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JHU Team Develops Microfluidic Chip to Study Neural Growth, Brain Formation

Investigators from the Johns Hopkins University Whiting School of Engineering have developed a microfluidic lab on a chip that enables them to flow cocktails of specific chemicals around individual neurons.
According to the scientists, this assay could potentially help scientists better understand how neurons communicate with one another to form the brain, and possibly elucidate other cellular processes involving chemotaxis of shear-sensitive cells.
Their work appears as the cover story in the February issue of Lab on a Chip.
Neuronal growth cones contain molecular machinery that precisely regulates their migration in response to external multichemical gradients, the authors said. The details of this regulation are largely unknown, partly because of the limitations of currently available technology.
Although microfluidic chips can generate complex, stable, and precisely controlled chemical gradients, their use in studying neuronal growth cone migration is limited in part because of the effects of shear stress, the researchers explained.     
The microfluidics-based assay chip that they designed can generate precise gradients of soluble guidance cues and fabricate complex composite gradients of diffusible and surface-bound guidance cues that mimic the conditions that the growth cones encounter in vivo, they said.
The researchers applied their assays to Xenopus embryonic spinal neurons and were able to demonstrate that the presence of a surface-bound laminin gradient can precisely repulse or attract growth cone responses toward gradients of brain-derived neurotrophic factor with the guidance outcome dependent on the mean concentration of BDNF. 
Andre Levchenko, an associate professor of biomedical engineering at the JHU Whiting School of Engineering and the corresponding author of the paper, spoke with CBA News this week about how this technology is applicable to drug discovery and how he and his team plan to further develop it.

Can you give me a little background on this work?
Basically, we tried to better understand the development of complex organs like the brain, a process involving multiple cellular interactions. How does everything become perfectly wired together?
The problem is that we do not have very good tools to address the question of how individual neurons find their way to other neurons and make these complex connections. They respond to multiple cues as they develop and make these connections. Each neuron can make up to 10,000 connections, and there are something like 20 billion cells in the human brain, for example.
The technical issue is that there are frequently many cues occurring simultaneously and cells have to make decisions based on all of these cues. We want to design a tool that will allow us to look at how cells make these decisions.
No such tool currently exists. We were kind of surprised by that and then decided that we would develop the tool ourselves.
We turned to microfluidic technology. Using microfluidics, you can present cells with cues, try to tell them where to go, and see if they will follow your directions.
So these microfluidic chips allow us to give the cells many different cues at the same time and see how they make their decisions on where to go. In this paper, we showed how a chip like this can be designed, fabricated, and used in these experiments.
We found out some interesting things about the neurons’ decision-making process. For example, when we presented the cells with conflicting cues, we found that they sometimes grew in random directions, which suggested that the cells did not choose one signal over the other.  
In the future, we would like to use this technology to try to understand this problem a little bit better. In addition, we can hopefully use it as a platform to screen drugs that could manipulate how the cells grow and turn according to the cues.
For example, we could screen for drugs that may promote neural tissue regeneration or that may battle some of the neurodegenerative diseases where these processes may become compromised.  
We are also thinking about using this technology to create relatively simple networks of cells where the cells may form contacts with each other like they do in the brain, but the result would be much simpler than in actual brain tissue.
However, we may start designing tissue within the microfluidic chip and see if we can wire cells together in specific ways.
How would this technology be applicable to drug discovery?
The assay itself involves using very complex methods to flow different types of liquids through the channels on the microchip that contain cells. These liquids can contain drugs. In fact, this method could rapidly test the effects of multiple drugs or combinations of drugs.
This chip can be used to rapidly screen a variety of drugs and determine their effects on neuron growth. We can easily change the duration of cellular exposure to the drugs or the concentration of the drugs.
What is the next step in your research?
We will probably continue this work in three different directions. It is hard to understand the fundamental mechanisms by which the cells make appropriate decisions when faced with multiple cues. We do not understand how, within the cell, these decisions get made.
We also want to try to use this as a platform for drug screening to determine if the processes by which these cells grow in certain ways will be affected by a certain set of drugs. We would really like to adapt this platform for drug screening.
The third direction is to try to design and build artificial networks of neurons by allowing them to make connections as they do in the brain, following the cues that we provide, so we can try to drive them together or apart, and ultimately create these complex connections and something that would resemble brain tissue.
Is this technology something that you plan to commercialize?
Yes, but in the current incarnation we decided not to do it, because we would like to make it widely available to whoever is interested, because we believe that it should be rapidly adopted by the community.      

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