3D Printing

Yale Researchers Create 3D Printable Neuron Model Database

Looking for something challenging to 3D print? How about one of the most complex 3D dimensional structures that exist and that make up the most efficient and powerful computing apparatus that we know of? Yale researchers have been working on 3D printing neuron models since 2013 and their project, which has since evolved into a 3D printable neuron model database, has just been published in the Frontiers in Neuroinformatics Journal, raising interest form neuroscientists everywhere.

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A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals (source: Wikipedia). Neurons make up the brain and the spinal chord in the central nervous system and consist of a cell body (soma), dendrites, and an axon. The dendrites, in particular, are extremely long and thin filaments and, thus, represent one of the most challenging shapes to reproduce physically through 3D printing.

neuro3The entire project, led by Robert A. McDougal and Gordon M. Shepherd of the Department of Neurobiology at Yale University, actually involves all aspects of 3D printing, not just the final materialisation itself, but also the use of a Python-based software process and complex algorithms to create the 3D models.  Then, a careful selection of technologies carry out the printing.

Over the past decades, scientists have three-dimensionally traced tens of thousands of neurons; many of these tracings are freely available through online repositories like NeuroMorpho.Org and ModelDB. The process for generating printable versions of the cells begins with the expansion of the dendrite and axon diameters, followed by the transformation of the tracing into a 3D object through a neuronal surface generating algorithm like Constructive Tessellated Neuronal Geometry (CTNG).

These neuron morphologies are loaded into the NEURON software, an internal Yale simulation environment for modeling individual neurons and networks of neurons. The NEURON system provides tools for conveniently building, managing, and using models in a way that is numerically sound and computationally efficient. Once the modeling is complete, the models have to be made printable – a process that almost everyone who has ever 3D printed something they have designed is familiar with.

neuron4The first step – as mentioned earlier – is to make the dendrite diameters comply with the technologies’ minimum requirements. Considering the 1 mm minimum that Shapeways recommends for its laser-sintered nylon 12 (one of the approaches used by Yale), this means that, with accurate proportions, a neuron cell model could measure more than half a meter in length and it would probably collapse under the pull of gravity.

Once the diameters have been modified, the neuron model meshes are made watertight by using Meshmixer software. Finally, the models are scaled down to printable size with MayaVi and exported in VRML format (or in STL if color is not needed). At this point the actual 3D printing challenges can begin.

The first approach involved using a professional Stratasys Dimension FDM 3D printer, housed at Yale’s Center for Engineering Innovation and Design (CEID), with ABS material and soluble supports. This was the first successful attempt, described in the 2013 publication. Further attempts to make this process more accessible in terms of costs involved using a MakerBot Replicator 2X 3D printer, but the use of a single material for the necessary support was deemed unfeasible. The final approach was the use of Shapeways’ online 3D printing service and its white (or dyed) nylon SLS technology.

Other attempts also involved the use of lost wax casting and metal 3D printing technologies, however that was also not practical for the complexity of the neuron shape. The use of full-color sandstone and binder jetting technology, on the other hand, was successful, but it required the dendrites to be thickened further to 5 mm.neuron1

While the opportunity to study physical 3D models of the neurons opens up a broad range of possibilities for scientists, arguably the biggest achievement of the Yale project is the establishment of the 3DModelDB repository for sharing the 3D printable neurons for educational and collaborative research purposes.

Once again, though, one of the most fascinating aspect of all this is how similar the experience of top Yale researchers is to that of a Maker, 3D printing away on his or her desktop. In fact, as the study’s authors themselves point out: “Researchers with their own printers may push the boundaries of their hardware as much as they want by risking print failure, but for those like ourselves, using commercial printers, we are limited by what the service is willing to attempt to print.” Anyone wanting to take up this challenge, here is the link to the “Neuroverse” where you can download the neuron models.