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. 2025 Nov 5;25:1752. doi: 10.1186/s12903-025-06819-0

Optimizing hydrogen peroxide shock treatment frequencies for dental unit waterlines contamination control: a pilot study

Ting Shuai 1,#, Jingcheng Wen 2,#, Wenjing Liu 2, Tianyi Shao 2, Huibin Pei 3, Yanying Li 3, Chanyuan Jin 1,✉, Xiue Li 4,✉
PMCID: PMC12590708  PMID: 41194147

Abstract

Objective

This study aims to determine the optimal disinfection frequency by comparing the effectiveness of different hydrogen peroxide (H2O2) shock treatment schedules in controlling contamination of dental unit waterlines (DUWLs).

Methods

Three dental units were randomly assigned to groups A, B, and C. After initial treatment with the Biofilm-Removing Set (BRS®), continuous treatment with 0.0141% H2O2 was applied. Shock treatment with 1.41% H2O2 was conducted every three weeks for group A, every 2 weeks for group B, and weekly for group C over 6 weeks. Water samples were collected thrice weekly to monitor bacterial counts, with a compliance threshold of 100 CFU/mL. Electron microscopy was used to assess biofilm morphology.

Results

A total of 132 samples were analyzed. Following BRS® treatment, bacterial counts decreased significantly to 15–45 CFU/mL. Groups B and C achieved 100% compliance, while group A had 68.42% compliance, with visible biofilm noted. There were significant statistical differences in compliance rates among three groups (p < 0.05).

Conclusions

Continuous treatment with 0.0141% H2O2, combined with biweekly or weekly 1.41% H2O2 shock treatment, may help control DUWLs contamination in the short term under the conditions tested. Future studies should expand the sample size and duration for long-term efficacy assessment.

Keywords: Dental unit waterlines, Infection control, Hydrogen peroxide, Shock treatment, Biofilm

Introduction

Dental unit waterlines (DUWLs) are composed of interconnected polyurethane or polyvinyl chloride tubing with internal diameters of approximately 1–4 mm and lengths of about 6 m, serving as a critical component of dental chair units (DCUs) by providing treatment water [1, 2]. DUWLs are particularly prone to microbial contamination due to their structural characteristics, including narrow lumens, stagnant water, backflow, and biofilm formation on inner surfaces [3]. According to the American Centers for Disease Control and Prevention (CDC) and the American Dental Association (ADA), treatment water used in DUWLs should meet a microbiological standard of ≤ 500 colony-forming units per milliliter (CFU/mL) [4]. However, reports frequently find contamination levels that far exceed the thresholds, often harboring opportunistic pathogens such as Legionella and Pseudomonas aeruginosa [5–8]. The water quality of DUWLs used in dental procedures directly impacts the health of both patients and healthcare professionals. For example, a 1985 U.S. survey revealed that 20% of dental healthcare personnel tested positive for Legionella IgM antibodies, significantly higher than the general population, highlighting the risks of DUWLs contamination [9]. In 2012, a case report in the Lancet described an 82-year-old woman who contracted Legionella pneumophila from dental treatment water and subsequently died, underscoring the potential severity of such infection [10]. The Coronavirus Disease 2019 (COVID-19) pandemic further amplified these concerns, as pathogens like severe acute respiratory syndrome coronavirus 2 can infiltrate DUWLs through dental handpiece backflow, colonize the tubing, and spread via aerosols generated during procedures [11, 12]. This poses a heightened risk, particularly to immunocompromised individuals [13, 14].

Over the past 30 years, research on DUWLs contamination has evolved significantly, with current control strategies primarily relying on a combination of physical and chemical disinfection methods. Physical measures, such as anti-retraction devices, flushing protocols, and improvements in tubing materials, have been partially effective in controlling microbial growth but fail to eliminate biofilms [15–17]. Chemical disinfectants, including sodium hypochlorite, hypochlorous acid, and hydrogen peroxide have shown broad-spectrum efficacy in reducing biofilm formation [18–21].

