Sacrificial capillary pumps to engineer multiscalar biological forms.

Natural tissues are composed of diverse cells and extracellular materials whose arrangements across several length scales-from subcellular lengths (micrometre) to the organ scale (centimetre)-regulate biological functions. Tissue-fabrication methods have progressed to large constructs, for example, through stereolithography and nozzle-based bioprinting, and subcellular resolution through subtractive photoablation. However, additive bioprinting struggles with sub-nozzle/voxel features and photoablation is restricted to small volumes by prohibitive heat generation and time. Building across several length scales with temperature-sensitive, water-based soft biological matter has emerged as a critical challenge, leaving large classes of biological motifs-such as multiscalar vascular trees with varying calibres-inaccessible with present technologies. Here we use gallium-based engineered sacrificial capillary pumps for evacuation (ESCAPE) during moulding to generate multiscalar structures in soft natural hydrogels, achieving both cellular-scale (<10 µm) and millimetre-scale features. Decoupling the biomaterial of interest from the process of constructing the geometry allows non-biocompatible tools to create the initial geometry. As an exemplar, we fabricated branched, cell-laden vascular trees in collagen, spanning approximately 300-µm arterioles down to the microvasculature (roughly ten times smaller). The same approach can micropattern the inner surface of vascular walls with topographical cues to orient cells in 3D and engineer fine structures such as vascular malformations. ESCAPE moulding enables the fabrication of multiscalar forms in soft biomaterials, paving the way for a wide range of tissue architectures that were previously inaccessible in vitro.