Cells maintained in 3d systems are often better representative of physiological phenomena than those grown in conventional 2d cultures. however, practical constraints on cost, technical expertise, and experimental flexibility have hindered the ubiquitous adoption of biomaterials for 3d cell culture. we describe here a novel 3d biomaterial platform with unprecedented ability to maintain, observe, retrieve, and interrogate cells as well as whole organisms across scales, without being constrained by specific media compositions or growth conditions. we achieve this at a fraction of the cost typically associated with 3d biomaterials, without requiring any specialized equipment or expensive reagents. our innovation - termed jammed agarose microgels - utilizes densely-packed microparticles of the biopolymer agarose, which serves as a 3d growth media. this offers a porous and granular matrix for culturing cells in conditions that structurally resemble complex physiological habitats like soil and tissues. jammed agarose microgels also possess remarkable material properties that allow the system to instantaneously self-heal from localized deforming stresses such as those imposed by seeding or retrieving cells. this enables the 3d printing-based fabrication of precisely-defined complex structures composed entirely out of live cells, which has significant implications for tissue bioengineering. importantly, our key innovation is a one-pot, rapid, inexpensive, and high-throughput synthesis strategy. this permits anyone with access to basic bench-top laboratory equipment to achieve the manufacture of 3d cell culture scaffolds in a matter of minutes without any specialized technical expertise or complex hardware. together, our work advances the accessibility and applicability of 3d cell culture platforms for manifold needs ranging from basic sciences to biomedical research.