Among these, hydrogen peroxide, in particular, is favored for its rapid action, low toxicity, and environmental friendliness. Periodic chemical disinfection alone is insufficient to maintain water quality standards due to the risk of dental handpiece backflow [22, 23]. Backflow can introduce microorganisms into the DUWLs during clinical procedures, leading to rapid recolonization and biofilm growth. Consequently, guidelines issued by the CDC and ADA recommended a combination of continuous low-concentration disinfectant use and periodic shock disinfection for effective contamination control [2, 24]. However, the instability of hydrogen peroxide over time limits its effectiveness. Recent advances in hydrogen peroxide-based compound disinfectants have improved stability and disinfection performance. A study in vitro demonstrated that continuous disinfection with Dentosept® S, combined with shock treatment every four weeks, achieved bacterial levels below 100 CFU/mL in all the biofilms [2]. Another study showed that continuous disinfection with Dentosept® S could achieve bacterial levels below 200 CFU/mL in over 91% of water samples [25]. Despite these promising results, our preliminary study in China revealed that this protocol achieved only an 89.9% compliance rate after 25 weeks, with bacterial counts rising during the third week of each cycle. This indicates that the standard four-week shock disinfection frequency is insufficient to maintain consistent water quality in clinical settings [26].

Given the limitations of existing protocols, including biofilm persistence and the variability of contamination control across different clinical settings, there is an urgent need to optimize shock treatment frequency. However, to date, there have been no studies directly exploring the optimal shock treatment interval in real-world clinical environments. Thus, based on both clinical practicality and observations from our previous work, we designed this pilot study to preliminarily explore the effects of weekly, biweekly, and triweekly shock treatments. By identifying a feasible interval that reliably maintains water quality standards, this research aims to provide evidence to inform future, larger-scale investigations and enhance infection control strategies in dental settings.

Methods

DCUs

The sample size was determined by the number of eligible DCUs available for the pilot study and thus three DCUs (Intego Pro, Dentsply Sirona, USA) from a dental teaching hospital in China were selected as research subjects. Three DCUs were from the prosthodontics department, equipped with automatic flush disinfecting systems, and were put into clinical use simultaneously. These DCUs were less than 1 year old at the time of the study, having been installed and operational for the same duration. The input water for all DCUs was filtered municipal water, and DUWLs were not replaced during the study period. Prior to the study, three DCUs had never undergone any chemical disinfection treatment. Three DCUs were randomly assigned to three groups (Group A, Group B, and Group C) using a random draw method. Each DCU was assigned a number, the numbers were placed in sealed envelopes, and an envelope was drawn at random to assign each DCU to a group.

Biofilm removal procedure before disinfection

On Saturday afternoon, a standardized biofilm removal procedure was performed on all DUWLs of three DCUs prior to disinfection to restore them to a near-original state. The Biofilm-Removing-Set (BRS®), manufactured by ALPRO MEDICAL GMBH (Germany), was used, following the ISO 16,954 − 2015 [27] standard test method for DUWLs biofilm treatment. The BRS® consists of BRS® PreCleaner, BRS® Remover, and BRS® Activator [27].

BRS® PreCleaner (10 g, powder sachet) was dissolved in 2 L of warm water (50 °C) and flushed through the DUWLs using a vibrating piston pump. BRS® Remover (160 g, sachet) was then dissolved in 2 L of warm water (50–60 °C), combined with 20 mL of BRS® Activator, and thoroughly mixed before being flushed through the DUWLs. Following this, Bilpron® (light blue solution, 1 L) was added to the DCUs’ built-in water tanks and allowed to sit for 24 h. After the holding period, the lines were flushed with municipal water until the blue solution was completely cleared, followed by an additional 30 sec flush. Finally, water samples were collected from dental handpiece and three-way syringe outlets immediately after the final flushing and again at 8:00 am the following morning to evaluate the total bacterial count. If the water quality did not meet the required standards, the biofilm removal process was repeated to restore the DUWLs as close as possible to their initial state.

Continuous treatment with disinfectants

Dentosept® S (ALPRO MEDICAL GMBH, Germany), a compound disinfectant containing 1.41% hydrogen peroxide as the active ingredient, was used for continuous low-concentration disinfection of DUWLs across all three DCUs. After confirming that the treatment water met the required standards, Dentosept® S was added to the water tanks of each DCU at a concentration of 1.41% hydrogen peroxide. During the 6-week study period, the DCU’s automatic disinfection system mixed municipal water with 1.41% hydrogen peroxide at a 100:1 ratio, achieving a final concentration of 0.0141% hydrogen peroxide in the treatment water used for continuous low-concentration disinfection (1.41% ÷ 100 = 0.0141%). The automatic disinfection system flushed the DUWLs for 2 min and then dried them at the start and end of each clinical day. Between the treatment of two consecutive patients, dental handpieces run idle for 30 s. This final concentration of 0.0141% hydrogen peroxide was selected according to the manufacturer’s recommendation for continuous dental unit waterline disinfection, as it effectively balances antimicrobial efficacy and equipment safety during routine clinical use.

