A fluid-walled microfluidic platform for human neuron microcircuits

Modelling human brain cells in functional circuits is essential to understand many neurological disorders. Much of what we know about brain circuits comes from studies performed in animals, and work in humans has been limited to brain imaging studies in life, or looking at post-mortem brain tissue after death. Here, we will bring together neuroscientists and engineers to develop the tools required to study circuits of living human neurons outside of the brain in the laboratory. The striatum is a region deep within the brain responsible for correctly assimilating sensory, motor, and cognitive information to initiate and complete a "go" or "no-go" instruction to the rest of the body. To help process the vast amount of information arriving, the striatum is also regulated by neuromodulators, such as dopamine released from dopamine neurons, which fine-tune communication between neurons to ensure tasks are performed successfully. Cortical, striatal and dopamine neurons all meet at the striatum to form an important brain circuit that plays a role in regulating movement and gives rise to disorders such as Parkinson's disease when it fails. The engineers in our team have previously constructed miniature chambers (about 3 mm wide) which can be connected together and used to grow human stem cell-derived neurons to communicate and mimic brain circuits. Uniquely, in this project we build these chambers using oil walls printed onto a glass or plastic surface, in a technique called fluid-wall microfluidics. The oil forms an unmixable, or immiscible, fluid interface with the water-based liquid used to grow the neurons, enabling the creation of micro-environments which retain their structure, prevent evaporation and allow long term studies of many months. The use of oil walls and the absence of solid plastic barriers allows direct experimental access to neurons from every angle while providing excellent visual access to study neurons with a microscope. The oil walls can also be moved and reconfigured during the experiment to mimic the dynamic and flexible nature of the brain. In this interdisciplinary collaborative work the neuroscientists in the team will convert human stem cells from healthy individuals into the three neuronal sub-types of interest (cortical, striatal and dopamine) and grow the neurons in separate, but interconnected, oil-walled chambers constructed by the engineers. We will study the function of each cell type, but focus on the striatal neurons, using electrical measurements and tracking fluorescent markers by live high-resolution microscopy. We will study communication between the different neuronal types using light-activatable proteins called opsins which will stimulate neuronal activity in a highly regulated way when we shine light on the cells, and we will look at the role of mitochondria, the energy powerplant of the cell, in neuronal communication. Neurons are extremely long cells with long projections called axons which extend long distances across the brain. We can see those long projections forming in our fluid wall system as neurons send projections along conduits from one chamber to another. We will use the oil wall technology to study gene expression and function within neuronal compartments. Finally, we will combine our fluid oil-wall system with existing electrical arrays to generate the first-of-a-kind microcircuit recordings of neuronal activity to understand how human brain circuits function in healthy individuals and provide us a tool to study neuronal failure in disease.