Scientists demonstrate the ability to make stem cells assemble into small inner ear structures in this research. This is a long way from building tissue masses that are easy to see with the naked eye, but it is progress nonetheless:
[Researchers] reported that by using a three-dimensional cell culture method, they were able to coax stem cells to develop into inner-ear sensory epithelia - containing hair cells, supporting cells and neurons - that detect sound, head movements and gravity. Previous attempts to "grow" inner-ear hair cells in standard cell culture systems have worked poorly in part because necessary cues to develop hair bundles - a hallmark of sensory hair cells and a structure critically important for detecting auditory or vestibular signals - are lacking in the flat cell-culture dish.
The team determined that the cells needed to be suspended as aggregates in a specialized culture medium, which provided an environment more like that found in the body during early development. The team mimicked the early development process with a precisely timed use of several small molecules that prompted the stem cells to differentiate, from one stage to the next, into precursors of the inner ear. But the three-dimensional suspension also provided important mechanical cues, such as the tension from the pull of cells on each other. "We were surprised to see that once stem cells are guided to become inner-ear precursors and placed in 3-D culture, these cells behave as if they knew not only how to become different cell types in the inner ear, but also how to self-organize into a pattern remarkably similar to the native inner ear."