DJ: This is a no-brainer and no doubt on the lips of everybody in the field — synthetic embryos. The culmination of so much work and a pivotal advance that encapsulates the great potential of pluripotent cells, but also illustrates the limitations of in vitro tissue engineering. But whether we are talking about synthetic embryos or pancreatic islets, vascular perfusion of tissues is fundamental to organogenesis. A multitude of cell-based therapies will find their way to clinical application in decades to come, but to really model the scale and complexity present in embryonic tissues or organs in vitro, some means of vascular perfusion must be developed. Bioengineers, get to work!

AS: I am personally most excited about the area of early mammalian embryo modelling, which has been growing rapidly over the past couple of years and holds tremendous potential for understanding the ‘black box’ of human development. The work of scientists such as Jacob Hanna, Jun Wu, Nicolas Rivron and Miki Ebisuya (who have been recent guests on our show) have demonstrated the ability to rapidly and reproducibly create advanced models of early embryo development (blastoids, fully stem-cell-derived synthetic embryos, gastruloids and so on), enabling high-throughput studies of mammalian development in ways that were impossible 10 years ago. However, I believe that these technical advancements are also coupled with the greatest overall challenge of emerging biotechnologies: how do we balance rapid scientific advancement with proper bioethical evaluation of new biotechnologies, such as early embryo models, that hold the potential to impact science and health policy on a global scale? We saw this challenge manifest in the genome-editing field recently, when CRISPR-based genome editing was used to modify human embryos that were ultimately carried to term. The resulting uproar sent shockwaves throughout the global scientific community and the general public, and I think that moving too fast in human genome editing gave the field a black eye. This is a situation I want to avoid in stem cell biology, which certainly has already had its own share of ethical conundrums over the past decades.