Growing a ‘Spine’ on a Chip

Microfluidic device allows for precise control of growth factor gradients, mimicking natural spinal cord development in vitro.

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uring embryonic development, molecular signals direct the cells of a fetus to divide, move and differentiate, eventually giving rise to all the organs necessary to sustain life outside the mother’s womb. In vertebrates, the spinal column is one of the most important structures to be defined along a directional axis of head to tail, and within the spinal column resides a variety of motor neurons connecting the brain to the muscles of the body.

Soh Boon Seng and colleagues at the Institute of Molecular and Cell Biology (IMCB) have now devised a microfluidic device that mimics the molecular cues directing the development plan of motor neurons in a spinal column. The device, which they have named the microHIVE platform, consists of a linear chamber in which stem cells can be seeded and flanked on both sides by an interlocking honeycomb lattice of hexagonal microstructures (microhexagons).

Specific growth factors can then be introduced into the chamber via the honeycomb lattice in a spatially-controlled manner. As the growth factors flow through the honeycomb lattice, they branch and mix at junctions between the hexagonal microstructures, giving rise to growth factor gradients.

“We know that growth factor gradients are important for tissue patterning in living organisms, so we collaborated with bioengineers to generate these gradients, allowing us to coax the stem cells to self-organize and achieve spatial diversification in vitro,” Soh explained.

By varying device parameters such as the number of fluid inlets for growth factor delivery, the size of each microhexagon, and the packing density of the microhexagons, the researchers were able to generate precise gradient profiles of retinoic acid and GDF11—key growth factors involved in patterning the spinal column from head to tail.

Notably, stem cells exposed to the retinoic acid and GDF11 gradient profile as determined by the microHIVE platform differentiated into motor neuron subtypes in the same arrangement as would have been observed in a developing fetus.

“Our 3D spinal cord model derived from human pluripotent stem cells can be used to study and model spinal cord injury,” said Soh. “This system could potentially be used to test or optimize cell-based therapy for spinal cord injury, or serve as a drug screening platform for diseases such as spinal muscular atrophy, which is characterized by muscle wastage due to the death of spinal motor neurons.”

The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology (IMCB).