Introduction: Print a Bone on the Ember Printer

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About: I tinker with things at Instructables.

This Instructable documentations the project led by Chris Venter at Genspace's workshop "Bioengineering, Biomaterials, and Bioaesthetics" on December 18, 2015. You will learn how to take a simple pen drawing and transform it into a tangible 3D printed, biocompatible bone scaffold, which may be seeded with stem cells to grow real bone.

A brief description of the workshop:

"Join us at Genspace for a Workshop with Dr. Nina Tandon, a biomedical engineer by training and a creative innovator by nature. Tandon who is the co-founder and CEO of EpiBone, a company that grows human bone tissue for skeletal reconstruction, will discuss How You Can Grow Your Own Bone in the lab and the use of cutting-edge bio-technology for artistic application. Joining her EpiBone’s Artist in Residence Maia Yoshida, who will demo her work and share her experience at EpiBone, and Chris Venter, senior research scientist, Autodesk Bio/Nano Research, who will discuss and demo biomaterial 3D printing technologies for advanced synthetic fabrication."

You can get most of the software for this project for free. The only thing you will have to purchase is Autodesk WithIn Medical. However, you can easily skip creating a trabecular lattice if you will not be seeding your bone scaffold with cells.

Required Software

Bill of Materials

  • Ember printer (Autodesk)
  • PEGDA resin (Autodesk... coming soon) or any other Ember printer resin (Autodesk)
  • White paper and sharpie marker

Files

All files used for this project can be downloaded from this page.

Additional Comments

For the rest of the Instructable, all photos will be labeled with a number corresponding to the step they illustrate. Images that don't refer to a step will not be labeled.

Attachments

Step 1: Some Background

First, let's clarify some technical jargon. What is the difference between a bone and a bone scaffold?

A bone is a living, growing tissue mostly made of collagen. Collagen is a protein that provides structure, and calcium phosphate is a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bone strong and flexible enough to withstand stress.

A bone scaffold is a frame that bone tissue can regenerate on. Collagen builds bone's natural frame. However, synthetic biomaterials are now being used as bone graft substitutes. Ideally, a scaffold should have the following characteristics:

  1. 3D and highly porous (very holey) with an interconnected pore network for cell growth and flow transport of nutrients and metabolic waste.
  2. Biocompatible (nontoxic to cells) with a controllable degradation (want the scaffold to degrade overtime and be replaced by bone mineralization).
  3. Suitable surface chemistry for cell attachment (want the cells to stick to the scaffold) and growth.
  4. Mechanical properties to match those of the tissues at the site of implantation (stem cells are partially predisposed to transform into either bone, muscle, or heart tissue depending on the "hardness", or durometer, of the material they sit on).

Citations:

Step 2: Draw

What am I doing?

Drawing a 2D image of a bone

How do I do it?

  1. Draw a closed, nonintersecting shape on paper.
  2. Take a picture of it with your smartphone. Choose bright location without shadows.
  3. Email the image to yourself

My notes

I drew a classic bone cartoon. You can download it in the file attached here. But you certainly don't have to design a bone-like object! Go ahead and be crazy. Why not design a violin grown from bone?

Step 3: Illustrator: Convert Your Drawing to an SVG File

What am I doing?

Transform a raster image to vector lines and save as a .svg file.

How do I do it?

  1. Open Adobe Illustrator. Select "File" -> "New". For "Page Dimensions", input "Width" = 64 mm and "Height" = 40 mm, which are the dimensions of Ember's build platform.
  2. Select "File" -> "Open" and open your drawing.
  3. The drawing will be much larger than the page size. Scale your drawing down and rotate if necessary so the drawing is within the page bounds.
  4. Make sure your drawing is selected. It will have a blue box around its perimeter. If not, click on the drawing to select it.
  5. Select "Edit" -> "Edit Colors" -> "Adjust Color Balance" -> "Convert to Grayscale". In the color mode dropdown bard select "Grayscale". Check the "Convert" box, and scale down the "Black %" to about -30%.
  6. Sure sure your drawing is still highlighted (it has a blue box around it). In the top toolbar, click the button "Image Trace", or select the dropdown menu next to this button to play around with thresholds. When the process is complete click "Expand", which is right beside the "Image Trace" button. This will transform your drawn lines into vector paths.
  7. As you can see, my tracing was not perfectly generated.There was a bit of shading left over from the shadow in my image, even when I decreased the "% Black". It's ok though because its not interfering with my main image, and I will just delete it later.
  8. If you zoom into your newly vectorized image, you’ll see multiple paths outlining your image. You’ll delete all but one. Right now, all your paths are selected (shown in blue). Click to highlight the path you like.
  9. While this path is still selected, create a new layer and copy and paste the path into this layer. Delete any remaining paths by deleting the other layer.
  10. Change the stroke settings so there is a black stroke of arbitrary thickness and no infill. This simply helps visualize the path.
  11. Select File -> "Save As" and save as a .svg file.

Step 4: Inkscape: Convert Your Drawing to an SVG (for Free)

What am I doing?

Adobe Illustrator is expensive, so use Inkscape, a free knockoff of Illustrator, instead.

How do I do it?