Shock treatment with disinfectants

In addition to continuous low-concentration disinfection with 0.0141% hydrogen peroxide, a shock treatment protocol was implemented for the three groups at varying intervals. Group A underwent shock treatment once every 3 weeks, Group B every 2 weeks, and Group C once a week. Shock treatments were initiated at the end of the clinical day every Friday during the 6-week study period. During the shock treatment, the automatic disinfection system filled the DUWLs with 1.41% hydrogen peroxide, which remained in DUWLs for 24 h. The following Saturday afternoon, the system automatically flushed the waterlines with municipal water and dried, ensuring readiness for subsequent use. To maintain safety and water quality, if a DCU remained unused for more than 3 consecutive days, a shock treatment was performed before clinical operations resumed.

Sampling of DUWLs

From April to May 2024, a total of 132 water samples were collected from the outlets of high-speed handpieces and air-water syringes across three DCUs. To establish the baseline microbial contamination levels in DUWLs, water samples were collected for three consecutive days prior to the implementation of BRS®. Each sampling was performed before the start of daily clinical work. The sampling process involved flushing each water outlet for 2 min, disinfecting the outlet with a 75% ethanol swab, and collecting 10 mL of water in sterile tubes. Immediately following the application of the BRS®, water samples were collected to assess the effectiveness of biofilm removal. Subsequently, during the 6-week disinfection period, water samples were obtained every Monday, Wednesday, and Friday morning before the start of clinical operations. These samples were collected following the same protocol as baseline sampling and were mixed with 30% sodium thiosulfate in a 3:1 ratio to neutralize residual hydrogen peroxide from the Dentosept® S disinfectant.

For biofilm analysis, tubing specimens were excised from the internal DUWLs at specific intervals. Before the implementation of BRS®, a 1 cm section of the waterline tubing supplying high-speed hand-piece from one DCU (Group C) was collected using sterile scissors. Then after the implementation of BRS®, the biofilm sample was collected from one DCU (Group C) tubing again. After the 6-week study, a 1 cm section of the waterline tubing supplying the high-speed handpiece was collected from each of the three DCUs using sterile scissors. All collected samples were immediately transported to the laboratory for microbial analysis. Samples that could not be tested within a short timeframe were stored in a 4 °C refrigerator and analyzed within 24 h to ensure sample integrity. Microbial cultures were initiated within the same period to accurately reflect microbial load and biofilm presence.

Total viable counts (TVCs) detection

1 mL of the neutralized water sample was added to a petri dish, followed by the addition of 20 mL of nutrient agar medium (Aoboxing Biotech Co., Beijing, China) at approximately 45–50 ℃. The water sample was thoroughly mixed with the medium. After cooling and solidifying, the petri dishes were inverted and incubated at 36 ℃ ± 1 ℃ for 48 h. After incubation, the total bacterial colony count was performed and reported. According to the Guidelines for Infection Control and Management in Dental Unit Waterlines in China, dental treatment water is considered acceptable if the total bacterial colony count does not exceed 100 CFU/mL [28].

Biofilm analysis

To evaluate biofilm presence and removal, sections of high-speed handpiece tubing were prepared for scanning electron microscopy (SEM) analysis using a JSM-5600 microscope (JEOL, Japan). Using sterile scissors, 0.1 cm was trimmed from each end of the tubing to remove potential contamination. The remaining tubing was carefully slit lengthwise to expose the inner surface.

Samples were fixed at room temperature with 2.5% glutaraldehyde for 1 h to preserve cellular structures and biofilm morphology. Following fixation, the samples underwent sequential dehydration in an ethanol gradient (10%, 30%, 50%, 75%, 90%, and 100%), with each step lasting 5 min. The 100% ethanol step was repeated three times to ensure complete dehydration, after which the samples were air-dried. Once dried, the samples were sputter-coated with a thin layer of gold to enhance electrical conductivity. Finally, the prepared samples were mounted on a SEM stub using conductive adhesive and observed under SEM for biofilm analysis.

