Those sheets were then stacked in layers, which can be sealed together using light to crosslink hydrogels. By covering layers of gels with plastic photomasks of varying shapes, the researchers could control how much of the gel was exposed to light, thus controlling the 3-D shape of the multilayer tissue construct.
This type of photolithography is also used to build integrated circuits onto semiconductors a process that requires a photomask aligner machine, which costs tens of thousands of dollars. However, the team developed a much less expensive way to assemble tissues using masks made from sheets of plastic, similar to overhead transparencies, held in place with alignment pins.
The tissue cubes can be made with a precision of 10 microns, comparable to the size of a single cell body. At the other end of the spectrum, the researchers are aiming to create a cubic millimeter of brain tissue with 100,000 cells and 900 million connections.
Answering fundamental questions
Because the tissues include a diverse repertoire of brain cells, occurring in the same ratios as they do in natural brain tissue, they could be used to study how neurons form the connections that allow them to communicate with each other.
"In the short term, there's a lot of fundamental questions you can answer about how cells interact with each other and respond to environmental cues," Boyden says.
As a first step, the researchers used these tissue constructs to study how a neuron's environment might constrain its growth. To do this, they placed single neurons in gel cubes of different sizes, then measured the cells' neurites, long extensions that neurons use to communicate with other cells. It turns out that under these conditions, neurons
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology