Fig. 1 ∣. Challenges in translating stem cell therapies with potential bioengineered solutions.

a, Present challenges culturing stem cells include maintenance of the stem cell state ex vivo^{16,18,20,21,23-25} and efficient expansion of naive stem cells^9,10,12,27. b, To fully realize the potential of stem cells, reliable protocols for altering cell state must be developed, including differentiation of stem cells to mature cell types^35-45 and reprogramming of somatic cells to pluripotent stem cells^47,48. c, Conventional cell delivery approaches do not address crucial obstacles in cell transplantation therapies, including maintaining the viability and potency of stem cells during injection^49-51, providing a supportive microenvironment for the cells after implantation^50,52-55, and controlling the fate of the cells by providing cues to guide regeneration in vivo^56,59. Engineering approaches are being applied to design materials to address these challenges.