Statistical analysis

Data entry and statistical analysis were performed using SPSS version 26.0 (Chicago, IL). Continuous variables following a normal distribution and with homogeneity of variance were described as mean ± standard deviation (Mean ± SD), and one-way analysis of variance (ANOVA) was used for between-group comparisons. When a significant difference was found by ANOVA, Tukey’s Honestly Significant Difference (HSD) post-hoc test was applied for multiple pairwise comparisons. For non-normally distributed continuous variables, the median (M) with interquartile range (min, max) was used for description. Categorical variables were described using frequency and percentage, and comparisons between groups were performed using the chi-square test. p < 0.05 was considered statistically significant.

Results

Baseline characteristics of DCUs

All three DCUs showed similar baseline bacterial contamination levels prior to implementing the biofilm removal and disinfection procedures, with no statistically significant differences among the groups (high-speed handpieces: F (2,6) = 1.12, p = 0.387, η² = 0.27, 95% CI [0.00 – 0.67]; air-water syringe: F (2,6) = 0.23, p = 0.801, η² = 0.07, 95% CI [0.00 – 0.36]) (seen in Table 1). Each DCU operated an average of 5.5 days per week, serving approximately 10 patients daily.

Table 1.

Total viable counts of output water of DCUs

Sampling time Group A (CFU/mL) Group B (CFU/mL) Group C (CFU/mL)
HSHP AWS HSHP AWS HSHP AWS
2 days before BRS® 10,708 9655 4620 710 5070 660
1 day before BRS® 6147 696 6680 1455 2576 2410
On the morning of BRS® 9455 5460 9436 8465 8895 6569
Immediately after BRS® 15 18 45 26 26 29
Day 1 15 18 46 35 31 15
Day 3 8 18 15 2 32 34
Day 5 24 30 22 19 9 56
Day 8 7 13 35 36 44 33
Day 10 13 21 26 75 9 27
Day 12 49 40 54 28 48 40
Day 15 80 60 26 17 17 29
Day 17 50 95 20 24 42 25
Day 19 56 88 15 9 13 9
Day 22 25 18 19 46 56 37
Day 24 12 13 31 21 15 21
Day 26 70 41 21 43 14 18
Day 29 225 110 36 47 35 31
Day 31 543 523 29 40 17 28
Day 33 416 401 33 43 39 45
Day 36 513 442 29 37 24 31
Day 38 362 284 41 38 32 38
Day 40 325 326 38 24 28 31
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Notes: CFU/mL colony-forming units per milliliter, HSHP high-speed handpieces, AWS air-water syringe, Group A: underwent shock treatment every 3 weeks, Group B: underwent shock treatment every 2 weeks; Group C: underwent shock treatment every week.

Effectiveness of BRS® treatment

Prior to biofilm removal with BRS®, the total bacterial counts in water samples collected from high-speed handpieces and air-water syringes were markedly high across all DCUs. Immediately following the biofilm removal procedure, the bacterial counts in all DCUs were significantly reduced to near-undetectable levels, with CFU/mL values ranging from 15 to 45. This drastic reduction demonstrates the effectiveness of BRS® in removing biofilm and reducing microbial contamination (seen in Table 1).

Effectiveness of disinfection among different frequencies of shock treatment

The trends in the total bacterial counts of the three groups of water samples over this period are shown in Fig. 1. The bacterial counts in Groups B and C fluctuated within the acceptable standard (below 100 CFU/mL), with a compliance rate of 100%. In Group A, the total bacterial count increased during the second week of the second disinfection cycle (with each cycle lasting 3 weeks) and exceeded the acceptable standard, resulting in a compliance rate of 68.42% over the 6 weeks. There were significant differences in the effects of disinfection among the different frequencies of shock treatment (χ2 = 13.41, p = 0.001, Cramer’s V = 0.49, 95%CI [0.28 – 0.68]) (seen in Table 2).

Fig. 1.

Fig. 1

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Trends in total viable counts in water samples from Groups A, B, and C over a 6-week period. A total viable counts in water samples from the high-speed handpiece outlet; B total viable counts in water samples from the air-water syringe outlet.

Table 2.

Qualified rates of total bacterial counts of three DCUs (n = 19)

Project Group A Group B Group C χ2 P
Qualified 13 19 19 13.41 0.001
Unqualified 6 0 0
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Notes: Group A underwent shock treatment every 3 weeks, Group B underwent shock treatment every 2 weeks, Group C underwent shock treatment every week, the qualified standard is a total bacterial count not exceeding 100 CFU/ml.

