Materials for fracture experiments

[Terrie S]

I was wondering if anybody has found a 3D printing material that works well for fracture studies. I am aware of Sawbones, but would like to explore the possibility of using CT scans to generate 3D printed bones of different size/age/sex for fracture/trauma studies.

 

Thanks!

Terrie

[Dr. Mike]

This sounds like an interesting project. I don't know the answer but I'm curious if anyone has experience with this type of application.

[mplishka]

Cool article about using Finite Element Analysis to predict bone fractures (I love FEA ).  https://www.asme.org/engineering-topics/articles/finite-element-analysis/bone-breaking-predictions-put-to-test-with-fea   It's very accurate, so to that end, it might not be necessary to create 3d models if the actual bone can be scanned, digitally modelled and then virtually stressed.   

 

What types of fracture studies are you planning (if you can share ;-) ) ?    Are you looking from a predictive standpoint or from a pure analysis standpoint; perhaps trying to figure out how to prevent certain fractures based upon certain loadings?  

 

I think it would be fascinating to print bone with integrated sensors to understand specific deformations at multiple points. It would not necessarily be essential to fail the bone, just understand how forces are transmitted.

 

Printing with multiple materials would be cool in the future to create the ultimate composite bone model.

 

I can see potential problems with micro-anomalies in the bone, or in any of the constraints.  The result would false negative/positive failures. 

 

One could also do a hybrid approach.  Do FEA and at certain points in the analysis, export the deformed file with colors and print it out.  You can take the bone apart and see how it's bending/twisting/etc. and what's happening inside it.

 

Just some thoughts

 

Good luck!

 

 

 

 

 

 

 

[mikefazz]

Hi Terrie,

 

I am familiar with sawbones are you looking for a material with similar mechanical properties to actual bone?  These days there are plenty of materials available yet I have doubts about being able to match the visco-elastic properties.  I have played around with altering the internal printing structure of a bone by printing the cortical bone solid and using 'infill' to alter density to simulate trabecular bone.

 

The picture below is from a while back where I printed a bone using 2 materials.  The red inside is just the infill material which is similar to a honeycomb structure.

 

Bone as a material is pretty strong so may not be easy to replicate as it is more like a composite.  I would be interested in looking into options

 

 

 

 

[Terrie S]

Thank you for the link and comments mplishka and mikefazz. With the ability to CT scan cadaver material, I was thinking it would be interesting to create physical replicates of an individual's geometry, potentially with 3D printing if there were an appropriate material that would fracture like bone.  The studies would build datasets for forensic interpretation. FEA might be the way to go for now. 

 

I like the idea of printing out a bone in different colors. Mikefazz, did you use a filament-based printer for the photo you posted?

[mikefazz]

I would agree that FEA may be the most accurate way to go to get numbers for a variety of loading scenarios.  My FEA experience is limited but with a complicated enough model and the right software this could be done.  Setting up a good biomechanical FEA model is no trivial task but if just isolated on a bone that would be more reasonable.

 

I looked a bit last night at the material properties for common FDM filaments available (ABS and PLA) and while their yield strengths are similar to bone their modulus of elasticity (stiffness) is 4+ times less that of bone.  There are other options available like carbon fiber PLA which is said to be 'stiffer than normal PLA'.  I haven't used it yet and don't see engineering values given for it to determine how much stiffer but would be a good place to start.

 

As to the model shown it was made with a filament based (FDM) printer as those are the types of printers I have.  One reason I have stayed with FDM printers is they are the most common and allow different material types to be used together.

 

Is your goal to do biomechanical testing on the synthetic bones vs using actual cadaveric bones?  3D printing could match the geometry and possibly the general material properties of bones but not the more intricate composite like nature of bones grain structure.  The cortical bone would be the most important part to match as I wouldn't expect the trabecular bone to play much of a part structurally.

[mplishka]

Instead of going the polymer route,  take a look at experimenting with materials like these from Biomet http://www.biomet.com/wps/wcm/connect/internet/ebf95c83-1ee4-41a1-9d02-d1cbedb07b7d/BMET0787+Biologics+US+Product+Portfolio.pdf?MOD=AJPERES&CONVERT_TO=url&CACHEID=ebf95c83-1ee4-41a1-9d02-d1cbedb07b7d and using a printer like this http://www.structur3d.io/#discov3ry  and try 3d printing synthetic bone that is not necessarily polymer based. 

