Green in Sherpa: Author can archive submitted version (i.e. pre-refereeing). Author can archive accepted version (i.e. final draft post-refereeing). Author can archive publisher's version / PDF. Conditions: Publisher's version/PDF may be used Eligible UK authors may deposit in OpenDepot Creative Commons Attribution License Copy of License must accompany any deposit. All titles are open access journals 'BioMed Central' is an imprint of 'Springer Verlag (Germany)'. -- 6.4.15-- MMM. - “VU paid APC for this article”, 5.9.16 -- MMM