RT Journal Article SR Electronic T1 Ethics of digital twins: four challenges JF Journal of Medical Ethics JO J Med Ethics FD BMJ Publishing Group Ltd and Institute of Medical Ethics SP medethics-2021-107675 DO 10.1136/medethics-2021-107675 A1 Matthias Braun YR 2021 UL http://jme.bmj.com/content/early/2021/08/10/medethics-2021-107675.abstract AB