Biofilm structures in waterline tubing

SEM was utilized to examine the biofilm structures within the waterline tubing of DCUs, with an accelerating voltage of 5.0 kV, secondary electron (SE) mode, and 5000× magnification, capturing images at a scale of 10 μm (Fig. 2). Before biofilm removal with BRS® and subsequent disinfection, the tubing supplying the high-speed handpiece from one DCU exhibited extensive, dense biofilm on the inner walls. The biofilm displayed prominently protruding structures, comprising a mixture of cocci and rod-shaped bacteria embedded in a dense extracellular matrix (Fig. 2 A). Following treatment with BRS®, the tubing appeared clean, with no visible biofilm structures remaining. Only minor impurities and residual mineral deposits were observed on the pipe walls (Fig. 2B). After 6 weeks of treatment with varying disinfection frequencies, distinct differences were noted across groups. In Group A, loosely structured biofilms persisted, with attached cocci and rod-shaped bacteria evident (Fig. 2 C). In contrast, Group B exhibited no discernible biofilm structures; only minor impurities and mineral deposits were present, with no typical bacteria or bacterial secretions detected (Fig. 2D). Group C also showed no mature biofilm formations, with a minimal amount of residual mineral deposits visible (Fig. 2E).

Fig. 2.

Fig. 2

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SEM images showing biofilm structures in waterline tubing of DCUs. A, biofilm structures before biofilm removal with BRS® and subsequent disinfection; B, biofilm structures following treatment with BRS®; C, biofilm structures after 6 weeks of treatment in Group A; D, biofilm structures after 6 weeks of treatment in Group B; E, biofilm structures after six weeks of treatment in Group C. Scale bar = 10 μm.

Discussion

Following the COVID-19 pandemic, infection control protocols in dental settings have been strengthened in some countries, with increased attention paid to the potential risks posed by waterlines [29–31]. As a result, regular monitoring and disinfection of DUWLs are now viewed as integral to ensuring patient safety and preventing waterborne infections. The present study is the first clinical controlled trial to explore the efficacy of different shock treatment frequencies in combination with continuous low-concentration disinfection using hydrogen peroxide-based Dentosept® S on DUWLs contamination.

The findings from this pilot study, which involved 3 DCUs randomly assigned to different shock treatment frequencies with a total of 132 water samples collected over a 6-week period, demonstrated that treating DUWLs biofilm with BRS®, followed by a protocol of continuous disinfection using 0.0141% hydrogen peroxide combined with shock treatments either weekly or biweekly, may help suppress suppress both TVCs in dental treatment water and the biofilm within DUWLs. In the present limited sample, this protocol was associated with TVCs generally remaining below 100 CFU/mL in the tested DCUs. In contrast, less frequent shock treatments, such as those applied every three weeks, were linked to periodic increases in bacterial loads, particularly in the third week post-shock treatment. These observations support guideline recommendations emphasizing a combined approach to disinfection, as highlighted in CDC guidance [32]. However, it is important to note that our data are preliminary and based on a small number of DCUs over a short follow-up.

The results from the pilot study further highlights the limitations of solely relying on continuous low-concentration disinfection, as noted by Schel et al. [25], whose research indicated that while continuous disinfection can reduce TVCs, some water samples still exceeded acceptable limits. Their study did not incorporate periodic shock treatments, reinforcing the need for a combined approach to effectively manage biofilm persistence and the risks posed by dental handpiece backflow.

With regard to BRS®, the observations from the pilot study are consistent with the results of a six-year study conducted in a French university hospital, which further supports the effectiveness of BRS® in restoring dental units to near-pristine conditions [33]. However, it is crucial to note that for older dental chairs, a thorough cleaning of biofilms before the implementation of any disinfection protocol is recommended. This preliminary step is essential for maintaining waterline quality and ensuring the overall effectiveness of the disinfection process. By addressing biofilm accumulation beforehand, the BRS® treatment can achieve optimal results, thereby enhancing the safety and hygiene of dental practices. Notably, the 2019 Hong Kong Infection Control Standing Committee also advocate for the use of biofilm removal agents in conjunction with continuous and periodic disinfection [34].