  1. Open your file.
  2. If you feel the need to crop your photo, follow the instructions here
  3. In the upper toolbar, select "Object" -> "Transform". The Transform toolbar appears on the right-hand side of the screen. Select the "Scale" tab within the Transform toolbar. Scale the image down so your drawing is within 20 mm x 20 mm.
  4. Check that the dimensions are truly < 20 mm by using the Ruler tool on the left-hand toolbar.
  5. Then follow this Instructable to create vector paths from your drawing: https://www.instructables.com/id/How-to-Make-An-Ink...
  6. Make sure to delete the original background image when you're finished creating your vector lines.
  7. Go to "File" -> "Save As" and save as SVG.

My notes

  • It's very easy to create vector paths in Inkscape. I got double lines while following Step 4 and was unable to clean up extra paths. However, you can simply follow the upcoming instructions without any problems.
  • If you accidentally have an open shape, you can join vector lines by dragging one line over the other (they must be intersecting), highlighting the nodes you want to join and selecting "Path" -> "Union" in the upper toolbar. You'll have to do this for any disconnected lines in your drawing, which is why you really want to create a closed shape.

Step 5: Fusion 360: Convert the Svg Into a 3D Model

What am I doing?

Importing the svg created in either Illustrator or Inkscape into Fusion 360 and extruding to make a 3D model.

What am I doing?

  1. Open Fusion 360 and select "Insert" -> "SVG"
  2. As you can see, the file conversion rescaled things, and the outline is now larger than Ember's print platform. Undo the Insert, redo insert, and before hitting "ok" rescale the image in the pop up window.
  3. Once imported, select "End Sketch" in the upper toolbar.
  4. Select "Create" -> "Extrude". For the option "Profile", click on the SVG image. To extrude, pull the blue handle up or input a hard value in the option "Distance". Then click "Ok".
  5. In left-hand "Browser" panel, open "Bodies" right click the extruded body file, and select "Save As STL". Export the body as an STL file. Going up to "File" -> "Save As" or even "File" -> "Export" won't let you export the body as an STL.

My notes

  • You can do the same thing in 123D Design, which is free! Get it here: http://www.123dapp.com/design
  • If you have two, non-overlapping solids, you can combine them with the "Modify" -> "Combine" tool and selecting one body as the body and the other as the tool, select "Join", and choose "Create New Body".

Step 6: WithIn Medical: Make a Trabecular Lattice

What am I doing?

Convert the model's bulk material into a trabecular structure, a lattice commonly found in titanium osteoimplants. Cells tend to adhere to this type of structure.

How do I do it?

  1. Click on the WithIn Medical icon in the upper left corner and select "Import". Find and open your STL file.
  2. In the lefthand toolbar make the following changes: See the pic complete settings. Changes will be shown in red in the Within user interface.
    1. Lattice target pore size = 0.45 mm, (beam) thickness = 0.3 mm
    2. Topology = trabecular
    3. Surface trim = advanced
  3. Click "Create Component Actions" in the upper toolbar and wait for WithIn to generate your lattice.
  4. Select "File" -> "Export" and choose "STL" as your file type.

Step 7: MeshMixer: Generate Support Structures

What am I doing?

Generating support structures, which are branching shafts that stabilize your model while it's printing and can be removed by hand after the print is complete.

How do I do it?

  1. Open Meshmixer. First thing first, we'll modify our settings. Fo to "MeshMixer" -> "Preferences" in the toolbar, select the "File" tab, and make sure to check "Flip Z-Y Axis".
  2. After you do this, select "Import" from the center screen.
  3. Position the model properly on the build platform by using the "Transform" and "Align" tools in the "Edit" menu. "Transform" will rotate the model. "Align" will automatically place the model onto the build platform.
  4. Select "Analysis" -> "Overhang" to make the supports. You'll have to fiddle with the settings a bit, but make sure to decrease the support density. Also don't worry if Meshmixer takes time to generate the supports. This is common with a trabecular lattice.
  5. Select "File" -> "Export" and save as "stl binary format".

Step 8: Spark: Print Your Bone Scaffold

What am I doing?

Sending your supported, trabecular bone scaffold to be printed on Autodesk's Ember printer.

How do I do it?

  1. Go to www.emberprinter.com and log into your account. Click “My Computer” to upload your supported trabecular model.
  2. You can wait for the 3D viewer to load a preview of your model, or click the "Next" button in the upper righthand corner of the screen to proceed.
  3. You have a few options in Print Settings. In this case we are using a nonstandard resin which you'll find after clicking "Browse Material Browser". Find PEGDA 44, Autodesk's PEGDA resin, which is currently on the third page of the library. Click the plus button next to PEGDA 44, then you should be able to find it within your material dropdown list. If you do not want to use PEGDA 44, select any other material in the library.
  4. Click "Next" to slice the mold. The slicing may take a while depending on the size and complexity of your model.
  5. Click "Next", send your print to the printer, and then manually hit start on your printer.
  6. To learn how to use the Autodesk Ember printer, visit the Ember support website


Step 9: Final Product

Here are the final images of my print! It's incredible that I can draw a simple image and transform it into a bone scaffold.

Step 10: Future Project Ideas

  • Instead of sketching a 2D shape, you can mold a 3D shape with clay, take a 123D catch of the sculpture, clean the mesh generated by 123D Catch in Meshmixer, and then trabecularize, add supports, and print.
  • Test different biocompatible resins on the Ember printer.
  • Seed coral cells on scaffold instead of stem cells.