To go along with mini thinking brain balls grown in lab, researchers have built functional, tiny organs as well—inching closer to the possibility of stitching together teeny-weeny Frankenstein monsters.

While the sci-fi-esque idea of full petri-dish people is just silliness (for now), miniaturized body parts could be highly useful for testing the safety and effectiveness of new drugs—perhaps someday replacing animal testing and some aspects of human trials, researchers speculate. And, in tests with prototypes of tiny, functional livers and hearts, researchers showed that the wee organs could successfully be implanted into living animals. The findings, reported in Nature Materials, suggest that the itsy-bitsy tissues could be used to repair full-sized organs some day, as well as for drug development.

While other lab-made mini organs have come before them, the new design offers a notable improvement to previous versions: vasculature and cell-to-cell connections.

To mimic real organ functions in lab, researchers can’t simply grow a mess of cell types in a dish. The cells have to form 3D structure with different types of cells connecting and interacting with each other. Additionally, those densely packed functional cell structures need networks of tiny channels—vascular systems—to carry nutrients, chemical signals, blood cells, and drugs throughout. Both features are tricky to pull off.

To do it, researchers led by tissue engineer Milica Radisic at the University of Toronto started with super-thin layers of a flexible, biodegradable elastomer, called poly(octamethylene maleate (anhydride) citrate) or POMaC. Each layer of POMaC was stamped with a pattern of little holes—about 50 to 100 micrometers wide. And when the thin layers were snapped together, those holes formed 3D channels that mimicked blood vessels. The whole chip (called the AngioChip) is about 5mm by 3mm, around the size of a grain of rice.

When researchers let cells wash over the chips, cells glommed onto the scaffold and settled in, forming functional tissue with blood vessel-like channels in a matter of days.

The researchers made mini livers from both rat liver cells and human stem cells. The mini organs mimicked the springiness and cell density of real livers. And, when blood flowed through the chips, the tissue metabolized drugs and released urea, a molecule made while detoxifying ammonia (a waste product of metabolism), just like normal liver tissue.

Researchers also made hearts-on-a-chip, again from rat cells and human cells. After several days of growing in lab, the tiny tickers beat like the real thing. The researchers also grafted their lab-grown rat heart tissue onto the femoral vein of a living rat. After just a few days, the tissue had melded into the rat’s tissue, with vascular tissue hooking up to the channels in the tissue chip.

Radisic and her team are hopeful that the organs-on-a-chip could one day help patch damaged organs in people—and even be tailored to individual patients by using the patient’s own cells to seed the scaffold. In the meantime, the researchers think it will be easy to use the organs for drug testing, pumping new compounds through the vasculature and looking for organ-specific effects and toxicities.

Nature Materials, 2015. DOI: 10.1038/NMAT4570 (About DOIs).