U.S. engineers say they\'ve borrowed microfabrication techniques used in the semiconductor industry to create 3D brain tissue in a lab dish. Researchers at the Massachusetts Institute of Technology and Harvard Medical School said the technique yields tissue constructs that closely mimic the cellular composition of those in the living brain. This could allow scientists to study how neurons form connections and to predict how cells from individual patients might respond to different drugs, an MIT release said Thursday. \"We think that by bringing this kind of control and manipulation into neurobiology, we can investigate many different directions,\" Utkan Demirci of the Harvard-MIT Division of Health Sciences and Technology said. Although researchers have had some success growing artificial tissues such as liver or kidney, \"the brain presents some unique challenges,\" MIT researcher Ed Boyden said. \"One of the challenges is the incredible spatial heterogeneity,\" he said. \"There are so many kinds of cells, and they have such intricate wiring.\" In their engineered tissues, researchers embedded a mixture of brain cells taken from rats into sheets of hydrogel, and then stacked the sheets into layers. In a technique similar to how semiconductor integrated circuits are made, the layers of gels are covered with plastic photomasks of varying shapes so the researchers could control how much of the gel was exposed to light, thus controlling the 3D shape of the multilayer tissue construct. Because the tissues include a diverse collections of brain cells, 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 said.