Photo-annealing of microtissues creates high-density capillary network containing living matter in a volumetric-independent manner

The vascular tree is crucial for the survival and function of large living tissues. Despite breakthroughs in 3D bioprinting to endow engineered tissues with large blood vessels, there is currently no approach to engineer high-density capillary networks into living tissues in a scalable manner. We here present photo-annealing of living microtissues(PALM) as a scalable strategy to engineer capillary-rich tissues. Specifically, in-air microfluidics was used to produce living microtissues composed of cell-laden microgels in ultra-high throughput, which could be photo-annealed into a monolithic living matter. Annealed microtissues inherently give rise to an open and interconnected pore network within the resulting living matter. Interestingly, utilizing soft microgels enables microgel deformation, which leads to the uniform formation of capillary-sized pores. Importantly, the ultra-high throughput nature underlying the microtissue formation uniquely facilitates scalable production of living tissues of clinically relevant sizes (>1 cm3 ) with an integrated high-density capillary network. In short, PALM generates monolithic, microporous, modular tissues that meet the previously unsolved need for large engineered tissues containing high-density vascular networks, which is anticipated to advance the fields of engineered organs, regenerative medicine, and drug screening