Despite the findings of Zemouri et al. [35], which demonstrated that low-concentration hydrogen peroxide combined with shock treatment every four weeks could achieve compliance in biofilm models, our findings from the pilot study and previous study indicate that a shock frequency of 3 or 4 weeks may not be insufficient to maintain water quality standards in real clinical environments. The discrepancies may arise from the differences between model simulations and actual clinical conditions. Zemouri’s study employed tap water in a 24-well plate for culturing, which did not account for critical factors present in dental units, such as backflow from dental handpieces and extended periods of stagnant water during overnight shutdowns. Our results that 2-week intervals appear more effective are consistent with those of Kramer et al. [36], which suggest the need for a shorter shock disinfection frequency. Kramer observed 18 DCUs undergoing continuous low-concentration disinfection combined with shock treatment every two weeks, noting a gradual decrease in colony counts and improved water quality, achieving full compliance after four weeks.

While the manufacturer of Dentosept® S recommends a combination of continuous low-concentration disinfection with shock treatment every 4 weeks, our study results indicate that a frequency of every two weeks may be more appropriate in our context. Several factors contribute to the necessity of increasing the frequency of disinfection in our setting. Firstly, the absence of silver ions in the disinfectants used in our study limits their antimicrobial efficacy compared to products that include silver, as noted in the research by Yan et al. [23]. Silver ions have been shown to enhance the effectiveness of hydrogen peroxide in controlling biofilm formation, which is particularly relevant in high-bacterial-load environments such as dental clinics. Secondly, the high patient turnover in dental practices in China exacerbates the risk of microbial contamination. The increased usage of DCUs may lead to a higher likelihood of biofilm reformation, necessitating more frequent disinfection to mitigate this risk. Additionally, the overall water quality standards in China may be lower than those in Europe or the United States, further complicating the management of microbial contamination in DUWLs. Moreover, our study focused on the prosthodontics department, which has been shown to harbor a greater diversity of microbial species, as indicated by high-throughput sequencing studies [4, 37]. This increased microbial diversity can lead to enhanced biofilm formation and resilience against standard disinfection protocols, reinforcing the need for a tailored approach to disinfection frequency.

Despite these insights, the present study has notable limitations. It was conducted in only three dental units within the prosthodontics department, with each intervention group comprising a single DCU. All DCUs had been in use for less than one year, which limits the applicability of our findings to older units. The scope of biofilm sampling was also constrained by tube accessibility. Collecting additional samples over time helped compensate for the small sample size by providing more trend data, but the overall generalizability remains restricted. Therefore, while our results indicate a potential benefit for more frequent shock disinfection in combination with continuous hydrogen peroxide use for short-term microbial control, long-term efficacy and overall superiority cannot be definitively concluded from this study alone. Future research using larger, multi-center samples that include older units and longer-term monitoring, as well as more comprehensive biofilm analysis, will be needed to validate these preliminary findings. Additionally, incorporating high-throughput sequencing could provide valuable insights into microbial diversity changes, further informing strategies to address DUWLs contamination.

Conclusions

Within the limitations of this pilot study, initiating a shock treatment with BRS®, followed by continuous disinfection with 0.0141% hydrogen peroxide and biweekly shock treatments, may assist in maintaining water and biofilm contamination at levels consistent with current guidelines for DUWLs contamination control in the tested setting. However, these findings should be considered preliminary and interpreted with caution. Further large-scale, long-term studies are necessary before definitive recommendations regarding disinfection superiority or sustainable long-term efficacy can be made for broader clinical practice.

Acknowledgements

The authors have no acknowledgments to declare.

Author contributions

TS: experimental design, project supervision, manuscript writing, manuscript review; JCW: experimental design, conducted experiment, data analysis, manuscript writing; WJL: conducted experiment, data collection, data organization; TYS, HBP, YYL: conducted experiment, data collection; CYJ: experimental supervision, manuscript review; XEL: experimental supervision, manuscript review. All authors read and approved the final manuscript.

Funding

The research was not funded by public, commercial, or non-profit organizations.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not Applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Ting Shuai and Jingcheng Wen contributed equally to this work and share first authorship.

Contributor Information

Chanyuan Jin, Email: jinchanyuanjcy@bjmu.edu.cn.

Xiue Li, Email: lixiue1216@163.com.

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Associated Data

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Data Availability Statement

No datasets were generated or analysed during the current study.

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