity with regards to the relevant terms, a site licence or a personal subscription
(to the extent of the conflict or ambiguity only). For Creative Commons-licensed articles, the terms of the Creative Commons license used will
apply.
We collect and use personal data to provide access to the Springer Nature journal content. We may also use these personal data internally within
ResearchGate and Springer Nature and as agreed share it, in an anonymised way, for purposes of tracking, analysis and reporting. We will not
otherwise disclose your personal data outside the ResearchGate or the Springer Nature group of companies unless we have your permission as
detailed in the Privacy Policy.
While Users may use the Springer Nature journal content for small scale, personal non-commercial use, it is important to note that Users may
not:
use such content for the purpose of providing other users with access on a regular or large scale basis or as a means to circumvent access
control;
use such content where to do so would be considered a criminal or statutory offence in any jurisdiction, or gives rise to civil liability, or is
otherwise unlawful;
falsely or misleadingly imply or suggest endorsement, approval , sponsorship, or association unless explicitly agreed to by Springer Nature in
writing;
use bots or other automated methods to access the content or redirect messages
override any security feature or exclusionary protocol; or
share the content in order to create substitute for Springer Nature products or services or a systematic database of Springer Nature journal
content.
In line with the restriction against commercial use, Springer Nature does not permit the creation of a product or service that creates revenue,
royalties, rent or income from our content or its inclusion as part of a paid for service or for other commercial gain. Springer Nature journal
content cannot be used for inter-library loans and librarians may not upload Springer Nature journal content on a large scale into their, or any
other, institutional repository.
These terms of use are reviewed regularly and may be amended at any time. Springer Nature is not obligated to publish any information or
content on this website and may remove it or features or functionality at our sole discretion, at any time with or without notice. Springer Nature
may revoke this licence to you at any time and remove access to any copies of the Springer Nature journal content which have been saved.
To the fullest extent permitted by law, Springer Nature makes no warranties, representations or guarantees to Users, either express or implied
with respect to the Springer nature journal content and all parties disclaim and waive any implied warranties or warranties imposed by law,
including merchantability or fitness for any particular purpose.
Please note that these rights do not automatically extend to content, data or other material published by Springer Nature that may be licensed
from third parties.
If you would like to use or distribute our Springer Nature journal content to a wider audience or on a regular basis or in any other manner not
expressly permitted by these Terms, please contact Springer Nature at
onlineservice@springernature.com
Available via license: CC BY 4.0
Content may be subject to copyright.