 

7 hours ago, mikefazz said:

 

Is your goal to do biomechanical testing on the synthetic bones vs using actual cadaveric bones?  3D printing could match the geometry and possibly the general material properties of bones but not the more intricate composite like nature of bones grain structure.  The cortical bone would be the most important part to match as I wouldn't expect the trabecular bone to play much of a part structurally.

 In general, Trabecular bone does play a large role in bone mechanics.   Cortical bone requires strains of less than 5 percent to fail in lab settings.  Trabecular fails with strains in the 70's.  Put the two together and you get a composite that behaves better than either on their own.  The loss of trabecular bone structure is one of the reasons why osteoporotic bone breaks so much easier. 

 

[Terrie S]

Thanks so much for the information! I suppose there's still much research to be done to explore the behavior/applicability of 3D printed bone models in these types of studies. 

[mikefazz]

Yeah there are various avenues to follow.  I would agree that using polymers looks to not be sufficient as far as matching cortical bone properties.  Printing a bone scaffold using the biomet materials if they are indeed printable may be a way to get similar material properties.  

 

If studying crack propagation is a goal I would expect difficulties as printed parts respond to loading differently depending on the orientation of the layers; parts may fail due to de-lamination instead of how a real bone would.

 

Since my capability is primarily polymers one potential solution would be to create models that follow scaled down bone material properties i.e. scale down trabecular and cortical bone material properties until they reach the realm of polymer properties.  This wouldn't likely give accurate numbers but could possibly give useful 'relative' results such as how the bone breaks and such.  

[Terrie S]

Any suggestions for software for FEA? I have Mimics but I do not currently have the FEA module for it.

[mikefazz]

Hmm there are many options.  The lab where I used to work initially used ANSYS for mesh creation and LS-DYNA for solving.  Simpleware is a good solution for going from dicom to mesh but like most engineering software rather pricey.  Abaqus and hypermesh are also good programs I have used a little, but I admit that FEA is a bit out of my expertise.

[mplishka]

14 hours ago, tsehrhardt said:

Any suggestions for software for FEA? I have Mimics but I do not currently have the FEA module for it.

Depends how in-depth and how much of futzing you want to do on your own.

 

I prefer to work my way up in FEA's.  In other words, I always try to see trends first, look for problem areas even in lower level programs and then depending on what types of non-linearities exist, I step up from there.  There are some powerful ones in Linux as well (I created a separate Linux Boot Disk on my Windows computer ;-) ) Some are open source as well and allow modification if that's your thing

 

http://mecway.com/  Very cost effective and the developer is really doing amazing things.  It's getting better all the time.

http://en.z88.de/  Free   These folks have been overhauling their software for the last year or so.  Great strides!  There's more great stuff coming from them, they just need to translate from German ;-)

http://www.dhondt.de/  Calculix is an open source offering. Various prepackaged versions exist.  Improving the GUI is what many have been working on like https://sourceforge.net/projects/calculixforwin/  and http://www.bconverged.com/products.php (55 bucks) though their GUI was lacking last time I tried it.  They've improved it since.  Might be worth my checking out

https://csc.fi/web/elmer  Elmer is a multiphysics program.  Powerful stuff. Linux and Windows and Mac.  Interface was kinda funky but there's also a newer version I'm checking out.  More info here http://www.elmerfem.org/   Elmer is also open source

https://www.simscale.com/  REALLY powerful and also has free offering if you don't mind putting your runs in the public domain.  The paid versions aren't unreasonable.  Check out their project page https://www.simscale.com/projects/

 

Autodesk, COMSOL and ANSYS are all possibilities depending on your budget.

 

Hope this is enough to get you going.  Please let me know if you have any  more questions.

 

Thanks,

 

Mike

 

 

 

[Terrie S]

Thanks so much for the suggestions! I will look into them. Do either of you know anything about the FEA module in Mimics?

[mplishka]

Haven't used it or played with it.  I'm not sure if it's a true FEA package or just a meshing package to create better quality meshes when sending to another FEA program.  I thought I saw, on their website, some webinar coming up (or perhaps already recorded) that was about meshing Trabecular Bone!