The Organoid Stage of the Tissue Engineering Revolution

The first stage for commercially useful tissue engineering is testing and further research, and that is actually well underway. Tissue sections for test and research purposes don't have to be large, and therefore the big problem of how to generate suitable blood vessel networks doesn't have to be solved yet. So researchers have been building organoids and other small sections of tissue, gaining experience and refining techniques. The first tissue types were being sold years ago by companies such as Organovo, and these days many more are being added at an accelerating pace by competing research and development groups. This is a staging ground for the near future construction of organs to order, built from scratch from a patient's own cells:

Efforts to grow stem cells into rudimentary organs have taken off. Using carefully timed chemical cues, researchers around the world have produced three-dimensional structures that resemble tissue from the eye, gut, liver, kidney, pancreas, prostate, lung, stomach and breast. These bits of tissue, called organoids because they mimic some of the structure and function of real organs, are furthering knowledge of human development, serving as disease models and drug-screening platforms, and might eventually be used to rescue damaged organs. "It's probably the most significant development in the stem-cell field in the last five or six years."

The current crop of organoids isn't perfect. Some lack key cell types; others imitate only the earliest stages of organ development or vary from batch to batch. So researchers are toiling to refine their organoids -- to make them more complex, more mature and more reproducible. Still, biologists have been amazed at how little encouragement cells need to self-assemble into elaborate structures. "It doesn't require any super-sophisticated bioengineering. We just let the cells do what they want to do."

Biologists know that their mini-organs are still a crude mimic of their life-sized counterparts. But that gives them something to aim for. "The long-term goal is that you will be able to replicate more and more of the functionality of a human organ." Already, the field has brought together developmental biologists, stem-cell biologists and clinical scientists. Now the aim is to build more-elaborate organs -- ones that are larger and that integrate more cell types. Even today's rudimentary organoids are facilitating discoveries that would have been difficult to make in an animal model, in which the molecular signals are hard to manipulate.



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