The term Ultrastructure, originating in the field of cellular biology, initially referred to the finely detailed, molecular structures within cells observed through electron microscopy. These structures enable living cells to perform essential, life-sustaining processes, such as photosynthesis, respiration, and cellular repair. By transforming basic components like sunlight, air, and nutrients into energy and structural materials, cells create and maintain a dynamic, self-sustaining environment on a micro-scale. It is within these “ultrastructures” — mitochondria, ribosomes, and cytoskeletal filaments — that life itself orchestrates growth, repair, and energy balance. In the mid-20th century, as scientists increasingly understood the biochemical genius of cellular processes, the concept of ultrastructure inspired new approaches in engineering and sustainable development. Just as cells operate through interwoven, self-replenishing networks, a vision emerged for human infrastructure systems that might mimic these cellular attributes. By the early 21st centuries, the term Ultrastructure began to be applied to describe deployable, small-scale infrastructure systems that follow the natural principles of balance, self-sufficiency, and regenerative cycles observed in living systems. In this broader sense, “Ultrastructure” came to refer to systems that meet basic human needs — food, water, shelter, energy, and waste — in ways that are open-source, accessible, and ecologically regenerative. Such systems are modular, capable of being assembled or repaired with local resources, and designed for minimal environmental impact. By using the term ultrastructure, modern designers highlight the ambition to replicate cellular efficiency and resilience in human infrastructure — to create “closed-loop” systems that recycle resources and energy locally, just as a cell reuses molecules to sustain life. These ultrastructural systems aspired to bypass and buffer the limitations and risks of the conventional centralized "infrastructure" systems of the 20th Century, which often resulted in ecological degradation, inefficiency, and reliance on extractive economies. Ultrastructure was not intended to immediately replace traditional infrastructure and grid systems, but rather to go "on top of" and work in tandem with these systems, reducing strain on aging infrastructures and offering local resilience and redundancy during emergencies when larger-scale systems failed. Such “ultrastructures” were not only engineering solutions but became critical components of a regenerative society that prioritizes ecological health and accessibility, much like the cells that inspired them. In this way, ultrastructure has evolved from describing molecular and cellular architecture, to a revolutionary framework for scalable, sustainable city-scale architecture, designed to support human life in balance with natural cycles.