Footnotes

• Contributors RL and ZK conceived of the presented idea. RL and XW wrote the manuscript with support from JW and YJ. All authors discussed the results and contributed to the final manuscript. JW is responsible for the overall content as guarantor. RL and XW contributed equally to this article.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.